AREA FORECAST DISCUSSION
NWS CHICAGO IL
AFDCHI 715 AM CST WED JAN 14 2004
.AVIATION DISCUSSION FOR 12 UTC TAFS
WILL USE THE GFS MODEL FOR THE MOVEMENT OF THE CYCLONE IN WESTERN
WISCONSIN. THE 3 HOUR ISSALOBARS SHOW -8 MB OVER CENTRAL WISCONSIN
AND 700 MB PROFILER WIND WAS 50 KNOTS AT 11 UTC. THE WATER VAPOR
LOOP SHOWS A STRONG CIRCULATION MOVING FROM NORTHERN MINNESOTA
INTO NORTHERN WISCONSIN. THE LOCAL WORKSTATION ETA MODEL SHOWS
A LARGE TEMPERATURE GRADIENT MOVING INTO NORTHERN ILLINOIS BY
18 UTC. THE COLD AIR AND PRECIPITATION WILL COINCIDE TO MAKE
THE PRECIPITATION TYPE ALL SNOW. WILL FORECAST LIGHT SNOW FOR
THE AIRPORTS STARTING AT 18 UTC. THIS IS AN INTENSE CYCLONE.
WILL RAISE THE WIND TO NORTHWEST AT 23 KNOTS GUST TO 30 KNOTS.
BECAUSE OF THE FAST MOVEMENT EASTWARD OF THE LOW THE WIND WILL
DIMINISH QUICKLY TONIGHT. ACARS SOUNDINGS AT ORD ARE VERY DRY
ABOVE 900 MB. THE BUFKIT SOUNDING FORCAST SHOWS THE AIR BECOME
MORE HUMID WITH NEAR SATURATION UP TO 5000 FT. THAT IS WHEN THE
SNOW WILL BE FALLING. WILL END THE SNOW AROUND 21 UTC AS THE
LOW MOVES INTO INDIANA AND SINKING AIR MOVES INTO THE REGION.
WHW
&&
.DISCUSSION FOR MORNING GRIDS/ZONES:
VIGOROUS CLIPPER S/WV OVER NRN MN AT 09Z...WITH CIRCULATION HIGHLY
VISIBLE IN VAPOR IMAGERY. SFC LOW NEAR FARMINGTON MN...WITH
IMPRESSIVE 7 MB RISE FALL COUPLET IN 3 HR SFC ISALLOBARIC FIELD.
STRONGEST PRES FALLS NOW VCNTY KMSP...CLOSE TO GFS/ETA 12 HR FCST OF
SFC LOW TRACK. IR SAT PICS AND SFC OBS INDICATE COLDEST CLD
TOPS/PCPN GENERALLY ALONG/NORTH TRACK OF SFC LOW AT THIS HOUR...WITH
MAINLY JUST MID CLDS ACROSS SRN MN/SW WI.
GFS/ETA CONTINUING TO TRACK LOW NORTH OF THE FA...ROUGHLY KMSP-KSBM
BY 18Z. BOTH CONTINUE TO GRAZE XTRM NRN/NERN FA WITH VERY LIGHT QPF
TODAY...THOUGH 290-295K ISENTROPIC SURFACES SHOW LOWEST CONDENSATION
PRESSURE DEFICITS WELL TO THE NORTH. WITH SYSTEM RACING ALONG...BEST
UPGLIDE MOVES THROUGH IN 12-18Z. TIME FRAME...THOUGH AGAIN MAINLY TO
OUR NORTH. THUS CURRENT FCST APPEARS ON TRACK...WITH CHC LGT SNOW
TDY MAINLY N/NERN PTNS OF CWA...WITH LITTLE OR NO ACCUMULATION
ESPECIALLY SOUTH OF A RFD/CHI LINE. SFC LOW CONTINUES QUICKLY TO
NEAR KCMH BY EVENING...WITH STRONG DEEP LAYERED SUBSIDENCE
DEVELOPING IN WAKE OF MID LVL TROUGH. WITH THOSE 7 MB SFC PRES RISES
BEHIND SYSTEM...ISALLOBARIC GRADIENT TO LEAD TO SOME RATHER WINDY
CONDITIONS ESPECIALLY THIS AFTN/EARLY EVE. WILL CARRY GUSTS 35-40
MPH JUST BELOW WIND ADVSRY CRITERIA.
