FXUS63 KLOT 041047
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
447 AM CST FRI DEC 4 2009
.DISCUSSION...
314 AM CST
.TODAY AND TONIGHT...THE SNOW SHOWERS THAT ARE OCCURRING THIS EARLY
MORNING WILL REMAIN NORTH OF INTERSTATE 88. THIS IS A BAND OF SNOW
RESULTING FROM WEAK SURFACE TROUGH MOVING THROUGH NORTHEASTERN
ILLINOIS. THE BLUE RIVER WISCONSIN PROFILER SHOWS THE WIND
BACKING BETWEEN 04 UTC AND 05 UTC. THE UPPER AIR TROUGH IS PASSING
THROUGH. THE POSITIVE VORTICITY ADVECTION AT 500 MB ON THE MODELS
SHOW THIS. BY 12 UTC WE EXPECT MOST OF THE SHOWERS TO END. WE WILL
FORECAST SCATTERED VERY LIGHT SNOW SHOWERS FOR THE REST OF THE
DAY. THE 850 MB ANALYSIS SHOWS VERY COLD AIR MOVING INTO OUR
FORECAST AREA TODAY. WE LOWERED THE HIGH TEMPERATURE FORECAST A
LITTLE TODAY. WE WILL FORECAST A LOWER TEMPERATURE THAN MODEL
OUTPUT STATISTICS FOR THE LOW TEMPERATURE TONIGHT.
SATURDAY THROUGH MONDAY...A LARGE HIGH WILL MOVE FROM THE ROCKY
MOUNTAINS AND GREAT PLAINS TO VIRGINIA BY MONDAY. WE EXPECT DRY
WEATHER SATURDAY AND SUNDAY. A COLD FRONT IS FORECAST TO MOVE
THROUGH SUNDAY NIGHT. WE WILL ADD A CHANCE OF SNOW SUNDAY NIGHT
AND MONDAY. WE USED THE ECMWF MODEL AND WE NOTE THAT THE POLAR JET
STREAM OVER ILLINOIS WILL MOVE EAST TO NEW ENGLAND BY SATURDAY
MORNING. THE HIGH TEMPERATURES WILL INCREASE TO THE MIDDLE 30S BY
SUNDAY AND WILL FALL TO THE LOWER 30S BY MONDAY.
OUTLOOK...A STRONG LOW IS FORECAST TO MOVE FROM OKLAHOMA TO
MICHIGAN TUESDAY NIGHT. THE LOW IS FORECAST OT BE IN ONTARIO BY
WEDNESDAY NIGHT. WE SEE THIS ON THE ECMWF AND THE GFS MODELS. WE
WILL KEEP THE CHANCE OF SNOW FOR TUESDAY THROUGH THURSDAY AT THIS
TIME.
&&
.AVIATION...
447 AM CST
1200 UTC TAFS...SNOW SHOWERS OVER EXTREME NE IL ASSOCIATED WITH
SMALL AREA OF ISENTROPIC UPGLIDE AHEAD OF NE-SW ORIENTED MID LEVEL
TROF ACROSS EASTERN AND SW WI...FAR NW IL AND E CENTRAL IA AT 10Z
PER SATELLITE PIX ALONG WITH PROFILER AND WSR-88D VAD WINDS. HAVE
BEEN TEMPO IFR VISIBILITIES WITH THE STRONGER SHSN WHILE CIGS
REMAIN MVFR.
BY BEGINNING OF 12Z TAFOR PD ONLY LINGERING FLURRIES FROM STRATOCU
TO BE LEFT ACROSS THE LOCAL AREA. AREAS OF SKC JUST S OF TERMINALS
AS WELL AS FURTHER W BEYOND FAR EASTERN IA. SIMPLE EXTRAPOLATION
OF RECENT MOVEMENT BRINGS SKC AREA TO RFD AROUND 14Z...AND CHI
AREA AROUND 16Z. HOWEVER BY 16Z EXPECT STRATOCU TO HAVE FORMED IN
MOIST LAYER TRAPPED UNDER DEVELOPING SUBSIDENCE INVERSION AROUND
850MB FILLING...AT LEAST PARTIALLY...THE CLEAR AREAS. AS DAY
PROGRESSES THIS MOIST LAYER DRIES AS SINGLE DIGIT F DEW POINTS
CURRENTLY UPSTREAM ADVECT ACROSS THE LOCAL AREA.
MODERATE PRES GRADIENT BETWEEN LOW PRES IN QUEBEC AND SFC RIDGE
BUILDING OVR THE OH VALLEY WILL KEEP WESTERLY SFC WIND GUSTING INTO
MID-UPPER TEENS KT RANGE THIS MORNING...THEN GRADUALLY DIMINISHING
AS LOW MOVES N-NNW RESULTING IN DECREASE IN THE GRADIENT ACROSS
THE LOCAL TERMINALS. WINDS WEAKEN AND BACK BOTH DIURNALLY AND AS
RIDGE BUILDS NEWRD ACROSS THE NE AND NEW ENGLAND WHILE LOW PRES
DROPS SOUTHEASTWARD OVER THE DAKOTAS.
TRS
&&
.MARINE...
200 AM CST
LOW PRESSURE MOVING NORTHWARD FROM SOUTHERN QUEBEC WITH A STRONG
RIDGE OF HIGH PRESSURE CONTINUING TO BUILD EAST OVER THE OH VALLEY
WILL MAINTAIN MODERATE W WINDS ACROSS LAKE MI TODAY...GRADUALLY
WEAKENING AND BACKING TO SW OVERNIGHT AND SAT AS THE LOW IN QUEBEC
CONTINUES TO MOVE NNW AND THE W-E RIDGE BECOMES ORIENTED SW-NE
FROM E TX ACROSS THE UPPER OH VALLEY TH THE ST. LAWRENCE VALLEY.
NEXT COLD FRONT/TROF SLIPS ACROSS NORTHERN LAKE MI LATE SAT NIGHT AND
EARLY SUN MORNING. LOW PRESSURE TO MOVE NE ALONG FRONT ACROSS THE
MID MS VALLEY SUN NIGHT REACHING LAKE MI BY MON MORNING.
WILL ALLOW SMALL CRAFT ADVISORY TO RIDE TIL 15Z MAINLY FOR
RESIDUAL WAVES AS WIND SPEEDS HAVE BEEN TRENDING DOWN AS NIGHT
PROGRESSES.
TRS
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...IN NEARSHORE WATERS TIL 9 AM FRI.
&&
$$
