FXUS63 KLOT 152103
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
303 PM CST TUE DEC 15 2009
.DISCUSSION...
258 PM CST
WITH POLAR HIGH PRESSURE SPRAWLED ACROSS THE PLAINS AND MS VLY
FORECAST TO SETTLE ACROSS MIDWEST WEDNESDAY...AND THE OH VLY BY
THURSDAY...WX WILL BE NIL NEXT 36 TO 48 HRS. MAIN FORECAST
CHALLENGE WILL BE TEMP FCSTS...ESPECIALLY MINS TONIGHT AS WINDS
DIE OFF AFTER SUNSET...SETTING UP GOOD RADIATIONAL COOLING. TEMPS
EXPECTED TO DROP BELOW ZERO OVER MOST OF N CNTRL IL WITH READINGS
HANGING UP IN UPPER SINGLE DIGITS OVER AREAS WITH BARE GROUND.
MAX TEMPS ON WEDNESDAY STILL LIKELY TO BE EFFECTED BY SNOW COVER
DESPITE SUNSHINE AND MODERATION IN TEMPS ALOFT. THOUGH SFC HIGH
SHIFTS JUST TO E OF AREA DURING THE DAY...AND H85 TEMPS WARM INTO
-4 TO -7 C RANGE...ACTUAL SFC/BOUNDARY LYR ADVECTION IS VERY WEAK
SO RESPONSE IN TEMPERATURE FIELD WILL BE LIMITED OVER SNOW COVER.
TEMPERATURES MODERATE MORE ON THURSDAY IN RESPONSE TO STRONGER
PUSH OF MODIFIED PACIFIC AIR AS FLOW ACROSS CONUS GOES ZONAL.
TREND THEN TO TURN MORE WINTRY WITH TIME AS SHORT WAVE DIGS SEWD
FROM NRN ROCKIES...TO CENTRAL PLAINS THURSDAY NIGHT. THIS SHOULD
INCREASE CLOUDINESS DOWNSTREAM ACROSS MS VLY. WARM ADVECTION INTO
LEAD PORTION OF THIS DIGGING VORT MAX FROM W LOOKS VERY LIMITED
AND SYSTEM WILL BE STARVED FOR MOISTURE...SO ANTICIPATE THIS SYS
WILL ONLY PRODUCE MID LVL CLOUDINESS AND PERHAPS SOME INTERMITTENT
VERY LIGHT SNOW...MAINLY ACROSS SRN PORTIONS OF FA ON FRIDAY.
AS THIS SYSTEM EVOLVES FURTHER TO S OF OH VLY ON FRIDAY...NELY
FLOW ACROSS WRN GRTLKS DEEPENS THROUGH AT LEAST 15 THSD FT BY
FRIDAY EVENING. HOWEVER...WILL ONLY MENTION LO CHC POPS OF SNOW
SHOWERS OFF LAKE FRIDAY-SATURDAY TIME FRAME AS LAPSE RATES IN
LLVL MOIST LYR OVR LAKE UNSTABLE ONLY TO AROUND 4 THSD FT.
THEREFORE...EXPECT SOME LAKE EFFECT CLOUDS AND SNOW SHOWERS TO
DVLP...BUT THEIR EXTENT AND INTENSITY LOOK PRETTY MEDIOCRE AT THIS
POINT DUE TO UNIMPRESSIVE DEPTH OF UNSTABLE AIR.
REMAINDER OF FCST...FROM NEXT WEEKEND INTO FIRST HALF OF NEXT
WEEK...LOOKS INTERESTING AS GFS CONTINUES TO DEVELOP UPR CLOSED
LOW OVER MIDWEST DURING THIS PERIOD. EUROPEAN ALSO HAS BEEN
ADVERTISING A HIGHLY DISTORTED UPR FLOW PATTERN BY EARLY NEXT
WEEK...THOUGH EVOLUTION IS QUITE DIFFERENT AMONG MODELS.
NONETHELESS...GIVEN OVERALL MODEL CONSISTENCY IN DEVELOPING A
TREND TOWARD A COLD AND SOMEWHAT UNSETTLED PATTERN OVER CNTRL-ERN
U.S...MOST LIKELY EVOLVING AS A SERIES OF VORT LOBES ROTATE
AROUND DEEPENING TROUGH...FEEL EXTENDED FCST SHOWING BELOW NORMAL
TEMPERATURES AND A CHANCE OF SOME LIGHT SNOW SEEMS TO BE A
REASONABLE TREND.
