Severe Thunderstorm Warning 165, NWS Lincoln, IL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1250 PM CDT WED AUG 19 2009

.DISCUSSION...
ISSUED 1022 AM CDT WED AUG 19 2009
WARM FRONT LIFTING NORTH ACROSS THE CWA THIS MORNING WITH TWO
DIFFERENT WAVES HEADED THIS WAY. SOME SHOWERS HAVE ALREADY
DEVELOPED...AND MORE ARE ANTICIPATED THROUGH THE AFTERNOON. ONLY
ISSUES WITH THE FORECAST OVERALL ARE TO TWEAK THE HOURLY
GRIDS...AND GO TO A BLANKET 70 POP ACROSS THE CWA. ZONE UPDATE OUT
MOMENTARILY.

&&

.AVIATION...
ISSUED 1245 PM CDT WED AUG 19 2009
WEATHER SPINNING UP AND WILL KEEP THIS BRIEF. SEVERAL ROUNDS OF
THUNDERSTORMS AND SHOWERS ANTICIPATED THROUGH NEXT 24 HRS. BROAD
TROF OVER THE REGION SHOULD KEEP LLVL CLOUDS IN PLACE AS WELL.
RAINFALL AND SFC MOISTURE SHOULD REMAIN HIGH...ALLOWING FOR VSBY
DROPS AND PATCHY FOG IN THE EARLY MORNING HOURS. CIGS SHOULD
REMAIN MVFR...AND VIS IFR THROUGH MUCH OF THE PERIOD. CANNOT RULE
OUT THE CHANCES FOR LIFR VIS FROM 10Z TO 14Z IN AREAS OF HEAVIEST
RAINFALL.

HJS
&&

.PREV DISCUSSION...
ISSUED 249 AM CDT WED AUG 19 2009

MAIN CONCERN WITH THIS FORECAST PACKAGE WILL BE THE THREAT FOR
HEAVY RAINFALL OVER THE NEXT 24 TO 36 HOURS.

UPPER AIR ANALYSIS SHOWS TWO MAIN FEATURES OF INTEREST TO THE
WEATHER ACROSS CENTRAL ILLINOIS. THE FIRST IS A SHORT-WAVE
CURRENTLY TRACKING OUT OF THE SOUTHERN ROCKIES...AND THE SECOND IS
A VIGOROUS UPPER LOW DROPPING SOUTHEASTWARD THROUGH SASKATCHEWAN.

SHORT TERM...TODAY THROUGH FRIDAY

AS SASKATCHEWAN UPPER LOW DIVES SOUTHEASTWARD...IT WILL EJECT
SOUTHERN ROCKIES SHORT WAVE NORTHEASTWARD INTO THE MIDWEST TODAY.
THIS WILL HELP LIFT A DEVELOPING WARM FRONT NORTHWARD INTO CENTRAL
ILLINOIS. 07Z SURFACE MAP SHOWS WINDS ALREADY BEGINNING TO BACK
TO E/SE AHEAD OF THIS FEATURE...AS WEAK HIGH PRESSURE OVER
NORTHERN ILLINOIS SLOWLY LOSES ITS INFLUENCE. LEAD SHORT-WAVE WILL
INTERACT WITH THE WARM FRONTAL BOUNDARY AND A VERY MOIST AIRMASS
TO PRODUCE SCATTERED SHOWERS AND THUNDERSTORMS....MOST NUMEROUS
ACROSS THE CENTRAL AND WESTERN ZONES IN CLOSER PROXIMITY TO THE
UPPER WAVE.

MAIN UPPER LOW WILL THEN BEGIN APPROACHING FROM THE NORTHWEST THIS
EVENING...PUSHING A STRONG COLD FRONT TOWARD ILLINOIS OVERNIGHT.
MODELS HAVE BEEN QUITE CONSISTENT WITH THE STRENGTH AND TIMING OF
THE FRONT...SWEEPING IT ACROSS THE KILX CWA ON THURSDAY. AHEAD OF
THE DEEP UPPER LOW AND ASSOCIATED SURFACE FRONT...INCREASING
SYNOPTIC LIFT WILL AID IN THE DEVELOPMENT OF WIDESPREAD SHOWERS/STORMS
TONIGHT. FORECAST SOUNDINGS INDICATE PRECIPITABLE WATER VALUES IN
EXCESS OF 2 INCHES...SUGGESTING A DISTINCT RISK FOR LOCALLY HEAVY
RAINFALL. 1-HR FLASH FLOOD GUIDANCE ACROSS CENTRAL ILLINOIS IS
GENERALLY ON THE ORDER OF 2 TO 2.5 INCHES...WHICH WILL PROBABLY BE
A BIT DIFFICULT TO ACHIEVE. IN ADDITION...HPC DAY 1 EXCESSIVE
RAINFALL OUTLOOK FOCUSES BEST THREAT FOR FLASH FLOODING FURTHER
WEST ACROSS NORTHERN MISSOURI AND EASTERN IOWA. WILL THEREFORE
HOLD OFF ON FLASH FLOOD WATCH AT THIS TIME...BUT THIS WILL
DEFINITELY NEED TO BE EXAMINED CLOSELY BY THE NEXT SHIFT. WILL
CARRY CATEGORICAL POPS TONIGHT...WITH TOTAL RAINFALL OF 1 TO 2
INCHES ACROSS THE WESTERN TWO-THIRDS OF THE CWA.

