Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 280828
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
328 AM CDT FRI AUG 28 2015

.SHORT TERM...(TODAY)
ISSUED AT 328 AM CDT FRI AUG 28 2015

LATEST SURFACE ANALYSIS HAD AN AREA OF HIGH PRESSURE CENTERED OVER
WESTERN PA & NY, WITH A RIDGE EXTENDING WEST ACROSS NORTHERN
ILLINOIS. MEANWHILE, WEAK LOW PRESSURE WAS CENTERED OVER THE CENTRAL
PLAINS. THIS AREA OF LOW PRESSURE, AND ITS DRIVING UPPER LEVEL SHORT
WAVE, WILL SLOWLY DRIFT EAST OVER THE NEXT FEW DAYS. MAIN CONCERN
FOR THE FORECAST TODAY IS IF ANY OF THE RAINFALL CURRENTLY
ASSOCIATED WITH THE LOW CAN MAKE IT EAST INTO THE FORECAST AREA
BEFORE TONIGHT.

FORECAST SOUNDINGS SUGGEST THE AIRMASS ACROSS CENTRAL AND SOUTHEAST
ILLINOIS SHOULD REMAIN RATHER DRY TODAY. WHILE CLOUDS WILL BE ON THE
INCREASE WITH THE APPROACH OF THE LOW/UPPER WAVE, THE DEEPER
MOISTURE SHOULD REMAIN WEST OF ILLINOIS THROUGH THE DAY. IN FACT,
SURFACE FLOW IS PROGGED TO REMAIN SOUTHEASTERLY ON THE SOUTH SIDE OF
THE HIGH PRESSURE RIDGE, CERTAINLY NOT A DIRECTION CONDUCIVE TO
SIGNIFICANT LOW LEVEL MOISTURE INCREASES. IN ADDITION TO THE
APPARENT LACK OF MOISTURE, DO NOT ANTICIPATE MUCH IN THE WAY OF
FORCING IN THE AREA TODAY. THE LOW LEVEL FLOW IS EXPECTED TO REMAIN
ANTICYCLONIC, WITH THE BETTER FORCING WITH THE UPPER WAVE STAYING
WELL WEST OF THE AREA TODAY FROM THE CENTRAL PLAINS INTO WESTERN
PORTIONS OF THE MIDWEST.

WITH THIS THINKING IN MIND, EXPECT DRY CONDTIONS TO PERSIST ACROSS
THE CENTRAL AND SOUTHEAST ILLINOIS TODAY. WILL HOLD ONTO A SLIGHT
CHANCE OF SHOWERS/STORMS ACROSS FAR NORTHWEST PORTION OF THE
FORECAST AREA, CLOSEST TO THE APPROACHING SYSTEM, BUT THE ODDS ARE
CERTAINLY BETTER THAT THIS AREA WILL STAY DRY. THE LOCAL AIRMASS
WILL CONTINUE TO MODIFY TODAY, UNDER PERSISTENT SOUTHERLY FLOW,
BECOMING A LITTLE WARMER AND MORE HUMID THAN YESTERDAY, BUT THESE
CONDITIONS WILL CERTAINLY REMAIN SEASONABLE FOR LATE AUGUST.

