Severe Thunderstorm Warning 208, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
258 PM CDT SAT JUL 1 2006

.DISCUSSION...
FRONTAL BOUNDARY CURRENTLY ACROSS NORTHWEST IOWA WILL CONTINUE TO
SAG SOUTH THE REMAINDER OF THE AFTERNOON BEFORE STALLING OVER
CENTRAL IOWA THIS EVENING. WEAK CONVECTION HAS BEEN ONGOING THIS
MORNING NEAR THE HIGHWAY 20 CORRIDOR WITHIN ZONE OF STRONG
ISENTROPIC LIFT ALONG THE 315K SFC AND 850 MB CONVERGENCE. DESPITE
THE FRONT BECOMING DIFFUSE BY THIS EVENING...SPEED MAX MOVING ACROSS
SOUTH DAKOTA COUPLED WITH INCREASING CONVERGENCE SHOULD ENHANCE
ACTIVITY CURRENTLY ONGOING OVER NORTHEAST NEBRASKA AND FOCUS ALONG
THE BOUNDARY. GIVEN THE DEPTH OF THE WARM LAYER TONIGHT AND LACK OF
STRONG EFFECTIVE SHEAR...IT WILL BE DIFFICULT TO MAINTAIN A SEVERE
HAIL THREAT FOR AN EXTENDED TIME TONIGHT. CONVECTIVE DOWNBURST
POTENTIAL APPEARS TO BE THE GREATER THREAT GIVEN STEEP LAPSE RATES
THOUGH DOWNDRAFT CAPES BELOW 750 J/KG ARE NOT REAL FAVORABLE. A MORE
VIGOROUS SHORT WAVE ARRIVES SUNDAY NIGHT AND EARLY MONDAY AND ALONG
WITH THE INFLUENCE OF THE RIGHT ENTRANCE WILL PROMOTE ADDITIONAL
THUNDERSTORM DEVELOPMENT ALONG THE BOUNDARY OVER THE SOUTHERN HALF
OF THE AREA AND HAVE UPPED POPS TO LIKELY OVER THIS REGION. FARTHER
NORTH...DESPITE DRY MID LEVEL AIR PUNCHING IN FROM THE NORTH...A
LACK OF A DRY PUSH AT THE SFC WILL LEAVE DEWPOINTS IN THE 60S NORTH
OF THE BOUNDARY AND THIS ALONG WITH TEMPERATURES IN THE MID TO UPPER
80S WILL CREATE AN UNCAPPED SITUATION. A FEW SCATTERED STORMS ARE
POSSIBLE DURING THE AFTERNOON AND EVENING HOURS. POPS CONTINUE ON
MONDAY. HAVE TEMPERED HIGHS BACK TO LOWER TO MID 80S BASED ON
EXPECTED CLOUD COVER AND CONVECTION AND MAY TO SCALE BACK FURTHER
WITH FUTURE ISSUANCES.

THE RIDGE AXIS PRESSES INTO THE AREA BEGINNING ON TUESDAY WITH DRIER
AIR FILTERING INTO THE STATE FOR THE MID TO END PORTION OF THE WEEK.
HAVE INCREASED THE DIURNAL RANGES DURING THE PERIOD BY COOLING
OVERNIGHT LOWS INTO THE MID 50S TO LOWER 60S WITH HIGHS IN THE 80S.
THE UPPER LEVEL RIDGE AMPLIFIES WITH HEIGHTS INCREASING OVER IOWA.
DESPITE THIS...FLOW FROM THE SFC HIGH TO THE EAST WILL PREVENT A BIG
WARM UP DURING THE PERIOD. NO PRECIPITATION IS FORECAST THROUGH THE
EXTENDED WITH THE REGION REMAINING INFLUENCED BY THE HIGH PRESSURE.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...NONE.

&&

DONAVON

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
322 PM CDT SAT JUL 1 2006

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-
081>086-092>097-021100-
EMMET-KOSSUTH-WINNEBAGO-WORTH-PALO ALTO-HANCOCK-CERRO GORDO-
POCAHONTAS-HUMBOLDT-WRIGHT-FRANKLIN-BUTLER-BREMER-SAC-CALHOUN-
WEBSTER-HAMILTON-HARDIN-GRUNDY-BLACK HAWK-CRAWFORD-CARROLL-GREENE-
BOONE-STORY-MARSHALL-TAMA-AUDUBON-GUTHRIE-DALLAS-POLK-JASPER-
POWESHIEK-CASS-ADAIR-MADISON-WARREN-MARION-MAHASKA-ADAMS-UNION-
CLARKE-LUCAS-MONROE-WAPELLO-TAYLOR-RINGGOLD-DECATUR-WAYNE-
APPANOOSE-DAVIS-
322 PM CDT SAT JUL 1 2006

THIS HAZARDOUS WEATHER OUTLOOK IS ALL OF CENTRAL IOWA.

.DAY ONE...TONIGHT

THUNDERSTORMS WILL INCREASE IN AREAL COVERAGE OVER THE NORTH THIRD
OF IOWA THROUGH THE EARLY EVENING...AND DROP SOUTH DURING THE NIGHT.
THE BEST CHANCE FOR SEVERE WEATHER WILL BE BETWEEN THE HIGHWAY 20
AND HIGHWAY 34 CORRIDORS. SOME SEVERE STORMS ARE POSSIBLE THIS
EVENING...WITH THE MAIN THREATS OF WIND GUSTS AROUND 60 MPH AND
MARGINALLY SEVERE HAIL.  OVERNIGHT THE MAIN THREAT WILL LIKELY SHIFT
TO HEAVY RAINFALL...WITH LOCAL AMOUNTS OF 1 TO 2 INCHES POSSIBLE.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SUNDAY AND
MONDAY...MAINLY DURING THE LATE AFTERNOON AND EVENING HOURS. LARGE
HAIL AND DAMAGING WIND ARE THE MAIN THREATS. LOCATIONS SOUTH OF
HIGHWAY 30 WILL BE THE MOST FAVORED FOR SEVERE WEATHER.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE REQUIRED THIS EVENING FROM 7 PM THROUGH
MIDNIGHT...AND AGAIN SUNDAY AND MONDAY...ESPECIALLY IN THE LATE
AFTERNOON AND EVENING HOURS.

MS JUL 06