Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 022002
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
302 PM CDT WED SEP 2 2015

.SHORT TERM...(TONIGHT)
ISSUED AT 300 PM CDT WED SEP 2 2015

EARLIER SHOWER ACTIVITY THAT HAD BEEN APPROACHING THE MISSISSIPPI
RIVER HAS LARGELY FADED OUT AS EXPECTED...WITH STILL A FAIR AMOUNT
OF ASSOCIATED CLOUD COVER SPREADING OVER AREAS WEST OF I-55.
LOCATIONS EAST A BIT SUNNIER THIS AFTERNOON...BUT WITH A FAIR AMOUNT
OF DIURNAL CUMULUS.

THE ASSOCIATED UPPER WAVE IS CURRENTLY MOVING ACROSS EASTERN IOWA
AND WESTERN WISCONSIN...AND IS EXPECTED TO START DIGGING SOUTHEAST
TONIGHT AS THE UPPER RIDGE OVER THE PLAINS BEGINS TO AMPLIFY.
SHOWERS AND THUNDERSTORMS HAVE BEEN DEVELOPING OVER NORTHERN
WISCONSIN THE LAST FEW HOURS...AND THESE WILL BE TRACKING SOUTHEAST
AS THE WAVE DIGS. THE GFS IS THE MOST GENEROUS IN BRINGING A
CONVECTIVE CLUSTER ALL THE WAY DOWN TO THE I-72 CORRIDOR BY SUNRISE.
AM FAVORING MORE OF A NAM/ECMWF BLEND WHICH KEEPS THE OVERNIGHT
ACTIVITY CLOSER TO NORTHEAST ILLINOIS.

&&

.LONG TERM...(Thursday THROUGH Wednesday)
ISSUED AT 300 PM CDT WED SEP 2 2015

THE OVERALL PATTERN OF AN UPPER LEVEL TROUGH IN THE WESTERN U.S. AND
BROAD RIDGING ACROSS THE CENTRAL AND EASTERN U.S. IS EXPECTED TO
REMAIN IN PLACE INTO THE UPCOMING WEEKEND. HOWEVER...AS IS OFTEN THE
CASE...SUBTLE, MAINLY SUB-SYNOPTIC FEATURES WILL PLAY A ROLE IN THE
WEATHER THURSDAY INTO SATURDAY.

FIRST OF ALL...THE UPPER RIDGING WILL KEEP A LARGE, VERY WARM
AIRMASS OVER THE ENTIRE FORECAST AREA THROUGH THE WEEKEND. THIS
MORNINGS UPPER AIR ANALYSIS OF THE LOWER ATMOSPHERE ONLY INDICATED
POCKETS OF HIGHER MOISTURE INSTEAD OF A FETCH OF TROPICAL GULF AIR.
IN ADDITION, CROP MOISTURE HAS BEEN FAIRLY STUNTED LATELY, SO REALLY
HIGH DEW POINTS INTO THE MID 70S OR HIGHER ARE NOT EXPECTED. THIS
WILL KEEP THE DAILY MAX HEAT INDEX IN THE 95-100 RANGE THROUGH THE
WEEKEND.

WITH RESPECT TO PRECIPITATION POTENTIAL THE NEXT FEW DAYS...A
SHORTWAVE TROUGH CRASHING THROUGH THE RIDGE IN WISCONSIN THIS
AFTERNOON WILL DROP SOUTHEAST INTO INDIANA THURSDAY. THIS SHOULD BE
ENOUGH LIFT TO PRODUCE ISOLATED SHOWERS/T-STORMS EAST OF A
BLOOMINGTON-TUSCOLA-PARIS LINE LATE THURS AM INTO THE AFTERNOON...
WITH A BETTER CHANCE TOWARD LATE IN THE AFTERNOON. THE ANTICIPATED
SLOW MOVEMENT OF THESE STORMS COULD RESULT IN POCKETS OF HEAVY
RAINFALL. MUCH OF THE SAME IS ANTICIPATED FRIDAY IN EAST CENTRAL IL
AND SATURDAY ALONG AND NORTH OF THE I-74 CORRIDOR FROM PEORIA-
DANVILLE AS WEAK SHORTWAVES ARE EXPECTED TO DROP INTO THE AREA FROM
THE NORTH.

IN THE LONGER RANGE...THE GFS AND EUROPEAN MODELS ARE INDICATING
SOME IMPORTANT DIFFERENCES IN HOW FAST THEY BREAK DOWN THE CENTRAL
U.S. RIDGE AND ALLOW SHORTWAVE TROUGHS AND AN ASSOCIATED FRONTAL
BOUNDARY TO IMPACT OUR WEATHER. THE EUROPEAN MODEL IS MUCH QUICKER
BREAKING DOWN THE RIDGE AND PUSHES A COOL FRONT INTO OUR FORECAST
AREA BY MONDAY MORNING. THE GFS KEEPS THE FRONT TO THE NORTH AND
WEST OF OUR REGION UNTIL WEDNESDAY. PREFER THE GFS SOLUTION SINCE IT
APPEARS THAT THE GREATEST UPPER LEVEL ENERGY SHOULD STAY TO OUR
NORTH WHICH WOULD CAUSE THE FRONT TO BECOME MORE PARALLEL TO THE
UPPER FLOW AND ALLOW FOR A SLOWER PROGRESSION TOWARD CENTRAL/SE IL.
THIS SCENARIO WOULD FAVOR SCATTERED SHOWERS/T-STORMS MONDAY INTO
EARLY TUESDAY...WITH BETTER CHANCES TOWARD MID-WEEK.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z Thursday AFTERNOON)
ISSUED AT 1217 PM CDT WED SEP 2 2015

CENTRAL ILLINOIS REMAINING ON THE PERIPHERY OF SURFACE HIGH
PRESSURE OVER THE OHIO VALLEY...RESULTING IN LITTLE CHANGE IN
TRENDS FROM THE PAST COUPLE DAYS. AREAS OF MVFR VISIBILITIES
POSSIBLE ONCE AGAIN THURSDAY MORNING WITH THE WARM AND HUMID AIR
MASS IN PLACE. MAIN CONCERN WILL BE WITH POTENTIAL FOR CONVECTION
ON THURSDAY...AS AN UPPER DISTURBANCE DROPS SOUTHEAST ACROSS THE
GREAT LAKES. AT THE MOMENT...ISOLATED SHOWERS/STORMS WOULD BE A
CONCERN AROUND KBMI/KCMI LATE THURSDAY MORNING...BUT COVERAGE IS
TOO SMALL TO WARRANT A VCTS MENTION AT THIS POINT.


&&

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

$$

SHORT TERM...Geelhart
LONG TERM...Miller
AVIATION...Geelhart



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