Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 261138
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
638 AM CDT TUE MAY 26 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 352 AM CDT TUE MAY 26 2015

MAIN FOCUS TODAY IS ON RAIN CHANCES. SYNOPTICALLY...THE EVER PRESENT
UPPER LOW WHICH HAS INFLUENCED THE PLAINS WEATHER FOR DAYS...IS
FINALLY OPEN AND MOVING EASTWARD SQUARELY ACROSS OUR FORECAST AREA
TODAY. IT WILL BE EAST OF OUR AREA TONIGHT. SHOWERS AND ISOLATED
THUNDERSTORMS HAVE BEEN OCCURRING THE PAST SEVERAL HOURS MAINLY IN
NORTHWEST IA...EXTREME NORTHEAST NEB...AND EXTREME SOUTHEAST SD
RIGHT ALONG THE 925MB WIND SHIFT LINE. AS THE UPPER LOW IS MOVING
SLOWLY EASTWARD...THE 925MB SHEAR AXIS FOLLOWS SUIT BUT AT A SNAILS
PACE THIS MORNING. THEREFORE THERE IS A DECENT CHANCE FOR SHOWERS
AND ISOLATED STORMS MAINLY IN NORTHWEST IA THIS MORNING...AND
ESPECIALLY IN THE EASTERN SECTIONS OF NORTHWEST IA BETWEEN 12Z AND
18Z. THE RAIN CHANCES THEN WANE THIS AFTERNOON IN OUR SOUTHEAST
ZONES AS THE WIND SHEAR CONTINUES TO MOVE EAST...LEADING INTO WHAT
WILL FINALLY BE A TOTALLY DRY NIGHT TONIGHT ACROSS THE FORECAST
AREA. CONCERNING HIGHS...THEY ARE RATHER BENIGN TODAY BUT PREFERRED
THE GUIDANCE VALUES WHICH HAD COOL VALUES IN THE 60S ACROSS OUR FAR
EASTERN ZONES DUE TO THE INCREASED CLOUD COVER. CONVERSELY A GOOD
PORTION OF OUR WESTERN ZONES SHOULD WARM INTO THE MID 70S. TONIGHT
WITH CLEARING OR CLEAR SKIES AND LIGHT WINDS...TEMPERATURES SHOULD
FALL TO 50 TO 55 DEGREES.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 352 AM CDT TUE MAY 26 2015

WEDNESDAY MORNING STARTS OFF FAIRLY TRANQUIL WITH CLEAR SKIES AND
LIGHT WINDS...HOWEVER...SURFACE RIDGE SHIFTS EAST AND FORECAST
SOUNDINGS INDICATE STRONG MIXING UNDER INCREASING SOUTHERLY FLOW.
WITH STEEP LAPSE RATES FROM AROUND 925 TO 700 MB LEADS TO
INSTABILITY ALOFT.  MODELS SUGGEST THE GREATEST INSTABILITY WILL BE
ACROSS SOUTHWEST MINNESOTA...WHERE BOTH THE CANADIAN AND SREF
DEVELOP PRECIPITATION.  BOTH NAM AND GFS INDICATE A FEW HUNDRED J/KG
OF UNCAPPED CAPE...BUT DO NOT PRODUCE PRECIP.  FOR NOW...KEPT
FORECAST DRY DUE TO A LACK OF A TRIGGER...BUT WILL NEED TO WATCH THE
POTENTIAL FOR AIRMASS THUNDERSTORM DEVELOPMENT IN THE EASTERN CWA
WEDNESDAY AFTERNOON.

WEDNESDAY NIGHT HAS BECOME EVEN MORE UNCLEAR WITH SHORT WAVES MAINLY
STAYING SOUTH OF THE FORECAST AREA...HOWEVER...MODEST 20-30 KNOT LOW
LEVEL JET DEVELOPS ACROSS THE PLAINS.  NOT A LOT OF CONVERGENCE
ACROSS OUR AREA...WITH THE CONVERGENCE FOCUSED FURTHER NORTH.  WITH
THE UNCERTAINTY ON FOCUS...DROPPED POPS BACK TO CHANCE.

APPEARS THAT DIRTY SOUTHWEST FLOW USHERS ADDITIONAL SHORTWAVES
ACROSS THE AREA ON THURSDAY.  HAVE RAISED POPS TO HIGH CHANCE/LOW
LIKELY ON THURSDAY.

ON FRIDAY...STRONG COLD FRONT MOVES ACROSS THE AREA WITH 925 HPA
TEMPS FALLING TO AROUND 5 C BEHIND THE FRONT.  WITH MUCH COOLER AND
STABLE AIR BEHIND THE FRONT...EXPECT CONVECTION TO BE CONTAINED
MAINLY ALONG AND AHEAD OF THE FRONT.

HOW FAR THE FRONT SURGES SOUTH IS UP FOR DEBATE...WITH MODELS IN
GENERAL STALLING THE FRONT STALLING THE FRONT BETWEEN HIGHWAY 20 AND
INTERSTATE 80.  WITH THE FRONT REMAINING IN THE VICINITY THROUGH THE
WEEKEND...COULD BE ACTIVE THOUGH FORECAST AREA IS ON THE COOL SIDE
OF THE FRONT.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)
ISSUED AT 632 AM CDT TUE MAY 26 2015

THERE ARE SOME MVFR AND UPPER END IFR CEILINGS DOTTING OUR EASTERN
ZONES EARLY THIS MORNING...PRIMARILY ALONG AND EAST OF THE I 29
CORRIDOR. UNFORTUNATELY THESE CLOUDS ARE BEING MASKED BY THICK
HIGH CLOUDS ON THE SATELLITE PICTURE SO WE CANNOT SEE THE EXPANSE
OF THEM NOR THERE MOVEMENT. FURTHER TO THE WEST...FAIRLY CONFIDENT
THAT KHON WILL REMAIN VFR THROUGH THE TAF PERIOD. BUT HEADING
EASTWARD...THERE IS DEFINITELY QUITE A BIT OF LOW END MVFR AND
UPPER END IFR AROUND KFSD WHICH HAS TO BE ACCOUNTED FOR IN THE
MORNING HOURS. THE NAM AND RAP13 SUGGEST THIS...HOWEVER THESE TWO
MODELS ARE LIKELY TOO HIGH WITH THE LOW LEVEL MOISTURE AROUND
KSUX. THAT SAID...WAYNE NEB IS STILL IFR NOT TOO FAR AWAY FROM
KSUX WHICH IS BOTHERSOME. THEREFORE PUT IN A TEMPO GROUP FOR LOWER
END MVFR AT KSUX WITH SHOWERS FOR A COUPLE OF HOURS THIS MORNING
TO ACCOUNT FOR SPOTTY LOWERED CEILINGS IN THAT AREA. THE AFTERNOON
HOURS SHOULD BE VFR ACROSS THE AREA LEADING INTO VFR TONIGHT.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
&&

$$

SHORT TERM...MJ
LONG TERM...
AVIATION...MJ


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