MERZLOCK
&&
.AVIATION...
1800 UTC TAFS...MAIN CONCERN FOR THE AFTERNOON AND EARLY EVENING
WILL BE WINDS.
NRN IL/IN IS CURRENTLY IN A WNWLY GRADIENT BETWEEN LOW PRESSURE
CENTERED OVER UPSTATE NEW YORK AND STRONG HIGH PRESSURE OVER THE
CNTRL PLAINS. THE PRESSURE GRADIENT IS SUFFICIENT TO SUPPORT
SUSTAINED WINDS OF 12-15KT...WHILE PRESSURE RISES ASSOCIATED WITH
THE LOW PULLING AWAY TO THE EAST AND THE HIGH APPROACHING FROM THE
WEST WILL SUPPORT GUSTS OF 22-25KT. FREQUENT GUSTS WILL CONTINUE
UNTIL EARLY THIS AFTERNOON WHEN THE PLAINS HIGH WILL BEGIN TO
SPREAD EAST OVER THE MISSISSIPPI RIVER. WITH THE HIGH BUILDING
EAST...WINDS WILL BACK THROUGH WLY OVERNIGHT...BECOMING WEAK AND
SWLY IN THE MORNING AS THE RIDGE AXIS PASSES OVER THE UPPER MIDWEST.
LATEST SATELLITE IMAGERY SHOWS THAT THE BACK EDGE OF THE ST DECK
HAS PUSHED EAST OF ILLINOIS...SO ALL TERMINALS WILL BE SKC...WITH
THE EXCEPTION OF GYY WHICH WILL SEE SCT ST/SC FOR A BRIEF PERIOD
BEFORE BECOMING SKC. LATEST MODEL MOISTURE PROFILE FORECASTS BRING
SOME MID AND HIGH LEVEL MOISTURE INTO THE REGION TOMORROW...BUT
CLOUD COVER IS EXPECTED TO REMAIN SCT...WITH SKIES REMAINING VFR
THROUGH THE PERIOD.
AS THE HIGH PRESSURE MOVES OVER THE REGION...THE LOW LEVELS WILL
BE QUITE DRY AND NO OBSTRUCTION TO VISBY IS EXPECTED THROUGH THE
PERIOD.
KREIN
&&
.MARINE...
230 PM CST
BRISK WNWLY WINDS TO 25 KT WILL CONTINUE OVER THE LAKE THROUGH
THIS EVENING AS LOW PRESSURE MOVES INTO THE CANADIAN MARITIMES AND
HIGH PRESSURE SETTLES OVER THE CENTRAL PLAINS. AS THE LOW MOVES
OFF TO THE NORTHEAST AND THE HIGH BUILDS EWD ACROSS THE
MISSISSIPPI VALLEY...WINDS AND WAVES WILL DECREASE OVER THE
LAKE...GOING ALMOST LIGHT AND VARIABLE ON WEDNESDAY NIGHT AS THE
RIDGE AXIS CROSSES LAKE MICHIGAN. BY THURSDAY...WINDS WILL BEGIN
TO INCREASE AND BECOME MORE SELY...HOWEVER...SPEEDS SHOULD ONLY
INCREASE TO ARND 15-20KT. THE RIDGE OF HIGH PRESSURE SHOULD REMAIN
IN PLACE OVER THE ERN GREAT LAKES INTO THE WEEKEND...WHILE A WEAK
TROUGH OF LOW PRESSURE TRACKS THROUGH THE OHIO VALLEY. THIS WILL
ALLOW WINDS TO BACK FROM SELY ON THURSDAY TO NWLY BY SATURDAY
NIGHT. CONDITIONS ON THE LAKE WILL BE RELATIVELY QUIET FOR THE
MIDDLE OF DECEMBER WITH NO GALES EXPECTED THROUGH THE FORECAST
PERIOD.
KREIN
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL
MIDNIGHT WEDNESDAY.
SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 6 AM WEDNESDAY.
&&
$$
