Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 242343
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
637 PM CDT FRI JUL 24 2015

...UPDATED FOR 25/00Z AVIATION FORECAST DISCUSSION...

.SHORT TERM /TONIGHT/...
ISSUED AT 341 PM CDT FRI JUL 24 2015

WITH MORNING CONVECTION SOUTH OF THE DMX CWA BY EARLY
AFTERNOON...FCST FOCUS WILL SHIFT TO EVENING CONVECTION AND
OVERNIGHT PRECIP CHANCES. A BOUNDARY ORIENTED FROM NE TO SW WILL BE
PROPAGATING SOUTHEASTWARD INTO NORTHERN AND CENTRAL IOWA. 12Z GFS
TIMING IS HORRIBLE WITH THIS BOUNDARY AS IT IS TOO FAST...BUT REST
OF THE SHORT TERM MODELS/NAM/EURO GENERALLY INITIALIZE AND HANDLE
BOUNDARY PROGRESSION BETTER...SO HAVE GONE WITH A BLEND THERE.
BOUNDARY SHOULD BE SLIGHTLY WEST OF KMCW AND OUR NORTHERN TIER OF
COUNTIES BY AROUND 00Z. SPC MESO ANALYSIS SHOWS ENVIRONMENT
DESTABILIZING IN THIS LOCATION WITH MOSTLY CLEAR SKIES. SBCAPE
VALUES AT THIS TIME PROJECTED TO BE AROUND 1500 TO 2000 J/KG...WHICH
IS NOT GREAT. KMCW FCST SOUNDING ALSO LOOKS VERY ELEVATED IN TERMS
OF ANY CONVECTION THAT WOULD GENERATE. MAIN THREAT WITH ANY STORMS
THAT DEVELOP WOULD BE STRONG WINDS AS DCAPE IS OVER 1500 J/KG. BULK
SHEAR AROUND 40 KTS WHICH IS MINIMAL FOR SUSTAINING STORMS. IN
ALL...TIMING WILL VERY LIKELY INHIBIT ANY STORMS THAT MAY DEVELOP
FROM REACHING SEVERE LEVELS. CONVECTION WILL DIE OFF WITH SUNSET.

THE OVERNIGHT PERIOD LOOKS FAR MORE ACTIVE ACROSS SOUTHERN IOWA. THE
RIDGE OF THE THETA-E AXIS WILL BE AROUND INDIANOLA. MODELS SHOW SOME
DECENTLY DEEP MOISTURE CONVERGENCE EXPECTED AROUND HIGHWAY 34 AND
SOUTH ALONG THE AFOREMENTIONED BOUNDARY WHICH WILL KEEP MOVING
SOUTHEAST. SIGNAL FOR MODERATE TO HEAVY PRECIP THERE AS PWATS AROUND
2 TO 2.2 INCHES APPEAR LIKELY. 0-6KM MIXING RATIOS ABOVE 8G/KG AND 0-
6KM MUCAPES AROUND 500 TO 1000 J/KG WILL SUPPORT UPWARD MOISTURE
FLUX. FCST SOUNDINGS PICK UP ON SOME DRY AIR ALOFT TO CONTEND PLUS
WARM CLOUD DEPTHS AROUND 12KFT...SO SYSTEM WON/T BE COMPLETELY
EFFICIENT IN PRODUCING PRECIP...BUT CERTAINLY ENOUGH SUPPORT FOR AT
LEAST HALF AN INCH OF RAIN. WITH SOME PLACES FURTHER SOUTH REACHING
AN INCH OR MORE. WITH HIGH PRESSURE AND SUBSIDENCE NORTH...NORTHERN
TIER OF DMX CWA SHOULD BE DRY OVERNIGHT.

