FXUS63 KLOT 092137
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
337 PM CST WED DEC 9 2009
.DISCUSSION...
336 PM CST
TONIGHT THROUGH FRIDAY...
OVERALL NO MAJOR CHANGES TO FORECAST MADE FROM PREVIOUS THINKING
EARLIER TODAY...WITH MAIN CHANGES BEING TO HEADLINES FOR TONIGHT.
WILL BE LETTING THE WINTER STORM WARNINGS EXPIRE WITH FORECAST
ISSUANCE THIS AFTERNOON AND WILL REPLACE WARNINGS WITH A WINTER
WEATHER ADVISORY FOR THIS EVENING WITH LINGERING GUSTY WINDS AND
AREAS OF BLOWING SNOW REDUCING VISIBILITIES...ESPECIALLY ACROSS OPEN
AREAS. A WIND CHILL ADVISORY WILL ALSO BE ISSUED FOR MUCH OF NORTH
CENTRAL ILLINOIS.
STRONGEST ISALLOBARIC COUPLET IS NOW SHIFTING INTO WEST CENTRAL
LOWER MICHIGAN ALTHOUGH BY PURE MIXING ALONE SEEING CONTINUED GUSTS
TO 40 TO 45 MPH ACROSS PORTIONS OF THE AREA...AND SHOULD GRADUALLY
SEE THESE GUSTS DIMINISH THIS EVENING. BAND OF SNOW WHICH SET UP
ALONG INTERSTATE 80 CORRIDOR PUT OUT SOME LIGHT AMOUNTS OF SNOW BUT
REPORTS FROM THIS AREA INDICATING OPEN AREAS BEING AFFECTED BY QUITE
LOW VISIBILITIES IN BLOWING SNOW. HAVE OPTED TO CANCEL THE WINTER
STORM WARNING WHICH WAS IN EFFECT THROUGH 00Z SINCE MOST OF THE
ACCUMULATING SNOWFALL HAS ENDED...BUT DUE TO STRONG WIND GUSTS
THROUGH EARLY EVENING WILL REPLACE THE WARNING WITH A WINTER
WEATHER ADVISORY FOR BLOWING SNOW. THE AREA OF THE WINTER WEATHER
ADVISORY HAS ALSO BEEN EXTENDED SOUTHWARD TO INCLUDE WILL COUNTY
DUE TO PRESENCE OF LIGHT SNOW BAND THAT PUT DOWN LIGHT DUSTING OF
SNOW. COULD SEE AS MUCH AS AN INCH OF ADDITIONAL SNOW EARLY THIS
EVENING WITH LAST IN SERIES OF MID LEVEL SHORT WAVES MOVING
THROUGH...BUT MOST LOCATIONS WILL LIKELY REMAIN UNDER AN INCH FOR
NEW SNOW ACCUMULATION.
OTHER CONCERN TONIGHT WILL BE ADVECTION OF BRUTALLY COLD AIR MASS
INTO THE REGION WITH 850 HPA TEMPS LOWERING TO -20 DEG C ACROSS FAR
NORTH CENTRAL ILLINOIS BY MORNING. GRADIENT WILL REMAIN SOMEWHAT
STRONG THROUGH THE NIGHT AND WOULD SUSPECT STRONG COLD AIR ADVECTION
AND LOW LEVEL INVERSION WILL ALLOW LOW CLOUDS TO STAY IN DURING THE
OVERNIGHT HOURS. DESPITE THESE FACTORS...PRESENCE OF FRESH SNOW PACK
AND UPSTREAM TREND SUGGESTING TRENDING TOWARD COLDER MET
GUIDANCE...OR EVEN A BIT COLDER THAN THIS. DID INCLUDE OVERNIGHT
LOWS IN THE ZERO TO 4 BELOW RANGE FOR FAR NORTHWEST COUNTIES AND
COMBINATION OF THESE TEMPERATURES WITH GUSTY WINDS TO 20 TO 25 MPH
THROUGH THE OVERNIGHT HOURS WILL PRODUCE WIND CHILLS APPROACHING
20 BELOW OR SLIGHTLY COLDER LATE TONIGHT INTO EARLY THURSDAY
MORNING. DID GO AHEAD AND ISSUE A WIND CHILL ADVISORY FOR MUCH OF
NORTH CENTRAL ILLINOIS COUNTIES THAT RUNS FROM 09Z TONIGHT THROUGH
THURSDAY MORNING.
SKIES WILL PARTIALLY CLEAR TOMORROW WITH CONTINUED DRY AIR ADVECTION
IN LOW LEVELS. DESPITE POTENTIAL FOR SOME SUN TOMORROW...CORE OF
BITTERLY COLD AIR MASS WILL BE IN PLACE AND WOULD SUSPECT AREAS WITH
SUBSTANTIAL NEW SNOW COVER WILL HAVE TROUBLE REACHING DOUBLE
DIGITS ABOVE ZERO TOMORROW. WILL START TO SEE LOW LEVEL WARM
ADVECTION FRIDAY AS SFC HIGH SLIDING ACROSS LOWER/MID MS RIVER
VALLEY TRACKS EASTWARD...ALTHOUGH TEMPS WILL BE SLOW TO MODERATE
ESPECIALLY FOR SNOW COVERED AREAS.
