FXUS63 KLOT 252356
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
556 PM CST FRI DEC 25 2009
.DISCUSSION...
300 PM CST
SHORT WAVE TROF NOW ROTATING NORTHWARD FROM CENTRAL IL AND
SOUTHERN IND EARLY THIS AFTERNOON. AREA OF PRECIP BECAME MORE
DEVELOPED ACROSS CENTRAL IL DURING THE MORNING AS THE TROF TURNED
NORTHEASTWARD ACROSS THE MID MS RIVER TO SOUTHERN IL IN RESPONSE
TO THE APPROACHING TROF.
PRECIP HAS SPREAD ACROSS NW IND AND NORTHERN IL INTO SOUTHERN WI
DURING THE LATE MORNING AND EARLY AFTERNOON. RA QUICKLY CHANGING
OVER TO SN AND WILL DO SO ACROSS FAR NE IL AND NW IND IN NEXT HR
OR TWO AS COLD LOW LEVEL AIR THAT HAS NOW WRAPPED ALL THE WAY
AROUND TO THE SW AND S SIDE OF THE SYSTEM RAPIDLY ADVECTS NNE ON
25-35KT LOW LEVEL FLOW.
WILL BE SOME MINOR ACCUMULATING SN MID AFTERNOON INTO EARLY
EVENING TIL UPPER TROF CROSSES OVER FAR NORTHERN IL. THIS LIGHT SNOW
ACCUMULATION...ALONG WITH THE RAPID DROP INTO THE 20S AS THE
OCCLUDED FRONT PUSHES THRU THE REMAINDER OF THE FA WILL LIKELY
RESULT IN SLICK SPOTS AS RAINFALL OF LAST NIGHT AND THIS MORNING
LIKELY WASHED ALL SALT AND OTHER MELTING AGENTS FROM PAVEMENT SO
ANY WET SPOTS TO QUICKLY FREEZE...ESPECIALLY USUAL CULPRITS:
BRIDGES...ELEVATED RAMPS...ETC AS THEY EXPERIENCE FREEZING TEMPS
FROM BOTH ABOVE AND BELOW.
THIS PD OF SNOW TO TAPER OFF/END DURING THE FIRST PART OF THE
EVENING BUT THEN THE NEARLY CONSOLIDATED UPPER LOW...CURRENTLY
OVER THE MO-IA BORDER...DRIFTS ENE THEN NE TO SE WI BY 12Z SAT.
EXPECT AT FIRST JUST FLURRIES AND SCATTERED A -SHSN NEAR/UNDER THE
UPPER LOW.
OVERNIGHT AND SAT H7 AND H8 LOWS PROGGED TO TRACK NEWRD FROM SE IA
TO OVR/NEAR S CENTRAL WI. MODELS SHOW AREA OF FAIRLY STRONG UVV
FROM ISENTROPIC UPGLIDE AS WAA TO BE OCCURRING IN THE LOWER-MID
LEVELS. MODELS GIVING 0.15 TO 0.2 QPF DURING THE DAY SAT AS A
RESULT SO FORECASTING A SNOWFALL OF 1-3 INCHES ACROSS MUCH OF FA.
UPPER LOW TO DO AN COUNTER-CLOCKWISE LOOP OVER SRN WI AND NORTHERN IL
DURING SAT AND SUN. THIS KEEPS CHANCES OF LIGHT SNOW AND SNOW
SHOWERS AND ACCOMPANYING MINOR ACCUMULATIONS GOING FOR THE AREA
TIL LATE SUN NIGHT WHEN UPPER LOW FINALLY MOVES FAR ENOUGH OFF TO
THE E OVR THE CENTRAL GRTLKS.
RIDGING BUILDS IN FROM THE PLAINS LATE MON INTO TUE AS ANOTHER UPPER
TROF MOVES FM THE ROCKIES OUT OVR THE HI PLAINS. AS THIS TROF
CROSSES THE CENTRAL MO VALLEY AND APPROACHES THE MID MS VALLEY
OVERNIGHT TUE CHC OF -SN WILL ALSO SPREAD E ACROSS THE REGION FOR
WED.
REGARDING HYDROLOGIC ISSUES...WATER LEVELS ON STREAMS AND RIVERS
WILL CONTINUE TO RISE TODAY AND TONIGHT THOUGH LATEST FORECASTS
ARE FOR CRESTS TO BE BELOW FLOOD STAGE...EXCEPT MINOR FLOODING
FOR VERMILION AND ILLINOIS RIVERS.
