Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 042008
AFDILX

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

.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 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1240 PM CDT TUE AUG 4 2015
STALLED BOUNDARY TO THE SW AND REGION MAINLY DOMINATED BY CIRRUS
BLOW OFF FROM OVERNIGHT AND CURRENT CONVECTION TO THE WEST AND
SOUTHWEST...SOME MID LEVEL IN SPI AND DEC CLOSER TO THE BOUNDARY.
LIGHT AND VARIABLE WINDS AS THE WEAK BOUNDARY DRIFTS SLIGHTLY.
WAVE MOVING INTO THE WEST LIKELY TO IMPACT SPI IN THE SHORT TERM
AND HAVE A TEMPO FOR TS. MAY NEED AN UPDATE FOR DEC SHOULD THE
STORMS HOLD TOGETHER. HOWEVER, MODELS HAVE BEEN CONSISTENTLY
ERODING THE STORMS WITH EASTERN PROGRESSION. MODELS VARYING ENOUGH
WITH FUTURE PRECIP TOMORROW MORNING THAT IT IS LEFT OUT OF THE TAF
ALTOGETHER.


&&

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

$$

SHORT TERM...SHIMON
LONG TERM...SHIMON
AVIATION...HJS



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