Severe Thunderstorm Warning 134, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
309 PM CDT THU JUL 3 2003

ACTIVE START TO JULY 4TH WEEKEND XPCD WITH TSTMS BEING PRIMARY
FOCUS...AND ASSOCD OUTFLOW COULD CAUSE PROBLEMS WITH TEMPS TOO.
CURRENT SCENARIO HAS JET MAX AHD OF TROF FM NRN PLAINS INTO CANADA.
WEAK SHRV NOTED ACRS CNTRL RCKYS MOVG INTO PLAINS.  VISIBLE/WV STLT
IMAGERY SHOWING INCRG UVM AHD OF FEATURE AND WL LIKELY HELP INITIATE
MCS TO OUR W OVNGT.  19Z SFC ANLYS SHOWS CNVGNC WITH OLD OUTFLOW
BNDRYS AND LRGR SCALE TROFS FM WI INTO W CNTRL IA AND NRN NE.
EVAPOTRANSPIRATION PRODUCING DWPNTS WELL INTO THE 70S ALG AND AHD OF
CNVGNC ZNS RESULTING IN STG THETA-E POOLING.  XPC CAP TO HOLD OFF
DVLP OVR WRN SXNS TIL TNGT.  ERN SXNS A BIT MORE PROBLEMATIC.
ALTHOUGH MLCAPES/CIN NOT AS IMPRESSIVE...SBCAPES INVOF KALO APCHG
5000 J/KG WITH LTL CIN.  STLT TRENDS SHOWING CU DMSHG HWVR SO UNLESS
TRENDS CHG WL FOLLOW LEAD OF MLCAPE/CIN INFO AND KEEP THIS EVE DRY
XCP FOR ISOLD ELEVATED SHWRS/TSTMS THAT FORMED SW.  BETTER CHCS MAY
BE FARTHER E.

MDLS FAIRLY SIMILAR WITH PROGRESSION OF IA WX NEXT SVRL
DAYS...ALTHOUGH GFS CONTS TO SUFFER FM AT LEAST SOME FEEDBACK.
AFOREMENTIONED PLAINS SHRT WV SHOULD IGNITE MCS OVNGT SPREADING INTO
IA EARLY FRI IN CONJUCTION WITH WEAK/MOD LOW LVL JET FOCUSED TWRD
NE/IA BORDER AND LOW LVL CNVGNC AFT 09Z.  SHOULD SEE MRNG MCS AND
PSBL REDVLPMT FRI AFTN AS TROF/FNT LAYS OUT ACRS HEART OF IA.  AMT
OF RECOVERY TIME WL BE KEY TO HOW BAD AFTN TSTMS BCM.  BOTH ETA/GFS
SHOW CNVNG AND HIGH INSTABILITY ACRS SRN SXNS LATE AFTN.  FEEL
EITHER MRNG OR AFTN ROUND COULD BE SVR SO ADD ADDED SVR/HVY RAIN
MENTION PER SPC MOD RISK OTLK.  FNT THEN MOVES ONLY SLOWLY SWD SO
HAVE KEPT CHCS GOING CNTRL/SRN PTNS FRI NGT AND SAT.  MORE CHCS SAT
NGT AS WRM ADVCTN SURGES NEWD AGN.  NO SGFNT COOLER AIR PUSH BHND
FNT SO HAVE COOLED TEMPS A FEW DEGREES OVR NEXT SVRL DAYS...BUT NO
TOO MUCH...ESSENTIALLY FOLLOWING GUIDANCE COMPROMISE.  WL HAVE TO
WATCH TEMPS TMRW.  IF CONVECTION OR OUTFLOW FAILS TO DVLP...MID
SHIFT MAY HAVE TO ISSUE HEAT ADVY.

