203 
FXUS63 KILX 211546
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1046 AM CDT FRI SEP 21 2012

.DISCUSSION...
ISSUED 1045 AM CDT FRI SEP 21 2012

SURFACE DATA THIS MORNING SHOWS OLD FRONTAL ZONE IN THE OH RIVER
VALLEY. LOW CENTER THAT WILL AFFECT OVER AREA WAS OVER IN
SOUTHERN IA. DIFFERENTIAL HEATING...INDUCED WARM FRONT...BECOMING
ESTABLISHED EXTENDING FROM LOW SOUTHEAST INTO SOUTH CENTRAL IL.
LIGHT PCPN OVER NORTHERN IL AND CENTRAL PARTS OF STATE DEVELOPED
IN RESPONSE TO LIFT FROM WEAK UPPER WAVE MOVING SOUTHEAST THROUGH
EASTERN IA. THE MORE SIGNIFICANT SYSTEM IS A UPPER LEVEL JET
DIVING SOUTHWARD THROUGH THE DAKOTAS THROUGH WESTERN IA...OF 100+
KTS. THIS WILL PROVIDE UPPER SUPPORT TO DEEPEN AND MOVE THE IA
SURFACE LOW TO THE EAST SOUTHEAST TODAY...WITH OVERRUNNING SHOWERS
AND POSSIBLE THUNDERSTORMS DEVELOPING THIS AFTERNOON...WITH THE
BEST CHANCES IN THE EAST HALF OF CWA. SURFACE AND 925MB DATA SHOWS
SOME RETURN MOIST SOUTHERLY WIND FLOW ALREADY THIS MORNING NORTH
OF THE OLD OH RIVER FRONT...OVER MO. WILL HAVE TO WATCH THE NEW
DEVELOPMENT AREA OF PCPN TO BE OVER EASTERN MO AND INTO WEST IL
EARLY THIS AFTERNOON AND SPREADING EAST OVER REST OF EAST IL INTO
EAST...AHEAD OF THE SURFACE LOW. 

GOETSCH
&&

.AVIATION...
ISSUED 657 AM CDT FRI SEP 21 2012...FOR THE 12Z TAFS

LOW PRESSURE IN WESTERN IOWA WILL SLIDE SOUTHEAST AND MOVE ACROSS
WESTERN TO SOUTHEASTERN ILLINOIS. SHOWERS WILL DEVELOP NEAR ALL OF
THE TERMINALS TODAY. A FEW THUNDERSTORMS WILL BE POSSIBLE THIS
AFTERNOON...AS THE LOW ENTERS FAR WESTERN IL. THUNDERSTORM CHANCES
WILL BE HIGHER IN OUR SOUTHEAST AREAS...WHERE SHEAR AND
INSTABILITY PARAMETERS WILL BE MORE FAVORABLE. THEREFORE...DEC
WILL HAVE SLIGHTLY HIGHER CHANCES FOR STORMS...POSSIBLY STRONG. WE
INCLUDED VCTS AT ALL TERMINALS FOR A FEW HOURS THIS
AFTERNOON. SHOWERS WILL BE DIMINISHING OR ENDING THIS EVENING.

WINDS WILL BE SHIFTING FROM SOUTH THIS MORNING...TO SOUTHEAST OR
EAST THIS AFTERNOON AS THE MOVES INTO WSW ILLINOIS. SUSTAINED
WINDS MAY REACH INTO THE 10-15KT RANGE AT TIMES THIS AFTERNOON. AS
THE LOW MOVES INTO SOUTHEAST IL...WINDS WILL SHIFT TO THE
NORTHEAST AND EVENTUALLY THE NORTH-NORTHWEST OVERNIGHT...BUT AT
LESS THAN 10KT IN GENERAL. 

CLOUD HEIGHTS SHOULD REMAIN MVFR AT THE LOWEST...BUT AN ISOLATED
PERIOD OF IFR MAY OCCUR IF ANY THUNDERSTORMS AFFECT A TERMINAL
SITE. 

SHIMON
&&

.PREV DISCUSSION...
ISSUED 300 AM CDT FRI SEP 21 2012

EARLY MORNING SURFACE MAP SHOWED A SMALL AREA OF HIGH PRESSURE
DRIFTING INTO FAR SOUTHERN ILLINOIS. DESPITE THIS...PLENTY OF MID
AND HIGH CLOUDS WERE SPREADING OVER THE FORECAST AREA...ASSOCIATED
WITH A WEAK SHORTWAVE RACING INTO THE MID MISSISSIPPI VALLEY. THE
WAVE WAS ON THE PERIPHERY OF THE DEEP AND BROAD UPPER TROUGH WHICH
HAS BEEN ANCHORED OVER OUR REGION FOR THE LAST FEW DAYS. 

