AREA FORECAST DISCUSSION
NWS SAN DIEGO CA
230 PM PST WED FEB 28 2007
.SYNOPSIS...
A FEW SHOWERS COULD LINGER IN SAN DIEGO COUNTY THIS
EVENING...OTHERWISE DECREASING CLOUDINESS TONIGHT AS DRIER NORTHWEST
FLOW DEVELOP ALOFT. LOCALLY WINDY IN THE MOUNTAINS AND DESERTS THIS
EVENING. BUILDING HIGH PRESSURE WILL BRING FAIR WEATHER AND WARMER
DAYS THURSDAY AND FRIDAY. MUCH WARMER THIS WEEKEND UNDER HIGH
PRESSURE WITH OFFSHORE FLOW. COOLER EARLY NEXT WEEK AS THE HIGH
WEAKENS.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
.SHORT TERM (TODAY-SAT)...
THERE WERE ISLAND EFFECT AND OROGRAPHIC SHOWERS EARLIER
TODAY...MAINLY IN SAN DIEGO COUNTY W OF THE MOUNTAINS. EARLY
AFTERNOON ACARS SOUNDINGS SHOWED STRONG WLY WINDS ALOFT. ONSHORE
GRADIENTS WITH ABOUT 4 MB SAN-IPL AND 8 MB SAN-TPH.
A FEW ISLAND EFFECT SHOWERS MAY CONTINUE IN SAN DIEGO COUNTY INTO
EARLY THIS EVENING. OTHERWISE...CLOUDS OVER AND W OF THE MOUNTAINS
WILL DECREASE AFTER SUNSET. THERE WILL LIKELY BE PATCHY GROUND FOG
IN LOW LYING INLAND AREAS LATE TONIGHT AND THU MORNING DUE TO
CLEARING SKIES AND WET GROUND. MOSTLY CLEAR SKIES EXCEPT FOR A FEW
CU OVER THE MOUNTAINS IN DRIER NW FLOW ALOFT THU. A LITTLE WARMER
THU. A WEAK SHORT WAVE WILL MOVE THROUGH LATE THU NIGHT AND FRI
MORNING...BUT MOISTURE IS LIMITED SO IT SHOULD JUST BRING A FEW
CLOUDS BUT NO PRECIP. FAIR AND WARMER FRI...ESPECIALLY W OF THE
MOUNTAINS AS UPPER LEVEL HIGH PRESSURE BUILDS OFF THE W COAST AND
OFFSHORE FLOW BEGINS TO DEVELOP. THE HIGH PRESSURE AND OFFSHORE FLOW
WILL INCREASE SAT FOR MORE WARMING...ESPECIALLY W OF THE MOUNTAINS.
LOCAL GUSTY WINDS LATE FRI NIGHT AND SAT MORNING...MAINLY THROUGH
AND BELOW MOUNTAIN CANYONS AND PASSES WHERE THEY COULD LOCALLY GET
TO NEAR ADVISORY STRENGTH.
.LONG TERM (SUN-WED)...
SLIGHTLY COOLER SUN AS THE HIGH ALOFT AND OFFSHORE FLOW WEAKEN. AN
UPPER TROUGH OF LOW PRESSURE WILL BRING MORE CLOUDS AND COOLING
EARLY NEXT WEEK.
&&
.AVIATION...
282021Z...AS DAYTIME HEATING ENDS...THE CONVECTIVE CUMULUS OVER THE
AREA WILL EVAPORATE...LEAVING MOSTLY CLEAR SKIES WITH UNRESTRICTED
VISIBILITY THROUGH THU...EXCEPT ON THE COASTAL SLOPES WHICH WILL
REMAIN PARTIALLY OBSCURED THROUGH AT LEAST 06Z AND ISOLATED CLOUDS
AND BRIEF SHOWERS GENERATED FROM THE ISLANDS. THESE BANDS MAY AFFECT
ISOLATED PARTS OF THE COAST THROUGH 03Z...BUT SHOULD BE CONFINED TO
SOUTHERN SAN DIEGO COUNTY THERE AFTER AS WINDS VEER MORE FROM THE
NW. ALSO...DUE TO THE RECENT PRECIPITATION...PATCHY GROUND FOG WILL
BE POSSIBLE. OTHERWISE A GENERAL DRYING TREND IS EXPECTED THROUGH
THURSDAY.
WINDS ALOFT WILL BEGIN TO DECREASE AFTER 02Z THIS EVENING...WHICH
WILL DECREASE THE RISK OF UDDFS AND TURBULENCE OVER THE HIGHER
TERRAIN. OVER THE COASTS AND VALLEYS...GUSTY SURFACE WINDS THIS
AFTERNOON WILL BECOME LIGHT AND VARIABLE AFTER 04Z. ABOVE FL050
WINDS WILL CONTINUE FROM THE NW AT 15 TO 25 KTS THROUGH 15Z THU...
THEN DECREASE TO 20 KT OR LESS.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
PUBLIC...DVA
AVIATION...JAD
AREA FORECAST DISCUSSION
NWS SAN DIEGO CA
930 PM PST MON FEB 26 2007
.SYNOPSIS...
A COLD FRONT WILL MOVE SLOWLY ACROSS SOUTHERN CALIFORNIA TONIGHT
THROUGH TUESDAY. A SECOND COLD FRONT IS EXPECTED TO MOVE ACROSS THE
AREA TUESDAY NIGHT AND WEDNESDAY. THIS WILL CAUSE PERIODS OF LIGHT
RAIN OVER THE COAST AND VALLEYS AND LIGHT TO MODERATE RAIN AND SNOW
IN THE MOUNTAINS. HIGH WIND WARNINGS ARE IN EFFECT FOR THE MOUNTAINS
AND DESERTS. TRAVEL WILL BE DIFFICULT IN THE MOUNTAINS TUESDAY AND
WEDNESDAY DUE TO GUSTY WINDS AND POOR VISIBILITY IN SNOW...BLOWING
SNOW...AND FOG. BLOWING SAND AND DUST OVER THE DESERTS WILL ALSO
CREATE POOR VISIBILITY AT TIMES. THE PRECIPITATION SHOULD END LATE
WEDNESDAY NIGHT. DRY BUT COOL WEATHER WITH NORTHEAST WINDS IS
EXPECTED FOR THURSDAY AND FRIDAY. THE WEEKEND SHOULD BE WARMER AS
HIGH PRESSURE BUILDS ALOFT.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
.SHORT TERM...TONIGHT THROUGH WEDNESDAY
TEMPORARY RIDGING/SUBSIDENCE AHEAD OF APPROACHING COLD FRONT LOWERED
MARINE LAYER TO AROUND 4000 FEET MONDAY AFTERNOON BUT SHOULD REBOUND
OVERNIGHT. UPSTREAM SOUNDINGS...SPEED OF MOVEMENT OF LEADING EDGE OF
CLOUDS ASSOCIATED WITH FIRST COLD FRONT...AND MODEL CROSS SECTIONS
ALL INDICATE AIR MASS WILL BE SATURATED TO 7500 FEET BY TUESDAY
MORNING. WINDS BETWEEN 6000 AND 10000 FEET WILL ALSO BE INCREASING
TO 45-60 KNOTS OVERNIGHT. LOCAL WIND PROGRAM IS GENERATING GUSTS 58
TO 70 MPH IN WIND PRONE LOCATIONS ALONG EAST SLOPES AND DESERTS
BETWEEN 10 PM AND 4 AM TONIGHT. HIGH WIND WARNINGS WENT INTO
EFFECT AT 6 PM AND SO FAR HAVE HAS SOME GUSTS OVER 40 MPH REPORTED
OVER THE COACHELLA VALLEY AND EASTERN SAN DIEGO COUNTY. AN INVERSION
IS EXPECTED TO PRESENT NEAR OR WITHIN 2000 FEET OF THE HIGHER RIDGES
ALL DAY TUESDAY. THIS COUPLED WITH SUSTAINED WEST +45 KNOT WINDS
OVER THE MOUNTAINS WILL CREATE SURFACING MOUNTAIN WAVES OVER THE
DESERT AREAS...CAUSING BLOWING SAND/DUST AND POOR VISIBILITY
IMPEDING GROUND TRANSPORTATION...IN ADDITION TO SEVERE TURBULENCE
FOR AIRCRAFT. POOR VISIBILITY IS LIKELY TO BE PRESENT IN THE
MOUNTAINS DUE TO FOG AND BLOWING SNOW. SNOW LEVEL EXPECTED TO REMAIN
AROUND 5500 FEET THROUGH TONIGHT THEN LOWER TO 4000 FEET TUESDAY
MORNING. THE MODELS MOVE THIS FIRST FRONT EAST OF THE AREA BY
TUESDAY AFTERNOON AND SHOW A SECOND IMPULSE COMING ACROSS THE AREA
TUESDAY NIGHT/WEDNESDAY MORNING...THIS MIGHT GIVE US A TEMPORARY
BREAK/PRECIPITATION TUESDAY AFTERNOON...BUT AIR MASS WILL CONTINUE
NEAR SATURATION ALONG WITH UPSLOPE FLOW SO ANY SUCKER HOLES SHOULD
QUICKLY CLOSE UP. COLDER AIR ARRIVING TUESDAY NIGHT WILL DROP THE
SNOW LEVEL TO 3500 FEET OR LOWER. ALL IN ALL LITTLE CHANGE EXPECTED
TUESDAY THROUGH WEDNESDAY WITH PROLONGED PERIOD OF LIGHT TO MODERATE
PRECIPITATION OVER MOUNTAINS...VALLEYS...AND COAST WHILE DESERT
AREAS GET SAND BLASTED WITH STRONG WINDS.
