Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 230343
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1043 PM CDT TUE APR 22 2014

.UPDATE...
ISSUED AT 947 PM CDT TUE APR 22 2014

THE CURRENT FORECAST IS RUNNING ALONG WELL...AND GIVEN THE NATURE
OF THE CURRENT AND UPSTREAM AIRMASS ACROSS THE AREA...EXPECT THAT
TO CONTINUE OVERNIGHT. VERY LOW LEVELS...PER KOAX/KTOP/KLBF...ARE
EXTREMELY DRY AND THE ELEVATED THETA E ADVECTION ABOVE 700 HPA HAS
HARDLY BEEN ABLE TO GENERATE BUT A FEW SPRINKLES. TRAJECTORY DOES
NOT SUGGEST A GREAT CHANGE IN LOWER LEVELS THROUGH MUCH OF THE
NIGHT...BUT WILL CONTINUE TO SEE INCREASE IN THE 700-500 HPA LAPSE
RATE AND WEAK DISTURBANCE IN THE WESTERN PLAINS WORKING INTO THE
RIDGE AXIS ACROSS THE AREA OVERNIGHT. ONGOING IDEA OF A LOW CHANCE
POP WORKING INTO THE WEST TOWARD MIDNIGHT...AND ENHANCING JUST A
BIT BY LATE TONIGHT AND TOMORROW MORNING TOWARD THE EAST SEEMS ON
TRACK. THE ONLY CHANGE OF SUBSTANCE WAS TO INCREASE WIND GUSTS
DURING THE MORNING AND MIDDAY HOURS...AS WINDS OF 35 TO 40 KNOTS
WILL BE WELL WITHIN ANY MIXED LAYER AND WILL NOT TAKE LONG TO
REALIZE ONE DIURNAL MIXING OCCURS.

&&

.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 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 1043 PM CDT TUE APR 22 2014

WINDS WILL BE THE MAIN ISSUE THROUGH 00Z ON WEDNESDAY. SOUTHEAST
WINDS ARE ALREADY GUSTING OVER 25 MPH IN THE JAMES VALLEY AND OVER
20 MPH ALONG AND WEST OF I29. WINDS WILL CONTINUE TO INCREASE
OVERNIGHT AS LOW LEVEL JET OF 50 TO 60 KTS SETS UP ACROSS THE
AREA. BY MID MORNING ON WEDNESDAY...WINDS GUSTING NEAR 40 KTS ARE
POSSIBLE AND ARE EXPECTED TO CONTINUE FROM MID AFTERNOON IN THE
JAMES VALLEY THROUGH EARLY EVENING ALONG AND EAST OF I29. A COLD
FRONT WILL THEN MOVE ACROSS THE AREA WITH WINDS DECREASING AND
THEN GRADUALLY SHIFTING TO NORTHWEST. AS FOR PRECIPITATION...THERE
WILL BE ISOLATED SHOWERS MUCH OF THE NIGHT AND ONE OR TWO
THUNDERSTORMS ARE NOT OUT OF THE QUESTION. HOWEVER THE PROBABILITY
OF HITTING ANY TAF LOCATION IS VERY LOW SO DID NOT INCLUDE. THERE
WILL ALSO BE THUNDERSTORMS DEVELOPING BY LATE WENDNESDAY AFTERNOON IN
NEBRASKA. THESE STORMS COULD EXTEND INTO THE JAMES VALLEY BUT THE
PROBABILITY IS LOW AND HAVE NOT INCLUDED IN KHON TAF. THUNDERSTORMS
WILL BECOME MORE NUMEROUS DURING THE EVENING ACROSS EASTERN
NEBRASKA AND SPREAD NORTHEAST TOWARD SIOUX CITY AND POSSIBLY SIOUX
FALLS. FOR NOW ONLY INCLUDED THE THUNDERSTORM WITH NO VSBY OR CIG
RESTRICTION IN BOTH TAFS ALTHOUGH MVFR CONDITIONS WITH STORMS WILL
BE POSSIBLE IF A STRONGER CELL MOVES IN THE VICINITY.

&&

.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.

&&

$$

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






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