Severe Thunderstorm Warning 122, NWS Quad Cities, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
205 AM CDT TUE OCT 1 2002

.OVERVIEW...UPPER AIR AND SURFACE ANALYSIS SUPPORT UNSETTLED AND WET
PERIOD STARTING.  WEST COAST TROUGH STARTING TO EJECT SHORT WAVES INTO
CENTRAL PLAINS WITH SOME STORMS DEVELOPING AT 06Z AHEAD AND ALONG SLOW
MOVING COLD FRONT.  SURFACE AND UPPER AIR MOISTURE INCREASING WITH 60+
DEWPOINTS NOW ACROSS UPPER MIDWEST.  HEIGHT FALL PATTERN SUGGEST LITTLE
CHANGE IN UPPER AIR FLOW WITH DECENT OVERRUNNING POTENTIAL AS COOL AIR
SLIDES INTO PLAINS AHEAD OF WEST COAST TROUGH.

...TIMING CLOUDS AND POPS TODAY AND ESPECIALLY TONIGHT WITH FRONT AND
ANY RISK OF SEVERE STORMS NEAR TERM ISSUE...THEN CONTINUING CLOUDS AND
POPS WITH OVERRUNNING SITUATION MEDIUM RANGE ISSUE INTO LATE WEEK...

.DIAGNOSIS AND DAYS 1-3...NEBRASKA COMPLEX HANDLED BEST BY AVN BUT ALL
MODELS SUPPORT ANALYSIS OF INCREASING CLOUDS WITH SHOWERS AND STORMS
MOVING INTO NW 1/2 AREA BY PM.   THEN FAVORABLE FORCING FOR LINE OF
SHOWERS AND STORMS MOVING ACROSS AREA TONIGHT.  APPEARS SEVERE POTENTIAL
WILL BE LIMITED TO ISOLATED HAIL AND MARGINALLY GUSTY WINDS UNLESS TEMPS
CAN RESPOND INTO UPPER 80S WHICH IS UNLIKELY WITH LOTS OF CLOUDS...THUS
PLAN ON NOT MENTIONING IN ZONES AND DAY FOLKS CAN ASSESS LATER TODAY.
ALL MODELS ARE TAD SLOWER WITH FROPA AND POPS INTO WEDNESDAY AND WITH
ANAFRONT SHEAR PROFILE (OVERRUNNING) SUPPORT TAKING THE SLOWEST SOLUTION
OF MODEL MIX. THUS...WILL UP POPS WEDNESDAY WITH LINGERING POST FRONTAL
RAIN AND SOME STORMS SOUTH SECTIONS.  THEN WAVES FORM ON FRONT WITH LOTS
OF TIMING VARIANCES ON MODELS SUPPORTING LIKELY WEDNESDAY NIGHT AND
CHANCE POPS THURSDAY AS WARM FRONT APPROACHES AND PASSES DURING THE DAY.
COMPLEX FEEDBACK OF POPS AND CLOUDS AND IMPACTS ON TEMPS HAVE GONE NEAR
TO SLIGHTLY ABOVE TEMP GUIDANCE BLEND WITH LARGE SCALE SE FLOW.  WELCOME
MODERATE TO HEAVY RAINS OF .5 TO 1.5 INCHES VERY LIKELY NEXT FEW DAYS
WITH ISOLATED HIGHER AMOUNTS QUITE POSSIBLE.  SINCE GROUND IS VERY DRY
NO NEED TO ISSUE ESF FOR NOW UNLESS LARGE SCALE HEAVIER RAINS DO OCCUR
TONIGHT AND ANOTHER HEAVY RAIN EVENT APPEARS MORE POSSIBLE LATE THIS
WEEK.

.EXTENDED...(FRI-MON)...REASONABLE SOLUTION OF STRONGEST UPPER LEVEL
STORM SYSTEM THIS FALL TO DATE TO PASS NEARLY OVERHEAD ON FRIDAY WITH
HIGH POPS AND SOME HEAVY RAIN POTENTIAL BUT WILL LEAVE HEAVY WORDING OUT
FOR NOW.  PLAN FOR NORMAL MODEL BIAS OF EJECTING SYSTEM 6-12 HOURS TOO
FAST WHICH IS WARRANTED SINCE MODELS HAVE SLOWED ITS PROGRESS BY 6 HOURS
OR MORE PAST 2 DAYS.  ALSO REASONABLE THAT SOME ADDED MOISTURE FROM LILI
WILL MOVE INTO ARKANSAS AHEAD OF THIS WAVE TO ADD MORE RAIN POTENTIAL.
STILL TOO EARLY TO IDENTIFY HOW MOISTURE PHASING TO MANIFEST ITSELF WITH
LILI ON FRIDAY EXCEPT WIDESPREAD LIGHT TO MODERATE RAINS EXPECTED AND
HEAVY RAIN POTENTIAL DEPENDING ON SURFACE LOW TRACK AND PHASING OF LILI
AND WEST COAST WAVE.  THEN CLEARING ON SATURDAY AND COOLER BUT NEXT
SHORT WAVE ON SUNDAY BEARS WATCHING FOR MORE POPS POTENTIAL BUT LEAVE
FOR DAY FOLKS TO DECIDE. EITHER WAY UPPER PATTERN DEFINITELY SHOWS A
COOLING TREND TO NEAR NORMAL TO MODERATELY BELOW NORMAL TEMPS SATURDAY
INTO EARLY NEXT WEEK.

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

NICHOLS