Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 300417
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1117 PM CDT FRI MAY 29 2015

.UPDATE...
ISSUED AT 830 PM CDT FRI MAY 29 2015

SHOWERS CONTINUE TO SLOWLY DISSIPATE OVER EAST AND SOUTHEAST IL
WHILE A BAND OF SHOWERS AND ISOLATED THUNDERSTORMS TRACKS
NORTHEAST OUT OF CENTRAL MISSOURI THIS EVENING AHEAD OF AN UPPER
LEVEL SHORTWAVE OVER SOUTHERN MO. THIS WILL BRING ANOTHER ROUND
OF SHOWERS AND THUNDERSTORMS TO THE FORECAST AREA OVERNIGHT...
STARTING OUT WEST AND GRADUALLY EDGING TO THE EAST DURING THE
EARLY MORNING HOURS. WE SHOULD SEE COVERAGE INCREASE LATE
TONIGHT AS MOST MODELS INDICATE SOME IMPRESSIVE 850 MB THETA-E
ADVECTION ACCOMPANIED BY A 35-45 KT LOW LEVEL JET FEEDING IN
UNSEASONABLY HIGH PRECIPITABLE WATER VALUES INTO THE REGION.
GREATEST 850 MB SPEED CONVERGENCE OVER WESTERN IL THRU 06Z
AND THEN SPREADS EAST OVERNIGHT WITH THE HIGHER THREAT FOR
SOME HEAVY RAINFALL OVER WEST CENTRAL THRU OUR NORTHERN
COUNTIES. WONDER WHAT AFFECT...IF ANY...THE LARGER COMPLEX
OF SEVERE STORMS OVER OKLAHOMA INTO ARKANSAS WILL HAVE ON
OUR MOISTURE FEED NORTHWARD TONIGHT.

HAVE MADE SOME ADJUSTMENTS TO THE HOURLY TEMP GRIDS THANKS TO
THE SCATTERED RAINFALL AND OUTFLOW BOUNDARIES...AS WELL AS SOME
TWEAKING TO THE POPS FOR THE OVERNIGHT HOURS ACROSS THE EAST.
SHOULD HAVE THE UPDATE OUT BY 900 PM.

&&

.SHORT TERM...(TONIGHT)
ISSUED AT 257 PM CDT FRI MAY 29 2015

DESPITE A MODERATELY UNSTABLE AIRMASS CHARACTERIZED BY SBCAPES OF
AROUND 2000J/KG...19Z/2PM RADAR IMAGERY SHOWS VERY LITTLE CONVECTION
ACROSS CENTRAL ILLINOIS.  VERY WEAK WIND SHEAR AND AN OVERALL LACK
OF SIGNIFICANT FORCING APPEARS TO BE KEEPING THE STORMS AT BAY THIS
AFTERNOON.  CLUSTERS OF CONVECTION ARE DEVELOPING FURTHER SOUTH FROM
JUST EAST OF SAINT LOUIS INTO THE OZARKS.  THIS ACTIVITY WILL SLOWLY
LIFT NORTHEASTWARD AND IMPACT PORTIONS OF THE KILX CWA LATE THIS
AFTERNOON...MAINLY ALONG AND SOUTH OF A DANVILLE TO SHELBYVILLE
LINE.  OVERALL AREAL COVERAGE WILL REMAIN RELATIVELY LOW...SO WILL
ONLY GO WITH CHANCE POPS THROUGH EARLY EVENING.  RAIN CHANCES WILL
BEGIN TO INCREASE TONIGHT AS STRONGER FORCING ASSOCIATED WITH A
SHORT-WAVE TROUGH OVER OKLAHOMA/EAST TEXAS APPROACHES FROM THE
SOUTHWEST.  MODELS ARE ALL OVER THE PLACE...HOWEVER CONSENSUS OF
HIGH-RES SOLUTIONS FOCUSES HIGHEST POPS ACROSS THE WESTERN HALF OF
THE CWA FROM MID-EVENING THROUGH THE OVERNIGHT HOURS.  BAND OF
PRECIP WILL GRADUALLY SPREAD INTO EAST-CENTRAL ILLINOIS TOWARD DAWN
SATURDAY...AS A COLD FRONT APPROACHES FROM THE WEST.

.LONG TERM...(SATURDAY THROUGH FRIDAY)
ISSUED AT 257 PM CDT FRI MAY 29 2015

MODELS GENERALLY SHOW A COLD FRONT REACHING AROUND I-55 BY MID
MORNING SATURDAY...REACHING SOUTHEASTERN ILLINOIS BY SATURDAY
EVENING AND EXITING THE CENTRAL IL FORECAST AREA. AHEAD OF THE
FRONT...MODEST SFC-6KM BULK SHEAR OF GENERALLY 20 KTS WILL
PREVAIL...INCREASING TO AROUND 30 KTS NEAR THE FRONT. INSTABILITY
GENERALLY AROUND 1500-2500 J/KG ARE INDICATED AHEAD OF THE
FRONT...DEPENDING ON SURFACE HEATING. THESE INGREDIENTS WILL COME
TOGETHER...ALONG WITH AN UPPER LEVEL SHORTWAVE...DURING THE DAY
SATURDAY FOR SCATTERED SHOWERS AND THUNDERSTORMS ESPECIALLY FROM
AROUND THE ILLINOIS RIVER SOUTHEASTWARD. THUNDERSTORM ACTIVITY WILL
SHIFT FARTHER SOUTHEASTWARD THROUGH THE DAY AND EVENING AS THE FRONT
SLIPS SOUTHEASTWARD. A MARGINAL THREAT FOR SEVERE THUNDERSTORMS IS
FORECAST BY SPC WITH THE MAIN THREAT BEING SEVERE WIND GUSTS. WITH
THE FRONTAL BOUNDARY LINGERING NEAR THE SOUTHERN TIP OF ILLINOIS
SUNDAY MORNING...AT LEAST A SLIGHT CHANCE OF THUNDERSTORMS WILL
REMAIN THROUGH SUNDAY SOUTH OF I-70 AS ANOTHER UPPER LEVEL WAVE
PASSES THROUGH THE AREA. TEMPERATURES WILL DROP OFF SUBSTANTIALLY
FOR SATURDAY AND SUNDAY. HIGHS AROUND 67 NEAR GALESBURG TO AROUND 80
JUST SOUTH OF I-70 SATURDAY...THEN MID TO UPPER 60S ACROSS THE AREA
SUNDAY. SOME LOWS NORTH OF I-72 SHOULD REACH INTO THE 40S SATURDAY
AND SUNDAY NIGHT.

