Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 270201
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
901 PM CDT WED AUG 26 2015

.UPDATE...
ISSUED AT 900 PM CDT WED AUG 26 2015

CLOUDS ASSOCIATED WITH THE UPPER TROUGH AND TO SOME EXTENT LAKE
MICHIGAN, HAVE SHIFTED E-NE OF OUR COUNTIES, LEAVING CLEAR SKIES
UNDER THE SURFACE RIDGE OF HIGH PRESSURE. LITTLE TO NO AIRMASS
CHANGES ARE EXPECTED OVERNIGHT AS WINDS BECOME LIGHT AND VARIABLE.
RADIATIONAL COOLING SHOULD ALLOW TEMPS TO DIP INTO THE LOW-MID 50S
IN MOST AREAS. TRIMMED A DEGREE OR SO FROM AREAS NORTHEAST OF THE
LAKE TO ALLOW FOR SOME 52 DEG READINGS, AND UPDATED THE SKY GRIDS
TO ACCOUNT FOR EARLIER CLEARING. OTHERWISE, THE FORECAST LOOKS ON
TRACK. UPDATED INFO IS ALREADY AVAILABLE.

&&

.SHORT TERM...(TONIGHT)
ISSUED AT 200 PM CDT WED AUG 26 2015

LARGE STRATOCUMULUS SHIELD THAT HAS PUSHED SOUTHWARD ACROSS THE
NORTHEAST QUARTER OF THE STATE WAS FINALLY STARTING TO SHOW SOME
CONTRACTION EARLY THIS AFTERNOON. HOWEVER...IT IS FLANKED ON MOST
SIDES BY DIURNAL DEVELOPMENT...SO NET RESULT CONTINUES TO BE QUITE A
BIT OF CLOUDS ESPECIALLY ACROSS THE EAST HALF OF THE CWA. THE 900 MB
PLOT OFF THE RAP MODEL CONTINUES TO DEPICT THE CLOUD SHIELD THE
BEST...AND SHOWS SOME CONTRACTION CONTINUING THIS AFTERNOON. MOST OF
THE DIURNAL CLOUDS SHOULD FADE WITH SUNSET. HOWEVER...SOME RESIDUAL
MOISTURE SHOULD LINGER FROM THE PERSISTENT CLOUDS...AND WILL GO WITH
PARTLY CLOUDY SKIES ACROSS THE NORTHEAST CORNER OF THE FORECAST AREA
NEAR DANVILLE AND CHAMPAIGN.

WITH HIGH PRESSURE OVERHEAD...ENOUGH CLEAR SKIES EXPECTED THAT MOST
AREAS SHOULD FALL INTO THE MID 50S OVERNIGHT. HOWEVER...SOME
ADJUSTMENTS MAY BE NEEDED ACROSS THE NORTHEAST IF THE CLOUDS DO NOT
CLEAR OUT FAST ENOUGH...AS HAS BEEN THE CASE THE LAST COUPLE NIGHTS.

.LONG TERM...(THURSDAY THROUGH WEDNESDAY)
ISSUED AT 200 PM CDT WED AUG 26 2015

LATEST MODEL SOLUTIONS IN REASONABLE AGREEMENT FOR ILLINOIS OVER
THE REST OF THE WEEK. MODELS DIFFER IN STRENGTH AND MOISTURE
AVAILABILITY OF SOUTHERN STREAM WAVE CURRENTLY OVER FOUR CORNERS
AREA AND EXPECTED TO RIDE OVER RIDGE INTO ILLINOIS THIS WEEKEND.

WATER VAPOR IMAGERY SHOWS WAVE OVER NORTHERN ARIZONA THIS MORNING
PUSHING NORTHWARD OVER STRONG ROCKIES RIDGE. MODEL SUITE CONSISTENT
ON BRINGING ENERGY UP OVER THE RIDGE AND INTO MIDWEST FRIDAY AND
SATURDAY. UNTIL THEN...DRY CONDITIONS AND A WARMING TREND IS
EXPECTED AS 850 TEMPS CLIMB 5-10 DEGREES C BETWEEN THIS MORNINGS
RAOB AND FRIDAY EVENING. INCREASING HIGH CLOUDS AHEAD OF THE WAVE
MAY INHIBIT WARMING A BIT FOR FRIDAY...BUT TEMPS SHOULD STILL MAKE
IT INTO THE 80S THROUGHOUT FORECAST AREA BY FRIDAY AFTERNOON.

