High Wind in Iowa, August 12, 2011

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1205 AM CDT FRI AUG 12 2011

.UPDATE...
ACTIVITY CONTINUES TO WORK ITS WAY TOWARD THE STATE FROM
SOUTHEASTERN SD...WITH TIMING EXPECTED TO APPROACH THE CWA
TOWARD LATE EVENING INTO THE OVERNIGHT HOURS. THEREFORE UPDATED THE
FORECAST TO REFLECT THE LATEST TRENDS BY REMOVING POPS FROM NOW
UNTIL 03Z...AND DELAYING SYSTEM PROGRESSION SOME LATE THIS EVENING
INTO THE OVERNIGHT. ALSO INCREASED MIN TEMPS ACROSS THE WESTERN HALF
OF THE CWA A DEGREE OR TWO AS TEMPERATURES NOT FALLING QUITE AS FAST
AS PREVIOUS FORECAST HAD DUE TO INCREASING CIRRUS SHIELD AHEAD OF
THE CONVECTION ACROSS SE SD.

.SHORT TERM /TONIGHT/...
MAIN CONCERN IS TSRA CHANCES AND RELATED QPF TONIGHT.

SURFACE HIGH PRESSURE WILL RETREAT EASTWARD DURING THE PD...ALLOWING
FOR A WAA REGIME TO SET UP ACROSS OUR CWA. SHORTWAVE WILL SPARK
CONVECTION FROM THE DAKOTAS INTO NEBRASKA THIS AFTN/EVE. IT IS THEN
EXPECTED TO EVOLVE INTO AN MCS. MEAN LAYER FLOW SUGGEST THE MCS WILL
TRACK EWD TOWARD IA...MAY ALSO DEVELOP SE PER CORFIDI VECTORS. SINCE
THE BEST FORCING AND MOISTURE TRANSPORT WILL REMAIN JUST TO THE W OF
OUR CWA DURING THE PD...THE MCS IS EXPECTED TO GENERALLY DECAY AS IT
MOVES INTO OUR CWA OVERNIGHT. OUR FAR WESTERN CWA HAS THE BEST
CHANCES FOR SEEING STRONGER STORMS DUE TO ITS PROXIMITY TO THE
GREATER FORCING AND STABILITY. ATTM SVR STORMS ARE NOT EXPECTED. FOR
SIMILAR REASONS...THE HIGHEST QPF AMOUNTS ARE EXPECTED TO REMAIN TO
THE W OF OUR CWA AS WELL. PWATS FROM ERN NE INTO FAR WRN IA GO AS
HIGH AS 1.4 TO 1.6 IN OVERNIGHT...WHICH IS ABOVE NORMAL /75TH TO
90TH PERCENTILE/. THE CHANCES FOR SEEING MEASURABLE PRECIP WILL
INCREASE FROM EAST TO WEST.

.LONG TERM /FRIDAY THROUGH THURSDAY/...
SHORTWAVE WILL DROP THROUGH THE DAKOTAS ON FRIDAY AND GRADUALLY WORK
INTO NORTHERN ILLINOIS BY SATURDAY EVENING.  INITIALLY...DECAYING
MCS IS EXPECTED TO BE PASSING INTO CENTRAL IOWA ON FRIDAY MORNING
WITH A LIMITED SEVERE THREAT MAINLY CONSISTING OF DAMAGING WINDS.
MODELS INDICATING MUCH OF THE STRONGER LOW LEVEL FLOW WILL BE
INTERCEPTED BY CONVECTION ACRS KS AND MO DURING THE DAY WHICH MAY
LIMIT THE AMOUNT OF CONVECTION THAT REDEVELOPS IN IA BY THE
AFTERNOON.  HOWEVER...BEST DPVA WILL BE ARRIVING IN IOWA DURING THE
AFTERNOON ALONG WITH THE FRONTAL BOUNDARY WHICH SHOULD HELP POP
STORMS DURING THE AFTERNOON...ESPECIALLY CENTRAL AND EAST BEFORE
HEADING INTO ILLINOIS BY THE EVENING.  SOME ADDITIONAL THREAT WILL
PERSIST LATE FRIDAY NIGHT INTO SATURDAY...PRIMARILY IN THE EAST AS
THE UPPER LOW DROPS THROUGH NORTHEAST IOWA WITH ASSOCIATED
INSTABILITY A GOOD MID LEVEL LAPSE RATES.  SURFACE RIDGING WILL THEN
BUILD INTO THE MIDWEST WITH SUBSIDENCE AND A SEASONABLY COOL
CANADIAN AIRMASS. OVERNIGHT LOW IN THE 50S AND LOWER 60S ARE
EXPECTED SATURDAY NIGHT AND SUNDAY NIGHT WITH PLEASANT DAYTIME HIGHS
ON SUNDAY WITH LIGHT WIND. EURO AND GFS BOTH COME BACK WITH DECENT
WAA AND INCREASING THETA-E ADVECTION ON MONDAY INTO MONDAY NIGHT.
ANTICIPATE CONVECTION TO BREAK OUT WITH THIS PUSH OF WARM MOIST AIR
INTO THE STATE DURING THIS TIME AND CONTINUE INTO TUESDAY.  THERMAL
RIDGING WILL BUILD INTO THE PLAINS AND TOWARD IOWA DURING THE MIDDLE
OF THE WEEK WHICH WILL PUSH TEMPERATURES TO OR ABOVE NORMAL BY
WEDNESDAY.