STG LLVL CAA BEHIND S/WV THIS EVE TO SET UP STEEP LAPSE RATES OVER
LK MICH...WITH POTENTIAL FOR LAKE EFFECT SNW SHOWERS. FLOW INITIALLY
MORE NORTHERLY THROUGH MIDNIGHT...AND WILL CARRY CHANCE ALONG IL
SHORE AREAS AS WELL AS NW IND. AFTER 06-08Z FLOW BACKS MORE 320-330
DEG SO ANY THREAT SHOULD BE CONFINED TO ERN LK/PORTER COUNTIES IN
IND. LK SFC/H85 DELTA T REACHES 16 TO 18 DEG TNGT WHICH SHOULD ALLOW
FOR SOME MINOR ACCUMULATION MAINLY NW IND...DESPITE STG SYNOPTIC
SUBSIDENCE.
ANOTHER WK S/WV ROTATES AROUND BACK SIDE OF NORTHEASTERN NA VORTEX
THURSDAY...WITH GFS/ETA BOTH INDICATING TIGHTENING OF LLVL THERMAL
GRADIENT AND ASSOCIATED FRONTOGENETIC FORCING. HAVE ADDED LOW CHC
POPS AS BOTH TRY TO SQUEEZE OUT A LITTLE LIGHT SN THURSDAY AFTN/NGT
BEFORE S/WV PASSES BY...THOUGH STG BAROCLINIC ZONE REMAINS IN PLACE
AND WILL KEEP SOME FLURRIES MENTIONED FOR FRI.
EXTENDED FCST REMAINS SOMEWHAT UNCLEAR AS GFS DEVELOPS SOME PHASING
BETWEEN N/S STREAM TROUGHS LATE FRI...AND MOVES SYSTEM OUT OF
PLAINS. PRECIP ASSOCIATED WITH SRN STRM SYSTEM BRUSHES CWA FRI
NGT...WITH SOME CONCERN OVR PCPN TYPE. EVEN THOUGH GFS HAS BEEN
RUNNING SIGNIFICANTLY COLDER THAN ETA LATELY...FCST PARTIAL
THICKNESS VALUES SUGGEST THREAT OF FZRA INTO SRN CWA FRI NGT...WITH
A MIX OF SN/PL ACROSS THE NORTH. TROUGHS MOVE EAST SAT...WITH DRY WX
INTO EARLY NXT WK AND BIG CHANGE TO LATER PDS AS GFS FLOPS TO A
TROUGH WEST/RIDGE EAST UPPER PATTERN. WELL SEE.
RATZER
&&
.AVIATION DISCUSSION FOR 00Z TAFS...
BKN CU TO MOVE OUT NEXT HOUR OR SO. MID CLOUDS BY MORNING AFTER L/V
WIND EARLY TONIGHT. WITH SUCH DRY AIR UPSTREAM DO NOT BELIEVE STRONG
OMEGA FIELD LATE TONIGHT TO BE SUFFICENT TO GENERATE SNOW IN TAF
AREA TIL MID MORNING. WITH 850-700-SFC LOWS ALL EXPECTED TO MOVE NE
OF TAF AREA...BELIEVE SNOW WILL COME FROM TRACK OF 500 VORT OVERHEAD
EARLY AFTERNOON. SO THAT IS WHEN PUT IN MAIN SNOW AND NOTHING REAL
HEAVY FOR ABOVE REASONS. SHOULD BE DONE AROUND MID AFTERNOON WITH
INCREASING NW WIND BEHIND DEPARTING LOW.
&&
.LOT...WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LK MI...SMALL CRFT ADVSRY IL/IND SHORES THIS AFTN. GL WRNG S HALF LK
MI LATE THIS AFTN/TNGT.
