FXUS63 KLOT 292040
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
240 PM CST SUN NOV 29 2009

.DISCUSSION...
240 PM CST

FORECAST CONCERNS TODAY REVOLVE LARGELY ON FIRST BOUT OF TRUE 
WINTER-LIKE WEATHER CURRENTLY PENCILED IN FOR A MID TO LATE WEEK 
ARRIVAL...JUST IN TIME FOR THE START OF METEOROLOGICAL WINTER.

BUT FIRST...SHORTWAVE RESPONSIBLE FOR OUR THUNDERY START TO THE DAY 
CONTINUES TO MOVE QUICKLY EASTWARD ACROSS ILLINOIS EARLY THIS 
AFTERNOON AS LARGER SCALE TROUGH DIGS INTO THE UPPER MISSISSIPPI 
VALLEY. SURFACE FRONTOGENESIS TAKING PLACE WITH FRONTAL BOUNDARY 
JUST GETTING READY TO CLEAR OUR FAR SE COUNTIES. WITH LEAD SHORTWAVE 
MOVING QUICKLY EASTWARD EXPECT PRECIP TO HAVE CLEARED THE CWA BY 00Z 
WITH DRY WEATHER TONIGHT. STRATUS DECK IS NOT OVERLY IMPRESSIVE 
UPSTREAM BUT COULD STILL SEE THIS FILL IN A BIT LATER THIS AFTERNOON 
INTO TONIGHT...WHICH IF IT DOES WOULD HOLD TEMPS UP A BIT TONIGHT 
MORE IN LINE WITH SLIGHTLY MORE MODERATE MAV TEMPS. 

A WEAK SHORTWAVE IS PROGGED TO RIDE THE NW FLOW INTO THE REGION 
LATER MONDAY AFTERNOON AND EVENING. STRENGTHENING WARM AIR ADVECTION 
IN ADVANCE OF THIS FEATURE EXPECTED TO LEAD TO SOME RAIN/SNOW 
BREAKING OUT MAINLY TO THE NORTH AND NORTHEAST OF THE CWA...BUT 
COULD BE CLOSE ENOUGH TO JUSTIFY SOME VERY SMALL POPS FOR OUR NE-ERN 
MOST COUNTIES MON EVENING. IF PRECIP DOES SNEAK INTO THE AREA IT 
CERTAINLY DOESNT LOOK LIKE ANY BIG DEAL. 

HEIGHTS WILL QUICKLY RISE IN THE WAKE OF THIS WAVE MONDAY NIGHT WITH 
FAIRLY IMPRESSIVE WARM AIR ADVECTION TAKING PLACE. STRONG WESTERLY 
FLOW FROM H8-H5 SHOULD BE QUITE EFFECTIVE IN ADVECTING CHINOOK 
WARMED AIR EASTWARD...BUT BIG QUESTION FOR OUR HIGH TEMPS IS HOW 
MUCH OF THIS WARM AIR ALOFT WILL BE MIXED DOWN TO THE SURFACE GIVEN 
LOW SUN ANGLE AND ONLY MODEST SFC WAA. GIVEN THE EXPECTATION OF 
CONSIDERABLE SUNSHINE...DID GO A BIT ABOVE MOS WITH HIGHS MOST AREAS 
POKING ABOVE 50F FOR WHAT WILL LIKELY BE ONE LAST GASP OF MILD-ISH 
AIR BEFORE THE BOTTOM STARTS DROPPING OUT. 

FIRST COLD FRONT SHOULD MOVE ACROSS THE AREA LATE TUES NIGHT INTO 
EARLY WED WITH AN INITIAL SHOT OF COLD AIR ADVECTION BRINGING TEMPS 
BACK DOWN CLOSER TO SEASONAL AVERAGES AND MARKING THE START OF THE 
MULTI-DAY DOWNWARD SLIDE IN TEMPS. FROPA LOOKS TO BE UNEVENTFUL  
WITH COLUMN FAIRLY DRY AND FORCING NOT OVERLY STRONG ALONG THE 
FRONT. 

THINGS GET MUCH MORE COMPLEX FROM THIS POINT ONWARD AND CONSEQUENTLY 
CONFIDENCE IN THE FORECAST BEGINS TO FALL ALMOST AS FAST AS THE 
TEMPS WILL BE FALLING! THE PROBLEM IS HOW THE MODELS HANDLE THE CUT 
OFF LOW CURRENTLY OVER THE NORTHERN BAJA CALIFORNIA AND TIMING OF 
PHASING OF THIS UPPER LOW/SOUTHERN STREAM SYSTEM WITH THE POLAR 
JET...BOTH THINGS THAT THE MODELS ARE NOTORIOUS FOR HANDLING POORLY. 
THIS GO AROUND APPEARS TO BE NO DIFFERENT WITH A FAIRLY WIDE 
SPECTRUM OF SOLUTIONS FOR WHEN THE UPPER LOW MOVES EAST AND HOW SOON 
IT PHASES WITH AMPLIFYING NORTHERN STREAM TROUGH. 