THE PRIMARY FORECAST CONCERNS FOR THIS PACKAGE INVOLVE RAIN
CHANCES TODAY...AND THE CHILLY WEATHER FOR THE WEEKEND...INCLUDING
POTENTIAL FOR ANY FROST. 

SHORT TERM...TODAY THROUGH MONDAY...

SURFACE LOW CURRENTLY IN EASTERN SOUTH DAKOTA WILL DROP SOUTHEAST
TO NEAR ST LOUIS BY SUNSET. DECENT LIFT WILL BE OVERSPREADING THE
CWA LATER THIS MORNING AHEAD OF THIS SYSTEM. HOWEVER...FORECAST
SOUNDINGS ARE RATHER PARCHED BELOW 700 MB THIS MORNING...SO IT
WILL LIKELY TAKE UNTIL AFTERNOON TO GET ANY DECENT RAIN GOING IN
OUR AREA. HAVE KEPT THE EASTERN CWA WITH ONLY SLIGHT CHANCE POPS
THIS MORNING. HOWEVER...ASSOCIATED WARM FRONT SHOULD SURGE INTO
THE SOUTHERN CWA THIS AFTERNOON WITH DEW POINTS RISING INTO THE
LOWER TO MID 50S. MOST OF THE EVENING MODELS BRING THE CONVECTIVE
CLUSTER CURRENTLY IN SOUTHERN MISSOURI NORTHEAST INTO SOUTHERN
PARTS OF THE CWA BY EARLY AFTERNOON...WITH THE WARM FRONT. BEST
CHANCES OF THUNDERSTORMS WILL LIKELY BE SOUTH OF I-72 NEAR THE
FRONT. STILL LOOKS LIKE INITIAL BATCH OF RAIN WILL BE OUT OF THE
FORECAST AREA BY MIDNIGHT. HOWEVER...A STRONGER WAVE WILL BE
RACING SOUTHEASTWARD OVERNIGHT...REACHING CHICAGO AROUND SUNRISE.
THIS WILL BRING ANOTHER ROUND OF SHOWERS LATE TONIGHT AND SATURDAY
MORNING...ALTHOUGH THESE WILL LARGELY BE IN NORTHERN ILLINOIS...
AND HAVE LIMITED ANY MENTION IN OUR AREA TO ABOUT THE I-74
CORRIDOR NORTHWARD. 

TEMPERATURES TODAY WILL HINGE ON TIMING OF THE RAIN AND HOW FAR
NORTH THE FRONT MAKES IT...BUT HAVE KEPT THE NORTHERN CWA CONFINED
TO THE 60S...WITH 70S SOUTH. THE STRONG WAVE TONIGHT WILL BE
ACCOMPANIED BY 850 MB TEMPERATURES QUICKLY FALLING TO NEAR ZERO
CELSIUS EARLY SATURDAY...RESULTING IN A RATHER COOL DAY WITH HIGHS
STRUGGLING INTO THE LOWER 60S IN SOME AREAS ACROSS THE NORTH...AND
NORTHWEST WINDS GUSTING UP TO 30 MPH. SIMILAR HIGHS EXPECTED
SUNDAY...ALTHOUGH WITH NOT AS MUCH WIND.

HIGH PRESSURE WILL PUSH SOUTHEAST INTO THE OHIO VALLEY THROUGH THE
WEEKEND. WITH THE UPPER TROUGH REMAINING IN PLACE TO POUR COLD AIR
ALOFT INTO THE AREA...WILL SEE DRY AIR AND TEMPERATURES FALLING
INTO THE 30S IN MOST OF THE CWA SATURDAY NIGHT AND SUNDAY NIGHT.
WILL LIKELY SEE SOME FROST DURING THE EARLY MORNINGS...ESPECIALLY
CLOSER TO THE CENTER OF THE HIGH WHERE WINDS WILL BECOME NEARLY
CALM. 

LONG TERM...TUESDAY THROUGH THURSDAY...

LONGER RANGE MODELS CONTINUE TO ADVERTISE THAT THE BROAD UPPER
TROUGHING WILL RETREAT SOMEWHAT EARLY THIS WEEK...WITH MORE OF A
ZONAL FLOW TRYING TO SET UP OVER ILLINOIS. HOWEVER...ANOTHER
ASSOCIATED TROUGH WILL LIKELY PUSH BACK INTO THE MIDWEST BY MID
WEEK. THE SURFACE BOUNDARY WILL ONLY PUSH SLOWLY SOUTHWARD.
THEREFORE...HAVE INTRODUCED RAIN CHANCES AS EARLY AS TUESDAY...
CONTINUING INTO WEDNESDAY NIGHT ALTHOUGH SHIFTING SOUTHWARD WITH
TIME. WITH THE CORE OF THE UPPER TROUGH PULLING AWAY...
TEMPERATURES WILL RETURN CLOSER TO NORMAL.

GEELHART

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$