Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 310817
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
317 AM CDT MON AUG 31 2015

.SHORT TERM...(TODAY)
ISSUED AT 317 AM CDT MON AUG 31 2015

08Z/3AM SURFACE ANALYSIS SHOWS DISSIPATING FRONTAL BOUNDARY
EXTENDING FROM NORTHERN INDIANA INTO CENTRAL ILLINOIS...GENERALLY
ALONG A FORT WAYNE TO QUINCY LINE.  AS WAS THE CASE LAST
NIGHT...QUITE A BIT OF FOG IS DEVELOPING ALONG/NORTH OF THE BOUNDARY
WHERE WINDS ARE NEARLY CALM AND LOW-LEVEL MOISTURE IS ABUNDANT.
LATEST OBS SHOW LOWEST VISBYS CONCENTRATED ALONG THE SOUTHERN SHORE
OF LAKE MICHIGAN ACROSS NORTHERN INDIANA INTO THE CHICAGO AREA.
HRRR HAS BEEN CONSISTENTLY SPREADING THIS THICKER FOG W/SW ALONG THE
FRONT INTO THE NORTHERN KILX CWA OVER THE NEXT COUPLE HOURS...AND AM
BEGINNING TO SEE THIS UNFOLDING WITH VISBY NOW DOWN TO 1/4SM AS FAR
SW AS KIKK.  FOLLOWING THE HRRR TREND...WILL MENTION AREAS OF DENSE
FOG ALONG/NORTHEAST OF A GALESBURG TO BLOOMINGTON-NORMAL LINE EARLY
THIS MORNING...WITH PATCHY/AREAS OF FOG ELSEWHERE AROUND THE AREA.

HIGH-RES MODELS SUCH AS THE HRRR AND RAPID REFRESH ARE SUGGESTING
THAT ISOLATED CONVECTION MAY DEVELOP ACROSS SOUTHEAST ILLINOIS OVER
THE NEXT COUPLE OF HOURS.  LATEST RADAR IMAGERY IS CLEAR...HOWEVER
SCATTERED MID-LEVEL CLOUDS ARE BEGINNING TO DEVELOP ON IR SATELLITE
IMAGERY ALONG/SOUTH OF I-70...SO HAVE OPTED TO CARRY SLIGHT CHANCE
POPS HERE EARLY THIS MORNING.  LATEST WATER VAPOR IMAGERY SHOWS A
SMALL BUT VIGOROUS SHORT-WAVE DROPPING SOUTHWESTWARD FROM NORTHEAST
INDIANA.  THIS FEATURE WILL LIKELY INTERACT WITH THE DECAYING FRONT
TO TRIGGER ISOLATED CONVECTION FURTHER NORTH INTO THE CWA THIS
AFTERNOON.  MOST MODELS ARE HINTING AT LEAST SOME QPF ACROSS THE
SOUTHERN TWO-THIRDS OF THE AREA...SO HAVE ADDED SLIGHT CHANCE POPS
ALONG/SOUTH OF A JACKSONVILLE TO BLOOMINGTON-NORMAL LINE FOR THE
AFTERNOON.

&&

.LONG TERM...(TONIGHT THROUGH SUNDAY)
ISSUED AT 317 AM CDT MON AUG 31 2015

MAIN WEATHER STORY THROUGH THE EXTENDED WILL BE THE VERY WARM AND
HUMID CONDITIONS THAT ARE EXPECTED TO PERSIST THROUGH EARLY NEXT
WEEK.  HIGH TEMPERATURES ON TUESDAY WILL REACH THE UPPER 80S TO
AROUND 90 DEGREES...THEN READINGS WILL CLIMB INTO THE LOWER 90S FOR
THE REMAINDER OF THE PERIOD.  DRY WEATHER WILL GENERALLY BE THE
RULE...HOWEVER ISOLATED CONVECTION CANNOT BE RULED OUT...ESPECIALLY
TUESDAY AFTERNOON AS A WEAKNESS IN THE MEAN 500MB RIDGE AXIS REMAINS
IN THE VICINITY.  MODELS ARE HINTING AT SOME QPF ACROSS THE E/NE CWA
AS THIS FEATURE GRADUALLY SHIFTS INTO THE GREAT LAKES BY WEDNESDAY.