GENERAL MODEL CONSENSUS IS FOR UPPER LOW TO TRACK EAST AND NOT START 
TO PHASE WITH NORTHERN STREAM JET UNTIL WED NIGHT ONCE IT IS SAFELY 
EAST OF OUR CWA...WITH SURFACE LOW PROGGED TO TRACK NEAR THE SPINE 
OF THE APPALACHIANS BEFORE SECONDARY SURFACE CYCLOGENESIS TAKES 
PLACE NEAR THE EAST COAST. THIS SOLUTION...WHICH IS SUPPORTED BY THE 
12Z ECMWF/12Z GFS/12Z NOGAPS...WOULD SAFELY KEEP MOST IF NOT ALL OF 
THE SYNOPTIC SNOWS SE OF OUR CWA. HAVE GENERALLY FOLLOWED THIS LINE 
OF THINKING BUT STILL AM STILL SOMEWHAT LEARY SINCE MODELS TEND TO 
KICK UPPER LOWS OUT TOO QUICKLY...AND SHOULD THE UPPER LOW MOVE OUT 
SLOWER IT WOULD BE MORE LIKELY TO GET PICKED UP BY AND PHASE WITH 
THE AMPLIFYING NORTHERN STREAM TROUGH FARTHER WEST AND POSE MORE OF 
A SNOW THREAT TO OUR CWA. THE 12Z GEM/12Z UKMET AND A HANDFUL OF 
MEMBERS FROM THE 12Z GFS ENSEMBLE SUITE SUGGEST THAT THIS IS A 
POSSIBILITY...SO CANNOT COMPLETELY RULE OUT AN ACCUMULATING SNOW 
DURING THE WED NIGHT/THURSDAY TIME RANGE. UNTIL THERE IS BETTER 
MODEL CONSENSUS JUST DECIDED TO CONTINUE WITH LOW CHANCE/SLIGHT 
CHANCE POPS FOR SNOW WED NIGHT INTO THURSDAY. 

IN ADDITION...AMPLIFYING NORTHERN STREAM TROUGH SHOULD ALLOW THE 
COLDEST AIR MASS THUS FAR THIS SEASON TO SPILL SOUTHWARD INTO THE 
AREA THURSDAY INTO FRIDAY. H8 TEMPS ARE PROGGED TO DROP INTO THE 
TEENS BELOW ZERO CELSIUS...WHICH SHOULD THIS VERIFY WOULD RESULT IN 
HIGHS NOT CLIMBING OUT OF THE 20S BY FRIDAY AND POSSIBLY FALLING 
INTO THE 20S THURSDAY AFTERNOON DEPENDING ON THE TIME OF ARRIVAL OF 
THE SECONDARY PUNCH OF VERY COLD AIR. DEEPENING TROUGH MOVING INTO 
THE AREA WITH STRONG COLD AIR ADVECTION SHOULD RESULT IN STEEPENING 
LAPSE RATES AND WITH CYCLONIC LOW LEVEL FLOW...SET THE STAGE FOR 
NUMEROUS FLURRIES AND POSSIBLY SOME SCATTERED SNOW SHOWERS THURSDAY 
INTO FRIDAY AS WELL...EVEN IF THE SYNOPTIC SNOWS MISS US TO THE 
SOUTH/EAST AS IS CAUTIOUSLY EXPECTED.

FINALLY...AS SURFACE LOW INITIALLY DEVELOPS AND DEEPENS TO OUR SOUTH 
AND VERY COLD AIR SPILLS INTO THE AREA IT LOOKS POSSIBLE THAT THERE 
COULD BE A WINDOW OF OPPORTUNITY FOR LAKE EFFECT SNOW TO AFFECT OUR 
NW IN COUNTIES AND MAYBE EVEN SNEAK WEST INTO FAR NE IL FOR A TIME 
WED NIGHT OR THURSDAY. AS SFC LOW MOVES NORTHEAST LOW LEVEL FLOW 
WILL BACK AND CAUSE ANY LAKE EFFECT SNOW TO SHIFT EAST INTO THE MORE 
TYPICAL LAKE EFFECT SNOW BELT AREAS OF NC IN AND SW LOWER MI. 

TO SUM THINGS UP...

