Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 312010
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
310 PM CDT SUN AUG 31 2014

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 309 PM CDT SUN AUG 31 2014

JUST WEST OF MARSHALL MN TO SIOUX FALLS SD TO JUST WEST OF SIOUX
CITY. EXPECT DEEP CONVECTION TO BE FOCUSED ALONG AND EAST OF THE
BOUNDARY. HAVE ADJUSTED THE HWO TO FOCUS ON THE HIGHWAY 60 AND EAST
CORRIDOR...WHERE STORMS ARE EXPECTED TO DEVELOP AROUND 22Z WITH THE
POTENTIAL FOR LARGE HAIL...DAMAGING WINDS AND ISOLATE TORNADOES.
WITH NEAR SURFACE LAYER FLOW BECOMING SOUTHWEST...STILL NOT A TON OF
DIRECTIONAL SHEAR...BUT STILL SOME DECENT SPEED SHEAR TO AID IN
STORM ORGANIZATION.  BETTER BACKED FLOW FURTHER TO THE SOUTH ALONG
THE I-80 CORRIDOR IN WESTERN AND CENTRAL IOWA AIDING IN BETTER
FELICITY. DO NOT EXPECT THIS BOUNDARY TO WORK MUCH FURTHER NORTH
THAN HIGHWAY 30 SOUTH OF OUR FORECAST AREA...THEREFORE...MAIN SEVERE
WEATHER THREATS SHOULD BE PRIMARILY WIND AND HAIL DRIVEN FOR THE
EASTERN PORTIONS OF OUR FORECAST AREA.  WITH AFOREMENTIONED SPEED
SHEAR AND CAPE VALUES AROUND 1500-2000 J/KG AND MINIMAL CAP...EXPECT
STORMS TO DEVELOP AS SHORTWAVE LIFTING FROM SOUTHEAST AIDS IN UPPER
LEVEL SUPPORT AND LIFT.

EXPECT SEVERE THREAT TO SHIFT EAST OF THE AREA AFTER 03Z.  STILL MAY
HAVE SOME POST FRONTAL SHOWERS SHIFT THROUGH THE AREA OVERNIGHT.

COOLER AND DRIER CONDITIONS ARE EXPECTED ON MONDAY...WITH NEAR
NORMAL HIGHS IN THE MID AND UPPER 70S.  FAST MOVING SHORT WAVE
APPROACHING FROM THE WEST MAY GENERATE A FEW LATE AFTERNOON
THUNDERSTORMS ACROSS CENTRAL SOUTH DAKOTA...BUT SHOULD REMAIN BELOW
SEVERE LIMITS WITH LIMITED AMOUNTS OF MOISTURE AND INSTABILITY.

.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 309 PM CDT SUN AUG 31 2014

A WEAK WAVE WILL MOVE THROUGH ON MONDAY NIGHT AND WILL CONTINUE WITH
MAINLY ISOLATED SHOWERS/THUNDER POTENTIAL. LOOKS LIKE AMOUNTS WOULD
BE LIGHT AND NOTHING SEVERE EXPECTED. LOWS MAINLY IN THE 50S.

TUESDAY LOOKS LIKE A VERY NICE DAY WITH RELATIVELY LOW
HUMIDITY...WINDS MAINLY LESS THAN 15 MPH AND HIGHS IN THE UPPER 70S
TO LOWER 80S.

TUESDAY NIGHT INTO WEDNESDAY WILL SEE SOUTHERLY RETURN FLOW DEVELOP
WITH INCREASING HUMIDITY. INCREASED LOW TEMPERATURES ON TUESDAY
NIGHT AS THE CONSRAW OUTPUT GENERALLY MORE ACCURATE WITH STRONGER
WINDS...SO MAINLY LOWER TO MIDDLE 60S. WARM AIR WILL SURGE NORTH AS
WELL SO WITH HIGHS IN THE MID AND UPPER 80S AND DEW POINTS IN THE
UPPER 60S TO AROUND 70 AFTERNOON HEAT INDICES WILL LIKELY REACH THE
MID 90S IN SOME SPOTS. WARM ADVECTION AND A WEAK WAVE ALSO SUPPORT
THE THREAT FOR ISOLATED SHOWERS AND THUNDERSTORMS IN MAINLY
SOUTHWEST MINNESOTA SO WILL KEEP A LOW CHANCE IN THERE.

IN THE OUTER PERIODS (THURSDAY THROUGH SUNDAY)...THE OVERALL PATTERN
LOOKS VERY EARLY FALL LIKE WITH A TROUGH OVER THE WEST COAST AND
STRONG WEST TO SOUTHWEST FLOW OVER THE NORTHERN PLAINS. WEDNESDAY
NIGHT INTO THURSDAY STILL SEES A FRONT COMING INTO THE AREA WHICH
SHOULD LEAD TOWARDS A WARM THURSDAY MORNING AND STILL WARM
THURSDAY...BUT WITH MODIFYING OR COOLING LOW LEVEL TEMPERATURES.
THIS COOLER AIR REMAINS LOCKED IN PLACE THROUGH AT LEAST SATURDAY.
POSSIBLY A BIT BREEZY ON FRIDAY BUT LIKELY LIGHT WINDS ON SATURDAY.
MODELS DIFFER A BIT ON PATTERN LEADING INTO SUNDAY WITH SOME LOCKING
THE COOL AIR IN THROUGH SUNDAY WHILE WEAK RETURN FLOW SETS UP ON A
FEW OTHERS. EITHER WAY LIKELY BELOW NORMAL TEMPERATURES FRIDAY INTO
SUNDAY. STILL REMAINS A DECENT CHANCE FOR SHOWERS AND ISOLATED
THUNDERSTORMS THURSDAY NIGHT INTO FRIDAY AS A GOOD RIGHT ENTRANCE
REGION FOLLOWS THE SURFACE COLD FRONT WITH WHAT APPEARS TO BE GOOD
MID LEVEL MOISTURE ON MOST OF THE MODELS. MAY UP POPS A BIT DURING
THIS TIME. MORE THAN LIKELY THE WEEKEND WILL REMAIN DRY AS HIGH
PRESSURE TRYS TO STAY IN CONTROL.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 1238 PM CDT SUN AUG 31 2014
CONVECTION IS THE PRIMARY AVIATION CONCERN FOR THE 18Z TAF
ISSUANCE. MODEL TRENDS HAVE BEEN TO ACCELERATE THE FRONT
SLIGHTLY...SO HAVE SHIFTED THE FOCUS FOR DEEP COMVECTION LATE THIS
AFTERNOON TO MAINLY NORTHWEST IOWA ALONG AND AHEAD OF A COLD
FRONT PUSHING THROUGH THE REGION. THESE STORMS WILL BE CAPABLE OF
PRODUCING LARGE HAIL...DAMAGING WINDS AND AN ISOLATED TORNADO OR
TWO. SIOUX CITY APPEARS TO BE ON THE WESTERN EDGE OF THE MAIN
THREAT AREA.

THERE REMAINS AN OUTSIDE POTENTIAL OF MVFR CEILING/VISIBILITY
THREAT WORKING SOUTHWARD BEHIND MAIN UPPER TROUGH AFTER 06Z INTO
KHON AND AFTER 09Z AT KFSD...BUT HAVE LEFT CLEAR AS APPEARS LOW
PROBABILITY FOR NOW.

&&

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

$$

SHORT TERM...
LONG TERM...08
AVIATION...


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