AREA FORECAST DISCUSSION...CORRECTED
NWS SAN DIEGO CA
621 AM PST TUE FEB 20 2007
.SYNOPSIS...
RESIDUAL MOISTURE WILL CAUSE A FEW CLOUDS AND LATE NIGHT AND EARLY
MORNING FOG...OTHERWISE FAIR AND WARMER THROUGH WEDNESDAY UNDER WEAK
HIGH PRESSURE. A STORM APPROACHING FROM THE NORTHWEST WILL BRING
ANOTHER ROUND OF MODERATE PRECIPITATION LATE WEDNESDAY NIGHT THROUGH
EARLY FRIDAY WITH SNOW LEVELS IN THE MOUNTAINS LOWERING TO AROUND
5000 FEET. NORTHWEST FLOW PATTERN FOR NEXT WEEKEND WILL BRING FAIR
AND A LITTLE WARMER WEATHER WITH LOCALLY BREEZY CONDITIONS IN THE
MOUNTAINS AND DESERTS AT TIMES.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
.SHORT TERM (TODAY THROUGH THURSDAY)...
WEAKENING LOW PRESSURE OVER ARIZONA AND NEW MEXICO WILL MOVE EAST
TODAY WITH SHORTWAVE RIDGING BUILDING OVER CALIFORNIA TODAY. THIS
HIGH PRESSURE WILL WEAKEN WEDNESDAY IN ADVANCE OF ANOTHER PACIFIC
STORM SYSTEM. THIS SYSTEM IS EXPECTED TO MOVE SLOWLY ACROSS
SOUTHWEST CALIFORNIA FROM LATE WEDNESDAY NIGHT THROUGH EARLY FRIDAY.
IN THE NEAR TERM...AREAS ALONG AND WEST OF THE MOUNTAINS WILL SEE
SOME CLOUDS THIS MORNING AS RESIDUAL MOISTURE LINGERS. THERE WILL
ALSO BE SOME PATCHY FOG...SOME LOCALLY DENSE...IN LOWER LYING AREAS
WEST OF THE MOUNTAINS. MORE CONSISTENT ECMWF IS PREFERRED WITH THE
NEXT SYSTEM. GFS ISN`T TOO DIFFERENT INITIALLY...BUT IS SLOWER
MOVING THE SYSTEM EAST ON FRIDAY. CURRENT TIMING WOULD BRING ARRIVAL
OF PRECIPITATION LATE WEDNESDAY NIGHT WITH PRECIPITATION CONTINUING
THURSDAY...DECREASING THURSDAY NIGHT...AND ENDING EARLY FRIDAY.
UNLIKE THE DEPARTING SYSTEM THAT PRODUCED HEAVIEST AMOUNTS OVER
CENTRAL AND SOUTHERN SAN DIEGO COUNTY WITH LIGHTER AMOUNTS TO THE
NORTH...AMOUNTS WITH THIS NEXT SYSTEM MAY BE MORE UNIFORMLY
DISTRIBUTED FROM NORTH TO SOUTH WITH A DISTRIBUTION FROM THE COAST
TO THE COASTAL SLOPES SIMILAR TO CLIMATOLOGY. PRELIMINARY TOTALS
WITH THIS NEXT SYSTEM OF ONE HALF TO ONE INCH AT THE COAST TO AROUND
2 INCHES ON SOUTHWEST FACING SLOPES. LOCALLY GREATER AMOUNTS ARE
POSSIBLE. SNOW LEVELS WILL LOWER TO AROUND 5000 FEET OR LOCALLY
LOWER THURSDAY AFTERNOON AND NIGHT.
&&
.LONG TERM (FRIDAY THROUGH MONDAY)...
PRECIPITATION IS EXPECTED TO END EARLY FRIDAY. WEAKLY CYCLONIC
NORTHWEST FLOW PATTERN WILL FOLLOW FOR NEXT WEEKEND. THIS WILL BRING
DRYING...MINOR WARMING...WITH GUSTY WINDS IN THE MOUNTAINS AND
DESERTS AT TIMES. ECWMF GENERALLY FAVORED. THERE`S ALSO A SLIGHT
CHANCE OF PRECIPITATION EARLY NEXT WEEK AS NORTHWEST FLOW PATTERN
MAY SAG SOUTHWARD INTO SOUTHERN CALIFORNIA AND ENTRAIN SOME MOISTURE
OFF THE PACIFIC.
&&
.AVIATION...CORRECTED
LATE EVENING ACARS SOUNDINGS INDICATE THE DEPTH OF THE MOISTURE WAS
AROUND 7500 FEET OVER THE AREA WITH MOST OF THE CLOUDS COVERING THE
SOUTHERN HALF OF SAN DIEGO COUNTY AND THE MOUNTAINS. MULTIPLE LAYERS
WITH THE LOWEST SCATTERED TO BROKEN LAYER AROUND 1500 FEET MSL WITH
ADDITIONAL LAYERS AROUND 3000 FEET AND 5000 FEET. EXPECT SLOW
CLEARING THROUGH THE LATE MORNING WITH SCATTERED CONDITIONS MOST
AREAS DURING THE AFTERNOON. MOSTLY CLEAR CONDITIONS TONIGHT EXCEPT
FOR AREAS OF VALLEY FOG ESPECIALLY VICINITY OF KCNO AND KONT.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...HIGH SURF ADVISORY UNTIL 2 PM PST THIS AFTERNOON FOR SAN DIEGO
COUNTY COASTAL AREAS.
PZ...NONE.
&&
$$
PUBLIC...MARTIN
AVIATION/MARINE...HORTON
NWS ON THE WEB AT WEATHER.GOV/SANDIEGO
AREA FORECAST DISCUSSION
NWS BALTIMORE MD/WASHINGTON DC
845 PM EST WED FEB 21 2007
.SHORT TERM...
