FXUS63 KLOT 030002
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
602 PM CST WED DEC 2 2009

.DISCUSSION...

308 PM...FORECAST CHALLENGES TONIGHT ARE MANY...INCLUDING QPF
AMOUNTS...CHANGE OVER/MIX TO SNOW...TIMING OF CHANGE OVER AS WELL
AS TEMPS. THEN MUCH COLDER TEMPS THRU THIS WEEKEND.

LOW PRESSURE OVER THE OHIO VALLEY WILL CONTINUE TO LIFT NORTHEAST
TO NEAR LAKE ONTARIO BY THURSDAY MORNING. AREA OF LIGHT/MODERATE
RAIN LIFTING NORTH/NORTHEAST ACROSS THE SOUTHEAST PART OF THE CWA
THIS AFTERNOON. AS THE LOW CONTINUES NORTHEAST...EXPECT THIS AREA
OF RAIN TO BEGIN TO PIVOT WITH THE BACK EDGE OF THE RAIN/PRECIP
LIKELY OCCURRING THRU THE CENTRAL PORTION OF THE CWA. THUS WILL
CONTINUE WITH JUST CHANCE POPS ACROSS THE NORTHWEST TO CAT POPS
ACROSS THE SOUTHEAST. WHILE MOST OBSERVATIONS HAVE ONLY REPORTED
LIQUID PRECIP TO OUR SOUTH THIS AFTERNOON...THERE HAVE BEEN A FEW
REPORTS OF SNOW MIXING WITH THE RAIN. THERMAL PROFILES WOULD
SUGGEST PRECIP TO START AS RAIN ACROSS MOST OF THE CWA BUT WITH
COOLER AIR SLOWLY FILTERING IN FROM THE NORTH AND ALREADY A FEW
REPORTS OF MIXED SNOW...HAVE OPTED TO START PRECIP AS A MIX OF
RAIN/SNOW GENERALLY NORTH OF A PNT/GYY LINE. IF PRECIP DOES START
AS RAIN...PROBABLY WON/T BE TOO LONG BEFORE IT BEGINS TO MIX.
FURTHER SOUTHEAST...EXPECT MAINLY LIGHT RAIN.

AMOUNTS HOWEVER...APPEAR TO BE RATHER LIGHT. THOUGH MODELS...
ESPECIALLY THE NAM SUGGESTS THE POTENTIAL FOR SOME LAKE
ENHANCEMENT DURING THE MID/LATE EVENING HRS OVER FAR NORTHEAST IL.
AND BY THE TIME THE COLUMN IS COOL ENOUGH TO SUPPORT ALL SNOW...
THE BULK OF THE PRECIP HAS SHIFTED TO THE EAST...THOUGH DO EXPECT
SOME LIGHT SNOW OVERNIGHT. IN ADDITION...THE WARM GROUND WILL
LIKELY BE A FACTOR...THUS ANY ACCUMULATIONS WILL LIKELY BE MINOR
AND ON GRASSY AND ELEVATED SURFACES. IN ADDITION...WHILE PRECIP
MAY FALL AS SNOW...OR A MIX...TEMPS TO OUR NORTH ARE NOT THAT COLD.
THUS DESPITE NORTHERLY FLOW...AIR ADVECTING INTO THE AREA IS NOT
SIGNIFICANTLY COOLER SO HAVE BUMPED TEMPS UP THRU THE EVENING AS
TEMPS SLOWLY SLIDE THRU THE UPPER 30S INTO THE MID 30S.

PROBABLY THE MOST SIGNIFICANT CHANGE WITH THIS SYSTEM IS THE MUCH
COLDER TEMPERATURES EXPECTED ACROSS THE AREA. WHILE NOT UNUSUAL
FOR EARLY DECEMBER...GIVEN THE MID 50S TUESDAY...MID 40S TODAY...
THE EXPECTED HIGHS IN THE MID 30S THURSDAY AND PERHAPS BARELY 30
ON FRIDAY WILL FEEL COLDER THAN THEY REALLY ARE. HAVE STAYED IN
LINE WITH GOING FORECAST HIGHS BOTH THURSDAY AND FRIDAY...WHICH
ARE SEVERAL DEGREES COLDER THAN GUIDANCE. WITH THE AMOUNT OF
SUNLIGHT APPROACHING ITS YEARLY MINIMUM AND COLD AIR ADVECTION
BOTH DAYS ALONG WITH CLOUD COVER...EXPECT LITTLE IF ANY RECOVERY
IN HIGH TEMPS. LOWS WELL INTO THE LOWER 20S FRIDAY MORNING WITH
TEENS EXPECTED SATURDAY MORNING.

