Severe Thunderstorm Warning 112, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
620 PM CDT FRI JUN 4 2010

...HEAVY RAIN AND FLASH FLOODING A CONCERN TONIGHT...

.SHORT TERM /TONIGHT/...
ACTIVE NIGHT HEADED OUR WAY WITH HYDRO CONCERNS FOR SHORT TERM INTO
TOMORROW. FRONT BECOMING EAST...WEST ORIENTED ACROSS SOUTHERN IOWA
WITH ZONAL FLOW ALOFT...MID LEVEL WAVE APPROACHING...AND H850 LOW
LEVEL JET EXPECTED TO STRENGTHEN OVERNIGHT INTO THE BOUNDARY.  SOUTH
OF THE BOUNDARY THIS AFTERNOON...DEW POINTS HAVE POOLED INTO THE 65
TO 70 DEGREE RANGE. AT H850 THIS MORNING...SUBJECTIVE ANALYSIS SHOWS
LARGE +15C POOL OF DEW POINTS COVERING MOST OF GULF COAST AND LOWER
MISSISSIPPI RIVER VALLEY. SOUNDINGS INDICATE EFFICIENT RAINFALL
OVERNIGHT WITH FREEZING LEVEL BETWEEN 15-15.5KFT.  THOUGH CAPE QUITE
IMPRESSIVE THROUGH THE EVENING...SOUNDINGS QUICKLY BECOME SATURATED
BY 06Z WHEN MCS EXPECTED TO DEVELOP. WITH THAT IN MIND...MAY BE SOME
SVR STORMS THROUGH EVENING HOURS OVER THE FAR SOUTH...BUT LATER IN
THE NIGHT IT WILL BECOME MORE DIFFICULT TO BRING WIND AND HAIL TO
SFC DUE TO SATURATED COLUMN AND WARM FREEZING LEVEL.  WILL BE
ISSUING A FF.A FOR THE SOUTHERN AREAS TNT FROM 02Z THROUGH 18Z
SATURDAY. THOUGH RAINFALL MAY EXTEND INTO THE AFTERNOON HOURS...
BEST DYNAMICS OVERNIGHT TNT AND LESSER HEADING INTO THE AFTERNOON.
WITH PWATS OF 1.7 TO 1.8 INCHES ACROSS THE BORDER LATE THIS
AFTERNOON...AND THAT TO SPREAD NORTH TNT...RAINFALL AMOUNTS MAY
REACH 2 TO 4 INCHES IN HEAVIER STORMS IN ANY AREAS THAT TRAIN DURING
THE NIGHT HOURS. GFS PEGGED I80 AS THE QPF MAX WHILE OTHER MODELS
AND ENSEMBLE HAD MAIN AXIS FARTHER SOUTH ALONG US 34. FFG GUIDANCE
AND EXAMINATION OF PREVIOUS 3 DAY RAINFALL TOTALS SHOW THE SOUTH IS
OF MOST CONCERN REGARDING FLASH FLOODING SO HAVE KEPT THE AREAL
COVERAGE FROM GENERALLY HIGHWAY 20 SOUTH TO THE BORDER COUNTIES.

.LONG TERM /SATURDAY THROUGH FRIDAY/...
OVERNIGHT MCS WILL BE ONGOING WITH CONTINUED FLASH FLOODING CONCERNS
SATURDAY MORNING...MOSTLY LIKELY OVER THE SOUTHEASTERN THIRD OF THE
AREA...AND WILL CONTINUE TO SHIFT EAST AND OUT OF THE AREA BY
MIDDAY. SFC BOUNDARY WILL BE DRAPED NEAR THE I-80 CORRIDOR IN THE
MORNING...BUT AS SFC LOW PRESSURE MOVES EAST ALONG THE MO/IA
BORDER...THE BOUNDARY WILL BE PULLED SOUTHWARD DURING THE DAY.
ANOTHER SHORTWAVE IS EXPECTED TO CROSS THE REGION SATURDAY
AFTN...BUT WITH THE JUICIEST AIR AND BEST SFC CONVERGENCE SHUNTED
SOUTH...THIS WAVE WILL HAVE TO WORK WITH AN ELEVATED FRONTAL
ZONE THAT SHOWS UP AROUND 850 MB MOVING SOUTH INTO IOWA. SO THE
UPSHOT IS THAT BEYOND THE MORNING RAIN...SHOWERS AND STORMS LATER
IN THE DAY ARE SOMEWHAT LESS CERTAIN AND SHOULD BE MORE SCATTERED IN
NATURE.

