Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 271735
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1235 PM CDT THU AUG 27 2015

...18Z AVIATION UPDATE...

.SHORT TERM /TODAY/...
ISSUED AT 322 AM CDT THU AUG 27 2015

PRIMARY CONCERN TODAY WILL BE EASTWARD ADVANCE OF CONVECTION
FOLLOWED BY TEMPERATURES. WY/MT SHORT WAVES CONTINUE TO DRIVE SD MCS
WITH BOTH THERMODYNAMIC AND KINEMATIC SUPPORT.  ALTHOUGH MUCAPES ARE
2000-3000 J/KG ALONG AND WEST OF THE MO RIVER...THE ASSOCIATED MUCIN
IS HIGH SO THIS POTENTIAL IS NOT BEING FULLY REALIZED. SOUNDINGS
INDICATE THE CONVECTION IS QUITE ELEVATED AND SHOULD REMAIN SO AS IT
ADVANCES INTO IA WITH PLENTY OF 1-3KM DRY AIR. THE MCS IS BEING MORE
ACCURATELY DEPICTED BY THE MORE AGGRESSIVE 00Z GFS VS 00Z ECMWF AND
WILL BE FAVORED WITH LIKELIES NW BY AFTERNOON. ANOTHER REASON FOR
THIS IS SUSPECTING MORE MOISTURE IS PRESENT THAN MODELS SUGGEST DUE
TO DEVELOPMENT OF 4-5KFT CEILINGS FROM SERN NE INTO WRN IA...WHICH
ARE CERTAINLY NOT SHOWN IN FORECAST SOUNDINGS. THUS EXPECT RECENT
SPOTTY DEVELOPMENT NEAR ONEILL NE TO CONTINUE GRADUALLY PUSHING
EASTWARD THROUGH THE DAY. DRY AIR MAY BE OVER DEPICTED IN
MODELS...BUT STILL SUFFICIENT TO LIMIT COVERAGE UNTIL LATER IN THE
AFTERNOON.  ESTIMATED EFFECTIVE SHEAR /2-5KM/ SUGGESTS MAX WILL
REMAIN WHERE IT IS NOW...SD INTO MN...AND LEAVE IA WITH ONLY
MARGINAL POTENTIAL FOR SEVERE WEATHER.

TEMP WISE...HAVE NUDGED HIGHS UP JUST A TAD ABOVE PERSISTENCE. THERE
WILL BE DECENT LOW LEVEL WARM ADVECTION...BUT DO NOT EXPECT MUCH
CHANGE WITH SURFACE WINDS STAYING EAST OF 180 DEGREES AND MID/HIGH
CLOUDINESS INCREASING WITH CONVECTION.

.LONG TERM /TONIGHT THROUGH WEDNESDAY/...
ISSUED AT 322 AM CDT THU AUG 27 2015

FOCUS STILL ON STRONG SHORTWAVE TROUGH TO MOVE THROUGH THE STATE
LATE TONIGHT INTO FRIDAY. STILL LOOKING LIKE WIDESPREAD RAINFALL
POSSIBLE...WITH STRONG WAA AND THETA E ADVECTION AHEAD OF THE SYSTEM
TONIGHT INTO FRIDAY. 40-50KT LLJ TO BE ORIENTED INTO WRN IA/CNTRL IA
BY LATE EVENING/OVERNIGHT HOURS WITH TWO MAIN PUSHES OF CONVECTION
EXPECTED. THE FIRST TO PUSH THROUGH THE NORTHERN/EASTERN HALF OF THE
CWA LATE TONIGHT...WITH THE LEAD IMPULSE MOVE THROUGH WITH THE
SYSTEM. SECOND AREA TO MOVE THROUGH ALONG AND AHEAD OF THE SFC
TROUGH AS THE AREA OF LOW PRESSURE SLIDES EASTWARD FROM SE SD TO NE
IA THROUGH THE DAY FRIDAY. COLD FRONT TO MOVE THROUGH LATER FRIDAY
AND MAY SEE SOME ADDITIONAL DEVELOPMENT WITH THIS FEATURE LATER
FRIDAY...WITH PRECIP CLEARING FROM WEST TO EAST FRIDAY NIGHT. PWATS
STILL HIGH AROUND 1.5 TO 2 INCHES THROUGH THE EVENT...ALONG WITH
STRONG FORCING SO HEAVY RAINFALL STILL AN ISSUE. A FEW OF THE MODELS
SUGGESTING HIGHEST PRECIP FURTHER SOUTH ACROSS CENTRAL IOWA AND
NORTHERN IOWA...SO HAVE GONE WITH MORE OF A BLEND OF THE TWO
SOLUTIONS. RAINFALL EXPECTED TO BE MORE CONVECTIVE IN NATURE
NOW...WHICH COULD INCREASE THE POTENTIAL FOR HEAVY RAINFALL. HOWEVER
FLASH FLOOD GUIDANCE STILL FAIRLY HIGH OVER THE CWA WITH THE SOILS
ALLOWED TO DRY OUT SOME OVER THE PAST WEEK. THEREFORE STILL NOT
THINKING THERE IS MUCH OF A FLASH FLOOD THREAT. SYSTEM TO PUSH EAST
OF THE AREA INTO SATURDAY WITH A LINGERING LOW STRATUS DECK MOST
LIKELY IN PLACE EARLY SATURDAY THEN CLEARING/ERODING THROUGH THE
DAY. LARGE UPPER LEVEL RIDGE TO THEN BUILD INTO THE CENTRAL US FOR
THE WEEKEND INTO NEXT WEEK. H85 TEMPS CLIMB BACK INTO THE 20S
CELSIUS WITH DRY CONDITIONS EXPECTED AS THE STATE REMAINS DOMINATED
BY A LARGE AREA OF HIGH PRESSURE. HAVE GONE WITH TEMPS ABOVE
GUIDANCE AT THIS TIME...BUT NOT QUITE AS HIGH AS THE EC AS OF NOW.
THIS SHOULD ALLOW MUCH OF THE AREA TO SEE TEMPS IN THE 80S SUNDAY
INTO NEXT WEEK...AND MAY NEED TO PUSH SOME AREAS INTO THE 90S AS THE
THERMAL RIDGE BUILDS ACROSS THE REGION.

&&

.AVIATION...27/18Z
ISSUED AT 1233 PM CDT THU AUG 27 2015

REMNANT SHOWERS THIS MORNING WILL CONTINUE TO DISSIPATE THIS
AFTERNOON WITH VFR PREVAILING WELL INTO THE EVENING. AS THE
PRIMARY SYSTEM APPROACHES THE REGION OVERNIGHT...PRECIP WILL MOVE
BACK IN AND CIGS WILL FALL TO NEAR OR BELOW VFR AROUND 8-10Z AND
REMAIN THROUGH THE REMAINDER OF THE PERIOD. RAINFALL MAY BE HEAVY
AT TIMES ALSO DROPPING VSBY INTO MVFR AND EVEN IFR AT TIMES. ONLY
HINTED AT MVFR CIGS AND VSBY DROPS FOR THE MOMENT GIVEN MUCH OF
THE ACTION IS 12+ HOURS OUT.

&&

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

$$

SHORT TERM...SMALL
LONG TERM...BEERENDS
AVIATION...CURTIS



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