.LONG TERM...WEDNESDAY NIGHT THROUGH SUNDAY
HIGH PRESSURE BUILDING TO THE NORTH WEDNESDAY NIGHT THROUGH THURSDAY
TURNS FLOW TO THE NORTHEAST AND PROVIDES DRYING BUT LITTLE WARMING.
OFFSHORE PRESSURE GRADIENT INCREASES TO AROUND 12 MB ON FRIDAY AND
THERE APPEARS TO BE SOME UPPER SUPPORT. THE WIND PROGRAM GENERATES
30 TO 45 MPH GUSTS AND THESE SEEM REASONABLE. ON SATURDAY THE
PRESSURE GRADIENT IS STRONGER BUT THE UPPER SUPPORT IS MISSING. THIS
WOULD BE A CRITICAL FIRE WEATHER PATTERN BUT THE FUEL CONDITIONS DUE
TO THE RECENT AND EXPECTED PRECIPITATION OVER THE NEXT 48 HOURS
SHOULD MITIGATE THE RAPID DRYING AND WARMING ON SATURDAY AND THE
LINGERING VERY DRY AND WARM CONDITIONS SUNDAY. THE OFFSHORE FLOW
ENDS SUNDAY MORNING AND THE RIDGE BREAKS DOWN BY SUNDAY
AFTERNOON...SO EXPECT A WIND REVERSAL AND INCREASING ONSHORE
FLOW/GUSTY SOUTHWEST WINDS OVER THE MOUNTAINS BY SUNDAY AFTERNOON.
&&
.AVIATION...
270400Z...THE MARINE LAYER WILL DEEPEN OVERNIGHT AND A COLD FRONT
WILL MOVE ACROSS THE AREA TOMORROW MORNING FROM THE
NORTHWEST...BRINGING WITH IT SCATTERED SHOWERS AND STRONG WINDS.
MULTIPLE LAYERS OF STRATOCU ARE EXPECTED WITH BASES BTWN 2500-3000
FT LOCALLY AT OR BELOW 2000 FEET MSL IN SHOWERS. THERE MAY BE SOME
BRIEF CLEARING TOMORROW AFTERNOON BEHIND THE FRONT...EXCEPT INLAND
VALLEYS AND MOUNTAINS WHERE CLOUDS AND SHOWERS WILL LINGER. STRONG
WESTERLY WINDS ALOFT WILL CAUSE CAUSE MOUNTAIN WAVE/ROTOR ACTIVITY
WITH STRONG UDDFS OVER THE MOUNTAINS AND IN THE DESERTS THROUGH
WEDNESDAY NIGHT. SURFACING WAVE ACTIVITY COULD GENERATE LOCAL WIND
GUSTS IN EXCESS OF 60 MPH WITH AREAS OF BLOWING DUST. A SECOND FRONT
WILL BRING AN ANOTHER ROUND OF SHOWERS ON WEDNESDAY.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...HIGH WIND WARNING UNTIL 10 PM PST WEDNESDAY FOR APPLE AND
LUCERNE VALLEYS-COACHELLA VALLEY-RIVERSIDE COUNTY MOUNTAINS-
SAN BERNARDINO COUNTY MOUNTAINS-SAN DIEGO COUNTY DESERTS-
SAN DIEGO COUNTY MOUNTAINS.
PZ...NONE.
&&
$$
PUBLIC/FIRE WEATHER...BALFOUR
AVIATION/MARINE.......SCV
NWS ON THE WEB AT WEATHER.GOV/SANDIEGO
AREA FORECAST DISCUSSION
NWS CHICAGO/ROMEOVILLE IL
1200 PM CST WED FEB 28 2007
.MORNING DISCUSSION...
BAND OF WARM ADVECTION ENHANCED RAIN...SLEET...SNOW EXTENDING FROM
WEST CENTRAL ILLINOIS INTO WEST CENTRAL INDIANA WILL CONTINUE TO
LIFT NORTHWARD THROUGH THE DAY AS STRONGER ISENTROPIC LIFT
OVERSPREADS NRN ILLINOIS/NWRN INDIANA. REGIONAL ACARS DATA FROM THIS
MORNING SUGGESTING POTENTIAL FOR MIXED PRECIP WHICH IS ALREADY WELL
COVERED IN GOING FORECAST. LOW LEVEL WARM LAYER MAGNITUDE SUGGESTS
THAT SLEET/SNOW MAY BE THE BIGGER CONCERN EARLY THIS AFTERNOON.
TEMPERATURES HOWEVER SHOULD CONTINUE TO INCREASE TO ABOVE FREEZING
THROUGH THE AFTERNOON HOURS SO NOT EXPECTING MIXED PRECIPITATION TO
CAUSE ANY WIDESPREAD TRAVEL HEADACHES.
EXPECTING THIS PRECIP BAND TO MOVE ACROSS NORTHERN SECTIONS OF THE
FORECAST AREA THIS EVENING WITH PERHAPS A LULL IN THE ACTIVITY SOUTH
OF INTERSTATE 80 BY LATER THIS EVENING. HOWEVER STRONG LLJ
DEVELOPING OVERNIGHT WITH APPROACHING STRONG UPPER JET STREAK FROM
THE CENTRAL PLAINS SHOULD ALLOW FOR SHOWERS AND THUNDERSTORMS TO
SPREAD BACK INTO THE AREA AGAIN LATER TONIGHT. WILL KEEP FLOOD WATCH
IN EFFECT FROM THIS EVENING INTO LATE TOMORROW NIGHT...ALTHOUGH
HEAVIER RAIN FOCUS SHOULD OCCUR AFTER MIDNIGHT AND INTO THURSDAY.
OTHER POTENTIAL BIG CONCERN WILL BE ON WINDS LATE TOMORROW AFTERNOON
INTO TOMORROW EVENING. THERE DOES SEEM TO BE POTENTIAL FOR WIND
ADVISORY LEVEL WIND SPEEDS IN THE WAKE OF OCCLUDED FRONT LATE
TOMORROW AFTERNOON/TOMORROW NIGHT WITH COLD AIR WRAPPING INTO THE
BACKSIDE OF THIS SYSTEM.
WILL BE UPDATING GRIDS/ZONES TO HIGHLIGHT MORE OF A MIXED PRECIP
POTENTIAL BY 18Z...ALTHOUGH WILL NOT BE ISSUING ANY WINTER WEATHER
HEADLINES FOR THIS AFTERNOON AT THIS TIME. NDM
&&
.DISCUSSION...
420 AM CST
POWERFUL JET MAX OF 160KTS PER AIRCRAFT REPORTS CROSSING NORTHERN
BAJA AT BASE OF WESTERN NOAM UPPER TROF. SATELITE SHOWS MULTIPLE
CIRCULATIONS IN THE TROF. ONE LIFTING NORTHWARD ACROSS THE NORTHERN
HI PLAINS WITH A TROF AXIS EXTENDING SOUTHEASTWARD ALL THE WAY TO
THE LOWER MO VALLEY WHERE STRONG WAA HAS REGENTLY GENERATED ELEVATED
TSRA. THE WAA PATTERN AND ASSOCIATED UVV WILL LIFT NORTHWARD INTO
THE MID MS VALLEY BY THIS EVE AS THE JET MAX CROSSES THE SOUTHERN
ROCKIES AND TURNS NORTHEASTWARD ACROSS THE SOUTHERN PLAINS.
MODELS SHOW H8 WARMFRONT LIFTING INTO SOUTHERN WI AND LOWER MI BY
06Z AND EXPECT INITIAL ROUND OF PRECIP TO CONTINUE TO MOVE NORTHWARD
INTO THE UPPER MIDWEST AND GREAT LAKES. LOWER LEVELS REMAIN
RELATIVELY DRY AS THIS PRECIP AREA MOVES IN DURING THE LATER
AFTERNOON AS H8 DEW POINT DEPRESSIONS WERE 20 TO 30 DEG C ACROSS THE
LOWER MS VALLEY LAST EVE. 00Z RAOBS DID SHOW MARGINAL MID LEVEL
MOISTURE OVER THE OZARKS AHEAD OF THE LEAD SHORT WAVE TROF WHILE
LOWER LEVELS WERE DRY EXCEPT FOR SHALLOW MOISTURE ALONG THE WESTERN
GULF COAST. THIS MOISTURE HAS SPREAD RAPIDLY INTO THE SOUTHERN
PLAINS WHERE SURFACE DEW POINTS APPROACHING 60F AS SOUTHERLY LOW
LEVEL WINDS CONTINUE TO INCREASE AHEAD OF THE RAPIDLY DEVELOPING LEE
SIDE LOW BUT THIS LOWER LEVEL MOISTURE DOES NOT REACH THE MID MS
VALLEY UNTIL THIS EVE.
