Severe Thunderstorm Warning 179, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1240 PM CDT TUE SEP 22 2015

.SHORT TERM /TODAY/...
ISSUED AT 457 AM CDT TUE SEP 22 2015

PRIMARY QUESTION TODAY WILL BE ONSET OF PRECIP...IF ANY.  STRONG
ONTARIO SHORT WAVE/PV ANOMALY CONTINUES TO PUSH COLD FRONT THROUGH
MN WITH ISALLOBARIC MAX TOWARD THE CANADIAN BORDER. MODELS SUGGEST
THE FRONT WILL BRIEFLY DRIFT INTO NRN IA BEFORE WAVE DEPARTS AND
HEIGHT RISES EVENTUALLY DIFFUSE IT AND PUSH WHAT IS LEFT OF THE
BOUNDARY NWD AGAIN. LOW LEVEL MOISTURE CONVERGENCE IS CURRENTLY
STRONG BUT SOUNDINGS SHOW LITTLE HOPE OF ANY SURFACE BASED
DEVELOPMENT DUE TO INVERSION. LOW LEVELS EVENTUALLY MIX BY
AFTERNOON...BUT WARM LAYER AROUND 2KM SHOULD KEEP ANYTHING MORE THAN
CU FROM FORMING WITH CONVERGENCE WEAKENING SIMULTANEOUSLY. ELEVATED
POTENTIAL LOOKS MINIMAL INITIALLY AS WELL WITH MOISTURE LACKING.
SOUNDINGS QUITE DRY ABOVE 2KM.  H7/H85 MOISTURE...THETA-E ADVECTION
AND FRONTOGENETICAL FORCING DO INCREASE SOMEWHAT INTO WRN IA BY
AFTERNOON HOWEVER.  THUS FORECAST IS ESSENTIALLY DRY OUTSIDE OF
SLIGHT CHANCES STARTING IN W CENTRAL IA BY LATE AFTERNOON.

MODELS SUGGEST STRATUS WILL MAINTAIN OR POSSIBLY EXPAND INTO THE
MORNING BEFORE MIXING OUT SOMEWHAT SOUTH. STRATUS MAY LINGER LONGER
NORTH IN THE VICINITY OF THE BOUNDARY HOWEVER SO HAVE HIT CLOUD
WORDING STRONGER THERE. GENERAL LOW LEVEL WARM ADVECTION REGIME WILL
CONTINUE BUT LOW CLOUDS WILL MAKE THE DEGREE OF ADDITIONAL WARMING
ABOVE PERSISTENCE PROBLEMATIC.  THUS HAVE AT OR JUST BELOW
PERSISTENCE NORTH AND SEVERAL DEGREES WARMER SOUTH.

.LONG TERM /TONIGHT THROUGH MONDAY/...
ISSUED AT 457 AM CDT TUE SEP 22 2015

RELATIVELY QUIET WEATHER FOR THE LONG TERM CONTINUES. WEDNESDAY INTO
THURSDAY LOOKS LIKE THE ONLY "ACTIVE" PERIOD IN THIS FCST.

