Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 312337
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
637 PM CDT SUN MAY 31 2015

...UPDATED AVIATION DISCUSSION...

.SHORT TERM /TONIGHT/...
ISSUED AT 315 PM CDT SUN MAY 31 2015

LARGE AREA OF HIGH PRESSURE OFF TO THE NORTHEAST OF THE CWA WITH
A DEVELOPING AREA OF LOW PRESSURE IN THE WESTERN HIGH PLAINS. AN
AREA OF LIGHT SHOWERS JUST OFF TO THE WEST IN WAA AREA
ALOFT...WITH WAA EXPECTED ACROSS THE CWA OVERNIGHT AND WINDS
EXPECTED TO BECOME MORE SOUTHEASTERLY. EXPECT MID CLOUD TO
INCREASE OVERNIGHT WITH SOME CLOUDS ALREADY PUSHING INTO WESTERN
IOWA. VERY DRY AIR NEAR THE SURFACE OFF THE AREA OF HIGH PRESSURE
SHOULD PRECLUDE ANY PRECIP FROM REACHING THE GROUND IF THE SHOWER
ACTIVITY HOLD TOGETHER INTO THE WEST THIS EVENING. OTHERWISE
EXPECT DRY CONDITIONS OVERNIGHT...WITH TEMPS STILL CHILLY
OVERNIGHT. EASTERN CWA WITH MORE OF AN EASTERLY FLOW AND COOLER
AIR REMAINING IN PLACE SHOULD SEE THE COOLEST TEMPS IN THE LOW TO
MID 40S BY EARLY MONDAY...WITH REMAINDER OF THE CWA IN THE UPPER
40S TO AROUND 50 WITH WINDS TURNING A BIT MORE SOUTHERLY STAYING
UP A BIT AND MORE CLOUD COVER.

.LONG TERM /MONDAY THROUGH SUNDAY/...
ISSUED AT 315 PM CDT SUN MAY 31 2015

THE FIRST HALF OF THE UPCOMING WEEK WILL BE CHARACTERIZED BY A
RETURN TO SEASONABLE TEMPERATURES...FOLLOWED BY OFF AND ON CHANCES
FOR PRECIPITATION FOR THE LATTER PART OF THE WEEK.

MONDAY MORNING WILL FEATURE A SURFACE RIDGE AXIS POSITIONED OVER
THE EASTERN CWA...WHICH WILL GRADUALLY SHIFT EASTWARD THROUGHOUT
THE DAY. WEAK 925-850 MB WAA DOES NOT COMMENCE UNTIL THE AFTERNOON
IN WESTERN IOWA...AND OVERNIGHT IN CENTRAL IOWA. RAISED HIGHS TO
AROUND 70 IN THE WEST CENTRAL AND SOUTHWEST CWA FOR MONDAY GIVEN
THE EARLIER ONSET OF WAA IN THESE AREAS. SOUNDINGS SHOW SOME
RESIDUAL MID LEVEL CLOUDS LINGERING BEHIND A 500 MB SHORTWAVE THAT
PASSES THROUGH THE CWA TONIGHT...BUT THESE SHOULD HAVE MINIMAL
IMPACTS ON HIGHS.

UPPER LEVEL RIDGE WILL SHIFT OVER IOWA FOR THE DAY ON
TUESDAY...BUT FLATTENS OUT ON WEDNESDAY AS IT INTERACTS WITH A
CUTOFF LOW OVER THE SOUTHEASTERN UNITED STATES AND AN APPROACHING
LONGWAVE TROUGH OVER THE PACIFIC NORTHWEST. THERE REMAINS SOME
DISCREPANCIES BETWEEN THE DOMESTIC AND FOREIGN MODELS OVER THE
TIMING OF THE DEPARTING SURFACE RIDGE AXIS...AND THUS HOW FAR EAST
THE WARMER AIR WILL ADVANCE FOR MONDAY NIGHT AND TUESDAY. THE
GFS/NAM PRESENT A FASTER SOLUTION AND THUS WARMER TEMPS FOR
TUESDAY...WHILE THE EC/UKMET HOLD THE RIDGE BACK AND LIMIT THE
STRONGEST WAA TO WESTERN IOWA. HAVE GONE WITH A COMPROMISE
SOLUTION FOR TUESDAY TEMPERATURES WHICH FALLS CLOSE IN LINE WITH
THE GEM. MODEL SOLUTIONS COME INTO BETTER ALIGNMENT TEMPERATURE-
WISE FOR WEDNESDAY WITH 850 MB TEMPS IN THE +13 TO +16 C RANGE.