WAVE APPROACHING FOR THE FIRST PART OF THE WEEKEND IS MOVING INTO A
RELATIVELY DRY BUT MOISTENING AIRMASS. IN ADDITION...DIGGING OF
NORTHERN STREAM ENERGY ALONG THE WEST COAST SHOULD SLOW PROGRESSION
OF SYSTEMS AND THEREFORE SLOW THE INCOMING WAVE. CHANCE OF STORMS
ARE EXPECTED IN THE NORTHWEST BY LATE AFTERNOON FRIDAY AND ACROSS
MUCH OF THE AREA FRIDAY NIGHT AND PARTICULARLY SATURDAY. MAIN MODEL
DIFFERENCES BEGIN TO SHOW UP TOWARD THE END OF THE WEEKEND. LATEST
AVAILABLE ECMWF RUNS HAVE BEEN CONSISTENT ON BEING STRONG ENOUGH
WITH THIS WAVE TO DEVELOP DECENT NVA IN ITS WAKE ON SUNDAY AND
SHUNTING MOISTURE EAST OF THE AREA.  THIS LEADS TO A RELATIVELY DRY
BUT INCREASINGLY HOT FORECAST AS THE LONGWAVE RIDGE AXIS MOVES
ACROSS THE AREA. MEANWHILE...THE 06Z AND 12Z GFS TRENDING WEAKER
WITH THE WAVE AND FORECAST AN EVOLUTION TO JUST A GENERAL WEAKNESS
OVER THE AREA THROUGH EARLY NEXT WEEK. THIS EVOLUTION SUGGESTS AT
LEAST A SLIGHT CHANCE OF THUNDERSTORMS AND LOWER TEMPERATURES
WITH GENERALLY MORE CLOUD COVER. AM LEANING TOWARD A COMPROMISE
WITH A NOD TOWARD THE GFS WHICH SEEMS TO BE SUPPORTED BY THE CMC
AND GEFS MEAN. A QUICK LOOK AT 12Z ECMWF ALSO SUGGESTS IT MAY BE
SWINGING BACK TOWARD A WEAKER SOLUTION.

ANY CONVECTION THAT DEVELOPS THIS WEEKEND INTO NEXT WEEK SHOULD HAVE
LIMITED SEVERE POTENTIAL DUE TO LOW SHEAR IN THE RIDGE AND LIMITED
INSTABILITY GIVEN THE WARM 500 MB TEMPS CLIMBING ABOVE -10C. BIGGEST
THREAT MAY BE LOCALLY HEAVY RAINFALL DUE TO SLOW MOVEMENT.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z THURSDAY EVENING)
ISSUED AT 630 PM CDT WED AUG 26 2015

MVFR CLOUDS IN NE ILLINOIS, APPARENTLY INFLUENCED BY AIR OFF LAKE
MICHIGAN, WILL LINGER NEAR CMI FOR A FEW HOURS THIS EVENING. 900MB
RH ON THE RAP MODEL SEEM TO BE HANDLING THE LOCATION OF THAT CLOUD
MASS, AND IT IS PROJECTED TO DRIFT SLOWLY EAST AWAY FROM CMI BY
MID EVENING. THE DIURNAL CUMULUS ACROSS THE REMAINDER OF CENTRAL
IL HAVE GENERALLY DISSIPATED, LEAVING MOSTLY CLEAR SKIES. CU RULES
SHOW THAT CLOUDS TOMORROW WILL BE MAINLY IN EASTERN IL, CLOSER TO
BMI AND CMI. HOWEVER, NO MVFR CEILINGS ARE EXPECTED.

WINDS WILL BECOME LIGHT AND VARIABLE FOR THE REST OF THE NIGHT AS
THE SURFACE RIDGE AXIS LINGERS FROM NE TO SW ACROSS ILLINOIS.
SOUTHEAST WINDS WILL DEVELOP THURSDAY MORNING AS THE RIDGE AXIS
MOVES EAST OF OUR COUNTIES. HOWEVER, WIND SPEEDS SHOULD PREVAIL AT
LESS THAN 1OKT THROUGH THE DAY TOMORROW.


&&

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

$$

UPDATE...SHIMON
SHORT TERM...GEELHART
LONG TERM...BARKER
AVIATION...SHIMON



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