Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 050409
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1109 PM CDT TUE AUG 4 2015

.UPDATE...
ISSUED AT 835 PM CDT TUE AUG 4 2015

FRONTAL BOUNDARY OVER FAR SOUTHERN ILLINOIS WILL CONTINUE TO BE
THE FOCUS FOR PERIODIC SHOWERS AND THUNDERSTORMS OVER THE NEXT
24 TO 36 HOURS WITH A GRADUAL SHIFT NORTHEAST INTO OUR FORECAST
AREA ON WEDNESDAY AS A WEAK SURFACE WAVE APPROACHES FROM THE
WEST. MOST OF THE SHORT TERM FORECAST SOLUTIONS FOR THE OVERNIGHT
HOURS KEEP THE BULK OF THE SHOWER ACTIVITY OVER SOUTHERN IL WITH
QUITE A BIT OF MID AND HIGH LEVEL CLOUD COVER EXPECTED TO ITS
NORTH OVER THE REMAINDER OF OUR FORECAST AREA. HIGHER POPS WILL
CONTINUE TO BE LOCATED OVER THE SOUTHERN AREAS WITH PROGRESSIVELY
LOWER POPS AS YOU HEAD NORTH. UPDATED ZONES SHOULD BE OUT BY 900
PM.

&&

.SHORT TERM...(TONIGHT)
ISSUED AT 303 PM CDT TUE AUG 4 2015

A STATIONARY FRONTAL BOUNDARY WILL LINGER ACROSS SOUTHERN IL
TONIGHT, WHERE BETTER CHANCES OF SHOWERS AND STORMS SHOULD START OUT
THE EVENING. NORTH OF THE BOUNDARY INTO OUR SOUTHERN COUNTIES, WEAK
ISENTROPIC LIFT AND MID LEVEL CONVERGENCE WILL WORK TO TRIGGER
SHOWERS AND A FEW STORMS TOWARD SPRINGFIELD TO MATTOON TONIGHT. THIS
AFTERNOON, SHOWERS/STORMS DEVELOPED WELL NORTH OF WHERE THE HRRR AND
RAP MODELS INDICATED, SO THE FACT THAT THEY CONTINUE TO SHOW DRY
CONDITIONS OVERNIGHT FOR OUR COUNTIES DOES NOT PRECLUDE THAT SHOWERS
REACH AS FAR NORTH AS LINCOLN TO MATTOON AGAIN OVERNIGHT. ONGOING
SHOWERS/STORMS LATE THIS AFTERNOON FROM SPRINGFIELD TO SHELBYVILLE
ARE EXPECTED TO DISSIPATE AS THEY PROGRESS EASTWARD. THEREFORE
WILL START OUT THE EVENING GRIDS WILL MAINLY SLIGHT CHANCE IN OUR
SOUTHERN COUNTIES, BUT MAY ADJUST POPS UP AS LATE AFTERNOON
CONDITIONS WARRANT. DESPITE THE DRY HIGH RESOLUTION MODELS
TONIGHT, THE CONSENSUS OF THE GFS, NAM, ECMWF AND CANADIAN
INDICATES ENOUGH FORCING FOR PRECIP REDEVELOPING ACROSS OUR
SOUTHERN COUNTIES. THEREFORE, HAVE NOT STRAYED FAR FROM THE
CURRENT FORECAST OF CHANCE POPS EXPANDING NORTH TO AREAS SOUTHWEST
OF A LINE FROM CANTON TO LINCOLN TO MATTOON.

LOW TEMPS TONIGHT WILL VARY BASED ON THE AMOUNT OF CLEARING THAT
DEVELOPS UNDER LIGHT ENE FLOW. AFTERNOON DEWPOINTS HAVE POINTED
TOWARD LOWS TONIGHT GENERALLY IN THE LOWER 60S NORTH OF I-74, WITH
UPPER 60S IN SOUTH OF I-70, WHERE CLOUDS MAY BE MORE PREVALENT LATER
TONIGHT.

.LONG TERM...(WEDNESDAY THROUGH TUESDAY)
ISSUED AT 303 PM CDT TUE AUG 4 2015

WEDNESDAY COULD START OUT WILL A LULL IN THE SHOWERS AS THE
ENERGY FROM THE OVERNIGHT CONVECTION SHIFTS EAST INTO INDIANA. THE
NEXT WAVE OF PRECIP LOOKS TO BE TIED TO THE ADVANCEMENT OF A LOW
PRESSURE SYSTEM FROM THE CENTRAL PLAINS ACROSS SOUTH CENTRAL IL.
THE 12Z MODELS HAVE CONTINUED WITH THE SOUTHWARD TREND OF TRACKING
THE LOW ACROSS IL WEDNESDAY NIGHT INTO THURSDAY. HOWEVER, THEY
ALSO CONTINUE TO PROJECT OVERRUNNING SHOWERS/STORMS DEVELOPING
AHEAD OF THE LOW WED AFTERNOON ACROSS OUR SOUTHERN COUNTIES.
WEDNESDAY NIGHT, PRECIP CHANCES ALONG AND SOUTH OF I-72 WILL RAMP
UP TO LIKELY, WITH CATEGORICAL POPS SOUTH OF I-70 AS THE LOW
PASSES JUST SOUTH OF STATE HWY 50. HEAVY PRECIP REMAINS POSSIBLE
WED NIGHT INTO THURSDAY MORNING SOUTH OF I-70, AS PRECIPITABLE
WATER VALUES CLIMB TO 1.8". WILL MONITOR FOR POSSIBLE FLASH FLOOD
WATCH, BUT DRY CONDITIONS RECENTLY MAY HELP PREVENT FLASH
FLOODING. ALSO, A DRIER TREND IN THE 12Z MODELS HAS LOWERED
CONFIDENCE IN VERY HEAVY RAINFALL IN OUR SOUTHERN COUNTIES.

