AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
311 PM CDT FRI OCT 14 2011
.DISCUSSION...
335 AM CDT
A NEGATIVELY TILTED UPPER TROUGH CONTINUES TO ROTATE
NORTHEASTWARD OVER THE UPPER GREAT LAKES EARLY THIS MORNING
AS A STRONG JET MAX PUNCHES SOUTHEAST ACROSS THE DAKOTAS TO THE
LOWER OH VALLEY. THE RAIN ASSOCIATED WITH THE UPPER TROUGH HAD
SHIFTED NORTHEAST AND EAST OF THE LOCAL FORECAST AREA LATE LAST
EVENING WITH RAPID CLEARING OF ANY CLOUDS FOLLOWING THE PASSAGE
OF THE SHARP TROUGH AXIS.
LAST FEW FRAMES OF WATER VAPOR AND IR SATELLITE LOOPS SHOW THE
BEGINNINGS OF THE UPPER LOW FORMATION OVER CENTRAL LAKE MI AS
DEPICTED BY THE MODELS. SLOWING OF THE EASTWARD PROGRESS OF THE
SYSTEM ANTICIPATED AS THE UPPER LOW FULLY FORMS AND HANDLED WELL
BY THE MODELS MOVING OVER THE CENTRAL AND EASTERN GREAT LAKES
LATER TODAY AND TONIGHT. SIGNIFICANT COOLING OF MID AND UPPER
LEVELS HAS BEEN OCCURRING FOLLOWING THE UPPER TROUGH PASSAGE LATE
THU EVENING. WITH SURFACE HEATING AND RESIDUAL LOW LEVEL MOISTURE
EXPECT TO SEE BROKEN CLOUD COVER BY LATER MORNING AND THROUGH THE
AFTERNOON AS DIURNAL STRATOCU SPREADS AIDED BY THE SMALL MID LEVEL
DISTURBANCE APPROACHING FROM SOUTHEAST MN.
ALONG WITH CLOUD FORMATION...HEATING WILL DEEPEN THE MIXED LAYER
UP TO AROUND 1.5KM AGL WHERE WEST-NORTHWEST WINDS OF 35-40KT ARE
FORECAST BY THE MODELS. MOMENTUM TRANSFER DOWN TO THE SURFACE
WILL BEGIN AROUND MID MORNING AS SURFACE TEMPERATURES WARM BACK
UP INTO THE MID 50S. BUFKIT SHOWS 30-35KT TRANSFER DOWN TO NEAR
GROUND LEVEL LATER TODAY. WINDS MAY OCCASIONALLY MEET OR EXCEED
ADVISORY CRITERIA OF 26KT SUSTAINED AND/OR GUSTS OF 39 KT BUT IT
APPEARS THAT PREVAILING CONDITIONS WILL REMAIN JUST BELOW THE
THRESHOLD.
NEXT THREAT OF PRECIPITATION ARRIVES LATER SAT NIGHT AND SUN AS
A SHORT WAVE CURRENTLY OVER NORTHERN B.C. DROPS SOUTHEAST ACROSS
THE DAKOTAS AND THE UPPER MS VALLEY...REACHING THE WESTERN GREAT
LAKES BY SUN EVENING. WITH THE SHORT WAVE TURNING EASTWARD AS IT
APPROACHES THE SOUTH SIDE OF THE UPPER LOW THAT TAKES UP
RESIDENCE OVER SOUTHERN HUDSON BAY THE THREAT OF RAIN WILL BEGIN
DROPPING OFF FOR SUN AFTERNOON.
RAIN CHANCES INCREASE AGAIN MON AS THE STRONG SHORT WAVE OVER THE
EASTERN ALEUTIAN PENINSULA CROSSES THE NORTHERN ROCKIES SUN NIGHT
AND CONTINUES OUT OVER THE CENTRAL PLAINS DURING MON. THIS SHORT
WAVE IS PROGGED TO CONTINUE TO DIG SOUTHEASTWARD MON NIGHT AND
TUE WHICH WOULD SUGGEST MOST PRECIPITATION WOULD OCCUR OVER
CENTRAL IL AND POINTS SOUTH BUT GIVEN THE FORECAST STRENGTH OF
THE SYSTEM AND THE ASSOCIATED WARM AIR ADVECTION PATTERN INTO
EAST CENTRAL AND NORTHEAST IL AS WELL AS NORTHWEST IND BY MON
MIGHT EXPECT THE ENTIRE LOCAL FORECAST AREA TO HAVE AT LEAST A
CHANCE OF RAIN.
