000
FXUS63 KLOT 212353
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
653 PM CDT THU AUG 21 2008
.DISCUSSION...
305 PM CDT
UPPER LOW LIFTING NNE ACROSS EASTERN IA EARLY THIS AFTERNOON WITH
FIRST IN SERIES OF SHORT WAVES EJECTING NE INTO SOUTHERN MANITOBA
AHEAD OF UPPER LOW CROSSING FROM FAR SE B.C. TO THE ALBERTA-MT
BORDER. AS THE WESTERN UPPER LOW CENTER PROGRESSES EASTWARD TO FAR
SOUTHERN SASKATCHEWAN BY 12Z FRI THE DISTURBANCE OVER IA CONTINUES
TO OPEN AS IT CONTINUES NNE TO NW WI.
MORE SUBSTANTIAL BUT STILL MAINLY LIGHT RAIN HAS BEEN CONFINED TO
AREAS CLOSER TO THE MS RIVER WHILE THE LOCAL FA HAS SEEN ONLY
SPOTTY LIGHT SHOWERS AND SPRINKLES AS DEEPER DRY AIR IN PLACE THIS
FAR E. THE MAIN DISTURBANCE WILL BE PASSING INTO SE WI BY LATE
AFTERNOON RESULTING IN A DECREASE IN PRECIP ACROSS NORTHERN IL.
HOWEVER...APPEARS TO BE A COUPLE OF MINOR SHORT WAVES RIDING NNE
UP THE WEST SIDE OF THE EASTERN NOAM UPPER RIDGE WITH SCATTERED
TSRA NOTED FROM CENTRAL IL SSW TO LA AND EASTERN TX. MUCH OF THIS
DIURNALLY DRIVEN BUT WILL KEEP CHANCE MENTION FOR OVERNIGHT AND
FRI AS THESE IMPULSES TRAVEL ACROSS THE MID MS VALLEY TO THE LOCAL
AREA.
POPS RISE FOR SAT AND SAT EVENING WITH A COLD FRONT SLOWLY
APPROACHING AND EVENTUALLY DROPPING THROUGH NORTHERN IL AND NW
IND IN RESPONSE TO THE CANADIAN SYSTEM PROGRESSING FURTHER E AND
REACHING NEAR JAMES BAY BY 06Z SUN. LOW LEVEL MOISTURE POOLING
AHEAD OF THE FRONT RESULTS IN INCREASING INSTABILITY/CAPE VALUES
WITH SOME TSRA AHEAD OF THE FRONT EXPECTED WITH HEATING DURING SAT
AND UNTIL FROPA SAT NIGHT.
LOW THREAT OF PRECIP ACROSS THE REGION BEYOND ANY LINGERING SHRA
IN THE FAR SOUTHERN PORTION OF THE FA EARLY SUN A.M. AS HIGH
PRESSURE BUILDING FROM S CENTRAL CANADA AND THE NORTHERN PLAINS E
ACROSS THE UPPER MIDWEST AND GREAT LAKES SUN THRU WED DOMINATES.
TRS
&&
.AVIATION...
0000 UTC TAFS...WITH THE HIGH PRESSURE TO THE EAST AND A
DEVELOPING TROUGH TO THE WEST...A SOUTHERLY GRADIENT HAS SET UP
ACROSS THE MIDWEST. THIS IS ALLOWING GULF MOISTURE TO STREAM
NORTHWARD. A SERIES OF UPPER LEVEL IMPULSES ARE RIPPLING THROUGH
THE SLY FLOW...AND ARE FOCUSING SCT SHRA/TSRA MOVING QUICKLY
THROUGH NRN IL. THE LATEST RADAR IMAGERY SHOWS THE PCPN MOVING
BETWEEN RFD AND DPA...SO ORD/MDW/GYY SHOULD REMAIN DRY FOR THE
EVENING RUSH. RFD AND DPA WILL HAVE THE BETTER CHANCE OF SEEING
ANY WETTING RAIN...AND ANY THUNDER WILL LIKELY BE CLOSER TO RFD.
WITH LITTLE EWD PROGRESSION TO THE PATTERN...EXPECT THAT WINDS
WILL REMAIN GENERALLY SOUTHERLY THROUGH THE PERIOD. THE PCPN
FORECAST REMAINS A SERIOUS CHALLENGE AS THE SHRA/TSRA WILL
GENERALLY BE SCATTERED...WITH OCNL PATCHES WITH GREATER COVERAGE
UNDER THE FOCUS OF THE INDIVIDUAL UPPER LEVEL IMPULSES. THESE HAVE
BEEN RATHER DIFFICULT TO TIME...BUT EXPECT THAT THEN NEXT MORE
EXTENSIVE PATCH OF RAIN WILL BE DURG THE EARLY MORNING HOURS AND
AGAIN DURG THE LATE AFTERNOON HOURS TOMORROW. GIVEN THE UPSTREAM
TRENDS AND THE SCT NATURE OF THE PCPN...DO NOT SEE MUCH POTENTIAL
FOR IFR CIGS FOR THE WRN TAFS...BUT RFD COULD POTENTIALLY SEE SOME
IFR CIGS AS THE MORE WIDESPREAD RAIN WILL BE IN THAT AREA.
KREIN
&&
.MARINE...
1245 AM CDT
HIGH PRESSURE OFF TO THE EAST PUSHING FURTHER EAST AS COLD FRONT
APPROACHING FROM THE UPR MS VLY LATE TNGT AND FRIDAY. WILL
MAINTAIN A MODERATE SW FLOW UNTIL FROPA SATURDAY NIGHT WHEN WINDS
SHIFT TO THE NORTHWEST. WINDS LIKELY TO PICK UP EARLY SAT TO 25
KTS WITH TIGHTER PRESSURE GRADIENT OUT AHEAD OF FRONT. WINDS
CONTINUING TO VEER TO NORTH AND NORTHEAST SUNDAY AND MONDAY AS
HIGH PRESSURE FILLS INTO THE LAKES. WINDS THEN BECOMING MORE SOUTH
WEDNESDAY AS HIGH PRESSURE SHIFTS OFF TO THE EAST. NO OUTLOOK FOR
GALES.
RLB
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&
$$
