Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 262052
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
352 PM CDT SUN JUL 26 2015

.SHORT TERM /TONIGHT/...
ISSUED AT 310 PM CDT SUN JUL 26 2015

PRIMARY CONCERNS TONIGHT WILL BE CONVECTION REDEVELOPING AND
RADIATION FOG POTENTIAL. IA REMAINS ON SRN EDGE OF MAIN
CO/SD/MN/WI WESTERLIES BUT IN THE SUBSIDENCE PORTION OF THE WAVE
TRAIN. NOTED DARKENING IN WATER VAPOR WHICH COINCIDES WITH H7/H5
QG IMPLIED DOWNWARD MOTION. THERMODYNAMICALLY...RECENT RAP DOES
DEPICT A WEAK H85/H7 WAVE ALONG THE IA/MN BORDER BUT FLOW IS VERY
WEAK WITH NEUTRAL ADVECTION...THUS CANNOT SEE WRN DAKOTAS/NE
CONVECTION MAINTAINING ITSELF TOO FAR EAST. THERE IS STILL SOME
PEAK HEATING POTENTIAL WITH RAP 0-1KM MOISTURE CONVERGENCE SHOWING
AN AXIS FROM N CENTRAL INTO S CENTRAL IA...BUT THE LOW LEVEL FLOW
IS QUITE WEAK AS WELL. OUTFLOW FROM ERN IA CONVECTION IS
APPROACHING IOWA FALLS AND GRINNELL BUT IS REALLY STRUGGLING TO
GENERATE ANYTHING AND WITH SURFACE FLOW BEHIND IT NEARLY PARALLEL
TO THE BOUNDARY ITS POTENTIAL MAY BE WANING. AIRMASS APPEARS TO BE
UNCAPPED AND BOUNDARY IS APPROACHING DEEPER CONVERGENCE AND HIGHER
INSTABILITY SO HAVE ADDED TOKEN ISOLATED WORDING INTO THE EARLY
EVENING HOURS.

HAVE ALSO ADDED PATCHY FOG WORDING AREA WIDE OVERNIGHT. MANY AREAS
RECEIVED AT LEAST A HALF INCH OF RAIN OVERNIGHT...AND SOME OVER AN
INCH...AND BOUNDARY LAYER HAS REMAINED QUITE MOIST WITH LITTLE
MIXING.  WINDS STILL NEARLY CALM IN MANY LOCATIONS AND TEMP/DEWPOINT
SPREADS ARE LOW FOR 20Z.

.LONG TERM /MONDAY THROUGH SUNDAY/...
ISSUED AT 310 PM CDT SUN JUL 26 2015

MAIN CONCERN FOR EXTENDED WILL FOCUS ON PRECIPITATION TRENDS AND
TEMPERATURES FOR BEGINNING OF PERIOD. LARGE LOW PRESSURE SYSTEM
PUSHING EAST ACROSS NORTHWESTERN US WILL PUSH RIDGE...CURRENTLY
ACROSS HIGH PLAINS...EAST INTO IOWA THROUGH TUESDAY. AS RIDGE
PUSHES EAST TEMPERATURES AND HUMIDITY WILL INCREASE...THOUGH
MODELS HAVE BACKED OFF SOMEWHAT ON AMOUNT OF WARM UP...AND HAVE
TRENDED TEMPS DOWN SLIGHTLY AS WELL. HOWEVER...HOTTEST DAY WILL
COME TUESDAY AHEAD OF BOUNDARY SET TO PUSH SOUTH TUESDAY INTO
WEDNESDAY. CURRENT FORECAST WOULD INDICATE NEED FOR HEAT ADVISORY
ACROSS MUCH OF SOUTHERN CWA TUESDAY...THOUGH TEMPERATURES TRENDS
ARE STILL SOMEWHAT UNCERTAIN...MODELS HAVE BEGUN TO SPEED UP
TIMING ON APPROACHING TUESDAY SYSTEM...AND PLACEMENT OF BOUNDARY
WILL HAVE LARGE IMPACT ON TEMPERATURES THROUGH THE AFTERNOON. IN
ADDITION...PRECIPITATION TRENDS MAY HAVE IMPACT ON AFTERNOON
WARMING AS WELL.

PRECIPITATION REMAINS CHALLENGING AHEAD OF BOUNDARY. WEAK BAND OF
ADVECTION PUSHES ACROSS THE NORTH MONDAY AFTERNOON...AND HAVE
INCLUDED MENTION FOR PRECIPITATION ACROSS THE NORTHWEST WITH
INSTABILITY SUFFICIENT FOR STORMS TO FORM. BEST CHANCES FOR
THUNDERSTORMS COME BEGINNING LATE MONDAY NIGHT INTO TUESDAY AS
WAVE LIFTS NORTHWEST AHEAD OF BOUNDARY. BEST FORCING REMAINS TO
THE NORTH...BUT MODELS ARE BEGINNING TO FOCUS SLIGHTLY FURTHER
SOUTH INTO NORTHWESTERN IOWA...AND HAVE TRENDED THIS WAY AS WELL.
AGAIN...BEST CHANCE COMES WITH BOUNDARY PUSHING SOUTH FOR
TUESDAY...AND MODELS ARE A BIT FASTER AND HAVE SPED UP PROGRESSION
OF PRECIPITATION. MAY SEE CHANCES FOR HEAVY RAIN WITH PWAT VALUES
NEAR 2 INCHES.

BEHIND BOUNDARY...CONDITIONS WILL BE PRIMARILY CALM AND DRY WITH
COOLER AIR PUSHING IN. TEMPERATURES WILL BE GENERALLY NEAR NORMAL
WITH HIGHS IN THE MID 80S AND LOWS IN THE 50S AND 60S. NEXT BEST
CHANCE FOR PRECIPITATION WILL COME NEAR END OF PERIOD FOR THE
WEEKEND WITH WEAK BOUNDARY PUSHING SOUTH...THOUGH DO NOT HAVE
HIGH CONFIDENCE IN TIMING OR PLACEMENT OF POPS ATTM.

&&

.AVIATION...26/18Z
ISSUED AT 100 PM CDT SUN JUL 26 2015

INITIAL CONCERN IS PEAK HEATING CONVECTION FOLLOWED BY RADIATION
FOG POTENTIAL OVERNIGHT. WATCHING AREA OF CONVERGENCE NEAR
KMCW/KALO THAT MAY DEVELOP ISOLATED SHOWERS AND STORMS INTO THE
EARLY EVENING. CONFIDENCE THAT ANY OF THESE WOULD IMPACT A
PARTICULAR SITE IS LOW HOWEVER SO ALL SITES VFR INTO THE EVENING.

WITH PERSISTENT CLOUDS INTO THE AFTERNOON IN THESE SAME
AREAS...LOW LEVEL RH WILL REMAIN HIGH LEADING TO FOG POTENTIAL
WITH CLEARING SKIES AND LIGHT WINDS. KMCW TEMP/DEWPOINT SPREAD IS
STILL ONLY 5F AT 18Z. HAVE MENTIONED VSBYS DOWN TO MVFR/IFR IN
THESE AREAS...ROUGHLY 09-15Z. SOME POTENTIAL FOR THIS TO OCCUR
EARLIER OR EVEN DOWN TO LIFR...BUT WILL HOLD OFF ON THAT UNTIL
CONFIDENCE INCREASES.


&&

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

$$

SHORT TERM...SMALL
LONG TERM...AWB
AVIATION...SMALL


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