WATER VAPOR LOOP SHOWS A SHORT WAVE MOVING EAST INTO THE
CAROLINAS...AS A VIGOROUS SHORT WAVE MOVES SOUTHEAST INTO THE GREAT
LAKES REGION. ACARS 400-250MB WIND OBSERVATIONS REVEAL ZONAL
FLOW...WITH THE 100-140KT NORTHERN STREAM JET FROM THE PACIFIC EAST
THROUGH THE MID ATLANTIC. A SOUTHERN STREAM 100-140KT JET EXTENDED
FROM NORTHERN MEXICO THROUGH THE CAROLINAS. 20Z SURFACE ANALYSIS
PLACED A 1009MB CYCLONE IN WESTERN NORTH CAROLINA...ALONG A WEST TO
EAST FRONTAL BOUNDARY. A SERIES OF COLD FRONTS ARE SLICING THROUGH
THE UPPER MIDWEST...EXTENDING SOUTHWEST FROM A 998MB OCCLUDED
CYCLONE IN NORTH CENTRAL MINNESOTA.
EXPECT STRATUS GROWTH TO THE NORTH OVERNIGHT AS WARM ADVECTION
BEGINS AHEAD OF THE VIGOROUS SHORT WAVE. 18Z NAM/GFS BUFKIT FORECAST
SOUNDINGS ARE MARGINALLY SUPPORTIVE OF DRIZZLE AS CEILINGS LOWER
TOWARD SUNRISE. EXPECT COLDEST TEMPERATURES IN THE NORTH TO NEAR
FREEZING DURING THE EARLY PORTION OF THE NIGHT BEFORE CLOUDS
INVADE...ALLOWING TEMPERATURES TO RISE A FEW DEGREES. THOSE OUT AND
ABOUT SHOULD WATCH OUT FOR SLICK SPOTS THAT MAY DEVELOP FROM THE
MELTING SNOW/SLEET DURING THE PREVIOUS SEVERAL DAYS.
A STRONG COLD FRONT SLICES THROUGH THE REGION TOMORROW FROM WEST TO
EAST...ASSOCIATED WITH THE VIGOROUS SHORT WAVE DROPPING SOUTHEAST
FROM THE GREAT LAKES. FIRST CONCERN REVOLVES AROUND CONVECTIVE
POSSIBILITY. BOTH 18Z NAM/GFS INDICATE SLIGHT INSTABILITY OCCURRING
JUST AHEAD OF THE COLD FRONT...WITH EQUILIBRIUM LEVELS NEAR 15KFT
SUPPORTIVE OF LOW TOPPED CONVECTION. WINDOW OF OPPORTUNITY WILL BE
NARROW BETWEEN CLOUDS/DRIZZLE AND COLD FRONT. STRONG DOWNSLOPE FLOW
WILL ALSO BE DEVELOPING WHICH LEADS TO THE BEST POSSIBILITY OF
SEEING A CONVECTIVE LINE DEVELOP ACROSS NORTH CENTRAL
MARYLAND...NEAR THE BALTIMORE METRO AREA. 18Z KLWX WRF-NMM AND 12Z
WRF-ARW SIMULATED REFLECTIVITY SUPPORT THIS IDEA.
GUSTY WEST-NORTHWEST WINDS WILL DEVELOP BEHIND THE COLD FRONT AND
LAST THROUGH THURSDAY NIGHT. THE 18Z NAM/GFS ARE CONSISTENT WITH
60KT 850MB WINDS SETTING UP NEAR THE BLUE RIDGE TOMORROW
EVENING...HOWEVER BOTH MODELS INDICATE MOMENTUM TRANSFER WILL BE
CLOSER TO THE 42-48KT RANGE. A HIGH WIND WATCH (WEST OF THE BLUE
RIDGE) AND SPECIAL WEATHER STATEMENT (EAST OF THE BLUE RIDGE) GO
INTO FURTHER DETAIL.
&&
.AVIATION...
WARM ADVECTION AHEAD OF A VIGOROUS SHORT WAVE SHOULD PROMPT STRATUS
GROWTH NORTH INTO THE TERMINALS LATE TONIGHT AND EARLY TOMORROW
MORNING...WITH AN OPPORTUNITY FOR SOME LIGHT RAIN OR DRIZZLE.
THERE IS A NARROW WINDOW OF OPPORTUNITY FOR A LINE OF GUSTY SHOWERS
OR THUNDERSTORMS DURING THE EARLY AFTERNOON ALONG THE COLD FRONT.
BEST FORCING APPEARS TO BE IN PENNSYLVANIA...SO HAVE INDICATED WITH
A CB GROUP FOR NOW GIVEN THE EXTENT OF DOWNSLOPE POST FRONTAL FLOW.
WIND GUSTS OF 35-40KTS EXPECTED FROM THE WNW BEHIND THE COLD FRONT.
&&
.MARINE...
12Z MET/MAV MOS AT THOMAS POINT INDICATE SUSTAINED WINDS 5KT OR LESS
THROUGH THE NIGHT. PROXIMITY 12Z GFS/18Z NAM BUFKIT FORECAST
SOUNDINGS DO NOT INDICATE ADDITIONAL WIND GUST POTENTIAL TONIGHT.
ICE COVERAGE HAS DECREASED DUE TO THE WARMER TEMPERATURES.
&&
.TIDES...
CURRENT TIDAL DEPARTURES ARE A HALF FOOT BELOW ASTRONOMICAL
PREDICTIONS. THE LUNAR CYCLE IS WAXING TOWARD A QUARTER MOON (23
PERCENT FULL). THE CHESAPEAKE BAY OPERATIONAL FORECAST SYSTEM
INDICATES WATER LEVELS WILL RETURN TO PREDICTED LEVELS THROUGH
TOMORROW.
&&
.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...HIGH WIND WATCH FROM THURSDAY AFTERNOON THROUGH FRIDAY
AFTERNOON FOR MDZ003-501-502.
VA...HIGH WIND WATCH FROM THURSDAY AFTERNOON THROUGH FRIDAY
AFTERNOON FOR VAZ021-025>031.
WV...HIGH WIND WATCH FROM THURSDAY AFTERNOON THROUGH FRIDAY
AFTERNOON FOR WVZ050>055-501>504.
MARINE...GALE WARNING FROM 5 PM THURSDAY TO 10 PM EST FRIDAY FOR
ANZ530>537.
&&
SHORT TERM/AVIATION/MARINE/TIDES...ROGOWSKI
AREA FORECAST DISCUSSION
NWS MARQUETTE MI
1008 PM EST WED FEB 21 2007
.UPDATE...