&&

.LONG TERM...(TONIGHT THROUGH THURSDAY)
ISSUED AT 328 AM CDT FRI AUG 28 2015

TONIGHTS TEMPERATURES CLOSE TO NORMALS FOR AUGUST FOR CENTRAL
ILLINOIS, AIDED PARTIALLY BY INCREASING CLOUDS WITH A SHORT WAVE
MOVING THROUGH THE MIDWEST. MODELS HAVE BEEN CONSISTENTLY
INCONSISTENT WITH THE TIMING OF THE ONSET OF THE PRECIP. HOWEVER,
MODELS HAVE BEEN IN AGREEMENT WITH THE GENERAL SLOWNESS OF THE WAVE,
RESULTING IN A SHOWERY WEEKEND FOR CENTRAL ILLINOIS.  BEST CHANCES
TOMORROW AND TOMORROW NIGHT, WITH A SLIGHTLY BETTER CHANCE IN THE
AFTERNOON WITH A DIURNAL ASSIST FROM MAX HEATING.  THAT BEING SAID,
TEMPERATURES WILL BE SLIGHTLY WARMER FOR SATURDAY WITH HIGHS IN THE
UPPER 70S NW OF THE ILLINOIS RIVER VALLEY, AND MORE SEASONABLE LOWER
80S SOUTH OF INTERSTATE 72. PRECIP CHANCES LINGER INTO SUNDAY
MORNING AND PROGRESSION OF THE WAVE TO THE EAST WILL HAVE A BIG
IMPACT ON CHANCES FOR PRECIP IN THE EAST SUN AFTERNOON.  FOR NOW,
ONLY SLIGHT CHANCES IN THE FORECAST ALONG THE INDIANA BORDER, BUT
WILL NEED TO KEEP AN EYE ON THE PROGRESSION OF THE SHORTWAVE IN THE
WEAK FLOW ALOFT.

THE REMAINDER OF THE FORECAST IS DOMINATED BY HIGH PRESSURE OVER
MUCH OF THE SOUTHEASTERN QUADRANT OF THE CONUS, REACHING ALL THE WAY
INTO THE MIDWEST/GREAT LAKES.  SOME SMALL WAVES MOVING THROUGH, BUT
GENERALLY TRACKING ALONG THE MORE PROGRESSIVE FLOW ACROSS THE GREAT
LAKES TO THE NORTH.  THE SHORTWAVE MOVING THROUGH THE REGION THIS
WEEKEND SHIFTS THE NORTHWESTERLY FLOW TO A SLIGHTLY LESS AMPLIFIED
PATTERN WITH A SOUTHWESTERLY TREND. HOT TEMPS UNDER THE RIDGE IN THE
SOUTHWESTERN CONUS DIFFUSE INTO THE REGION WITH THE PATTERN SHIFT
AND TEMPS THROUGH THE MIDDLE OF NEXT WEEK SIGNIFICANTLY ABOVE
NORMALS WITH MAX TEMPS APPROACHING THE 90 MARK BEFORE MIDWEEK.
GUIDANCE RUNNING ON BOTH SIDES OF THE 90 DEGREE MARK, SO WILL HAVE
TO KEEP AN EYE ON THE VARIANCE THERE.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1147 PM CDT THU AUG 27 2015

VFR CONDITIONS SHOULD PREVAIL FOR THE MAJORITY OF THIS VALID TAF
PERIOD THROUGH 06Z SAT. HIGH PRESSURE IS DEPARTING SLOWLY TO THE
EAST, WHILE A LOW PRESSURE SYSTEM OVER EASTERN NEBRASKA
APPROACHES. THE LOW IS EXPECTED TO REACH NORTHEAST IOWA BY FRIDAY
EVENING. LIGHT EAST-SOUTHEAST WIND THE REST OF TONIGHT WILL BECOME
MORE SOUTHERLY FRIDAY MORNING AS THE GRADIENT BEGINS TO TIGHTEN
AHEAD OF THE APPROACHING LOW. SPEEDS WILL LIKELY INCREASE TO
10-14KTS BY 16Z, THEN GUST TO 16KT OR HIGHER FRIDAY AFTERNOON.

AS FOR CLOUDS, SCT MID-HIGH CLOUDS WILL FILTER INTO IL ON NW FLOW
ALOFT OVERNIGHT. THERE IS SOME POTENTIAL FOR LIGHT/SHALLOW GROUND
FOG LATE TONIGHT INTO FRIDAY MORNING BUT OVERALL EFFECTS WILL BE
MINIMAL AT ANY TAF LOCATION.

RAIN CHANCES WILL HOLD OFF TOMORROW, AS MID AND HIGH CLOUDS
CONTINUE TO THICKEN DURING THE AFTERNOON. A VCSH WAS INCLUDED AT
PIA AFTER 04Z, BASED ON FORECAST SOUNDINGS IN THE SHORT TERM
MODELS. BETTER CHANCES OF RAIN SHOULD COME AFTER THIS TAF VALID
PERIOD.


&&

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

$$

SHORT TERM...BAK
LONG TERM...HJS
AVIATION...SHIMON


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