Severe Thunderstorm Warning 72, NWS Quad Cities, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
225 AM CDT TUE MAY 30 2000

ANALYSIS SHOWS LAST NIGHT/S FORECAST MCC HAS INDEED DEVELOPED AND IS NOW
ENTERING WESTERN IOWA FROM WEST AT 45-50 KTS.  THIS PHENOMENA IS A
IMPRESSIVE WIND VEHICLE WITH GOOD OUTFLOW BOUNDARY RUNNING AHEAD OF
COLD POOL AT 06Z EXTENDING FROM WEST CENTRAL IOWA TO SE NEBRASKA AND
BACK TO NEAR GOODLAND. THIS CONVECTIVE COMPLEX ALSO HAS AN IMPRESSIVE
CONVECTIVE WAKE LOW WITH AN ASYMMETRICAL CONFIGURATION. AS EXPECTED...
MODELS DON/T HANDLE THESE NON-HYDROSTATIC PROCESSES WELL WITH THE ETA
THE LEAST POOR. LARGER SCALE FEATURES STILL IN PLACE FROM YESTERDAY WITH
GOOD ZONAL JET AND BAROCLINIC ZONE REFLECTED BY LEE SIDE LOW IN HIGH
PLAINS AND SLOW MOVING FRONT SAGGING INTO PLAINS AND INTO MIDWEST.  FOR
REASONS MENTIONED ABOVE WILL MODIFY AND HEAVILY BASE NEW FORECAST
BLENDING TONIGHT/S ONGOING CONVECTION AND APPLY OUTFLOW BOUNDARIES AND
CONCEPTUAL MODELS TO BEST AVAILABLE MODEL GUIDANCE. LATEST 88D/S IN THE
PAST HOUR SUGGEST COMPLEX STARTING TO WIND DOWN AS OUTFLOW BOUNDARY
OUTRACES CONVECTION BUT LIKELY TO TAKE SEVERAL MORE HOURS SO PORTIONS
OF COMPLEX SHOULD AFFECT NORTHERN 1/2 TO 2/3 OF FORECAST AREA THIS AM.

...NEAR TERM ISSUE IS THE EVOLUTION AND DECAY OF MCC THIS AM AND ANY
IMPACTS ON CLOUDS AND TEMPS...AND THEN REDEVELOPMENT IMPACTS LATER
TONIGHT FROM CURRENT MCC OUTFLOW BOUNDARY AND IT/S EVENTUAL INTERACTION
WITH SLOW MOVING FRONT...

ETA VERIFIES CLOSEST OVERALL WITH AVN VERY POOR ON CONVECTION AND NGM
HALFWAY.  USING OUTFLOW FROM CURRENT CONVECTION SUPPORT DEVELOPMENT
AGAIN LATE PM AND THIS EVENING TO DEVELOP ALONG OUTFLOW BOUNDARY OF N KS
AND S NE AND MOVE RAPIDLY ENE AGAIN ALONG FRONT/BOUNDARY WITH BEST
PROGGED AXIS ALONG/JUST SOUTH OF I-80. THIS IS SLIGHTLY SOUTH OF ETA AND
WILL ADJUST POPS WITH SEVERE WORDING NEEDED AS CONVECTIVE COMPLEX SHOULD
BE SIMILAR IN SEVERE WEATHER DYNAMICS TO THE CURRENT SITUATION.  WITH
HIGH DEWPOINTS...WILL ALSO MENTION LOCALLY HEAVY RAINS AS SOME
TRAINING POSSIBLE ALONG BOUNDARY.

TODAY...WILL PROBABLY USE MORNING AND AFTERNOON WORDING FOR DECAYING
CONVECTION AND POSSIBLE RE-IGNITION LATE PM ALONG BOUNDARY NORTH.
TONIGHT...LIKELY WORDING FOR STORMS ALONG I-80 AND HIGH CHANCE POPS
NORTH/SOUTH FOR REASONS DISCUSSED PARAGRAPHS ABOVE.

