Severe Thunderstorm Warning 36, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
313 PM CDT TUE MAY 30 2000

CHALLENGES TO INCLUDE TIMING AND PLACEMENT OF THUNDERSTORMS DURING
FORECAST AND HOW CLOUDS WL MESS WITH TEMPS.  CURRENTLY...CLOUDS WITH
ISOLD SHRA CONTINUE TO MOVE ACRS MUCH OF CWA.  AREAS IN THE SW WHICH
HAVE CLEARED HAVE SEEN TEMPS JUMP TO NEAR 90.  MOISTURE CONVERGENCE
HAS PERSISTED IN W CENTRAL ZONES AS WEAK WAVE IN S CENTRAL NEBRASKA
MOVES EAST.  MAIN QUESTION IS STRENGTH OF CAP AND IF IT WL HOLD.
18Z RUC HAS THE CAP BREAKING BY 00Z WITH ANY THUNDERSTORMS MOVING
RAPIDLY TO THE EAST.  MDT RISK IN LARGE SWATH ACRS CENTRAL IA AND WL
HAVE SEVERE WORDING IN ZONES AS ANY STORMS THAT FORM SHOULD RAPIDLY
INTENSIFY WITH DAMAGING WINDS AND LARGE HAIL THE MAIN THREAT.

MODELS STILL A BIT DIFFERENT TODAY WITH FRONTAL POSITIONING THROUGH
FRIDAY MORNING WITH A COMPROMISE THE BEST AT THIS POINT.  SO...FOR THE
BIG PICTURE...THE FRONT HEADS A BIT FARTHER SOUTH OVERNIGHT BEFORE
RETREATING BACK NORTH BY WEDNESDAY EVENING.  IT WL THEN MOVE
SOUTHEAST ACRS THE CWA BY LATER ON THURSDAY.  MOST CONVECTION WL
REMAIN ALONG AND NORTH OF THE FRONT AT THE EDGE OF THE CAP.  TIMING
OF CONVECTIVE SYSTEMS THROUGH CWA A BIG PROBLEMS BUT KNOWING THAT
FRONT WL BE IN CENTRAL OR NORTHERN IA LEAVES BEST PCPN CHANCES ACRS
THE NORTH.  TEMPS WL AGAIN BE TRICKY WITH RESIDUAL CLOUD COVER LEFT
OVER FROM CONVECTIVE SYSTEMS WL INHIBIT SOLAR INSOLATION.  WL AGAIN
KEEP IT ON THE WARM SIDE IN THE SOUTH LEANING TOWARDS COOLER
GUIDANCE IN THE NORTH.

IN THE EXTENDED...WL SEE FRONT PUSH SOUTHWARD ON FRIDAY WITH NORTH
DRYING OUT BUT SHOWERS CONTINUING SOUTH.  SATURDAY 9MAY SEE A BRIEF
BREAK BUT EXPECT WAA TO ONCE AGAIN INCREASE CHC FOR PCPN BY LATER IN
THE DAY.  SUNDAY APPEARS TO HAVE A DECENT CHC FOR THUNDERSTORMS
THROUGH THE DAY.

.DSM...NONE.

COGIL

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-081>086-
092>097-311100-

CENTRAL IOWA THUNDERSTORM OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
152 PM CDT TUE MAY 30 2000

HAZARD--SCATTERED SEVERE THUNDERSTORMS CAPABLE OF PRODUCING WIND
GUSTS TO 85 MPH AND HAIL OF UP TO AN INCH IN DIAMETER.

AREA OF CONCERN--ALL OF THE DES MOINES COUNTY WARNING AREA HAS THE
POSSIBILITY OF SEVERE WEATHER.  THE GREATEST THREAT IS THAT PART OF
IOWA NORTH OF U.S. HIGHWAY 34 AND SOUTH OF U.S. HIGHWAY 18.

TIMING DETAILS--AFTER 600 PM OVER THE WESTERN PART OF THE FORECAST
AREA...SPREADING TO THE REST OF THE AREA BY AROUND MIDNIGHT.

METEOROLOGICAL COMMENTS--A POTENTIALLY EXPLOSIVE WEATHER SITUATION
IS TAKING SHAPE OVER PARTS OF THE CENTRAL U.S.  A NEARLY STATIONARY
FRONT EXTENDS FROM CENTRAL WISCONSIN...ACROSS NORTHWEST IOWA...INTO
A LOW PRESSURE OVER NORTH CENTRAL KANSAS.  THE FRONT WILL MOVE
LITTLE AS THE LOW IN KANSAS MOVES NORTHEAST ALONG THE FRONT.  STRONG
SOUTH WINDS OF 25 TO 40 MPH ACROSS KANSAS WERE DRAWING MOISTURE
NORTH INTO EASTERN NEBRASKA AND SOUTHWEST IOWA.  DEW POINT
TEMPERATURES HAVE CLIMBED INTO THE LOW TO MID 70S FROM WEST CENTRAL
IOWA...SOUTH INTO THE SOUTHERN PLAINS.  THE ATMOSPHERE IS CAPPED AT
PRESENT WITH A LAYER OF VERY WARM AIR MOVING OVER THE REGION.
ALTHOUGH TEMPERATURES APPROACHING 100 DEGREES ARE PRESENT AS FAR
NORTH AS SOUTHEAST NEBRASKA...THE CAP IS LIKELY TO HOLD UNTIL LATER
TODAY.  TEMPERATURES ALOFT WILL BEGIN TO COOL SOMEWHAT AFTER DARK
AND THE CAP IS LIKELY TO BREAK OVER EAST CENTRAL NEBRASKA OR WESTERN
IOWA TOWARD SUNSET OR SHORTLY AFTER.  THUNDERSTORMS WILL QUICKLY
FORM INTO A MESOSCALE CONVECTIVE COMPLEX AND RACE EAST.  THE FAST
MOVEMENT SUGGESTS THE POSSIBILITY OF HIGH WINDS...SUCH AS OCCURRED
OVER NEBRASKA LAST NIGHT...TO SWEEP ACROSS IOWA.

PRECAUTIONS--SKYWARN...SPOTTER GROUPS...AMATEUR RADIO GROUPS AND LAW
ENFORCEMENT PERSONNEL MAY BE REQUIRED THIS EVENING INTO THE NIGHT.
STAY ABREAST OF LATER FORECASTS...STATEMENTS AND POSSIBLE WATCHES
AND WARNINGS THAT MAY BE ISSUED LATER THIS AFTERNOON OR TONIGHT.

FOR MORE INFORMATION GO TO THE DES MOINES NATIONAL WEATHER SERVICE
WEBSITE AT WWW.CRH.NOAA.GOV/DMX.

MS MAY 00