Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 281805
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
104 PM CDT THU MAY 28 2015

.SHORT TERM /TODAY/...
ISSUED AT 310 AM CDT THU MAY 28 2015

A SURFACE HIGH PRESSURE AREA DOMINATING THE REGION EARLY THIS
MORNING WILL SLIDE OFF TO THE EAST TODAY...ALLOWING FOR A RETURN OF
MODEST SOUTHEAST TO SOUTH FLOW ACROSS OUR FORECAST AREA. THIS SHOULD
PROMOTE FAIRLY MILD TEMPERATURES ONCE AGAIN. HOWEVER...AT 500 MB THE
RIDGE AXIS CURRENTLY OVERHEAD WILL ALSO SHIFT EASTWARD AS A BROAD
SHORTWAVE TROUGH APPROACHES SLOWLY FROM THE SOUTHWEST. THIS FEATURE
IS RESPONSIBLE FOR THE CLOUDS AND THUNDERSTORMS CURRENTLY AFFECTING
EASTERN KANSAS...AND WILL SPREAD SHOWERS AND STORMS UP INTO OUR AREA
LATER TODAY TEMPERING THE POTENTIAL FOR WARMING ESPECIALLY IN OUR
SOUTHWEST AND WEST. THE TRICKY FORECAST QUESTION IS THE TIMING OF
RAIN BEGINNING AS IT SLOWLY SPREADS FROM SOUTHWEST TO NORTHEAST.
HOWEVER...GIVEN THE SUBSIDENCE ASSOCIATED WITH THE HIGH PRESSURE
CURRENTLY OVER IOWA WHICH WILL BE SLOW TO DEPART...AS REFLECTED IN
THE VERY LIMITED INSTABILITY FORECAST BY HIGH RES MODELS FOR
TODAY...HAVE CONTINUED THE TREND OF SLOWING THE LEADING EDGE OF POPS
WHICH WILL PRIMARILY BE CONFINED TO OUR SOUTHWESTERN COUNTIES UNTIL
LATE IN THE DAY. AT ANY RATE...GIVEN THE AFOREMENTIONED RELATIVE
LACK OF INSTABILITY ALONG WITH WEAK DEEP LAYER SHEAR...SEVERE
WEATHER PROBABILITY WILL BE QUITE LOW AND NO SIGNIFICANT IMPACTS ARE
EXPECTED.

.LONG TERM /TONIGHT THROUGH WEDNESDAY/...
ISSUED AT 310 AM CDT THU MAY 28 2015

PRIMARY CONCERN WILL BE PRECIP WINDOW FROM TONIGHT INTO EARLY
SATURDAY. BROAD WEAK FORCING AHEAD OF CURRENT NV/ID SHORT WAVES HAS
PRODUCED SCATTERED LOW END CONVECTION FROM NE INTO THE DAKOTAS
OVERNIGHT.  MUCH OF THE FORCING IS IN THE H85/H7 LAYER WITH AN
EXTENDED PERIOD OF THETA-E ADVECTION...AND THIS SHOULD ENTER IA
LATER TODAY AND CONTINUING THROUGH FRI...ESPECIALLY SE. THE
BAROCLINIC ZONE IS NOT IMPRESSIVE SO IT MAY BE DRIVEN MORE BY
PERSISTENT MOISTURE TRANSPORT THAN ANYTHING.  SURFACE BASED
POTENTIAL WILL ALSO COME INTO PLAY FRI AFTERNOON AND EVENING WITH
FRONTAL PASSAGE. MLCAPES TYPICALLY VARY FROM 500-1500 J/KG AND
APPEAR TO BE UNCAPPED. WIND PROFILES ARE NOT TOO IMPRESSIVE SO DEEP
SHEAR SHOULD BE MARGINAL.  THUS AGREE WITH SPC LOW END OUTLOOK AND
DO NOT EXPECT MUCH SEVERE WEATHER.  ALTHOUGH DO NOT EXPECT AMOUNTS
TO BE EXTREME...LOCALLY HEAVY RAINS MAY BE MORE OF A CONCERN WITH
NAEFS SPECIFIC HUMIDITIES...PWAT AND INTEGRATED WATER VAPOR
TRANSPORT IN THE 90TH PLUS PERCENTILE. WITH WARM CLOUD DEPTHS 11KFT
AND HIGHER...A PROLONGED PERIOD OF SW-NE MEAN WIND MAY RESULT IN
SOME REPETITIVE BURSTS THU NIGHT INTO FRI.  THE FRONT SHOULD EXIT
THE FORECAST AREA SE FRI NIGHT...BUT HIGHER BASED WEAK FORCING MAY
LINGER BEHIND THE FRONT AHEAD OF THE H7/H5 TROUGH INTO SAT MORNING.

A COOLER AND ESPECIALLY DRIER AIRMASS WILL THEN FOLLOW FOR THE
WEEKEND.  THE PERIOD OF DRY WEATHER IS EXPECTED TO CONTINUE INTO
EARLY NEXT WEEK WITH THE PASSAGE OF SHORT WAVE RIDGING.  UPPER LEVEL
FLOW AMPLITUDE WILL THEN INCREASE SLIGHTLY HEADING INTO MID WEEK
WITH ANOTHER ITERATION OF A WRN CONUS TROUGH.  ALTHOUGH ANY SURFACE
FEATURE AFFECTS WILL BE BEYOND THE VALID PERIOD...WEAK MID LEVEL
FORCING MAY BRING SOME SCATTERED WEAK CONVECTION AROUND WED.
STRENGTHENING RETURN FLOW WELL AHEAD OF THIS SYSTEM SHOULD FINALLY
RETURN TEMPS TO NORMAL AND JUST ABOVE BY THIS TIME AS WELL.

&&

.AVIATION...28/18Z
ISSUED AT 104 PM CDT THU MAY 28 2015

COMPLEX FORECAST AS THERE WILL BE SEVERAL ROUNDS OF SHOWERS/STORMS
AFFECTING TAF LOCATIONS.  REMNANT SHOWERS HAVE LIFTED OUT OF MO AND
ADDITIONAL DEVELOPMENT WILL BE AIDED BY A SHORTWAVE LIFTING OUT OF
THE SW MOVING ACROSS THE FORECAST AREA.  AS THE SHORTWAVE MOVES
ACROSS IT SHOULD PROVIDE ENOUGH FORCING FOR THUNDERSTORMS TO
DEVELOP.  THERE WILL THEN BE A BREAK LATE TONIGHT/FRIDAY MORNING
BEFORE THE COLD FRONT MOVES THROUGH AND ADDITIONAL STORMS FORM. A S
TO SE SFC FLOW WILL BE COMMON THROUGH THE FCST PD AT 15-25KTS AND
DIMINISH AFTER SUNSET.  LOCAL MVFR CONDITIONS WILL BE POSSIBLE IN
SHOWERS AND POSSIBLY SOME FOG LATE TONIGHT.

&&

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

&&

$$

SHORT TERM...LEE
LONG TERM...SMALL
AVIATION...FAB



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