Winter Storm in Illinois, March 4 to 5, 2003

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
310 AM CST TUE MAR 4 2003

BUSY MORNING...SO WILL GET RIGHT TO IT. MODELS OVERALL IN AGREEMENT WITH
INCOMING SYSTEM CONSIDERING BIG DIFFERENCES JUST 24 HRS AGO.
FOCUS OF FORECAST IS WITH SIGNIFICANT SNOW POTENTIAL THIS AFTERNOON AND
TONIGHT. LATEST SURFACE ANALYSIS SHOWS LOW PRESSURE
OVER GREAT LAKES WITH COLD FRONT EXTENDING SOUTHWESTWARD THROUGH EASTERN
IA INTO NORTHERN KS TO SECONDARY SFC LOW IN EASTERN CO.
DEEPENING UPPER LEVEL TROUGH ALONG CA COAST WITH POTENT 140 KT JET ON
BACKSIDE SUPPORTIVE OF DIGGING. PLUME OF MOISTURE RAPIDLY ADVANCING
E/NE FROM SOUTHWEST STATES IN ASSOCIATION WITH UPPER JET NOSING INTO THE
BAJA OF CAL. JET MAX NOTED ALONG NE/SD BORDER WITH JET COUPLING
AND STRONG FRONTOGENETICAL AND ISENTROPIC LIFT GENERATING AREA OF SNOW
IN PLAINS STREAKING EASTWARD. CHECK OF OBS SHOWS VSBYS GENERALLY 1-4 MI WITH
AREAS LESS THAN 1 MI.

FRONTAL ZONE TO PUSH SOUTH THROUGH THE AREA TODAY...WHILE LOW PRESSURE
GATHERS STRENGTH OVER SOUTHERN PLAINS IN RESPONSE TO
INCREASE JET DYNAMICS...WITH SURFACE LOW MOVING E/NE ALONG FRONTAL ZONE.
STRONG BAROCLINIC ZONE WILL EXIST ACROSS THE REGION...WITH STILL
SOME CONCERNS ON THE EXACT PLACEMENT AS IT COULD BE FURTHER NORTHWEST THAN
MODELS INDICATE WHICH WOULD SHIFT HEAVY SNOW BAND. FORCING IS QUITE
IMPRESSIVE THIS AFTERNOON AND TONIGHT WITH COUPLING OF JETS AIDING IN
STRONG UPPER DIVERGENCE. STRONG ISENTROPIC AND FRONTOGENETICAL FORCING ALSO
PRESENT. BULK OF VVEL/OMEGA WITHIN FAVORED DENDRITIC ZONE.
MOISTURE ABUNDANT WITH GARCIA MIXING RATIOS YIELDING 3-4 G/KG SUGGESTIVE
OF 6-8 INCH POTENTIAL. ALSO...CROSS SECTIONS FROM MODELS SHOW
NEG EPV INDICATING ELEVATED INSTABILITY. CLOSER INSPECTION OF THETA-E AND
GEOSTROPHIC MOMENTUM SHOWS REGIONS OF PSI UNSTABLE TO SLANTWISE
CONVECTION. H7-H5 LAPSE RATES IMPRESSIVE AT 6-6.5 C/KM ACROSS THE SOUTHERN
1/3-1/2 LATE THIS AFTERNOON AND TONIGHT. ALL THIS POINTS TO POTENTIAL
FOR CONVECTIVE BANDS AND HIGHER AMOUNTS S/E. SECONDARY AREA OF HIGHER SNOW
AMOUNTS POSSIBLE NORTHWEST OF H85 LOW. MODELS FAIRLY SIMILAR IN TAKING
H85 LOW ACROSS FAR NORTHEAST MO INTO WEST CENTRAL IL...THOUGH
TRENDING SLOWER WHICH IS A BIT CONCERNING. BASED ON H85 TRACK COULD SEE
SWATH OF HIGHER SNOW AMOUNTS TO THE NORTHWEST OF THE TRACK FROM ROUGHLY CID
TO FREEPORT IL. ALL BEING SAID AND PER COORDINATION WITH SURROUNDING
OFFICES WILL UPGRADE WATCH TO WINTER STORM WARNING ALL AREAS FOR THIS AFTERNOON
AND TONIGHT. BULK OF SNOW IN 18-06Z TIMEFRAME...WITH EARLIER SHUT OFF IN
THE WEST AND LATER IN THE EAST. WILL BE GOING 5-8 INCHES MOST LOCATIONS
IN WARNING. THESE AMOUNTS COULD BE A BIT CONSERVATIVE IF CONVECTIVE POTENTIAL
IS REALIZED. STILL CONCERNS AS WELL WITH HOW FAR COLD AIR WILL INVADE
WITH IMPACTS TO LOCATION OF THERMAL ZONE AND AMOUNTS. ALSO SOME CONCERNS
WITH MIXED PCPN IN SOUTH. ANY MIX IN FAR SOUTH SHOULD QUICKLY CHANGE TO SNOW
GIVEN DYNAMICS...SO ANTICIPATE LITTLE IMPACT TO AMOUNTS. WINDS INCREASE
TONIGHT AS SURFACE WAVE PULLS AWAY THUS POTENTIAL FOR SOME BLOWING AND
DRIFTING.

