Special Weather Statement, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
633 PM CDT WED AUG 6 2014

.SHORT TERM /TONIGHT/...
ISSUED AT 328 PM CDT WED AUG 6 2014

ANOTHER ROUND OF HEAVY RAINFALL IS POSSIBLE FOR THE CWA
TONIGHT...MAINLY SOUTHERN PORTIONS. TWO SHORTWAVES...PRESENTLY
MOVING THROUGH SE SOUTH DAKOTA AND NORTH CENTRAL KS...WILL HELP
PROVIDE THE LARGE-SCALE FORCING FOR OVERNIGHT PCPN. LLJ IS EXPECTED
TO DEVELOP AGAIN TONIGHT AND POINT INTO IA...PROVIDING AMPLE
MOISTURE. PWATS ARE PROGGED TO BE INVOF THE 2.0 IN RANGE...WHICH
AGAIN WILL BE AROUND +2 SD VS CLIMO. WARM CLOUD DEPTHS WILL APPROACH
THE 12 KFT RANGE. MODEL FCST SOUNDINGS DO TEND TO MOISTEN THE COLUMN
ACROSS SOUTHERN IA THIS EVENING...MORE SO THAN LAST NIGHT...WHICH
WOULD TEND TO SUPPORT THE HEAVY RAIN THREAT TONIGHT.

MODEL SOLUTIONS DO VARY ON THE AMOUNT OF FORCING AND RESULTING
RAINFALL. THE NAM IS THE WETTEST AND BRINGS A RIBBON OF FORCING
ALONG WITH STRONG THETA-E ADVECTION INTO SOUTH CENTRAL AND SOUTHWEST
IA. THE GFS ON THE OTHER HAND IS NOT AS INTENSE THAT FAR NORTH. HAVE
TENDED TO SPLIT THE DIFFERENCE...AND EXPECT THE HEAVIEST RAINFALL
TONIGHT TO REMAIN SOUTH OF IA HWY 92.

WILL GO WITH A FLASH FLOOD WATCH FOR SOME OF THE SOUTH CENTRAL AND
SOUTHWEST IA COUNTIES ALONG AND SOUTH OF 92...GIVEN LAST NIGHT/S
HEAVY RAINFALL AND RELATIVELY LOWER FLASH FLOOD GUIDANCE VALUES.
ALTHOUGH AM NOT OVERLY CONCERNED ABOUT FLASH FLOOD POTENTIAL
THERE...CONFIDENCE IS AROUND THE 40 TO 50 PERCENT THRESHOLD WHICH
WOULD BE THE LOW-END FLASH FLOOD WATCH CRITERIA.

SEVERE WEATHER POTENTIAL THIS EVENING AND OVERNIGHT IS MINIMAL BUT
CANNOT BE ENTIRELY RULED OUT. ALTHOUGH CAPE VALUES HAVE INCREASED
THIS AFTN IN SW IA...WITH VALUES APPROACHING THE 1000 TO 1500 J/KG
RANGE. DEEP-LAYER SHEAR IS MINIMAL HOWEVER...WHICH WOULD TEND TO
PRECLUDE ORGANIZED TSTM DEVELOPMENT. ATTM ANTICIPATE THE GREATEST
THREAT WOULD BE HEAVY RAINFALL FROM ANY STORMS THAT DO DEVELOP.