&&

.AVIATION...12/06Z
LINE OF STORMS WEAKENING AND DISSIPATING AS IT CONTINUES TO WORK
ITS WAY EAST/SOUTHEAST INTO THE CWA. HAVE HANDLED WITH SOME
SHRA/CB MENTIONS AS FEEL LIGHTNING WILL BE LIMITED ACROSS THE
AREA. ADDITIONAL THUNDERSTORM DEVELOPMENT IS EXPECTED TOWARD
MIDDAY FRIDAY AND EXPECTED TO CONTINUE THROUGH MUCH OF THE
FORECAST PERIOD.

&&

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

&&

UPDATE...BEERENDS
SHORT TERM...ZOGG
LONG TERM...COGIL
AVIATION...BEERENDS

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
542 AM CDT THU AUG 11 2011

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-081>086-
092>097-121100-
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-
542 AM CDT THU AUG 11 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...TODAY AND TONIGHT

SCATTERED THUNDERSTORMS WILL SPREAD INTO WESTERN IOWA THIS
EVENING...AND OVER ALL OF THE AREA BY FRIDAY MORNING. SEVERE
WEATHER IS NOT EXPECTED.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

THUNDERSTORMS ARE EXPECTED FRIDAY INTO SATURDAY. SOME OF THE
STORMS MAY BE SEVERE FRIDAY AFTERNOON AND EVENING...WITH THE
PRIMARY THREATS BEING HIGH WINDS AND LARGE HAIL. THERE WILL BE
INTERMITTENT THUNDERSTORMS AGAIN TUESDAY AND WEDNESDAY. IT IS TOO
EARLY TO BE VERY SPECIFIC ABOUT THE SEVERE POTENTIAL...HOWEVER IT
CAN NOT BE RULED OUT.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED LATE FRIDAY AND FRIDAY EVENING.

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE DES MOINES IA
1034 PM CDT THU AUG 11 2011

IAZ004-015-023-033-034-044-045-120545-
EMMET-PALO ALTO-POCAHONTAS-SAC-CALHOUN-CRAWFORD-CARROLL-
INCLUDING THE CITIES OF...ESTHERVILLE...EMMETSBURG...POCAHONTAS...
SAC CITY...ROCKWELL CITY...DENISON...CARROLL
1034 PM CDT THU AUG 11 2011

...THUNDERSTORMS WITH GUSTY WINDS AND BRIEF HEAVY RAIN HEADING
INTO THE AREA THIS EVENING...

A LINE OF THUNDERSTORMS OVER WESTERN IOWA WILL MOVE INTO THE
REGION BETWEEN 1030 PM AND 1115 PM CDT THIS EVENING. THE STORMS
MAY PRODUCE WIND GUSTS TO 35 TO 45 MPH AND BRIEF HEAVY RAINS WHICH
MAY REDUCE VISIBILITY AND RESULT IN POOR DRIVING CONDITIONS FOR A
SHORT PERIOD OF TIME.

PERSONS TRAVELING ACROSS THE REGION TONIGHT SHOULD EXPECT TO BE
IMPACTED BY THIS LINE OF THUNDERSTORMS FOR ABOUT 1 TO 2 HOURS. THE
STORMS ARE MOVING TO THE SOUTHEAST AT 35 MPH.

REV