Severe Thunderstorm Warning 148, NWS Quad Cities, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
250 AM CDT MON SEP 11 2000

.OVERVIEW...POTENTIAL FOR SIGNIFICANT SEVERE WEATHER EVENT LATE THIS
AFTERNOON AND EVENING.  SFC ANALYSIS SHOWS STRONG UPPER TROUGH OVER
PACIFIC NORTHWEST ON 100 KT JET.  SFC LOW NOW IN SOUTH CENTRAL SOUTH
DAKOTA WITH ASSOCIATED FRONT DRAPED FROM LAKE WINNIPEG TO LOW NEAR
PIERRE SD AND SW INTO WYOMING. STRONG SFC BAROCLINICITY AND ENERGY NOTED
WITH 850 MB DIFFERENCES OF 20C WITH LOW LEVEL JET NOW IN EXCESS OF 50
KTS IN SOUTHERN PLAINS AHEAD OF SYSTEM. SFC DEWPOINTS AROUND 70 DEGREES
WELL ENTRENCHED ACROSS IOWA.  SO ALL FACTORS IN PLACE WITH LOTS OF
MOISTURE...ENERGY AND STRONG FRONT FOR STORMS.

...ASSESSING MAGNITUDE OF SEVERE WEATHER POTENTIAL NEAR TERM AND POPS
THEN COOL DOWN LONG TERM...

.DIAGNOSIS...ETA MODEL OVERALL AGAIN BEST CHOICE AS VERIFIED BEST AT
06Z PER SFC/PROFILERS AND AVAILABLE SATELLITE/RUC..BUT EVEN ETA TOO
WEAK ON SOUTHERN PLAINS LOW LEVEL JET WITH INDICATIONS APPROACHING FRONT
POSSIBLY SLIGHTLY STRONGER PER PRESSURE RISE/FALL COUPLET AND 06-07Z
PROFILERS THAN ETA. THIS SUPPORTS STRONG...IMPRESSIVE FAST MOVING SYSTEM
WITH TIMING CLOSE TO ETA. CURRENT EAST-WEST WEAK WARM FRONT AHEAD OF LOW
AND 06Z PRESSURE FALLS AXIS SUPPORT SD LOW MOVING DUE EAST TODAY INTO
SOUTHERN MINNESOTA CLOSE TO ETA. LIMITED CURRENT CONVECTION AHEAD OF
THIS SYSTEM SUPPORTS COPIOUS ENERGY AVAILABLE LATER TODAY FOR STRONG
FIRING ALONG FRONT...KATABATIC SHEAR PROFILE SUGGESTS CONVECTION TO
EVENTUALLY RACE AHEAD OF FRONT BY LATE EVENING BUT COLD AIR TO ENHANCE
POST CONVECTION/FRONT STRATIFORM PRECIP TONIGHT.

.TODAY...GOOD HEATING...STRONG GRADIENT AND STRONG LOW LEVEL JET
SUPPORTS SOUTH TO SOUTHWEST WINDS INCREASING TO 20 TO 30 MPH WITH
SOME HIGHER GUST THIS PM FOR WINDY WORDING...ESPECIALLY WEST.  GOOD
HEATING AND DOWNSLOPE AND APPROACHING FRONT SUPPORT SUPERADIABATIC
CONDITIONS TODAY TO BUMP TEMPS ABOVE FWC/FAN AS LIKE YESTERDAY WHICH
WORKED FOR LOW 90S WITH HEAT INDICES APPROACHING 100. ALL FACTORS
SUPPORT CONVECTION TO FIRE ALONG BOUNDARY BETWEEN 18 AND 21Z IN WESTERN
AND CENTRAL IOWA. WITH HEATING...CAPES OF 2500 TO 3500 J/KG REASONABLE
AND SOME SHEAR FOR BRN OF AROUND 70 FOR SOME POTENTIAL ROTATION AND
ISOLATED SUPERCELLS AS LINE FORMS.  SOME DRY AIR ALOFT TO SUPPORT HAIL
AND MODERATELY UNSTABLE BL AND MOMENTUM TRANSFER FOR 60 MPH PLUS WINDS.
AGREE WITH SPC FOR MODERATE RISK NORTH HALF AND WILL STRONGLY WORD ZONES
WITH HEAVY EMPHASIS IN HAZARDOUS WEATHER OUTLOOK FOR ABOVE FACTORS. POPS
WILL GO CHANCE WEST LATE PM TODAY WEST AND DRY ELSEWHERE AND THEN
CATEGORICAL TONIGHT AS ALL AREAS TO RECEIVE WELCOME RAINS WITH ISOLATED
HEAVY RAIN POTENTIAL.  FRONT TO MOVE THROUGH BETWEEN 00Z AND 06Z
TONIGHT. POPS TONIGHT A TAD HIGHER NORTH WITH SLIGHT CHANCE WEST AND
TURNING COOLER.  LOWS NEAR CURRENT FORECAST WHICH NOW FAN/FWC/MAV
SUPPORT AS WELL.

