Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 182342
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
642 PM CDT MON AUG 18 2014

.SHORT TERM /TONIGHT/...
ISSUED AT 311 PM CDT MON AUG 18 2014

COLD FRONT FROM NWRN MN THROUGH THE NEBRASKA PANHANDLE WILL MOVE
SOUTHEAST THROUGH THE CWA TONIGHT INTO TUE BEFORE STALLING OUT.
AIRMASS HAS BECOME UNSTABLE AHEAD OF THE FRONT WITH 2500 TO 3500
J/KG OF CAPE AVAILABLE IN AN UNCAPPED LOW SHEAR ENVIRONMENT.
THUNDERSTORMS ARE EXPECTED TO FOR RM A BROKEN LIKE AHEAD OF THE COLD
FRONT AND DROP SOUTHWARD ACROSS THE CWA...THOUGH WEAKENING AS IT MOVES
AWAY FROM THE DYNAMICS.  THERE IS SOME POTENTIAL FOR SEVERE WITH
ZERO TO 3 CAPE RUNNING NEAR 100 J/KG.  LCL IS FAIRLY HIGH LIMITING
THE CHANCE FOR TORNADIC DEVELOPMENT.  THOUGH HAIL IS POSSIBLE WITH
STRONGER STORMS...DEEP WARM CLOUD DEPTH WILL LIMIT THAT AS WELL.

.LONG TERM /TUESDAY THROUGH MONDAY/...
ISSUED AT 311 PM CDT MON AUG 18 2014

WEATHER PATTERN SETTING UP FOR EXTENDED WILL BE ACTIVE FOR IOWA
WITH VARYING CHANCES FOR THUNDERSTORMS. PATTERN WILL BE MARKED BY
HIGH PRESSURE SYSTEM ATTEMPTING TO PUSH NORTH INTO CENTRAL PLAINS
FROM GULF COAST REGION...WHILE UPPER LEVEL LOW PRESSURE SYSTEM
PUSHES EAST ACROSS CANADA...WITH IOWA GENERALLY IN BETWEEN THESE
TWO SYSTEMS. WITH HIGH AND RIDGE BUILDING INTO THE SOUTHERN
PLAINS...TEMPERATURES WILL WARM THROUGHOUT THE PERIOD...AND IF
RIDGE PUSHES FURTHER NORTH...WILL BE TOO LOW ON TEMPERATURES FOR
EXTENDED. HOWEVER...AS IS WILL SEE AN INCREASE IN HUMIDITY ACROSS
THE REGION...AND WITH HIGHER TEMPERATURES WILL SEE HEAT INDEX
VALUES IN THE MID TO UPPER 90S NEAR 100 ACROSS THE SOUTH THROUGH
THE WEEK. AS HIGH PUSHES NORTH...SURFACE LOW WILL PUSH
EAST...LIFTING NORTH ACROSS IOWA THROUGH THE DAY WEDNESDAY.
MODELS HAVE COME INTO BETTER AGREEMENT ON TIMING OF
SYSTEM...HOWEVER WITH DRY AIR PUSHING IN WITH HIGH...HAVE CUT BACK
ON PRECIPITATION CHANCES WEDNESDAY THOUGH STILL ANTICIPATE WIDELY
SCATTERED THUNDERSTORMS. IN ADDITION...INSTABILITY WILL BE QUITE
HIGH WITH LIMITED...THOUGH SUFFICIENT SHEAR...SO MAY HAVE CUT
BACK TOO AGGRESSIVELY. IN ADDITION...SYSTEM WILL NEED TO BE
WATCHED FOR CHANCES FOR SEVERE THUNDERSTORMS. ATTM...THREAT
APPEARS LOW.

LOW WILL CONTINUE TO LIFT NORTH WITH SECONDARY BOUNDARY PUSHING
ACROSS IOWA LATE THURSDAY. UPPER LOW WILL INCREASE IN STRENGTH AND
PUSH EASTWARD THROUGH THE END OF THE WORK WEEK..BEGINNING TO PUSH
HIGH FURTHER EAST...AND WILL SEE INCREASING PRECIPITATION
CHANCES. HOWEVER...MODELS ARE NOT IN GOOD AGREEMENT WITH TIMING
AND STRENGTH OF THIS SYSTEM. HAVE TRENDED TOWARDS THE GFS
ATTM...THOUGH THIS IS A SLIGHTLY MORE AGGRESSIVE SOLUTION. BEHIND
THIS SECONDARY LOW...WILL SEE COOLER TEMPERATURES AGAIN FOR VERY
END OF PERIOD.

&&

.AVIATION...19/00Z
ISSUED AT 642 PM CDT MON AUG 18 2014

MAINLY VFR CONDITIONS EXPECTED DURING THE NEXT 24 HOURS. SCT TSRA
WILL SPREAD ACROSS ABOUT THE NE HALF OF IOWA THIS EVE AND
TONIGHT AND HAVE INCLUDED VCTS IN ALL TERMINALS...HOWEVER SOME
STATIONS ESPECIALLY DSM/OTM HAVE A LOWER PROBABILITY AND EFFECTS
OF ANY STORMS WILL BE FOR BRIEF PERIODS ONLY. SOME BR ALSO
POSSIBLE AGAIN EARLY TUES MORNING...BUT ATTM BELIEVE IT WILL BE
ONLY MVFR AND FOR A COUPLE HOURS AROUND SUNRISE.

&&

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

&&

$$

SHORT TERM...MS
LONG TERM...AWB
AVIATION...LEE



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