Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 222342
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
642 PM CDT TUE APR 22 2014

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 329 PM CDT TUE APR 22 2014

RETURN FLOW GRADUALLY INCREASING FROM WEST TO EAST ACROSS THE AREA
LATE THIS AFTERNOON AHEAD OF AN APPROACHING TROUGH.  AS OF
20Z...TROUGH WAS OVER THE PACIFIC NORTHWEST BUT IS EXPECTED TO
RAPIDLY SHIFT EAST THROUGH THE OVERNIGHT.  850 -700 MB THETA-E
ADVECTION IS STRONG ENOUGH THROUGH THE OVERNIGHT TO POTENTIALLY
CREATE A FEW SCATTERED SHOWERS/ISOLATED THUNDER THROUGH THE
OVERNIGHT.  THE STRONG THETA-E ADVECTION SHIFTS EAST THROUGH THE
MORNING HOURS ON WEDNESDAY.

VERY WINDY DAY EXPECTED AHEAD OF THE APPROACHING LOW.  925 HPA WINDS
START OFF AROUND 40 KNOTS AND GRADUALLY DECREASE THROUGHOUT THE DAY
AS TROUGH APPROACHES FROM THE WEST.  WITH STRONG WINDS ALOFT AND
MIXING...SHOULD SEE ADVISORY CONDITIONS ACROSS MUCH OF THE AREA AND
HAVE ISSUED A WIND ADVISORY ACROSS THE AREA.  TOUGH CALL IN TERMS OF
SEVERE WEATHER AS SYNOPTIC WARM FRONT VERY BRIEFLY NOSES INTO THE
FORECAST AREA.  MAINLY ELEVATED INSTABILITY AHEAD OF THE APPROACHING
LOW AND INSTABILITY REMAINS ABOVE MUCH OF THE EFFECTIVE SHEAR.
THEREFORE...MAINLY EXPECTING STORMS TO REMAIN BELOW SEVERE LIMITS
BUT COULD HAVE AN ISOLATED HAILER APPROACH THE LOW END OF SEVERE
LIMITS IN THE MISSOURI RIVER LATE WEDNESDAY AFTERNOON.

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 329 PM CDT TUE APR 22 2014

THE THREAT FOR LOW END SEVERE WILL CONTINUE INTO EARLY WEDNESDAY
EVENING OVER MAINLY THE SOUTHEAST QUARTER OF THE CWA...WITH ELEVATED
HAILERS THE MAIN CONCERN. STILL EXPECTING A FAIRLY BROAD AREA OF
RAINFALL HOWEVER WITH A DECREASING THREAT FOR THUNDER TO THE WEST.
THE BETTER FORCING SHIFTS EAST THROUGH THE NIGHT WITH MOST OF THE
PRECIPITATION EAST OF THE I-29 CORRIDOR BY LATE NIGHT. THE UPPER
LEVEL SUPPORT WILL GRADUALLY ROTATE TO THE NORTHEAST WHICH WILL
LEAVE A SMALL THREAT FOR SHOWERS AND ISOLATED THUNDERSTORMS OVER THE
NORTHEAST THIRD OF THE CWA. THE MAIN THREAT COULD BE DURING THURSDAY
AFTERNOON AS WE HEAT OUT AND A LITTLE BIT OF SURFACE BASED CAPE
DEVELOPS...ABOUT 500 J/KG OR LESS. WITH A VERY LOW FREEZING LEVEL
SOME SMALL HAIL WILL BE POSSIBLE.

THE OTHER CONCERN ON THURSDAY WILL BE FIRE WEATHER. VERY DEEP MIXING
WILL LEAD TO WINDS LIKELY GUSTING TO AROUND 35 TO 40 MPH AND SURFACE
RELATIVE HUMIDITY VALUES IN THE TEENS TO LOWER 20S...SO IF THE
FORECAST HOLDS RED FLAG CONDITIONS WILL BE VERY POSSIBLE.

