Area Forecast Discussion
Issued by NWS Des Moines, IA

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860
FXUS63 KDMX 161632
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1132 AM CDT SAT MAY 16 2015

.SYNOPSIS...
ISSUED AT 400 AM CDT SAT MAY 16 2015

WARM FRONT FROM NORTHERN NEBRASKA THROUGH CENTRAL IOWA WILL LIFT
NORTH TODAY AS LOW PRESSURE OVER THE HIGH PLAINS AWAITS THE UPPER
LOW EJECTING FORM THE SOUTHWEST. LOW WILL MOVE TO THE MINNESOTA
ARROWHEAD BY MONDAY MORNING WITH ITS COLD FRONT EXTENDING SOUTH
THROUGH EASTERN IOWA. COOL CANADIAN HIGH PRESSURE WILL FOLLOW
THROUGH MID WEEK.

&&

.UPDATE...
ISSUED AT 1131 AM CDT SAT MAY 16 2015

ADDED LOW END/ISOLATED MENTION OF CONVECTION TO NORTH AND EAST
AREAS A BIT SOONER THAN PREVIOUSLY DEPICTED.
UNORGANIZED...ISOLATED ELEVATED CONVECTION DEVELOPED OVER MO
EARLIER THIS MORNING AND HAS OOZED INTO FAR SERN SECTIONS. IT MAY
BECOME ROOTED LOWER AND MORE SURFACE BASED WITH TIME. 16Z SRN IA
MLCAPES ARE UNCAPPED 1000-1500 J/KG AND MUCAPES 2-3K J/KG WITH NIL
CINH REGARDLESS. CONVERGENCE AND EFFECTIVE SHEAR IS WEAK FOR THE
TIME BEING SO CONVECTION SHOULD REMAIN UNORGANIZED AND BELOW
SEVERE LIMITS THROUGH 00Z.

&&

.SHORT TERM /TODAY/...
ISSUED AT 400 AM CDT SAT MAY 16 2015

A LINE OF SHOWERS AND THUNDERSTORMS HAD DEVELOPED AND MOVED TO THE
HIGHWAY 20 CORRIDOR BY 4 AM.  THE LINE OF CONVECTION IS TIED TO THE
850MB FRONTAL BOUNDARY SHIFTING NORTH ACROSS THE CWA AS A SURFACE
LOW LIFTS OUT OF THE CENTRAL PLAINS INTO THE NORTHERN PLAINS.  THE
SURFACE AND 850 FRONTAL BOUNDARY WILL BE NORTH OF THE CWA BY 15Z.
THUS I EXPECT THE SHOWERS/STORMS TO LIKEWISE LIFT NORTH OF THE CWA
BY EARLY MORNING.

THERE WILL THEN BE A DRY PERIOD FOR THE FORECAST AREA FOR THE REST
OF THE MORNING INTO THE AFTERNOON.  SOUNDINGS SHOW US LOSING OUR CAP
HOWEVER BY 18Z.  INSTABILITY QUICKLY INCREASES THROUGH THE MORNING
AND BY EARLY AFTERNOON WE WILL HAVE 2200 CAPE ACROSS OUR CWA.  EVEN
THOUGH WE WILL BE UNSTABLE I CANT FIND MUCH TO FOCUS CONVECTION ON
NEAR THE SURFACE. IN ADDITION...SHEAR IS VERY WEAK AND
UNIDIRECTIONAL UNTIL 00Z OR LATER SO ANY STORMS THAT WOULD DEVELOP
JUST IN THE INSTABILITY AXIS ACROSS CENTRAL IOWA WOULD NOT LIKELY
BECOME SEVERE.

ALOFT WE HAVE RIDGING IN PLACE OVER IOWA THROUGH THE MORNING THEN AS
LOW PRESSURE DEEPENS OVER THE CENTRAL AND SOUTHERN PLAINS AND THE
RIDGE OF HIGH PRESSURE PUSHES EAST.  THERE IS INDICATION THAT A
SUBTLE SHORT WAVE WILL LIFT INTO WESTERN IOWA BEGINNING IN MID
AFTERNOON AND THERE IS SOME FORCING WITH THIS FEATURE.  GIVEN OUR
INSTABILITY I FELT AT LEAST SLIGHT CHANCE POPS WERE WARRANTED FOR
THE FAR SOUTH AND WEST IN THE AFTERNOON.  I STARTED PULLING POPS
INTO THE WEST BETWEEN 16 AND 18Z WHICH MAY BE A LITTLE EARLY BUT IF
THE FORCING COME IN A LITTLE EARLY AND WE BREAK OUT IN ENOUGH
SUNSHINE AHEAD OF THE SHORTWAVE IT IS POSSIBLE TO SEE SOME
CONVECTION. AGAIN...CONFIDENCE IS LOW AT THIS POINT BUT I FELT THE
INSTABILITY COULD NOT BE IGNORED.