MED RANGE MDLS IN GOOD AGREEMENT INTO EARLY NEXT WEEK BUT DVRG
SPCLLY BY WED.  BY THIS TIME ECMWF IS MORE PROGRESSIVE PUSHING UPR
LVL RDG INTO NRN PLAINS WHILE OTHER MDLS SHOW LESS AMPLIFIED
SOLUTIONS.  GFS AND CANADIAN ENSEMBLES SUGGEST A BIT FASTER MOVMT
THAN OPERATION RUNS WOULD TEND TO AGREE WITH NCEP FAVORING JUST A
BIT FASTER THAN RECENT GFS RUNS.  THIS LEADS TO CHCS SUN...MAINLY
DRNG THE MRNG...DUE TO LINGERING NIGHTTIME CONVECTION AND ALSO ALG
APCHG CDFNT LATE IN THE DAY.  FNT THEN PUSHES EVER SO SLOWLY SWD
ACRS IA LEADING TO CHCS FA WIDE SUN NGT...AND THEN MON AND MON NGT
CNTRL/SRN PTNS.  LOOKS LIKE SUFFICIENT CNVGNC AND ISENT LIFT WITH
LOW LVL JET FOR EITHER SFC BASED OR NOCTURNAL DVLPMT RESPECTIVELY.
NRN PLAINS HIGH PRESSURE SHOULD THEN GIVE US A BREAK TIL APCH OF
TROF OR WEAK FNT FM W TWRD DAY 7.  CONFIDENCE NOT HIGH ENOUGHT TO
PUSH POPS ABV CLIMO HWVR SO HAVE LEFT DRY FOR NOW.  TEMPS SHOULD BE
CLOSE TO CLIMO THRU PD BUT GENERALLY RAISED A FEW DEGREES TO ACCT
FOR COOL BIAS IN MOS.

.DSM...NONE

SMALL

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-081>086-
092>097-041100-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
557 AM CDT THU JUL 3 2003

THIS HAZARDOUS WEATHER OUTLOOK IS FOR CENTRAL IOWA.

.DAY ONE...TODAY AND TONIGHT

TEMPERATURES THIS AFTERNOON IN THE MID 90S WILL COMBINE WITH
DEWPOINTS AS HIGH AS THE MID 70S TO PRODUCE HEAT INDICES AROUND 105
DEGREES FOR SEVERAL HOURS...MAINLY ALONG AND WEST OF A LINE FROM
STORM LAKE TO LAMONI.

A COLD FRONT WILL MOVE INTO IOWA TONIGHT AND PROVIDE THE FOCUS FOR
ANOTHER ROUND OF THUNDERSTORMS. A FAST MOVING LINE OF THUNDERSTORMS
IS EXPECTED TO TRACK ACROSS NORTHERN IOWA LATE TONIGHT...WITH THE
POTENTIAL FOR DAMAGING WINDS AND ISOLATED LARGE HAIL. THERE IS A
MODERATE RISK FOR SEVERE WEATHER NORTH OF HIGHWAY 20. THUNDERSTORMS
COULD PRODUCE SEVERAL INCHES OF RAIN THURSDAY NIGHT INTO EARLY
FRIDAY MORNING NORTH OF HIGHWAY 20...WITH THE POTENTIAL FOR FLASH
FLOODING.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

THUNDERSTORMS WILL BE ONGOING EARLY FRIDAY MORNING OVER THE NORTHERN
HALF OF CENTRAL IOWA...WITH A CONTINUED THREAT FOR SEVERE STORMS AND
HEAVY RAIN...DIMINISHING THROUGH THE COURSE OF THE MORNING.
ADDITIONAL THUNDERSTORMS ARE EXPECTED FROM MIDDAY FRIDAY INTO FRIDAY
NIGHT AS THE COLD FRONT SAGS INTO SOUTHERN IOWA. A FEW STORMS COULD
BE SEVERE...MAINLY SOUTH OF HIGHWAY 30...WITH DAMAGING
WINDS...ISOLATED LARGE HAIL...AND LOCALLY HEAVY RAIN. THIS
SCENARIO...AND THE MOST FAVORED AREAS FOR SEVERE WEATHER AND FLASH
FLOODING...COULD CHANGE DEPENDING ON HOW THE CONVECTION EVOLVES
THURSDAY NIGHT AND EARLY FRIDAY...AND THOSE PLANNING OUTDOOR HOLIDAY
ACTIVITIES SHOULD STAY INFORMED WITH THE LATEST FORECASTS.

ACTIVE WEATHER WILL RESUME LATE SATURDAY NIGHT THROUGH
TUESDAY...WITH PERIODS OF SHOWERS AND THUNDERSTORMS EXPECTED ACROSS
CENTRAL IOWA. SEVERE THUNDERSTORMS ARE POSSIBLE LATE SATURDAY NIGHT
INTO SUNDAY...AND AGAIN ON MONDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS LIKELY TONIGHT NORTH OF HIGHWAY 20...AND
POSSIBLE SOUTH TO HIGHWAY 34. ACTIVATION IS POSSIBLE AGAIN FRIDAY
OVER ALL OF CENTRAL IOWA.
&&

MORE INFORMATION CAN BE OBTAINED AT WWW.CRH.NOAA.GOV/DMX (ALL LOWER
CASE).

KINNEY