Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 022032
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
332 PM CDT TUE SEP 2 2014

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 331 PM CDT TUE SEP 2 2014

MAIN CONCERN FOR THE NEXT 24 HOURS WILL BE THE POTENTIAL FOR
THUNDERSTORMS LATE TONIGHT AND TOMORROW AND HOW WARM AND HUMID IT
WILL BE TOMORROW AFTERNOON.

TONIGHT WILL START OFF CLEAR WITH SOUTH TO SOUTHWEST WINDS. AS THE
PRESSURE GRADIENT TIGHTENS THIS EVENING...EXPECT THAT WINDS WILL
GRADUALLY TURN TO THE SOUTHEAST ...ESPECIALLY ALONG AND WEST OF I29.
IN ADDITION...A STRONG LOW LEVEL JET IS EXPECTED TO DEVELOP TOWARD
MIDNIGHT AND CONTINUE INTO WEDNESDAY MORNING. WITH A FAIRLY STRONG
NEAR SURFACE INVERSION IN PLACE ACROSS SOUTHWEST MINNESOTA...THIS
HAS THE POTENTIAL TO RESULT IN A DOWNSLOPE WINDS FROM MARSHALL DOWN
TO TRACY OVERNIGHT WITH GUSTS OVER 20 MPH POSSIBLE AROUND DAWN.
MEANWHILE...700-500 MB LAPSE RATES WILL BE INCREASING THROUGH THE
NIGHT. WITH MOISTURE INCREASING BELOW THE ELEVATED MIXED
LAYER...CAPES WILL BE INCREASING AFTER MIDNIGHT. THE NAM IS LIKELY
OVERDONE WITH MUCAPES APPROACHING 2500 J/KG IN SW MN BUT MUCAPES
APPROACHING 1000 J/KG ARE POSSIBLE BY 12Z WED. AT THE SAME
TIME...WITH STRONG WARM AIR ADVECTION AND WEAK SYNOPTIC SCALE
FORCING FOR ASCENT...EXPECT THE POSSIBILITY OF ELEVATED
THUNDERSTORMS WILL INCREASE AFTER 06Z. THE FIRST STORMS MAY DEVELOP
AS FAR WEST OF HURON...SIOUX FALLS AND STORM LAKE BUT THE MOST
LIKELY AREA WILL BE IN SW MN AFTER 09Z. EFFECTIVE SHEAR WILL BE
LIMITED...20 TO 30 KTS...AS WILL INSTABILITY...BUT STRONG ENOUGH
UPDRAFTS MAY DEVELOP TO RESULT IN SMALL HAIL IN THE STRONGEST STORMS
PRIOR TO 12Z. LOWS TONIGHT WILL GENERALLY BE IN THE 60S...WITH
WARMEST READINGS IN SOUTH CENTRAL SD AND COOLEST READINGS AROUND SPW.

