Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 062040
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
340 PM CDT FRI MAY 6 2016

.SHORT TERM.../TONIGHT/
ISSUED AT 340 PM CDT FRI MAY 6 2016

A COLD FRONT WILL APPROACH THE NORTHERN BORDER OF IOWA LATE THIS
EVENING AND BE IN THE NORTHERN TIER OR TWO OF COUNTIES BY MIDNIGHT.
BY 12Z THE FRONT WILL BE BISECTING THE STATE SOMEWHERE NEAR THE
HIGHWAY 30 CORRIDOR.  THERE IS WEAK FORCING ASSOCIATED WITH THE
FRONT AND THE BEST INSTABILITY WILL RESIDE WEST OF THE FORECAST AREA
BUT INITIALLY CAPE VALUES ACROSS THE FAR NORTH WILL BE SOMEWHERE AROUND
1000 J/KG.  WE SHOULD SEE WIDELY SCATTERED TO ISOLATED THUNDERSTORMS
ASSOCIATED WITH THE FRONT BEGINNING AROUND 9 OR 10 PM ACROSS THE FAR
NORTH AND WORKING TOWARD THE HIGHWAY 20 CORRIDOR AFTER MIDNIGHT.
OVERNIGHT WE LOSE SOME INSTABILITY SO I CHANGED THE WORDING IN THE
GRIDS TO SCATTERED SHOWERS WITH ISOLATED THUNDERSTORMS.  THE RISK OF
SEVERE STORMS WITH THE FRONT OVERNIGHT IS MINIMAL.  STORMS HOWEVER
MAY PRODUCE GUSTY WIND AS SOUNDINGS DO SHOW 30 KTS IN THE MIXED
LAYER.

.LONG TERM.../SATURDAY THROUGH FRIDAY/
ISSUED AT 340 PM CDT FRI MAY 6 2016

MAIN CHALLENGES THROUGH THE PERIOD WILL BE THUNDER/RAIN CHANCES AND
TO A LESSER DEGREE TEMPERATURES. FRONTAL BOUNDARY DROPPING SOUTH ON
SATURDAY LIKELY TO BRING SOME SHOWERS AND PERHAPS ISO THUNDER...BUT
COVERAGE LOOKS TO BE ON THE DECREASE THROUGH THE LATE MORNING AND
AFTERNOON HOURS AND INSTABILITY REMAINS LOW. FOR NOW HAVE TRIMMED
BACK ON CHANCES AND COVERAGE. BOTH GFS/EURO CONTINUE TO FOCUS
DEVELOPMENT IN RESPONSE TO A SHORTWAVE TRACKING SOUTHEAST ALONG
THE BOUNDARY WITH LESS ACTIVITY IN THE AFTERNOON HOURS. HIRES
MODELS SHOW GENERAL LACK OF WIDESPREAD DEVELOPMENT...LIKELY DUE TO
THE LIMITED MOISTURE AVAILABLE THROUGH AT LEAST SUNDAY. HIGHS WILL
BE COOLER SATURDAY AND OVERNIGHT LOWS SAT NIGHT WILL BE MUCH COOLER
NORTH AS HIGH SETTLES INTO THE REGION THERE. ELSEWHERE SOME LINGERING
SHOWERS/THUNDER MAY STILL OCCUR OVER THE FAR SOUTH SATURDAY NIGHT.
ANY CHANCES FOR STRONG THUNDERSTORMS LOOK TO BE SOUTH INTO MISSOURI/KANSAS
OR WEST INTO NEBRASKA. THERE REMAINS CONSIDERABLE UNCERTAINTY SUNDAY...
AS TO HOW QUICKLY THE WARM FRONT WILL LIFT BACK NORTH WITH TIME.
MODELS DIFFER ON TIMING WITH THE GFS SLIGHTLY FASTER TO BRING THE
FRONT NORTH WHILE THE EURO HOLDS THE BOUNDARY SOUTH UNTIL LATE
SUNDAY/SUNDAY NIGHT. FOR NOW HAVE KEPT THE MAJORITY OF THE AREA
DRY ON SUNDAY WITH THE EXCEPTION OF THE FAR SOUTH WHERE IMPACTS
OF THE BOUNDARY LIFTING NORTH WOULD BE FELT FIRST. BY SUNDAY NIGHT
THE ENTIRE H500 LONGWAVE TROUGH AND ATTENDANT SHORTWAVE BEGIN TO
LIFT NORTHEAST WITH THE FIRST REAL PULSE OF MOISTURE. THIS WILL
RESULT IN WIDESPREAD THUNDER OVER THE REGION THROUGH 12Z MONDAY.
THE FIRST SHORTWAVE WILL LIFT TOWARD THE IA MN BORDER AROUND 18Z
WITH PERHAPS A FEW BREAKS IN THE CLOUDS SOUTH BY 18Z. BOTH THE
GFS/EURO STILL SUGGEST THAT THE SFC BOUNDARY WILL BE SOMEWHERE IN
SOUTHERN IA BETWEEN 18-00Z...SOUTH OF DES MOINES BUT NORTH OF THE
IA MO BORDER. THIS SHOULD RESULT IN MUCAPE INCREASING TO WELL
ABOVE 1000 J/KG THOUGH MLCAPE REMAINS IN 500-700 J/KG RANGE AND
MAINLY OVER THE SOUTHWEST. CHANCES FOR SOME STRONGER STORMS REMAIN
MONDAY AFTERNOON...THOUGH CONFIDENCE ON COVERAGE REMAIN A QUESTION
AT THIS POINT. THE GFS IS NOW CLOSER TO THE EURO IN THAT BY
TUESDAY THE MAIN AREA OF MOISTURE TRANSPORT SHIFTS TO THE EAST AND
SOUTHEAST OF OUR AREA. INSTABILITY MAY STILL BE ENOUGH TO HAVE
SOME RISK FOR STRONGER STORMS ON TUESDAY. TEMPERATURE TRENDS
CONTINUE ON TRACK THROUGH MIDWEEK WITH MORE CLOUDS/RAIN CHANCES
KEEPING HIGHS IN THE 60S/70S WITH LOWS IN THE 40S/50S. BOTH
EURO/GFS CONTINUE TO SHOW QPF AMOUNTS GENERALLY 1-2 WITH LOCALLY
HIGHER AMOUNTS THROUGH WED... WITH UNCERTAINTY OF MAX PLACEMENT
DUE TO DIFFERENCES IN MODEL FORCINGS.


&&

.AVIATION.../FOR THE 18Z TAFS THROUGH 18Z SATURDAY MORNING/
ISSUED AT 1240 PM CDT FRI MAY 6 2016

CLEAR SKIES AND UNRESTRICTED VISIBILITIES ARE FORECAST THROUGH 06Z
BUT AFTER 06Z A COLD FRONT WILL SINK SOUTH ACROSS TAF SITES.
MOISTURE IS LIMITED SO VFR CIGS ARE EXPECTED.  LIKEWISE INSTABILITY
IS NOT GREAT SO WHILE AN ISOLATED THUNDERSTORM IS POSSIBLE...
UNCERTAINTY AS TO PROXIMITY OF THE TAF LOCATION AND THE LIMITED
MOISTURE WARRANTS JUST A MENTION OF VCSH AT THIS TIME.


&&

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

$$

SHORT TERM...FAB
LONG TERM...REV
AVIATION...FAB


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