MAIN FCST ISSUES OVERNIGHT ARE WINDS AND SNOW.
WATER VAPOR IMAGERY AND RUC ANALYSIS SHOW A POTENT SHORTWAVE WITH
TIGHT CIRCULATION NEARING WRN LAKE SUPERIOR NEAR KDLH. SHORTWAVE
PASSED OVER KINL WHERE 00Z SOUNDING INDICATED 12HR 500MB HEIGHT FALL
OF 70M. AT THE SFC...ASSOCIATED LOW PRES WAS ELONGATED OVER LAKE
SUPERIOR WITH CENTER APPARENTLY JUST E OF COPPER HARBOR.
ARCTIC COLD FRONT WAS SURGING SE THRU MN...ASSISTED BY A HEALTHY
7MB/3HR PRES RISE MAX OVER NW MN. SCT MOSTLY -SHRA SPREAD ACROSS THE
FCST AREA EARLIER THIS EVENING. SEVERAL LIGHTNING STRIKES
WERE INDICATED BY THE LIGHTNING DETECTION NETWORK OVER WRN LAKE
SUPERIOR/NW WI AND WRN UPPER MI...BUT NO NEW STRIKES HAVE OCCURRED
SINCE 0145Z. SPOTTERS IN WAKEFIELD/IRONWOOD VCNTY REPORTED HVY SNOW
AND SLEET/PEA SIZE HAIL WITH THE THUNDERSTORMS THAT PASSED THRU
THERE. VIGOROUS DYNAMICS COMBINED WITH VERY STEEP MIDLEVEL LAPSE
RATES AROUND 7-7.5C/KM ARE SUPPORTING THE CONVECTION.
OVERALL...HEADLINES FOR THE OVERNIGHT LOOK OKAY. HOWEVER...SHORTWAVE
IS TAKING A TRACK SLIGHTLY S OF WHAT WAS EXPECTED BY THE PREVIOUS
SHIFT. THIS RAISES CONCERN OF EXPANDING HEADLINES AS WRAP-AROUND AND
WEAK LAKE ENHANCEMENT ON THE BACKSIDE OF THE VIGOROUS SHORTWAVE
SHOULD IMPACT AREAS SLIGHTLY FARTHER S THAN WHAT WAS ANTICIPATED.
00Z RUC/NAM SEEM TO BE CATCHING ONTO THIS POSSIBILITY WITH INCREASED
PCPN INDICATED OVER ONTONAGON/GOGEBIC COUNTY OVERNIGHT. WITH THE
GUSTY WINDS EXPECTED...WILL INCLUDE ONTONAGON COUNTY IN SNOW/BLSN
ADVY. GOGEBIC COUNTY SEEMS TO BE A MARGINAL CASE AS ICE COVER OVER
THE WRN LAKE SHOULD LIMIT ENHANCEMENT POTENTIAL. WILL LEAVE GOGEBIC
OUT OF ADVY WITH EXPECTATION OF LIGHTER SNOW ACCUMULATIONS AND THUS
LESS BLSN TO REDUCE VSBY. ELSEWHERE OVER THE W...PLAN TO INCREASE
POPS AND SNOW AMOUNTS (GENERALLY 1 TO 2 INCHES) FOR THE OVERNIGHT
GIVEN MORE SRLY TRACK OF SHORTWAVE. SLIGHTLY MORE SRLY TRACK OF
SHORTWAVE SHOULD RESULT IN STRONGEST WINDS PASSING S OF FCST AREA.
THAT SAID...STRONG CAA COMBINED WITH INCOMING PRES RISE MAX WILL
STILL LEAD TO WINDY CONDITIONS...BUT WINDS WON`T BE AS STRONG AS
THEY COULD HAVE BEEN.
&&
.PREV DISCUSSION (ISSUED AT 415 PM EST)...
SYNOPSIS...
WV IMAGERY AND RUC ANALYSIS INDICATED A ZONAL PATTERN ACRS THE
CONUS WITH A POTENT SHRTWV AND TIGHT CIRCULATION OVER NW MN. AT THE
SFC(20Z)...A 998 MB LOW WAS LOCATED NEAR KINL WITH A FRONT DRAPED TO
THE SOUTH THROUGH ERN MN. A 6 MB/3 HR PRES RISE MAX OVER NRN ND
TRAILED A SECONDARY COLD FRONT FROM NW MN INTO S CNTRL ND. RADARS
INDICATED THE INITIAL PCPN BAND...SUPPORTED BY STRONG 700-500
QVECTOR CONV AND 295K ISENTROPIC LIFT...WAS MOVING INTO W UPR MI. SO
FAR...ONLY SCT PCPN LIGHT PCPN WAS NOTED OVER THE NRN MN. CANADIAN
RADARS SHOWED THE MAIN SNOW BAND FROM NEAR CYQT TO THE WNW. WITH SFC
TEMPS INTO THE UPPER 40S OVER NW WI INTO W UPR MI AND WARM PROFILE
INDICATED ON AREA TAMDAR SNDGS...RAIN WAS NOTED OVER MOST OF THE
AREA WITH SNOW FROM NE MN...KCKC TO CYQT.
SHORT TERM(TONIGHT AND THU)
EXPECT THE INITIAL BAND OF PCPN TO SWING QUICKLY ACRS THE AREA WITH
MAINLY RAIN BECOMING MIXED WITH OR CHANGING TO SNOW THIS EVENING AS
THE PCPN MOVES INTO THE COLDER AIR TO THE NORTHEAST. SOME
EVAPORATIVE COOLING INTO THE 950-700 DRY LAYER ALONG WITH DYNAMICS
LIFT AS THE AREA OF STRONG QVECTOR CONV AND HEIGHT FALLS MOVE IN
SHOULD ALSO AID IN TRANSITION TO SNOW. UPSTREAM TRENDS AND
NAM/GFS/LAPSWRF-ARW SUGGEST QPF TO AROUND 0.10 INCH WOULD BE
POSSIBLE FROM LATE AFTERNOON THROUGH EARLY EVENING. HOWEVER...WITH
WARM TEMPS ANY SNOWFALL THIS EVENING SHOULD REMAIN LESS THAN
INCH...EXCEPT OVER THE NRN KEWEENAW WHERE A QUICK INCH OR TWO MAY BE
POSSIBLE.
