Hail and Damaging Winds in Illinois, September 18 to 19, 2005

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
840 PM CDT SUN SEP 18 2005

.DISCUSSION...
ELEVATED CONVECTION HAS BEEN INCREASING THIS EVENING OVER NORTHEAST
MISSOURI WITH A RECENT DEVELOPMENT TREND INTO SOUTHEASTERN IOWA.
MEAN WIND IN THE 850-500MB LAYER SUGGESTS THAT THE STRONGER CLUSTER
SOUTH OF QUINCY SHOULD VEER TO OUR SOUTH IN THE SHORT TERM...HOWEVER
THE ACTIVITY FURTHER NORTH WILL LIKELY MAKE IT INTO OUR WESTERN
COUNTIES LATER ON. 00Z LINCOLN SOUNDING REVEALS A VIRTUALLY
IMPENETRABLE LOW LEVEL CAP...SO ANY MOISTURE INCREASE FROM 850MB ON
DOWN SHOULD NOT BE TOO MUCH OF A FACTOR. HOWEVER...STEEP LAPSE RATES
ABOVE THE CAP SUGGEST THAT ANY ELEVATED CONVECTION THAT CAN SURVIVE
THIS FAR EAST MAY PRODUCE HAIL. MID LEVEL MOISTURE IS INITIALLY
PRETTY SPARCE OVER CENTRAL ILLINOIS...BUT SOUNDINGS TO OUR WEST SHOW
MUCH BETTER MID LEVEL MOISTURE...AND SATELLITE LOOPS SHOW THIS
MOISTURE SPREADING EAST. THE CURRENT CONVECTION APPROACHING THE
MISSISSIPPI RIVER IS LIKELY ON THE NOSE OF THIS WARM/MOIST
ADVECTION. BOTTOM LINE IS THAT GRADUALLY INCREASING POPS WITH TIME
TONIGHT STILL LOOKS ON TRACK. WILL UPDATE THE ZONES TO ADJUST
EVENING WORDING...BUT OVERALL FORECAST GRIDS LOOK GOOD.

SECONDARY CONCERN IS FOCUSED ON THE MCS DEVELOPMENT THAT WILL BE
TAKING PLACE OVER WESTERN IOWA OVERNIGHT. MUCH OF THIS ACTIVITY
SHOULD BE TO OUR NORTHWEST FOR MUCH OF THE OVERNIGHT HOURS. ANY
LEFTOVERS WILL MOVE ACROSS THE AREA EARLY IN THE SECOND PERIOD...
AND MAY HAVE AN IMPACT ON HOW MUCH REDEVELOPMENT CAN OCCUR WITH THE
FRONT EARLY MONDAY AFTERNOON.

&&

.PREV DISCUSSION...
MAIN CONCERNS ARE ON SEVERE WEATHER CHANCES TONIGHT AND MONDAY
AFTERNOON, THEN THE NEXT SYSTEM FOR FRIDAY. A WIDER SPREAD OF
SOLUTIONS THIS FORECAST THAN YESTERDAY. THE NAM INITIALIZED POORER
THAN GFS/CAN GLOB/UKMET. GFS AND NAM BOTH INDICATE RAPID
CYCLOGENESIS WITH THE PLAINS LOW AND BOTH HAVE CONV FEEDBACK ISSUES.
ALSO, GFS IS FASTER THAN THE NAM ONCE THE SYSTEMS DEEPEN. THE 20 KM
WRF/CANADIAN GLOB/UKMET DONT SUPPORT THIS SOLUTION, AND SEEM LIKE
ARE A GOOD COMPROMISE. TRIED TO FOLLOW CLOSER TO THEM.

.SHORT TERM...TONIGHT THROUGH TUESDAY.
THE 20 KM WRF HAD A GOOD HANDLE ON THE CONVECTION SO FAR TODAY, AND
INDICATES THAT CONVECTIVE INITIATION IS MOST LIKELY LATE THIS
AFTERNOON IN E NEBRASKA AND WILL MOVE ACROSS IOWA THIS EVENING...
REACHING OUR WESTERN CWA SHORTLY AFTER MIDNIGHT. THIS WAS A SIMILAR
THEME AMONG MOST MODELS... GENERATING STORMS IN THE STRONG H85 WAA
ALONG WITH A 40KT H85 LLJ. MUCAPE/TT/AND LIS ALL INDICATE POTENTIAL
FOR SVR STORMS AFTER MIDNIGHT. SPC HAS US IN A SLIGHT RISK FOR
TONIGHT. BRN AND BULK SHEAR INDICATE LOWER SHEAR VALUES, SO FEEL THAT
MAIN HAZARDS ARE WIND AND HAIL. THE BEST INSTABILITY AND FORCING FOR
PRECIP WILL BE IN THE N HALF OF OUR CWA, CLOSER TO THE MAIN
SHORTWAVE. INCREASED THE POPS TO LIKELY 70S IN THE NORTH, AND
TAPERED TO CHC POPS SOUTH OF THERE. FRONTOLOSYS DOMINATES OUR W CWA
IN THE MORNING, AS OPPOSING H85 WAA CONTINUES SOUTH OF THE WARM
FRONT.

