Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 290503
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1203 AM CDT MON JUN 29 2015

.SHORT TERM /TONIGHT/...
ISSUED AT 329 PM CDT SUN JUN 28 2015

MAIN CONCERNS SHORT TERM CONTINUE TO BE THE LOW OVER CENTRAL IOWA
COMBINED WITH AN UPPER LEVEL VORT MAX OVER IOWA DIGGING SOUTH. WE
REMAIN RATHER UNSTABLE WITH MLCAPE 1000-1500J/KG AND SBCAPE OF 2000
TO 2500 J/KG ALONG AN AXIS NEAR AND JUST BEHIND THE TROUGH AT 20Z.
SFC CONVERGENCE IS RATHER MEAGER ALONG WITH BULK SHEAR VALUES JUST
REACHING 30 TO 35 KTS AT THIS TIME. SOME WEAK CELLS HAVE DEVELOPED
FROM NEAR AND EAST OF THE TROUGH AXIS THIS HOUR. EXPECT THIS
ACTIVITY TO EXPAND IN COVERAGE THIS AFTERNOON AS THE SYSTEM TRACKS
SOUTHEAST. WILL CONTINUE SVR WORDING IN SOUTHEAST/EAST ZONES FOR THE
AFTERNOON...THOUGH COVERAGE MAY REMAIN SCT THROUGH 00Z. LCL HEIGHTS
EAST OF I35 REMAIN AT 750M (~2450 FT) AND LOW LEVEL CAPE HAS
INCREASED TO 100-150 J/KG ALONG THE TROUGH AXIS...SO WILL NEED TO
MONITOR ANY STORMS FOR POTENTIAL BRIEF FUNNEL. AS THE SYSTEM PULLS
SOUTHEAST THIS EVENING...DIURNAL HEATING WILL DIMINISH AND STORMS
WILL DISSIPATE AFTER 01-02Z. HRRR MODEL CONTINUES TO BUBBLE UP
ACTIVITY THROUGH THIS TIME. 4KM WRF ALSO SUGGESTS SOME ACTIVITY OVER
SOUTHEAST MN MAY EXPAND INTO NORTHEAST IOWA BETWEEN 21 AND 00Z AS
WELL. WITH PASSAGE OF THE BOUNDARY...DEW POINTS DROP TO THE UPPER
50S TO LOWER 60S...SO LOWS WILL COOL TO THE LOWER TO MID 60S BY
MORNING. PATCHY FOG MAY DEVELOP IN THE CEDAR RIVER VALLEY TOWARD
MORNING.

.LONG TERM /MONDAY THROUGH SUNDAY/...
ISSUED AT 329 PM CDT SUN JUN 28 2015

THERE HAS BEEN LITTLE CHANGE IN FORECAST THINKING FROM PREVIOUS
SHIFTS. IOWA WILL REMAIN BENEATH NORTHWESTERLY FLOW ALOFT THROUGH
THE END OF THE WEEK...KEEPING TEMPERATURES A LITTLE BELOW SEASONAL
NORMALS AND LESSENING THE OVERALL SEVERE WEATHER THREAT. EVEN
SO...THINGS WILL REMAIN FAIRLY ACTIVE AS A SERIES OF SHORTWAVE
TROUGHS MOVING THROUGH THIS FLOW WILL RESULT IN PERIODIC CHANCES
FOR SHOWERS AND THUNDERSTORMS ACROSS OUR FORECAST AREA. THE FIRST
SUCH OPPORTUNITY COME LATE ON MONDAY AS A SUBTLE IMPULSE PUSHES AN
ATTENDANT WEAK SURFACE TROUGH FROM MINNESOTA DOWN ACROSS IOWA.
DESPITE A RELATIVE LACK OF LOW LEVEL MOISTURE...THE BROAD ASCENT
AHEAD OF THIS IMPULSE COMBINED WITH FAIRLY STEEP MID LEVEL LAPSE
RATES SHOULD BE SUFFICIENT TO GENERATE SOME
THUNDERSTORMS...ESPECIALLY ACROSS OUR NORTHERN AND EASTERN
COUNTIES...FROM LATE IN THE AFTERNOON INTO EARLY MONDAY NIGHT.
HAVE INTRODUCED DETAILS IN TIMING OF POP FORECAST TO ACCOUNT FOR
THIS SCENARIO.

