Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 291928
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
228 PM CDT SAT AUG 29 2015

.SHORT TERM...(TONIGHT)
ISSUED AT 228 PM CDT SAT AUG 29 2015

LATEST SURFACE MAP SHOWING FRONTAL BOUNDARY ARCING FROM THE
NORTHEAST TIP OF ILLINOIS TO EAST CENTRAL IOWA...BEFORE EXTENDING
SOUTHWEST INTO SOUTHEAST KANSAS. PRECIPITATION HAS LARGELY REMAINED
LIGHT AND SCATTERED...AND HAS BEEN MOSTLY EAST OF I-55 THE LAST
SEVERAL HOURS. DECENT SLUG OF DRY AIR ALOFT SEEN ON WATER VAPOR
IMAGERY SOUTH OF A SHORTWAVE...WHICH IS CURRENTLY DROPPING INTO
SOUTHERN IOWA. SHORT-RANGE MODEL GUIDANCE IS HAVING A BIT OF
DIFFICULTY AS TO THE AMOUNT OF REDEVELOPMENT...BUT THE HRRR IS
PERFORMING HALFWAY DECENTLY AND CONTINUES TO SUGGEST MAINLY SCATTERED
SHOWERS. THUNDER HAS BEEN STAYING AWAY FROM OUR AREA SO FAR...AND
WHILE MESOANALYSIS SHOWS RESPECTABLE CAPE VALUES OF 1000-1500 J/KG
THIS AFTERNOON...MID LEVEL LAPSE RATES ARE FAIRLY MODEST. THEREFORE
WILL CONTINUE MENTION WITH ONLY ISOLATED THUNDERSTORMS THROUGH
TONIGHT...WITH THE THREAT DIMINISHING FROM NORTHWEST TO SOUTHEAST.

SOME CONCERNS LATER IN THE NIGHT WITH POTENTIAL FOR SOME FOG...
MAINLY ACROSS THE NORTHWEST CWA. STILL QUITE A BIT OF LOWER
STRATOCUMULUS ACROSS MOST OF IOWA AND WISCONSIN. LATEST RAP MODEL
GUIDANCE SUGGESTS THIS CONTRACTING SOME MORE OVER THE NEXT SEVERAL
HOURS...BEFORE SIGNIFICANTLY EXPANDING AGAIN THIS EVENING WITH HIGH
PRESSURE EXPANDING OVER THE MIDWEST. MUCH OF THE AREA UNDERNEATH
THIS HIGH SAW FROM 1 TO SEVERAL INCHES OF RAIN IN THE LAST COUPLE
DAYS...AND IS MOST FAVORED FOR DENSE FOG POTENTIAL. HOWEVER...THE
RAP SHOWS THE FOG FIELD OOZING SOUTHWARD AFTER MIDNIGHT...PERHAPS AS
FAR AS PEORIA. THAT AREA ALREADY HAD PATCHY FOG IN THE GRIDS...BUT
AM THINKING IT WILL BE A BIT MORE WIDESPREAD AND WILL GO WITH AREAS
OF FOG INSTEAD.

&&

.LONG TERM...(SUNDAY THROUGH SATURDAY)
ISSUED AT 228 PM CDT SAT AUG 29 2015

SHOWERS AND ISOLATED THUNDERSTORMS COULD LINGER IN THE SOUTHEASTERN
PART OF THE CWA SUNDAY MORNING BUT THEN SPREAD BACK WEST
SOME...COVERING THE EASTERN HALF OF THE CWA...MAINLY EAST OF I-55.
THIS SHOULD BE THE END OF THE PCPN AS THE FRONTAL SYSTEM DIMINISHES
OVER THE AREA REMAINDER OF THE WEEKEND. FOG AND LOWER CLOUDS WILL
SEEN THIS MORNING ALONG AND BEHIND THE FRONT...SO THINKING IS THAT
THE FOG WILL CONTINUE INTO THE FIRST FEW HOURS OF SUNDAY MORNING.
HAVE INCLUDED A SLIGHT CHANCE OF SHOWERS FOR SUNDAY NIGHT...AGAIN
MAINLY EAST OF I-55 TIL MIDNIGHT...AND THEN IN THE EXTREME SOUTHEAST
AFTER MIDNIGHT.