THURSDAY SHOULD SEE DRY CONDITIONS RETURN BY AFTERNOON AS THE LOW
PULLS AWAY TO THE EAST AND HIGH PRESSURE GAINS CONTROL OF THE LOCAL
WEATHER. RIDGING ALOFT WILL REACH WESTERN IL, WITH HEIGHT RISES
HELPING HIGHS REACH THE LOW 80S.

LOW PRESSURE TRACKING FROM THE DAKOTAS THURSDAY AFTERNOON TO EASTERN
LAKE SUPERIOR SATURDAY MORNING COULD DRAG A WEAKENING COLD FRONT
INTO NORTHERN IL LATE FRIDAY INTO FRI EVENING. WE ONLY ACKNOWLEDGED
THAT FEATURE WITH SLIGHT CHANCE POPS WEST OF I-55 FOR NOW.

THERE ARE INDICATIONS IN THE EXTENDED MODELS THAT AN MCS COULD
DEVELOP IN NEBRASKA ON SATURDAY, THEN PROGRESS EASTWARD INTO CENTRAL
IL SAT NIGHT-SUNDAY. THE CANADIAN IS THE NORTHERN OUTLIER WITH THE
TRACK OF THE SYSTEM, KEEPING IT GENERALLY NORTH OF OUR COUNTIES,
WHILE THE GFS/ECMWF BOTH PUSH THE WAVE INTO CENTRAL IL. WILL KEEP
CHANCE POPS FOR THE ENTIRE FORECAST AREA SUNDAY INTO SUNDAY NIGHT,
WITH DECREASING CHANCES FROM WEST TO EAST ON MONDAY. DRY
CONDITIONS ARE EXPECTED FOR TUESDAY AS AN UPPER TROUGH BUILDS INTO
THE AREA.

HEAT AND HUMIDITY ARE PROJECTED TO INCREASE SATURDAY AND CONTINUE
INTO MONDAY, WITH HIGHS IN THE MID 80S AND HEAT INDICES IN THE LOWER
90S.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 1102 PM CDT TUE AUG 4 2015

FORECAST CONCERN WILL BE COVERAGE OF SHOWERS AND THUNDERSTORMS
LATE TONIGHT INTO WEDNESDAY AND THEIR AFFECT ON CIGS...ESPECIALLY
AT KSPI AND KDEC...AS A WEATHER SYSTEM DRIFTS ACROSS SOUTHERN
ILLINOIS. WIDELY SCATTERED SHOWERS AND STORMS WERE NOTED OVER
PARTS OF CENTRAL MISSOURI LATE THIS EVENING AND THOSE ARE EXPECTED
TO DRIFT EAST TOWARDS THE MISSISSIPPI RIVER OVER THE NEXT SEVERAL
HOURS. THE AIR MASS IN OUR AREA LATE THIS EVENING WAS QUITE STABLE
SO IT APPEARS AT LEAST THE INTENSITY WILL WEAKEN AS THEY DRIFT
EAST BUT CONFIDENCE ON COVERAGE OF THE RAIN OVER WESTERN IL LATE
TONIGHT IS NOT VERY HIGH AS MODELS CONTINUE TO SUGGEST A DECREASE
IN COVERAGE AS THEY MOVE INTO THE MORE STABLE ENVIRONMENT. AS A
RESULT...UNLESS WE SEE AN INCREASE IN COVERAGE TO OUR WEST OVER
THE NEXT HOUR OR SO...WILL ONLY INCLUDE A VCTS AT KSPI IN THE 06Z
TO 09Z TIME FRAME.

AS THE WEAK SURFACE WAVE MOVES ALONG THE STALLED FRONTAL BOUNDARY
TO OUR SOUTH ON WEDNESDAY...THE HIGHER THREAT FOR SHOWERS AND
STORMS WILL BE ROUGHLY FROM SPRINGFIELD TO DECATUR AND SOUTH.
STILL THINKING MAINLY SOME SCATTERED TO BKN MID CLOUDS WITH SOME
HIGHER OVERCAST FURTHER NORTH...WITH LOWER VFR CIGS AT KSPI AND
KDEC. SURFACE WINDS WILL REMAIN LIGHT AND VARIABLE OVERNIGHT AND
BECOME LIGHT EASTERLY ON WEDNESDAY WITH SPEEDS OF 10 KTS OR LESS.

&&

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

$$

UPDATE...SMITH
SHORT TERM...SHIMON
LONG TERM...SHIMON
AVIATION...SMITH


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