BETTER CHANCES FOR STRONG STORMS WILL COME BY LATE AFTERNOON IN THIS
AREA WHEN DEEP SHEAR BEGINS TO MOVE IN.  STORMS WILL BE COME MORE
ORGANIZED.  IN ADDITION...THERE WILL BE STORMS DEVELOPING FURTHER
WEST ALONG A SURFACE COLD FRONT AND DRY LINE.  TIMING WILL BE KEY
HERE BUT IT APPEARS THIS WILL BE VERY LATE THIS AFTERNOON AND BY THE
TIME THEY MOVE INTO/NEAR OUR CWA THEY WILL MOVE INTO AN INCREASINGLY
UNFAVORABLE ENVIRONMENT TO MAINTAIN THE LEVEL OF SEVERITY THEY WILL
HAVE FURTHER WEST.  SO EVEN THOUGH SOME STORMS COULD BE STRONG
ACROSS THE WEST AND FAR SOUTHWEST LATE AFTERNOON INTO THE EVENING I
AM NOT LOOKING FOR MUCH IN THE WAY OF SEVERE DURING THE TODAY
FORECAST PERIOD.

.LONG TERM /TONIGHT THROUGH FRIDAY/...
ISSUED AT 400 AM CDT SAT MAY 16 2015

AN OVERALL FAIRLY CLASSIC DRY SLOW EVENT IS UNFOLDING WITH THE
NEGATIVELY TILTED TROUGH LIFTING THROUGH THE UPPER MIDWEST. THE
SURFACE DRY LINE IS FORECAST TO BE WELL TO THE WEST THOUGH THE
NIGHT BY ALL MODELS. THIS WILL TEND TO LIMIT SEVERE WEATHER FOR
TONIGHT. IT CERTAINLY CAN`T BE RULED OUT WITH THE LOW LEVEL JET
IN EXCESS OF 40 ITS. WIND AND HAIL WOULD SEEM TO BE THE PRIMARY
THREATS. TIMING WILL BE AN ISSUE FOR SUNDAY. AT THIS TIME IT
APPEARS MUCH OF THE THREAT WILL BE EAST OF THE CWA...BUT TIMING
DIFFERENCE OF A FEW HOURS WILL MAKE A BIG DIFFERENCE.

A TURN TOWARD COOLER WEATHER LOOKS TO BE ABOUT ON TRACK AS THE
PATTERN SHIFTS TOWARD TROUGHINESS IN THE EAST. TEMPS WILL BE WELL
BELOW NORMAL THROUGH A GOOD PART OF THE WEEK WITH WAA RAIN
BEGINNING TO SHOW UP LATER IN THE WEEK INTO THE WEEKEND WHEN A
SITUATION SIMILAR TO THIS WEEKEND UNFOLDS.

IT IS LIKELY THAT ANOTHER PERIOD SUB-NORMAL WEATHER WILL FOLLOW
THE WEATHER SYSTEM. THE CHANGE IN TREND TOWARD COOLER WEATHER
APPEARS TO BE IN PART TO THE RECURVATURE OF TYPHOON NOUL...AND
AFTER NEXT WEEKEND THE RECURVATURE EXPECTED WITH TYPHOON DOLPHIN.

&&

.AVIATION...16/12Z
ISSUED AT 655 AM CDT SAT MAY 16 2015

A LINE OF THUNDERSTORMS FORMED ALONG AN 850MB WARM FRONTAL BOUNDARY
ALONG THE HIGHWAY 20 CORRIDOR AND AS OF 12Z RESIDE FROM SW MN TO
NEAR ALO.  THE STORMS WILL CONTINUE TO MOVE TO THE NORTHEAST AND OUT
OF THE TAF LOCATIONS.  LOW CLOUDS AND FOG WILL KEEP MVFR VSBYS AND
IFR CIGS BUT THESE SHOULD IMPROVE AFT 15Z. THROUGH 21Z WE SHOULD VFR
TO MVFR CIGS ACROSS TAF LOCATIONS.  AFT 00Z STORMS WILL FORM ALONG A
BOUNDARY OUT WEST OF IOWA BUT AS WE DESTABILIZE ADDITIONAL STORMS
SHOULD DEVELOP OVER WESTERN IOWA AND MOVE ACROSS LOCATIONS W OF I-
35.  AFT 04Z THE STORMS OVER THE PLAINS SHOULD THEN MOVE INTO AND
ACROSS IA THROUGH MUCH OF THE NIGHT.  SFC FLOW WILL REMAIN SRLY AT
10-20KTS.


&&

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

$$

UPDATE...SMALL
SYNOPSIS...MS MAY 15
SHORT TERM...FAB
LONG TERM...MS MAY 15
AVIATION...FAB



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