FXUS63 KLOT 052332
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
532 PM CST SAT DEC 5 2009
.DISCUSSION...
300 PM CST
CURRENT SATELLITE IMAGERY SHOWS ONLY SOME WISPS OF CI MAKING
THEIR WAY EWD IN ZONE OF UPR LVL CONFLUENCE BETWEEN TROUGH OVER
ONTARIO AND EJECTING SHORT WAVE MOVING THROUGH SRN RCKYS. THIS
WILL ALLOW FOR BENIGN WX THROUGH TONIGHT. MODEST WARM ADVECTION ON
BACK SIDE OF RETREATING RIDGE SHOULD ALLOW TEMPS TO STABILIZE
AFTER INITIAL DROP OFF THIS EVENING...SO OVERNIGHT LOWS GENERALLY
NOT AS COLD AS LAST NIGHT.
LARGE AREA OF MID/HIGH LVL CLOUDINESS ASSD WITH SWRN SHORT WAVE
WILL BE OVERSPREADING AREA DURING SUNDAY...BUT WITH LTL LLVL
MOISTURE TO WORK WITH...WILL HOLD OFF ON ANY PRECIP MENTION UNTIL
SUNDAY NIGHT. GIVEN FCST PATH OF VORT MAX AND ASSD WEAK SFC
LOW...EXPECT BAND OF STEADIER LIGHT SNOW TO SET UP FROM ERN IA
ACROSS SRN WI IN REGION OF WEAK DEFORMATION AXIS. HOWEVER...SRN
EDGE OF STEADIER SNOW IS EXPECTED TO CLIP NWRN PORTIONS OF FA SO
WILL GO WITH 1-3 INCH AMTS ACROSS RFD AREA. ELSEWHERE...ALG/S OF
H5 VORT MAX/PATH OF H7 LOW...SNOW IS EXPECTED TO OCCUR WITHIN A
MUCH MORE BRIEF PERIOD OF TIME LATE SUNDAY NIGHT INTO ERLY MONDAY
AS VORT LOBE LIFTS THROUGH AND BECOMES HIGHLY SHEARED WITH TIME.
GIVEN BRIEF PERIOD OF SNOWFALL OVER REMAINDER OF AREA WILL ONLY BE
GOING WITH AN INCH OR LESS FOR ACCUMULATIONS. SFC RIDGING FCST TO
BUILD ACROSS MO VLY BY MONDAY AFTN...THEN SETTLE ACROSS FA MONDAY
NIGHT. THIS SHOULD ALLOW FOR CLRG SKIES AND A DECENT RADIATIONAL
COOLING SET UP MONDAY NIGHT.
FOCUS OF DISCUSSION ALREADY BECOMING CENTERED ON STORM SYS FCST TO
AFFECT MIDWEST TUESDAY NIGHT-WED. MODEL CONSENSUS SEEMS TO BE
BUILDING A SCENARIO OF A DEEPENING LOW REACHING SWRN MO BY 06Z
WED. THIS WOULD BE SPREADING A LARGE SHIELD OF WARM ADVECTION
PRECIP ACROSS NRN IL/NWRN IND TUESDAY EVENING. GIVEN DEGREE OF
ISENTROPIC LIFT/VERTICAL MOTION...THIS SHOULD BE MAINLY SNOW
THROUGH MIDNIGHT TUESDAY NIGHT WITH SEVERAL INCHES LIKELY
ACCUMULATING DURING THE EVENING HRS. THEREAFTER...FCST OF PRECIP
TYPE AND SNOW ACCUMULATION BECOMES MORE PROBLEMATIC. BOTH 12Z GFS
AND EUROPEAN BRING AN INTENSIFYING LOW TO NWRN INDIANA...NR LAF BY
12Z...THEN ACROSS LWR MI BY 18Z. SUSPECT THAT IF THIS AMOUNT OF
INTENSIFICATION DOES TAKE PLACE...LOW TRACK WILL BE EVEN FURTHER W
THAN CURRENTLY FCST...LEADING TO AN ALL OUT SWILLFEST ACROSS NERN
IL AND NWRN INDIANA. THEREFORE..WILL BE GOING WITH A GREATER
LIKELIHOOD OF PRECIP MIXING WITH OR CHG TO RAIN GENERALLY ALONG
AND E OF THE I-55 CORRIDOR. HEADING WEST OF THE FOX RIVER
VALLEY...STILL LOOKS LIKE PRECIP WILL BE ALL SNOW...AND WILL
PROBABLY BE GOING WITH A WINTER STORM WATCH FOR THIS AREA SOMETIME
TOMORROW IF SUBSEQUENT MODEL RUNS REMAIN CONSISTENT.
