FXUS63 KLOT 160751
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
151 AM CST WED DEC 16 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...
06Z TAFS...NO CONCERNS...VFR THRU THE PERIOD. A LARGE RIDGE OF
HIGH PRESSURE EXTENDS FROM MINNESOTA SOUTH TO THE ARKLATEX. THIS
RIDGE WILL MOVE EAST ACROSS ILLINOIS WEDNESDAY...REACHING THE
EASTERN GREAT LAKES BY THURSDAY MORNING. WESTERLY WINDS 5 TO 10
KTS WILL SLOWLY DIMINISH TO 5 KTS OR SO BY MORNING...BECOMING
SOUTHWEST DURING THE MORNING THEN BECOMING LIGHT AND VRB BY
EVENING.
A BAND OF MID CLOUDS EXTENDS FROM CENTRAL MINNESOTA SOUTHEAST
INTO CENTRAL WISCONSIN AND IS MOVING SOUTHEAST. EXPECT SOME OF
THIS CLOUD DECK TO REACH THE TERMINALS BETWEEN 08Z-10Z...BUT FOR
SIMPLICITY WILL JUST INCLUDE SCATTERED MENTION WITH THE START OF
THIS FORECAST. THIS AREA OF MID CLOUDS WILL SHIFT EAST BY MID/
LATE WEDNESDAY MORNING LEAVING PRIMARILY CIRRUS FOR THE REMAINDER
OF THE PERIOD. CMS
&&
.MARINE...
151 AM CST
HIGH PRESSURE CENTERED OVER THE MID MISSISSIPPI VALLEY THIS
MORNING...WILL DRIFT EAST ACROSS THE WESTERN GREAT LAKES TODAY
ALLOWING WINDS AND WAVES TO DIMINISH. THE HIGH WILL CONTINUE
MOVING EAST TO THE EASTERN GREAT LAKES AND SOUTHERN ONTARIO
THURSDAY. WEAK LOW PRESSURE WILL THEN MOVE SLOWLY EAST FROM THE
MID MISSISSIPPI VALLEY ACROSS THE OHIO VALLEY FRIDAY AND SATURDAY
WHILE HIGH PRESSURE SITS OVER ONTARIO AND MANITOBA CANADA. LOW
PRESSURE WILL MOVE FROM EASTERN QUEBEC WESTWARD INTO THE GREAT
LAKES SUNDAY AND MONDAY...BRINGING INCREASING NORTHWEST WINDS TO
LAKE MICHIGAN.
ALLSOPP
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 6 AM WEDNESDAY.
&&
$$
