Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 041758
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1258 PM CDT MON MAY 4 2015

.UPDATE...
ISSUED AT 1045 AM CDT MON MAY 4 2015

15Z/10AM SURFACE ANALYSIS SHOWS STATIONARY FRONTAL BOUNDARY
EXTENDING FROM SOUTHERN LAKE MICHIGAN TO KANSAS. WIDELY SCATTERED
SHOWERS ARE CURRENTLY ONGOING NEAR AND JUST SOUTH OF THE FRONT
ACROSS MUCH CENTRAL ILLINOIS...ALTHOUGH AREAL COVERAGE OF PRECIP
HAS BEEN DIMINISHING OVER THE PAST COUPLE OF HOURS. 12Z NAM
SUGGESTS THE GREATEST INSTABILITY AND STRONGEST LOW-LEVEL WIND
SHEAR WILL OVERLAP NEAR AN AREA OF LOW PRESSURE ALONG THE BOUNDARY
FROM SOUTHERN IOWA SOUTHWESTWARD INTO KANSAS LATER THIS AFTERNOON.
THINK THIS WILL BE THE PRIMARY AREA WHERE WIDESPREAD CONVECTION
WILL DEVELOP...WITH ONLY SCATTERED SHOWERS/STORMS FURTHER EAST
ACROSS ILLINOIS WHERE INSTABILITY/SHEAR WILL BE WEAKER. HRRR SHOWS
THIS TREND AS WELL...WITH CONVECTION DEVELOPING/SPREADING EASTWARD
ACROSS THE NORTHERN HALF OF THE KILX CWA AFTER SUNSET. HAVE MADE
SOME MINOR ADJUSTMENTS TO THE FORECAST...MAINLY TO FEATURE
SCATTERED POPS ALONG/NORTH OF I-72 TODAY AND ONLY ISOLATED FURTHER
SOUTH. BETTER RAIN CHANCES WILL ARRIVE TONIGHT. WITH SOME PARTIAL
SUNSHINE...AFTERNOON HIGH TEMPERATURES WILL RISE INTO THE UPPER
70S AND LOWER 80S.

&&

.SHORT TERM...(TODAY)
ISSUED AT 342 AM CDT MON MAY 4 2015

OUTFLOW BOUNDARY FROM CONVECTION THAT DEVELOPED AHEAD OF A FRONTAL
BOUNDARY EXTENDING THROUGH THE GREAT LAKES AND INTO THE CENTRAL
PLAINS HAS MOVED INTO PORTIONS OF THE CENTRAL IL FORECAST
AREA...EXTENDING FROM NEAR PEORIA TO PONTIAC. BOUNDARY CONTINUES TO
TRIGGER SCATTERED THUNDERSTORMS BEHIND IT...WHILE AHEAD LIGHT
SHOWERS ARE WIDELY SCATTERED ACROSS CENTRAL IL. MID-LEVEL
INSTABILITY ACROSS THE REGION WILL CAUSE SHOWERS AND THUNDERSTORMS
TO CONTINUE TO DEVELOP ACROSS MUCH OF CENTRAL IL MAINLY FROM I-70
NORTHWARD THROUGH MORNING. A POSSIBLE LULL IN PRECIPITATION
INDICATED BY MODEL FORECASTS LATE MORNING AS CURRENT AREA OF
CONVECTION SHIFTS NORTHEASTWARD AND RE-DEVELOPMENT OF CONVECTION
TAKES PLACE ALONG THE APPROACHING FRONTAL BOUNDARY FOR THE
AFTERNOON. SPC CONTINUES TO ADVERTISE A MARGINAL RISK FOR SEVERE
STORMS CONTAINING HAIL/STRONG WIND GUSTS THIS AFTERNOON/EVENING
THROUGH MUCH OF CENTRAL AND NORTHERN IL NEAR THE FRONTAL BOUNDARY
WHERE AT LEAST SOME OVERLAP OF MODERATE BULK SHEAR MAY COMBINE WITH
1000-2000 J CAPE. HIGH TEMPERATURES QUITE WARM AGAIN TODAY...UPPER
70S TO LOW 80S...WITH BREEZY SW WINDS 10-15 MPH.

