AREA FORECAST DISCUSSION...UPDATED
NWS CHICAGO IL
AFDCHI 230 PM CST WED JAN 8 2003
DISCUSSION FOR 330 PM GRIDS/ZONES...UPDATED FOR LAKE EFFECT POTENTIAL
SPRINGTIME IN JANUARY WITH BALMY 50+ DEGREE TEMPS ACROSS THE
FORECAST AREA THIS AFTERNOON. CHANGE IS ON THE HORIZON
HOWEVER...WITH WEAK PACIFIC COLD FRONT/TROUGH APPROACHING
MISSISSIPPI RIVER VALLEY FROM THE WEST. STRONGER COLD FRONT ACROSS
SOTHERN CANADA MARKING INTRUSION OF ARCTIC AIR ARRIVES HERE LATER
THURSDAY HOWEVER...WHICH WILL SET THE STAGE FOR COLD SPELL LASTING
INTO NEXT WEEK. MAIN FORECAST CHALLENGES REMAIN TEMP FORECAST NEXT
FEW PERIODS...AND POTENTIAL FOR FLURRIES OR LIGHT SNOW SHOWERS AS
SERIES OF SHEARED WAVES ROTATE AROUND NORTHERN QUEBEC VORTEX NEXT
FEW DAYS.
FOR SHORT TERM...PASSAGE OF PACIFIC FRONT THIS EVENING NOT EXPECTED
TO RESULT IN QUICK CHANGE...WITH TEMPS BEHIND THE FRONT UPSTREAM
STILL IN THE 40S AND 50S INTO THE DAKOTAS. BASED ON THIS HAVE GONE
ON THE HIGH SIDE OF GUIDANCE MINS TONIGHT...WITH MAIN EFFECT OF
FROPA BEING A CHANGE IN WIND DIRECTION TO NORTHWEST. MAIN PUNCH OF
COLDER AIR ARRIVES THURSDAY AFTERNOON...WITH MAX TEMPS 20 DEGREES
COLDER THAN TODAY...BUT STILL A BIT ABOVE NORMAL. COLDER TEMPS
THEREAFTER...THOUGH WITH TROUGHINESS ALOFT WILL LIKELY HAVE SOME
CLOUD COVER TO HELP KEEP READINGS EVENED OUT. PERIOD OF BELOW NORMAL
TEMPS WITH HIGHS IN LO-MID 20S AND MINS IN TEENS AND SINGLE DIGITS
INTO EARLY NEXT WEEK.
AS FOR PRECIP...SATELLITE SHOWING NOTHING BUT THIN CIRRUS ACROSS THE
AREA FOR NOW. MODEL TIME SECTIONS REMAIN DRY THROUGH TONIGHT...THEN
INCREASE LOW LEVEL MOISTURE WITH ARRIVAL OF COLDER AIR THURSDAY.
SHORT WAVE APPROACHES THURSDAY NIGHT AND HAVE KEPT GOING FORECAST OF
CHANCE SNOW SHOWERS WITH THIS FEATURE...AND HAVE ADDED CHANCE
MENTION OF FLURRIES ESPECIALLY NORTHERN 1/2 OF CWA INTO SATURDAY AS
FLOW REMAINS GENERALLY CYCLONIC WITH PERIODIC VORT MAXES SHEARING
AROUND BASE OF TROUGH ALOFT.
HAVE BROKEN OFF PORTER COUNTY FOR CHANCE LAKE EFFECT SNOW SHOWERS
THURSDAY NIGHT INTO SATURDAY AS LAKE SURFACE TO H85 DELTA T'S
APPROACH 20 DEG C BY FRIDAY AFTERNOON. LAKE INDUCED CAPES OF 300-600
J/KG AND EQUILIBRIUM LEVELS ABOVE 6 KFT...THOUGH FETCH LENGTH
GENERALLY UNDER 60 NM...WITH LOW LEVEL WINDS FROM AROUND 300 DEGREES
FOR THE DURATION. THIS SUGGESTS MAIN LAKE EFFECT THREAT TO REMAIN
JUST EAST OF PORTER COUNTY.
