Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 272347
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
647 PM CDT MON JUL 27 2015

.SHORT TERM /TONIGHT/...
ISSUED AT 416 PM CDT MON JUL 27 2015

FORECAST CONCERNS CONTINUE TO REVOLVE AROUND PRECIPITATION TRENDS.
ONGOING CONVECTIVE SYSTEM ACROSS CENTRAL IOWA THROUGHOUT THE DAY
TODAY WILL CONTINUE TO INFLUENCE CONVECTIVE TRENDS THROUGH THE
OVERNIGHT. HAVE KEPT POPS ACROSS THE AREA AS INSTABILITY WILL ALLOW
ONGOING PRECIPITATION TO CONTINUE TO PUSH EAST AND DROP SOUTHEAST.
IN ADDITION...CONCERNS FOR THE AFTERNOON REDEVELOPMENT TO THE WEST.
EXPECT BEST CHANCE TO BE FURTHER WEST INTO EASTERN IOWA ALONG
BOUNDARY...HOWEVER...THETA-E ADVECTION IS EXPECTED TO INCREASE
ACROSS WESTERN IOWA IN THE LATE AFTERNOON HOURS WHICH MAY SPARK
ADDITIONAL THUNDERSTORMS. CURRENT MESO ANALYSIS SHOWS CAPPING ACROSS
THIS AREA...AND HAVE TRENDED PRECIPITATION IN THIS AREA
DOWN...EXPECTING CAP TO HOLD.

NEXT FOCUS WILL BE PRECIPITATION TRENDS OVERNIGHT AS WAVE PUSHES
NORTH AHEAD OF BOUNDARY IN THE DAKOTAS. MODELS CONTINUE TO BE FASTER
WITH THIS SOLUTION...AND HAVE TRENDED THIS WAY. WILL BE SOME SEVERE
POTENTIAL WITH INSTABILITY REMAINING ACROSS THE AREA...THOUGH MAIN
CONCERN WILL BE WITH HEAVY RAIN POTENTIAL. PWAT VALUES NEAR 1.8
INCHES WITH GOOD MOISTURE TRANSPORT INTO THE REGION AND WARM CLOUD
DEPTHS. GIVEN ANTICIPATED BEST FORCING FURTHER NORTH OF IOWA...AND
QUICK PROGRESSION OF SYSTEM...WILL KEEP FLASH FLOOD HEADLINES OUT
FOR NOW.

.LONG TERM /TUESDAY THROUGH MONDAY/...
ISSUED AT 416 PM CDT MON JUL 27 2015

WE HAVE AN ACTIVE DAY LINED UP FOR TUESDAY...FOLLOWED BY A MUCH
MORE CLIMATOLOGICAL LEANING FCST PERIOD FOR THE REST OF THE LONG
TERM. MODELS IN GOOD AGREEMENT WITH PUSHING A COLD FRONT THROUGH
THE CWA FROM NW TO SE DURING TUESDAY. THREE MAJOR CONCERNS FOR
TUESDAY ARE STRONG TO SEVERE THUNDERSTORM POTENTIAL...HEAVY
RAINFALL POTENTIAL...AND NEAR HEADLINE HEAT INDEX VALUES.

FOR TUE HEAVY RAIN POTENTIAL...PWATS IN THE 2.1 TO 2.25 INCH
RANGE...ESPECIALLY OVER OUR NE CWA...ARE AROUND +3 TO +4 STD DEV.
NAM HAS PWATS APPROACHING 2.5 INCHES. IN TERMS OF MOISTURE AND
DWPTS...NAM ON THE HIGHER END AM LEANING TOWARDS IT SINCE IT IS
INITIALIZING WELL...PLUS THE TIME OF YEAR SUPPORTS MOIST. THE GFS IS
TOO DRY PER USUAL. PLENTY OF MOISTURE TRANSPORT VIA 30 KT LLJ AND
PLENTY OF SFC MOISTURE CONV WITH COLD FROPA. MIXING RATIOS ABOVE 8
G/KG PLUS 0-6 KM MUCAPES ABOVE 1500 J/KG WILL SUPPORT UPWARD
MOISTURE FLUX. TIME OF YEAR WOULD TYPICALLY BE A HUGE NEGATIVE FOR
FLOODING/FLASH FLOODING POTENTIAL. HOWEVER...SIGNIFICANT RAINFALL
OVER THE PAST 48 HOURS IN SOME LOCATIONS MAY LEAVE SOME AREAS FAIRLY
SATURATED.

