Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 202331
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
631 PM CDT SAT SEP 20 2014

.SHORT TERM...(THIS EVENING THROUGH SUNDAY)
ISSUED AT 256 PM CDT SAT SEP 20 2014

POTENT SHORTWAVE BEGINNING TO MOVE ACROSS NORTH DAKOTA THIS
AFTERNOON AS A STRONG 140+ KNOT UPPER JET NOSES INTO THE NORTHERN
PLAINS.  CONVECTION HAS BROKEN OUT AHEAD OF A STRONGER COLD FRONT
DROPPING SE THROUGH THE REGION. FURTHER SOUTHWEST...A WEAK PRE-
FRONTAL TROUGH CONTINUES TO EDGE EASTWARD TOWARD THE JAMES RIVER
VALLEY AHEAD OF THE MORE POTENT FRONT...WITH DEW POINTS DROPPING
INTO THE 40S AND TEMPERATURE QUICKLY MIXING INTO THE LOWER 80S.
THROUGH THE REMAINDER OF THE AFTERNOON...WILL CONTINUE TO MONITOR FOR
ADDITIONAL DEVELOPMENT ACROSS MAINLY NORTHERN AND NORTHEASTERN ZONES
AS THE UPPER WAVE PIVOTS THROUGH THE AREA.  LATEST HI-RES DATA
CONTINUES TO INDICATE POTENTIAL FOR TAIL END STORMS ON THE SWRN
FLANK OF MORE ORGANIZED MCS MOVING THROUGH SOUTHWESTERN MN LATE THIS
AFTERNOON. LOW INSTABILITY AND HIGH SHEAR SETUP WOULD SUPPORT LOW
TOPPED CONVECTION...AND EVEN A FEW MINI-SUPERCELLS.  THE MAIN RISKS
WOULD BE DAMAGING WINDS GIVEN AMBIENT FLOW BEHIND THE FRONT AND
STEEP LOW LVL LAPSE RATES. GIVEN THIN CAPE PROFILES AND PROGRESSIVE
NATURE OF THE ACTIVITY...WOULD LEAN AGAINST A LARGE HAIL RISK.

ANY RISK OF CONVECTION WILL BE LIMITED TO THE VERY EARLY EVENING
HOURS...WITH THE EFFECTIVE FRONT MOVING THROUGH THE AREA BY 7PM.
ANTICIPATING A BRIEF WINDOW OF RATHER GUSTY WINDS AS THE FRONT MOVES
THROUGH.

HIGH PRESSURE WILL SETTLE SOUTHWARD THROUGH THE OVERNIGHT HOURS AND
SUNDAY WILL BE VERY PLEASANT.  WINDS WILL REMAIN FROM THE NORTH WITH
TEMPERATURES EITHER SIDE OF THE 70 DEGREE MARK.

.LONG TERM...(SUNDAY NIGHT THROUGH SATURDAY)
ISSUED AT 256 PM CDT SAT SEP 20 2014

SUNDAY NIGHT STARTS WITH HIGH PRESSURE AND PRETTY CLEAR SKIES OVER
THE AREA. WITH LIGHT WINDS IT SHOULD PRODUCE LOWS IN THE 40S AND BE
THE COOLEST NIGHT IN THIS STRETCH. MONDAY AND TUESDAY WILL BRING THE
SLOW APPROACH FROM THE SW OF CURRENT SOUTHERN CA TROUGH CUTTING
THROUGH THE ROCKIES RIDGE. THIS SYSTEM IS LIKELY TO BRING HALF
DECENT MID LEVEL MOISTURE BUT NOT TOO MUCH LIFT AND INSTABILITY.
TIMING PUTS THE THREAT OF SHOWERS AND POSSIBLE A VERY FEW
THUNDERSTORMS STARTING MONDAY NIGHT IN SOUTHEAST SD...OVER THE AREA
FOR TUESDAY THROUGH WEDNESDAY...AND DECREASING THREAT OF
THUNDERSTORMS WEDNESDAY NIGHT. TEMPERATURES DURING THIS TIME OF
PLENTY OF CLOUD COVER WILL BE MARKED BY A LOW DIURNAL RANGE WITH
LOWS IN THE MID TO UPPER 50S AND HIGHS MOSTLY IN THE UPPER 60S TO
LOW 70S.

THE ABATING OF THE SHOWERS WILL TAKE PLACE WITH THE PASSING OF THE
WAVE. GFS THEN SHOWS A WAVE BREAKING OFF FROM THE CANADIAN JET AND
DIGGING AROUND REBUILDING ROCKIES UPPER RIDGE. THE EC SHOWS A BROAD
BUILDING OF HEIGHTS OVER THE EASTERN TWO THIRDS OF THE USA WITH A
VERY WEAK INVERTED UPPER TROUGH SLIDING SLOWLY WEST ACROSS THE
CENTRAL PLAINS SOUTH OF OUR AREA. BECAUSE THIS FEATURE IS SHOWN SO
WEAK...THIS WOULD TEND TO BRING IN DRY AIR FROM THE RIDGING TO THE
EAST. WILL THEREFORE GO WITH DRY WEATHER ESPECIALLY SINCE EVEN THE
GFS SHOWS WEAK THERMODYNAMICS...INCLUDING WEAK INSTABILITY...WITH
ITS STRONGER SYSTEM. DAYTIME TEMPERATURES THURSDAY THROUGH SATURDAY
WOULD WARM BACK FULLY INTO THE 70S WHILE LOWS WOULD STAY IN THE MID
TO UPPER 50S.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)
ISSUED AT 627 PM CDT SAT SEP 20 2014

A WIND SHIFT FROM A WEST TO NORTHWEST DIRECTION WILL BE MOVING
SOUTHWARD ACROSS THE FORECAST AREA THIS EVENING...WITH FREQUENT
GUSTS OF AROUND 30 KNOTS MAINLY ALONG AND NORTH OF THE I 90
CORRIDOR THROUGH SUNSET. AT THAT POINT...THE SURFACE WINDS WILL
DECOUPLE FROM THE STRONGER WINDS ABOVE THE SURFACE. THEREFORE BY
THE TIME THE WIND SHIFT GETS TO KSUX SHORTLY AFTER SUNSET...THE
KSUX TAF SITE MAY ESCAPE THE GUSTY WINDS.

&&

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

$$

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


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