Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 311755
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1255 PM CDT FRI JUL 31 2015

.UPDATE...
ISSUED AT 1026 AM CDT FRI JUL 31 2015

15Z/10AM SURFACE ANALYSIS SHOWS WEAK COLD FRONT DROPPING SOUTHWARD
THROUGH WISCONSIN/IOWA. SO FAR VERY LITTLE CU HAS DEVELOPED
ALONG/AHEAD OF THE BOUNDARY...HOWEVER SOME 12Z MODELS ARE STILL
TRYING TO FIRE A FEW THUNDERSTORMS LATE THIS AFTERNOON INTO THE
EVENING. AIRMASS IS NOT PARTICULARLY MOIST AND CONVERGENCE ALONG
THE FRONT IS PALTRY AT BEST...SO AM NOT EXPECTING MUCH PRECIP AT
ALL. WILL MAINTAIN JUST SLIGHT CHANCE POPS AFTER 21Z...WITH
AFTERNOON HIGHS TOPPING OUT IN THE UPPER 80S TO AROUND 90 DEGREES.
CURRENT FORECAST IS RIGHT ON TRACK...SO NO UPDATE IS NEEDED AT
THIS TIME.

&&

.SHORT TERM...(TODAY)
ISSUED AT 243 AM CDT FRI JUL 31 2015

HIGH PRESSURE RIDGE OVER CENTRAL MO WILL SLIDE SOUTH THIS MORNING
AND ALLOW A WEAK COLD FRONT TO DROP INTO THE AREA FOR THIS
AFTERNOON. CONVERGENCE AND MOISTURE ALONG THIS FRONT WILL BE VERY
LIMITED SO BELIEVE ANY CONVECTION COVERAGE WILL BE VERY SPOTTY. IN
KEEPING WITH THE CURRENT THINKING/FORECAST WITH THIS FRONT...WILL
HAVE A SLIGHT CHANCE OF PCPN IN THE FORECAST FOR LATE THIS
AFTERNOON...IN LINE WITH PEAK HEATING. FORECAST CAPE VALUES REACH
NEAR 1500 WITH VERY LOW SHEAR. SO ONLY EXPECTING ISOLATED
CONVECTION. AFTERNOON TEMPS WILL AGAIN GET QUITE WARM...IN THE
UPPER 80S...WHICH IS AROUND GUIDANCE.

.LONG TERM...(TONIGHT THROUGH THURSDAY)
ISSUED AT 243 AM CDT FRI JUL 31 2015

NOT A LOT OF CHANGE IN THE UPPER PATTERN EXPECTED THE NEXT FEW
DAYS...AS THE RIDGE CONTINUES TO BUILD ACROSS THE WESTERN U.S. AND A
NORTHWEST FLOW PREVAILING FOR US. LONGER RANGE MODELS EXHIBITING
SOME DIFFERENCES TOWARD THE MIDDLE OF NEXT WEEK AS THE RIDGE STARTS
TO BREAK DOWN AND SHIFT EAST...WITH THE GFS HANGING ON TO THE RIDGE
LONGER...BUT THE NET RESULT WILL BE A GRADUAL COOLING TREND OVER
CENTRAL ILLINOIS BEGINNING ON TUESDAY...WITH HIGHS IN THE 70S IN
MANY AREAS BY THE SECOND HALF OF NEXT WEEK.

PRECIPITATION ISSUES WILL BE TIED TO THE TIMING OF VARIOUS WAVES IN
THE NORTHWEST FLOW...WITH CONFIDENCE LOWERING THROUGH NEXT WEEK AS
THE MODELS DIVERGE. GENERAL AGREEMENT EXISTS ON THE SHORTWAVE
PASSING THROUGH LATE SATURDAY NIGHT...WITH MOST MODELS FEATURING
SOME SORT OF MCS ACTIVITY DEVELOPING TO OUR NORTHWEST AND ROLLING
TOWARD OUR AREA OVERNIGHT. WILL CONTINUE TO FOCUS POP`S ON THE
NORTHWEST HALF OF THE FORECAST AREA LATE SATURDAY NIGHT...AND AREA-
WIDE ON SUNDAY AS THE MCS WEAKENS OVER OUR AREA. STRENGTH OF A
SECOND WAVE SUNDAY NIGHT IS MUCH WEAKER...AND ONLY THE GFS REALLY
GENERATES ANYTHING IN OUR AREA...SO WILL MAINLY GO WITH SLIGHT
CHANCES THEN.

TUESDAY AND WEDNESDAY BECOME MORE OF A QUESTION MARK DUE TO THE
SPEED OF THE BREAKDOWN OF THE RIDGE. SOME INDICATIONS IN THE LONGER
RANGE MODELS OF THE BOUNDARY HANGING UP FOR A TIME MONDAY NIGHT
THROUGH TUESDAY IN A CORRIDOR NORTHWEST-SOUTHEAST OVER CENTRAL
ILLINOIS. THE ECMWF IS THEN MUCH MORE PRONOUNCED WITH A LARGER UPPER
TROUGH MID WEEK GENERATING MORE WIDESPREAD SHOWER AND THUNDERSTORM
ACTIVITY...WHILE THE GFS MAINLY KEEPS US ON THE COOLER SIDE OF THE
BOUNDARY WITH LIGHT SHOWERS. HAVE LEANED MORE TOWARD THE ECMWF
COVERAGE BUT NOT AS HIGH WITH THE POP`S.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1255 PM CDT FRI JUL 31 2015

WEAK COLD FRONT CONTINUES TO SAG SOUTHWARD INTO NORTH-CENTRAL
ILLINOIS EARLY THIS AFTERNOON. CU-FIELD REMAINS LARGELY ABSENT
ALONG THE BOUNDARY THUS FAR...EXCEPT ACROSS NORTHERN INDIANA INTO
NORTHEAST ILLINOIS. THIS CLOUD TREND FITS VERY WELL WITH THE RAPID
REFRESH...WHICH SHOWS WIDELY SCATTERED CONVECTION DEVELOPING
ACROSS THIS AREA OVER THE NEXT COUPLE OF HOURS...WHILE KEEPING THE
REMAINDER OF THE FRONTAL BOUNDARY TOTALLY DRY. AS A RESULT...WILL
ONLY MENTION VCTS AT KCMI BETWEEN 18Z AND 22Z. FEW-SCT DIURNAL
CLOUDS ALONG/AHEAD OF THE FRONT WILL QUICKLY DISSIPATE TOWARD
SUNSET...WITH CLEAR SKIES EXPECTED TONIGHT THROUGH SATURDAY
MORNING. WINDS WILL INITIALLY BE FROM THE NORTHWEST GUSTING TO
BETWEEN 15 AND 18KT THIS AFTERNOON...THEN WILL BECOME WESTERLY AT
LESS THAN 5KT TONIGHT.

&&

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

$$

UPDATE...BARNES
SHORT TERM...AUTEN
LONG TERM...GEELHART
AVIATION...BARNES



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