EVEN AS THIS INITIAL SYSTEM PUSHES OFF TO THE SOUTH ON TUESDAY
ANOTHER SHORTWAVE WILL BE APPROACHING FROM THE NORTHWEST...HOWEVER
BY TUESDAY NIGHT AND WEDNESDAY A SURFACE RIDGE WILL HAVE BUILT
ACROSS THE AREA INCREASING DRY AIR AND SUBSIDENCE IN THE LOWER
SECTIONS OF THE ATMOSPHERIC COLUMN. THIS WILL MITIGATE
PRECIPITATION CHANCES AND INTENSITY...BUT EVEN SO CHANCE POPS ARE
WARRANTED THOUGH NO REAL IMPACTS ARE ANTICIPATED. FINALLY...THE
STRONGEST 500 MB TROUGH OF THE WEEK WILL TRAVERSE THE REGION
AROUND THURSDAY AND THURSDAY NIGHT IN CONJUNCTION WITH THE
AFOREMENTIONED SURFACE HIGH SLIDING OFF TO THE EAST AND A MODEST
RETURN OF LOW LEVEL MOISTURE. THIS APPEARS TO BE THE BEST
OPPORTUNITY FOR WIDESPREAD PRECIPITATION THIS
WEEK...HOWEVER...MODEL CONSISTENCY HAS NOT BEEN THE GREATEST WITH
THIS SYSTEM AND THERE ARE STILL TIMING ISSUES SO POPS HAVE BEEN
HELD GENERALLY IN THE 40S FOR NOW. IT IS EXPECTED THAT IF THIS
SCENARIO HOLDS UP AND WE CAN REFINE THE ARRIVAL OF THE RAIN THEN
POPS FOR PART OF THIS TIME FRAME WILL LIKELY INCREASE IN THE
COMING DAYS. IN ANY EVENT...THE SEVERE WEATHER THREAT LATER THIS
WEEK DOES NOT APPEAR PARTICULARLY NOTEWORTHY.

LOOKING INTO THE EXTENDED FORECAST...THERE CONTINUE TO BE
INDICATIONS THAT IN WAKE OF THE THURSDAY/THURSDAY NIGHT TROUGH
PASSAGE A PERIOD OF DEEP LAYERED RIDGING SHOULD FOLLOW...PROVIDING
A COUPLE OF DAYS OF SUNNY AND RELATIVELY COOL WEATHER RIGHT AROUND
THE FOURTH OF JULY. OBVIOUSLY ANYONE WITH OUTDOOR HOLIDAY PLANS
SHOULD CONTINUE TO MONITOR THE FORECAST THROUGHOUT THE WEEK BUT
EARLY SIGNS POINT TO GOOD WEATHER AROUND SATURDAY.

&&

.AVIATION...29/06Z
ISSUED AT 1200 AM CDT MON JUN 29 2015

TWO ISSUES THROUGH THE PERIOD WILL BE RADIATION FOG INTO THIS
MORNING AND DIURNAL CONVECTION MON AFTERNOON. TEMP/DEWPOINT
SPREADS ARE ALREADY QUITE LOW WITH WEAK SFC FLOW AND GRADIENT.
CONDITIONS ARE NOT IDEAL WITH OCCASIONAL SCT/BKN MID CLOUDS...BUT
WITH MOIST SOIL FROM RECENT RAINS AND ALREADY HIGH RH EXPECT AT
LEAST MVFR VSBYS TO DEVELOP...LIKELY IFR OR LESS IN MORE FAVORED
SPOTS. ISOLATED TO SCT PEAK HEATING CONVECTION IS ALSO EXPECTED
MON AFTERNOON. THIS COULD OCCUR ANYWHERE...BUT ONLY INCLUDED VCSH
WORDING IN MORE FAVORED ERN SITES FOR NOW.

&&

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

&&

$$

SHORT TERM...REV
LONG TERM...LEE
AVIATION...SMALL



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