AFTER THE INITIAL SHOT OF WAA PRECIP EXPECT A BREAK UNTIL INGREDENTS
COME TOGETHER OVERNIGHT. THIS INCLUDES GULF MOISTURE SPREADING INTO
CENTRAL IL...DIFLUENT UPPER FLOW AS TROF BECOMES NEGATIVELY TILTED
AND DIVERGENCE ALOFT AT LEFT EXIT OF STRONG JET. STEEP MID LEVEL
LAPSE RATES AND STRONG DYNAMICS WILL RESULT IN CONVECTIVE RAIN
BREAKING OUT AND SPREADING ACROSS THE MID MS VALLEY. PRECIPITABLE
WATER VALUES CLIMB TO AROUND 1 INCH AND MODERATE TO HEAVY RAINFALL
POTENTIAL DUE TO EXPECTED CONVECTIVE NATURE AND FLOOD WATCH WILL BE
CONTINUED GIVEN ALREADY SOME FLOODING PROBLEMS AND MOISTURE CONTENT
OF SNOWPACK.
UPPER LOW LINGERING OVER THE CANADIAN MARITIMES SLOWS THE PROGRESS
OF THIS STORM AND IT BECOMES STACKED DURING THU AS IT LIFTS INTO IA.
WINDS WILL GRADUALLY DIE DOWN AS LOW STARTS GRADUAL FILLING. DRY
SLOT PUNCHES NORTHWARD DURING THU WITH OCCLUDED FRONT SWEEPING EAST
AND NORTHEAST THRU THE FA. THIS WILL CURTAIL RAIN BUT WITH COLD AIR
WRAPPED INTO SYSTEM AND IT/S SLOW MOVEMENT INTO THE CENTRAL GREAT
LAKES THU NIGHT AND FRI WILL KEEP A CHANCE OF OCCASIONAL LIGHT SNOW
AND SNOW SHOWERS GOING.
TRS
&&
.AVIATION DISCUSSION REGARDING 18Z TAFS...
1200 PM CST
MAIN CONCERNS THROUGH NEAR TERM OF FCST DEAL WITH INITIAL BAND OF
CONVECTION NOW LIFTING NEWD ACRS CNTRL IL. THIS HAS DEVELOPED AT
NOSE OF STG WARM ADVECTION AHD OF DVLPG LOW PRES OVR PLAINS STAS.
VIS SATLT IMAGERY STILL SHOWS FAIRLY WIDESPREAD CONVECTIVE ELEMENTS
WITH THIS BAND AND INDEED...CURRENT LIGHTNING DETECTION DATA SHOWS
FQT STRIKES FROM NR GBG-BMI-SW OF LAF. RADAR LOOPS INDICATE THIS
BAND WILL OVERSPREAD TERMINAL AREA FROM SW-NE BTWN 21Z AND 23Z. FOR
NOW HAVE KEPT THUNDER OUT OF TAFS DURG THIS PERIOD THINKING PCPN
ELEMENTS WILL STRATIFY OUT MORE AS THEY LIFT FURTHER NEWD INTO
RETREATING COLD AMS. OTHER PROBLEM WITH THIS INITIAL BURST OF PCPN
WILL BE FREEZING PRECIP. SFC TEMPS HAVE RISEN ABV FREEZING AND
DOUBT THAT THEY WILL DROP BACK BELOW BY THE TIME THIS PCPN MOVES IN
DUE TO TIME OF DAY. HOWEVER...FCST SOUNDINGS SHOW LLVL TEMPS RMNG
RIGHT ARND FREEZING INTO THIS EVENING SUGGESTING A SNOW/ICE
PELLET/RAIN MIXTURE THROUGH ERLY THIS EVENING...WITH MORE SNOW AND
ICE PELLETS ASSD WITH BETTER DVLPD CONVECTIVE CELLS. TEMPS FCST TO
RISE FAR ENUF ABV FREEZING TO PRODUCE ALL LIQUID AFT ABOUT 03Z.
OFF AND ON SHWRS MOST OF OVERNIGHT PERIOD WITH CIGS/VIS OCNLLY LWRG
TO IFR.
NXT BIG PROBLEM THAT MAY IMPACT TRAFFIC FLOW IS EXPECTED THUR MRNG
AHD OF STG FRONTAL PASSAGE DUE TO PASS THRU NRN IL/NWRN IND LATE
MRNG-ERLY AFTN. ALL INDICATIONS SUGGEST THIS WILL BE PRECEDED BY A
LINE OF SHWRS/PSBL TSTMS WITH GUSTS LIKELY TO EXCEED 40 KTS.
MERZLOCK
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
.IL...FLOOD WARNING PORTIONS KANKAKEE AND UPPER IL RIVERS. FLOOD
WATCH TONIGHT THRU THU.
.IN...FLOOD WARNING PORTIONS KANKAKEE RIVER. FLOOD WATCH TONIGHT
THRU THU.
.LM...NONE.
&&
$$
AREA FORECAST DISCUSSION
NWS CHICAGO/ROMEOVILLE IL
1130 AM CST WED FEB 28 2007
.MORNING DISCUSSION...
BAND OF WARM ADVECTION ENHANCED RAIN...SLEET...SNOW EXTENDING FROM
WEST CENTRAL ILLINOIS INTO WEST CENTRAL INDIANA WILL CONTINUE TO
LIFT NORTHWARD THROUGH THE DAY AS STRONGER ISENTROPIC LIFT
OVERSPREADS NRN ILLINOIS/NWRN INDIANA. REGIONAL ACARS DATA FROM THIS
MORNING SUGGESTING POTENTIAL FOR MIXED PRECIP WHICH IS ALREADY WELL
COVERED IN GOING FORECAST. LOW LEVEL WARM LAYER MAGNITUDE SUGGESTS
THAT SLEET/SNOW MAY BE THE BIGGER CONCERN EARLY THIS AFTERNOON.
TEMPERATURES HOWEVER SHOULD CONTINUE TO INCREASE TO ABOVE FREEZING
THROUGH THE AFTERNOON HOURS SO NOT EXPECTING MIXED PRECIPITATION TO
CAUSE ANY WIDESPREAD TRAVEL HEADACHES.
EXPECTING THIS PRECIP BAND TO MOVE ACROSS NORTHERN SECTIONS OF THE
FORECAST AREA THIS EVENING WITH PERHAPS A LULL IN THE ACTIVITY SOUTH
OF INTERSTATE 80 BY LATER THIS EVENING. HOWEVER STRONG LLJ
DEVELOPING OVERNIGHT WITH APPROACHING STRONG UPPER JET STREAK FROM
THE CENTRAL PLAINS SHOULD ALLOW FOR SHOWERS AND THUNDERSTORMS TO
SPREAD BACK INTO THE AREA AGAIN LATER TONIGHT. WILL KEEP FLOOD WATCH
IN EFFECT FROM THIS EVENING INTO LATE TOMORROW NIGHT...ALTHOUGH
HEAVIER RAIN FOCUS SHOULD OCCUR AFTER MIDNIGHT AND INTO THURSDAY.
OTHER POTENTIAL BIG CONCERN WILL BE ON WINDS LATE TOMORROW AFTERNOON
INTO TOMORROW EVENING. THERE DOES SEEM TO BE POTENTIAL FOR WIND
ADVISORY LEVEL WIND SPEEDS IN THE WAKE OF OCCLUDED FRONT LATE
TOMORROW AFTERNOON/TOMORROW NIGHT WITH COLD AIR WRAPPING INTO THE
BACKSIDE OF THIS SYSTEM.
WILL BE UPDATING GRIDS/ZONES TO HIGHLIGHT MORE OF A MIXED PRECIP
POTENTIAL BY 18Z...ALTHOUGH WILL NOT BE ISSUING ANY WINTER WEATHER
HEADLINES FOR THIS AFTERNOON AT THIS TIME. NDM
&&
.DISCUSSION...
420 AM CST
POWERFUL JET MAX OF 160KTS PER AIRCRAFT REPORTS CROSSING NORTHERN
BAJA AT BASE OF WESTERN NOAM UPPER TROF. SATELITE SHOWS MULTIPLE
CIRCULATIONS IN THE TROF. ONE LIFTING NORTHWARD ACROSS THE NORTHERN
HI PLAINS WITH A TROF AXIS EXTENDING SOUTHEASTWARD ALL THE WAY TO
THE LOWER MO VALLEY WHERE STRONG WAA HAS REGENTLY GENERATED ELEVATED
TSRA. THE WAA PATTERN AND ASSOCIATED UVV WILL LIFT NORTHWARD INTO
THE MID MS VALLEY BY THIS EVE AS THE JET MAX CROSSES THE SOUTHERN
ROCKIES AND TURNS NORTHEASTWARD ACROSS THE SOUTHERN PLAINS.