.LONG TERM /THURSDAY THROUGH WEDNESDAY/...
ISSUED AT 328 PM CDT WED AUG 6 2014

MAIN CHALLENGES THIS PERIOD WILL BE MAINLY IN THE SHORTER TERM WITH
EVOLUTION OF SYSTEM NEXT 24 HOURS. CURRENTLY SFC SHORT WAVE SOUTH OF
THE AREA WITH BOUNDARY OVER NORTHERN MO AND WEAK TROUGH EXTENDING
ACROSS NORTH CENTRAL IOWA WITH WELL DEFINED DEFORMATION AXIS AND
THETAE AXIS ALOFT ACROSS THE REGION. ISENTROPIC UPGLIDE CONTINUES TO
FEED THIS AREA WHERE PERSISTENT LIGHT RAIN IS FALLING. MODELS HAVENT
QUITE REACHED A CONSENSUS ON THE EVENTUAL DEPARTURE OF THE SYSTEM
FOR THURSDAY/THURSDAY NIGHT. THIS IS IN PART DUE TO THE PERSISTENT
RIDGE AXIS WHICH EXTENDS FROM SOUTHERN CANADA TO THE SOUTHEAST US.
THE GENERAL TREND HAS BEEN FOR A SLOWER TRANSITION OUT OF THE AREA
THURSDAY INTO THURSDAY NIGHT. THURSDAY MORNING MOST OF THE FORCING
WILL REMAIN STRONGEST ACROSS THE SOUTHEAST WITH CONTINUED UPGLIDE
WRAPPING AROUND THE SYSTEM BACK INTO CENTRAL AND NORTHERN IOWA
DURING THE DAY. THOUGH THE H850 MOISTURE CHANNEL WILL GRADUALLY
SHIFT TO THE EAST WITH TIME...LIGHT TO MODERATE RAIN SHOULD CONTINUE
THROUGH MUCH OF THE DAY THURSDAY THEN SLOWLY TAPER OFF DURING THE
EVENING HOURS. BOTH THE EURO/GFS/NAM HIT THE EAST/SOUTHEAST WITH
QUITE A BIT OF QPF FOCUSED BETWEEN 12-18Z USING A SLIGHTLY FARTHER
NORTH TRACK OF THE H850 LOW. WPC CONTINUES TO PREFER A MORE SOUTHERN
SOLUTION MORE IN LINE WITH MESO HRRR AND NMM MODELS. CURRENTLY THE
SYSTEM IS TRACKING FAIRLY WELL WITH ALL MODELS BUT WITH EXPECTED
MESO CONVECTION TO DEVELOP OVER NORTHERN MO THIS EVENING...TRACK
EXPECTED TO END UP BEING FARTHER SOUTH THAN SYNOPTIC MODELS INDICATE
AND CLOSER TO THE HRRR/NMM. FOR NOW WILL TREND TOWARD THAT SOLUTION
...IN LINE WITH WPC AS WELL BUT WILL NEED TO WATCH DURING THE
EVENING SHIFT FOR ANY POTENTIAL ADJUSTMENTS FARTHER NORTH. ANY
DEVIATION NORTH WOULD RESULT IN RAINFALL TOTALS BEING HIGHER IN THE
FORECAST AREA THURSDAY. EVENTUALLY THE SYSTEM BECOMES SHEARED OUT
AND WEAKENS...AND HANGS ON INTO FRIDAY WITH LINGERING SHOWERS OR ISO
THUNDER OVER THE SOUTH.  ALREADY INTO THE WEEKEND NOW SOME
UNCERTAINTY REGARDING THE NEXT UPSTREAM WAVE APPROACHING FROM THE
WEST FOR SATURDAY AND SUNDAY. GREAT LAKES HIGH NOW BEING MODELED TO
STRENGTHEN OVER THE REGION AND IS NOW TRENDING TO KEEP AREA DRIER
THAN PREVIOUSLY FORECAST. HAVE REDUCED POP CHANCES FOR BOTH DAYS...
BUT HAVE NOT CUT OUT YET DUE TO CONFIDENCE CONCERNS AND CONSENSUS
WITH NEIGHBORING OFFICES AT THIS POINT. IF TRENDS CONTINUE WITH
TONIGHTS MODEL PACKAGES...THEN FURTHER REDUCTION IN RAIN CHANCES
WILL BE WARRANTED. TEMPERATURES WILL REMAIN COOL THURSDAY WITH
EXTENSIVE CLOUD COVER AND SHOWERS. BY FRIDAY SOME MODERATION IS
EXPECTED WHICH SHOULD CONTINUE INTO THE WEEKEND. NORTHEAST FLOW WILL
DEVELOP BY THURSDAY AFTERNOON AND CONTINUE THROUGH FRIDAY WITH SOME
RISK FOR PATCHY FOG OVERNIGHT AS CLOUDS AND HIGH MOISTURE REMAINS IN
THE BOUNDARY LAYER. LOOKING AHEAD TO NEXT WEEK....LESSENING CHANCES
FOR RAIN WILL CONTINUE THROUGH THE PERIOD AS A RIDGE OF HIGH
PRESSURE REMAINS IN THE AREA. SOME HINT AT RETURN MOISTURE BY NEXT
WEDNESDAY AS A TROUGH DEVELOPS OVER THE HIGH PLAINS AND MOVES INTO
THE CENTRAL PLAINS.

