Area Forecast Discussion
Issued by NWS Des Moines, IA

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188
FXUS63 KDMX 170458
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1158 PM CDT SAT MAY 16 2015

...UPDATED AVIATION DISCUSSION...

.SHORT TERM /TONIGHT/...
ISSUED AT 324 PM CDT SAT MAY 16 2015

CONVECTIVE TRENDS WILL REMAIN THE PRIMARY CONCERN INTO THE NIGHT.
THE CURRENT SITUATION HAS ISOLATED WEAK ELEVATED CONVECTION DRIFTING
ACROSS ERN IA WHICH HAS BECOME MORE SURFACE BASED WITH TIME AS
MLCAPES AND CINHS TRENDED MORE FAVORABLE.  EFFECTIVE SHEAR AND
CONVERGENCE ARE FAIRLY WEAK HOWEVER SO EXPECT PERSISTENCE OR EVEN A
SLIGHT DOWNWARD TREND INTO THE EARLY EVENING HOURS.

ATTENTION WILL THEN TURN UPSTREAM AND BECOMES MORE PROBLEMATIC.
UNCAPPED 1500-2000 J/KG MLCAPES ARE IN PLACE AHEAD OF KS CONVECTION
WITH INCREASED EFFECTIVE SHEAR FARTHER WEST LEADING TO THE POTENTIAL
OF MORE ORGANIZATION. TRENDS ARE LEANING TOWARD THE POTENTIAL FOR
MORE ROBUST SURFACE BASED POTENTIAL JUST WEST OF THE MO RIVER.  MOST
CONVECTION ALLOWING MODELS EXPAND AND DEVELOP THIS INTO WRN IA
DURING THE EVENING WITH THE MEAN WIND.  NAM ELEVATED CAPE LOOKS
BELOW 1000 J/KG INTO THE NIGHT...SO WHILE INSTABILITY WILL NOT BE
EXTREME BOTH SHALLOW AND DEEP SHEAR INCREASE WITH LOW LEVEL JET
INCREASING TO 50KTS OR SO. MAIN THREATS WOULD BE HAIL AND WIND BUT
CANNOT RULE OUT A QLCS TORNADO EITHER AS 0-1KM SHEAR INCREASES INTO
THE NIGHT. SHEAR WILL CERTAINLY BE THERE...BUT QUESTION WILL BE HOW
ROBUST THE MCS IS BY THE TIME IT REACHES IA. WHATEVER REACHES US
SHOULD PERSIST INTO THE NIGHT IN SOME FORM HOWEVER WITH PERSISTENT
STRONG LOW LEVEL MOISTURE TRANSPORT.

.LONG TERM /SUNDAY THROUGH SATURDAY/...
ISSUED AT 324 PM CDT SAT MAY 16 2015

MAIN FORECAST CONCERN WILL BE WITH PRECIPITATION CHANCES FOR
BEGINNING OF PERIOD. EXPECT LINGERING PRECIPITATION FROM OVERNIGHT
TO BE ONGOING IN THE NORTH AND EAST...THOUGH EXPECT PRECIPITATION
TO BECOME MORE SCATTERED THROUGH THE MORNING HOURS. UPPER LEVEL
LOW WILL CONTINUE TO LIFT NORTHEAST FROM NEBRASKA THROUGH THE DAY
SUNDAY...REACHING NORTHERN MINNESOTA BY LATE IN THE DAY. CONCERN
WILL BECOME PLACEMENT OF BOUNDARY ACROSS CENTRAL IOWA...MODELS ARE
IN GOOD AGREEMENT WITH TIMING AND PLACEMENT OF SYSTEM...WITH
BOUNDARY PUSHING EAST QUICKLY AFTER 18Z. NEAR BOUNDARY COULD SEE
POTENTIAL FOR SEVERE THUNDERSTORMS WITH MODELS INDICATING CAPE
VALUES OF NEAR/OVER 2000 J/KG...INCREASING TO THE EAST. SHEAR
VALUES WILL SUFFICIENT TO SUPPORT THUNDERSTORMS WHICH DEVELOP
WITH BULK SHEAR OF NEAR 40KTS. THIS COULD LEAD TO A WINDOW OF
SEVERE POTENTIAL IN THE AFTERNOON EAST OF INTERSTATE 35...BEFORE
QUICKLY PUSHING EASTWARD OUT OF CWA. HOWEVER...STILL SOME
UNCERTAINTY IF THESE PARAMETERS WILL BE ABLE TO BE REALIZED WITH
LINGERING PRECIPITATION AND CLOUDS FROM OVERNIGHT
CONVECTION...WITH CONDITIONS BEING MORE FAVORABLE TO THE EAST OF
THE CWA. WINDS WILL BE STRONG AND GUSTY TOMORROW WITH GOOD
SOUTHERLY FLOW AND MIXING. TOP OF MIXED LAYER WINDS IN THE NORTH
ARE NEAR 40KTS...AND MAY BE NEAR ADVISORY CRITERIA AT TIMES IN
THE NORTH. HOWEVER...AGAIN WITH EXPECTED LINGERING
PRECIPITATION/CLOUDS IN THE NORTH MAY HELP LIMIT MIXING.

