Severe Thunderstorm Warning 103, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
244 PM CDT WED MAY 19 2004

.SHORT TERM...TNGT THRU THU NGT

NEAR TERM FORECAST ISSUES DEAL WITH SEVERE POTENTIAL TONIGHT AND ANY
THREAT FOR FLOODING ESPECIALLY SW CWA.  CURRENT SYNOPSIS SHOWING
UPPER LEVEL 300HPA JET STREAK THROUGH GREAT BASIN INTO WRN DAKOTAS
WITH GOOD 40 TO 80 METER HEIGHT FALLS AT 500 BELOW LEFT EXIT REGION
IN ERN MT/ND. 500 RIDGING EXTENDING THROUGH THE CENTRAL PLAINS WITH
SOMEWHAT OF A WEAKLY DIFFLUENT FLOW OVER THE STATE. BETTER THAN 50
DEG TDS AT 850 FROM BIS SOUTH TO MPX AND ILX WITH 850 WARM FRONT
EVIDENT IN ANALYSIS FROM WRN KS TO CENTRAL MO. SFC ANALYSIS HAS SEEN
FRONTAL BOUNDARY SURGING NORTHWARD THROUGH EASTERN KS/NW MO AND IS
FAVORED AREA FOR CONVECTIVE INITIATION THIS EARLY THIS AFTERNOON
ALONG SFC INSTABILITY GRADIENT AS H5 SHORT WAVE EJECTS INTO AREA
FROM NORTHERN PLAINS. GIVEN EXTREME INSTABILITY...GREAT LOCALIZED
BULK SHEAR AND STEEP LOW LEVEL THETA-E LAPSE RATES THINK DAMAGING
WIND POTENTIAL IS HIGH WITH ANY LONG LIVED SUPERCELLS THIS EVENING.
FORECAST SOUNDING HWBZS AROUND 11K  SHOWING GOOD LARGE HAIL
POTENTIAL. TOR IS POTENTIAL IN FAR SW WITH EHIS APPROACHING 3 AND
WILL LIKELY EXPAND THROUGH S-CENTRAL.  LIMITING FACTOR OVERALL
APPEARS TO BE EXTENSIVE CLOUD COVER OVER THE CWA...BUT THIS IS
STEADILY ERODING ON THE SOUTHERN EDGE...BEGINNING TO TURN FROM
OVERCAST TO CLOUD STREETS.

POTENTIAL FOR FLASH FLOODING EXISTS WITH CURRENT PWATS 1-1.25 INCHES
AND AVERAGING 150-170 PERCENT OF NORMAL IN COMBINATION WITH RECENT
FLOODING OVER WEEKEND WILL NEED FLOOD WATCH. QUESTION WILL BE HOW
EXTENSIVE OF AN AREA TO COVER. POTENTIAL EXISTS FOR SIGNIFICANT
TRAINING OF CELLS IF ANY SYSTEM SHIFTS TO LINEAR CONVECTIVE MODE
LATE. LOWEST FFG GUIDANCE NUMBERS ARE FOUND SOUTH OF I-80 AND WEST
OF I-35 CORRIDOR. ACTIVE PATTERN CONTINUES WITH ETA PLAYING OUT
RELEASING INSTABILITY CENTERED MORE OVER EASTERN THIRD OF IOWA ALONG
SYNOPTIC BOUNDARY. ALOT WILL DEPEND ON LOCALIZED MESOSCALE
BOUNDARIES LEFT OVER FROM TONIGHT HOWEVER. THE PROLONGED PERIOD OF
POTENTIAL HEAVY RAINS LENDS VALIDITY TO FLOOD WATCH.

.LONGER TERM...FRI THROUGH WED

REGION REMAINS IN ZONAL TO INCREASING SWRLY FLOW ALOFT INTO WEEKEND.
BOTH THE ECMWF AND GFS ARE CONSISTENT WITH LOW SFC PRESSURE OVER
PLAINS AND SYNOPTIC THERMAL BOUNDARY LIFTING TO GENERALLY TO NORTH
OF STATE PLACING BEST POPS OVER NRN FORECAST AREA ON FRIDAY/FRIDAY
NIGHT. AS FOCUS FOR STORMS...LOW POPS PDS EXIST STILL IN THE MONDAY
TIMEFRAME. MADE MINOR UPWARD ADJUSTMENTS TO TEMPS IN SRN CWA OVER
WEEKEND. ADDED DAY 7 (WED) POPS GIVEN PERSISTENT PVA REGIME.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...FLOOD WATCH WEDNESDAY NIGHT
THROUGH THURSDAY ALONG AND SOUTH OF I-80 AND ALONG AND WEST OF I-35.

&&

RUSSELL

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
351 PM CDT WED MAY 19 2004

IAZ044-045-057>059-070>072-081>083-092>094-192145-
ADAIR-ADAMS-AUDUBON-CARROLL-CASS-CLARKE-CRAWFORD-DALLAS-DECATUR-
GUTHRIE-MADISON-RINGGOLD-TAYLOR-UNION-
351 PM CDT WED MAY 19 2004

...EXPLOSIVE DEVELOPMENT OF SEVERE THUNDERSTORMS LIKELY BY 5 PM...
ISOLATED SUPERCELL THUNDERSTORMS ARE LIKELY OVER THE NEXT 1 TO 2
HOURS ALONG A WARM FRONT WHICH LIES JUST WEST OF AUDUBON...CASS...
...ADAMS AND TAYLOR COUNTIES.  THIS INCLUDES AREAS IN AND AROUND
AUDUBON...ATLANTIC...CORNING...GREENFIELD...BEDFORD...CRESTON...
AND MOUNT AYR.  THESE STORMS COULD BECOME DANGEROUS QUICKLY...WITH
FAST DEVELOPING TORNADOES AND VERY LARGE HAIL.  BE PREPARED TO TAKE
APPROPRIATE ACTION IF A WARNING IS ISSUED. && STORM SPOTTER GROUPS
SHOULD BE READY FOR ACTIVATION SOON.

KULA