FXUS63 KLOT 151126
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
526 AM CST TUE DEC 15 2009
.DISCUSSION...
248 AM CST
FAIRLY BENIGN WEATHER PATTERN OVER THE NEXT SEVERAL DAYS WITH ONLY
REAL FORECAST CHALLENGE BEING TEMPS AND CLOUD COVER.
PERSISTENT STRATUS DECK STILL BLANKETING (FIGURATIVELY AND
LITERALLY) THE CWA THIS MORNING. CLOUD COVER HAS KEPT TEMPS SOMEWHAT
IN CHECK DESPITE THE MODERATE NORTHWEST WINDS. BACK EDGE OF THE
STRATUS SHOULD MOVE ACROSS THE CWA THIS MORNING WITH MOST AREAS
BECOMING SUNNY BY MIDDAY. DESPITE THE SUNSHINE NOT ANTICIPATING
TEMPERATURES TO REALLY GO ANYWHERE TODAY...EXCEPT POSSIBLY DOWNWARD
A BIT THIS MORNING AS HEART OF THE SHALLOW ARCTIC AIR MASS OOZES
SOUTHEASTWARD INTO THE AREA.
CENTER OF SPRAWLING HIGH PRESSURE SHOULD MAKE PROGRESS TOWARD THE
MID MISSISSIPPI VALLEY REGION TONIGHT WITH WINDS DIMINISHING QUICKLY
AFTER SUNSET. WHILE WINDS PROBABLY WONT QUITE GO CALM...THE FAIRLY
LIGHT NORTHWEST WINDS...SNOW PACK...AND CLEAR SKIES SHOULD ALLOW FOR
A RAPID TEMP DROP THIS EVENING. STILL APPEARS AS THOUGH WARM AIR
ADVECTION WILL BEGIN IN EARNEST ALOFT TONIGHT IN ADVANCE OF
SHORTWAVE CRESTING THE WESTERN RIDGE AND RIDING THE NW FLOW TOWARD
THE UPPER MS VALLEY. STILL APPEARS AS THOUGH 500MB 12 HOUR HEIGHT
RISES ON THE ORDER OF 120M WILL OCCUR TONIGHT WITH 925MB TEMPS
PROGGED TO WARM ABOUT 5C. EVEN WITH CLEAR SKIES THESE COULD BE
ENOUGH TO SLOW TYPICAL NOCTURNAL TEMPERATURE CRASH. GFS...WRF-NAM
AND WRF-ARW ALL SUGGEST A SUBSTANTIAL INCREASE IN RH FROM 600-300MB
TONIGHT IN RESPONSE TO THE INCREASING WARM AIR ADVECTION WITH
SCT-BKN CIRRUS DECK LIKELY TO OVERSPREAD THE REGION OVERNIGHT. THE
COMBINATION OF THE ABOVE FACTORS WILL LIKELY LEAD TO TEMPS LEVELING
OFF BY MID/LATE EVENING WITH TEMPS BECOMING NEARLY STEADY OR
POSSIBLY INCHING UP A COUPLE DEGREES AFTER MIDNIGHT. THIS EXPECTED
ATYPICAL DIURNAL TEMP CYCLE IS REFLECTED IN THE GRIDS.
DAY SHIFT LIKELY RIGHT ON TRACK WITH CUTTING BACK ON TEMPS DURING
THE DAY WEDNESDAY AS SHALLOW ARCTIC AIR MASS AT THE SURFACE WILL BE
SLOW TO MODIFY WITH SURFACE RIDGE OVERHEAD. HAVE CONTINUED TO TREND
HIGHS DOWN A COUPLE MORE DEGREES WEDNESDAY AND INTO WEDNESDAY
NIGHT...PARTICULARLY OVER THE DENSER SNOW PACK. EVEN HAVE DOUBTS
ABOUT WHETHER THURSDAY WILL BE AS MILD AS CURRENT GRIDS HAVE BUT
WILL LET CURRENT FORECAST RIDE FROM THURSDAY ONWARD FOR NOW AND LET
DAY SHIFT RE-EVALUATE.
IZZI
&&
.AVIATION...
1200 UTC TAFS...ONLY FORECAST CONCERNS FOR THIS SET OF TAFS ARE
BRISK WNW WINDS AND TIMING THE CLEARING OF STRATUS.
BASED ON SURFACE OBS AND ENHANCED IR SATELLITE IMAGERY...RAGGED
BACK EDGE OF CLOUD DECK WAS FROM KOSH TO KRFD TO KGBG AT 11Z. RFD
SHOULD CLEAR WITHIN AN HOUR OF TAF ISSUANCE...AND CHICAGO AREA
TAFS SHOULD CLEAR LATE MORNING TO AROUND NOON. OTHERWISE CLEAR
SKIES THROUGH THIS EVENING. WEAK MID LEVEL IMPULSE IN FAST NWLY
FLOW WILL DROP THROUGH WISCONSIN LATE TONIGHT INTO WEDNESDAY MORNING.
MAY SEE SOME MID AND HIGH CLOUDS IN WARM AIR ADVECTION PATTERN
ASSOCIATED WITH THIS WAVE. BUT VFR CONDITIONS WILL PREVAIL.
WNW WINDS EXPECTED TO HOLD AROUND 12-15 KNOTS WITH GUSTS TO AROUND
20 KNOTS THROUGH MOST OF THE DAY TODAY. STRONG HIGH PRESSURE OVER THE
NORTHERN PLAINS WILL BUILD EAST TOWARD THE MISSISSIPPI VALLEY
TONIGHT. EXPECT WINDS WILL BE AT OR BELOW 10 KNOTS BY SUNSET
AND GUSTINESS WILL CEASE.
ALLSOPP
&&
.MARINE...
103 AM CST
LOW PRESSURE OVER LAKE ONTARIO WILL CONTINUE MOVING EAST ACROSS
NEW ENGLAND AND THE MARITIMES TODAY AND TONIGHT. A STRONG HIGH
PRESSURE RIDGE FROM CENTRAL CANADA TO THE GREAT PLAINS EARLY THIS
MORNING WILL MOVE SOUTHEAST REACHING THE MISSISSIPPI VALLEY AND
WESTERN GREAT LAKES WEDNESDAY. STRONG WEST NORTHWEST WINDS ACROSS
LAKE MICHIGAN WILL SLOWLY SUBSIDE LATE TONIGHT AND WEDNESDAY AS
THE HIGH BUILDS EASTWARD. HIGH PRESSURE WILL THEN REMAIN
STATIONARY OVER THE WESTERN LAKES WEDNESDAY NIGHT THROUGH
FRIDAY...PRODUCING A PERIOD OF LIGHT WINDS. LOW PRESSURE OVER
QUEBEC WILL DRIFT WEST INTO ONTARIO FRIDAY NIGHT AND SATURDAY
BRINGING STRONGER NORTHERLY WINDS TO LAKE MICHIGAN FOR THE
WEEKEND.
ALLSOPP
&&
.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.
&&
$$