SLIGHT THERMAL MODERATION TOWARD MID NEXT WEEK WITH MRF SHOWING OLD
QUEBEC VORTEX DRIFING EAST AND NEW ENERGY DIGGING INTO NORTHERN
PLAINS. BY WEDNESDAY...MRF DEVELOPS S/WV AND SURFACE LOW OVER LOWER
MISSOURI VALLEY THAT WOULD BRING DECENT CHANCE OF SNOW TO REGION IF
IT VERIFIES. OF COURSE THAT'S A LONG WAY OFF FROM HERE...BUT FOR NOW
WORTH CHANCE MENTION OF SNOW WEDNESDAY.
.CHI...GALE WRNG LK MI.
RATZER
AVIATION DISCUSSION FOR 18Z TAFS...
SW WINDS ARE SLOWLY INCREASING AS STEEP INVERSION THIS MORNING
MODIFIES UNDER SUN AND WARM ADVECTION ALOFT. WINDS IN LOWEST LAYERS
VIA ACARS ARE RUNNING 15-20KT SO SFC GUSTS SHOULD HOLD IN THAT
RANGE. PRES FALLS WORKING INTO NRN ILLINOIS FROM WEST HAVE HELD
WINDS FROM THE SW. FAST MOVING TROUGH FROM ABOUT MSP TO OMA WILL
PUSH THRU AREA THIS EVE WITH WINDS SHIFTING TO WNW AND BE GUSTY
UNDER COLD ADVECTION. LITTLE MEANINGFUL CLOUDS SEEN THROUGH MOST OF
NIGHT BUT WITH NEXT SURGE OF COLD AIR LIKELY LATE THUR SOME INCR IN
MID CLOUDS ARE LIKELY TOWARD END OF FORECAST PERIOD.
KL
AREA FORECAST DISCUSSION
NWS CHICAGO IL
AFDCHI 1200 PM CST WED JAN 8 2003
AVIATION DISCUSSION FOR 18Z TAFS...
SW WINDS ARE SLOWLY INCREASING AS STEEP INVERSION THIS MORNING
MODIFIES UNDER SUN AND WARM ADVECTION ALOFT. WINDS IN LOWEST LAYERS
VIA ACARS ARE RUNNING 15-20KT SO SFC GUSTS SHOULD HOLD IN THAT
RANGE. PRES FALLS WORKING INTO NRN ILLINOIS FROM WEST HAVE HELD
WINDS FROM THE SW. FAST MOVING TROUGH FROM ABOUT MSP TO OMA WILL
PUSH THRU AREA THIS EVE WITH WINDS SHIFTING TO WNW AND BE GUSTY
UNDER COLD ADVECTION. LITTLE MEANINGFUL CLOUDS SEEN THROUGH MOST OF
NIGHT BUT WITH NEXT SURGE OF COLD AIR LIKELY LATE THUR SOME INCR IN
MID CLOUDS ARE LIKELY TOWARD END OF FORECAST PERIOD.
KL
DISCUSSION RE GRIDS/ZONES FORECASTS...
NO SIGNIFICANT CHANGES TO CURRENT FCSTS ANTICIPATED. MAIN CHALLENGE
IS TEMP TRENDS...ESPECIALLY TODAY...AND THEN WITH CFP TONIGHT AND
ANOTHER THU NIGHT.
WARMEST 850MB TEMPS AT 00Z WERE FROM SRN SASKATCHEWAN SE ACROSS THE
MO RIVER VALLEY TO MID MS VALLEY. CORE OF WARM AIR FCST OVER CENTRAL
PLAINS AT 12Z THEN OVER SRN PLANS...OZARKS...LOWER OH VALLEY BY 00Z
THU. COLDER AIR OVERSPREADS NRN PLAINS AND UPPER MIDWEST AS JET AXIS
SINKS S OF 49TH PARALLEL INTO GREAT LAKES TODAY AND TONIGHT.
WITH VERY STRONG LOW LEVEL INVERSION H8 TEMPS NOT BEST PREDICTOR OF
SFC TEMPS AND WILL USE ETA 925MB TEMPS AS GUIDELINE. ACARS DATA
SHOWS TRENDS FORECAST BY ETA VERIFYING...WITH 925 MB TEMPS FALLING
TO +11C AT MSP AND RISING TO +13 AT RFD & +11 AT ORD. 925 TEMPS +13
TO +15 ACROSS AREA AT 12Z FALL TO +9 TO + 11 BY 18Z AND FURTHER TO +
6 TO +8 BY 00Z. EXPECT FAIRLY QUICK RISE IN TEMPS AFTER
SUNRISE...THOUGH NEXT BATCH OF THICKER CI SEEN MOVING SE OUT OF NRN
PLAINS WILL BE OVER AREA AND CUT WEAK LOW ANGLE WINTER SUN. TEMPS
THEN EXPECTED TO LEVEL OUT AROUND MIDDAY IN LOWER AND MID 50S.