MODELS SHOW H8 WARMFRONT LIFTING INTO SOUTHERN WI AND LOWER MI BY
06Z AND EXPECT INITIAL ROUND OF PRECIP TO CONTINUE TO MOVE NORTHWARD
INTO THE UPPER MIDWEST AND GREAT LAKES. LOWER LEVELS REMAIN
RELATIVELY DRY AS THIS PRECIP AREA MOVES IN DURING THE LATER
AFTERNOON AS H8 DEW POINT DEPRESSIONS WERE 20 TO 30 DEG C ACROSS THE
LOWER MS VALLEY LAST EVE. 00Z RAOBS DID SHOW MARGINAL MID LEVEL
MOISTURE OVER THE OZARKS AHEAD OF THE LEAD SHORT WAVE TROF WHILE
LOWER LEVELS WERE DRY EXCEPT FOR SHALLOW MOISTURE ALONG THE WESTERN
GULF COAST. THIS MOISTURE HAS SPREAD RAPIDLY INTO THE SOUTHERN
PLAINS WHERE SURFACE DEW POINTS APPROACHING 60F AS SOUTHERLY LOW
LEVEL WINDS CONTINUE TO INCREASE AHEAD OF THE RAPIDLY DEVELOPING LEE
SIDE LOW BUT THIS LOWER LEVEL MOISTURE DOES NOT REACH THE MID MS
VALLEY UNTIL THIS EVE.
AFTER THE INITIAL SHOT OF WAA PRECIP EXPECT A BREAK UNTIL INGREDENTS
COME TOGETHER OVERNIGHT. THIS INCLUDES GULF MOISTURE SPREADING INTO
CENTRAL IL...DIFLUENT UPPER FLOW AS TROF BECOMES NEGATIVELY TILTED
AND DIVERGENCE ALOFT AT LEFT EXIT OF STRONG JET. STEEP MID LEVEL
LAPSE RATES AND STRONG DYNAMICS WILL RESULT IN CONVECTIVE RAIN
BREAKING OUT AND SPREADING ACROSS THE MID MS VALLEY. PRECIPITABLE
WATER VALUES CLIMB TO AROUND 1 INCH AND MODERATE TO HEAVY RAINFALL
POTENTIAL DUE TO EXPECTED CONVECTIVE NATURE AND FLOOD WATCH WILL BE
CONTINUED GIVEN ALREADY SOME FLOODING PROBLEMS AND MOISTURE CONTENT
OF SNOWPACK.
UPPER LOW LINGERING OVER THE CANADIAN MARITIMES SLOWS THE PROGRESS
OF THIS STORM AND IT BECOMES STACKED DURING THU AS IT LIFTS INTO IA.
WINDS WILL GRADUALLY DIE DOWN AS LOW STARTS GRADUAL FILLING. DRY
SLOT PUNCHES NORTHWARD DURING THU WITH OCCLUDED FRONT SWEEPING EAST
AND NORTHEAST THRU THE FA. THIS WILL CURTAIL RAIN BUT WITH COLD AIR
WRAPPED INTO SYSTEM AND IT/S SLOW MOVEMENT INTO THE CENTRAL GREAT
LAKES THU NIGHT AND FRI WILL KEEP A CHANCE OF OCCASIONAL LIGHT SNOW
AND SNOW SHOWERS GOING.
TRS
&&
.AVIATION DISCUSSION FOR 06Z TAFS...
630 AM CST
THE CYCLONE WAS OVER COLORADO THIS MORNING AS SEEN ON THE SURFACE
MAP AT 12 UTC. THE 850 MB 12 UTC ANALYSIS SHOWS A 50 KNOT WIND IN
WESTERN MISSOURI. THE WATER VAPOR LOOP SHOW THE RAPID EASTWARD
MOVEMENT OF THE TROUGH INTO THE WESTERN UNITED STATES. THIS CYCLONE
IS GOING TO BE A VERY DYNAMIC SYSTEM. THE LOCALLY RUN WRF ARW MODEL
SHOWS THE STRONG 850 MB WIND WILL MOVE INTO ILLINOIS. THE EQUIVALENT
POTENTIAL TEMPERATURE HAS A LARGE GRADIENT TONIGHT AS THE WARM AIR
RETURNS TO CENTRAL ILLINOIS. THE NEGATIVE OMEGA AT 700 MB IS
FORECAST TO BE LARGE BETWEEN 09 AND 12 UTC THURSDAY MORNING. THE
LIFTED INDEX GRADIENT IS LARGE IN CENTRAL ILLINOIS AS WELL. WILL
KEEP THE WIND FORECAST 15 KNOTS WITH GUST TO 24 KNOTS TONIGHT. WE
EXPECT SOME REAL UNSTABLE AIR MOVING INTO THE TAF FORECAST AREA. SO
WILL ADD THUNDERSTORMS TO THE FORECAST BETWEEN 8 TO 12 UTC. THIS
EVENING... AS THE ISENTROPIC LIFT BEGINS MIXED PRECIPITATION MAY
OCCUR WITH RAIN AND SNOW AND POSSIBLY ICE PELLETS. THE WRF FROM
NCEP...GFS AND NGM MODELS WERE USED AND THE LOCAL WRF ARW WAS ALSO
USED.
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
.IL...FLOOD WARNING PORTIONS KANKAKEE AND UPPER IL RIVERS. FLOOD
WATCH TONIGHT THRU THU.
.IN...FLOOD WARNING PORTIONS KANKAKEE RIVER. FLOOD WATCH TONIGHT
THRU THU.
.LM...NONE.
&&
$$
AREA FORECAST DISCUSSION
NWS MARQUETTE MI
425 AM EST TUE FEB 27 2007
...ANOTHER SIGNIFICANT SNOWFALL POSSIBLE WED NIGHT INTO SAT...
.SYNOPSIS...
H5/H7/H85 LOW RESIDES NORTHEAST WI INTO NORTHERN LK MI. SFC LOW IS
OVR CNTRL LK MI. SHORTWAVES/VORT MAXES MOVING AROUND THE LOW ARE OVR
SOUTHERN LOWER MI MOVING TO THE EAST AND OVR NORTHEAST MN MOVING TO
THE WEST. REGIONAL RADAR SHOWING NUMEROUS ECHOES ALONG AND NORTH OF
THE LOW CENTER WITH MORE SCATTERED ACTIVITY TO ITS SOUTH. PCPN IS
NOT ALL SNOW THOUGH...DESPITE LATEST SOUNDINGS FM APX/GRB AND TAMDAR
SOUNDINGS FM KSAW WHICH POINT TO TEMPS COLD ENOUGH FOR SNOW. MOIST
LAYER ON ALL SOUNDINGS EXTENDS TO 750-650MB. AS UPR LOW OVR REGION
WEAKENS FURTHER...PCPN CHANCES CONTINUE TO TAIL OFF NEXT 24 HRS. UPR
LOW SHOULD COMPLETELY DISSIPATE BY WED AS UPR RIDGING WORKS IN FM
WEST IN RESPONSE TO LARGE UPR TROUGH DIGGING INTO FAR WEST CONUS.
THIS SYSTEM EVENTUALLY MOVES EAST AND DEEPENS FURTHER AS IT
APPROACHES THE GREAT LAKES THU. SIGNIFICANT SNOW WITH THE SYSTEM
IS THE MAIN FOCUS OF THE FORECAST.
&&
.DISCUSSION...
LGT PCPN (FLURRIES/FREEZING DRIZZLE) LOOKS LIKE IT WILL PERSIST
TODAY AS UPPER LOW CONTINUES TO DECAY. PRIMARY INSTIGATOR FOR PCPN
IS MOIST PROFILE THROUGH 800MB. ALTHOUGH IN THE LAYER TEMPS ARE AS
COLD AS -11C...STILL EXPECT CHANCE OF FREEZING DRIZZLE BASED ON WHAT
HAS OCCURRED LAST EVENING INTO THE OVERNIGHT HOURS. FOR SOME REASON
TEMPS ARE NOT COLD ENOUGH TO ACTIVATE ALL THE ICE NUCLEI PRESENT. TO
START THE DAY THERE IS AT LEAST WEAK LARGE SCALE LIFTING WITHIN THE
PERIFERY OF UPR LOW AS SHOWN BY H85-H5 Q-VECTOR CONVERGENCE. RISING
HEIGHTS EVENTUALLY LEAD TO LESS LIFTING WITH Q-VECTORS BECOMING
DIVERGENT TONIGHT. CONSIDERED PLACING FREEZING DRIZZLE IN FOR
TONIGHT...BUT NOT SURE IF ANY PCPN WILL BE OCCURRING AT ALL WITH
INCREASINGLY NEGATIVE MECHANISMS FOR LARGE SCALE LIFT. THUS...KEPT
ONLY FLURRIES THROUGH WED. AT THE MINIMUM...BKN-OVC CLOUDS PERSIST
...KEEPING RANGE BTWN MIN AND MAX TEMPS LIMITED.
ON WED ATTN QUICKLY TURNS TO LEAD SHORTWAVE HEADING OUT ONTO THE
NORTHERN PLAINS AHEAD OF MAIN TROUGH SETTING UP OVR WESTERN CONUS.
