Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 070206
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
906 PM CDT WED MAY 6 2015

.UPDATE...
ISSUED AT 906 PM CDT WED MAY 6 2015

SURFACE DEWPOINTS HAVE STARTED TO INCREASE AGAIN, AFTER BEING
THOROUGHLY MIXED OUT THIS AFTERNOON. CWA WILL REMAIN IN SOUTHERLY
SURFACE FLOW OVERNIGHT AS THE WARM FRONT HAS LIFTED WELL NORTH OF
THE STATE AND ANY FRONTAL ACTIVITY REMAINS WELL WEST OF THE AREA.
SKIES HAVE BECOME PARTLY CLOUDY TO MOSTLY CLEAR AND THIS WILL
CONTINUE OVERNIGHT. CURRENT FORECAST LOOKS ON TRACK EXCEPT WILL
LIKELY MAKE SOME TWEAKS TO THE CLOUD COVER GRIDS. SINCE MINOR
CHANGES TO SKY COVER EXPECTED, WILL NOT BE SENDING AN UPDATE THIS
EVENING.

&&

.SHORT TERM...(TONIGHT)
ISSUED AT 326 PM CDT WED MAY 6 2015

18Z/1PM VISIBLE SATELLITE IMAGERY SHOWS AN EXTENSIVE CU-FIELD ACROSS
THE REGION. TWO AREAS OF MORE ROBUST DEVELOPMENT ARE NOTED...ONE
FROM JUST WEST OF SAINT LOUIS SOUTHWARD INTO THE OZARKS AND ANOTHER
FURTHER EAST ACROSS KENTUCKY INTO SOUTH-CENTRAL INDIANA. THE RAPID
REFRESH IS SUGGESTING WIDELY SCATTERED CONVECTION WILL DEVELOP
ACROSS BOTH THESE AREAS OVER THE NEXT COUPLE OF HOURS. WILL NEED TO
KEEP A PARTICULARLY CLOSE EYE ON THE MISSOURI CONVECTION AS IT
DRIFTS NORTHWARD AND COMES CLOSE TO THE FAR WESTERN KILX CWA LATE
THIS AFTERNOON INTO THE EARLY EVENING. WITH ALL MODEL GUIDANCE
KEEPING SHOWERS JUST WEST OF THE AREA, WILL MAINTAIN A DRY FORECAST
ACROSS THE BOARD. WHILE AFTERNOON CU WILL RAPIDLY DISSIPATE BY
SUNSET, BAND OF MID-LEVEL CLOUDS ASSOCIATED WITH A SHORT-WAVE TROUGH
OVER THE PLAINS WILL ROTATE N/NE INTO WEST-CENTRAL ILLINOIS LATER
THIS EVENING. NAM FORECAST SOUNDINGS INDICATE THESE CLOUDS WILL
SPILL INTO AREAS ALONG/WEST OF I-55 BY MID-EVENING BEFORE
DISSIPATING OVERNIGHT. WILL THEREFORE GO WITH A PARTLY CLOUDY
FORECAST ACROSS THE WESTERN HALF OF THE CWA...WITH MOSTLY CLEAR
SKIES EAST. OVERNIGHT LOWS WILL GENERALLY BE IN THE LOWER TO MIDDLE
60S...BUT WILL DROP INTO THE UPPER 50S SOUTH OF I-70 WHERE AIRMASS
IS SLIGHTLY DRIER.

.LONG TERM...(THURSDAY THROUGH WEDNESDAY)
ISSUED AT 326 PM CDT WED MAY 6 2015

THE SHORT AND MEDIUM RANGE MODELS ARE IN FAIRLY GOOD AGREEMENT
INDICATING AND EXTENDED PERIOD OF SHOWERS AND THUNDERSTORMS ACROSS
CENTRAL AND EASTERN ILLINOIS FROM LATE THURSDAY NIGHT THROUGH THE
WEEKEND AND INTO MONDAY. PLENTY OF WARM AND RELATIVELY UNSTABLE AIR
FEEDING INTO THE REGION WILL BE IN PLACE AS THE MAIN DYNAMICS BEGIN
TO APPROACH LATE THURSDAY. THE GFS AND EUROPEAN ARE A BIT QUICKER
AND FARTHER EAST THAN THE NAM WITH THE SURFACE FRONT. VEERING UPPER
LEVEL FLOW AND COLD POOLS FROM CONVECTION NEAR THE FRONT SHOULD HELP
IT MOVE CLOSER TO THE MS VALLEY BY DAYBREAK FRIDAY, PROVIDING A
FOCUS FOR WEST CENTRAL IL. WEAK SHORTWAVE TROUGHS LIFTING TO THE
NORTHEAST INTO WESTERN IL SHOULD ALSO PROVIDE ENOUGH LIFT TO GET T-
STORMS GOING LATE THURSDAY NIGHT-EARLY FRIDAY MORNING.