AS THE LOW MOVES THROUGH ERN LK SUPERIOR AROUND 06Z AND TO NEAR THE
NORTH END OF LK HURON BY 12Z STRONG WINDS AND WRAP-ROUND MOISTURE
WILL MOVE INTO NORTH AND EAST UPPER MI. THE 12Z/18Z NAM IN GENERALLY
AGREEMENT WITH THE GFS/CANADIAN GEM SHOWED A REASONABLE DEPICTION OF
THE EXPECTED LOW TRACK AND WAS USED FOR THE DETAILS. THE STRONGEST
ISALLOBARIC PUSH AHEAD OF A 7 MB/3 HR PRES RISE MAX LINED UP BEST
WITH THE PREVAILING NW OR NNW WINDS NEAR 12Z FROM MARQUETTE
EASTWARD. THE KEWEENAW IS ALSO CLOSE ENOUGH TO THIS FEATURE TO SEE
STRONG WINDS AFTER MIDNIGHT. SO...EXPECT WINDS INTO THE 20-30 MPH
RANGE WITH SOME GUSTS TO 40-50 MPH FOR SEVERAL HOURS...ESPECIALLY
THE LAKE SHORE AND OVER EXPPOSED HIGHER TERRAIN. ALTHOUGH THE 850 MB
TEMPS TO AROUND -10C WILL ONLY PROVIDE MARGINAL INSTABILITY...THE
CONVERGENT CYCLONIC FLOW AND DEEP MOISTURE SHOULD BE ENOUGH TO
PRODUCE LAKE ENHANCED SNOW WITH AMOUNTS IN THE 1-3 INCH RANGE.
SO...SN/BLSN ADVY WAS ISSUED TO COVER THE COMBINATION OF HAZARDS
EXPECTED LATE TONIGHT INTO THU MORNING.
AS THE DEEPER MOISTURE DEPARTS BY MIDDAY AND THE SFC RDG BUILDS
TOWARD THE AREA ANY LES SHOULD TAPER OFF QUICKLY WITH ONLY MINIMAL
ADDITIONAL ACCUMULATIONS.
LONG TERM (THURSDAY NIGHT THROUGH WEDNESDAY)...
MAIN FORECAST DILEMMA THIS PERIOD WILL BE OUR WEEKEND STORM
SYSTEM...WINDS ACROSS THE LAKES AND SNOW. NO LARGE SCALE CHANGES
WERE MADE WITH THIS FORECAST PACKAGE...AND SINCE THIS STORM IS STILL
SEVERAL DAYS AWAY...WILL NOT DO MUCH MORE THAN REFRESH THE WORDING
IN THE HWO TO HIGHLIGHT THE SCALE OF THE SYSTEM.
WILL BEGIN THE PERIOD THURSDAY NIGHT WITH THE SURFACE LOW AND
INVERTED TROUGH CONTINUING TO SLOWLY EXIT THE AREA...AS HIGH
PRESSURE SLIDES IN FROM NORTHWESTERN ONTARIO. EVEN WITH THE RIDGE
OVERHEAD...A FEW LAKE EFFECT FLURRIES ALONG THE AREA MAY STILL BE
POSSIBLE...GIVEN NE WINDS DEVELOPING AS COOL 850MB TEMPS SLIDE IN.
850MB TEMPS WILL BE THE COOLEST...AT LEAST COMPARED TO THE PAST
SEVERAL DAYS...WITH LAKESHORE READINGS AROUND -15C THURSDAY EVENING.
AFTERWARD...WITH THE LARGE RIDGE TAKING HOLD...YET ANOTHER WARMING
TREND IS FIGURED...WITH 850MB TEMPERATURE READINGS BECOMING TOO WARM
TO PRODUCE LAKE EFFECT PRECIPITATION. HIGH CLOUDS ARE FIGURED TO
ENCROACH ON THE REGION FRIDAY AFTERNOON...WITH A SLOW THICKENING AND
LOWERING THROUGH SATURDAY AFTERNOON.
HIGH PRESSURE WILL THEN GENERALLY BE IN CONTROL OF THE REGION
THROUGH THE END OF THE WORK WEEK...BEFORE BEING SQUEEZED OUT OF THE
PICTURE AHEAD OF OUR NEXT STORM SYSTEM. DID MAKE MINOR CHANGES TO
OVERNIGHT LOW TEMPERATURES FRIDAY NIGHT INTO SATURDAY
MORNING...COOLER EAST AND WARMER WEST UNDER MORE ABUNDANT CLOUDS.
THE 500MB RIDGE WILL BE DIRECTLY OVERHEAD FROM 12Z SATURDAY THROUGH
12Z SUNDAY. WE WILL CONTINUE TO MONITOR THE DEVELOPMENT OF THE
SYSTEM ACROSS THE FOUR CORNERS REGION FRIDAY NIGHT INTO SATURDAY.
ONCE AGAIN AT 500MB...THE NAM IS THE FIST OF THE OUTLIERS TO BE
NOTED...DEVELOPING THE CUT OFF LOW MUCH FURTHER SOUTH AND EASTWARD
BY 06Z SATURDAY. AT THIS POINT...12Z SATURDAY...THE CANADIAN AND
ECMWF...SLOWER AND SLIGHTLY MORE NORTHWEST WITH THIS FEATURE SEEM TO
BE ON THE MARK. THE GFS IS BEING SINGLED OUT WITH POSSIBLE FEEDBACK
ISSUES OVER THE SOUTHERN PLAINS STATES TO START OUT THE WEEKEND.
THIS MAY BE RESULTING IN A SOLUTION THAT IS CLOSER TO THE NAM. IT
TOO HAS BEEN DISCREDITED FOR OUR WEEKEND STORM SYSTEM. AS A
RESULT...HAVE UTILIZED HPC GRIDS...WHICH IS A COMBINATION OF THE
SLOWER AND MORE NORTHWESTWARD ECMWF AND TO A LESSER EXTEND THE
CANADIAN MODEL. THE 12Z GFS SEEMED TO HAVE AN EVEN BETTER GRASP ON
THE SITUATION...BEING CONSISTENT WITH ITS 06Z RUN...AND NOT TOO FAR
FROM THE PREVIOUSLY FAVORED ECMWF SOLUTION.