NEXT CONCERN IS PCPN POTENTIAL LATE WED/WED NIGHT WITH UPPER TROUGH.
AVN/GFS INDICATING SOME -SN WITH VORT MAX TRACKING ACROSS THE SOUTHERN ZONES.
CURRENT FORECAST IS DRY AND WILL CONTINUE SIDING WITH UKMET AND ETA
SHOWING SURFACE RIDGING. DAY CREW CAN TAKE A HARDER LOOK.

TEMPERATURES CHALLENING TO SAY THE LEAST. WILL GIVE IT MY BEST SHOT.
INTERESTING LATE WEEK WITH MRF TRYING TO PIN 50 DEGS ON US WHICH WON/T HAPPEN
WITH EXPECTED SNOW COVER. OVERALL WILL BE UNDERCUTTING GUIDANCE
AFTER TODAY.

THANKS TO MKX...DMX...LOT...ILX...EAX...ARX FOR COORDINATION.

.DVN...
IA...WINTER STORM WARNING THIS AFTERNOON AND TONIGHT.
IL...WINTER STORM WARNING THIS AFTERNOON AND TONIGHT.
MO...WINTER STORM WARNING THIS AFTERNOON AND TONIGHT.

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IAZ040>042-051>054-063>068-076>078-087>089-098-099-ILZ001-002-007-
009-015>018-024>026-034-035-MOZ009-010-051130-

HAZARDOUS WEATHER OUTLOOK...CORRECTED FOR HIGHWAY 20
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
635 AM CST TUE MAR 4 2003

...SIGNIFICANT SNOW ACCUMULATION EXPECTED ACROSS MUCH OF EASTERN
IOWA...NORTHWEST AND WEST CENTRAL ILLINOIS AND FAR NORTHEAST MISSOURI

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF EASTERN IOWA...
NORTHWEST AND WEST CENTRAL ILLINOIS...AND NORTHEAST MISSOURI.

.DAY ONE...TODAY AND TONIGHT...

POCKETS OF DENSE FOG...REDUCING VISIBILITIES TO LESS THAN ONE
QUARTER MILE...WILL BE FOUND THROUGH SUNRISE BEFORE GRADUALLY LIFTING
AS WINDS INCREASE FROM THE NORTH.

A COLD FRONT WILL SAG JUST SOUTH OF THE AREA TODAY. LOW PRESSURE
OVER THE SOUTHERN PLAINS WILL MOVE NORTHEAST ALONG THE FRONT
WITH MOISTURE OVERRIDING THE COLD AIR AT THE SURFACE...RESULTING IN
PERIODS OF SNOW...HEAVY AT TIMES. MANY AREAS ALONG AND NORTH
OF HIGHWAY 20 WILL SEE A QUICK PERIOD OF SNOW THIS MORNING...WITH
AMOUNTS OF AROUND 1 INCH. SNOW WILL THEN BECOME WIDESPREAD
ACROSS THE REGION THIS AFTERNOON AND CONTINUE INTO TONIGHT BEFORE
TAPERING TO FLURRIES LATE THIS EVENING AND OVERNIGHT.
CURRENT INDICATIONS ARE THAT MOST LOCATIONS WILL SEE BETWEEN 5 AND
8 INCHES OF SNOW. HOWEVER...THERE ARE A COUPLE OF FACTORS WHICH
COULD RESULT IN SNOW ACCUMULATIONS BEING HIGHER. ONE FACTOR IS THE
LOCATION OF THE FRONT AND EXTENT OF POST FRONTAL COOLING. SHOULD THE
FRONT MOVE FURTHER SOUTH THEN SURFACE TEMPERATURES WILL BE SEVERAL
DEGREES COLDER. THIS WOULD RESULT IN HIGHER SNOW TO WATER RATIOS.
A SECOND FACTOR WHICH COULD RESULT IN LOCALLY HIGHER SNOW AMOUNTS IS
THUNDERSNOW. SEVERAL COMPUTER MODELS USED IN FORECASTING
THE WEATHER SHOW SUFFICIENT INSTABILITY ALOFT. SHOULD THIS
INSTABILITY BE REALIZED...THEN THUNDER AND LIGHTNING WOULD ACCOMPANY
SOME OF THE SNOW...RESULTING IN VERY HEAVY SNOWFALL RATES OF 2
INCHES PER HOUR FOR A FEW HOURS.

OVERALL...ROAD CONDITIONS ARE EXPECTED TO DETERIORATE RAPIDLY BY MID
TO LATE AFTERNOON OVER MUCH OF THE AREA. TRAVEL WILL LIKELY BE
DIFFICULT...AND QUITE HAZARDOUS TONIGHT.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY...

THE PROBABILITY OF WIDESPREAD HAZARDOUS WEATHER IS LOW.

.SPOTTER INFORMATION STATEMENT...

ANY SNOWFALL AMOUNTS RELAYED TO THE NATIONAL WEATHER SERVICE IN THE
QUAD CITIES FROM SPOTTERS...EMERGENCY MANAGERS AND THE MEDIA WOULD
BE GREATLY APPRECIATED.

&&

MORE INFORMATION MAY BE OBTAINED AT THE FOLLOWING URL:
HTTP://WWW.CRH.NOAA.GOV/DVN (ALL LOWER CASE)

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