THE NEXT SIGNIFICANT CHANCE FOR RAIN WILL NOT ARRIVE UNTIL EARLY
NEXT WEEK...WHEN A STRONG SHORT-WAVE FLATTENS THE UPPER RIDGE AND
PUSHES A COLD FRONT INTO THE REGION.  MODELS ARE IN DISAGREEMENT
CONCERNING THE SPEED OF THIS PROCESS...WITH THE GFS BEING ABOUT 24
HOURS FASTER THAN THE ECMWF/GEM.  THE 00Z AUG 31 GFS SHOWS THE COLD
FRONT PASSING THROUGH CENTRAL ILLINOIS LATE SUNDAY NIGHT INTO
MONDAY...WHILE THE ECMWF/GEM HAVE DELAYED FROPA UNTIL LATE MONDAY
NIGHT INTO TUESDAY.  GIVEN PERSISTENT AND HIGHLY AMPLIFIED RIDGE
POSITIONED ACROSS THE MIDWEST...THINK A SLOWER BREAK DOWN TO THE
PATTERN IS PRUDENT.  HAVE THEREFORE TRENDED THE FORECAST TOWARD THE
SLOWER ECMWF/GEM CONSENSUS.  AS A RESULT...AM EXPECTING DRY
CONDITIONS THROUGH SUNDAY NIGHT...WITH HIGHER RAIN CHANCES ARRIVING
BY LATE MONDAY.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 1153 PM CDT SUN AUG 30 2015

FOG AND LOW CLOUD FORMATION LATER TONIGHT REMAIN THE PRIMARY
CONCERNS. THE STALLED OUT FRONTAL BOUNDARY ACROSS CENTRAL IL IS
BEGINNING TO WASH OUT, BUT RESIDUAL MOISTURE IN THE BOUNDARY LAYER
HAS ALLOWED DEWPOINTS TO LINGER IN THE UPPER 60S TO LOW 70S
THROUGH THE EVENING. THE POTENTIAL FOR MVFR FOG IS HIGH IN A
MAJORITY OF THE AREA OVERNIGHT. HRRR/RAP OUTPUT ARE POINTING
TOWARD THE POTENTIAL OF LOCALIZED VLIFR FOG NEAR PIA AND BMI, AND
TO SOME EXTENT SPI AND DEC. THE NAM FORECAST SOUNDINGS SHOW AT
LEAST AN MVFR CLOUD LAYER WILL DEVELOP LATER TONIGHT AT MOST TAF
LOCATIONS. HAVE INCLUDED LIFR FOG AT PIA AND BMI WITH VLIFR CIGS
AT BMI. WILL CONTINUE WITH ONLY IFR FOG LATER TONIGHT FOR SPI, DEC
AND CMI, FOR NOW.

FOG SHOULD DISSIPATE BY MID MORNING, WITH MVFR CLOUDS POSSIBLY
LINGERING TO AROUND 17-18Z. VFR CONDITIONS SHOULD DEVELOP AT ALL
TAF SITES FOR THE AFTERNOON AND THROUGH THE EVENING.

WINDS WILL REMAIN LIGHT AND VARIABLE THE REST OF THE NIGHT, WITH
A PREVAILING S-SW WIND DEVELOPING AFTER SUNRISE TOMORROW. WIND
SPEEDS DURING PEAK MIXING TOMORROW SHOULD REMAIN 10KT OR LESS.


&&

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

$$

SHORT TERM...BARNES
LONG TERM...BARNES
AVIATION...SHIMON



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