MARSILI
FRIDAY NIGHT THROUGH WEDNESDAY...
FOR THE PERIOD FROM FRIDAY NIGHT ONWARD...FEW CHANGES TO PREVIOUS
FORECAST EXCEPT TO INTRODUCE LOW CHANCE POPS SAT NIGHT INTO SUNDAY
FOR WEAK SHORTWAVE ENERGY PASSING THROUGH AS INDICATED BY GFS AND
ECMWF AS WELL AS ENSEMBLES. TEMPERATURES SHOULD MODERATE THROUGH
THE WEEKEND INTO EARLY NEXT WEEK AS WINDS TURN TO THE SOUTH BEHIND A
DEPARTING RIDGE AND THE NEXT APPROACHING LOW PRESSURE SYSTEM...
THOUGH EXPECT VALUES TO TREND TOWARD THE COOLER GUIDANCE NUMBERS
ESPECIALLY IN AREAS WITH EXTENSIVE SNOW COVER. HAVE OPTED TO KEEP
LOW CHANCE POPS FOR EARLY NEXT WEEK AS A LONGWAVE TROUGH SETS UP
OVER THE WESTERN HALF OF THE US AND EJECTS PULSES OF SHORTWAVE
ENERGY ACROSS THE AREA. GFS AND ECMWF DIFFER ON HOW EFFECTIVE
THIS ENERGY WILL BE AT DEVELOPING SURFACE CYCLONES...WITH THE GFS
ACTIVE ACROSS THE OHIO AND TENNESSEE VALLEYS AND THE ECMWF TAKING
ITS SURFACE SYSTEMS THROUGH THE GREAT LAKES. WILL WAIT TO PIN
THINGS DOWN BETTER AFTER THE MODELS COME INTO CLOSER AGREEMENT.
LENNING
&&
.AVIATION...
1800 UTC TAFS...LAST REMNANT BANDS OF HEAVIER SNOW WILL MOVE THRU
EARLY IN TAF PERIOD WITH BLOWING SNOW THE MAIN ISSUE. REDUCED VSBY
AS HIGH WINDS TO 40 KTS KICKS UP DEPOSITED SNOW AMNTS FROM THIS
MRNGS SNOW BANDS. EARLIER AND HEAVIER SNOWS PROBABLY PACKED WELL AND
EVEN CRUSTED OVER AND NOT EXPECTED TO ADD TO VSBY REDUCTION. CIGS
ARE OTHER ISSUE. SHUD DROP TO IFR WITH THESE LINGERING BANDS OF
SNOW...OTHERWISE LOW MVFR FROM 1K TO 2K UNTIL TONIGHT. THEN CIGS
LIFTING TO VFR AROUND MDNGT TNGT AS COLD AND WET WRAPAROUND PULLS
AWAY AND HIGH PRESSURE PUSHES IN ANTICYCLONIC FLOW. CIGS LIKELY TO
START BREAKING UP BY MRNG WITH WINDS DROPPING OFF TO 25 KTS. SO
QUITE CONFIDENT OF VFR CONDS FOR THURSDAY DESPITE A CHILLY START
IN THE SINGLE DIGITS.
RLB
&&
.MARINE...
1230 PM CST
DEEP SURFACE LOW OVER LAKE HURON THIS EVENING SHOULD KICK OUT FOR
SRN QUEBEC BY MRNG BUT STILL MAINTAIN GALE FORCE WINDS OVER THE
LAKE. EVEN WITH LOW TRACKING NE TO NRN QUEBEC FRIDAY...PRESSURE
GRADIENT ACROSS THE LAKES STILL QUITE STRONG AS HEFTY HIGH
PRESSURE PATTERN FROM THE NRN ROCKIES AND PLAINS BUILDS SE ACROSS
THE MS VLY TO THE MID ATLANTIC COAST THRU THAT PERIOD. FINALLY GET
SOME RELAXATION OF WINDS LATE FRIDAY NIGHT INTO SATURDAY AS SFC
LOW PULLS OFF THE EAST COAST OF CANADA...AND THE WESTERN PORTION
OF RIDGING ACROSS THE OHIO VLY BUILDS NORTHWEST OVER THE LAKES.
WINDS OVER LAKE GENERALLY WEST TO NW AT GALES FORCE THRU FRIDAY
BUT FINALLY BACKING TO SW LATE FRI NGT AND SAT.
RLB
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER WEATHER ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-
ILZ010-ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-
ILZ022 UNTIL 10 PM WEDNESDAY.
WIND CHILL ADVISORY...ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-
ILZ012-ILZ019...3 AM THURSDAY TO NOON THURSDAY.
WIND ADVISORY...ILZ023-ILZ032-ILZ033-ILZ039 UNTIL 6 PM WEDNESDAY.
IN...WIND ADVISORY...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 6 PM
WEDNESDAY.
LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-
LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...9 PM WEDNESDAY TO 1 AM
SATURDAY.
STORM WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-
LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 9 PM WEDNESDAY.
GALE WARNING...NEARSHORE WATERS UNTIL 6
PM THURSDAY.
&&
$$