WARM AIR ADVECTION H85-H7 IMPRESSIVE...AS IS ISENTROPIC LIFT ON
280-290K SFCS (H9-H7). TAP TO GULF MOISTURE PRESENT WITH PWATS NEAR
200 PCT OF NORMAL STREAMING AHEAD OF SHORTWAVE. MIXING RATIOS
INDICATE THIS ON ISENTROPIC SFCS WITH 3-4G/KG UPSTREAM OF CWA WED
NIGHT. H85 WINDS INCREASE TO 40KT PRODUCING SHARP LIFTING ON THESE
SFCS. SATURATION PROCESS SHOULD BE SWIFT AS SOME MOISTURE OVR AREA
NOW WILL STILL BE IN THE REGION. SOUNDINGS SHOWING QUICK MOISTENING
LOOK ON TRACK. ACTUALLY...GFS/ECMWF/UKMET/CANADIAN ALL AGREE IN
MEASURABLE QPF REACHING SW BORDER BY 00Z THU. STRONG DEEP MOIST
ASCENT CONTINUES INTO THU AFTN AHEAD OF APPROACHING UPR LOW...
ALREADY BECOMING CLOSED OFF AT H5...AND POTENT MID 980S SFC LOW
MOVING NORTHEAST FM CNTRL IA TO CNTRL WI. DEEP INSTABILITY PRESENT
AS MID LEVEL DRY SLOTTING DEVELOPS BY LATE AFT. GFS SHOWS H7-H5
LAPSE RATES NEARING 8.0C/KM INTO SCNTRL UPR MI BY LATE THU AFTN.
COULD BE SOME THUNDER IN THESE AREAS. LEANED HEAVILY ON HPC QPF
LATER WED NIGHT INTO THU AND THIS YIELDS A SIGNIFICANT PCPN EVENT
ACROSS UPR MI. SFC LOW TRACK TOWARD SCNTRL UPR MI THROUGH THU
NIGHT BRINGS POSSIBILITY OF ELEVATED WARM LAYER INTO PICTURE. GFS
SOUNDINGS APPEARED TOO COLD WITH THE WARM LAYER SINCE UPR LOW IS
ALREADY CLOSED OFF AS EARLY AS LATE WED NIGHT. INSTEAD...USED
WARMER ECMWF AND NAM H85 TEMPS TO HIGHLIGHT POTENTIAL OF MIXED SLEET
AND SNOW THU INTO THU EVENING OVR SCNTRL AND EAST CWA. BAND OF
POTENTIALLY HEAVY SNOW SHOULD CONTINUE OVR WEST AND NCNTRL CWA
DURING THIS TIME AND IT COULD EVEN EXTEND INTO FRI/FRI NIGHT.
WENT BACK AND FORTH WHETHER TO ISSUE A WATCH AS THE MAIN EVENT IS
MORE OF A LATE 4TH PERIOD AND BEYOND ONE AND SYSTEM IS STILL JUST
BEGINNING TO EMERGE ON THE WEST COAST. STILL...SIGNALS IN MAJORITY
OF GUIDANCE AND GFS ENSEMBLES ARE PRESENT THAT IF THE TRACK OF
SYSTEM EVEN REMAINS SOMEWHAT CLOSE TO WHAT IS SHOWN BY MOST GUIDANCE
ATTM...A WARNING EVENT WOULD MATERIALIZE. STRONG WINDS WITH DEEP SFC
LOW MAY ALSO LEAD TO BLSN/REDUCED VISIBILITY. SO...DESPITE THE FACT
THAT EVENT IS PRETTY FAR OUT IN TIME...COORD WITH GRB AND DLH AND
DECIDED TO ISSUE A WINTER STORM WATCH ALONG THE WI BORDER FOR WED
NIGHT THROUGH THU NIGHT. ATTM DID NOT ISSUE ANY OTHER HEADLINES FOR
NORTHWEST AND NORTH CENTRAL CWA SINCE THE MAJORITY OF THE SNOW FOR
THOSE AREAS WILL OCCUR THU-THU NIGHT INTO FRI. REALLY SEE NO REASON
WHY IF CURRENT SOLNS PERSIST THESE AREAS WILL NOT NEED TO BE ADDED
INTO A WATCH WITHIN THE NEXT 24 HRS.
LINGERED HIGHER POPS ON INTO SAT WITH SLOWER TREND TO THE DEPARTING
OF SYSTEM. LAKE ENHANCEMENT ALSO LIKELY IN NNW FLOW AREAS AS DEEP
MOISTURE TO H7 REMAINS WITH H85 TEMPS TUMBLING TO -15C.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH WED NIGHT THROUGH THU NIGHT MIZ009-012.
&&
$$
JLA
AREA FORECAST DISCUSSION
NWS TWIN CITIES/CHANHASSEN MN
846 PM CST WED FEB 28 2007
.UPDATE...
UPDATED FOR ISOLATED THUNDER ACROSS SOUTH CENTRAL MN EARLIER. TOPS
HAVE WARMED BELOW 25K FT FOR THE MOST PART. FRONTOGENETICALLY
FORCED BAND OF SNOW LIFTING ACROSS CENTRAL MN AT THIS TIME.
MOVEMENT WAS NORTH AROUND 20 KTS OR SO...WITH LITTLE DEVELOPMENT
NOTED ON ITS SOUTHERN END. THIS SHOULD LIFT INTO NORTHERN CWA
AFTER MIDNIGHT...WITH DRY MID LEVEL AIR INTRUSION EXPECTED INTO
SOUTHERN MN AFTER THAT. THIS SHOULD LEAVE STRATUS/ZL-/S-- THE MAIN
THREAT ACROSS THE FAR SOUTH AFTER MIDNIGHT. WILL ANXIOUSLY AWAIT
00Z MODELS FOR DEVELOPMENT OF STORM FOR THURSDAY. 00Z NAM/WRF
CONTINUES TREND OF STRONG UVV DEVELOPING MAINLY AFTER 12Z THU.
STILL SHOWING VERY TIGHT K-INDEX GRADIENT INTO SOUTHEAST MN.
SHOULD SEE POTENTIAL OF MORE THUNDERSNOW INTO FAR SOUTHERN
MINNESOTA AT LEAST IN THE MORNING. THEN AS UPPER LOW PIVOTS
NORTHEAST/ATTENDANT SURFACE LOW MOVES SLOWLY EAST AND OCCLUDES.
THIS SHOULD CONTINUE THE SNOW...AND WINDS WILL INCREASE DURING THE
DAY THURSDAY/THURSDAY NIGHT. PROBABILITY OF BLIZZARD INCREASING...
DEVELOPING THURSDAY AFTERNOON. WILL HAVE TO BE WATCHED CLOSELY.
SNOWFALL AMOUNTS LIKELY IN HEAVIER SNOW BAND OF 17 TO 22
INCHES...WITH LOCATIONS ACROSS CENTRAL/SOUTH CENTRAL MN...FAIRMONT-
TWIN CITIES AREA-ST CLOUD...SEEING THE HEAVIER AMOUNTS. OVERALL
FORECAST LOOKING GOOD.
&&
.DISCUSSION...
&&
.PREV DISCUSSION... /ISSUED 156 PM CST WED FEB 28 2007/
DISCUSSION...
INITIAL STAGES OF THE IMPENDING WINTER STORM IS SITTING ON OUR
DOORSTEP. LEADING EDGE OF NORTHWARD MOVING 88D ECHOES EXTENDS FROM
APPROXIMATELY OWATONNA TO REDWOOD FALLS TO ORTONVILLE. SURFACE
OBSERVATIONS INDICATING THAT THIS IS NOT REACHING THE GROUND IN
MUCH OF OUR FORECAST AREA AS OF YET /SAINT JAMES IS THE ONLY SITE
REPORTING SNOW ATTM/...AS THE BULK OF THE MOISTURE IS EVAPORATING
IN THE LOW TO MID LEVEL DRY LAYER INDICATED IN AREA TAMDAR
SOUNDINGS AND THE 12Z KMPX SOUNDING. HOWEVER...WITH THE MID LEVEL
ECHOES INDICATING REFLECTIVITIES AS HIGH AS 35 TO 40 DBZ...WHEN
THE LAYER IS FULLY SATURATED...THE SNOWFALL RATES SHOULD BE FAIRLY
HIGH...SOMETHING THAT IS REINFORCED BY SEVERAL SURFACE OBSERVATION
SITES IN SOUTH DAKOTA REPORTING VISIBILITIES UNDER A MILE AT
TIMES.