.LONG TERM /SATURDAY THROUGH FRIDAY/...
ISSUED AT 341 PM CDT FRI JUL 24 2015

IA WILL BE ON THE FRINGE OF THE WESTERLIES AND VARIED INFLUENCE OF
THE S CENTRAL CONUS RIDGE INTO EARLY NEXT WEEK. AT ONSET ATTENTION
WILL BEGIN UPSTREAM WITH WEAK RIPPLES TOPPING RIDGE ALONG AZ/CO/NE
MOISTURE RIBBON NOTED IN WATER VAPOR IMAGERY. REMNANTS MAY TRACK
ALONG CURRENT SIOUXLAND FRONTAL BOUNDARY SAGGING SOUTHEASTWARD
TOWARD MO BORDER BY DAYBREAK...OR WHAT IS LEFT OF CURRENT SWRN IA
OUTFLOW FROM ERN IA CONVECTION TODAY. THIS TOGETHER WILL LIKELY BE
SUFFICIENT FOR MCS OF SOME FORM TO SUSTAIN IN WEAK WARM ADVECTION
REGIME SAT...MAINLY OVER CENTRAL SRN SECTIONS.

WEAK WARM/THETA-E ADVECTION WILL THEN PERSIST INTO SAT NIGHT WITH
AFOREMENTIONED FRONTAL ZONE BEGINNING TO LIFT NORTHWARD BACK THROUGH
IA. THUS HAVE PUSH POPS WELL THROUGH THE CHANCE CATEGORY SW-NE BY
EARLY SUN MORNING. ANY REMNANTS SHOULD EXIT DURING THE DAY SUN
LEADING TO ANOTHER INCREASE IN HEAT AND HUMIDITY. TEMPS AND
DEWPOINTS SHOULD BE SEVERAL DEGREES WARMER THAN SAT WITH HEAT
INDICES TOPPING 100F IN SPOTS.  ALTHOUGH THERE IS NOT MUCH TO FOCUS
ON...HAVE KEPT SLIGHT CHANCES GOING INTO SUN NIGHT AND CONTINUED
WEAK WARM ADVECTION.  FORECAST MONDAY IS MORE PROBLEMATIC. NAM AND
ECMWF SUGGEST LITTLE WILL HAPPEN HOWEVER THE 12Z GFS DEPICTS
SIGNIFICANT CO/KS/NE PEAK HEATING CONVECTION SUSTAINING ITSELF
OVERNIGHT IN THE WARM ADVECTION AND CROSSING IA DURING THE DAY. HAVE
GONE DRY FOR NOW...BLENDING IN ADJACENT OFFICE CONSENSUS...HOWEVER
THIS WILL BE A PERIOD TO WATCH FOR ADDITION OF POPS IN THE COMING
DAYS.

PATTERN WILL BEGIN TO CHANGE GOING FURTHER IN THE NEXT WORK WEEK.
WAVE CURRENTLY OFF THE BC COAST WILL MIGRATE EASTWARD AS POTENT
SHORT WAVE DRAGGING FRONT AND ASSOCIATED DEEP FORCING THROUGH IA.
TIMING APPEARS TO BE THE ONLY QUESTION.  MOST LIKELY SCENARIO NOW
HAS SIOUXLAND PEAK HEATING SURFACE BASED DEVELOPMENT MOVING THROUGH
REMAINDER OF IA INTO TUE NIGHT AND POSSIBLY SE IA WED. THE REST OF
THE EXTENDED LOOKS DRY WITH TEMPS AND DEWPOINTS NO WORSE THAN
SEASONAL LEVELS.

&&

.AVIATION...25/00Z
ISSUED AT 637 PM CDT FRI JUL 24 2015

SFC COLD FRONT WILL SWEEP INTO IA OVERNIGHT AND MOVE
SOUTHWARD...STALLING OUT FROM ROUGHLY WEST TO EAST ACROSS THE
CENTRAL OR SOUTHERN PORTIONS OF THE STATE...APPROXIMATELY BETWEEN
THE I-80 AND US 34 CORRIDORS...BY SUNRISE SATURDAY. BORDERLINE MVFR
CIGS WILL AFFECT SOME OF THE TERMINALS THROUGH TONIGHT. SHRA/TSRA
MAY AFFECT THE KDSM AND KOTM TERMINALS LATER TONIGHT...WITH MVFR OR
EVEN IFR CONDITIONS POSSIBLE IN THE STORMS.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
HEAT ADVISORY UNTIL 8 PM CDT THIS EVENING FOR ADAIR-ADAMS-
AUDUBON-CARROLL-CASS-CRAWFORD-GUTHRIE-RINGGOLD-SAC-TAYLOR-UNION.

&&

$$

SHORT TERM...KOTENBERG
LONG TERM...SMALL
AVIATION...ZOGG



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