Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 040003
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
703 PM CDT THU SEP 3 2015

.UPDATE...
ISSUED AT 656 PM CDT THU SEP 3 2015

ISOLATED SHOWER/STORM WORDING HAS BEEN ADDED N CENTRAL TO E
CENTRAL IA. ELEVATED CONVECTION HAS DEVELOPED ON LEADING EDGE OF
WEAK WARM ADVECTION...LIKELY ROOTED FAIRLY HIGH ABOVE 2KM BASED ON
FORECAST SOUNDINGS. HAVE ONLY ADDED A FEW HOURS AT THIS
POINT...BUT MAY HAVE TO EXTEND AS IT MAY MAINTAIN ITSELF INTO THE
NIGHT WITH TYPICAL NOCTURNAL WARM ADVECTION CYCLE.

&&

.SHORT TERM /TONIGHT/...
ISSUED AT 332 PM CDT THU SEP 3 2015

MAIN FORECAST CONCERN WAS FOCUSED ON TEMPERATURES AND FOG
POTENTIAL OVER NORTHERN IOWA. OVERNIGHT LOWS LOOK TO FINALLY REACH
THE CROSSOVER TEMP BY B/T 07-09Z OVER THE NORTH AND LIKELY SEE FOG
DEVELOP DURING THAT TIME FRAME. NAM/SREF SUGGEST FOG DEVELOPING FROM
MOW TO EST AND POSSIBLY AS FAR SOUTH AS HIGHWAY 20. THE CAVEAT IS
A WEAK SHORTWAVE OVER NEBRASKA/SOUTH DAKOTA MAY BRING IN SOME
HIGHER CLOUDS TOWARDS FRIDAY MORNING...SO ONLY MENTIONED PATCHY
FOG ATOM. THE LATEST HRRR (03.18Z) AND EVEN THE GFS HAVE A HINT
OF CONVECTION DEVELOPING OVER THE NORTHWEST TOWARDS FRIDAY MORNING
IN RESPONSE TO THE LAW DEVELOPING AND ASSOCIATED WITH
AFOREMENTIONED WEAK SHORTWAVE. THINKING THE NAM/ECMWF HAS A BETTER
HANDLE ON TIMING AND LOCATION AND LEFT FORECAST DRY.

.LONG TERM /FRIDAY THROUGH THURSDAY/...
ISSUED AT 332 PM CDT THU SEP 3 2015

PATTERN REMAINS SIMILAR THROUGH THE BEGINNING OF THE MID/LONG RANGE
WITH UPPER RIDGING IN PLACE ALOFT WITH A TROUGH DIGGING INTO THE
WESTERN US. A FEW WEAK IMPULSES WILL MOVE JUST TO THE WEST OF THE
CWA WHICH COULD LEAD TO SOME INCREASED CLOUDINESS...BUT OVERALL
CHANCE OF PRECIPITATION IS SMALL SO HAVE A DRY FORECAST INTO
SATURDAY. UPPER LEVEL RIDGE TO FLATTEN SOME OVER THE WEEKEND AS THE
WESTERN US TROUGH LIFTS NORTHEASTWARD INTO SOUTHERN CANADIAN PRAIRIE
PROVINCES BY LATE SUNDAY. SOUTHERLY FLOW WILL INCREASE AHEAD OF THIS
SYSTEM SATURDAY NIGHT INTO SUNDAY...WITH MOISTURE ADVECTION AND
MOISTURE TRANSPORT BECOMING ORIENTED INTO WESTERN IOWA. MAY SEE SOME
STORMS BUBBLE UP ACROSS THE WESTERN/NORTHWESTERN CWA...BUT OVERALL
WIDESPREAD PRECIPITATION CHANCES NOT EXPECTED UNTIL THE PASSAGE OF
THE COLD FRONT ASSOCIATED WITH THE CANADIAN SYSTEM SUNDAY NIGHT.
THIS FRONT WILL ELIMINATE THE CURRENT HOT AND MUGGY CONDITIONS...AS
H85 TEMPS DROP INTO THE TEENS BEHIND THE FRONT. LONG RANGE IN MODELS
IN SOME DISAGREEMENT INTO NEXT WEEK WITH HOW FAST TO PUSH THE FRONT
SOUTH...WITH THE EC HANGING THE FRONT UP ACROSS SOUTHERN IOWA WITH
CHANCES FOR STORMS CONTINUING INTO MONDAY/MONDAY NIGHT. GFS TRIES TO
PUSH IT INTO MISSOURI...WHICH WOULD KEEP IOWA DRIER MONDAY. FULL
 WESTERN US TROUGH TO SHOVE EAST TUESDAY WITH THE FRONT LIFTING
BACK NORTHWARD AS A WARM FRONT LATE MONDAY NIGHT/EARLY TUESDAY
BEFORE A STRONGER COLD FRONT PUSHES THROUGH LATE TUESDAY INTO
TUESDAY NIGHT. H85 TEMPS TO DROP ANOTHER CATEGORY INTO THE LOW
TEENS BEHIND THIS FRONT WITH HIGH PRESSURE EXPECTED TO BUILD IN
FOR THE REST OF THE WEEK. THIS SHOULD LEAD TO MAINLY DRY
CONDITIONS FOR MUCH OF WEDNESDAY INTO THE END OF THE WEEK. MODELS
DO HINT AT A WEAK TROUGH CLIPPING NORTHERN IOWA THURSDAY WHICH
COULD BRING SOME SPRINKLES TO MAINLY NORTHEASTERN IOWA. HAVE A
SMALL AREA OF SLIGHT CHANCE POP FOR THIS FEATURE. OTHERWISE
RELEGATED POPS MAINLY TO THE TIME PERIODS WITH THE FRONTAL
PASSAGES WITH TEMPS EXPECTED TO FALL MORE TOWARD OR SLIGHTLY BELOW
THE SEASONAL AVERAGES.

&&

.AVIATION...03/18Z
ISSUED AT 1229 PM CDT THU SEP 3 2015

ONLY CONCERN THROUGH THE PERIOD WILL BE RADIATION FOG POTENTIAL
NORTH IN VICINITY OF WARM FRONT ALONG IA/MN BORDER. HAVE
ESSENTIALLY FOLLOWED PERSISTENCE AT KMCW WITH CONDITIONS
LIKELY DETERIORATING TO LIFR AGAIN. COULD BE EVEN WORSE WITH LESS
MIXING TODAY BUT DID NOT WANT TO BE THAT AGGRESSIVE AT THIS POINT.
OTHERWISE EXPECT VFR WITH NOTHING BEYOND SCT/BKN MID CLOUDS AT
OTHER LOCATIONS. CURRENT ISOLATED CONVECTION IS NOT AFFECTING TAF
SITES AND SHOULD REMAIN THAT WAY FOR THE SHORT TERM.

&&

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

&&

$$

UPDATE...SMALL
SHORT TERM...PODRAZIK
LONG TERM...BEERENDS
AVIATION...CURTIS


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