TAKING A BETTER LOOK AT THE SURFACE PATTERN...THE LOW DEVELOPING OFF
THE ROCKIES FRIDAY NIGHT INTO SATURDAY MORNING WILL PROGRESS OUR
WAY. IT IS ANTICIPATED TO BE OVER SOUTHERN WISCONSIN BY 00Z
MONDAY...BEFORE SLIDING ACROSS CENTRAL LAKE MICHIGAN OVERNIGHT AND
OVER THE NORTHCENTRAL MICHIGAN BY 12Z MONDAY. WITH THE LOW TRACKING
THAT FAR TO THE SOUTH OF THE UPPER PENINSULA...IT WILL BE DIFFICULT
TO WRAP ENOUGH WARM AIR AROUND...TO PRODUCED ANY MIXED
PRECIPITATION. THE WARMEST 850MB TEMPS OVER THIS TIME PERIOD ARE -3
TO -4C 00-12Z SUNDAY ACROSS LUCE...EASTERN ALGER AND DELTA
COUNTIES. SO...HAVE KEPT SNOW ONLY.
AFTER THIS SYSTEM KICKS OUT OF THE FORECAST AREA MONDAY NIGHT INTO
TUESDAY...A ZONAL TO MORE RIDGE TYPE PATTERN WILL SET UP ACROSS THE
NATION...AND IN PARTICULAR THE UPPER PENINSULA.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
SNOW AND BLOWING SNOW ADVISORY FROM 5 AM TO 1 PM EST THURSDAY FOR
MIZ006-007-014-085.
SNOW AND BLOWING SNOW ADVISORY FROM 3 AM TO 11 AM EST THURSDAY
FOR MIZ005.
SNOW AND BLOWING SNOW ADVISORY FROM MIDNIGHT TONIGHT TO 11 AM EST
THURSDAY FOR MIZ001>003.
GALE WARNING LAKE SUPERIOR AND LMZ248.
&&
$$
ROLFSON (UPDATE)
JLB (PREV DISCUSSION SHORT TERM)
KF (PREV DISCUSSION LONG TERM)
AREA FORECAST DISCUSSION
NWS MARQUETTE MI
1205 PM EST TUE FEB 20 2007
.UPDATE...
GOING FCST JUST NEEDED A COUPLE TWEAKS. PUBLISHED GRIDS AND ZFPMQT
UPDATE ALREADY SENT. UPDATED TO DECREASE SKY COVER OVR WEST HALF OF
CWA AND AS A RESULT...INCREASED TEMPS A FEW DEGREES UPWARD. ONGOING
LES IS WEAK WITH MINIMAL INVERSION AND ONLY MARGINAL TEMPS AT
INVERSION TOP (-10C). KERY STILL HAD FLURRIES AN HOUR AGO. LES
SHOULD FADE AS TEMPS AT INVERSION TOP WARM FURTHER. SFC TROUGH IS
LINGERING FM SFC LOW OVR QUEBEC ACROSS LK SUPERIOR AND WEST TO SFC
LOW IN NORTHEAST NORTH DAKOTA. DESPITED WEAK WINDS WITHIN TROUGH
AXIS...MORNING TAMDAR SOUNDINGS INDICATED MOIST LAYER OVER CWA WAS
BTWN 925MB AND 875MB...PRETTY THIN. SUNSHINE HAS DIMINISHED MOST OF
THIS LAYER WITH IT JUST LINGERING OVR KEWEENAW AND OVR NORTHEAST CWA
WHERE THIS IS STILL ON ONSHORE COMPONENT TO THE WINDS. JUST NORTH OF
TROUGH OVR SOUTHERN MANITOBA INTO ONTARIO THERE IS A TIGHT GRADIENT
IN H85 TEMPS WITH -19C AT CWPL AND -8C AT KINL. THIS BAROCLINIC ZONE
HAS BEEN FOCUS OF SWATH OF LGT SNOW THIS MORNING. THE SNOW IS NOW AS
FAR EAST AS CYQT. RUC/NAM KEEP BAROCLINIC ZONE OVR FAR NORTHERN LK
SUPERIOR TODAY...SO DO NOT EXPECT ANY SYNOPTIC SNOW TO MAKE IT INTO
CWA.
SHORTWAVE AND WARM AIR ADVECTION OVR SOUTHWEST MANITOBA WILL SLIDE
ESE WITHIN ZONAL FLOW AND REACH WESTERN LAKE SUPERIOR THIS EVENING.
GREATER MOISTURE WITH THE FEATURE WILL REMAIN MOSTLY OVR KEWEENAW
INTO LK SUPERIOR. TO THE SOUTH OF THAT AREA...GFS SOUNDINGS SHOW
LAYER BLO 750MB REMAINS DRY. SO...THERE WILL BE SOME CUTOFF TO THE
SNOW FM NORTH TO SOUTH. CURRENT GRIDS SHOW THIS WELL. ANOTHER
GROWING CONCERN IS STRONGER SHORTWAVE CURRENTLY MOVING INTO
WASHINGTON STATE. THIS WAVE CRUISES EAST IN ZONAL FLOW MOVES INTO
UPR MI WED EVENING. GFS/UKMET ARE NOW QUITE STRONG WITH THIS SYSTEM
AND BACK EARLIER TRENDS. TRACK OF THE WAVE AND ASSOCATED CLIPPER LOW
PRES MAY PRODUCE WIDESPREAD SNOW OVR PORTIONS OF CWA LATE WED INTO
WED NIGHT. WILL BE CHECKING THIS OUT FURTHER THIS AFTN AND MAKE ANY
CHANGES TO GRIDS AT THAT TIME.
&&
.PREV DISCUSSION (405 AM EST)...
MAIN FCST CONCERNS ARE LOW CLOUDS TODAY...SHRTWV TROUGH FOR WED/WED
NIGHT AND STORM SYSTEM FOR THE WEEKEND.
