Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 180457
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1157 PM CDT SUN AUG 17 2014

...UPDATED FOR AVIATION FORECAST...

.SHORT TERM /TONIGHT/...
ISSUED AT 309 PM CDT SUN AUG 17 2014

VERY WEAK RIDGE WILL MOVE THROUGH THE CWA TONIGHT AS A WEAK COLD
FRONT APPROACHES FROM THE NORTHWEST.  DO NOT EXPECT TO SEE FOG AS
WIDESPREAD AS WHAT OCCURRED THIS MORNING WITH A BIT MORE MIXING AND
THE APPROACH OF THE COLD FRONT.  EXPECT TO SEE SHOWERS AND
THUNDERSTORM ACTIVITY DEVELOP OVER THE NORTH AND WEST PART OF
THE CWA AFTER 06Z TONIGHT.

.LONG TERM /MONDAY THROUGH SUNDAY/...
ISSUED AT 309 PM CDT SUN AUG 17 2014

FRONTAL BOUNDARY WILL PUSH EASTWARD ACROSS THE STATE THROUGH THE
DAY MONDAY. THIS WILL ALLOW FOR PRECIPITATION TO SPREAD ACROSS
THE AREA AS WELL. MODELS ARE A BIT SLOWER ON THE PROGRESSION OF
THE FRONT AND HAVE THEREFORE SLOWED DOWN EASTWARD PUSH OF
PRECIPITATION...ANTICIPATING THE BOUNDARY TO BE NEAR CENTRAL IOWA
AROUND 18Z. HOWEVER...MODELS CONTINUE TO PIN POINT NORTHERN IOWA
AS THE FOCUS FOR BEST PRECIPITATION CHANCES...WHILE SOUTHERN IOWA
APPEARS TO HAVE THE BEST FORCING. THEREFORE...HAVE SPREAD
PRECIPITATION CHANCES FURTHER SOUTH THROUGHOUT THE DAY. IN
ADDITION...STORMS MAY BE SEVERE WITH HIGH SURFACE BASED
INSTABILITY...2000 J/KG OR HIGHER...AND LITTLE CAP WITH BOUNDARY
PUSHING THROUGH WILL LIKELY ALLOW FOR STORMS TO FIRE.
HOWEVER...WITH SHEAR LIMITED...DO NOT ANTICIPATE WIDESPREAD STORMS
NOR WIDESPREAD SEVERE STORMS. HAIL AND DAMAGING WINDS WILL ALSO BE
THE MAIN THREATS. IN ADDITION...PWAT VALUES WILL BE
HIGH...GREATER THAN 1.5 INCHES AND THUNDERSTORMS WILL BE CAPABLE
OF HEAVY RAINFALL.

SYSTEM WILL CONTINUE TO PUSH EASTWARD...WITH LINGERING
PRECIPITATION INTO MONDAY NIGHT. WEAK SURFACE HIGH WILL BUILD IN
BRIEFLY FOR TUESDAY...BEFORE UNSETTLED PATTERN CONTINUES. SURFACE
LOW IN CENTRAL PLAINS WILL PUSH NORTH AS RIDGE OF HIGH PRESSURE
BUILDS IN ACROSS SOUTHERN PLAINS. PREVIOUS MODEL RUNS WERE MORE
AGGRESSIVE WITH STRENGTH OF HIGH...QUICKLY LIFTING LOW ACROSS
IOWA. HOWEVER...LATEST MODEL RUNS BRING LARGE LOW PRESSURE SYSTEM
ON SHORE ACROSS WESTERN CANADA...WHICH BATTLES HIGH...LINGERING
PRECIPITATION ACROSS IOWA. CURRENT THINKING IS FOR BEST CHANCE FOR
PRECIPITATION ACROSS IOWA THURSDAY...A BIT FASTER THAN PREVIOUS
FORECAST. HOWEVER...PREVIOUS MODEL RUNS ALSO BUILT RIDGE INTO
CENTRAL PLAINS FOR REMAINDER OF EXTENDED...WHILE LATEST RUNS
CONTINUE TO PUSH UPPER LEVEL LOW EASTWARD KEEPING RIDGE FURTHER
SOUTH AND PRECIPITATION CHANCES ACROSS IOWA THROUGH MUCH OF
EXTENDED. HAVE GENERALLY KEPT TEMPERATURES NEAR GOING...WITH
COOLING LATE IN THE PERIOD WHEN LOW FINALLY PUSHES EAST AND COOL
CANADIAN AIR PUSHES SOUTH.

&&

.AVIATION...18/06Z
ISSUED AT 1057 PM CDT SUN AUG 17 2014

ANOTHER CHALLENGING AVIATION FCST. CONFIDENCE NOT THE HIGHEST...SO
MAY NEED ADJUSTMENTS THROUGH OVERNIGHT. FROM PVS FCST...LIFTED
KDSM AND KALO TO MVFR...AND KFOD TO IFR OVERNIGHT. TEMPS STAYING
UP AND DWPT DEPRESSION MAY NOT BE TIGHT ENOUGH...GIVEN RECENT DRY
CONDITIONS...FOR WIDESPREAD FOG. MODELS MISSING ST OVER
NEBRASKA...SO WENT OVC AT KDSM. DIFFERENT STORY FOR KMCW AND
KOTM. OBS COMING IN WITH HIGHER DWPTS AT KMCW RELATIVE TO KALO AND
FCST MODELS. THUS HAVE KMCW DROPPING TO LIFR. WITH RECENT
RAINS...MORE MOISTURE ON GROUND FOR KOTM. BR ALREADY SHOWING UP AT
04Z OBS. HAVE LIFR AT KOTM AS WELL.

&&

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

$$

SHORT TERM...MS
LONG TERM...AWB
AVIATION...KOTENBERG


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