AT THIS POINT...WITH A LOW DEGREE OF CONFIDENCE...HAVE OPTED TO 
FOLLOW THE MAJORITY (ALBEIT A SOMEWHAT SMALL MAJORITY) OF THE MODEL 
GUIDANCE WITH THE POWERFUL STORM MOVING UP THE EAST COAST AND 
LARGELY BYPASSING OUR CWA WITH ITS ACCUMULATING SYNOPTIC SNOWS. 
WOULDN'T BE SURPRISED TO SEE MODEL SOLUTIONS WAFFLE AROUND MORE OVER 
THE NEXT COUPLE OF DAYS BEFORE COMING TO MORE OF A CONSENSUS. SO 
BOTTOM LINE IS THAT WE WILL NEED TO KEEP A WEARY EYE ON THE FORECAST 
FOR LATER THIS WEEK.

IZZI

&&

.AVIATION...
1134 AM CST

1800 UTC TAFS...MID LEVEL SHORT WAVE TROF THAT BROUGHT SCT SHRA
AND ISOLD TS TO LOCAL AREA THIS MORNING DUE TO STEEP MID LEVEL
LAPSE RATES HAS CROSSED SOUTHERN LAKE MI AND OVER SW LOWER MI AS
OF 17Z. ANOTHER SMALL AREA OF -RA HAD DEVELOPED AS ANOTHER WEAKER
SHORT WAVE FOLLOWS RIGHT ON ITS HEELS. EXCEPT FOR KGYY THIS -RA
SHOULD BE E OF LOCAL TERMINALS BY 18Z...AND END SHORTLY THEREAFTER
AT KGYY. FIRST SHORT WAVE PASSAGE PROVIDED A SOUTHEASTWARD PUSH
ON THE COLD FRONT AND CURRENTLY EXTENDS FM SAGINAW BAY TO THE
SOUTHERN CHI METRO AREA AND ON SOUTHWESTWARD TO N OF KSTL. CAA IN
LOW LEVELS WITH CFP RESULTING IN ST/STRATOCU AND BR WITH IFR
CONDITIONS DUE TO CIGS.

MAIN H7 TROF STILL BACK OVER CENTRAL U.P. OF MI SW ACROSS WI AND
FAR EASTERN IA INTO NE MO WITH MODEL PROGS FOR 30/06Z POSITIONING
IT NE-SW ACROSS LOWER MI...NW IN...CENTRAL IL NE MO. ANOTHER NUDGE
OF FRONT DEEPER ACROSS THE LOCAL AREA SHOULD RESULT IN SOME DRYING
OF LOW LEVELS WITH PREVAILING IFR CIGS IMPROVING TO MVFR. 

VISIBLE SATELLITE SHOWS SOME BREAKS IN CLOUDS IN SUBSIDENCE/DRYING
IMMEDIATE BEHIND MAIN MID LEVEL TROF...THO PLENTY OF STRATOCU A
LITTLE FURTHER UPSTREAM INTO THE COLD AIR. WITH INCREASED NNW-NW 
LOW LEVEL FLOW ADVECTING DRIER AIR INTO THE LOCAL AREA EXPECT MVFR
CIGS TO LIFT TO VFR EARLY TO MID EVENING BEFORE SCATTERING OUT
OVERNIGHT. 

TRS

&&

.MARINE...
400 AM CST

A WEAK COLD FRONT STRETCHES FROM LAKE HURON SOUTHWEST THROUGH
NORTHWEST ILLINOIS...TO CENTRAL TEXAS...WITH A WEAK LOW PRESSURE
CENTER NEAR ST. LOUIS. THIS FRONT WILL MOVE SLOWLY SOUTHEAST AS
THE WEAK LOW TRACKS NORTHEAST INTO LOWER MICHIGAN BY SUNDAY
AFTERNOON. FOLLOWING THE PASSAGE OF THE COLD FRONT...COOLER AIR
WILL OVERSPREAD THE LAKE AND WINDS WILL BECOME WLY-NWLY AND
INCREASE TO 15-25KT. EXPECT SMALL CRAFT ADVISORY CONDITIONS TO
DEVELOP BY LATE THIS AFTERNOON AND PERSIST THROUGH TUESDAY
MORNING. A LARGE RIDGE OF HIGH PRESSURE OVER THE ROCKIES WILL
SPREAD EAST ACROSS THE PLAINS SUNDAY AND INTO THE MISSISSIPPI
VALLEY SUNDAY NIGHT AND MONDAY. THE RIDGE WILL BUILD ACROSS THE
LAKE LATE TUESDAY ALLOWING WINDS AND WAVES TO SUBSIDE.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$