TODAY...WEAK UPPER TROUGH OVER MINNESOTA IS PROGGED TO SLIDE ACROSS
THE CWA EARLY THIS AFTERNOON...ALLOWING THE SURFACE RIDGE OVER THE
DAKOTAS TO BUILD IN. THEREFORE THROUGH THE DAY...WE SHOULD SEE
DIMINISHING/BACKING WINDS AND GRADUAL WARMING OF THE LOW LEVELS.
THEREFORE ONGOING LAKE EFFECT IS EXPECTED TO DIMINISH. THERE ARE
INDICATIONS THAT A SHRTWV ON THE WEST SIDE OF THIS WEAK TROUGH WILL
BRING A POCKET OF SOME MID LEVEL MOISTURE ACROSS...ENOUGH THAT SOME
LIGHT SNOW OR FLURRIES MAY FALL. MOST OF THIS LOOKS TO FALL ACROSS
LAKE SUPERIOR...THOUGH. THE MAIN QUESTION FOR TODAY IS WHETHER OR
NOT WE CAN BREAK OUT OF THE LOW CLOUDS. ALTHOUGH THE 00Z BISMARCK
SOUNDING IS DRIER...GFS/NAM LOW LEVEL RH FIELDS SUGGEST THAT THE DRY
AIR WILL BE SHUNTED TO THE SOUTH. FIND IT HARD TO BELIEVE THAT SINCE
WINDS ARE PROGGED TO BACK TO THE WEST AND THEN SW LATE THIS
AFTERNOON...WHICH SHOULD BRING THE DRIER AIR IN. ALTHOUGH IT IS ONLY
MID FEBRUARY...DAYTIME HEATING SHOULD HELP SOME TOO. 06Z RUC SEEMS
TO FIT BOTH THE OBSERVED CLOUD COVER AND ALSO SUGGESTS MORE
CLEARING...THEREFORE HAVE ADJUSTED SKY GRIDS TO ITS SCENARIO. GIVEN
THE SUNSHINE...TEMPERATURES ALONG THE WISCONSIN BORDER SHOULD
REBOUND TO YESTERDAYS HIGHS. EVEN FARTHER NORTH...TEMPERATURES
SHOULD COME CLOSE SINCE THE AIRMASS IS NOT THAT MUCH COLDER THAN
YESTERDAY AND READINGS ARE RELATIVELY MILD TO BEGIN WITH.
TONIGHT...SHRTWV TROUGH OVER SOUTHERN BRITISH COLUMBIA IS PROGGED TO
REACH SOUTHERN MANITOBA BY 12Z WED...WITH A 993MB SURFACE LOW
ASSOCIATED WITH IT LOCATED NEAR WINNIPEG. ISENTROPIC LIFT DEPICTED
ON THE 285 AND 290K SURFACES AHEAD OF THIS SHRTWV OVER THE CWA
SUGGESTS THE DEVELOPMENT OF AT LEAST A MID CLOUD DECK. GFS/NAM
SOUNDINGS SUGGESTS THAT THERE WILL BE ENOUGH MOISTENING TO RESULT IN
SOME LIGHT SNOW FROM THE ISENTROPIC LIFT...PARTICULARLY IN THE
NORTHERN U.P. AND OVER LAKE SUPERIOR. THE PREVIOUS FCST REFLECTS
THIS WELL AND THE ONLY CHANGE BEING MADE IS TO SPEED UP THE TIMING
FOR THE LIGHT SNOW BY 3 HOURS. WITH THE MID CLOUDS AROUND AND A
LIGHT SW WIND...TEMPERATURES AGAIN SHOULD NOT DROP MUCH. RAISED
TEMPERATURES A FEW DEGREES FROM THE PREVIOUS FCST.
WED INTO WED NIGHT...SHRTWV TROUGH OVER SOUTHERN MANITOBA IS NOW
PROGGED TO DROP FARTHER SOUTH...MOVING INTO NORTHERN WISCONSIN AND
WESTERN UPPER MICHIGAN BY 00Z THU AND TO LAKE ERIE AND NIAGARA FALLS
BY 12Z THU. THIS SOUTHWARD DROP ALSO RESULTS IN THE SURFACE LOW
DROPPING FARTHER SOUTH...CROSSING THE TIP OF THE KEWEENAW WED
EVENING. THE NAM WAS THE ONLY MODEL THAT DID NOT SHOW THIS TRACK...
STAYING FARTHER NORTH. HOWEVER...SINCE IT WAS THE ONLY MODEL AND THE
FACT THAT THE SHRTWV TROUGH LOOKS PRETTY IMPRESSIVE AT THE MOMENT...
THINK A FARTHER SOUTH TRACK WILL PROBABLY VERIFY. WHAT IS MOST
IMPRESSIVE WITH THIS SHRTWV TROUGH ARE 60 METER HEIGHT FALLS AT
500MB AND STEEP MID LEVEL LAPSE RATES THAT ARE ADVECTED IN AHEAD
OF IT. THEREFORE THE 700-300MB Q-VECTOR CONVERGENCE WITH THIS SHRTWV
IS FAIRLY STRONG. HOWEVER...MOISTURE DOES APPEAR TO BE LACKING...AS
NOTED BY 850MB DEWPOINT DEPRESSIONS AROUND 5C AND MODEL QPF FIELDS
NOT SHOWING A LOT. STILL...GIVEN THE IMPRESSIVE DYNAMICS AND
700-500MB LAPSE RATES AROUND 7.5C/KM...THERE SHOULD BE SOME BAND OR
BANDS OF CONVECTIVE SNOW AHEAD OF THE SHRTWV. THEREFORE HAVE
EXPANDED POPS DURING THIS TIME PERIOD AND INCREASED THEM ACROSS THE
NORTH WHERE THE BEST JUXTAPOSITION OF DYNAMICS AND MOISTURE COME
TOGETHER. A DRY SLOT MOVING IN WED EVENING MAY BRIEFLY END THE SNOW
WEST TO EAST...THEN A COMBINATION OF WRAP-AROUND SNOW AND LAKE
ENHANCED SNOW LOOKS POSSIBLE AS 850MB TEMPS COOL TO -10C. AS FAR AS
TEMPERATURES GO...THE DEVELOPMENT OF CLOUDS ON WED WILL LIKELY
HAMPER TEMPERATURES FROM CLIMBING TOO FAR ABOVE NORMAL...AS 850MB
TEMPS MIGHT SUGGEST (AROUND 0C). THEREFORE HAVE STAYED TOWARDS THE
COOLER MAV GUIDANCE. PREVIOUS FCST LOWS LOOK REASONABLE.