ON FRIDAY THE MODELS HAVE COME AROUND TO A SLIGHTLY WARMER AND MORE
MIXED DAY WITH THE 12Z GFS QUITE A BIT COLDER THAN THE NAM/ECMWF/GEM
OUTPUT. SO RAISED HIGHS A BIT MORE INTO THE UPPER 50S TO UPPER 60S.
ANOTHER FAIRLY BREEZY DAY BUT FOR NOW IT LOOKS LIKE SURFACE RELATIVE
HUMIDITY VALUES WILL BE A BIT BELOW WHATS NEEDED FOR RED FLAG
CONDITIONS.

IN THE OUTER PERIODS(SATURDAY THROUGH TUESDAY)...MODELS INCONSISTENT
AND DIVERGING A BIT SO CONFIDENCE NOT REAL STRONG...AT LEAST ON SOME
OF THE DETAILS. ONE THINGS SEEMS ALMOST FOR CERTAIN AND THAT IS FOR
BELOW NORMAL TEMPERATURES...BUT AT LEAST FOR THE WEEKEND EVEN THAT
IS NOT COMPLETELY GUARANTEED. THE LATEST ECMWF HAS COME IN MUCH
WARMER...FARTHER NORTH WITH THE WARM FRONT...THAN EITHER THE GFS OR
GEM. AT THIS TIME SIDING WITH THE GFS/GEM OUTPUT WHICH KEEPS THE
DEVELOP UPPER LEVEL LOW A LITTLE FARTHER SOUTH WHICH SHOULD IN TURN
KEEP THE WARMER AIR LOCKED UP TO THE SOUTH AS WELL. BY MONDAY INTO
TUESDAY COOLER AIR SETTLES IN ON ALL THE MODELS SO A BIT MORE
CONFIDENT FOR COLDER CONDITIONS THESE DAYS. STILL A VERY GOOD CHANCE
FOR RAIN SUNDAY INTO MONDAY...BUT WILL NEED TO SEE IF THE MODELS CAN
BECOME A BIT MORE CONSISTENT BEFORE BRINGING IN HIGHER
PROBABILITIES.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)
ISSUED AT 640 PM CDT TUE APR 22 2014

LARGEST AVIATION ISSUE OVER THE NEXT 24 HOURS WILL BE THE VERY
STRONG WINDS. A CONTINUED INCREASE IN THE GRADIENT IS EXPECTED
OVERNIGHT...AND WILL GET WINDS STRONG ENOUGH ALOFT TO WARRANT SOME
NEAR 40 KNOT GUSTS AS EARLY AS 14-15Z. AT THIS TIME...WILL LIKELY
END UP WITH SURFACE WINDS STRONG ENOUGH TO AVOID MENTION OF LOW
LEVEL WIND SHEAR PRIOR TO MIXING OUT NEAR SURFACE INVERSION BY
MID MORNING. WHILE DO ACKNOWLEDGE THE FACT THAT COULD BE SOME
SHOWERS AND ISOLATED THUNDER BY LATER TONIGHT AND EARLY MORNING...
THEN AGAIN TOWARD LATER AFTERNOON FOR KHON...THE PROBABILITY AT
THIS TIME WILL KEEP FROM MENTIONING WITH LIKELIHOOD THAT ANY
SHOWERS WOULD ALSO CONTAIN VFR CEILINGS AND VISIBILITIES.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...WIND ADVISORY FROM 10 AM TO 8 PM CDT WEDNESDAY FOR SDZ040-055-
     056-062-066-067-070-071.

     WIND ADVISORY FROM 10 AM TO 4 PM CDT WEDNESDAY FOR SDZ038-039-
     050-052>054-057>061-063>065-068-069.

MN...WIND ADVISORY FROM 10 AM TO 8 PM CDT WEDNESDAY FOR MNZ071-072-
     080-081-089-090-097-098.

IA...WIND ADVISORY FROM 10 AM TO 8 PM CDT WEDNESDAY FOR IAZ001>003-
     012>014-020>022-031-032.

NE...WIND ADVISORY FROM 10 AM TO 8 PM CDT WEDNESDAY FOR NEZ013-014.

&&

$$

SHORT TERM...
LONG TERM...08
AVIATION...CHAPMAN/SCHUMACHER






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