TRS
&&
.AVIATION...
545 PM CST
0000 UTC TAFS...THE DEEP LOW PRESSURE SYSTEM PARKED OVER WRN IOWA
CONTINUES TO HAVE A SIGNIFICANT IMPACT ON THE WEATHER OVER NRN
IL/NWRN INDIANA.
THE COLD FRONT HAS PUSHED THROUGH THE REGION...WITH SFC TEMPERATURES
DROPPING WELL BELOW FREEZING AND WINDS SETTING INTO A SSWLY
DIRECTION. AT ISSUANCE TIME...A BAND OF HEAVIER SNOW...WITH
VISIBILITY DROPPING TO 2-3SM...WAS PUSHING THROUGH THE TERMINALS
AND WINDS INCREASING WITH GUSTS AROUND 30KT. THE BAND OF HEAVIER
SNOW IS FAIRLY NARROW AND SHOULD ONLY IMPACT THE TERMINALS FOR
ABOUT 2 HOURS. HAVE NOTED ISOLD REPORTS OF VISIBILITY LESS THAN
1/2SM AT THE NON-TAF SITES...BUT THE DURATION OF LOWER VISIBILITY
WAS BRIEF. WHILE THERE IS STILL THE POSSIBILITY OF VISIBILITY
DROPPING TO LIFR LEVELS...THE DURATION OF SUCH DROPS IN VISIBILITY
WILL LIKELY BE TOO BRIEF TO TRY TO PIN DOWN IN THE TAF.
OTHERWISE...THE PREVAILING CONDITION WILL BE FOR MVFR CIGS/VIS
BTWN 1500-2000FT. LIGHT SNOW WILL CONTINUE THROUGH THE NIGHT AND
INTO TOMORROW AS THE CENTER OF THE LOW PRESSURE SYSTEM ROTATES
AROUND IOWA. THERE IS STILL THE LIKELIHOOD OF HEAVIER BANDS OF
SNOW ROTATING AROUND THE LOW UNTIL THE SYSTEM BEGINS TO LIFT NEWD
SATURDAY NIGHT. HOWEVER...THESE SMALL SCALE FEATURES ARE VERY
DIFFICULT TO RESOLVE IN THE LONGER TERM...SO WILL HAVE PIN THEM
DOWN WITH SHORT TERM UPDATES. ON THE LARGER SCALE...THE MODEL
GUIDANCE IS INDICATING THAT THE SNOW SHOULD BECOME MORE WIDESPREAD
TOMORROW AS A STRONG UPPER LEVEL IMPULSE ROTATES AROUND THE LOW
PRESSURE SYSTEM TOMORROW. THEREFORE...HAVE INTRODUCED 2SM
VISIBILITY...BEGINNING LATE MORNING AT RFD AND SPREADING EWD
THROUGH THE LATE MORNING HOURS.
KREIN
&&
.MARINE...
123 PM CST
WINDS ARE GRADUALLY SUBSIDING OVER THE LAKE TODAY AS A LOW OVER
IOWA BEGINS TO OCCLUDE AND GRADUALLY FILL. ANTICIPATE BEING ABLE
TO CANCEL GALE WARNING EARLY FOR SOUTHERN LAKE MICHIGAN AND
NORTHERN PORTIONS SHOULD BE ABLE TO EXPIRE ON SCHEDULE THIS
EVENING. SFC LOW SHOULD WANDER AROUND IOWA THROUGH TOMORROW BEFORE
A MORE DECISIVE NORTHEASTERLY MOTION COMMENCES SATURDAY NIGHT. THE
LOW IS EXPECTED TO MOVE ACROSS NORTHERN PORTIONS OF THE LAKE EARLY
SUNDAY WITH MODEST WNW WINDS LOCKING IN BEHIND THE LOW. COLD FRONT
EXPECTED TO DROP DOWN THE LAKE MONDAY WITH RENEWED COLD AIR
ADVECTION AND TIGHTENING PRESSURE GRADIENT LEADING TO A FRESHENING
UP OF THE WINDS TO AROUND 30 KNOTS. FAIRLY QUICK DROP OFF IN WINDS
EXPECTED MONDAY NIGHT AS SURFACE RIDGE BUILDS EASTWARD ALLOWING
GRADIENT TO BEGIN RELAXING.
IZZI
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
LMZ868 UNTIL 9 PM FRIDAY.
SMALL CRAFT ADVISORY...NEARSHORE WATERS
UNTIL 4 AM SATURDAY.
&&
$$