THIS INITIAL AREA OF PRECIPITATION IS ASSOCIATED WITH A NORTHWARD
MOVING WARM FRONT AND A SHORTWAVE EJECTING AHEAD OF THE MAIN
TROUGH. MID LEVEL FRONTOGENESIS OCCURS AS THE SHORTWAVE CATCHES UP
TO THE FRONTAL SURFACE LATER TODAY...WITH THE MAIN BAND EXPECTED
TO SET UP ACROSS THE NORTHERN THIRD TO HALF OF THE FORECAST AREA
DURING THE LATE EVENING AND OVERNIGHT HOURS. THE PRECIPITATION
TYPE WILL BE A LITTLE TRICKY...ESPECIALLY ACROSS THE SOUTHERN PART
OF THE FORECAST AREA. THE LATEST MODEL GUIDANCE...INCLUDING THE
ECMWF...NAM...SREF...AND GFS...INDICATES THAT THE WARM NOSE GETS
VERY CLOSE TO THE AREA. IT WILL BE A BATTLE BETWEEN THE WARM
ADVECTION AND THE EVAPORATIVE COOLING MENTIONED ABOVE...AND AT
THIS TIME...WE THINK THAT MOST EVERYTHING WILL REMAIN IN THE FORM
OF SNOW INITIALLY...EXCEPT FOR PERHAPS ALONG AND SOUTH OF THE
INTERSTATE 90 CORRIDOR. HOWEVER...WE EXPECT TO HAVE A PERIOD
AFTER MIDNIGHT TONIGHT WHEN WE LOSE MID AND UPPER LEVEL
SATURATION...AND CONSEQUENTLY...OUR SOURCE OF ICE CRYSTALS...OVER
THE SOUTHERN HALF OF THE AREA...WHICH WILL LEAD TO THE POSSIBILITY
OF FREEZING DRIZZLE...MAINLY FROM ABOUT NEW ULM TO THE SOUTHERN
SECTIONS OF THE TWIN CITIES TO CHIPPEWA FALLS.
THE REAL SHOW WILL BEGIN MID MORNING THURSDAY AS THE MAIN TROUGH
BECOMES NEGATIVELY TILTED AND HINTS OF A COUPLED UPPER LEVEL JET
LEAD TO STRONG CYCLOGENESIS OVER THE CENTRAL PLAINS. THE 12Z NAM
AND GFS ARE BOTH SHOWING THE TRAILING DEFORMATION ZONE SETTING UP
ACROSS CENTRAL MINNESOTA BY MID MORNING BEFORE ROTATING NORTH
NORTHEASTWARD INTO NORTHEAST MINNESOTA AND WESTERN WISCONSIN BY
THURSDAY NIGHT. HOWEVER...THE SLIGHT DIFFERENCES IN THE MAXIMUM
FRONTOGENESIS AREA WILL HAVE SIGNIFICANT IMPLICATIONS FOR THE TWIN
CITIES. THE GFS WOULD FAVOR THE HEAVIEST SNOW DIRECTLY OVER THE
TWIN CITIES AROUND MIDDAY TOMORROW...WHILE THE NAM WOULD FAVOR
AREAS JUST WEST OF THE CITIES. DESPITE WHICH SOLUTION IS
SELECTED...THOUGH...SIGNIFICANT ACCUMULATIONS ARE IN STORE FOR ALL
AREAS.
NEXT ISSUE BECOMES THE WINDS AND ITS EFFECT ON VISIBILITIES. SOME
AREAS WILL SEE NEAR BLIZZARD CONDITIONS...ESPECIALLY ACROSS
SOUTHWEST AND SOUTH CENTRAL MINNESOTA. THIS WILL HAVE TO BE
WATCHED CLOSELY IN LATER SHIFTS FOR POSSIBLE WARNING UPGRADE.
SNOW BEGINS TO TAPER OFF FRIDAY NIGHT AS THE LOW SHIFTS TO THE
NORTHEAST. CYCLONIC CURVATURE ON THE BACKSIDE WILL KEEP LIGHT SNOW
THROUGH FRIDAY NIGHT BEFORE SIGNIFICANT DRYING MOVES IN WITH THE
APPROACHING RIDGE AXIS.
TEMPERATURES OVER THE WEEKEND WILL BE COOL...ESPECIALLY OVERNIGHT
LOWS...WITH A SURFACE RIDGE OVER THE AREA...LACK OF CLOUDS...AND
FRESH SNOW PACK. WARM ADVECTION WILL ENSUE LATE WEEKEND AND INTO
NEXT WEEK AS A COUPLE OF WEAK...BUT DRY...SYSTEMS APPROACH THE
AREA.
THANKS FOR THE COLLABORATION SURROUNDING WFOS.
MPX WATCHES/WARNINGS/ADVISORIES...
MN...WINTER STORM WARNING UNTIL 6 PM CST FRIDAY FOR ANOKA-BENTON-BLUE
EARTH-CARVER-CHISAGO-DAKOTA-FARIBAULT-FREEBORN-GOODHUE-
HENNEPIN-ISANTI-KANABEC-LE SUEUR-MCLEOD-MEEKER-MILLE LACS-
MORRISON-NICOLLET-RAMSEY-RICE-SCOTT-SHERBURNE-SIBLEY-
STEARNS-STEELE-TODD-WASECA-WASHINGTON-WRIGHT COUNTY(IES).
WINTER STORM WARNING UNTIL 6 PM CST FRIDAY FOR BROWN-CHIPPEWA-
DOUGLAS-KANDIYOHI-LAC QUI PARLE-MARTIN-POPE-REDWOOD-
RENVILLE-STEVENS-SWIFT-WATONWAN-YELLOW MEDICINE COUNTY(IES).
WI...WINTER STORM WARNING FROM 6 PM THIS EVENING TO 6 PM CST FRIDAY
FOR BARRON-CHIPPEWA-DUNN-EAU CLAIRE-PEPIN-PIERCE-POLK-RUSK-
ST. CROIX COUNTY(IES).
$$
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...WINTER STORM WARNING UNTIL 6 PM CST FRIDAY FOR ANOKA-BENTON-BLUE
EARTH-BROWN-CARVER-CHIPPEWA-CHISAGO-DAKOTA-DOUGLAS-
FARIBAULT-FREEBORN-GOODHUE-HENNEPIN-ISANTI-KANABEC-
KANDIYOHI-LAC QUI PARLE-LE SUEUR-MARTIN-MCLEOD-MEEKER-MILLE
LACS-MORRISON-NICOLLET-POPE-RAMSEY-REDWOOD-RENVILLE-RICE-
SCOTT-SHERBURNE-SIBLEY-STEARNS-STEELE-STEVENS-SWIFT-TODD-
WASECA-WASHINGTON-WATONWAN-WRIGHT-YELLOW MEDICINE
COUNTY(IES).
WI...WINTER STORM WARNING UNTIL 6 PM CST FRIDAY FOR BARRON-CHIPPEWA-
DUNN-EAU CLAIRE-PEPIN-PIERCE-POLK-RUSK-ST. CROIX
COUNTY(IES).
&&
$$
JVM/DWE
AREA FORECAST DISCUSSION
NWS TWIN CITIES/CHANHASSEN MN
156 PM CST WED FEB 28 2007
.DISCUSSION...
INITIAL STAGES OF THE IMPENDING WINTER STORM IS SITTING ON OUR
DOORSTEP. LEADING EDGE OF NORTHWARD MOVING 88D ECHOES EXTENDS FROM
APPROXIMATELY OWATONNA TO REDWOOD FALLS TO ORTONVILLE. SURFACE
OBSERVATIONS INDICATING THAT THIS IS NOT REACHING THE GROUND IN
MUCH OF OUR FORECAST AREA AS OF YET /SAINT JAMES IS THE ONLY SITE
REPORTING SNOW ATTM/...AS THE BULK OF THE MOISTURE IS EVAPORATING
IN THE LOW TO MID LEVEL DRY LAYER INDICATED IN AREA TAMDAR
SOUNDINGS AND THE 12Z KMPX SOUNDING. HOWEVER...WITH THE MID LEVEL
ECHOES INDICATING REFLECTIVITIES AS HIGH AS 35 TO 40 DBZ...WHEN
THE LAYER IS FULLY SATURATED...THE SNOWFALL RATES SHOULD BE FAIRLY
HIGH...SOMETHING THAT IS REINFORCED BY SEVERAL SURFACE OBSERVATION
SITES IN SOUTH DAKOTA REPORTING VISIBILITIES UNDER A MILE AT
TIMES.
THIS INITIAL AREA OF PRECIPITATION IS ASSOCIATED WITH A NORTHWARD
MOVING WARM FRONT AND A SHORTWAVE EJECTING AHEAD OF THE MAIN
TROUGH. MID LEVEL FRONTOGENESIS OCCURS AS THE SHORTWAVE CATCHES UP
TO THE FRONTAL SURFACE LATER TODAY...WITH THE MAIN BAND EXPECTED
TO SET UP ACROSS THE NORTHERN THIRD TO HALF OF THE FORECAST AREA
DURING THE LATE EVENING AND OVERNIGHT HOURS. THE PRECIPITATION
TYPE WILL BE A LITTLE TRICKY...ESPECIALLY ACROSS THE SOUTHERN PART
OF THE FORECAST AREA. THE LATEST MODEL GUIDANCE...INCLUDING THE
ECMWF...NAM...SREF...AND GFS...INDICATES THAT THE WARM NOSE GETS
VERY CLOSE TO THE AREA. IT WILL BE A BATTLE BETWEEN THE WARM
ADVECTION AND THE EVAPORATIVE COOLING MENTIONED ABOVE...AND AT
THIS TIME...WE THINK THAT MOST EVERYTHING WILL REMAIN IN THE FORM
OF SNOW INITIALLY...EXCEPT FOR PERHAPS ALONG AND SOUTH OF THE
INTERSTATE 90 CORRIDOR. HOWEVER...WE EXPECT TO HAVE A PERIOD
AFTER MIDNIGHT TONIGHT WHEN WE LOSE MID AND UPPER LEVEL
SATURATION...AND CONSEQUENTLY...OUR SOURCE OF ICE CRYSTALS...OVER
THE SOUTHERN HALF OF THE AREA...WHICH WILL LEAD TO THE POSSIBILITY
OF FREEZING DRIZZLE...MAINLY FROM ABOUT NEW ULM TO THE SOUTHERN
SECTIONS OF THE TWIN CITIES TO CHIPPEWA FALLS.
