Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 201130
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
630 AM CDT MON APR 20 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 313 AM CDT MON APR 20 2015

07Z/2AM WATER VAPOR IMAGERY SHOWS LONG-WAVE TROUGH AXIS EXTENDING
FROM MINNESOTA TO NORTHERN TEXAS, WITH VIGOROUS SHORT-WAVE NOTED ON
ITS EAST SIDE OVER SOUTHEAST MISSOURI.  WITH MAIN WAVE STILL TO THE
WEST, SCATTERED SHOWERS ARE ONGOING ACROSS CENTRAL ILLINOIS EARLY
THIS MORNING.  AS SOUTHEAST MISSOURI WAVE TRACKS INTO THE OHIO RIVER
VALLEY, THINK AREAL COVERAGE OF SHOWERS WILL DIMINISH AFTER SUNRISE,
WITH LITTLE OR NO PRECIP OCCURRING FOR THE BALANCE OF THE MORNING.
DESPITE LOW-LEVEL DRYING IN THE WAKE OF THIS FEATURE, SYNOPTIC-SCALE
CYCLONIC FLOW ALOFT WILL LEAD TO STEEP LAPSE RATES AND PERHAPS A FEW
SHOWERS FROM LATE MORNING INTO THE AFTERNOON.  MOST MODEL GUIDANCE
REMAINS DRY: HOWEVER, BOTH THE HRRR AND 4KM WRF-NMM SUGGEST AT LEAST
ISOLATED SHOWERS AS THE ATMOSPHERE DESTABILIZES.  WILL CARRY SLIGHT
CHANCE POPS ACROSS THE BOARD TO COVER THIS POSSIBILITY.  COLD FRONT
CURRENTLY APPROACHING THE I-55 CORRIDOR WILL SWEEP EASTWARD THIS
MORNING AND EXIT INTO INDIANA BY MIDDAY.  STRONG/GUSTY WINDS WILL
DEVELOP BEHIND THE FRONT AS PRESSURE GRADIENT TIGHTENS.  LATEST OBS
ARE ALREADY SHOWING GUSTS IN THE 25 TO 30MPH RANGE AND THINK MIXING
OF HIGHER MOMENTUM AIR ALOFT WILL RESULT IN GUSTS OF 30 TO 35MPH
DURING THE DAY.  HIGH TEMPERATURES WILL BE IN THE UPPER 50S AND
LOWER 60S.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 313 AM CDT MON APR 20 2015

A COOL AND MOSTLY DRY WEEK IS ON TAP ACROSS CENTRAL ILLINOIS, WITH
THE NEXT SIGNIFICANT CHANCE FOR RAIN LIKELY HOLDING OFF UNTIL NEXT
WEEKEND.  A DEEP UPPER LOW OVER THE GREAT LAKES WILL BE THE DOMINANT
WEATHER FEATURE EARLY IN THE PERIOD, KEEPING THE MIDWEST LOCKED IN A
NORTHWESTERLY FLOW PATTERN.  THANKS TO A TIGHTENING PRESSURE
GRADIENT AHEAD OF AN APPROACHING COLD FRONT, STRONG WESTERLY WINDS
WILL ONCE AGAIN DEVELOP ON TUESDAY.  NUMERIC GUIDANCE AND FORECAST
SOUNDINGS BOTH SUGGEST GUSTS REACHING 30 TO 35MPH AT TIMES.  THE
FRONT WILL PASS THROUGH THE AREA TUESDAY NIGHT INTO WEDNESDAY
MORNING: HOWEVER, DEEP-LAYER MOISTURE WILL BE LACKING, SO PRECIP
CHANCES WILL REMAIN NEGLIGIBLE.  WILL ONLY CARRY LOW CHANCE POPS
ACROSS THE SOUTHERN KILX CWA AS THE FRONT PASSES.  AN EVEN COOLER
AIRMASS WILL ARRIVE FOR THE MIDDLE AND END OF THE WEEK BEHIND THE
DEPARTING FRONT, WITH HIGHS DROPPING INTO THE UPPER 50S/LOWER 60S
FOR WEDNESDAY THROUGH FRIDAY.  OVERNIGHT LOWS WILL DIP INTO THE 30S,
WITH THE BEST POTENTIAL FOR FROST LIKELY SETTING UP FOR WEDNESDAY
NIGHT AND THURSDAY NIGHT AS SKIES REMAIN CLEAR AND WINDS DIMINISH.

FURTHER OUT, MAJOR MODEL DISCREPANCIES HAVE DEVELOPED CONCERNING THE
NEXT POTENTIAL SYSTEM FOR THE END OF THE WEEK.  THE 00Z APR 20 GFS
HAS MADE A MAJOR SHIFT FROM ITS PREVIOUS RUNS AND NOW SHOWS RAIN
SPREADING INTO CENTRAL ILLINOIS FROM AN APPROACHING UPPER LOW AS
EARLY AS FRIDAY.  MEANWHILE, BOTH THE ECMWF AND GEM ARE MUCH SLOWER,
WITH RAIN NOT ARRIVING UNTIL LATE FRIDAY NIGHT INTO SATURDAY.  GIVEN
INITIAL PRESENCE OF A STRONG RIDGE AXIS ACROSS THE MIDWEST, THINK
THE RAPID PROGRESSION OF RAIN INTO THE DRY AIRMASS SEEMS SUSPECT.
IN ADDITION, THE SLOWER ECMWF/GEM HAVE MAINTAINED GOOD CONSISTENCY
WITH THEIR EARLIER RUNS.  AS A RESULT, HAVE REJECTED THE GFS IN
FAVOR OF THE ECMWF/GEM CONSENSUS FOR THE END OF THE WEEK.  HAVE
THEREFORE KEPT FRIDAY DRY, THEN HAVE INTRODUCED POPS MAINLY ACROSS
THE CENTRAL AND SOUTHERN CWA FRIDAY NIGHT INTO SATURDAY.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 630 AM CDT MON APR 20 2015

CLOUDS OVER THE TAF SITES ARE AT MVFR LEVELS, EXCEPT FOR BMI THAT
IS AT IFR RIGHT NOW. BELIEVE THAT BMI WILL IMPROVE TO LOWER MVFR
SOON, BUT STILL HAVE A TEMPO GROUP FOR A COUPLE HOURS TO COVER.
MVFR CIGS WILL CONTINUE THIS MORNING. SATELLITE TRENDS SHOW
CLEARING TO THE WEST OF SPI, BUT BELIEVE ONCE SUN GETS LITTLE
HIGHER, CU/SC WILL DEVELOP QUICKLY, KEEPING CLOUDS OVER SPI LATE
THIS MORNING. HIRES MODELS CONTINUE TO SHOW SCATTERED SHOWERS
DEVELOPING TO THE WEST AND MOVING INTO THE AREA. AGREE WITH THIS
FORECAST SO HAVE INCLUDED VCSH AT ALL TAF SITES FOR THIS
AFTERNOON. CLOUDS AND PCPN WILL BE DIURNAL, SO SKIES SHOULD CLEAR
JUST AFTER SUNSET. BIGGEST ISSUE WILL BE THE GUSTY WEST WINDS.
WILL HAVE GUSTS TO 25-28KTS THIS MORNING, BUT THEN INCREASE TO
30KTS FOR THIS AFTERNOON. WINDS WILL DIMINISH THIS EVENING.

&&

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

$$

SHORT TERM...BARNES
LONG TERM...BARNES
AVIATION...AUTEN



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