Area Forecast Discussion
Issued by NWS Des Moines, IA

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220
FXUS63 KDMX 182017
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
317 PM CDT MON MAY 18 2015

.SHORT TERM /TONIGHT/...
ISSUED AT 316 PM CDT MON MAY 18 2015

MAIN CONCERNS THIS EVENING WILL BE CLOUD AND TEMP TRENDS. MORE
AGGRESSIVE HRRR/RAP CIG OUTPUT VS WRF NMM/ARW SEEMS TO BE VERIFYING
BEST INTO THE AFTERNOON AND SUGGESTS A GRADUAL DISSIPATION INTO THE
EVENING AS THE CYCLONIC LOW LEVEL FLOW EXITS.  STILL PLENTY OF
CLOUDS NORTH INTO THE EARLY EVENING.

FROST POTENTIAL IS SOMEWHAT PROBLEMATIC. POSITIVE ASPECTS WILL BE
SKIES BECOMING MOSTLY CLEAR LATE AND SURFACE DEWPOINTS REMAINING
JUST BELOW FREEZING. HOWEVER WINDS REMAIN QUITE BRISK NORTH AND
DO NOT EXPECT SUSTAINED SPEEDS TO DIP BELOW 10KTS THROUGH SUNRISE.
THUS HAVE ONLY PATCHY FROST MENTION FOR THE TIME BEING ALTHOUGH
TEMPS ARE FAVORABLE. BEST FROST POTENTIAL MAY BE OVER WEST
CENTRAL SECTIONS WHERE COOL TEMPS AND LIGHTER WINDS ARE
PHASED...BUT AREAL COVERAGE WOULD NOT BE GREAT ENOUGH TO ISSUE A
HEADLINE. FAR NW NEAR ESTHERVILLE MAY JUST TOUCH FREEZING...BUT
AGAIN WITHOUT SUFFICIENT AREAL COVERAGE OR DURATION TO JUSTIFY A
FREEZE WARNING.

.LONG TERM /TUESDAY THROUGH MONDAY/...
ISSUED AT 316 PM CDT MON MAY 18 2015

UNSEASONABLY COOL TEMPERATURES WILL BE THE MAIN STORY THROUGH THE
BEGINNING OF THE EXTENDED...WITH TEMPERATURES EXPECTED TO BE MORE
THAN 10 DEGREES BELOW ZERO. HAVE DROPPED TEMPERATURES A FEW DEGREES
THROUGH MUCH OF THE EXTENDED GIVEN LACK OF WARMING TODAY. TUESDAY
AND WEDNESDAY WILL BE COOLEST DAYS...WITH PERSISTENT NORTHERLY
SURFACE FLOW AS TROUGH CONTINUES TO PULL EAST ACROSS SOUTHERN
CANADA. WEDNESDAY WILL BE COOLEST DAY WITH CLOUDS AND RAIN EXPECTED
ACROSS MUCH OF THE CWA HELPING TO LIMIT WARMING. SYSTEM EXPECTED TO
PUSH EAST INTO IOWA BEGINNING TUESDAY NIGHT. WITH GENERALLY ZONAL
FLOW ACROSS IOWA AND LITTLE FOR FORCING OF SYSTEM...AND GIVEN HIGH
PRESSURE IN PLACE ACROSS MOST OF CWA...HAVE CONTINUED TO PUSH BACK
ONSET OF PRECIPITATION TUESDAY NIGHT. SOUNDINGS INDICATE GOOD
SATURATION BEGINNING EARLY WEDNESDAY...AND HAVE KEPT HIGHEST POPS
WEDNESDAY. STILL SOME UNCERTAINTY IN NORTHERN EXTENT OF
PRECIPITATION...WITH MODELS KEEPING BEST FORCING FURTHER
SOUTH...INTO MISSOURI. HOWEVER...GIVEN ISENTROPIC ANALYSIS INDICATE
ENOUGH MOISTURE AND FORCING ACROSS CENTRAL IOWA TO WARRANT POPS.

SYSTEM WILL PUSH OUT QUICKLY WITH CONTINUED NORTHWESTERLY FLOW ALOFT
KEEP TEMPERATURES COOLER THROUGH THE END OF THE WEEK...THOUGH CLOSER
TO NORMAL. ATTENTION WILL THEN SHIFT TO THE WEEKEND SYSTEM. MODELS
REMAIN CONSISTENT BRINGING LARGE UPPER LEVEL LOW PRESSURE SYSTEM
ONSHORE ACROSS SOUTHERN CALIFORNIA LATE THURSDAY. THIS WILL PUSH
EAST...THOUGH MODELS ARE NOT IN GOOD AGREEMENT WITH HANDLING OF
THIS SYSTEM. GFS IS MOST AGGRESSIVE WITH A FASTER EASTERN
PROGRESSION...WHILE ECMWF AND GEM ARE SLOWER AND BRING LOW INTO
PLAINS AS MORE OPEN WAVE. HAVE TRENDED TOWARDS SLIGHTLY SLOWER
SOLUTION...WITH BEST CHANCES SATURDAY NIGHT. WILL NEED TO BE
MONITORED FOR SEVERE POTENTIAL DEPENDING ON HOW SYSTEM EVOLVES AND
PLACEMENT OF LOW.

&&

.AVIATION...18/18Z
ISSUED AT 1247 PM CDT MON MAY 18 2015

MVFR CIGS PERSIST ALONG AND NORTHWEST OF AN KADU-KDSM-KCCY LINE AT
17Z AND SHOULD DRIFT TO THE EAST THIS AFTERNOON BEFORE LIFTING
THE NORTH DURING THE EVENING. THIS WILL RESULT IN THE LONGEST
RESIDENCY OVER NERN SITES /KMCW/KALO/. MIXING AND BRISK NW WINDS
MAY LAST LONGER THAN WHAT TYPICALLY OCCURS...PAST SUNSET INTO THE
EARLY EVENING...SHOULD SHOULD DIMINISH WEST TO EAST AS SKIES CLEAR
AND CONDITIONS RETURN TO VFR.

&&

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

&&

$$

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



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