&&

.AVIATION...07/00Z
ISSUED AT 629 PM CDT WED AUG 6 2014

SURFACE LOW WILL TRACK EAST TONIGHT ACROSS MISSOURI WITH EASTERLY
LOW LEVEL FLOW ACROSS IOWA. BAND OF RAIN ACROSS CENTRAL IOWA WILL
CONTINUE TO SLIDE EAST THIS EVENING. EASTERLY FLOW WILL CONTINUE
THROUGH THE FORECAST PERIOD WITH ABUNDANT MOISTURE. EXPECT
IFR/MVFR CIGS MUCH OF THE TIME IN CENTRAL AND SOUTHERN IOWA. THE
NORTHERN TAFS MAY BE VFR MUCH OF THE TIME WITH DRIER AIR IN THE
PART OF THE STATE.

&&

.HYDROLOGY...
ISSUED AT 328 PM CDT WED AUG 6 2014

THREAT OF HEAVY RAINS WILL PERSIST THROUGH TODAY THURSDAY
WITH AMPLE MOISTURE IN PLACE BEING TRANSPORTED INTO THE STATE.
URBAN AREAS WOULD BE MOST LIKELY TO EXPERIENCE ANY FLOODING
ISSUES AS MOST RURAL LOCATIONS HAVE DRY ANTECEDENT CONDITIONS.
MINIMAL RISES ARE ANTICIPATED ON AREA RIVERS.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH THROUGH THURSDAY MORNING FOR ADAIR-CLARKE-
DECATUR-LUCAS-MADISON-RINGGOLD-UNION-WAYNE.

&&

SHORT TERM...ZOGG
LONG TERM...REV
AVIATION...JOHNSON
HYDROLOGY...ZOGG

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
341 PM CDT WED AUG 6 2014

IAZ057>062-070>075-081>086-092>097-072045-
AUDUBON-GUTHRIE-DALLAS-POLK-JASPER-POWESHIEK-CASS-ADAIR-MADISON-
WARREN-MARION-MAHASKA-ADAMS-UNION-CLARKE-LUCAS-MONROE-WAPELLO-
TAYLOR-RINGGOLD-DECATUR-WAYNE-APPANOOSE-DAVIS-
341 PM CDT WED AUG 6 2014

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...THIS AFTERNOON AND TONIGHT

THUNDERSTORMS ARE EXPECTED ACROSS MUCH OF CENTRAL IOWA LATE THIS
EVENING AND TONIGHT. WHILE SEVERE WEATHER IS NOT EXPECTED...SOME
STORMS MAY PRODUCE MARGINALLY SEVERE HAIL AND WIND. HEAVY RAIN IS
ANTICIPATED WITH THE STORMS...WITH THE POTENTIAL FOR AREAS OF
FLASH FLOODING MAINLY SOUTH OF IOWA HIGHWAY 92.

A FLASH FLOOD WATCH IS IN EFFECT FOR A PORTION OF THE AREA. SEE
WEATHER.GOV/DESMOINES FOR MORE INFORMATION.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

THE THREAT FOR NON SEVERE THUNDERSTORMS WILL PERSIST INTO THURSDAY
EVENING WITH LOCALIZED HEAVY RAIN POSSIBLE. ISOLATED TO SCATTERED
STORMS WILL STAY IN THE FORECAST INTO THIS WEEKEND...WITH THE
THREAT OF SEVERE WEATHER REMAINING LOW.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT ANTICIPATED.

IAZ004>007-015>017-023>028-033>039-044>050-072045-
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-
341 PM CDT WED AUG 6 2014

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...THIS AFTERNOON AND TONIGHT

THUNDERSTORMS ARE EXPECTED LATE THIS EVENING AND TONIGHT. WHILE
SEVERE WEATHER IS NOT EXPECTED...SOME STORMS MAY PRODUCE HEAVY
RAIN WITH THE POTENTIAL FOR LOCALIZED MINOR FLOODING.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

THE THREAT FOR NON SEVERE THUNDERSTORMS WILL PERSIST INTO THURSDAY
EVENING WITH LOCALIZED HEAVY RAIN POSSIBLE. ISOLATED TO SCATTERED
STORMS WILL STAY IN THE FORECAST INTO THIS WEEKEND...WITH THE
THREAT OF SEVERE WEATHER REMAINING LOW.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT ANTICIPATED.

ZOGG

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