Tornadoes and Flash Flood in Illinois, March 28, 2007

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
225 PM CDT WED MAR 28 2007

.DISCUSSION...
MODELS NOW ARE IN REASONABLE AGREEMENT AS A SIGNIFICANT SHORTWAVE
SLOWLY PUSHES OUT INTO THE PLAINS LATE THU INTO FRIDAY AND THEN
EDGES TOWARDS THE MIDWEST ON SATURDAY. MAIN FORECAST CHALLENGE WITH
THIS FCST PACKAGE WILL BE WITH RAIN CHANCES...ESPECIALLY ON FRIDAY
AS WARM FRONT STARTS TO SHIFT NORTH ACRS THE AREA AND WITH THE FROPA
ON SATURDAY. FURTHER OUT IN TIME...SHORTWAVE FCST TO PUSH INTO THE
LAKES AND MIDWEST ON TUESDAY BRINGING SOME CHANGES TO TEMPS AND POPS
EARLY NEXT WEEK.

LATEST SFC ANALYSIS INDICATING FRONTAL BOUNDARY STRETCHING FROM NEAR
QUINCY EAST THRU SW INDIANA WITH A LARGE COOL HIGH PRESSURE SYSTEM
PUSHING EAST JUST NORTH OF THE LAKES. WATER VAPOR LOOP AND PROFILERS
INDICATING SHORTWAVE/SHEAR AXIS PUSHING NE ACRS WRN IL EARLY THIS
AFTN WITH UPPER LEVEL RIDGING BUILD IN ITS WAKE TO OUR WEST.

.SHORT TERM...TONIGHT THROUGH SATURDAY...
SHORTWAVE TROF/SHEAR AXIS SHIFTING NWD ACRS THE FCST AREA LATE THIS
AFTN AND EVENING WL BE THE FOCUS FOR SCT SHOWERS OR THUNDERSTORMS.
MODELS INDICATING FEATURE TO PUSH TO THE NORTH AND EAST OF US OVERNIGHT
ENDING THE THREAT OF ANY ADDL RAINFALL. WL CARRY SCATTERED WORDING THIS
EVENING...ESP ACRS THE NORTH AND EAST AND THEN PULL BACK ON POPS
OVERNIGHT. LOW TO MID 60 DEGREE DEW POINTS ADVECTING SLOWLY NWD THRU
SRN MO AND IL SHOULD HELP PRODUCE SOME FOG AND KEEP LOWER CLOUDS
AROUND OVERNIGHT. ANY BREAKS IN THE CLOUD COVER OVERNIGHT WL ONLY
ENHANCE THE FOG THREAT ACRS CNTRL OR SE IL.

WITH WEAK UPPER LEVEL RIDGING BUILDING ACRS THE MIDWEST ON THU...WL
CONTINUE WITH THE CURRENT DRY FCST BUT GETTING RID OF THE CLOUD
COVER MAY BE A DIFFERENT STORY...ESPECIALLY NORTH OF THE STALLED OUT
FRONTAL BOUNDARY. FCST SOUNDINGS SHOWING QUITE A BIT OF LOW LVL
MOISTURE TRAPPED BENEATH AN INVERSION BETWEEN 850 AND 900 MB MOST OF
THE DAY TOMORROW SO WL KEEP IT MO CLDY THRU THE DAY WITH OUR WARMEST
TEMPS SOUTH OF THE BNDRY ACRS SE IL. WEAK EAST TO SOUTHEAST FLOW WL
CONTINUE THU NIGHT INTO EARLY FRIDAY WITH ANY SUBSTANTIAL FORCING FOR
PRECIP REMAINING TO OUR WEST AND SOUTH.

AS THE MAIN SYSTEM ACRS THE ROCKIES PULLS OUT INTO THE PLAINS
FRIDAY...THE BNDRY TO OUR SOUTH WL START TO PUSH BACK NORTH AS A
WARM FRONT DURING THE AFTN AND EVENING WITH THUNDERSTORM CHANCES
INCREASING ALONG IT. INSTABILITY AXIS ACRS THE MISSISSIPPI RIVER
WITH LI/S AROUND -4 AND SURFACE BASED CAPES NEAR 1200 J/KG TO OUR
SW. FRIDAY NIGHT INTO SATURDAY MORNING...850 MB FNT ACRS CNTRL IL
WITH SOME LOW LVL CONVERGENCE NOTED AT 950 AND 850 MB BUT LOW LVL
JET POSITIONED MORE TO OUR WEST...SO BEST DVLPMT OF OVERNIGHT
CONVECTION WILL OCCUR TO OUR WEST AND WORK ITS WAY INTO A LESS
FAVORABLE ENVIRONMENT ACRS CNTRL IL EARLY SATURDAY. CONDITIONS START
TO CHANGE ON SATURDAY AS MAJOR PORTION OF UPPER WAVE THAT WL BE
EDGING SLOWLY EWD OVER THE NEXT SVL DAYS BRING LOW PRESSURE NE INTO
THE MIDWEST. THE WARM FRONT SHOULD BE ACRS OUR NORTHERN COUNTIES BY
LATE MORNING AND AS THE UPPER LEVEL FORCING AND COLD AIR ALOFT PUSH
INTO THE MIDWEST...IT WILL INTERACT WITH AN INCREASINGLY FAVORABLE
ENVIRONMENT FOR STRONG TO SEVERE STORMS. BULK SHEAR VALUES (0-6KM)
AROUND 35 KTS WITH WIND PROFILES BY EARLY AFTN BECOME MORE
UNIDIRECTIONAL SUGGESTING LINEAR TYPE ORGANIZATION AHEAD OF THE
FRONTAL BOUNDARY. IF WARM FRONTS NWD TRACK IS HELD BACK BY
OVERNIGHT CONVECTION...LOW LVL WIND PROFILE MAY SUPPORT DISCRETE
CELLS...AT LEAST FOR A SHORT TIME SAT AFTN...BEFORE THE STORM MODE
BECOMES MORE LINEAR. FRONT SHOULD BEGIN TO ACCELERATE EWD DURING THE
EVENING AS THE DEEPENING SFC LOW TRACKS INTO WRN WISCONSIN SATURDAY
EVENING.