WITH CONTINUED DEEPENING OF SYSTEM WED-WED NIGHT...PRECIP SHOULD
QUICKLY CHANGE BACK TO SNOW OR SNOW SHOWERS OVER ENTIRE FA WED
MORNING. PRIMARY CONCERN BY THIS TIME WOULD BE WIND...BLOWING SNOW
AND FALLING TEMPS. ADJUSTMENTS WERE MADE EARLIER TO UNSEEMLY MILD
TEMPS IN EXTENDED PORTION OF FCST...SO LITTLE OR NO CHANGE MADE TO
INHERITED GRIDS LATTER PORTION OF NEXT WEEK.
MERZLOCK
&&
.AVIATION...
0000 UTC TAFS...RIDGE OF HIGH PRESSURE FROM S TX TO THE LOWER
GREAT LAKES EARLY THIS EVENING BRINGING CLEAR SKIES AND LIGHT S
WINDS TO THE REGION. AS THE HIGH DRIFTS SOUTHEAST OVERNIGHT A COLD
FRONT WILL APPROACH FROM THE NORTHWEST AND A WEAK WAVE OF LOW
PRESSURE WILL RIDE ALONG THE FRONT ACROSS IA. THIS WILL TIGHTEN UP
THE PRESSURE GRADIENT SOMEWHAT. WINDS GENERALLY AROUND 5 KNOTS
EARLY THIS EVENING MAY PICK UP A BIT LATE TONIGHT AND SUNDAY
MORNING TO NEAR 10 KNOTS. AS COLD FRONT DROPS INTO NORTHERN IL
SUNDAY AFTERNOON PRESSURE GRADIENT WILL WEAKEN ALLOWING WINDS TO
DROP TO ABOUT 5 KNOTS AGAIN BY SUNDAY EVENING.
CIELINGS AND VISIBILITIES WILL BE UNRESTRICTED OVERNIGHT. AS UPPER
LEVEL WAVE MOVES OUT OF THE SW US...MID AND HIGH CLOUDS WILL
GRADUALLY OVERSPREAD THE AREA. EXPECT A FAIRLY SOLID MID CLOUD
DECK TO BE IN PLACE BY SUNDAY AFTERNOON. LOOKS LIKE SNOW WILL HOLD
OFF UNTIL WELL AFTER MIDNIGHT SUNDAY NIGHT OR INTO DAYBREAK
MONDAY MORNING...WELL BEYOND THE RANGE OF THIS TAF ISSUANCE.
ALLSOPP
&&
.MARINE...
135 PM...MAIN FORECAST FOCUS/CHALLENGE CONTINUES TO BE A STRONG
AREA OF LOW PRESSURE WHICH WILL MOVE ACROSS THE GREAT LAKES...
WHILE DEEPENING...TUESDAY NIGHT AND WEDNESDAY.
IN THE SHORT TERM...A LARGE RIDGE OF HIGH PRESSURE EXTENDS FROM
THE SOUTHERN LAKES TO THE GULF OF MEXICO. THIS RIDGE WILL SHIFT
EAST TO THE ATLANTIC COAST BY SUNDAY EVENING. A WEAK COLD FRONT
WILL MOVE SOUTHEAST ACROSS THE WESTERN LAKES SUNDAY NIGHT AS A
WEAK AREA OF LOW PRESSURE DEVELOPS ALONG THIS FRONT OVER EASTERN
IA AND WESTERN IL MONDAY MORNING. THIS LOW WILL QUICKLY LIFT
NORTHEAST ACROSS THE EASTERN LAKES BY MONDAY EVENING. COMBINATION
OF A SLIGHTLY TIGHTER GRADIENT ALONG WITH SOME COOLER AIR...WILL
LIKELY ALLOW WINDS TO INCREASE TO 15-25KTS FOR A SHORT TIME...
ESPECIALLY OVER SOUTHERN LAKE MICHIGAN. A FAST MOVING RIDGE OF
HIGH PRESSURE WILL MOVE ACROSS THE LAKES REGION BY TUESDAY
MORNING...THUS WINDS SHOULD QUICKLY DIMINISH BY THIS TIME PERIOD.
AS THIS HIGH SHIFTS EAST...WINDS WILL FLIP AROUND TO EASTERLY AS
A NEW AREA OF LOW PRESSURE OVER THE SOUTHERN PLAINS TUESDAY LIFTS
NORTHEAST ACROSS THE SOUTHERN GREAT LAKES LATE TUESDAY NIGHT INTO
WEDNESDAY. TRENDS HAVE BEEN FAIRLY CONSISTENT SHOWING THIS LOW
DEEPENING AS MOVES THROUGH THE SOUTHERN LAKES...BUT EXTENT OF
DEEPENING AND HOW STRONG IT BECOMES CONTINUES TO VARY FROM RUN TO
RUN AND MODEL TO MODEL. WHILE THE SPECIFICS REGARDING TIMING AND
EXACT TRACK/WIND DIRECTIONS ARE STILL SOMEWHAT UNCERTAIN...
CONFIDENCE CONTINUES TO INCREASE THAT GALES WILL DEVELOP ONCE THE
LOW PASSES...ESPECIALLY OVER SOUTHERN LAKE MICHIGAN. CMS
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&
$$
