Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 031946
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
246 PM CDT THU SEP 3 2015

.SHORT TERM...(TONIGHT)
ISSUED AT 244 PM CDT THU SEP 3 2015

WEAK FRONTAL BOUNDARY/WIND SHIFT LINE AS OF 200 PM WAS LOCATED
BETWEEN MILWAUKEE AND CHICAGO WITH MID AND UPPER 70 DEW POINTS
POOLING ALONG THE BOUNDARY OVER PARTS OF SOUTHWEST WISCONSIN INTO
NORTHEAST IOWA. ACROSS OUR AREA...DEW POINTS ONCE AGAIN HAVE MIXED
DOWN INTO THE MID AND UPPER 60S WHILE EARLY AFTERNOON TEMPERATURES
WERE IN THE LOWER 90S PRODUCING HEAT INDEX VALUES MOSTLY IN THE
MIDDLE 90S. MAIN CONCERN IN THE SHORT TERM WILL BE CHANCES FOR RAIN
TONIGHT AS THE WEAK FRONT APPROACHES OUR FAR NORTHEAST/NORTHERN
COUNTIES BEFORE BECOMING STATIONARY. EXCEPT FOR THE NCEP WRF-NMM,
MOST OF THE HIGH RES MODELS SUGGEST THE BULK OF THE CONVECTION WILL
STAY NORTH OF THE AREA THIS EVENING BEFORE DISSIPATING TOWARDS
MIDNIGHT, SO WILL NOT ADD ANY MENTION ACROSS OUR NORTH AND NORTHEAST
AT THIS TIME. OTHERWISE, ANOTHER WARM NIGHT AS EARLY MORNING LOWS
STRUGGLE TO DROP INTO THE UPPER 60S TO LOWER 70S BY DAWN ACCOMPANIED
BY A LIGHT SOUTHERLY BREEZE. MAY SEE SOME LIGHT FOG AND HAZE AROUND
AGAIN BY TOMORROW MORNING, BUT IT APPEARS COVERAGE ACROSS OUR AREA
WILL BE PATCHY AT BEST, SO WILL NOT INCLUDE IN THE GRIDS.

&&

.LONG TERM...(Friday THROUGH Thursday)
ISSUED AT 244 PM CDT THU SEP 3 2015

THE FORECAST THROUGH SUNDAY WILL BE DOMINATED WITH HEAT AND
HUMIDITY, AS AN UPPER RIDGE IN THE PLAINS SLOWLY DRIFTS EASTWARD.
THE ADVANCEMENT OF THE RIDGE WILL BE SLOWED BY A COUPLE OF UPPER
SHORTWAVES STALLED OVER THE WESTERN GREAT LAKES. THOSE TWO WAVES
WILL BE RESPONSIBLE FOR SHOWER AND THUNDERSTORM CHANCES IN OUR
NORTHEAST COUNTIES TOMORROW AND SATURDAY, MAINLY NORTHEAST OF A LINE
FROM LACON TO PARIS. WE KEPT THE SLIGHT CHANCE POPS IN THAT AREA FOR
BOTH DAYS. OTHERWISE, EXPECT HIGHS IN THE 89 TO 94 RANGE EACH DAY,
WITH AFTERNOON AND EARLY EVENING HEAT INDEX READINGS OF 95 TO 102.

THE NEXT CONCERN IS THE TIMING OF THE PATTERN CHANGE FOR NEXT WEEK.
THE SYSTEM THAT IS EXPECTED TO BREAK DOWN THE RIDGE IS CURRENTLY IN
BRITISH COLUMBIA. THE MODELS ARE IN GENERAL AGREEMENT ON DROPPING
THAT LOW SOUTH OF BRITISH COLUMBIA INTO OREGON ON SATURDAY, THEN
LIFTING IT NORTHEAST IN MANITOBA BY MONDAY AND STALLING IT
THERE. DURING THAT TIME, A SURFACE LOW IS EXPECTED TO DEVELOP
AHEAD OF THE UPPER LOW IN WESTERN SOUTH DAKOTA ON SATURDAY, THEN
MOVE INTO NORTHWEST ONTARIO ON SUNDAY NIGHT-MONDAY, DRAGGING A
DISSIPATING COLD FRONT INTO ILLINOIS ON MONDAY. THAT FRONT IS
PROJECTED TO STALL OUT ACROSS IL AS IT BECOMES PARALLEL TO THE
STEERING WINDS, PROVIDING SCATTERED STORM CHANCES FROM LATER
SUNDAY NIGHT THROUGH TUESDAY. THERE ARE VARYING SOLUTIONS AS TO
SHORT WAVE PROGRESSION ALONG THE FRONT, BUT WITH ONLY MARGINAL
CONVERGENCE ALONG THE FRONT, WILL KEEP POPS IN THE LOW CHANCE
RANGE THROUGH TUESDAY.

ADDITIONAL QUESTIONS REMAIN ON THE TIMING OF THE SUBSEQUENT PUSH OF
COLD AIR TO GIVE US OUR AIRMASS CHANGE. THE ECMWF AND CANADIAN ARE
BOTH SHOWING A MUDDIER PICTURE OF THAT NEXT COLD FRONTAL PASSAGE,
WHILE THE GFS IS A BIT MORE PROGRESSIVE AND GETS THE FRONT EAST OF
OUR COUNTIES BY LATE WED AFTERNOON. THE EC/CANADIAN BRING THE
SECOND FRONT INTO IL ON TUES NIGHT INTO WED, BUT INDICATE YET
ANOTHER SHORTWAVE RIDING ALONG THE FRONT STARTING LATE WED/WED
NIGHT, KEEPING PRECIP CHANCES INTO THURSDAY. WILL KEEP SOME CHANCE
POPS SE OF I-55 WED NIGHT, AND ONLY SLIGHTS IN THE FAR SOUTH
COUNTIES ON THURSDAY FOR NOW.

RELIEF FROM THE HEAT SHOULD DEVELOP STARTING ON TUESDAY, BUT MORE
SIGNIFICANTLY ON WED AND THURS, WHEN HIGHS ONLY CLIMB INTO THE UPPER
70S TO LOWER 80S.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z Friday AFTERNOON)
ISSUED AT 1204 PM CDT THU SEP 3 2015

VFR CONDITIONS ARE EXPECTED THRU THIS EVENING WITH THE POTENTIAL
FOR SOME PATCHY MVFR VSBYS IN FOG LATE TONIGHT. STILL A THREAT
FOR AN ISOLATED SHOWER OR STORM THIS AFTERNOON BUT COVERAGE...IF
ANY DO DEVELOP...TOO LIMITED TO INCLUDE IN ANY OF THE TAFS. BASES
OF CUMULUS CLOUDS THIS AFTERNOON WILL RANGE FROM 4500-6000 FEET
WITH THE BETTER COVERAGE EXPECTED FROM DECATUR TO CHAMPAIGN.
SURFACE WINDS WILL BE OUT OF THE SOUTHWEST AT 10 TO 15 KTS THIS
AFTERNOON...AND THEN LIGHT SOUTH TO SOUTHWEST WINDS EXPECTED
TONIGHT.


&&

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

$$

SHORT TERM...Smith
LONG TERM...Shimon
AVIATION...Smith


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