PERIOD 3 AND 4 SEE LITTLE REASON TO CHANGE ABOVE SCENARIO WITH FRONT
NEARBY AND SHORT WAVES...WILL MODIFY TEMPS DOWNWARD MOST AREAS NORTH FOR
MORE CLOUDS CLOSER TO ETA SOLUTION. CONTINUE TO USE HIGH CHANCE POPS
WITH WORDING FOR POSSIBLE SEVERE AND LOCALLY HEAVY RAINS AGAIN.  PLAN TO
ISSUE ANOTHER ESF TO UPDATE FLOOD POTENTIAL NEXT 2-3 DAYS.

...EXTENDED...THU-FRI-SAT...
LATEST MIX OF MODELS SUPPORT SHOWERS AND STORMS LIKELY THURSDAY AND
LEFTOVER SHOWERS ON FRIDAY AS FRONT SLIDES SOUTH.  THEN DIVERGE
BY SATURDAY WITH UKMET/CANADIAN DRY AND ECMWF SUGGESTING ANOTHER CHANCE
FOR MORE SHOWERS/STORMS AS WAVE FORMS ON FRONT ON SATURDAY. PLAN TO
USE LATEST UKMET/CANADIAN AND PEAK AT MRF FOR MINOR ADJUSTMENTS.

COORDINATED WITH ARX...DSM...ILX...THX.

.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-MOZ009-010-311000-

SIGNIFICANT WEATHER OUTLOOK
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
440 AM CDT TUE MAY 30 2000

...STRONG TO SEVERE THUNDERSTORMS POSSIBLE...MAINLY LATE THIS
AFTERNOON AND INTO THE OVERNIGHT HOURS ALONG AND NORTH OF I-80...

A SLOW MOVING COLD FRONT WILL STALL ACROSS EASTERN IOWA THIS EVENING AND
TRAIL BACK INTO SOUTHWESTERN IOWA. THIS FRONT WILL COMBINE WITH UPPER
LEVEL DISTURBANCES AND BOUNDARIES CREATED BY THIS MORNING/S CONVECTION
IN IOWA EARLIER TODAY TO ALLOW FOR THE REDEVELOPMENT OF ANOTHER ROUND OF
THUNDERSTORMS. THE MOST FAVORED AREAS OF SEEING STORMS AT THIS TIME WILL
BE MAINLY ALONG AND NORTH OF I-80 LATE THIS AFTERNOON INTO THE OVERNIGHT
HOURS.  OVER THE NEXT SEVERAL HOURS...SKIES WILL GRADUALLY BECOME PARTLY
SUNNY BY MID DAY AS SHOWERS AND A FEW THUNDERSTORMS MOVE EAST AND
DISSIPATE BY EARLY AFTERNOON FROM WEST TO EAST. TODAY/S HEATING SHOULD
PROVIDE ENOUGH INSTABILITY TO COMBINE WITH MODERATE TO STRONG WIND
SHEAR...OR THE CHANGE OF WIND SPEED AND DIRECTION WITH HEIGHT TO SUPPORT
THE DEVELOPMENT OF BROKEN LINES OF CONVECTION ALONG AND AHEAD OF THIS
FRONT.

THE PRIMARY THREAT LATE THIS EVENING AND INTO THE OVERNIGHT HOURS WOULD
BE STRONG WINDS WITH WIND GUSTS OF 60 MPH OR MORE POSSIBLE WITH HAIL A
SECONDARY THREAT. SIGNIFICANT RAINS ALSO ARE POSSIBLE...MAINLY ALONG AND
NORTH OF I-80 TONIGHT AND ESPECIALLY ALONG THE US-20 CORRIDOR.

THE FRONTAL SYSTEM WILL REMAIN NEARLY STATIONARY OVER THE REGION THRU
THURSDAY...SO CONDITIONS WILL REMAIN FAVORABLE FOR MORE THUNDERSTORMS
REDEVELOPING WHICH MAY ALSO BE SEVERE BOTH WEDNESDAY AND INTO THURSDAY
WITH LOCALLY HEAVY RAINS.

SPOTTER ACTIVATION MAY BE REQUIRED AFTER 3 PM THIS AFTERNOON AND INTO
THE OVERNIGHT HOURS....MAINLY FOR AREAS NORTH OF US-34 AND ESPECIALLY
NORTH OF I-80. EMERGENCY MANAGERS AND SPOTTERS SHOULD MONITOR CHANGING
CONDITIONS FOR FURTHER UPDATES.

NICHOLS