Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 312017
AFDILX

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

.SHORT TERM...(TONIGHT)
ISSUED AT 315 PM CDT FRI JUL 31 2015

19Z/2PM SURFACE ANALYSIS SHOWS WEAK COLD FRONT SETTLING INTO CENTRAL
ILLINOIS...EXTENDING FROM NEAR RANTOUL TO JUST SOUTH OF QUINCY.
MINIMAL CONVERGENCE ALONG THE FRONT AND AN OVERALL LACK OF DEEP
LAYER MOISTURE HAS LARGELY PREVENTED CONVECTION.  THE EXCEPTION HAS
BEEN FURTHER NORTHEAST ACROSS NORTHERN INDIANA WHERE A FEW CLUSTERS
OF THUNDERSTORMS HAVE DEVELOPED.  HRRR CONTINUES TO OVER-EMPHASIZE
DEWPOINT POOLING ALONG THE FRONT AND PRODUCES NUMEROUS THUNDERSTORMS
WITH ITS 1 AND 2-HOUR FORECAST.  MEANWHILE...THE RAPID REFRESH HAS
CONSISTENTLY PRESENTED A MORE REALISTIC SCENARIO...SUGGESTING ONLY
ISOLATED STORMS MAINLY ACROSS THE E/NE KILX CWA OVER THE NEXT 2-4
HOURS.  GIVEN THIS IS THE LOCATION WHERE CU-FIELD IS CURRENTLY MOST
PRONOUNCED...WILL CONTINUE TO FOLLOW THIS SOLUTION CLOSELY.  AS A
RESULT...WILL CARRY SLIGHT CHANCE POPS ALONG/NORTHEAST OF A
CHAMPAIGN TO MARSHALL LINE THROUGH THE AFTERNOON.  ANY ISOLATED
CONVECTION THAT DEVELOPS WILL QUICKLY DISSIPATE TOWARD
SUNSET...FOLLOWED BY MOSTLY CLEAR AND DRY CONDITIONS TONIGHT.
SLIGHTLY DRIER AIRMASS WILL TRICKLE IN FROM THE NORTHWEST ONCE THE
FRONT PASSES...WITH OVERNIGHT LOW TEMPERATURES DROPPING INTO THE
LOWER TO MIDDLE 60S.

&&

.LONG TERM...(SATURDAY THROUGH FRIDAY)
ISSUED AT 315 PM CDT FRI JUL 31 2015

OVERALL A FAIRLY PERSISTENT WNW FLOW PATTERN WILL REMAIN ACROSS IL
AND MUCH OF THE MIDWEST THROUGH THE WEEKEND AND INTO EARLY NEXT
WEEK. QUITE A BIT OF MODEL UNCERTAINTY REGARDING A BREAKDOWN OF THE
WESTERN RIDGE AND DEEPENING OF THE EASTERN TROUGH FOR THE MIDDLE OF
NEXT WEEK.

IN THE NEAR TERM...VERY WARM AND INCREASINGLY HUMID CONDITIONS WILL
BE ON TAP FOR CENTRAL AND EASTERN IL SATURDAY. AN ADVANCING WARM
FRONT AND A CLUSTER OF CONVECTION FROM IOWA/NEBRASKA IS EXPECTED TO
APPROACH AREAS WEST OF THE IL RIVER VALLEY LATE SATURDAY NIGHT AND
INTO SUNDAY MORNING. THE REMNANTS OF THE EARLY MORNING T-STORMS ARE
THEN EXPECTED TO SPREAD ACROSS MOST OF CENTRAL AND EASTERN IL SUNDAY
MORNING AND EARLY AFTERNOON. RESIDUAL BOUNDARIES FROM THIS
CONVECTION SHOULD RESULT IN REDEVELOPMENT OF T-STORMS SUNDAY
AFTERNOON AND INTO THE EVENING...ESPECIALLY ALONG AND NORTH OF I-74.
SOME OF THE STORMS LATER IN THE DAY SUNDAY COULD BE STRONG...MAINLY
DUE TO MODERATE LEVELS OF WIND SHEAR AND INSTABILITY.

MOST OF THE FORECAST AREA WILL BE IN THE WARM SECTOR OF AN ADVANCING
FRONTAL BOUNDARY...YIELDING VERY WARM AND SOMEWHAT HUMID CONDITIONS
MONDAY. THE AFOREMENTIONED FRONT IS EXPECTED TO SLOWLY MOVE INTO
CENTRAL ILLINOIS MONDAY NIGHT AND THEN REMAIN NEARLY STATIONARY FOR
MUCH OF THE WEEK. THIS SHOULD RESULT IN A RATHER UNSETTLED WEATHER
PATTERN WITH THE POTENTIAL FOR SEVERAL PERIODS OF RAIN FROM LATE
MONDAY...ON AND OFF...THROUGH THE END OF THE WEEK.

THE UNCERTAINTY IN THE MODELS REVOLVES AROUND THE DETAILS OF
POSSIBLE SHORTWAVE ENERGY BREAKING THROUGH THE WESTERN U.S. RIDGE
AND INTERACTING WITH THE FRONT. THE GFS IS A BIT MORE AGGRESSIVE WITH
THIS THAN THE EUROPEAN MODEL. HOWEVER...THE EUROPEAN NOT ONLY
UNDERPLAYS THE AFFECTS OF THIS BUT KEEPS THE SURFACE FRONT FARTHER
NORTH. UNTIL THE DETAILS ARE WORKED OUT IT IS HARD TO PIN DOWN
WHERE A THREAT OF PERSISTENT...POSSIBLY HEAVY RAIN MAY SET UP THE
MIDDLE OF NEXT WEEK. THUS...WILL NOT MAKE TOO MANY MAJOR CHANGES
TO THE FORECAST AND KEEP CHANCE POPS FOR THUNDERSTORMS ACROSS A
LARGE PART OF THE FORECAST AREA.

THE ONE THING THE MODELS DO AGREE ON IS THAT WITH THE PERIODS OF
CONVECTION AND RESIDUAL CLOUD COVER...TEMPERATURES SHOULD BE BELOW
SEASONAL NORMALS.

&&

.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.
&&

$$

SHORT TERM...BARNES
LONG TERM...MILLER
AVIATION...BARNES



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