THE REAL SHOW WILL BEGIN MID MORNING THURSDAY AS THE MAIN TROUGH
BECOMES NEGATIVELY TILTED AND HINTS OF A COUPLED UPPER LEVEL JET
LEAD TO STRONG CYCLOGENESIS OVER THE CENTRAL PLAINS. THE 12Z NAM
AND GFS ARE BOTH SHOWING THE TRAILING DEFORMATION ZONE SETTING UP
ACROSS CENTRAL MINNESOTA BY MID MORNING BEFORE ROTATING NORTH
NORTHEASTWARD INTO NORTHEAST MINNESOTA AND WESTERN WISCONSIN BY
THURSDAY NIGHT. HOWEVER...THE SLIGHT DIFFERENCES IN THE MAXIMUM
FRONTOGENESIS AREA WILL HAVE SIGNIFICANT IMPLICATIONS FOR THE TWIN
CITIES. THE GFS WOULD FAVOR THE HEAVIEST SNOW DIRECTLY OVER THE
TWIN CITIES AROUND MIDDAY TOMORROW...WHILE THE NAM WOULD FAVOR
AREAS JUST WEST OF THE CITIES. DESPITE WHICH SOLUTION IS
SELECTED...THOUGH...SIGNIFICANT ACCUMULATIONS ARE IN STORE FOR ALL
AREAS.
NEXT ISSUE BECOMES THE WINDS AND ITS EFFECT ON VISIBILITIES. SOME
AREAS WILL SEE NEAR BLIZZARD CONDITIONS...ESPECIALLY ACROSS
SOUTHWEST AND SOUTH CENTRAL MINNESOTA. THIS WILL HAVE TO BE
WATCHED CLOSELY IN LATER SHIFTS FOR POSSIBLE WARNING UPGRADE.
SNOW BEGINS TO TAPER OFF FRIDAY NIGHT AS THE LOW SHIFTS TO THE
NORTHEAST. CYCLONIC CURVATURE ON THE BACKSIDE WILL KEEP LIGHT SNOW
THROUGH FRIDAY NIGHT BEFORE SIGNIFICANT DRYING MOVES IN WITH THE
APPROACHING RIDGE AXIS.
TEMPERATURES OVER THE WEEKEND WILL BE COOL...ESPECIALLY OVERNIGHT
LOWS...WITH A SURFACE RIDGE OVER THE AREA...LACK OF CLOUDS...AND
FRESH SNOW PACK. WARM ADVECTION WILL ENSUE LATE WEEKEND AND INTO
NEXT WEEK AS A COUPLE OF WEAK...BUT DRY...SYSTEMS APPROACH THE
AREA.
THANKS FOR THE COLLABORATION SURROUNDING WFOS.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...WINTER STORM WARNING UNTIL 6 PM CST FRIDAY FOR ANOKA-BENTON-BLUE
EARTH-CARVER-CHISAGO-DAKOTA-FARIBAULT-FREEBORN-GOODHUE-
HENNEPIN-ISANTI-KANABEC-LE SUEUR-MCLEOD-MEEKER-MILLE LACS-
MORRISON-NICOLLET-RAMSEY-RICE-SCOTT-SHERBURNE-SIBLEY-
STEARNS-STEELE-TODD-WASECA-WASHINGTON-WRIGHT COUNTY(IES).
WINTER STORM WARNING UNTIL 6 PM CST FRIDAY FOR BROWN-CHIPPEWA-
DOUGLAS-KANDIYOHI-LAC QUI PARLE-MARTIN-POPE-REDWOOD-
RENVILLE-STEVENS-SWIFT-WATONWAN-YELLOW MEDICINE COUNTY(IES).
WI...WINTER STORM WARNING FROM 6 PM THIS EVENING TO 6 PM CST FRIDAY
FOR BARRON-CHIPPEWA-DUNN-EAU CLAIRE-PEPIN-PIERCE-POLK-RUSK-
ST. CROIX COUNTY(IES).
&&
$$
KAT
AREA FORECAST DISCUSSION
NWS SEATTLE WA
435 PM PST WED FEB 28 2007 ...UPDATED
UPDATED AVIATION SECTION BELOW FOR CONVERGENCE ZONE SNOW
DISCUSSION...AND UPDATED ADVISORIES SECTION.
.SYNOPSIS...LOW PRESSURE ALOFT OVER THE REGION ASSOCIATED WITH COLD
MOIST UNSTABLE AIR WILL MAINTAIN SOME RAIN OR SNOW SHOWERS INTO
THURSDAY. AFTER A BRIEF BREAK...A CHANGE IN THE WEATHER PATTERN WILL
BRING WARMER YET WET WEATHER FRIDAY AND SATURDAY AS A PACIFIC
WEATHER SYSTEM MOVES ONSHORE. HIGHER PRESSURE ALOFT IS EXPECTED TO
BRING A BREAK IN THE WET WEATHER ON SUNDAY BEFORE WET WEATHER RENEWS
NEXT WEEK.
&&
.SHORT TERM...THE SHARP UPPER TROF MOVED INTO WESTERN WA THIS
AFTERNOON. ASSOCIATED AIR MASS QUITE COOL AND UNSTABLE. ACARS DATA
SHOWS THE FREEZING LEVEL NEAR 1500 FEET. SATELLITE PICTURES SHOW
QUITE AN ARRAY OF OPEN CELLULAR CU UPSTREAM IN THE NW FLOW ALOFT
LIKELY TO MOVE ONSHORE TONIGHT AND THU AM. THE PUGET SOUND
CONVERGENCE ZONE RECONVENED ACROSS THE NORTH SOUND THIS AFTERNOON
AND WILL LIKELY SAG S IN THE NW FLOW TONIGHT BEFORE DYING OUT THU AM
AS PRESSURE GRADIENTS EASE. SO WITH LOW SNOW LEVELS..LIKELY TO HAVE
SOME SNOW SHOWERS WITH ROOFTOP/GRASSY SNOW ACCUMULATIONS IN THE
LOWLANDS. WILL ISSUE AN SPS IN A BIT.
SATELLITE IMAGERY SHOWS A WEAK SHORTWAVE HEADING SE ACROSS VANCOUVER
ISLAND THAT WILL LIKELY ENHANCE THE SHOWERS IN OUR AREA TONIGHT.
ANOTHER SHORTWAVE IN THE NW FLOW ALOFT NEAR 50N 140W THIS AFTERNOON
THAT THE PROGS TAKE PRIMARILY INTO OREGON THU. SO MUCH OF WESTERN
WASHINGTON SHOULD GET A BIT OF A BREAK THU PM BEFORE.........
NEG TILT UPPER RIDGE IS NEAR 155W WITH A VIGOROUS UPPER TROF
UPSTREAM. THIS SHORTWAVE SHOULD KNOCK THE RIDGE DOWN AND PHASE WITH
THE COLD UPPER LOW OVER AK AND THE YUKON FRI TO LIKELY INCREASE THIS
SYSTEMS BAROCLINICITY. WITH A TAP INTO SOME SUBTROPICAL MOISTURE..
LOOK FOR A MORE ZONAL FLOW PATTERN WITH A RETURN TO WARMER AND WET
WEATHER FRI AND SAT. WILL HAVE TO KEEP AN EYE ON QPF AMOUNTS AND HOW
MUCH THE FREEZING LEVEL RISES. RIVERS ARE LOW RIGHT NOW BUT SHOULD
RISE WITH THE RAIN AND HIGHER SNOW LEVEL. SO IT LOOKS LIKE MARCH IS
GOING TO COME IN LIKE A LION. BUEHNER
.LONG TERM...MUCH BETTER RUN TO RUN CONSISTENCY IN THE MODELS WITH
AN UPPER LEVEL RIDGE TO BUILD ALONG THE WEST COAST BY SUN AS AN
UPPER TROF DIGS OFFSHORE. THIS SHOULD PUSH THE BAROCLINIC ZONE NORTH
INTO BRITISH COLUMBIA. THEN THE RIDGE AXIS SHIFTS INLAND AS THE
OFFSHORE TROF APPROACHES FOR A SEQUENCE OF SHORTWAVES BEGINNING MON
THRU MIDDAY. BUEHNER
&&
.AVIATION...UPDATED...