THINK THERE WILL BE A BREAK IN THE ACTION IN MOST OF OUR CWA
ON MONDAY MORNING, UNTIL THE COLD FRONT AND STRONG QG FRONTOGENESIS
PUSH ACROSS THE CWA IN THE AFTERNOON. SPC HAS US IN A SLIGHT RISK FOR
MONDAY, AND FEEL THAT OUR STORM CHANCES WILL BE MAXIMIZED DURING PEAK
HEATING. GUSTY WINDS AHEAD OF THE COLD FRONT, ALONG WITH UNI-
DIRECTIONAL SHEAR, INDICATE THAT STRAIGHT LINE WINDS AND HAIL WILL
ONCE AGAIN BE THE MAIN THREAT. BASED ON WHERE THE COLD FRONT SHOULD
MOVE TO BY PEAK HEATING, OUR EASTERN CWA WILL HAVE THE BEST CHANCE
AT SEVERE WEATHER MONDAY AFTERNOON. KEPT THE HIGHEST POPS THERE. DRY
HIGH PRESSURE WILL PUSH IN BEHIND THE COLD FRONT. LINGERING SHOWERS
WILL BE POSSIBLE IN OUR S CWA, ALONG THE COLD FRONT MONDAY NIGHT AND
TUESDAY MORNING. OTHERWISE, TUESDAY SHOULD TURN OUT QUITE
SEASONABLE, WITH COOLER AIR AND PLENTY OF SUNSHINE.

LONG TERM...WEDNESDAY THROUGH SUNDAY...
THE HIGH PRESSURE WILL REMAIN IN CONTROL THROUGH THURSDAY, WHEN THE
NEXT COLD FRONT APPROACHES THE AREA FROM THE PLAINS. TEMPS ON WED
AND THURSDAY APPEAR ON TRACK, AND GUID NUMBERS DID NOT DEVIATE MUCH
FROM THE GOING FCST. THE UKMET AND GFS BOTH INDICATE CYCLOGENESIS
WILL OCCUR IN THE N PLAINS ON THURSDAY...WITH MOST OF THE WAA,
FRONTOGENESIS, AND OTHER FORCING FOR PRECIP WILL BE MOSTLY NORTH OF
OUR CWA. KEPT A SLIGHT CHANCE FOR OUR NW ZONES ON WEDNESDAY NIGHT,
AS WE WILL BE IN THE WARM SECTOR AND STORMS THAT DEVELOP CLOSER TO
THE COLD FRONT MAY MOVE INTO THAT AREA. KEPT IT DRY ELSEWHERE.
THURSDAY APPEARS DRY AS THE LOW PULLS FARTHER N AND E OF ILLINOIS,
AND THE CONVECTION AHEAD OF THE COLD FRONT WANES. KEPT PRECIP
CHANCES MAINLY AS THEY WERE FOR THURSDAY NIGHT THROUGH SUNDAY, AS
THE POSITION OF THE COLD FRONT AND TRACK OF VARIOUS H5 SHORTWAVES
THROUGH THAT TIME REMAINS IN QUESTION.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
IL...NONE.

04/SHIMON

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE LINCOLN IL
1153 AM CDT SUN SEP 18 2005

ILZ027>029-036-037-040>042-047>051-191100-
KNOX-STARK-PEORIA-FULTON-TAZEWELL-SCHUYLER-MASON-LOGAN-CASS-
MENARD-SCOTT-MORGAN-SANGAMON-
1153 AM CDT SUN SEP 18 2005

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL
ILLINOIS.

.DAY ONE...THIS AFTERNOON AND TONIGHT

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS TONIGHT...AS A
WEATHER SYSTEM APPROACHES THE AREA FROM THE WEST. THUNDERSTORMS
ARE EXPECTED TO DEVELOP ACROSS PORTIONS OF IOWA AND MISSOURI THIS
EVENING...THEN MOVE INTO ILLINOIS LATER TONIGHT. SOME OF THE STORMS
COULD PRODUCE DAMAGING WINDS AND LARGE HAIL.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ON MONDAY AS A
COLD FRONT MOVES SOUTHEASTWARD THROUGH THE AREA. THE PRIMARY
THREAT FROM THESE STORMS WILL BE DAMAGING WINDS.

ANOTHER WEATHER SYSTEM WILL MOVE INTO THE AREA LATER IN THE WEEK
AND BRING A CHANCE OF THUNDERSTORMS TO THE REGION FOR THURSDAY
NIGHT AND FRIDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE REQUIRED LATER TONIGHT...MAINLY BETWEEN
10 PM AND 6 AM.

ILZ030-031-038-043>046-052>057-061>063-066>068-071>073-191100-
MARSHALL-WOODFORD-MCLEAN-DE WITT-PIATT-CHAMPAIGN-VERMILION-
CHRISTIAN-MACON-MOULTRIE-DOUGLAS-COLES-EDGAR-SHELBY-CUMBERLAND-
CLARK-EFFINGHAM-JASPER-CRAWFORD-CLAY-RICHLAND-LAWRENCE-
1153 AM CDT SUN SEP 18 2005

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

.DAY ONE...THIS AFTERNOON AND TONIGHT

A WEATHER SYSTEM IN THE PLAINS WILL PRODUCE THUNDERSTORMS ACROSS
IOWA AND MISSOURI THIS EVENING. THESE STORMS ARE EXPECTED TO MOVE
INTO ILLINOIS DURING THE OVERNIGHT HOURS. HOWEVER...SEVERE
WEATHER IS NOT EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ON MONDAY AS A
COLD FRONT MOVES SOUTHEASTWARD THROUGH THE AREA. SOME OF THESE
STORMS COULD PRODUCE DAMAGING WINDS.

ANOTHER WEATHER SYSTEM WILL MOVE INTO THE AREA LATER IN THE WEEK
AND BRING A CHANCE OF THUNDERSTORMS TO THE REGION FOR THURSDAY
NIGHT THROUGH SATURDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT ANTICIPATED AT THIS TIME.

BARNES