SOME MODERATION IN TEMPS OVER THE WEEKEND ESPECIALLY SUNDAY AS THE
FLOW TURNS SOUTHERLY WHICH SHOULD HELP TEMPS WARM BACK INTO THE
UPPER 30S. BUT A WEAK LOW LIFTS NORTH ACROSS THE MIDWEST/WESTERN
LAKES SUNDAY NIGHT/EARLY MONDAY AND WHILE IT WILL HAVE LIMITED
MOISTURE...THIS MAY BE ABLE TO SQUEEZE OUT ENOUGH QPF FOR A
DUSTING OF SNOW...TEMPS WILL CERTAINLY BE COLD ENOUGH FOR ALL
SNOW. NEXT SYSTEM MOVES FROM THE PLAINS TO THE OHIO VALLEY TUESDAY
NIGHT INTO WEDNESDAY. TOO EARLY FOR ANY DETAILS...BUT THIS WILL
NEED TO BE MONITORED FOR THE POTENTIAL FOR AN ACCUMULATING SNOW.
CMS

&&

.AVIATION...
602 PM CST

0000 UTC TAFS...MAIN QUESTION MARK FOR TONIGHT IS ON PRECIP
CHANCES...WHICH APPEAR TO BE DWINDLING. A LOW PRESSURE SYSTEM
CURRENTLY OVER CENTRAL KENTUCKY IS EXPECTED TO QUICKLY LIFT
NORTHEAST INTO THE EASTERN GREAT LAKES TONIGHT. ALL OF THE BETTER
DYNAMICS WITH THIS SYSTEM APPEAR TO BE OFF TO THE EAST TO THE
POINT WHERE ORD/MDW WILL LIKELY ONLY GET GRAZED BY THE PRECIP.
CURRENT THINKING IS THAT THE BEST CHANCES WILL BE LATER THIS
EVENING IN THE 3-7Z TIMEFRAME AS THE LOW LIFTS UP INTO THE GREAT
LAKES. FAIRLY DECENT AMOUNT OF DRY LOW LEVEL AIR THAT NEEDS TO BE
OVERCOME...SO PRECIP DEVELOPMENT WILL LIKELY ALSO BE DELAYED BY
THIS. OVERALL...CONFIDENCE IN ANY PRECIP ACTUALLY REACHING THE
ORD/MDW/DPA TERMINALS IS LOW...AND ANY THAT DOES WILL BE OF LOW
IMPACT WITH CEILING CONDITIONS STAYING AT MVFR.

QUESTION THEN IS...IF THE PRECIP DOES FALL...WHAT FORM WILL IT BE
IN. WITH SOME HELP FROM THE WARMER LAKE AND SOME NORTHERLY
WINDS...TEMPS SHOULD STAY UP ENOUGH INITIALLY FOR THE PRECIP TO
START OUT AS RAIN. EVENTUALLY...WOULD EXPECT SOME SNOW TO MIX IN
AS EVAPORATIVE COOLING LOWERS THE LOW LEVEL TEMPS. BY THE TIME THE
REALLY COLD AIR MOVES IN AROUND 7Z...IT APPEARS THAT THE BEST
CHANCES FOR PRECIP WILL HAVE SHIFTED OFF TO THE EAST...THUS
ELIMINATING ANY CHANCES FOR AN ALL OUT SWITCH OVER.

AFTER A DRY PERIOD WITH UPPER LEVEL RIDGING MOVING IN THURSDAY
MORNING...SOME SCATTERED SNOW SHOWERS ARE EXPECTED TO DEVELOP AS
THE NEXT UPPER LEVEL STORM SYSTEM MOVES IN FROM THE DAKOTAS.

WINDS THROUGH THE PERIOD WILL REMAIN GUSTY AND BACK FROM THE NORTH
THIS EVENING...TO THE NORTHWEST VERY EARLY THURSDAY MORNING...AND
EVENTUALLY TO THE WEST LATE THURSDAY MORNING.

EXPECT MAINLY MVFR CIGS TO PERSIST THROUGHOUT MOST OF THE FORECAST
PERIOD...WITH SOME POSSIBLE BREAKS TO VFR TOWARD RFD.

HALBACH

&&

.MARINE...
153 PM CST

NORTHWEST WINDS WILL BE MAINTAINED ACROSS THE LAKE TODAY AS AN
AREA OF LOW PRESSURE DEPARTS TO THE NORTHEAST AND A SECONDARY AREA OF
LOW PRESSURE TRACKS NORTHEAST INTO THE LOWER MIDWEST. WITH THIS
AREA OF LOW PRESSURE MOVING INTO THE REGION...PRESSURE GRADIENT OVER
THE LAKE WILL INCREASE THIS AFTERNOON INTO THE EVENING. THIS ALONG
WITH A GOOD AMOUNT OF COLD AIR ADVECTION...WILL HELP INCREASE
NORTH GUSTS ACROSS THE LAKE TO JUST ABOVE 30 KT. WIND GUSTS WILL
STAY BELOW GALES AS MAIN LOW WILL STAY SOUTH OF THE LAKE...BUT A
BRIEF GUST TO GALE FORCE WOULD NOT BE OUT OF THE QUESTION. AREA OF
LOW PRESSURE WILL CONTINUE OFF TO THE NORTHEAST ON THURSDAY WITH
WINDS BACKING TO MORE OF A NORTHWESTERLY COMPONENT...AND WITH
WINDS ALSO DECREASING THROUGHOUT THE DAY. WEST WINDS WILL BE
MAINTAINED THROUGH FRIDAY AS THE NEXT SYSTEM DROPS SOUTH OUT OF
CANADA INTO THE LOWER MIDWEST.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 3 PM THURSDAY.

     SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 6 PM THURSDAY.

&&

$$