Severe Thunderstorm Warning 75, NWS Quad Cities, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
300 PM CDT TUE MAY 30 2000

AT 18Z SFC ANALYSIS SHOWS COLD FRONT SAGGING INTO NW AND NCNTRL IA
THEN TRAILING SW INTO SFC LOW OVER NCNTRL KS. HARD TO PICK OUT WHATS
LEFT OF WARM FRNT THAT WAS OVR IA NRN IL ERLY THIS MORNING. AREA OF
MID/HIGH CLOUDS WAS HELPING CREATE A FAIRLY GOOD SFC TMP GRADIENT...
ESPECIALLY OVR SW IA WHERE TMPS GO FROM THE LOW-MID 90S IN CLOUD FREE
AREA TO THE LOW 80S UNDER CLOUDS. CAPES IN THE "HOT" AIR HAVE CLIMBED
TO ABOVE 4000 BASED ON RUC2 DATA FROM SPC.  HOWEVER STRONG CAP ON MRNG
SOUNDINGS THIS AREA WAS SUPPRESSING ANY CONVECTION.

OVERALL MODEL SOLNS ARE ABOUT THE SOME WITH THE EXCEPTION OF SOME
TIMING AND PLACEMENT DIFFS OF FEATURES LATE IN THE FCST PD.  WL PREFER
THE AVN/ETA SOLNS THIS PACKAGE WITH KEEPING SFC SYSTEMS FURTHER SOUTH
THAN NGM.  NGM APPEARS TO MV FNT/SFC LOW TO FAR N AFTER 36 HRS IN
RESPONSE TO DIGGING S/W MVNG OUT OF SWRN CANADA.

STILL SEEING SOME PRESS RISES BEHIND COLD FRONT MVNG SE THRU IA THIS
AFTN.  THINK FNT WILL SETTLE INTO TO SFC PRES TROF ROUGHLY ALONG I-80
CORRIDOR TONIGHT.  WITH CAP SUPPRESSING VERY UNSTABLE AIR TO THE SW
BLV CONVECTION WILL WAIT FOR INCREASING LOW LVL JET THIS EVENING.  BLV
BEST CHC FOR MCS WILL OVR NRN THIRD OF IA WHERE CAP IS WEAKEST.  WILL
GO WITH LIKELY POPS ACRS NRN THIRD TNGT AND TAPER OFF TO THE SOUTH
WITH LOW CHC POPS NE MO/WCNTRL IL TO ACCOUNT FOR ONGOING SHRA AND
DEBRIS FROM MCS LATE TONIGHT AND WED MORNING. WITH MOD RISK TNGT OVR
NRN SECTIONS OF CWA WILL MNT POSSIBLE SEVERE.  HVY RAIN THREAT ALSO
EXISTS WITH DIFFL THICKNESS PATTERN NEAR MS RIVER.  LAST NIGHT
CONVECTION JUST BRUSHED NRN MOST COUNTIES AND WITH FFG OF 2-3 INCHES
OVER NRN CWA BLV MOST AREAS CAN TAKE A GOOD RAIN. WILL HAVE TO KEEP AN
EYE ON THIS AREA WED NIGHT THOUGH.  IF HEAVY RAINS DEVELOP TONIGHT...IT
WILL PRIME THE AREA FOR POSSIBLE FLOODING WITH ANY CONVECTION THAT MVS
THROUGH WEDNESDAY NIGHT. AVN/ETA HOLDING FRONT IN PLACE WED THEN IT
SHIFTS NORTH IN REPONSE TO DVLPNG SFC LOW OVR PLAINS WED NGT AND
THURSDAY. EXPECT FRONT TO BE N OF CWA BY THUR MRNG. WILL DROP POPS SOUTH
 BEHIND RETREATING FRONT...BUT WILL HAVE TO CARRY POPS NRN SECTIONS
THROUGH PD DUE TO PROXIMITY OF WRM FNT. AVN BRINGS FRONT BACK THROUGH
CWA AS CD FRONT THURSDAY NIGHT AND WILL RE INTRODUCE POPS ALL GROUPS.

TEMPS FORECAST WILL FAVOR COOLER FAN NUMBERS NORTH OF FRONT AND WILL GO
WITH OR CLOSE TO WRMR FWC NUMBERS IN WARM SECTOR.  FOR THURS MRNG WITH
MOST OF AREA IN WARM SECTOR AND STRONG SLY FLOW WILL GO A LITTLE ABV
FWC MINS.

...EXTENDED...
UPPER AIR PATTERN UNDERGOING TRANSITION TO MORE AMPLIFIED FLOW DURING
EXTENDED PD.  THIS IS REFL IN LONG RANGE MODELS AS SUB-TROPICAL HIGH
OVR SERN U.S. IS SUPRESSED SOUTH AND BROAD TROF DVLPS OVR GRT LAKES AND
NERN U.S. LATE IN WEEKEND.  THIS TROFING IS IN RESPONSE TO RIDGE
BUILDING OVR WRN CANADA.  AS UPR TROF DEVELOPS SFC FRONT WILL
BE SUPRESSED SOUTH.  WL CONT LOW POPS EARLY FRI AND KEEP SATURDAY DRY
WITH MODELS AGREEING ON SFC HI MOVING THRU REGION AND SFC FNT PUSHED S
INTO LWR MS AND OH VALLEYS. BIG QUEST IS SUNDAY WITH MODELS SUGGESTING5
ENERGY DROPPING OUT OF NRN ROCKIES MAY PULL FRONT BACK NORTH.  BLV CHC
POPS ARE WARRENTED FOR SRN CWA ESPECIALLY IF STRONGER ECMWF VERIFIES.

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

DLF

IAZ040>042-051>053-063>065-076-077-087-310600-

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
740 PM CDT TUE MAY 30 2000

...A TORNADO WATCH THAT INCLUDES PART OF EAST CENTRAL IOWA IS IN EFFECT
UNTIL 1 AM CDT...

THE NATIONAL WEATHER SERVICE HAS ISSUED A TORNADO WATCH UNTIL 1AM CDT
FOR PARTS OF EAST CENTRAL IOWA.  THE WATCH IS WEST OF A LINE FROM
WASHINGTON TO DUBUQUE.  SOME CITIES AND TOWNS INCLUDED IN THE WATCH
ARE WASHINGTON...IOWA CITY...CEDAR RAPIDS...MANCHESTER...ANAMOSA AND
DUBUQUE.

STRONG THUNDERSTORMS WERE DEVELOPING JUST WEST OF A WATERLOO...DES
MOINES LINE. THE STORMS WERE MOVING EAST AT 25 MPH.  THESE STORMS HAVE
THE POTENTIAL TO PRODUCE LARGE HAIL...DAMAGING WINDS AND EVEN AN
ISOLATED TORNADO.

PEOPLE IN EAST CENTRAL IOWA SHOULD KEEP A CLOSE WATCH ON THE SKY THIS
EVENING...AND LISTEN TO LOCAL MEDIA OUTLETS OR NOAA WEATHER RADIO FOR
MORE INFORMATION AS THIS SERIOUS WEATHER SITUATION UNFOLDS.  BE PREPARED
TO TAKE COVER IF SEVERE THUNDERSTORMS THREATEN YOUR AREA.

IN ADDITION TO THE SEVERE WEATHER...THESE STORMS WILL ALSO HAVE THE
POTENTIAL TO PRODUCE VERY HEAVY RAIN. IT IS POSSIBLE THAT SOME AREAS
COULD SEE SUFFICIENT RAINFALL AMOUNTS TO CAUSE LOCALIZED FLOODING.

DLF