Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 220453
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1153 PM CDT THU MAY 21 2015

.UPDATE...
ISSUED AT 842 PM CDT THU MAY 21 2015

CLEAR SKIES AND LIGHT WESTERLY BREEZES ACROSS CENTRAL IL THIS
EVENING AS A WEAK DRY COLD FRONT APPROACHES FROM THE NORTH WHILE
GENERAL SUBSIDENCE REMAINS OVER THE AREA DUE TO BUILDING HIGH
PRESSURE. COOL TEMPERATURES EXPECTED TO DROP INTO THE MID 40S
TONIGHT...BUT WINDS SHOULD HELP KEEP THEM FROM DROPPING FURTHER.
COLD FRONT TO PASS THROUGH MID MORNING TO EARLY AFTERNOON SHIFTING
WINDS TO NORTHERLY. CURRENT FORECASTS ARE IN GOOD SHAPE AND NO
UPDATES ANTICIPATED THIS EVENING OTHER THAN MINOR MODIFICATIONS TO
TEMPERATURE...HUMIDITY...WIND FOR EVENING TRENDS.

&&

.SHORT TERM...(TONIGHT)
ISSUED AT 229 PM CDT THU MAY 21 2015

CLOUD COVER ASSOCIATED WITH A SHORT-WAVE TROUGH CONTINUES TO DROP
SLOWLY SOUTHWARD THIS AFTERNOON...WITH 19Z/2PM SATELLITE IMAGERY
STILL SHOWING OVERCAST CONDITIONS ALONG/SOUTH OF A PARIS TO
EFFINGHAM LINE.  CLEARING WILL CONTINUE TO WORK ITS WAY SOUTHWARD AS
THE DAY PROGRESSES...HOWEVER DIURNAL CU DEVELOPING ALONG THE BACK
EDGE OF THE MAIN CLOUD AREA MAY LINGER ACROSS THE FAR SE KILX CWA
THROUGH EARLY EVENING.  ELSEWHERE AROUND THE AREA...SKIES WILL BE
CLEAR BY SUNSET.  A WEAK COLD FRONT ANALYZED FROM NORTHERN MICHIGAN
INTO THE EASTERN DAKOTAS WILL SAG SOUTHWARD LATER TONIGHT.  CURRENT
SATELLITE SHOWS SOME FAIRLY ROBUST CU ALONG THE BOUNDARY ACROSS
WISCONSIN/MICHIGAN...BUT LITTLE OR NO CLOUD COVER FURTHER WEST.
SEVERAL MODELS ARE SUGGESTING THAT WIDELY SCATTERED SHOWERS WILL
DEVELOP ALONG THE FRONT LATE THIS AFTERNOON...THEN DROP INTO
NORTHERN INDIANA OVERNIGHT.  BASED ON TRAJECTORY OF BEST CLOUD FIELD
AND MODEL CONSENSUS...THINK THIS ACTIVITY WILL REMAIN WELL E/NE OF
CENTRAL ILLINOIS TONIGHT.  AS A RESULT...WILL CONTINUE WITH A MOSTLY
CLEAR AND DRY FORECAST WITH OVERNIGHT LOWS IN THE MIDDLE TO UPPER
40S.