LEE CYCLOGENESIS TAKES PLACE OVER THE NORTHERN HIGH PLAINS MONDAY
NIGHT/TUESDAY MORNING. THE SURFACE LOW WILL LIFT ENE TO MINNESOTA
BY WEDNESDAY AFTERNOON AND DRAG A WEAK COLD FRONT IN ITS WAKE. THE
12Z GFS/EC/NAM HINT AT A DECAYING MCS WORKING E ACROSS NEBRASKA
AND INTO WESTERN IOWA BY MID MORNING WEDNESDAY AHEAD OF THE
ATTENDANT FRONTAL BOUNDARY. NAM BUFR SOUNDINGS DEPICT A ROBUST EML
AND RESULTANT MUCAPE VALUES OF OVER 2000 J/KG IN WESTERN IOWA
AROUND SUNRISE. THE LACK OF ANY DEEP SHEAR SHOULD MINIMIZE THE
SEVERE THREAT WITH THE STORM BECOMING OUTFLOW DOMINANT BEFORE IT
REACHES IOWA. ADDITIONAL CONVECTION IS POSSIBLE ON ANY OUTFLOW
BOUNDARY IF THIS INSTABILITY IS REALIZED...AND HAVE REFLECTED THIS
POSSIBILITY IN THE POP GRIDS FOR WEDNESDAY MORNING.

THE AFOREMENTIONED FRONTAL BOUNDARY SINKS SOUTHEASTWARD OVER IOWA
WEDNESDAY NIGHT AND DOES NOT EXIT THE STATE UNTIL LATE FRIDAY. THE
TIMING OF PRECIP IS RATHER UNCERTAIN GIVEN THE BROAD WSW FLOW
ALOFT AND MULTIPLE...POORLY-RESOLVED UPPER LEVEL SHORTWAVES
WORKING THROUGH THE FLOW. MULTIPLE ROUNDS OS STORMS ARE LIKELY
BEFORE THE FRONT DEPARTS. POP COVERAGE IN CENTRAL IOWA FOR
WEDNESDAY AFTERNOON IS LIKELY A BIT GENEROUS GIVEN THE CAPPING
INVERSION ALOFT THAT WILL LIMIT SURFACE-BASED CONVECTION. BETTER
CHANCES FOR THUNDERSTORMS WILL BE ON THURSDAY AND FRIDAY CLOSER TO
THE SURFACE BOUNDARY.

NEXT WEEKEND LOOKS TO START OUT MAINLY DRY WITH EASTERLY FLOW OFF
A GREAT LAKES HIGH. THE EVOLUTION OF THE NEXT SYSTEM ON SUNDAY IS
RATHER UNCERTAIN WITH THE GFS MUCH MORE AGGRESSIVE ON THE
DEVELOPMENT OF A CYCLONE OVER THE DAKOTAS VERSUS THE OPEN WAVE
DEPICTED BY THE EC.

&&

.AVIATION...01/00Z
ISSUED AT 637 PM CDT SUN MAY 31 2015

VFR CONDITIONS WILL PREVAIL THROUGH THE ENTIRE TAF PERIOD WITH
ONLY CONCERN WITH WINDS SHIFTING MORE SOUTHEAST AND MIXING TO NEAR
12 KNOTS BY MONDAY.

&&

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

&&

$$

SHORT TERM...BEERENDS
LONG TERM...SKOW
AVIATION...PODRAZIK



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