.LONG TERM...(TONIGHT THROUGH SUNDAY)
ISSUED AT 342 AM CDT MON MAY 4 2015

SOME CONVECTION SETTLING INTO THE MIDWEST THIS MORNING ALONG AND
AHEAD OF THE BOUNDARY JUST TO THE NORTHWEST. SAME BOUNDARY PROVIDING
THE FOCUS FOR SHOWERS TODAY WILL KEEP THE THREAT FOR SOME SHOWERS
AND THUNDERSTORMS THROUGH THE OVERNIGHT IN THE NORTHERN HALF OF THE
STATE.  EXACT LOCATION OF THE STALLED BOUNDARY VARIES A BIT FROM
MODEL TO MODEL.  SMALL WAVES MOVING ALONG THE BOUNDARY WILL KEEP
PRECIP CHANCES IN THE NORTHERN TIER OF THE STATE THROUGH TUESDAY.
HIGH PRESSURE SLOWLY BUILDING IN WITH SOME SOUTHERLY WINDS PUSHING
THE FRONT BACK TO THE NORTH AND OUT OF THE FORECAST AREA FOR TUESDAY
NIGHT THROUGH WED NIGHT. PRECIP CHANCES SLOWLY EDGING BACK INTO
CENTRAL ILLINOIS AS AN UPPER LEVEL WAVE PUSHES OUT OF THE SW.  THE
ENERGY IS PART OF A GENERAL PATTERN SHIFT TO MORE SOUTHWESTERLY FLOW
WITH THE UPPER LEVEL TROF DIGGING BACK IN OVER THE SWRN CONUS.  THE
SFC LOW WITH THAT STORM MOVES OUT INTO THE UPPER MIDWEST AND INTO
CANADA BY THE END OF THE WEEK, BUT IN SHIFTING TO MORE SOUTHWESTERLY
FLOW ALOFT, OPENS THE DOOR TO A SERIES OF SHORTWAVES THAT KEEP THE
FORECAST WET FOR THE END OF THE WORK WEEK AND INTO THE WEEKEND.
TEMPS RATHER WARM THROUGH THE FORECAST WITH OVERCAST AND RAINY SKIES
KEEPING THE OVERNIGHT LOWS UP A BIT, BUT LIKELY NOT NEARLY AS WARM
AS THE TREND IN THE GUIDANCE.  HAVE KNOCKED THEM DOWN A COUPLE
DEGREES. SOUTHERLY FLOW AND A RELATIVELY WARM AIRMASS KEEPING THE
HIGHS A BIT ABOVE NORMS.  HOWEVER, WITH THE LIFTING OF THE DEEP TROF
OVER THE SW INTO THE GREAT LAKES, THE WARMER AIRMASS IS SHUNTED OFF
TO THE EAST AND COOLER AIR MOVES INTO THE MIDWEST AT LEAST BRIEFLY
AT THE END OF THE FORECAST PD.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 1258 PM CDT MON MAY 4 2015

MODELS CONTINUE TO SHOW FRONTAL BOUNDARY CURRENTLY ACROSS NORTHERN
ILLINOIS DROPPING SLOWLY SOUTHWARD INTO THE AREA TONIGHT. SHOWERS
AND THUNDERSTORMS WILL DEVELOP ALONG/NEAR THIS BOUNDARY AFTER
01/02Z...WITH THE LONGEST PERIOD OF RAIN EXPECTED AT THE NORTHERN
TERMINALS OF KPIA AND KBMI. WILL CARRY PREDOMINANT SHOWERS AT
THESE SITES THROUGHOUT THE NIGHT. BIG QUESTION WILL BE WHETHER OR
NOT CEILINGS WILL LOWER INTO THE MVFR CATEGORY NORTH OF THE FRONT.
NAM FORECAST SOUNDINGS CONTINUE TO SHOW VFR CEILINGS EVEN AT
KPIA/KBMI WHERE WINDS BECOME E/NE LATER THIS EVENING, WHILE THE
HRRR HINTS AT LOWER CEILINGS AROUND 2500FT. LATEST REGIONAL OBS
SHOW A FEW MVFR CEILINGS NORTH OF THE FRONT ACROSS CENTRAL IOWA,
SO DO NOT WANT TO COMPLETELY IGNORE THE POSSIBILITY. HAVE
THEREFORE INCLUDED SCT025 AT BOTH KPIA AND KBMI AFTER 04Z AND WILL
CONTINUE TO MONITOR LATER OBS AND MODEL RUNS TO MAKE A FINAL
DETERMINATION. ALL MODELS SHOW THE BOUNDARY SHIFTING BACK
NORTHWARD TUESDAY MORNING, RESULTING IN DIMINISHING RAIN CHANCES
AND WINDS RETURNING TO THE S/SE.


&&

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

$$

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


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