&&
$$
AREA FORECAST DISCUSSION...CORRECTION
NWS CHICAGO IL
AFDCHI 316 AM CST WED JAN 14 2004
.AVIATION DISCUSSION FOR 12 UTC TAFS
WILL USE THE GFS MODEL FOR THE MOVEMENT OF THE CYCLONE IN WESTERN
WISCONSIN. THE 3 HOUR ISSALOBARS SHOW -8 MB OVER CENTRAL WISCONSIN
AND 700 MB PROFILER WIND WAS 50 KNOTS AT 11 UTC. THE WATER VAPOR
LOOP SHOWS A STRONG CIRCULATION MOVING FROM NORTHERN MINNESOTA
INTO NORTHERN WISCONSIN. THE LOCAL WORKSTATION ETA MODEL SHOWS
A LARGE TEMPERATURE GRADIENT MOVING INTO NORTHERN ILLINOIS BY
18 UTC. THE COLD AIR AND PRECIPITATION WILL COINCIDE TO MAKE
THE PRECIPITATION TYPE ALL SNOW. WILL FORECAST LIGHT SNOW FOR
THE AIRPORTS STARTING AT 18 UTC. THIS IS AN INTENSE CYCLONE.
WILL RAISE THE WIND TO NORTHWEST AT 23 KNOTS GUST TO 30 KNOTS.
BECAUSE OF THE FAST MOVEMENT EASTWARD OF THE LOW THE WIND WILL
DIMINISH QUICKLY TONIGHT. ACARS SOUNDINGS AT ORD ARE VERY DRY
ABOVE 900 MB. THE BUFKIT SOUNDING FORCAST SHOWS THE AIR BECOME
MORE HUMID WITH NEAR SATURATION UP TO 5000 FT. THAT IS WHEN THE
SNOW WILL BE FALLING. WILL END THE SNOW AROUND 21 UTC AS THE
LOW MOVES INTO INDIANA AND SINKING AIR MOVES INTO THE REGION.
WHW
&&
.DISCUSSION FOR MORNING GRIDS/ZONES:
VIGOROUS CLIPPER S/WV OVER NRN MN AT 09Z...WITH CIRCULATION HIGHLY
VISIBLE IN VAPOR IMAGERY. SFC LOW NEAR FARMINGTON MN...WITH
IMPRESSIVE 7 MB RISE FALL COUPLET IN 3 HR SFC ISALLOBARIC FIELD.
STRONGEST PRES FALLS NOW VCNTY KMSP...CLOSE TO GFS/ETA 12 HR FCST OF
SFC LOW TRACK. IR SAT PICS AND SFC OBS INDICATE COLDEST CLD
TOPS/PCPN GENERALLY ALONG/NORTH TRACK OF SFC LOW AT THIS HOUR...WITH
MAINLY JUST MID CLDS ACROSS SRN MN/SW WI.
GFS/ETA CONTINUING TO TRACK LOW NORTH OF THE FA...ROUGHLY KMSP-KSBM
BY 18Z. BOTH CONTINUE TO GRAZE XTRM NRN/NERN FA WITH VERY LIGHT QPF
TODAY...THOUGH 290-295K ISENTROPIC SURFACES SHOW LOWEST CONDENSATION
PRESSURE DEFICITS WELL TO THE NORTH. WITH SYSTEM RACING ALONG...BEST
UPGLIDE MOVES THROUGH IN 12-18Z. TIME FRAME...THOUGH AGAIN MAINLY TO
OUR NORTH. THUS CURRENT FCST APPEARS ON TRACK...WITH CHC LGT SNOW
TDY MAINLY N/NERN PTNS OF CWA...WITH LITTLE OR NO ACCUMULATION
ESPECIALLY SOUTH OF A RFD/CHI LINE. SFC LOW CONTINUES QUICKLY TO
NEAR KCMH BY EVENING...WITH STRONG DEEP LAYERED SUBSIDENCE
DEVELOPING IN WAKE OF MID LVL TROUGH. WITH THOSE 7 MB SFC PRES RISES
BEHIND SYSTEM...ISALLOBARIC GRADIENT TO LEAD TO SOME RATHER WINDY
CONDITIONS ESPECIALLY THIS AFTN/EARLY EVE. WILL CARRY GUSTS 35-40
MPH JUST BELOW WIND ADVSRY CRITERIA.