WEDNESDAY AND THURSDAY...
06Z TUE WATER VAPOR IMAGERY PICKING UP ON MOISTURE FROM THE
REMNANTS OF DECAYING TROPICAL DEPRESSION 16-E ADVANCING OVER THE
SW CONUS. UPSTREAM IS A MID-LEVEL CUT-OFF LOW WHICH IS PHASING IN
ENERGY WITH THE TROPICAL SYSTEM. THIS SYSTEM BECOMES POSITIVELY
TILTED AS IT PROPAGATES NEWARD TOWARDS THE MIDWEST. THROUGHOUT
THIS SEASON...MODELS HAVE GENERALLY UNDERDONE QPF WITH SYSTEMS
THAT TAP INTO ENERGY/MOISTURE BEING ADVECTED ACROSS THE SW CONUS
INTO IOWA. DIFFERENCE IN THIS EVENT IS THAT THERE WILL BE A
NOTABLE LACK OF REINFORCING MOISTURE TRANSPORT FROM THE GULF OF
MEXICO AS EASTERLY FLOW WILL BE PRESENT ACROSS THE SOUTHEASTERN
CONUS. 00Z TUE MODEL RUNS IN GOOD AGREEMENT WITH SQUEEZING OUT
PWATS IN THE 1.5 TO 1.75 INCH RANGE...OR +1 TO +2 STD DEV. WITH
THE EXCEPTION OF DAYTIME HEATING WEDNESDAY...CAPE NOT THE
STRONGEST. DURING DAYTIME HEATING HOURS...WESTERN IOWA HAS CAPE
VALUES IN THE 1500 TO 2000 J/KG RANGE. WHILE INSTABILITY
PRESENT...LACK OF STRONG FORCING MECHANISM PLUS 0-6KM BULK SHEAR
VALUES LESS THAN 30 KTS WILL EFFECTIVELY NULLIFY SVR WX CHANCES AS
STORMS WILL STRUGGLE TO ORGANIZE ENOUGH TO BECOME SVR. FOR
EXCESSIVE RAINFALL POTENTIAL IN DMX CWA...WARM CLOUD DEPTHS IN THE
10 TO 12KFT RANGE...PLUS AFOREMENTIONED PWATS...WITH MARGINAL CAPE
VALUES SUGGEST LOWER CHANCES FOR EXCESSIVE RAINFALL. BY LATE
THURSDAY...THIS SYSTEM ESSENTIALLY LOSES ITS ENERGY AND HIGH
PRESSURE TAKES OVER FROM THE EAST.

FRIDAY THROUGH MONDAY...
HIGH PRESSURE WILL KEEP US DRY. MSLP IS IN THE +1 TO +2 STD DEV
RANGE. 850MB TEMPS NEAR 0 STD DEV INITIALLY SUGGEST NEAR NORMAL
TEMPERATURES DURING THIS TIME PERIOD. FURTHER EXAMINATION HOLDS
PERSISTENT 850MB TEMPS IN THE 13 TO 16C RANGE. THUS HAVE GONE IN
THE MID 70S TO LOW 80S. MONDAY AND BEYOND...THE GFS AND EURO VARY
WILDLY. THE EURO BRINGS A HIGH THROUGH SOUTHERN
SASKATCHEWAN/MANITOBA INTO THE CONUS...WHICH WOULD BRING BIG TIME
CAA TO IOWA. THE GFS HAS THE COMPLETE OPPOSITE AND WAA INTO IOWA.
WILL STICK WITH PERSISTENCE UNTIL PROVEN OTHERWISE.

&&

.AVIATION...22/18Z
ISSUED AT 1237 PM CDT TUE SEP 22 2015

PREDOMINATELY VFR CONDITIONS ARE EXPECTED THROUGH THE PERIOD WITH
A SOUTH TO SOUTHEASTERLY WIND OF 5 TO 10 KTS. PERIODS OF SUB VFR
CONDITIONS ARE POSSIBLE IN ANY STORMS THAT IMPACT WESTERN IOWA
THIS AFTERNOON AND INTO TOMORROW...BUT CONFIDENCE IN PRECIP
PLACEMENT AND TIMING WAS TOO LOW TO MENTION IN ANY SPECIFIC TAF.

&&

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

SHORT TERM...SMALL
LONG TERM...KOTENBERG
AVIATION...SKOW

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
425 AM CDT TUE SEP 22 2015

IAZ075-085-086-095>097-230930-
MAHASKA-MONROE-WAPELLO-WAYNE-APPANOOSE-DAVIS-
425 AM CDT TUE SEP 22 2015

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...TODAY AND TONIGHT

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED.

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>074-
081>084-092>094-230930-
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-ADAMS-UNION-CLARKE-
LUCAS-TAYLOR-RINGGOLD-DECATUR-
425 AM CDT TUE SEP 22 2015

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...TODAY AND TONIGHT

A FEW THUNDERSTORMS ARE POSSIBLE OVERNIGHT. SEVERE WEATHER IS NOT
EXPECTED.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

SCATTERED THUNDERSTORMS WILL BE POSSIBLE THROUGH THURSDAY NIGHT.
SEVERE WEATHER IS NOT ANTICIPATED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED.