FXUS63 KLOT 070948
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
348 AM CST MON DEC 7 2009
.DISCUSSION...
240 PM CST
CURRENT WATER VAPOR IMAGERY SHOW SHORT WAVE LIFTING NEWD ACROSS
KS/ERN OK. SOME ENHANCED CLOUD TOPS OVR MO VLY IN ASSN WITH THIS
DISTURBANCE ARE PRODUCING AN AREA OF LGT SNOW. THIS FEATURE IS
FCST TO TO CONTINUE NEWD...TO EXTEND FROM ERN IA-CNTRL IL BY 12Z
MON. THEREFORE...WILL GO WITH LIKELY POPS FOR LIGHT
SNOW...ESPECIALLY OVR FAR NRN/NWRN PORTION OF FA WHERE WEAK
COLD FRONT IS FCST TO BE LOCATED AS DAMPENING SHORT WAVE MOVES
THROUGH. NOT A LOT OF MOISTURE FOR THIS SYS TO WORK WITH...AND
GIVEN SCANT QPF...DON'T SEE MUCH MORE THAN AN INCH
ACCUMULATION...GENERALLY N OF I-88. REMAINDER OF AREA WILL
PROBABLY SEE A PERIOD OF LIGHT SNOW AS WELL...HOWEVER...IN
SOMEWHAT MILDER AIR AHEAD OF WEAK BOUNDARY...MUCH OF THIS MAY NOT
REACH THE GROUND AND AM LOOKING AT ANY ACCUMULATION BEING VERY
MINOR.
THIS SYS ZIPS OFF TO THE E BY NOON MONDAY AS IT CONTINUES TO SHEAR
OUT. IN ITS WAKE...SOME WEAK LLVL COLD ADVECTION WILL ALLOW FOR
MINOR REINFORCEMENT OF COLD AIR OVER REGION MONDAY NIGHT.
MOST ATTENTION...OF COURSE...HAS ONCE AGAIN BEEN FOCUSED ON BIG
HULLABALOO EXPECTED TO ARRIVE LATE TUESDAY-TUESDAY EVENING. MODELS
SEEM TO BE ZEROING IN ON A TRACK THAT WILL BRING SFC LOW JUST SE
OF CHICAGO BY 12Z WED. EXPANSIVE AREA OF WARM ADVECTION PRECIP
WILL LIKELY DVLP AHEAD OF THIS SYS TUESDAY AFTN-EVENING...WITH
STRONGEST ISENTROPIC UPGLIDE AND MOISTURE ADVECTION TAKING PLACE
TUESDAY EVENING. EXPECT THAT PRECIP WILL STAY MAINLY SNOW AS THIS
AREA OF PRECIP LIFTS NWD ACROSS AREA TUESDAY EVENING. ONCE THIS
DYNAMIC COOLING OF COLUMN RELAXES...FCST SOUNDINGS GENERALLY PUMP
ENOUGH WARM AIR ACROSS AREA TO CHG PRECIP TO RAIN/DRIZZLE ALONG
AND E OF I-55. FROM FOX RIVER WWD...PRECIP LOOKS MORE LIKELY TO
REMAIN MOSTLY SNOW. GIVEN HIGH QPF FROM MODELS AS WELL AS HPC
GUIDANCE...FEEL CONFIDENT IN HEADLINING A WINTER STORM WATCH FOR
THESE AREAS. FCST OF PRECIP TYPE AND AMOUNT IS HIGHLY PROBLEMATIC
AT THIS POINT. GIVEN STRENGTH OF WAA PRECIP TUESDAY
EVENING...SEVERAL INCHES OF SNOW COULD PILE UP EVEN E OF WATCH
AREA BEFORE PRECIP CHANGES TO LIQUID AND DIMINISHES AS BETTER
FORCING LIFTS TO N AND E. OF NOTE IS THAT MODELS SEEM TO WANT TO
KEEP THIS SYSTEM AN OPEN WAVE CYCLONE...RATHER THAN DEEPENING IT
INTO A CLOSED SYSTEM. THIS LENDS SUPPORT TO KEEPING THE SFC/LLVL
CIRCULATION ON A GENERAL NELY COURSE...RATHER THAN HAVING IT BCM
VERTICALLY STACKED...CURLING IT ANY FURTHER TO LEFT /WEST/. BASED
ON THIS...HAVE A LITTLE MORE CONFIDENCE IN MODEL CONSENSUS
REGARDING TRACK OF LOW.
SOME WRAP AROUND SNOW/SNOW SHOWERS ON WED...BUT MAIN CONCERN BY
THAT TIME WILL BE WIND AND FALLING TEMPS. HAVE KEPT WINTER STORM
WATCH VALID THROUGH THE DAY WEDNESDAY AS BLOWING SNOW MAY BE QUITE
SIGNIFICANT...PARTICULARLY ACROSS AREAS RECEIVING MAINLY SNOW
THROUGH THE EVENT.
REGARDLESS OF WHAT HAPPENS WITH TUESDAY NIGHTS STORM...COLDEST AIR
THUS FAR THIS SEASON APPEARS HEADED FOR MIDWEST. WILL GO WITH LOWS
NEAR ZERO LATTER PORTION OF WEEK FOR THOSE AREAS EXPECTED TO BE
SNOW COVERED...WITH MINS IN 10-15 RANGE OVR AREAS FCST TO RETAIN
BARE GROUND.
MERZLOCK
&&
.AVIATION...
0600 UTC TAFS...
MVFR AND IFR CIGS AND VIS...ALONG WITH LATE-DAY MONDAY WIND
SHIFT...CONTINUE TO BE FOCUS FOR THIS TAF CYCLE AS COMPLICATED
FORECAST SCENARIO PLAYS OUT ACROSS THE AREA.
REGIONAL RADAR INDICATES LARGE AREA OF LIGHT SNOW ACROSS EASTERN
IOWA AND PARTS OF WESTERN ILLINOIS. HEAVIEST SNOW THIS EVENING HAS
BEEN ACROSS SOUTHEASTERN IOWA...IN WHAT APPEARS TO BE AN AREA OF
WAA/TROWAL AT OR AROUND 850 MB PER 00Z RAOB AND PROFILER
ANALYSIS...ALL OCCURRING JUST TO THE NORTH OF THE SURFACE LOW...AND
VERY CLOSE TO CENTER OF 850 CIRCULATION. THIS HEAVIER SNOW IS ALSO
OCCURRING JUST TO THE NORTH OF A STALLED WEAK FRONTAL BOUNDARY...A
PORTION OF WHICH IS DRAPED ACROSS NORTHERN ILLINOIS VERY CLOSE TO
RFD TERMINAL. SHORT TERM MODEL GUIDANCE CONTINUES TO INDICATE THIS LOW
WILL LIFT NORTHEAST ACROSS THE AREA THROUGH EARLY TO MID MORNING
MONDAY...WITH THE HEAVIEST SNOW CONTINUING TO OCCUR JUST NORTH
OF THE LOW AND SURFACE FRONT.
WITH THAT IN MIND...RFD APPEARS TO BE THE TAF LOCATION WITH THE
BEST BET OF SEEING PERIODS OF IFR CIGS AND VIS. OBS ALL EVENING
ACROSS IOWA HAVE GENERALLY BEEN SOLIDLY IFR WITHIN THE HEAVIEST
AREA OF SNOW...HOWEVER CONFIDENCE IS A BIT LOWER FURTHER EAST AS
SUBSTANTIAL DEW POINT DEPRESSIONS...ON THE ORDER OF 10-12
DEGREES...WILL RESULT IN A GOOD DEAL OF EVAPORATION BEFORE THE
FIRST FLAKES MAKE IT TO THE SURFACE. HAVE CONTINUED IDEA OF
PREVIOUS FORECASTS WITH A PERIOD OF HIGH END IFR CIGS AND VIS AT
RFD STARTING IN THE EARLY MORNING HOURS...AND FOR THIS FORECAST
HAVE INDICATED TEMPO GROUP OF LOWER IFR CONDITIONS. FOR OTHER TAF
SITES...REALLY CONSIDERED THE POSSIBILITY OF IFR CIGS AND VIS FOR A
TIME JUST BEFORE DAYBREAK...BUT DEPTH AND MAGNITUDE OF DRY AIR
COMBINED WITH BEST UVV JUST TO THE NORTH PRECLUDED THEIR
INCLUSION AT THIS TIME. LATER SHIFTS WILL HAVE TO MONITOR AND MAY
NEED TO AMEND SHOULD UPSTREAM OBS BE A LITTLE WORSE THAN CURRENTLY
EXPECTED.
AS FAR AS WIND IS CONCERNED...STALLED OUT FRONTAL BOUNDARY NEAR
RFD AT THIS HOUR HAS RESULTED IN EASTERLY TO VARIABLE WIND AT
RFD...WITH LIGHT SOUTHERLY FLOW AT THE OTHER TERMINALS.
TONIGHT...EXPECT THE BOUNDARY TO LIFT NORTH EVER SO SLIGHTLY AS
SURFACE LOW RIDES NORTH ALONG IT...LIKELY RETURNING RFD TO
SOUTHERLY FLOW FOR A TIME IN THE EARLY MORNING HOURS. BEHIND THE
LOW...THE FRONT SHOULD DROP SOUTH ACROSS THE TERMINALS MONDAY
AFTERNOON AND EARLY EVENING...WITH A GRADUAL VEERING OF THE WINDS
TO WEST AND THEN NORTHWEST.
BOXELL
&&
.MARINE...
345 AM CST
GALE WATCH EXPANDED TO ENTIRE LAKE WITH START TIME MOVED UP TO TUE
NIGHT AS WELL AS LENGTHENED INTO LATE THU NIGHT.
WEAK LOW IN NORTHEAST MO TO MOVE NORTHEAST AND ACROSS SOUTHERN
LAKE MI AND CENTRAL LOWER MI DURING THE MORNING.
POTENT LOW TO TRACK NORTHEAST ACROSS THE MID MS VALLEY TUE NIGHT
AND BE NEAR OR OVER SOUTHERN LAKE MI BY WED MORNING. GALES ON THE
LAKE A GIVEN BUT WITH SOME DIFFERENCES IN TRACK OF THE LOW BETWEEN
VARIOUS MODELS TIMING IS A QUESTION. SFC LOW POSITIONS AT 12Z WED
BASED ON SFC WIND STREAMLINES VARY FROM BETWEEN VPZ AND SBN PER
FURTHEST SOUTH GFS ENSEMBLE CLUSTER AND MEAN...TO JUST SOUTH OF
SBM PER FURTHEST NORTH NAM. BEST GUESS AT THIS TIME IS FOR LOW TO
REACH WESTERN SHORE OF THE LAKE AT OR A BIT NORTH OF THE WI STATE
LINE.
HIGH POTENTIAL FOR GALES ON VARYING PORTIONS OF THE LAKE AHEAD OF
THE APPROACHING DEEPENING LOW TUE NIGHT AS WELL AS WHILE IT
CONTINUES TO DEEPEN AS IT LIFTS NORTHEASTWARD THROUGH THE CENTRAL
GREAT LAKES WED AND INTO SOUTHERN QUEBEC WED NIGHT.
TRS
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-
ILZ012-ILZ019...6 PM TUESDAY TO 7 PM WEDNESDAY.
IN...NONE.
LM...GALE WATCH...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-LMZ872-
LMZ874-LMZ876-LMZ878...9 PM TUESDAY TO 2 AM FRIDAY.
&&
$$