ELEVATED CONVECTION IS EXPECTED TO CONTINUE TOMORROW
MORNING...PRIMARILY IN SW MN. LAPSE RATES AND MOISTURE WILL CONTINUE
TO INCREASE THROUGH THE MORNING ACROSS THE AREA. A VERY WARM LAYER
FROM 800 TO 700 HPA WILL BECOME ESTABLISHED OVER MUCH OF SE SD...NE
NEBRASKA...AND NW IA BY LATE MORNING WHICH IS EXPECTED TO SUPPRESS
CONVECTION IN THESE AREAS. HOWEVER...IF STORMS ARE ABLE TO DEVELOP
ON THE SW SIDE OF THE PRECIPITATION BAND OVER DURING THE MID TO LATE
MORNING...INCREASING CAPES...APPROACHING 1500 TO 2000 J/KG AND
SHEAR...APPROACHING 40 KTS...WOULD SUPPORT UP TO HALF DOLLAR SIZE
HAIL. BUT CONFIDENCE OF THIS HAPPENING IS LOW. THERE IS ANOTHER WAVE
MOVING FROM EAST CENTRAL SD INTO CENTRAL MN LATE WED AFTERNOON. AT
THIS POINT...THE BEST CHANCE FOR LATE AFTERNOON DEVELOPMENT WILL BE
ALONG AND EAST OF THE MINNESOTA RIVER. HOWEVER...IT IS POSSIBLE THAT
THE PRESENCE OF LEFT OVER OUTFLOW BOUNDARIES AND/OR DIFFERENTIAL
DIABATIC HEATING COULD RESULT IN A ONE OR TWO STORMS DEVELOPING IN
THE VICINITY OF MARSHALL. WHILE A VERY LOW PROBABILITY...LESS THAN
20 PERCENT...IF STORMS DO DEVELOP...THEY WOULD HAVE THE POTENTIAL TO
EVOLVE INTO SEVERE SUPERCELLS AS CAPES WOULD BE GREATER THAN 2000
J/KG AND EFFECTIVE SHEAR GREATER THAN 40 KTS. FOR NOW WILL HIGHLIGHT
THE LOW PROBABILITY OF SEVERE STORMS IN THE MORNING. HIGHS TOMORROW
ARE VERY DEPENDENT ON CLOUD COVER. WEST OF THE JAMES RIVER...EXPECT
HIGHS TO REACH THE LOW 90S WITH LOTS OF SUN...WHILE IN SW MN LOWER
80S ARE EXPECTED WITH CLOUDS MUCH OF THE DAY. WITH A STRONG
INVERSION IN PLACE...DEW POINTS WILL RISE INTO THE 70S RESULTING IN
HEAT INDICES OF 90 TO 100 DEGREES WEST OF I29 WEDNESDAY AFTERNOON.

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 331 PM CDT TUE SEP 2 2014

MODELS ARE IN PRETTY GOOD AGREEMENT THAT SURFACE LOW PRESSURE WILL
DEEPEN OVER CENTRAL SOUTH DAKOTA ON WEDNESDAY NIGHT...THEN RAPIDLY
LIFT NORTHEAST INTO NORTHERN MINNESOTA BY MIDDAY THURSDAY. A MID
LEVEL SHORTWAVE LIFTING INTO EAST CENTRAL MINNESOTA WILL ALLOW ANY
ISOLATED THUNDERSTORM ACTIVITY NEAR THE BUFFALO RIDGE AREA EARLY
WEDNESDAY EVENING TO EXIT THE FORECAST AREA QUICKLY. EARLY WEDNESDAY
NIGHT HOWEVER...A FAIRLY POTENT COLD FRONT DROPS INTO CENTRAL SOUTH
DAKOTA AND MOVES INTO THE JAMES VALLEY REGION LATE AT NIGHT.
SCATTERED TO ISOLATED SHOWERS WITH A FEW RUMBLES OF THUNDER WILL
DEVELOP ALONG AND JUST BEHIND THE FRONT. DID SPEED UP THE TIMING OF
THE FRONT SLIGHTLY...WHICH BRINGS IT INTO THE I29 CORRIDOR LATE
MORNING AND ACROSS OUR SOUTHEASTERN CWA THURSDAY LATE AFTERNOON.
STRONG CAPPING AND SOMEWHAT WEAK SUPPORT ATTENDING THE FRONT WILL
KEEP PRECIPITATION CHANCES LIMITED TO LOW END CHANCES FOR SHOWERS AND
NON SEVERE THUNDERSTORMS.

DRY AIR FILTERS INTO THE REGION THURSDAY NIGHT AS SURFACE HIGH
PRESSURE RAPIDLY EXPANDS INTO THE REGION. COOL AND DRY NORTHWEST
FLOW SETS UP FRIDAY INTO THE WEEKEND...LEADING TO SOME
PLEASANT...BUT UNSEASONABLY COOL WEATHER CONDITIONS. AFTERNOON HIGHS
ONLY TOP OUT IN THE UPPER 60S AND LOWER 70S ON FRIDAY AND
SATURDAY...AND IMPROVING A FEW DEGREES ON SUNDAY. OVERNIGHT LOWS
HAVE THE POTENTIAL TO BE QUITE COOL AS WELL WITH MOSTLY CLEAR SKIES
AND RELATIVELY LIGHT WINDS. LOWS SHOULD DROP INTO MID 40S TO LOW
50S...AND HAVE CONTINUED TO TREND BELOW THE ALLBLEND GUIDANCE.