BEYOND THIS UPPER LEVEL RIDGING WILL BUILD INTO THE NORTHERN PLAINS
AND NORTHERN MISS VALLEY. ON THE SFC...HIGH PRESSURE RIDGING WILL
BUILD BACK TOWARD THE AREA FROM THE SOUTHEAST. THE COMBINATION OF
THE TWO SHOULD HELP TO KEEP THE AREA DRY THROUGH THE BEGINNING OF
THE WEEK. TEMPS WILL BE IN THE LOWER TO MIDDLE 80S TOMORROW...BUT
THEN WARM INTO THE MIDDLE TO UPPER 80S FOR MONDAY INTO TUESDAY.

THE REMAINDER OF THE WEEK LOOKS TO BE DRY...THOUGH SOME OF THE
MODELS CONTINUE TO BRING SOME SPOTTY POPS IN THE AREA DUE TO
SOUTHERLY FLOW ON THE SFC. FOR NOW...WILL ONLY HAVE SLIGHT CHC POPS
FOR WED ACROSS AREAS ALONG AND NORTH OF I-74 AND EAST OF I-57.
REMAINDER OF THE WEEK WITH BE DRY...EVEN INTO THE BEGINNING OF THE
LABOR DAY WEEKEND. TEMPS WILL REMAIN WELL ABOVE NORMAL IN THE
EXTENDED PERIOD SO HEAT COULD BE AN ISSUE LATER...BUT DEWPOINTS WILL
REMAIN LOW SO HEAT INDEX VALUES ARE NOT EXPECTED TO GET OVER 100
THROUGH THE PERIOD.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1230 PM CDT SAT AUG 29 2015

MAINLY VFR CONDITIONS OVER CENTRAL ILLINOIS AT MIDDAY...WITH A FEW
SHOWERS EAST OF KBMI-KSPI. WATCHING AN AREA OF MVFR/IFR CEILINGS
DROPPING DOWN FROM IOWA AND NORTHWEST ILLINOIS AHEAD OF AN UPPER
LEVEL DISTURBANCE...AND MVFR CEILINGS ARE NOT TOO FAR AWAY FROM
KPIA. SOME QUESTION AS TO THE SOUTHWARD PROGRESS...WITH THE RAP
MODEL KEEPING KPIA JUST ABOVE VFR LEVEL AND THE NAM DIPPING INTO
MVFR TERRITORY. HAVE INCLUDED SOME TEMPO CEILINGS AROUND 2500 FEET
THERE INITIALLY AND WILL CONTINUE TO EVALUATE THE PROGRESSION OVER
THE NEXT HOUR OR SO. MORE OF THE CONCERN FOR MVFR CONDITIONS OVER
CENTRAL ILLINOIS WILL BE AFTER 06Z...AS A WEAKENING FRONTAL
BOUNDARY BECOMES NEARLY STATIONARY OVERHEAD. THE WIDESPREAD LOW
CLOUDS CURRENTLY TO OUR NORTHWEST ARE NOT LIKELY TO COMPLETELY
ERODE AND MORE LIKELY WOULD EXPAND OVERNIGHT...WITH THE RAP
HINTING AT POTENTIAL IFR/LIFR CONDITIONS AT KPIA LATE IN THE
NIGHT. HAVE HIT CONDITIONS AT KPIA THE HARDEST WITH TEMPO CEILINGS
AND VISIBILITIES THAT LOW...BUT MAINTAINED MVFR CONDITIONS
ELSEWHERE LATE TONIGHT INTO SUNDAY MORNING.

&&

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

$$

SHORT TERM...GEELHART
LONG TERM...AUTEN
AVIATION...GEELHART



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