BEHIND BOUNDARY ANOTHER ROUND OF COOLER AIR WILL PUSH IN AS LOW
MOVES EAST. NAM IS MOST AGGRESSIVE WITH THE COOLING...AND FEEL IT
IS TOO AGGRESSIVE GIVEN TIME OF YEAR...AND HAVE KEPT TEMPERATURES
NEAR GOING...TRENDING TOWARDS GFS. COLDEST NIGHT WILL BE MONDAY
NIGHT...WITH DRY AIR AND HIGH PRESSURE WORKING SOUTH MAY BE TOO
WARM ON LOWS...WHICH COULD DROP READINGS TO NEAR FREEZING IN THE
NORTH. HOWEVER...WINDS WILL REMAIN UP WHICH SHOULD HELP LIMIT
COOLING SOMEWHAT. NEXT CHANCES FOR PRECIPITATION WILL COME
TUESDAY AS SYSTEM LIFTS NORTH FROM FOUR CORNERS REGION.
HOWEVER...WITH HIGH PRESSURE IN PLACE ACROSS THE NORTHERN PLAINS
HAVE KEPT PRECIPITATION CHANCES TO THE SOUTH AND MAY BE TOO
AGGRESSIVE. ANOTHER ROUND OF PRECIPITATION CHANCES COMES FOR THE
WEEKEND AS LOW PRESSURE SYSTEM COMES ONSHORE IN SOUTHERN
CALIFORNIA AND PUSHES HIGH EAST FOR VERY END OF PERIOD. ATTM
MODELS ARE IN GOOD AGREEMENT WITH THE TIMING AND PLACEMENT OF THIS
SYSTEM..THOUGH GFS IS A BIT MORE AGGRESSIVE AND HAVE JUST KEPT
CHANCES POPS ATTM.

&&

.AVIATION...17/06Z
ISSUED AT 1153 PM CDT SAT MAY 16 2015

OUT AHEAD OF THE SHOWERS AND STORMS CONDITIONS SHOULD REMAIN VFR.
MOST AREAS WITHIN THE SHOWERS AND STORMS WILL SEE AT LEAST PERIODS
OF MVFR OR BORDERLINE VFR CIGS. WITH SLOW PROGRESSION OF SHOWERS
EASTWARD AND WEAKENING...HAVE HANDLED PRECIP AT MCW...ALO..AND OTM
WITH VCSH. SUNDAY WILL BE HIGHLIGHTED BY RAPIDLY INCREASING WINDS
WITH SUSTAINED TO AROUND 20KTS AND GUSTS TOWARDS 30KTS OR MORE.
WAS NOT CONFIDENT ENOUGH TO PUT PREVAILING 30KT PLUS GUSTS.
STORMS...ESPECIALLY IN THE EAST...MAY FIRE UP LATER IN THE
AFTERNOON SUNDAY TOO...BUT HAVE KEPT THOSE OUT OF TAFS FOR THE
TIME BEING.

&&

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

$$

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



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