Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 261720
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1220 PM CDT WED AUG 26 2015

.UPDATE...
ISSUED AT 945 AM CDT WED AUG 26 2015

MAIN CONCERN IS WITH THE LOWER CLOUD DECK NUDGING SOUTHWARD.
LATEST VISIBLE SATELLITE IMAGERY SHOWS THIS CLOSE TO MOVING INTO
BLOOMINGTON...EXTENDING NORTHWARD THROUGH ROCKFORD AND THEN
EASTWARD. HRRR CLOUD GUIDANCE TRIES TO BREAK THIS UP OVER THE NEXT
COUPLE HOURS...BUT NOT REALLY SEEING ANY EVIDENCE OF THIS
YET...WITH THE CLOUD DECK RATHER SOLID UP INTO CENTRAL WISCONSIN.
RAP 900 MB HUMIDITY PLOT SHOWS THIS BETTER...AND STARTS MORE OF A
BREAKUP AFTER NOON. TIMING OF THE BREAKUP WILL IMPACT FORECAST
HIGHS...WHICH ARE IN THE MID 70S IN THAT AREA.

DID SOME ADJUSTMENTS OF THE CLOUD TRENDS ACROSS THE EASTERN
CWA...BUT NO CHANGES WERE NEEDED TO THE WORDED FORECASTS AT THIS
TIME.

&&

.SHORT TERM...(TODAY)
ISSUED AT 324 AM CDT WED AUG 26 2015

DEEP UPPER LOW NORTH OF LAKE ERIE EARLY THIS MORNING CONTINUES TO
SLOWLY EDGE AWAY FROM THE MIDWEST. HOWEVER, SEVERAL WEAK SHORTWAVES
CONTINUE TO ROTATE SOUTHWARD AROUND THE WESTERN PERIPHERY OF THE
UPPER LOW ACROSS THE LOWER GREAT LAKES BRINGING CLOUD COVER MUCH
FURTHER INTO OUR FORECAST AREA THAN WHAT GUIDANCE SUGGESTED. THAT
WILL BE THE MAIN FORECAST CONCERN TODAY, AMOUNT OF CLOUD COVER OVER
CENTRAL IL AND ITS AFFECT ON TEMPERATURES. RAP FORECAST SOUNDINGS
AND TIME HEIGHT CROSS SECTIONS SHOWING QUITE A BIT OF MOISTURE AT OR
JUST BELOW 850 MB INTO EARLY THIS AFTERNOON, ESPECIALLY OVER THE
EASTERN HALF OF THE FORECAST AREA. WILL HIT THE CLOUD COVER A BIT
HEAVIER ACROSS THE EAST TODAY WITH TEMPS CUT BACK A FEW DEGREES AS A
RESULT, MAINLY IN THE MID 70S, WHILE FURTHER WEST, A BIT MORE SUN
SHOULD ALLOW AFTERNOON TEMPERATURES TO RISE INTO THE UPPER 70S.
SOUNDINGS INDICATE SOME GUSTS UP TO 20 MPH POSSIBLE AGAIN FROM THE
NORTHWEST LATER THIS MORNING INTO THE AFTERNOON HOURS, ESPECIALLY
ACROSS THE WEST WHERE THERE WILL BE DEEPER MIXING OCCURRING.

.LONG TERM...(TONIGHT THROUGH TUESDAY)
ISSUED AT 324 AM CDT WED AUG 26 2015

SLIGHTLY COOLER THAN CLIMATOLOGICAL NORMS THROUGH THE END OF THE
WEEK, ALBEIT IN A SLIGHT WARMING TREND. FORECAST ISSUE IN THE
LONGER TERM REMAINS THE SYSTEM FOR THE BEGINNING OF THE WEEKEND. A
SHORT WAVE DIVES INTO THE MIDWEST RIPPLING THROUGH THE
PREDOMINANTLY NWRLY FLOW. MODELS HAVE BEEN INCONSISTENT WITH THE
TIMING AND THE SPEED OF THE SYSTEM ITSELF WITH ITS OWN FORWARD
MOTION. WAVE REACHES THE MIDWEST AND SLOWS CONSIDERABLY. EITHER
WAY, SOME CONSENSUS APPEARS AS TO ONSET OF PRECIP IN CENTRAL
ILLINOIS AFTER 00Z SATURDAY BTWN THE GFS/ECMWF/NAM. HOWEVER, AT
THIS POINT, THE PRECIP STARTS TO BECOME LESS IN COVERAGE. EXPECTED
THROUGH THE OVERNIGHT FRI NIGHT PERHAPS WITH THE LOSS OF A DIURNAL
COMPONENT, BUT LESS EXPECTED DURING THE DAY ON TUESDAY. THAT BEING
SAID, THE SOUNDINGS ARE NOT REPRESENTATIVE FOR RAIN, DRYING OUT
CONSIDERABLY WHILE THE MODELS ARE GENERATING QPF. A RATHER DRY
AIRMASS FOR DAYS...THE MODELS SEEM TO BE OVERDOING THE BOUNDARY
LAYER AVAILABLE MOISTURE. OVERBLOWN RH IN THE LOW LEVELS IN THE
NAM IS EXPECTED AND SO FAR, IT IS TRUE TO FORM IN PRODUCING
SIGNIFICANTLY MORE QPF. THE TREND, THOUGH, IS MORE TO A POTENTIAL
SHOWERY SITUATION. HAVE EASED BACK POPS WHERE COLLABORATIVELY
POSSIBLE, AND SWITCHED THE WORDING TO COVERAGE INSTEAD OF
PROBABILITY.

BEYOND THE POPS ON THE WEEKEND, THE FLOW SWITCHES TO A LESS
AMPLIFIED PATTERN.  THE WEAK SOUTHWESTERLY FLOW ALLOWS THE HEAT OVER
THE DESERT SW TO ESCAPE OUT FROM UNDER THE PERSISTENT RIDGE AND
BRING A WARMING TREND FOR THE FIRST COUPLE DAYS OF NEXT WEEK.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 1220 PM CDT WED AUG 26 2015

LARGE MVFR STRATOCUMULUS DECK CONTINUES TO EDGE SOUTHWARD...
HAVING CLIPPED KBMI AND IS COMING FAIRLY CLOSE TO KCMI AT MIDDAY.
LATEST RAP GUIDANCE DOES NOT SHOW A LOT MORE FURTHER PROGRESS.
HAVE MAINTAINED THE MVFR CONDITIONS AT KBMI AND INCLUDED A TEMPO
MVFR CEILING AT KCMI FOR THE NEXT FEW HOURS. TAF SITES FURTHER
WEST MAINLY BEING AFFECTED BY DIURNAL CUMULUS CLOSER TO 4000
FEET...AND THIS SHOULD FADE WITH SUNSET. VFR CONDITIONS EXPECTED
OVERNIGHT...WITH LIGHT WINDS GRADUALLY TRANSITIONING MORE TOWARD
THE SOUTHEAST AS AN AREA OF HIGH PRESSURE PASSES.

&&

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

$$

UPDATE...GEELHART
SHORT TERM...SMITH
LONG TERM...HJS
AVIATION...GEELHART


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