Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 290812
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
312 AM CDT SAT AUG 29 2015

.SHORT TERM...(TODAY)
ISSUED AT 312 AM CDT SAT AUG 29 2015

07Z/2AM SURFACE ANALYSIS SHOWS A WEAK FRONTAL BOUNDARY EXTENDING
FROM WISCONSIN SOUTHWESTWARD TO THE TEXAS PANHANDLE.  A PLUME OF
MAINLY MID-LEVEL MOISTURE AHEAD OF THE FRONT HAS RESULTED IN
SCATTERED LIGHT SHOWERS/SPRINKLES ACROSS THE WESTERN HALF OF THE
KILX CWA EARLY THIS MORNING.  00Z UPPER AIR SOUNDING SHOWED PLENTY
OF DRY AIR BELOW 850MB...SO PRECIP HAS BEEN HAVING A HARD TIME
REACHING THE GROUND IN MANY AREAS.  FORECAST SOUNDINGS SHOW A
GRADUAL MOISTENING OF THE PROFILE TODAY...HOWEVER DEEP-LAYER
MOISTURE REMAINS LACKING.  IN ADDITION...WIDESPREAD CLOUD COVER WILL
LIMIT INSTABILITY...WITH GFS SBCAPE VALUES ONLY REACHING THE 500 TO
1000J/KG RANGE.  END RESULT WILL BE SCATTERED SHOWERS WITH PERHAPS A
RUMBLE OF THUNDER.  THINK AREAL COVERAGE OF PRECIP WILL REMAIN
LOW...SO WILL ONLY CARRY 30-40 POPS.  HIGH TEMPERATURES WILL RANGE
FROM THE UPPER 70S ALONG/NORTHWEST OF THE ILLINOIS RIVER...TO THE
MIDDLE 80S ALONG/SOUTHEAST OF I-70 WHERE CONDITIONS WILL REMAIN DRY
UNTIL A FEW SHOWERS ARRIVE DURING THE AFTERNOON.

&&

.LONG TERM...(TONIGHT THROUGH FRIDAY)
ISSUED AT 312 AM CDT SAT AUG 29 2015

FRONTAL BOUNDARY WILL SLOWLY PUSH EASTWARD LATER TODAY INTO
TONIGHT...WITH MODEL CONSENSUS SHOWING IT REACHING A CHICAGO TO
KIRKSVILLE LINE BY 12Z SUN. SCATTERED SHOWERS WILL BE ONGOING
AHEAD OF THE FRONT ACROSS MUCH OF THE AREA THIS EVENING...THEN
WILL SHIFT TO MAINLY LOCATIONS ALONG/EAST OF I-57 OVERNIGHT. MAIN
WEATHER CONCERN FOR TONIGHT WILL BE THE POTENTIAL FOR FOG ACROSS
THE W/NW CWA. AS THE SLOW-MOVING FRONT ARRIVES...WINDS WILL BECOME
LIGHT/VARIABLE ACROSS THIS AREA. DUE TO THE NEARLY CALM
WINDS...ADDED LOW-LEVEL MOISTURE FROM SHOWERS TODAY...AND PARTIAL
CLEARING LATE TONIGHT...THINK AT LEAST PATCHY FOG WILL FORM. BOTH
FORECAST SOUNDINGS AND NUMERIC GUIDANCE SUGGEST A REDUCTION IN
VISBY OVERNIGHT. CURRENT OBSERVATIONS IN THE VICINITY OF THE FRONT
ACROSS IOWA SHOW WIDESPREAD FOG...WITH A FEW VISBYS DOWN TO AROUND
1/4 MILE. THINK THIS SAME SCENARIO WILL UNFOLD FURTHER EAST
TONIGHT...SO HAVE INCLUDED PATCHY FOG IN THE FORECAST WEST OF I-55
AFTER MIDNIGHT.

THE FRONTAL BOUNDARY WILL SLOWLY DISSIPATE ON SUNDAY...HOWEVER
ENOUGH UPPER-LEVEL SUPPORT WILL PERSIST TO SUPPORT AT LEAST A
MENTION OF A FEW SHOWERS/THUNDERSTORMS.  MOST MODELS PRODUCE LIGHT
QPF ACROSS NEARLY THE ENTIRE CWA AS THE BOUNDARY HAS SLOWED SLIGHTLY
FROM PREVIOUS RUNS.  AS A RESULT...HAVE PULLED POPS FURTHER WEST TO
INCLUDE SLIGHT CHANCES AS FAR WEST AS THE ILLINOIS RIVER SUNDAY
AFTERNOON/EVENING.

AFTER THAT...THE REMAINDER OF THE EXTENDED LOOKS WARM AND DRY AS
UPPER-LEVEL RIDGING DOMINATES THE EASTERN CONUS THROUGH THE END OF
THE COMING WEEK.  A SLIGHT WEAKNESS IN THE RIDGE APPEARS TO DEVELOP
ACROSS ILLINOIS INTO THE OHIO RIVER VALLEY...POTENTIALLY TRIGGERING
ISOLATED AFTERNOON/EVENING CONVECTION TUESDAY THROUGH FRIDAY.
HOWEVER...MID-LEVEL WARMING BENEATH THE RIDGE WILL LIKELY LEAD TO
CAPPING AND AN OVERALL SUPPRESSION OF CONVECTION.  AS A
RESULT...WILL MAINTAIN A DRY FORECAST WITH HIGH TEMPERATURES
CLIMBING INTO THE UPPER 80S TO AROUND 90 DEGREES EACH DAY.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1142 PM CDT FRI AUG 28 2015

LOW PRESSURE CENTERED IN WESTERN IOWA WILL CONTINUE TO DRIFT EAST
TONIGHT. IT WILL GRADUALLY DISSIPATE NEAR WESTERN ILLINOIS
SATURDAY AFTERNOON/EVE. SHOWERS HAVE EXPANDED IN COVERAGE BETWEEN
04Z-05Z, AND RAIN IS STARTING TO REACH THE GROUND FROM CLOUD
BASES AT 8K FT OR HIGHER. SCATTERED RAIN SHOWERS WILL PERIODICALLY
AFFECT THE TERMINAL SITES OVER THE NEXT 18 HOURS, BEFORE
DISSIPATING SATURDAY EVENING. THE CHANCES ONLY WARRANTED A VCSH
AND VFR CLOUD COVER, BASED ON FORECAST SOUNDINGS FROM HRRR AND
RAP/NAM OUTPUT. USED ONLY VCSH IN ALL TAFS TO ACCOUNT FOR PRECIP,
AS TIMING WILL BE HIGHLY VARIABLE IN TERMS OF TIMING AND LOCATION.
ENDED ALL MENTION OF PRECIP BEFORE 00Z/30. WINDS ARE EXPECTED TO
REMAIN SOUTH THROUGH AT LEAST 18Z, THEN BEGIN TO SHIFT TO THE
SOUTHWEST AS THE LOW AND COLD FRONT APPROACH WESTERN ILLINOIS.
PREVAILING WIND SPEEDS SHOULD REMAIN 10KT OR LESS THROUGH TOMORROW
AFTERNOON.


&&

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

$$

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


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