Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 191749
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1249 PM CDT TUE MAY 19 2015

.UPDATE...
ISSUED AT 1037 AM CDT TUE MAY 19 2015

SURFACE HIGH PRESSURE CENTERED OVER THE NORTHERN PLAINS WILL
CONTINUE TO SHIFT EASTWARD TODAY BRINGING LIGHT NORTHERLY WINDS
AND CONTINUED ADVECTION OF COOL AND RELATIVELY DRY AIR INTO
CENTRAL IL. GENERAL SUBSIDENCE ALOFT IS INDICATED BY MODEL
FORECASTS AND CURRENT WATER VAPOR IMAGERY, HOWEVER A BAND OF LOW
CLOUD OVER PORTIONS OF IL MAINLY NORTH OF I-72 PERSISTS THIS
MORNING. MODEL TIME-HEIGHT PLOTS NOW INDICATE THIS LAYER FAIRLY
WELL AND HRRR HALTS THE PROGRESS OF THE BAND AROUND THE CURRENT
LOCATION. SURFACE HEATING WILL TEND TO RAISE THE CEILING HEIGHT
THROUGH THE AFTERNOON...BUT ENOUGH MOISTURE SHOULD PERSIST THAT
THE LAYER SHOULD TRANSITION INTO A SCATTERED SHALLOW CUMULUS LAYER
AROUND 4000-5000 FEET. FORECAST IS MORE OR LESS ON TRACK, BUT HAVE
MADE SOME MODIFICATIONS TO CLOUD COVER THROUGH THE AFTERNOON TO
BETTER DEPICT THE SITUATION.

&&

.SHORT TERM...(TODAY)
ISSUED AT 331 AM CDT TUE MAY 19 2015

CANADIAN HIGH PRESSURE WILL BEGIN TO BUILD INTO CENTRAL AND
SOUTHEAST ILLINOIS TODAY, ACCOMPANIED BY A CONTINUED FEED OF
COOLER/DRIER AIR IN THE WAKE OF YESTERDAY`S COLD FRONT. THIS
SCENARIO SUPPORTS A DRY DAY, WITH AFTERNOON HIGH TEMPERATURES
MAINLY IN THE 60S.

ONE FLY IN THE OINTMENT, ONE THAT MAY IMPACT TEMPERATURES ACROSS
NORTHERN PORTIONS OF THE FORECAST AREA, IS A LARGE AREA OF WRAP-
AROUND CLOUDINESS THAT HAS STARTED TO SINK INTO FAR NORTHERN
PORTIONS OVER THE FORECAST AREA OVER THE PAST FEW HOURS. NONE OF THE
MODEL GUIDANCE HAS A VERY GOOD HANDLE ON THE CURRENT SOUTHERN EXTENT
OF THE CLOUD SHIELD, OR IN MANY CASES EVEN INDICATES IT AT ALL. AT
THIS POINT, HAVE USED SIMPLE EXTRAPOLATION OF THE CURRENT CLOUD
SHIELD INTO MID-MORNING. THEN, AS DIURNAL MIXING GETS GOING, HAVE
ALLOWED THE SOUTHERN EDGE OF THE CLOUD SHIELD TO MIX-OUT/ERODE AND
BE NORTH OF THE AREA BY MIDDAY. SO, BASICALLY, MUCH OF THE FORECAST
AREA ALONG/NORTH OF I-74 WILL BE CLOUDY TO START THE DAY, GRADUALLY
BECOMING MOSTLY SUNNY BY AFTERNOON.

.LONG TERM...(TONIGHT THROUGH MONDAY)
ISSUED AT 331 AM CDT TUE MAY 19 2015

CANADIAN HIGH PRESSURE WILL BE SPRAWLED NORTH OF IL ACROSS WI
TONIGHT KEEPING CENTRAL IL DRY. MID/HIGH CLOUDS TO INCREASE FROM THE
WEST DURING TONIGHT AHEAD OF NEXT WEATHER SYSTEM EJECTING INTO THE
CENTRAL PLAINS. LOWS TONIGHT IN THE MID TO UPPER 40S WITH COOLEST
READINGS OVER EAST CENTRAL IL WHERE CLOUDS MOVE IN LATER.