WILL HAVE A BRIEF RESPITE FROM THE STORMY WEATHER SATURDAY NIGHT
THROUGH SUNDAY NIGHT AS SFC HIGH PRESSURE MOVING SOUTH THROUGH
THE CENTRAL PLAINS SUPPRESSES BOUNDARY WELL SOUTH OF OUR AREA.
HOWEVER...NEXT SHORTWAVE TROUGH ALOFT IN THE QUASI-ZONAL FLOW COMES
SHOOTING ACROSS THE NRN ROCKIES MONDAY...AND BY MONDAY NIGHT AND
EARLY TUESDAY WE WILL BE SEEING A PATTERN VERY SIMILAR TO TONIGHT. A
SFC TROUGH MOVING INTO CENTRAL IA...WITH SFC LOW PRESSURE DEVELOPING
IN AREA OF FRONTOGENESIS OVER THE CENTRAL PLAINS. STRONG WARM
ADVECTION AND MOISTURE TRANSPORT OVER A DEVELOPING WARM FRONT...AND
UNDER STRONG MID-LEVEL FLOW WILL SET UP ANOTHER NIGHT OF MCS
ACTIVITY LIKELY THROUGH CENTRAL/SOUTHERN IA. IF WE GET A LOT OF RAIN
TONIGHT...ADDITIONAL RAIN WITH THIS MONDAY NIGHT SYSTEM WILL
HEIGHTEN OUR CONCERN FOR FLOODING AGAIN. TIMING OF ALL OF THESE
WAVES AND EVENTUALLY PLACEMENT OF BOUNDARIES ALL WILL HAVE A SAY IN
THE DAY TO DAY FLUCTUATION IN RAIN CHANCES. IF WE HAD TO PICK
ANOTHER TIME OF RELATIVELY LOWER CHANCES OF RAIN...WEDNESDAY INTO
THURSDAY LOOKS LIKE A GOOD TIME. WE MAY REALLY WARM UP TOWARD THE
END OF THE WEEK AS THE UPPER FLOW AMPLIFIES AND A STRONG RIDGE
BUILDS OVER THE MIDWEST. NOT AS EXCITED ABOUT THE LOW POPS LATE
THURSDAY INTO FRIDAY AS WARMER AIR ALOFT WILL CONTRIBUTE TO GREATER
CONVECTIVE INHIBITION. BUT STRENGTH OF WARM ADVECTION AHEAD OF THE
CAP MAY SET OFF STORMS...MAINLY ACROSS NRN AREAS.

&&

.AVIATION...
05/00Z...MAIN THUNDERSTORM ACTIVITY THAT WAS SUPPOSED TO BE ACROSS
THE SOUTHEASTERN AREA BY KOTM HAS PUSHED SOUTH OF THE AREA. NEXT
FOCUS SHIFTS TO PRECIP/THUNDER CHANCES WITH UPPER LEVEL DISTURBANCE
MOVING THROUGH OVERNIGHT. MAIN TRACK OF THIS SYSTEM EXPECTED TO BE
ACROSS THE CENTRAL CWA IMPACTING KDSM...KALO...KFOD...AND KOTM MORE
THAN KMCW WHICH SHOULD BE JUST TO THE NORTH OF THE WIDESPREAD
ACTIVITY WHICH IS EXPECTED TO MOVE THROUGH AFTER 06Z FOR THE MOST
PART. OTHERWISE SHOWERS AND MAYBE A FEW ISOLATED THUNDERSTORMS
POSSIBLE THROUGH THE DAY SATURDAY...WITH THE MAIN AREA OF
INSTABILITY ACROSS THE SOUTH AT KDSM AND KOTM.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH FROM 9 PM CDT THIS EVENING THROUGH 1 PM CDT
SATURDAY AFTERNOON FOR ADAIR-ADAMS-APPANOOSE-AUDUBON-BOONE-
CASS-CLARKE-DALLAS-DAVIS-DECATUR-GUTHRIE-JASPER-LUCAS-MADISON-
MAHASKA-MARION-MARSHALL-MONROE-POLK-POWESHIEK-RINGGOLD-STORY-
TAMA-TAYLOR-UNION-WAPELLO-WARREN-WAYNE.

&&

SHORT TERM...REV
LONG TERM...MOYER
AVIATION...BEERENDS

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
654 PM CDT FRI JUN 4 2010

IAZ004>007-015>017-023>028-033>039-044>046-051000-
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-
654 PM CDT FRI JUN 4 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...TONIGHT

THUNDERSTORMS WILL DEVELOP LATER TONIGHT...MAINLY SOUTH OF HIGHWAY
20. LOCALLY HEAVY RAIN WILL BE THE MAIN THREAT...AND AN ISOLATED
SEVERE STORM OR TWO IS POSSIBLE...PRODUCING HAIL UP TO QUARTER
SIZE AND DAMAGING WIND GUSTS.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

SCATTERED MAINLY NON SEVERE THUNDERSTORMS ARE POSSIBLE SATURDAY.
ADDITIONAL CHANCES FOR THUNDERSTORMS WILL OCCUR MONDAY...TUESDAY
AND THURSDAY. THE SEVERE WEATHER POTENTIAL FOR THIS PERIOD WILL BE
BETTER DEFINED IN THE COMING DAYS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT ANTICIPATED AT THIS TIME.

IAZ047>050-057>062-070>075-081>086-092>097-051000-
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-
654 PM CDT FRI JUN 4 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...TONIGHT

THUNDERSTORMS WILL REDEVELOP LATER THIS EVENING...AND ARE EXPECTED
TO MOVE WEST TO EAST ACROSS THE SOUTHERN HALF OF IOWA THROUGH THE
OVERNIGHT HOURS. HEAVY RAINFALL WILL BE THE MAIN THREAT
OVERNIGHT...BUT A FEW THUNDERSTORMS COULD ALSO BE SEVERE WITH HAIL
TO THE SIZE OF QUARTERS AND DAMAGING WIND GUSTS.

A FLASH FLOOD WATCH IS IN EFFECT FOR THE AREA. PLEASE REFER TO
THE NATIONAL WEATHER SERVICE WEBSITE AT WEATHER.GOV/DESMOINES FOR
FURTHER DETAILS.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

SCATTERED THUNDERSTORMS ARE POSSIBLE SATURDAY...WITH SOME STORMS
IN THE AFTERNOON POSSIBLY BECOMING SEVERE. LARGE HAIL AND DAMAGING
WINDS WILL BE THE MAIN THREAT. ADDITIONAL CHANCES FOR THUNDERSTORMS WILL
OCCUR MONDAY...TUESDAY AND THURSDAY. THE SEVERE WEATHER POTENTIAL
FOR THIS PERIOD WILL BE BETTER DEFINED IN THE COMING DAYS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED LATE TONIGHT AND SATURDAY.

MJB