.LONG TERM...SUNDAY THROUGH WEDNESDAY...
LONGER TERM MODEL CONSENSUS (ECMWF AND UK) NOW SUGGESTING NEXT
SHORTWAVE EARLY NEXT WEEK HAVING A BIT MORE AMPLITUDE AND AS A
RESULT A BIT SLOWER IN ITS EWD TRACK INTO THE MIDWEST. UPPER LEVEL
RIDGING OVER THE ERN PACIFIC NWD INTO ALASKA WL HELP TO PUSH THE
SHORTWAVE INITIALLY TO THE SOUTHEAST ACRS THE PLAINS EARLY NEXT
WEEK. THIS FEATURE WILL HAVE A BETTER CHANCE OF BRINGING WARMER AIR
INTO THE REGION MONDAY AND TUESDAY THAN EARLIER THOUGHT. HAVE MADE
SOME UPWARD ADJUSTMENTS TO THE TEMPS FOR BOTH DAYS WITH CHANCES FOR
THUNDERSTORMS INCREASING AGAIN LATE MONDAY NIGHT INTO TUESDAY.
LATEST ECMWF AND GFS SUPPORT THIS TROF DEEPENING IN ACRS THE ROCKIES
ON MONDAY AND EJECTING EWD INTO THE MIDWEST ON TUESDAY. FAIRLY
STRONG DYNAMICS AND WIND FIELDS SUGGEST ANOTHER SHOT AT SOME ACTIVE
WX EARLY NEXT WEEK BEFORE COOLER AND DRIER WX SETTLES IN FOR THE
REMAINDER OF THE PERIOD.

&&

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

SMITH

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE LINCOLN IL
1153 AM CDT WED MAR 28 2007

ILZ027>031-036>038-040>057-061>063-066>068-071>073-291100-
CASS-CHAMPAIGN-CHRISTIAN-CLARK-CLAY-COLES-CRAWFORD-CUMBERLAND-
DE WITT-DOUGLAS-EDGAR-EFFINGHAM-FULTON-JASPER-KNOX-LAWRENCE-LOGAN-
MACON-MARSHALL-MASON-MCLEAN-MENARD-MORGAN-MOULTRIE-PEORIA-PIATT-
RICHLAND-SANGAMON-SCHUYLER-SCOTT-SHELBY-STARK-TAZEWELL-VERMILION-
WOODFORD-
1153 AM CDT WED MAR 28 2007

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

.DAY ONE...THIS AFTERNOON AND TONIGHT

FLOODING IS EXPECTED TO CONTINUE ON SOME AREA RIVERS AND STREAMS...
INCLUDING PORTIONS OF THE ILLINOIS AND WABASH RIVERS.

A STALLED OUT FRONT NEAR I-74 WILL BECOME A FOCUS FOR AFTERNOON
SHOWERS AND THUNDERSTORMS. AFTERNOON HEATING... COUPLED WITH AN
UPPER LEVEL IMPULSE... SHOULD ALLOW SHOWERS AND STORMS TO BECOME
MORE NUMEROUS AFTER 1 PM. THE STORMS WILL BE MOST WIDESPREAD
WITHIN 40 MILES OF THE I-74 CORRIDOR. ELSEWHERE... COVERAGE IS
EXPECTED TO BE MORE ISOLATED.

THE THUNDERSTORMS ARE NOT EXPECTED TO REACH SEVERE LIMITS.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

FLOODING IS EXPECTED TO CONTINUE INTO EARLY NEXT WEEK ON SOME AREA
RIVERS...INCLUDING PORTIONS OF THE ILLINOIS AND WABASH RIVERS.

PERIODIC CHANCES OF THUNDERSTORMS ARE EXPECTED THROUGH SATURDAY. THE
MOST FAVORED PERIOD FOR STORMS AT THIS POINT APPEARS TO BE ON
SATURDAY. ANY HEAVY RAINFALL FROM THESE STORMS MAY AGGRAVATE THE
FLOODING ALREADY OCCURRING ON AREA RIVERS AND STREAMS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT ANTICIPATED THROUGH TONIGHT.

HARDIMAN