THE CONVERGENCE ZONE IS NOW PRODUCING RATHER HEAVY SNOW SHOWERS FROM
NORTHERN HOOD CANAL TO ARLINGTON AND SOUTH TO NORTHERN KING CO. THE
CONVERGENCE ZONE IS HEAVY WITH PRECIP ALL FALLING AS SNOW. SO EXPECT
ACCUMULATIONS OF AN INCH OR TWO AT PLACES LIKE KPAE. KBFI IS ON THE
EDGE OF WHERE THE CURRENT PSCZ SHOULD MAKE IT THIS EVENING...THOUGH
WITH TIME OVERNIGHT IT WILL SHIFT S AS THE UPPER TROUGH DRIVES E OF
THE AREA.
USERS IN THE PUGET SOUND AREA SHOULD EXPECT TAF AMENDMENTS AS
CONDITIONS CHANGE...AND 1-2 INCH ACCUMULATIONS AT KBFI AND KSEA
OVERNIGHT CANNOT BE RULED OUT IF THE PSCZ DROPS JUST A FEW MILES
FURTHER S THAN CURRENTLY EXPECTED.
FROM PREVIOUS AVIATION DISCUSSION...SHOWERS AND CONVERGENCE ZONE
ACTIVITY DIES OFF 15Z-18Z AS WARM ADVECTION CLOUDS APPROACH FROM THE
WEST AND ONSHORE PRES GRADIENTS COLLAPSE.
CIGS GENERALLY VFR...WITH LOCAL IFR CIGS VC THE CONVERGENCE
ZONE...HEAVIER SHOWERS AND HIGHER TERRAIN. WINDS AT KSEA 20010KT
DECREASING TO 18007KT AFTER 06Z. ALBRECHT
$$
.SEW WATCHES/WARNINGS/ADVISORIES...
.SNOW ADVISORY THIS EVENING FOR PORTIONS OF THE PUGET SOUND
AREA--EVERETT AND VICINITY--ADMIRALTY INLET AREA--NORTHERN
KITSAP PENINSULA--AND EASTERN PUGET SOUND LOWLANDS.
.SMALL CRAFT ADVISORY COAST...STRAIT...AND PUGET SOUND AND HOOD
CANAL.
.SMALL CRAFT ADVISORY FOR ROUGH BAR CONDITIONS GRAYS HARBOR BAR.
$$
AREA FORECAST DISCUSSION
NWS SEATTLE WA
300 PM PST WED FEB 28 2007
.SYNOPSIS...LOW PRESSURE ALOFT OVER THE REGION ASSOCIATED WITH COLD
MOIST UNSTABLE AIR WILL MAINTAIN SOME RAIN OR SNOW SHOWERS INTO
THURSDAY. AFTER A BRIEF BREAK...A CHANGE IN THE WEATHER PATTERN WILL
BRING WARMER YET WET WEATHER FRIDAY AND SATURDAY AS A PACIFIC
WEATHER SYSTEM MOVES ONSHORE. HIGHER PRESSURE ALOFT IS EXPECTED TO
BRING A BREAK IN THE WET WEATHER ON SUNDAY BEFORE WET WEATHER RENEWS
NEXT WEEK.
&&
.SHORT TERM...THE SHARP UPPER TROF MOVED INTO WESTERN WA THIS
AFTERNOON. ASSOCIATED AIR MASS QUITE COOL AND UNSTABLE. ACARS DATA
SHOWS THE FREEZING LEVEL NEAR 1500 FEET. SATELLITE PICTURES SHOW
QUITE AN ARRAY OF OPEN CELLULAR CU UPSTREAM IN THE NW FLOW ALOFT
LIKELY TO MOVE ONSHORE TONIGHT AND THU AM. THE PUGET SOUND
CONVERGENCE ZONE RECONVENED ACROSS THE NORTH SOUND THIS AFTERNOON
AND WILL LIKELY SAG S IN THE NW FLOW TONIGHT BEFORE DYING OUT THU AM
AS PRESSURE GRADIENTS EASE. SO WITH LOW SNOW LEVELS..LIKELY TO HAVE
SOME SNOW SHOWERS WITH ROOFTOP/GRASSY SNOW ACCUMULATIONS IN THE
LOWLANDS. WILL ISSUE AN SPS IN A BIT.
SATELLITE IMAGERY SHOWS A WEAK SHORTWAVE HEADING SE ACROSS VANCOUVER
ISLAND THAT WILL LIKELY ENHANCE THE SHOWERS IN OUR AREA TONIGHT.
ANOTHER SHORTWAVE IN THE NW FLOW ALOFT NEAR 50N 140W THIS AFTERNOON
THAT THE PROGS TAKE PRIMARILY INTO OREGON THU. SO MUCH OF WESTERN
WASHINGTON SHOULD GET A BIT OF A BREAK THU PM BEFORE.........
NEG TILT UPPER RIDGE IS NEAR 155W WITH A VIGOROUS UPPER TROF
UPSTREAM. THIS SHORTWAVE SHOULD KNOCK THE RIDGE DOWN AND PHASE WITH
THE COLD UPPER LOW OVER AK AND THE YUKON FRI TO LIKELY INCREASE THIS
SYSTEMS BAROCLINICITY. WITH A TAP INTO SOME SUBTROPICAL MOISTURE..
LOOK FOR A MORE ZONAL FLOW PATTERN WITH A RETURN TO WARMER AND WET
WEATHER FRI AND SAT. WILL HAVE TO KEEP AN EYE ON QPF AMOUNTS AND HOW
MUCH THE FREEZING LEVEL RISES. RIVERS ARE LOW RIGHT NOW BUT SHOULD
RISE WITH THE RAIN AND HIGHER SNOW LEVEL. SO IT LOOKS LIKE MARCH IS
GOING TO COME IN LIKE A LION. BUEHNER
.LONG TERM...MUCH BETTER RUN TO RUN CONSISTENCY IN THE MODELS WITH
AN UPPER LEVEL RIDGE TO BUILD ALONG THE WEST COAST BY SUN AS AN
UPPER TROF DIGS OFFSHORE. THIS SHOULD PUSH THE BAROCLINIC ZONE NORTH
INTO BRITISH COLUMBIA. THEN THE RIDGE AXIS SHIFTS INLAND AS THE
OFFSHORE TROF APPROACHES FOR A SEQUENCE OF SHORTWAVES BEGINNING MON
THRU MIDDAY. BUEHNER
&&
.AVIATION...THE AIR MASS HAS DESTABILIZED SUFFICIENTLY THAT CLEARING
IS NOW SEEN BETWEEN SHOWERS AND ON EITHER SIDE OF THE PUGET SOUND
CONVERGENCE ZONE. DESPITE LOCAL WARMING INTO THE MID 40S...DEWPOINT
TEMPERATURES ARE LOW AND TEMPERATURES AND SNOW LEVELS EFFICIENTLY
FALL IN HEAVIER SHOWERS WITH MANY SHOWERS DOWN TO SEA LEVEL FALLING
IN THE FORM OF SNOW OR RAIN/SNOW MIXED.
A SHORT WAVE TROUGH MOVING SE THROUGH VANCOUVER ISLAND INTO THE AREA
HAS TEMPORARILY PULLED THE CONVERGENCE ZONE TO THE NORTH OF THE
SNO-KING LINE. EXPECT THE CONVERGENCE ZONE TO SLIDE TO THE S BY 5 PM
AS INFLOW THRU THE STRAIT INCREASES AND THE SHORT WAVE TROUGH
PASSES. THE CONVERGENCE ZONE WILL THEN LIFT BACK TO THE N A BIT
DURING THE MORNING HOURS AS GRADIENTS BECOMING INCREASINGLY SLY WITH
THE APPROACH OF A WARM FRONT NOW WELL OFFSHORE.
SNOW SHOWERS BECOME AN ISSUE AGAIN OVERNIGHT...AND ESPECIALLY AFTER
MIDNIGHT WITH DIURNAL COOLING. SOME LIGHT ACCUMULATIONS OF AN INCH
OR SO ARE POSSIBLE ESPECIALLY WITH THE PUGET SOUND CONVERGENCE ZONE.
AT THIS POINT EXPECT A GRASS/ROOF/CAR ACCUMULATION IF AT ALL WITH
RUNWAYS...TAXIWAYS...AND ROADS REMAINING WARM AND TRAVELED ENOUGH TO
KEEP THINGS JUST WET OR OCNLLY SLUSHY.
SHOWERS AND CONVERGENCE ZONE ACTIVITY DIES OFF 15Z-18Z AS WARM
ADVECTION CLOUDS APPROACH FROM THE WEST AND ONSHORE PRES GRADIENTS
COLLAPSE.
CIGS GENERALLY VFR...WITH LOCAL IFR CIGS VC THE CONVERGENCE
ZONE...HEAVIER SHOWERS AND HIGHER TERRAIN. WINDS AT KSEA 20010KT
DECREASING TO 18007KT AFTER 06Z. ALBRECHT
$$
.SEW WATCHES/WARNINGS/ADVISORIES...
.SMALL CRAFT ADVISORY COAST AND STRAIT.
.SMALL CRAFT ADVISORY FOR ROUGH BAR CONDITIONS GRAYS HARBOR BAR.
$$
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