THU THROUGH FRI...COLD ADVECTION CONTINUES INTO THU BEHIND THE
SHRTWV TROUGH...850MB TEMPS DROPPING TO -8 TO -13C OVER LAKE
SUPERIOR...BUT THE AIR BECOMES INCREASING ANTICYCLONIC AND DRIER AS
A STRONG SURFACE RIDGE BUILDS IN FROM THE PLAINS. THEREFORE THE
PREVIOUS FCST INDICATING LAKE EFFECT DIMINISHING BY THU NIGHT STILL
LOOKS OKAY AT THIS POINT. HOWEVER...GIVEN THE COLDER AIR...DID LOWER
BOTH HIGHS AND LOWS DURING THIS PERIOD. IN FACT...TEMPERATURES COULD
GET RELATIVELY COLD IN THE EASTERN U.P. THU NIGHT WITH THE SURFACE
FLOW DRAINING COLD AIR OUT OF ONTARIO. HAVE LOWERED NEWBERRYS LOWS
CLOSER TO MEX GUIDANCE...BUT THIS MAY NOT BE LOW ENOUGH.
BEYOND FRI...AFTER QUITE A FEW MODEL RUNS OVER THE PAST COUPLE DAYS
SUGGESTING THE STORM SYSTEM THAT DEVELOPS IN THE CENTRAL PLAINS
MOVING TOWARDS UPPER MICHIGAN...THE BEGINNINGS OF A FARTHER SOUTH
TRACK ARE BEGINNING TO CREEP IN. THIS EVENING...EXTRA UPPER AIR
OBSERVATIONS WERE INCLUDED INTO THE 00Z MODEL SUITE OVER THE EASTERN
PACIFIC AND WESTERN U.S. FROM C-130 AIRCRAFT. NOW ALL OF THE 00Z
MODELS...INCLUDING THE 00Z GFS ENSEMBLES...HAVE SHIFTED FARTHER
SOUTH WITH THE TRACK OF THE STORM SYSTEM...WITH ONLY 1 GFS ENSEMBLE
MEMBER ACTUALLY TAKING THE SURFACE LOW ACROSS UPPER MICHIGAN. NOT
SURE WHETHER OR NOT THE AIRCRAFT DATA WAS THE CULPRIT FOR CAUSING
THE MODELS TO SHIFT THE TRACK SOUTH...BUT IT IS A POSSIBILITY.
NEVERTHELESS...THIS SOUTHWARD TREND MEANS THAT ANY PRECIPITATION
THAT DOES FALL WILL HAVE TO BE SNOW SINCE NOT ENOUGH WARM AIR IS
ABLE TO WRAP AROUND IT. THEREFORE...FOR THE HWO AND FCST PURPOSES...
HAVE REMOVED ANY MIXED PCPN MENTION. IN ADDITION...HAVE ADJUSTED
WIND AND TEMPERATURE FORECASTS AROUND DUE TO MORE EASTERLY FLOW
BETWEEN A HUDSON BAY SURFACE HIGH AND THE STORM SYSTEM. ANOTHER
MAJOR CONCERN IS THE POSSIBILITY FOR THE SYSTEM TO GO SO FAR SOUTH
THAT WE SEE NO PCPN AT ALL. THE 00Z UKMET SHOWS THIS AND THE 00Z
CANADIAN IS SIMILAR...THOUGH SLIGHTLY FARTHER NORTH. WILL NOT CHANGE
THE FCST TOWARDS THESE MODELS...BUT THE FACT THAT THEY ARE ALLOWING
THE SYSTEM TO PUSH DUE EASTWARD INTO AN UPPER RIDGE AHEAD OF
IT...INSTEAD OF LIFTING IT NE OVER THE TOP OF THE RIDGE...IS
SOMETHING THAT NEEDS TO BE WATCHED.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
UPDATE...JLA
PREV DISCUSSION...AJ
AREA FORECAST DISCUSSION
NWS SEATTLE WA
830 AM PST TUE FEB 20 2007
.SYNOPSIS...POST FRONTAL ONSHORE FLOW WILL CONTINUE TO PRODUCE
SHOWERS TODAY...MAINLY IN THE MOUNTAINS AND ALONG THE COAST.
SCATTERED SHOWER ACTIVITY WILL CONTINUE THROUGH THURSDAY NIGHT AS A
COOL UPPER LEVEL TROUGH SETTLES IN OVER THE AREA. THE AIR MASS WILL
BE COOL ENOUGH THAT PRECIPITATION THAT FALLS ON HIGHER HILLS DURING
THE LATE NIGHT AND MORNING HOURS COULD BE IN THE FORM OF SNOW. BUT
NO SIGNIFICANT ACCUMULATIONS ARE EXPECTED. AFTER A MAINLY DRY DAY ON
FRIDAY...ANOTHER FRONTAL SYSTEM WILL BRING RAIN AND LOCALLY WINDY
CONDITIONS TO THE AREA FRIDAY NIGHT AND SATURDAY.
&&
.SHORT TERM...THE LONG WAVE PATTERN IS TRANSITIONING TO A WEST COAST
TROUGH. THIS IS BRINGING A RETURN TO WINTER IN THE MOUNTAINS...AND
AFTER OUR SPRINGLIKE DAY SATURDAY...IT APPEARS THAT TRADITIONAL PAC
NW WINTER HAS RETURNED FOR THE NEXT COUPLE WEEKS IN THE LOWLANDS AS
WELL.