A BUILDING HIGH PRESSURE RIDGE SHOULD  BRING SUBSIDENCE AND DRY
CONDITIONS THROUGH THE EARLY PART OF NEXT WORK WEEK. BY MID TO LATE
WEEK...A CUT-OFF UPPER LOW OVER THE GULF COAST COULD HELP TRANSPORT
A RETURN OF MOIST/UNSTABLE CONDITIONS TO THE MIDWEST...WITH
PRECIPITABLE WATER VALUES AROUND 1.5-1.75 INCHES POSSIBLE. MODELS
CONTINUE TO DISAGREE ON THE POSITION OF THE RIDGE/CUT-OFF...AND THIS
WILL IMPACT THE MOISTURE RETURN. ALTHOUGH A STRONG LIFTING MECHANISM
ISNT EXPECTED AT THIS TIME...DAILY CHANCES FOR THUNDERSTORMS WILL BE
POSSIBLE MAINLY DRIVEN BY DAYTIME HEATING AND CONVECTIVE
OUTFLOWS...PERHAPS AN MCS OVER THE UPPER MIDWEST. EXPECT A GRADUAL
WARMING TREND THROUGH THE WEEK WITH HIGHS IN THE LOW 70S MONDAY
REACHING THE MID 80S FOR THURSDAY AND FRIDAY.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1105 PM CDT FRI MAY 29 2015

NEXT WEATHER SYSTEM ALREADY STARTING TO MOVE INTO FAR WEST CENTRAL
ILLINOIS LATE TONIGHT AND WILL CONTINUE TO PUSH NORTH-NORTHEAST
INTO THE FORECAST AREA DURING THE EARLY MORNING HOURS. VFR CIGS
ARE EXPECTED TO GRADUALLY DETERIORATE TO MVFR WITH SOME LOCAL
IFR CIGS IN THE HEAVIER SHOWERS THAT WILL PUSH ACROSS THE WEST
AND NORTHERN AREAS LATE TONIGHT AND THRU A GOOD PORTION OF SAT.
BASED ON SOUNDING DATA...IT APPEARS SPI AND PIA WILL BE THE
FIRST TO GO TO MVFR CIGS IN THE RAIN AND ISOLD TSRA LATE
TONIGHT...ROUGHLY IN THE 08Z-11Z TIME FRAME...WITH ONLY A SLOW
SHIFT EAST DURING THE MORNING WITH CMI NOT SEEING THE LOWER
CIGS UNTIL AROUND 15 0R 16Z. VSBYS IN SOME OF THE HEAVIER
SHOWERS WILL DROP TO 1-2 MILES BUT TIMING OF THAT OCCURRENCE
HARD TO PINPOINT FROM THIS FAR OUT SO WILL LOWER TO 3-4 MILES
FOR NOW.

A COLD FRONT WILL SHIFT SOUTHEAST ACROSS THE AREA ON SATURDAY
AS LOW PRESSURE DRIFTS OVER SOUTH CENTRAL ILLINOIS LATE TOMORROW
MORNING INTO THE AFTERNOON HOURS. MOST MODELS DEPICTING THIS
NOW...SO FEEL MORE CONFIDENT ON THE WIND SHIFTS MOST AREA STARTING
AROUND 12-15Z AT PIA BUT NOT GETTING OVER TO CMI UNTIL AFTER 20Z.
LIGHT SOUTH TO SOUTHWEST WINDS TONIGHT INTO SATURDAY MORNING WILL
SHIFT INTO THE NORTH TO NORTHEAST ACROSS PIA IN THE MORNING AND
BMI IN THE EARLY AFTERNOON HOURS...WITH WINDS GOING MORE INTO
THE WEST TO NORTHWEST FOR OUR TAF SITES FURTHER SOUTH WITH CMI
SEEING THE WIND SHIFT IN THE 19-22Z TIME FRAME. ONCE THE FRONT
SHIFTS SOUTHEAST OF THE AREA LATE TOMORROW...LOOK FOR NORTH
TO NORTHEAST WINDS OF 15 TO 20 KTS...WITH SOME HIGHER GUSTS
POSSIBLE...ESPECIALLY EARLY IN THE EVENING.

LATEST SATELLITE DATA AND SURFACE OBSERVATIONS CONTINUE TO SHOW A
LARGE AREA OF MVFR AND IFR CIGS BEHIND THE COLD FRONT SO ONCE THAT
COLDER AIR STARTS TO FILTER IN LATE TOMORROW...IT APPEARS WE WILL
SEE A PERIOD OF LOW CIGS THRU AT LEAST THE EVENING HOURS OF SAT.

&&

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

$$

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



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