Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 202008
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
308 PM CDT MON APR 20 2015

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 306 PM CDT MON APR 20 2015

BROAD CYCLONIC CIRCULATION CONTINUING OVER THE MIDWEST THIS
AFTERNOON...WITH SURFACE LOW PRESSURE CENTERED OVER THE EAST TIP OF
LAKE SUPERIOR AND AN UPPER LOW OVER NORTHWEST MINNESOTA. HAVE BEEN
SEEING SOME FAST MOVING LIGHT SHOWERS/SPRINKLES MOVING THROUGH THE
FORECAST AREA...BUT AS THE SHOWERS AND CLOUDS ARE HIGHLY CELLULAR IN
NATURE...THESE SHOULD FADE WITH LOSS OF DAYTIME HEATING. WEST
PORTION OF THE CWA SHOULD BE MAINLY CLEAR BY SUNSET...BUT IT MAY
TAKE UNTIL MID EVENING FOR THE EAST TO SCATTER OUT. GUSTY WINDS OF
30-40 MPH THIS AFTERNOON WILL BE DIMINISHING WITH SUNSET AS WELL...
BUT WINDS SHOULD STILL AVERAGE AROUND 10 MPH MUCH OF THE NIGHT. MADE
LITTLE CHANGE TO FORECAST LOW TEMPERATURES...WHICH ARE MAINLY A
COUPLE DEGREES EITHER SIDE OF 40.

&&

.LONG TERM...(TUESDAY NIGHT THROUGH MONDAY)
ISSUED AT 306 PM CDT MON APR 20 2015

WINDY CONDITIONS WILL BE THE HIGHLIGHT FOR TUESDAY AS UPPER AND
LOWER LEVEL JETS INTENSIFY ACROSS IL. UNUSUALLY DEEP MIXING
HEIGHTS FORECAST BY THE NAM/GFS UP TO 9-11K FT APPEAR TO BE A BIT
OVERDONE. HOWEVER, EVEN MIXING HEIGHTS HALF THAT DEEP WILL CAUSE
STRONG WINDS TO MIX DOWN TO THE GROUND DURING THE DAY. IT APPEARS
THAT GUSTS OF 30-40MPH WILL BE COMMON AGAIN TOMORROW. THERE IS A
CHANCE THAT A WIND ADVISORY MAY BE NEEDED ACROSS OUR NORTHERN
COUNTIES, BUT CURRENT INDICATIONS ARE THE SUSTAINED WINDS SHOULD
PREVAIL JUST BELOW THE CRITERIA OF SUSTAINED 30-39 MPH WINDS FOR
AT LEAST AN HOUR.

THE UPPER TROUGH WILL REMAIN ENTRENCHED ACROSS THE GREAT LAKES FOR
THE REST OF THE WEEK, PROVIDING SUSTAINED NW FLOW AND COOLER THAN
NORMAL CONDITIONS. A SHORTWAVE AND COLD FRONT WILL BE PUSHED ACROSS
IL ON TUESDAY NIGHT...TRIGGERING SCATTERED SHOWERS. THE
NAM/GFS/ECMWF ARE INDICATING A MESO-SCALE BAND OF ENHANCED LIFT
ACROSS OUR NORTHERN COUNTIES OVERNIGHT, SO WE INCREASED POPS INTO
THE CHANCE CATEGORY THERE, WITH SLIGHT CHANCES ACROSS THE SOUTH.
FORCING FOR PRECIP WANES QUICKLY WEDNESDAY MORNING, SO WE WENT WITH
DRY CONDITIONS WED. REINFORCING COLD AIR BEHIND THE COLD FRONT WILL
KEEP HIGHS FOR THE REMAINDER OF THE WEEK IN THE UPPER 50S TO NEAR
60, WITH OVERNIGHT LOWS IN THE 30S. FROST CONDITIONS STILL LOOK
POSSIBLE MAINLY NORTH OF I-74 WED NIGHT AND THUR NIGHT, AS WINDS
BECOME LIGHT AND SKIES CLEAR OUT. LOWS MAY DIP TO 34-35 IN SPOTS. A
FROST ADVISORY MAY BE NEEDED FOR ONE OR BOTH OF THOSE NIGHTS FOR OUR
NORTHERN COUNTIES.

THE EXTENDED MODELS HAVE COME INTO A LITTLE BETTER AGREEMENT ON HOW
FAST THE NEXT SYSTEM MAY TRIGGER RAIN SHOWERS AHEAD OF THE
APPROACHING SOUTHERN STREAM LOW. THE ECMWF HAS JOINED THE GFS IN
ADVANCING SHOWERS INTO CENTRAL IL ON FRIDAY, WHILE THE CANADIAN IS
NOT FAR OFF, SHOWING RAIN IN OUR FAR WESTERN COUNTIES FRIDAY
AFTERNOON. WE INTRODUCED SLIGHT CHANCE POPS SW OF A LINE FROM
RUSHVILLE TO LAWRENCEVILLE TO TREND PRECIP INTO THE FORECAST.

DESPITE DIFFERENCES IN THE TRACK OF THE SURFACE LOW FROM THE PLAINS
INTO ILLINOIS FRIDAY NIGHT INTO SATURDAY, THERE REMAINS SOME
AGREEMENT ON THE FORCING FOR PRECIP ACROSS IL AHEAD OF THE LOW. RAIN
NOW APPEARS LIKELY ACROSS OUR S-SW COUNTIES, WITH CHANCE POPS
INCLUDED IN THE REMAINDER OF THE AREA FRIDAY NIGHT. CHANCE POPS WERE
INCLUDED ACROSS THE BOARD ON SATURDAY, WITH DRY CONDITIONS
RETURNING SAT NIGHT AS THE LOW DEPARTS TO THE EAST.

AS THE UPPER TROUGH FINALLY MOVES TOWARD THE EAST COAST NEXT
WEEKEND, A ZONAL WESTERLY FLOW WILL PUSH ADDITIONAL SHORTWAVES
TOWARD ILLINOIS. WE COULD SEE A FEW SHOWERS DEVELOP SUNDAY NIGHT AND
MONDAY IN OUR WESTERN COUNTIES AS THE NEXT WAVE ARRIVES.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 1229 PM CDT MON APR 20 2015

WEST WINDS WILL REMAIN GUSTY THROUGH THE AFTERNOON WITH SOME
PERIODS OVER 30 KNOTS. WINDS WILL SUBSIDE THIS EVENING...ALTHOUGH
SUSTAINED SPEEDS REMAIN 10 KNOTS OR SO MUCH OF THE NIGHT. SPEEDS
EXPECTED TO PICK UP AGAIN EARLY TUESDAY...WITH THE GFS THE MOST
AGGRESSIVE WITH GUSTS OVER 30 KNOTS AS EARLY AS 15Z. DID NOT GO
QUITE THAT HIGH YET...BUT HAVE INCLUDED GUSTS 25-28 KNOTS AT ALL
SITES TUESDAY MORNING.

SOME LINGERING MVFR CONDITIONS CONTINUING FOR ANOTHER HOUR OR TWO
AT KCMI...BUT GENERAL TREND WILL BE FOR CEILINGS 3500-4500 FEET
ACROSS CENTRAL ILLINOIS THIS AFTERNOON. CLOUDS ARE DIURNAL IN
NATURE AND SHOULD DISSIPATE EARLY EVENING WITH LOSS OF DAYTIME
HEATING.


&&

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

$$

SHORT TERM...GEELHART
LONG TERM...SHIMON
AVIATION...GEELHART



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