STG LLVL CAA BEHIND S/WV THIS EVE TO SET UP STEEP LAPSE RATES OVER
LK MICH...WITH POTENTIAL FOR LAKE EFFECT SNW SHOWERS. FLOW INITIALLY
MORE NORTHERLY THROUGH MIDNIGHT...AND WILL CARRY CHANCE ALONG IL
SHORE AREAS AS WELL AS NW IND. AFTER 06-08Z FLOW BACKS MORE 320-330
DEG SO ANY THREAT SHOULD BE CONFINED TO ERN LK/PORTER COUNTIES IN
IND. LK SFC/H85 DELTA T REACHES 16 TO 18 DEG TNGT WHICH SHOULD ALLOW
FOR SOME MINOR ACCUMULATION MAINLY NW IND...DESPITE STG SYNOPTIC
SUBSIDENCE.
ANOTHER WK S/WV ROTATES AROUND BACK SIDE OF NORTHEASTERN NA VORTEX
THURSDAY...WITH GFS/ETA BOTH INDICATING TIGHTENING OF LLVL THERMAL
GRADIENT AND ASSOCIATED FRONTOGENETIC FORCING. HAVE ADDED LOW CHC
POPS AS BOTH TRY TO SQUEEZE OUT A LITTLE LIGHT SN THURSDAY AFTN/NGT
BEFORE S/WV PASSES BY...THOUGH STG BAROCLINIC ZONE REMAINS IN PLACE
AND WILL KEEP SOME FLURRIES MENTIONED FOR FRI.
EXTENDED FCST REMAINS SOMEWHAT UNCLEAR AS GFS DEVELOPS SOME PHASING
BETWEEN N/S STREAM TROUGHS LATE FRI...AND MOVES SYSTEM OUT OF
PLAINS. PRECIP ASSOCIATED WITH SRN STRM SYSTEM BRUSHES CWA FRI
NGT...WITH SOME CONCERN OVR PCPN TYPE. EVEN THOUGH GFS HAS BEEN
RUNNING SIGNIFICANTLY COLDER THAN ETA LATELY...FCST PARTIAL
THICKNESS VALUES SUGGEST THREAT OF FZRA INTO SRN CWA FRI NGT...WITH
A MIX OF SN/PL ACROSS THE NORTH. TROUGHS MOVE EAST SAT...WITH DRY WX
INTO EARLY NXT WK AND BIG CHANGE TO LATER PDS AS GFS FLOPS TO A
TROUGH WEST/RIDGE EAST UPPER PATTERN. WELL SEE.
RATZER
&&
.AVIATION DISCUSSION FOR 00Z TAFS...
BKN CU TO MOVE OUT NEXT HOUR OR SO. MID CLOUDS BY MORNING AFTER L/V
WIND EARLY TONIGHT. WITH SUCH DRY AIR UPSTREAM DO NOT BELIEVE STRONG
OMEGA FIELD LATE TONIGHT TO BE SUFFICENT TO GENERATE SNOW IN TAF
AREA TIL MID MORNING. WITH 850-700-SFC LOWS ALL EXPECTED TO MOVE NE
OF TAF AREA...BELIEVE SNOW WILL COME FROM TRACK OF 500 VORT OVERHEAD
EARLY AFTERNOON. SO THAT IS WHEN PUT IN MAIN SNOW AND NOTHING REAL
HEAVY FOR ABOVE REASONS. SHOULD BE DONE AROUND MID AFTERNOON WITH
INCREASING NW WIND BEHIND DEPARTING LOW.
&&
.LOT...WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LK MI...SMALL CRFT ADVSRY IL/IND SHORES THIS AFTN. GL WRNG S HALF LK
MI LATE THIS AFTN/TNGT.
&&
$$