THE COLD FRONT THAT BROUGHT RAIN...HEAVY MOUNTAIN SNOW...AND WINDY
CONDITIONS TO THE AREA HAS NOW MOVED WELL TO THE EAST. WE ARE NOW
LEFT IN COOL ONSHORE FLOW WITH MOST SHOWER ACTIVITY CONFINED TO THE
MOUNTAINS...THE COAST...AND TO A PUGET SOUND CONVERGENCE ZONE THAT
SITS ACROSS NORTHERN SNOHOMISH COUNTY. SNOWFALL IN THE MOUNTAINS
CONTINUES...WITH HEAVIEST ACTIVITY IN THE CONVERGENCE ZONE TO THE
NORTH OF THE MAIN PASSES. ACARS SOUNDINGS SHOW SNOW LEVELS NEAR THE
2000 FT LEVEL. SNOWFALL RATES IN THE MAIN PASSES APPEAR TO SUPPORT
THE CURRENT ADVISORY...AND THAT WILL BE CONTINUED THRU 4 PM THIS
AFTERNOON. THE COLDEST AIR ALOFT APPEARS TO BE SLIDING EAST ALONG
ABOUT 49N. A ROGUE TSTM CAN`T BE RULED OUT...BUT THEY SHOULD BE
CONFINED MAINLY TO VANCOUVER ISLAND AND THE BRITISH COLUMBIA COASTAL
RANGES AS THE UPPER TROUGH ALONG 128W MOVES E. ANY WET SNOW MIXED
WITH RAIN SHOWERS THIS MORNING...AS IS BEING REPORTED AT PORT
ANGELES...WILL GO TO ALL RAIN SHOWER ACTIVITY IN THE LOWLANDS WITH
INSOLATION OVER THE NEXT COUPLE HOURS.
UPPER TROUGHING IS DIGGING OFFSHORE. HENCE THE CONVERGENCE ZONE
SHOULD STAY N OF SEATTLE. IT DOES APPEAR THE DOWNTOWN SEATTLE
SOUTHWARD WILL BE EXPOSED TO SHOWERS SNEAKING IN TO THE S OF THE
OLYMPICS THRU THE CHEHALIS GAP AS THE FLOW ALOFT BECOMES MORE SWLY.
PRECIPITATION TYPE WILL BE A CHALLENGE DURING THE LATE NIGHT AND
MORNING HOURS. THE AIR MASS ALOFT IS RATHER COOL. FREEZING LEVELS
NEAR 2000 FT WITH A NEARLY ISOTHERMAL LAYER AT +1 TO +2C AND
DEWPOINT TEMPERATURES -2C SUGGEST THAT HEAVIER SHOWERS DURING THE
PERIOD FROM 3 AM TO 10 AM COULD BE A MIX OF SNOW AND RAIN...OR SNOW
WITH LIGHT ACCUMULATIONS POSSIBLE ON HIGHER HILLS AWAY FROM WATER.
THIS WILL BE THE CASE BOTH WEDNESDAY AND THURSDAY MORNINGS. SHOWER
ACTIVITY MAY BE A LITTLE MORE WIDESPREAD THURSDAY MORNING THAN ON
WEDNESDAY MORNING AS AN IMPULSE ROTATES AROUND THE DIGGING TROUGH
JUST OFFSHORE.
AT THIS POINT IT APPEARS THAT FRIDAY WILL BE THE NICEST DAY OF THE
WEEK AS A SHORT WAVE TROUGH MOVES ACROSS THE AREA. DAYTIME
TEMPERATURES WILL STRUGGLE TO REACH 50 THOUGH IN THE COOL AIR MASS
IN PLACE.
WHILE SNOW LEVELS APPEAR TO BE A FEW HUNDRED FEET HIGH DURING THE
EARLY MORNING HOURS...WILL AWAIT MAKING UPDATES UNTIL THIS AFTERNOON
AFTER LOOKING AT ALL NEW GUIDANCE. ALBRECHT
.LONG TERM...PREVIOUS LONG TERM DISCUSSION...THE BROAD UPPER LEVEL
TROUGH ALONG THE WEST COAST SHIFTS INLAND ON FRIDAY. THIS COULD LEAD
TO A REASONABLY DRY DAY FOR THE REGION...BUT THAT IS SHORT-LIVED AS
THE EXTENDED MODELS REMAIN CONSISTENT WITH BRINGING A STRONG FRONT
INTO THE REGION SATURDAY MORNING...WITH ANOTHER COOL SHOWERY TROUGH
AND MORE LOW SNOW LEVELS TO BEGIN NEXT WEEK. 27
&&
.AVIATION...A PGTSND CONVERGENCE ZONE WAS LOCATED BETWEEN KPAE AND
MOUNT VERNON OR ESSENTIALLY ON TOP OF KAWO. THE CONVERGENCE ZONE
WILL LIKELY REMAIN N OF KPAE AS CONTINUED SLY WINDS TO NEAR 4K FT
WILL TEND TO PREVENT THE CONVERGENCE ZONE FROM SAGGING TO THE S.
ALSO...THE WLY FLOW THRU THE STRAIT HAS ALREADY PEAKED AND IS
EXPECTED TO SLOLY WEAKEN AS THE DAY PROGRESSES.
MEANWHILE...EXPECT SCATTERED SHRA TODAY. CIGS WILL GENERALLY BE AT
OR ABOVE 5K FT...EXCEPT NEAR 1500 FT WITH THE HEAVIER SHOWERS IN THE
CONVERGENCE ZONE. GRAUPEL OR SMALL HAIL IS ALSO POSSIBLE WITHIN THE
CONVERGENCE ZONE.
AT KSEA...EXPECT SCATTERED TO BROKEN CLOUDS AT OR ABOVE 5K FT. THERE
MAY BE A BRIEF PERIOD OF BROKEN CIGS NEAR 1K FT TIL 19Z. THE BEST
CHANCE OF SHOWERS WILL BE BETWEEN 21Z AND 02Z. WINDS WILL REMAIN S
OR SW AT 11-16 KT WITH OCCASIONAL GUSTS NEAR 25 KT TIL 00Z.
$$
.SEW WATCHES/WARNINGS/ADVISORIES...
.SNOW ADVISORY FOR THE OLYMPICS AND THE CASCADES THROUGH 4 PM.
.SMALL CRAFT ADVISORY ALL WATERS.
$$
WEATHER.GOV/SEATTLE
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