.TUESDAY...GOOD COLD AIR ADVECTION TO SUPPORT NW WINDS OF 10 TO 20 MPH
AND ALL MODELS AGREE WITH MOSTLY SUNNY WORDING AND MUCH COOLER TEMPS
IN LINE WITH CURRENT FORECAST AS MOVES OVER AREA.  LOWS TONIGHT LOOK IN
LINE WITH CURRENT PACKAGE FOR CHILLY 40S AND LOWER 50S.

.EXTENDED (WED-FRI)...LATEST UKMET/ECMWF AND AVNEXT SUGGEST VIGOROUS
SHORT WAVE TO REINFORCE COLD AIR LATE WEDNESDAY AND THURSDAY FOR CHANCE
SHOWERS. THIS IS IN CURRENT FORECAST WITH TEMPS STAYING BELOW NORMAL.
WILL TRY AND CHECK LATEST MRF FOR ANY SIGNIFICANT ISSUES BEFORE ZONE
ISSUANCE.

.DVN...
IA...NONE.
IL...NONE.
MO...NONE.

NICHOLS

IAZ040>042-051>054-063>068-076>078-087>089-098-099-ILZ001-002-007-009-
015>018-024>026-034-035-MOZ009-010-120900-

SIGNIFICANT WEATHER OUTLOOK
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
520 AM CDT MON SEP 11 2000

...THUNDERSTORMS TO DEVELOP LATE THIS AFTERNOON AND INTO THE EVENING
WITH SOME SEVERE STORMS...

A STRONG...EARLY AUTUMN COLD FRONT WILL MOVE ACROSS THE AREA BY THIS
EVENING. THE FRONT WILL FIRE A LINE OF THUNDERSTORMS BY MID AFTERNOON
ACROSS CENTRAL IOWA WHICH WILL MOVE EAST OVER EASTERN IOWA AND THEN INTO
NORTHWESTERN ILLINOIS BETWEEN LATE THIS AFTERNOON AND MIDNIGHT TONIGHT.
SOUTHWEST WINDS WILL INCREASE TO 20 TO 30 MPH BY AFTERNOON AHEAD OF THE
FRONT TO CREATE WINDY CONDITIONS. TEMPERATURES WILL RISE WELL INTO THE
90S BY MID AFTERNOON WITH POSSIBLY NEAR RECORD HIGHS. AS THE FRONT SLAMS
INTO REGION...IT WILL ENCOUNTER UNSTABLE AIR WITH ENOUGH FORCE TO CREATE
SOME STORMS THAT WILL BE SEVERE WITH LARGE HAIL...POTENTIALLY UP TO THE
SIZE OF GOLF BALLS AND STRONG WINDS OF 60 MPH OR POSSIBLY STRONGER. THE
STRONG SOUTHWEST WINDS AHEAD OF THE SYSTEM MAY ALLOW FOR ISOLATED...
ROTATING UPDRAFTS CALLED SUPERCELL THUNDERSTORMS LATE THIS AFTERNOON AND
INTO THE EARLY EVENING HOURS ALONG AND AHEAD OF THE SQUALL LINE WHICH
MAY SPAWN A BRIEF TORNADO.

AT THIS TIME...ALL THE AREA HAS THE RISK FOR SEVERE WEATHER LATE THIS
AFTERNOON AND THIS EVENING...BUT THE AREAS ALONG AND NORTH OF US-30 MAY
EXPERIENCE MORE SIGNIFICANT AND WIDESPREAD SEVERE WEATHER.

SPOTTERS...EMERGENCY MANAGERS AND LOCAL LAW ENFORCEMENT OFFICIALS SHOULD
MONITOR CONDITIONS FOR UPDATES AND LIKELY RAPIDLY DEVELOPING CONDITIONS
THIS AFTERNOON THROUGH NOAA WEATHER RADIO OR THEIR FAVORITE MEDIA
OUTLET.

NICHOLS