SHORT WAVE TO WEAKEN AS IT EJECTS INTO CENTRAL IL WED AFTERNOON AND
LIKELY SPREADING LIGHT RAIN SHOWERS EAST ACROSS CENTRAL AND SE IL
DURING THE DAY WED. SPC KEEPS CHANCES OF THUNDER SOUTH OF I-64 OVER
SOUTHERN IL ON WED BUT KEPT SLIGHT CHANCE OF THUNDER WED AFTERNOON
OVER SW CWA. NE FLOW AROUND HIGH PRESSURE OVER THE GREAT LAKES WILL
TRY TO BRING DRIER AIR INTO NE CWA WHERE RAINFALL AMOUNTS ONLY ONE
TO TWO TENTHS WHILE A QUARTER TO A THIRD OF AN INCH OF RAIN SW CWA.
BEST RAIN CHANCES SHIFT INTO SE IL WED EVENING WHILE THE IL RIVER
VALLEY DRIER OUT AS WEAKENING SYSTEM GETS SHUNTED TO THE SE AS
ANOTHER HIGH PRESSURE SYSTEM NOSES INTO IL FROM THE CENTRAL PLAINS.
WENT A FEW DEGREES COOLER THAN MET/MAV GUIDANCE FOR HIGHS WED
ESPECIALLY CENTRAL AND WESTERN AREAS WHERE HIGHER CHANCES OF
RAIN WITH MID TO UPPER 50S NORTH AND LOWER 60S IN SOUTHEAST IL.

HIGH PRESSURE SETTLES INTO MO THU AFTERNOON INTO THU NIGHT AND TO
BRING DRY WEATHER TO IL WITH RETURN OF PARTLY TO MOSTLY SUNNY SKIES
BY THU AFTERNOON. MILDER HIGHS IN THE MID TO UPPER 60S BUT STILL
BELOW NORMAL HIGHS IN THE MID 70S. LOWS THU NIGHT IN THE MID TO
UPPER 40S. A NICE DAY IN STORE FRIDAY AS HIGH PRESSURE SETTLES OVER
IL WITH AMPLE SUNSHINE...FAIRLY LIGHT WINDS AND HIGHS IN THE LOWER
70S. DRY CONDITIONS CONTINUE FRIDAY NIGHT ACROSS IL WITH LOWS IN THE
LOW TO MID 50S.

MOST OF CENTRAL AND ESPECIALLY EASTERN IL APPEAR TO STAY DRY YET ON
SATURDAY WITH INCREASING CLOUDS AND HIGHS IN THE MID 70S AS HIGH
PRESSURE SLIPS OFF THE MID ATLANTIC COAST BY SUNSET SATURDAY AND
UPPER LEVEL RIDGE INTO IL. HAVE SLIGHT CHANCE OF SHOWERS AND
THUNDERSTORMS SAT AFTERNOON OVER WEST CENTRAL IL WHILE BETTER
CHANCES OF SHOWERS AND THUNDERSTORMS TO SPREAD NE ACROSS CENTRAL IL
DURING SAT NIGHT AND SUNDAY WITH SHORT WAVES EJECTING NE FROM THE
LARGE UPPER LEVEL TROF OVER THE ROCKIES. INCREASING GULF MOISTURE
WITH SOUTHERLY FLOW TO PROVIDE GOOD CHANCES OF SHOWERS AND
THUNDERSTORMS SUNDAY INTO MONDAY AND TO EVEN LINGER INTO NEXT
TUESDAY. A WARMER AND MORE HUMID STRETCH OF WEATHER FROM SUNDAY
THROUGH TUESDAY WITH HIGHS IN THE UPPER 70S (LOWER 80S IN SOUTHEAST
IL) AND DEWPOINTS IN THE 60S.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1249 PM CDT TUE MAY 19 2015

VFR CONDITIONS OVER MOST OF CENTRAL/SE IL THIS AFTERNOON...WITH
LINGERING MVFR CEILINGS KPIA-KBMI NORTHWARD. WITH DAYTIME
HEATING...CEILINGS SHOULD RAISE ABOVE MVFR THRESHOLDS WITHIN A FEW
HOURS ACROSS THE AREA...ALTHOUGH AREAS OF CLOUD COVER SCT-
BKN035-050 WILL LINGER THROUGH THE AFTERNOON ESPECIALLY KPIA-KBMI
NORTHWARD. LOW LEVEL CLOUD COVER DIMINISHING
EVENING/OVERNIGHT...THEN INCREASING LOW CLOUD COVER AND RAIN
SHOWERS AFTER 12Z. MODEL TIME-HEIGHT SECTIONS AND GUIDANCE
GENERALLY DEPICT CEILINGS REMAINING IN VFR RANGE UNTIL 18Z SO HAVE
INTRODUCED VCSH WITH CIGS/VSBY VFR STARTING 14-16Z. WINDS NNW
8-12 KTS DECREASING OVERNIGHT...THEN BECOMING ENE AROUND 10 KTS
AFTER 15Z WEDNESDAY.

&&

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

$$

UPDATE...ONTON
SHORT TERM...BAK
LONG TERM...07
AVIATION...ONTON



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