THE BIGGEST QUESTION FOR FRIDAY AND SATURDAY IS HOW FAR WILL THE
FRONTAL BOUNDARY SINK INTO CENTRAL IL. THE MODELS TYPICALLY HAVE A
HARD TIME WITH THIS DURING THE CONVECTIVE SEASON BECAUSE OF THE
INTERACTIONS WITH CONVECTIVE OUTFLOWS/COLD POOLS AND LOW LEVEL
SOUTHERLY INFLOW. THE GFS HAS A HARD TIME PUSHING THE FRONT SOUTH OF
I-74 THROUGH SATURDAY, WHILE THE EUROPEAN TRIES TO SINK IT TOWARD I-
72. DUE TO THE UNCERTAINTY WILL STICK WITH PERSISTENCE AND MODEL
BLENDS AND KEEP THE HIGHEST POPS ON FRIDAY IN CENTRAL IL, AND IN A
LARGE PART OF CENTRAL AND SE IL FOR SATURDAY. MODERATE LEVELS OF
INSTABILITY BUT GENERALLY WEAK SHEAR SHOULD RESULT IN ONLY A FEW
STRONG STORMS FRIDAY IN WEST CENTRAL IL AND POSSIBLY AREAS SOUTH OF
I-72 ON SATURDAY.

AN UPPER LEVEL TROUGH LIFTING FROM THE FOUR CORNERS AREA OF THE
SOUTHWESTERN U.S. TO THE NORTHERN PLAINS BY SUNDAY WILL RESULT IN A
STRENGTHENING AREA OF LOW PRESSURE IN NEBRASKA, WHICH WILL INCREASE
THE SOUTHERLY FLOW IN OUR REGION. THIS SHOULD PUT THE ENTIRE
FORECAST AREA IN THE WARM SECTOR FOR SUNDAY. TEMPERATURES COULD BE
TEMPERED BY CLOUDS AND SCATTERED CONVECTION, BUT ANY BREAKS IN THE
SKY COVER COULD CAUSE TEMPERATURES TO SHOOT UP TOWARD THE LOWER 80S.
STUCK WITH SCATTERED T-STORMS/CHANCE POPS FOR SUNDAY IN THE WARM
SECTOR. LATER IN THE DAY WHEN THE FRONT TO THE WEST APPROACHES
WESTERN IL, WILL GO BACK TO LIKELY POPS - ESPECIALLY FOR THE IL
RIVER VALLEY WHERE INSTABILITY AND DEEP LAYER SHEAR COULD RESULT IN
SEVERE STORMS. EXPECT THE FRONT TO PASS THROUGH ON MONDAY. HOWEVER,
IF THE BOUNDARY SLOWS DOWN, MUCH OF CENTRAL AND EASTERN IL COULD BE
IN FOR ANOTHER ROUND OF STRONG TO SEVERE STORMS.

NOT BE OVERLOOKED IS THE ANTICIPATED RAINFALL WITH THESE STORMS.
SHOULD SEE WIDESPREAD 1.00 TO 2.00 INCH AMOUNTS...WITH LOCALLY
HEAVIER TOTALS...DUE TO NUMEROUS ROUNDS OF T-STORMS FROM FRIDAY INTO
MONDAY.

AFTER THE FRONTAL PASSAGE, A RETURN TO COOLER THAN NORMAL
TEMPERATURES AND DRIER AIR IS ANTICIPATED FROM TUESDAY THROUGH
MIDWEEK.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z THURSDAY EVENING)
ISSUED AT 605 PM CDT WED MAY 6 2015

GUSTY SOUTHERLY WINDS WILL SUBSIDE UNDER 10 KTS AND BACK TO THE
SOUTHEAST WITH SUNSET. THE LEADING EDGE OF A SHORTWAVE OVER THE
PLAINS, WILL SPREAD SOME BROKEN TO SCATTERED MID CLOUDS ACROSS THE
TERMINALS THIS EVENING. OTHERWISE SKIES WILL BE MOSTLY CLEAR FOR
THURSDAY. BRISK SOUTH WINDS WILL ONCE AGAIN DEVELOP AFTER SUNRISE,
AND GUST OVER 20 KTS FROM LATE MORNING THROUGH THE AFTERNOON.


&&

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

$$

UPDATE...AUTEN
SHORT TERM...BARNES
LONG TERM...MILLER
AVIATION...25


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