Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 051751
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1251 PM CDT TUE MAY 5 2015

.SYNOPSIS...
ISSUED AT 326 AM CDT TUE MAY 5 2015

SOUTHWEST FLOW ALOFT WILL CONTINUE INTO THE WEEKEND AS A FRONTAL
BOUNDARY REMAINS IN THE VICINITY. A STRONG NEGATIVELY TILTED
TROUGH WILL KICK THE FRONT THROUGH THE AREA SUNDAY AND SUNDAY
NIGHT.

&&

.SHORT TERM /TODAY/...
ISSUED AT 326 AM CDT TUE MAY 5 2015

MANY FORECAST ELEMENTS WILL BE PROBLEMATIC TODAY WITH PLENTY OF
CONCERNS. ALTHOUGH MUCH OF THE RESPONSE IS EAST OF THE AREA...THE
RIGHT ENTRANCE REGION OF THE GREAT LAKES JET SEGMENT CONTINUES TO
AID LIFT BACK INTO IA.  OTHER KINEMATIC FORCING SUCH AS DPVA IS NOT
REALLY PRESENT HOWEVER WITH NO SIGNIFICANT SHORT WAVES UPSTREAM.
THERE IS PLENTY OF MOISTURE EMBEDDED WITHIN THE PRESENTLY STALLED
WEAK BAROCLINIC ZONE HOWEVER WITH SURFACE BOUNDARY JUST SOUTH OF I80
AT 08Z. MUCAPES AND EFFECTIVE SHEAR ARE QUITE LOW AND ANY RECENT
PRECIP...WHICH SEEMS TO BE DRIVEN BY WEAK WARM/THETA-E ADVECTION...
HAS BEEN LOW TOPPED WITH LITTLE LIGHTNING AND FAIRLY EFFICIENT
RAINFALL PRODUCTION.

THIS BASIC SCENARIO WILL CHANGE LITTLE THROUGH THE MORNING WITH
SCATTERED SHOWERS POSSIBLE AS BAROCLINIC ZONE AND FRONTAL BOUNDARY
START THEIR SLOW NORTHWARD PROGRESSION. SITUATION MAY CHANGE
SOMEWHAT DURING THE AFTERNOON AS NAM AND GFS BOTH DEPICT INCREASING
POTENTIALLY SURFACE BASED INSTABILITY WITH UNCAPPED 1000-2000 J/KG
MLCAPES. DO NOT SEE MUCH CHANGE IN MID LEVEL MOISTURE HOWEVER SO
WILL IT MAY BE DIFFICULT TO GET SURFACE BASED CONVECTION TO FIRE
ALONG A RETREATING WARM FRONT.  NONE OF THE HI RES MODELS ARE
PARTICULARLY IMPRESSIVE WITH DEVELOPMENT INTO THE AFTERNOON...BUT
PUTTING THEM TOGETHER THE 00Z SPC SSEO ENSEMBLE DOES HAVE FAIRLY
HIGH PROBABILITIES OF SOMETHING SO HAVE PLAYED THE MIDDLE GROUND
KEEPING CHANCES IN THE FORECAST. 0-6KM SHEAR SEEMS WEAK TO MODERATE
SO IF SOMETHING DID FIRE IT WOULD SEEM TO BE MARGINALLY SEVERE AT
BEST.

LOW CONFIDENCE IN TEMP FORECAST DUE TO PRECIP QUESTIONS...FRONTAL
PROGRESSION AND MIXING POTENTIAL...SO STAYED NEAR A CONSENSUS/WARM
END BLEND. DO NOT HAVE TOO FAR TO GO TO REACH THAT CONSIDERING
CURRENT OBS.

.LONG TERM /TONIGHT THROUGH MONDAY/...
ISSUED AT 326 AM CDT TUE MAY 5 2015

FRONTAL BOUNDARY ACROSS SOUTHERN IA THIS MORNING WILL LIFT NORTH
OF THE STATE BY MID DAY WEDNESDAY WITH A SOUTHERLY FLOW OF
UNSTABLE AIR OVER THE REGION EXPECT A RELATIVELY DRIER PERIOD
TONIGHT INTO WED...BUT AS THE FIRST IMPULSE LIFTS NORTHEAST OUT
OF THE WESTERN TROUGH A COLD FRONT WILL ADVANCE ACROSS THE HIGH
PLAINS. THE FRONT WILL MOVE INTO SOUTHERN AND EASTERN IOWA...THEM
BECOME STATIONARY.

A STRONGER SHORT WAVE WILL LIFT OUT SUNDAY THROUGH MONDAY. THE
FRONT WILL LIFT NORTH AS A WARM FRONT IN RESPONSE TO THE
APPROACHING SHORT WAVE. THIS WILL MAKE THE HIGH TEMPS FOR SUNDAY
TRICKY. THE POTENTIAL IS THERE FOR THE DRY SLOT TO MOVE INTO
DURING THE AFTERNOON WITH A DECENT EML IN PLACE. OPTED TO RAISE
TEMPERATURES A FEW DEGREES...AND WOULD BE SURPRISED OF THEY NEED
TO BE UPPED ANOTHER CATEGORY OR SO.

OVERALL...BELIEVE THE ECMWF HAS THE BEST FORECAST. CERTAINLY IS
HAS BEEN THE MOST CONSISTENT WITH THE SYSTEM OVER THE
WEEKEND...WHICH IS THE MOST SIGNIFICANT ONE. THE GFS OFFERS
DIFFERENT SOLUTIONS WITH TIMING AND STRENGTH DIFFERENCE. THE
ECMWF LOOKS REASONABLE WITH IT`S TIMING AND RESOLUTION OF THE
PATTERN. ONCE THE FRONT MOVES THROUGH SUNDAY NIGHT...A MUCH COOLER
FEW DAYS WILL BE IN STORE FOR THE FIRST PART OF NEXT WEEK.

&&

.AVIATION...05/18Z
ISSUED AT 1238 PM CDT TUE MAY 5 2015

FRONTAL BOUNDARY IS DRAPED ACROSS THE THE STATE...LOCATED JUST
SOUTH OF FOD AND ALO SITES. WITH ALO AND FOD JUST NORTH OF THE
BOUNDARY...CIGS AND VSBY HAVE BEEN IN IFR AND MVFR MOST OF THE
DAY FROM. IMPROVEMENT AT THOSE SITES WILL BE SLOW AS CIGS
GRADUALLY MOVE TOWARDS VFR THIS EVENING AND OVERNIGHT AS THE FRONT
SLOWLY SHIFTS NORTH. DSM AND OTM SHOULD REMAIN VFR THROUGH MUCH OF
THE TAF PERIOD...WITH CHANCES OF FOG OVERNIGHT. THE NORTHERN SITES
MAY SEE PRECIPITATION THIS EVENING...INCLUDING OCCASIONAL
THUNDER...BUT NONE OF THE MODELS ARE IN GREAT AGREEMENT ON TIMING
AND INTENSITY...SO MENTIONED ONLY VCSH FOR NOW AT ALO AND MCW.

&&

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

$$

SYNOPSIS...MS MAY 15
SHORT TERM...SMALL
LONG TERM...MS MAY 15
AVIATION...CURTIS



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