TROF/DEVELOPING COLD FRONT MOVES THRU THIS EVE SETTING UP STRONG CAA
TONIGHT...WITH SECOND CFP THU NIGHT AS UPPER JET AXIS SINKS S INTO
NRN IL. CONT CAA FRI AS UPPER TROF ROTATES AROUND ERN CANADA VORTEX
THRU THE GREAT LAKES.
FAIR SKIES WITH ONLY SCT TO BKN CI TODAY THRU TONIGHT. MODELS BRING
HIER LOW LEVEL RH DOWN OUT OF CANADA WITH COLD AIR AND OVERSPREADS
AREA THU MORNING. COULD BE A FEW FLURRIES THEN BUT GREATEST BETTER
CHANCE OF -SHSN WILL BE THU NIGHT AS MINOR SHORT WAVE ZIPS THRU.
LINGERING CHC OF FLURRIES FRI AS ARCTIC AIR ARRIVES.
.CHI...NONE
TRS
AREA FORECAST DISCUSSION
NWS TWIN CITIES/CHANHASSEN MN
AFDMSP 915 PM CST WED JAN 8 2003
FCST CONCERN TONIGHT...EVERYTHING. WINDS/TEMPS/CLDS ALL PROBLEMATIC
BUT WINDS SEEM TO BE THE MAIN ISSUE. HAVE SEEN GUSTS POKING 35 MPH
IN MANY AREAS AND CLOSE TO 40 MPH IN THE WIND PRONE AREAS. 00Z RAOBS
AND BUFR SHORT TERM GUIDANCE SUGGESTS THIS SHUD HOLD THRU THE NIGHT.
00Z RAOBS IMPRESSIVE TONIGHT IN UPR MIDWEST...WITH MANY LIMITING
ANGLES AT H3/H2 OWING TO STRNG JET SAGGING SOUTH AS IT MIGRATES INTO
LAKES. ACARS REPORT IN NRN MN SHOWING 155KT...SO PLENTY OF WIND UP
THERE..VERIFIED BY KGRB/KABR/KINL SOUNDINGS. HEIGHT FALLS VRY
IMPRESSIVE WITH H5/12HR FALLS OF 220M AT KINL THIS EVE. TEMPS ALOFT
COOLING RAPIDLY...AND THAT SEEMS TO BE THE MODE TONIGHT. ARCTIC
FRONT STILL WELL NORTH OF MN...BUT NOW COMING SOUTH WITH SC DECK AND
FLURRIES. SHUD GAIN SPEED AS ONE VRY STRONG S/W/UPR JET PULLS INTO
LAKES AND ANOTHERT DIVES ACROSS MN LATE TONIGHT INTO THUR MORNING.
ONCE LOW LEVELS START TO COOL SIGNIFICANTLY...AND LL LAPSE RATES
STEEPEN...NICE LINKAGE AND REMAINING STRONG WIND FIELDS DO SHOW A
PERIOD OF VRY GUSTY WINDS TOMORROW MORNING. MOMENTUM XFER PER BUFR
SHOW WINDS/GUSTS MAY APPROACH/EXCEED ADVRY CRITERIA FOR SEVERAL
HOURS. BEEFED UP WINDS IN ZONES. WITH GUD MIXING TONIGHT...AND COLD
AIR STILL FAR NORTH...UPPED TEMPS A CAT MOST AREAS. CAA SHUD BE
PROLONGED AND STRONG THRU THUR NIGHT...WHEN A SECOND SURGE
ARRIVES...AND THIS WILL HAVE OUR BEST CHANCE OF SNOW SHOWERS. CLOUDS
WILL ARRIVE AFT MIDNIGHT...AND HANG AROUND FOR A WHILE. TEMPS
TOMORROW SHOW LITTLE HOPE OF LEVELING OFF...AND SEEMS A SLOW FALL IS
MORE LIKELY...CONSIDERING WE WILL BE STARTING OFF QUITE HIGH.
UPDATED ZONES ALREADY OUT.
.MSP...NONE.
$$
BINAU