ON THE BACK SIDE OF THIS SYSTEM IS EQUALLY STRONG COLD AIR
ADVECTION WITH 850HPA TEMPERATURES FALLING TO AROUND -2C OVER THE
AREA BY 00Z WED. STRONG NORTH WINDS DOWN THE RELATIVELY WARM LAKE
WATERS APPEARS TO BE A GOOD SETUP FOR LAKE EFFECT RAIN SHOWERS
ALONG THE IMMEDIATE IL SHORES AND ON INTO NORTHWEST IND FOR TUE
NIGHT. THESE SHOULD SHIFT EASTWARD WITH TIME AS THE LOW LEVEL FLOW
GRADUALLY BACKS.
TEMPERATURES TO BE IN NORMAL RAGE FOR MID OCT THROUGH THE WEEKEND
AND INTO EARLY NEXT WEEK BUT AS THE STRONG SHORT WAVES MOVES
ACROSS THE MID MS VALLEY LATE MON NIGHT AND TUE MORNING THE COLD
AIR THAT HAS BEEN KEPT FAR NORTH OVER NORTHERN CANADA WILL BE
SPILLING SOUTHWARD FOR MID NEXT WEEK WHEN HIGHS WILL BE LIMITED TO
THE LOWER AND MID 50S WITH OVERNIGHT LOWS FROM MID 30S TO MID 40S.
TRS
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 20Z...
* WLY WINDS GUSTS TODAY AND ON SATURDAY.
KJB
//DISCUSSION...UPDATED 18Z...
LOW PRESSURE ACROSS THE UPPER GREAT LAKES WILL CONTINUE TO INTENSIFY
AS IT SLOWLY LIFTS NORTHWARD INTO CANADA TODAY AND TONIGHT. THIS WILL
CONTINUE TO PRODUCE STRONG GUSTY WESTERLY WINDS AT THE TERMINALS
TODAY THROUGH SATURDAY. THE WIND GUSTS WILL LIKELY ABATE SOME LATER
THIS EVENING. HOWEVER...THEY SHOULD QUICKLY PICK BACK UP AGAIN
SATURDAY MORNING AS SATURDAY WILL ALSO BE WINDY ACROSS THE AREA.
VFR CONDITIONS ARE EXPECTED THROUGH THE PERIOD. HOWEVER...A BKN DECK OF
DIURNALLY GENERATED STRATO CU AROUND 5,000 FT AGL WILL THROUGH THE
AFTERNOON.
KJB
//ORD AND MDW CONFIDENCE...UPDATED 20Z...
* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS.
KJB
//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...
SATURDAY...VFR WITH GUSTY W WINDS.
SUNDAY THROUGH TUESDAY...VFR WITH PERIODIC RAIN CHANCES...SOME
MVFR POSSIBLE.
WEDNESDAY...VFR.
JEE
&&
.MARINE...
251 PM CDT
LOW PRESSURE CURRENTLY OVER SOUTHERN ONTARIO WILL MOVE
NORTHEASTWARD AND STRENGTHEN TONIGHT. HIGH PRESSURE OVER THE
NORTH-CENTRAL GREAT PLAINS WILL SINK SOUTH INTO THE SOUTHERN
MISSISSIPPI RIVER VALLEY TONIGHT. ISOBARS WILL REMAIN TIGHT OVER
THE GREAT LAKES TONIGHT...RESULTING IN WEST TO WEST-NORTHWEST
GALES TO 45 KT ACROSS THE LAKE. GALES UP TO 40 KT WILL LINGER
OVER THE EXTREME NORTHERN PART OF LAKE MICHIGAN TOMORROW MORNING.
SHOWERS WILL ALSO REMAIN OVER THE NORTHERN END OF THE LAKE ON
SATURDAY. WINDS WILL SLOWLY WEAKEN THROUGHOUT THE DAY TOMORROW.
ANOTHER CHANCE OF SHOWERS WILL PASS OVER THE SOUTHERN HALF OF THE
LAKE SATURDAY NIGHT THROUGH SUNDAY.
JEE
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-
LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 1 AM SUNDAY.
GALE WARNING...NEARSHORE WATERS UNTIL 1
PM SATURDAY.
&&
$$