COLD FRONT WILL PUSH INTO CENTRAL ILLINOIS THURSDAY MORNING...SO
WILL GO WITH LIKELY POPS ACROSS THE BOARD FOR THE MORNING
HOURS...DECREASING TO CHANCE POPS FOR THE AFTERNOON. WILL CARRY
HIGHEST RAIN CHANCES ALONG AND EAST OF I-57 DURING THE
AFTERNOON...WHERE ADDITIONAL STORMS MAY FIRE ALONG THE FRONT
BEFORE IT PUSHES INTO INDIANA BY 00Z.

VERY COOL AIRMASS WILL SPILL INTO THE REGION FOR THE END OF THE
WEEK...AS UNSEASONABLY DEEP UPPER LOW TRACKS FROM THE UPPER
MIDWEST INTO THE GREAT LAKES. 500MB TEMPS ARE PROGGED TO DROP INTO
THE -8 TO -10C RANGE ON FRIDAY...LEADING TO STEEP MID-LEVEL LAPSE
RATES AND CONSIDERABLE AFTERNOON CLOUD COVER. MAY EVEN SEE A FEW
SCATTERED SHOWERS AS WELL...WITH TEMPERATURES REMAINING WELL BELOW
NORMAL IN THE MIDDLE TO UPPER 70S.

LONG TERM...SATURDAY THROUGH TUESDAY

UPPER LOW WILL TRACK INTO THE NORTHEAST U.S. OVER THE
WEEKEND...ALLOWING THE FLOW TO BECOME ZONAL. THIS WILL LEAD TO A
GRADUAL MODERATION IN TEMPERATURES...WITH HIGHS RETURNING TO NEAR
NORMAL IN THE LOWER TO MIDDLE 80S BY EARLY NEXT WEEK.

BARNES

&&

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

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE LINCOLN IL
253 PM CDT WED AUG 19 2009

ILZ027>031-036>038-040>044-047>051-053-201200-
CASS-DE WITT-FULTON-KNOX-LOGAN-MACON-MARSHALL-MASON-MCLEAN-MENARD-
MORGAN-PEORIA-PIATT-SANGAMON-SCHUYLER-SCOTT-STARK-TAZEWELL-
WOODFORD-
253 PM CDT WED AUG 19 2009

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL
ILLINOIS.

.DAY ONE...THIS AFTERNOON AND TONIGHT

THUNDERSTORMS ARE LIKELY THROUGH TONIGHT....WITH A SLIGHT CHANCE OF
SEVERE THUNDERSTORMS THROUGH EARLY EVENING. THE STORMS MAY BECOME
SEVERE THIS AFTERNOON AND EARLY THIS EVENING WITH DAMAGING WIND
GUSTS...LARGE HAIL...FREQUENT LIGHTNING...VERY HEAVY RAINS OF 1 TO
1.5 INCHES IN LESS THAN A HALF HOUR AND POSSIBLE TORNADOES.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

ADDITIONAL THUNDERSTORMS REMAIN POSSIBLE UNTIL A COLD FRONT PUSHES
THROUGH THE REGION THURSDAY...ESPECIALLY THURSDAY MORNING.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NEEDED THROUGH 7 PM TODAY.

ILZ045-046-052-054>057-061>063-066>068-071>073-201200-
CHAMPAIGN-CHRISTIAN-CLARK-CLAY-COLES-CRAWFORD-CUMBERLAND-DOUGLAS-
EDGAR-EFFINGHAM-JASPER-LAWRENCE-MOULTRIE-RICHLAND-SHELBY-
VERMILION-
253 PM CDT WED AUG 19 2009

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL
ILLINOIS...EAST CENTRAL ILLINOIS AND SOUTHEAST ILLINOIS.

.DAY ONE...THIS AFTERNOON AND TONIGHT

THUNDERSTORMS ARE LIKELY THROUGH TONIGHT ACROSS EASTERN ILLINOIS.
THERE IS A SLIGHT CHANCE OF SEVERE THUNDERSTORMS NORTHWEST OF I-70
INTO MID EVENING. THE PRIMARY THREAT WITH THESE STORMS IS
EXPECTED TO BE HEAVY RAIN AND LIGHTNING ESPECIALLY LATE THIS
AFTERNOON AND EVENING. HOWEVER...SOME OF THE STORMS MAY BECOME
SEVERE NORTHWEST OF I-70 WITH DAMAGING WIND GUSTS...FREQUENT
LIGHTNING...VERY HEAVY RAINS OF 1 TO 1.5 INCHES IN LESS THAN A
HALF HOUR AND POSSIBLE HAIL.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

ADDITIONAL THUNDERSTORMS REMAIN POSSIBLE UNTIL A COLD FRONT PUSHES
THROUGH THE REGION THURSDAY WITH A SLIGHT CHANCE OF SEVERE
THUNDERSTORMS AGAIN.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED BETWEEN 4 AND 8 PM TODAY.

HUETTL

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE LINCOLN IL
241 PM CDT WED AUG 19 2009

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0240 PM     HEAVY RAIN       VIRGINIA                39.95N 90.21W
08/19/2009  M1.20 INCH       CASS               IL   CO-OP OBSERVER

            RAINFALL IN 20 MINUTES

&&

DPK