Severe Thunderstorm Warning 47, NWS Quad Cities, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
220 PM CDT FRI MAY 31 2002

.OVERVIEW...PRIME LATE SPRING AND EARLY SUMMER PATTERN WITH STRONG JET
ALONG CANADIAN US/CANADA BORDER. SURFACE BOUNDARY SETTING UP JUST SOUTH
OF FORECAST AREA WITH STRONG BAROCLINIC ZONE OF 90 TO 100 DEGREE TEMPS
SOUTH OF FRONT AT 18Z IN PLAINS AND 75 TO 85 NORTH.  LOTS OF MOISTURE
POOLING WITH 70 TO 73 DEWPOINTS IN NORTHERN MISSOURI AND INTO EXTREME SC
IOWA. LITTLE COHERENT TRIGGER TO HANG HAT ON EXCEPT CONVECTIVE TEMPS TO
BE REACHED LATE PM FOR STRONG TO INTENSE CONVECTION ALONG BOUNDARY INTO
TONIGHT.

...LOCATION OF CONVECTION TONIGHT WITH ANY SEVERE POTENTIAL AND IMPACTS
ON BOUNDARY NEAR TERM ISSUES...THEN MORE SIGNIFICANT THREAT AND TIMING
OF HEAVY RAIN AND SEVERE WEATHER POTENTIAL INTO EARLY NEXT WEEK FORECAST
CHALLENGES...

.DIAGNOSIS AND DAYS 1-3...MODELS VARY QUITE A BIT DEPENDING ON WHEN AND
WHERE CONVECTION STARTS AND THEN IMPACTS ON BOUNDARY.  AT 18Z...TOO
EARLY TO ASSESS JUST WHERE CONVECTION TO FIRE SO MAY HAVE TO GO WITH
MODEL BLEND.  BEST GUESS IS SC NEBRASKA INTO NW MO AND THEN TRAVELING
EAST TO EAST SOUTHEAST.  SOME SEVERE POTENTIAL WITH BAROCLINICITY BUT
BETTER CHANCE LATE SATURDAY AND SATURDAY NIGHT IF ETA CORRECT.  BY
THEN...EXTREME INSTABILITY WITH HEATING WOULD SUPPORT INTENSE BOW ECHO
AND DERECHO ENVORONMENT WELL INTO EARLY MORNING HOURS SUNDAY AM.  BLEP
TECHNIQUE OF T/TD 92/72 AND AS LOW AS 85/70 SUPPORTS MAX STRAIGHT LINE
WINDS NEAR OR POSSIBLY IN EXCESS OF 100 KTS INTO MID EVENING HOURS
SATURDAY...AND ABOVE 50 KTS (OR WARNING CRITERIA) WELL INTO OVERNIGHT
HOURS.  PROJECTED PATTERN IS SIMILAR TO MANY LOCAL DERECHO EVENTS SO
BEAR CLOSE WATCHING ON THIS RISK.  KEY WILL BE WHAT HAPPENS TONIGHT AND
ANY LINGERING ACTIVITY EARLY SATURDAY. WILL MENTION SOME SEVERE NEXT FEW
DAYS WITH PRESENT POTENTIAL RISK VERY SUBSTANTIAL AND ALSO INCLUDE HEAVY
RAINS WHERE CONFIDENCE IS BEST...MAINLY LATE SUNDAY INTO MONDAY WITH
HIGHEST POPS.  TEMPS WITH POTENTIAL LAKE EFFECT AND BOUNDARY TO BE A
BEAR...PROBABLY SUN/MON AS EXPECT SOMETIME NEXT 3 DAYS TO SEE A 20+
DEGREE GRADIENT IN TEMPS WITH BOUNDARY AND CLOUDS. WILL DO BEST TO
INCORPORATE INTO FWC/MAV. HIGHER CONFIDENCE IN HEAVY RAINS AND POTENTIAL
TRAINING WARRANT MAINTAINING ESF INTO EARLY NEXT WEEK.  WOULD BE
SURPRISED IF MOST AREAS DON/T RECEIVE AT LEAST 2 INCHES BY WEDNESDAY PM
WITH SEVERAL 5 INCH PLUS AMOUNTS...WILL HAVE TO WAIT ON TIMING.

.EXTENDED (TUE-FRI)...COOLER AND DRIER PATTERN SETTING UP THURSDAY INTO
FRIDAY. OTHERWISE...WILL DO BEST TO INCORPORATE CLOUDS AND IMPACTS ON
TEMPS...ESPECIALLY TUE/WED AS BOUNDARY LIKELY TO JUST SOUTH FOR COOLER
HIGHS AND MILDER LOWS THAN FMR/MEX GUIDANCE.

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

NICHOLS