.LONG TERM...(FRIDAY THROUGH THURSDAY)
ISSUED AT 229 PM CDT THU MAY 21 2015

12Z NORTH AMERICAN UPPER AIR ANALYSIS SHOWS AN UNSEASONABLY DEEP LOW
CENTERED OVER THE SOUTHERN TIP OF HUDSON BAY AND ANOTHER LOW FURTHER
WEST OFF THE COAST OF CALIFORNIA.  AS THE HUDSON BAY LOW SHIFTS
EASTWARD AND THE CALIFORNIA LOW CROSSES THE ROCKIES...A SIGNIFICANT
DOWNSTREAM RIDGE WILL DEVELOP OVER THE SOUTHEAST CONUS EARLY NEXT
WEEK...RESULTING IN A WARM/UNSETTLED SOUTHWESTERLY FLOW ACROSS THE
MIDWEST.  AS IS TYPICALLY THE CASE WITH SUCH A MAJOR PATTERN
CHANGE...THE MODELS HAVE BEEN TOO FAST WITH BRINGING THE WESTERN
CONUS LOW AND ITS ASSOCIATED FRONTAL BOUNDARY EASTWARD.  LATEST
MODELS HAVE CONTINUED THEIR SLOWING TREND...WITH MOST SOLUTIONS
NOW KEEPING CENTRAL ILLINOIS DRY UNTIL SUNDAY.  NAM REMAINS THE
MOST AGGRESSIVE...PUSHING SHOWERS INTO THE AREA AS EARLY AS
SATURDAY NIGHT.  GIVEN OVERALL SLOWING TREND ASSOCIATED WITH
AMPLIFYING UPPER PATTERN AND THE PRESENCE OF AN INITIALLY DRY
AIRMASS...HAVE CUT POPS SATURDAY NIGHT TO FEATURE JUST LOW CHANCES
ACROSS THE WESTERN CWA AFTER MIDNIGHT.  HAVE A FEELING THESE WILL
BE REMOVED BY FUTURE SHIFTS AS WESTERN LOW SLOWS FURTHER.

SURFACE LOW PRESSURE WILL DEVELOP IN THE LEE OF THE ROCKIES ACROSS
EASTERN COLORADO ON SATURDAY...THEN WILL TRACK SLOWLY NORTHEASTWARD
INTO SOUTHERN ONTARIO BY TUESDAY.  AS PARENT UPPER LOW LIFTS
NORTHEASTWARD AND WEAKENS CONSIDERABLY...TRAILING COLD FRONT WILL
DISSIPATE AS IT PUSHES EASTWARD AND WILL NEVER PASS THROUGH CENTRAL
ILLINOIS.  SHOWERS AND THUNDERSTORMS AHEAD OF THIS SYSTEM WILL
BECOME WIDESPREAD ALONG/WEST OF THE MISSISSIPPI RIVER ON
SUNDAY...THEN WILL SHIFT INTO ILLINOIS ON MONDAY.  HAVE CUT BACK
POPS ACCORDINGLY...KEEPING LIKELY CONFINED TO THE WESTERN HALF OF
THE CWA SUNDAY/SUNDAY NIGHT...THEN INTRODUCING LIKELY EVERYWHERE
ON MONDAY. WHILE MUCAPE VALUES INCREASE INTO THE 1000-2000J/KG
RANGE BY MONDAY...0-6KM BULK SHEAR REMAINS RATHER MODEST AT
25-30KT. AS A RESULT...THINK OVERALL SEVERE RISK WILL BE LOW.
MAIN STORY WILL BE THE WARM/HUMID CONDITIONS AND THE POTENTIAL
FOR BOUTS OF LOCALLY HEAVY RAINFALL SUNDAY INTO MONDAY.

MODELS ARE SUGGESTING THAT THE EFFECTIVE BOUNDARY WILL SHIFT EAST OF
ILLINOIS MONDAY NIGHT...WITH THE HIGHEST RAIN CHANCES FOCUSING
FURTHER EAST ACROSS THE OHIO RIVER VALLEY TUESDAY INTO WEDNESDAY.
HAVE THEREFORE REDUCED POPS INTO THE CHANCE CATEGORY...AS A
WARM/SUMMERLIKE REGIME WITH ONLY SCATTERED SHOWERS/THUNDERSTORMS
TAKES HOLD FOR THE MIDDLE AND END OF THE WEEK.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1153 PM CDT THU MAY 21 2015

EXPECT VFR CONDITIONS FOR THE NEXT 24 HOURS AS PREDOMINANT
SUBSIDENCE RESIDES OVER CENTRAL IL WITH HIGH PRESSURE BUILDING
OVER THE AREA. WINDS SW 4-8 KTS THROUGH 10-12Z...THEN LIGHT AND
VARIABLE UNTIL 16Z...THEN BECOMING NE 4-8 KTS AFTER A WEAK DRY
COLD FRONT CROSSES NORTH TO SOUTH ACROSS THE AREA.

&&

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

$$

UPDATE...ONTON
SHORT TERM...BARNES
LONG TERM...BARNES
AVIATION...ONTON



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