MODELS SHOWING BETTER AGREEMENT THIS AFTERNOON REGARDING THE PATTERN
EVOLUTION EARLY NEXT WEEK. FLOW TURNS MORE ZONAL ON SUNDAY AND
SUNDAY EVENING...WITH A SOUTHERLY LOW LEVEL FETCH. THIS WILL ALLOW A
GREATER MOISTURE RETURN SUNDAY NIGHT INTO MONDAY NIGHT AHEAD OF THE
STRONG WAVE EMERGING FROM THE INTERMOUNTAIN WEST INTO CENTRAL HIGH
PLAINS MONDAY AFTERNOON. WITH WARM AIR ADVECTION AND INCREASED
MOISTURE...THUNDERSTORM CHANCES INCREASE MONDAY AND TUESDAY. MODELS
SUGGEST SOME CYCLOGENESIS FORMS IN THE VICINITY OF WESTERN SOUTH
DAKOTA EARLY TUESDAY. GIVEN THE DECENT AGREEMENT IN PLACEMENT
BETWEEN THE GFS AND ECMWF...AGREE WITH THE HIGH END CHANCE POPS FOR
MUCH OF THE FORECAST AREA. TEMPERATURES CONTINUE TO WARM A FEW
DURING THIS PERIOD...BUT SHOULD REMAIN NEAR OR JUST BELOW NORMAL.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1222 PM CDT TUE SEP 2 2014

MAIN ISSUE FOR TAFS ARE CONVECTION...POTENTIAL FOR LOW LEVEL WIND
SHEAR AND LOW CLOUDS. THROUGH 06Z WED...VFR CONDITIONS EXPECTED
ALTHOUGH WINDS WILL GRADUALLY BACK TO SOUTHEAST IN ALL LOCATION IN
THE EVENING. AFTER 06Z...A STRENGTHENING LOW LEVEL JET AND
INCREASING INSTABILITY ARE EXPECTED TO RESULT IN THE DEVELOPMENT
OF THUNDERSTORMS PRIOR TO DAWN. WHILE A STORM IS POSSIBLE IN KFSD
OR KHON...THE BEST CHANCE WILL BE IN SW MN. THEREFORE DID NOT
INCLUDE TSRA IN TAF FOR EITHER SITE. HOWEVER...WITH A 40 TO 50 KT
LOW LEVEL JET FROM SOUTHEAST SD IN SW MN LATE TONIGHT AND EARLY
THU MORNING...THERE IS THE POTENTIAL FOR NON CONVECTIVE LOW LEVEL
WIND SHEAR. WITH CORE OF THE JET GOING THROUGH THE KFSD AREA...DID
ADD LOW LEVEL WIND SHEAR FOR SIOUX FALLS...BUT SUBSEQUENT SHIFTS
WILL NEED TO EXAMINE POTENTIAL IN KHON. THE OTHER CONCERN IS
DEVELOPMENT OF MVFR CEILINGS WEDNESDAY MORNING. ALL MODELS SHOW
MOISTURE INCREASING BELOW A FAIRLY STRONG INVERSION SO EXPECT CIGS
FROM 1000 TO 2000 FT TO DEVELOP AT KFSD AND KSUX SHORTLY AFTER
SUNRISE. WITH LESS MOISTURE EXPECTED AT KHON...KEPT VFR CONDITIONS
FOR NOW.


&&

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

$$

SHORT TERM...SCHUMACHER
LONG TERM...
AVIATION...SCHUMACHER



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