FOR TUE SVR WX POTENTIAL...MAIN FOCUS WILL BE DAMAGING WINDS AND
SLIGHT TOR THREAT. WITH PWATS EXPECTED TO BE SO HIGH...UPDRAFTS WILL
LIKELY BE WATER LOADED...MAKING SEVERE HAIL PRODUCTION DIFFICULT.
BOTH GFS AND NAM PICK UP ON A POCKET OF 200 M2/S2 0 TO 3 KM HELICITY
WITH THE BOUNDARY TO OUR NORTH. LCL HEIGHTS WELL BELOW 1000M. IN
SHORT...NOT AN OUTBREAK ENVIRONMENT...BUT WORTH WATCHING.

FOR HEAT POTENTIAL...WENT WITHOUT ANY HEADLINES FOR NOW. MORNING
PRECIP/CLOUD COVER PLUS TIMING OF BOUNDARY ARRIVAL WILL LIKELY KEEP
TEMPS DOWN VERSUS FCST IN PREVIOUS FEW DAYS. REGARDLESS OF SFC
TEMPS...WILL STILL BE HOT AND HUMID WITH SFC DWPTS IN THE MID TO
UPPER 70S. HEAT INDEX VALUES WILL LIKELY TOP OUT IN THE UPPER 90S TO
LOW TRIPLE DIGITS IN AND SE OF THE DSM METRO. OVERNIGHT SHIFT MAY
NEED TO ISSUE ADVISORY IN OUR SE.

THE FRONT AND ANY LINGERING PRECIP SHOULD BE EAST OF OUR CWA BY
SUNRISE WEDNESDAY. A SFC ANTICYCLONE WILL HELP KEEP WEDNESDAY AND
THURSDAY QUIET AND DRY. 850 MB TEMPS DROP TO THE 14C TO 18C RANGE
WHICH WILL HELP PUSH TEMPS DOWN TO THE LOW 80S FOR WEDNESDAY.

FOR THE MIDDLE TO END OF THE WEEK...WE RETURN TO ZONAL FLOW. MID
LEVEL WINDS ARE ABOUT +1 TO +2 STD DEV FROM THE WEST. GIVEN ALL OF
THIS...LEFT BROAD-BRUSHED POPS THROUGH THE WEEKEND IN
ANTICIPATION OF SHORTWAVE TRAIN EXPECTED TO START CHUGGING AGAIN.
850MB TEMPS RETURN TO THE 19C TO 22C RANGE WHICH IS NEAR NORMAL
FOR THIS TIME OF YEAR. SUBSEQUENTLY...HAVE HIGHS CLOSE TO
CLIMO...IN THE MID TO UPPER 80S.

&&

.AVIATION...28/00Z
ISSUED AT 647 PM CDT MON JUL 27 2015

COMPLICATED FORECAST NEXT 24 HOURS...FIRST MCS EXITING THE REGION
NOW OVER THE SOUTHEAST WITH A BREAK IN THE TSRA THROUGH 04-05Z.
VARIOUS SOLUTIONS SHOW SOME REDEVELOPMENT AFT 04-05Z IN ZONE OF
WARM AIR ADVECTION...WITH POSSIBLE MCS AGAIN FROM NEBRASKA MOVING
THROUGH REGION BY 14-15Z. WITH APPROACH OF FRONT ON TUESDAY...
ANOTHER ROUND OF CONVECTION WITH POTENTIAL FOR SEVERE STORMS FROM
18Z-00Z ESPECIALLY NORTH SITES AT KFOD...KMCW...KALO. SOME HINT
THAT ADDITIONAL DEVELOPMENT WILL LINGER OVER THE EAST THROUGH 06Z.
WILL REEVALUATE FOR 06Z PACKAGE. /REV

&&

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

$$

SHORT TERM...AWB/KA
LONG TERM...KOTENBERG
AVIATION...REV


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