Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 242040
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
340 PM CDT MON AUG 24 2015

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 339 PM CDT MON AUG 24 2015

VERY QUIET WEATHER IN THE SHORT TERM. BREEZY NORTHWEST WINDS WILL
GRADUALLY WEAKEN THIS EVENING AS SFC RIDGE AXIS MOVES OVERHEAD.
RATHER CHILLY OVERNIGHT EXPECTED WITH TEMPERATURES FALLING INTO THE
LOWER 40S...ONLY A FEW DEGREES FROM RECORD LOWS.  WITH THE COLD
TEMPS...SEVERAL HIGH RES MODEL RUNS INDICATING A BIT OF FOG IN
WARMER RIVER VALLEYS.

PICTURE PERFECT DAY ON TUESDAY AS WINDS REMAIN LIGHT AND
VARIABLE...TEMPERATURES AVERAGE IN THE 70S...AND HUMIDITY LEVELS ARE
VERY LOW.


.LONG TERM...(TUESDAY NIGHT THROUGH MONDAY)
ISSUED AT 339 PM CDT MON AUG 24 2015

HIGH PRESSURE WILL MOVE EAST OF I29 ON TUESDAY. THIS WILL SET UP A
RETURN SOUTHEASTERLY FLOW WEST OF I29 THAT WILL KEEP LOWS IN THE
LOW TO MID 50S WHILE LIGHT WINDS AND CLEAR SKIES WILL MEAN LOWS IN
THE MID TO UPPER 40S ALONG AND EAST OF I29.

MODELS CONTINUE TO SHOW POTENTIAL FOR ALTOCUMULUS OR EVEN ACCAS
SHOWERS LATE TUESDAY NIGHT AND WEDNESDAY MORNING WITH STEEP 700 TO
500 MB LAPSE RATES AND A VERY WEAK SHORTWAVE MOVING ACROSS THE
DAKOTAS. HOWEVER...700 MB WARM ADVECTION IS WEAK DUE TO LIGHT
WINDS SO CONTINUE WITH A DRY FORECAST FOR LATE TUESDAY NIGHT AND
WEDNESDAY MORNING. OTHERWISE...WEDNESDAY WILL SEE INCREASING WINDS
AND MOISTURE WITH PARTLY TO MOSTLY SUNNY SKIES. HIGHS COULD REACH
90 IN SOUTH CENTRAL SOUTH DAKOTA WHILE EAST OF THE JAMES RIVER IT
WILL REMAIN THE MID TO UPPER 70S.

THE ONLY SIGNIFICANT PRECIPITATION CHANCE WILL BEGIN LATE
WEDNESDAY NIGHT AS A STRONG UPPER LEVEL WAVE MOVES OVER THE TOP OF
THE RIDGE. THE NAM WAS A SIGNIFICANT OUTLIER WITH THE UPPER WAVE
AND PRECIPITATION GOING ACROSS NORTHERN SD AND INTO MN. ALL THE
OTHER MODELS KEPT THE UPPER WAVE CLOSER TO THE NEBRASKA AND SOUTH
DAKOTA BORDER...MOVING SOUTHEAST INTO IOWA BY THURSDAY NIGHT AND
FRIDAY. THERE ARE VERY UNSTABLE LAPSE RATES AS THIS WAVE
APPROACHES BUT THERE WILL ALSO BE A SIGNIFICANT CAP TO OVERCOME
BETWEEN 850 AND 700 MB. ADD TO THE FACT THAT THE FRONTAL BOUNDARY
IS RATHER WEAK SO THAT MOST OF THE LIFT WILL BE ASSOCIATED WITH
THE UPPER WAVE. THIS WILL MEAN IT WILL TAKE A FEW HOURS TO ERODE
THE CAP AND DELAY THE ONSET OF PRECIPITATION. THIS IS ALSO
EXPECTED TO KEEP GREATEST CHANCE FOR PRECIPITATION IN THE
MISSOURI VALLEY INITIALLY...THEN SLOWLY SPREADING NORTHEAST
THURSDAY AFTERNOON AND THURSDAY NIGHT. AM A LITTLE CONCERNED THAT
IF WIDESPREAD CONVECTION DEVELOPS IN NORTHERN NEBRASKA AND/OR FAR
SOUTHERN SOUTH DAKOTA...PRECIPITATION MAY NOT EVEN MAKE IT TO
BROOKINGS AND MARSHALL. FOR THIS REASON HAVE LOWER POPS AND LESS
QPF IN SW MN AND EAST CENTRAL SD THAN IN THE MISSOURI VALLEY AND
NORTHWESTERN IOWA.

FOR TIMING EXPECT SHOWERS COULD REACH SOUTH CENTRAL SOUTH DAKOTA
LATE WEDNESDAY BUT THE STRONGER FORCING AND BETTER CHANCE FOR
PRECIPITATION BEGINS ON THURSDAY AFTERNOON AND CONTINUES THROUGH
THURSDAY NIGHT BEFORE ENDING ON FRIDAY MORNING. GIVEN THAT THE
GREATEST PRECIPITATION POTENTIAL LOOKS TO HOLD OFF UNTIL LATER ON
THURSDAY...KEPT HIGHS IN THE 70S WITH WARMEST TEMPS AROUND
MARSHALL. MORE CLOUDS IN SOUTH CENTRAL SD SHOULD KEEP HIGHS BELOW
80 AND IF RAIN AND CLOUD SPREAD IN SOONER THAN FORECAST...HIGHS
COULD BE CLOSER TO 70 THAN 80. WITH CLOUDS AND RAIN AROUND
THURSDAY NIGHT...LOWS SHOULD BE WITHIN A COUPLE OF DEGREES OF 60.

GENERALLY A DRY PERIOD EXPECTED FOR FRIDAY THROUGH MONDAY.
GENERALLY SIDED A LITTLE CLOSER TO THE ECMWF WHICH KEEPS
TEMPERATURES AT OR BELOW NORMAL THROUGH SUNDAY BEFORE WARMER AIR
MOVES IN MONDAY. WITH A BUILDING RIDGE...THE ONLY CHANCE OF
PRECIPITATION AT THIS TIMES APPEARS TO BE WITH THE EXITING WAVE ON
FRIDAY...PRIMARILY EAST OF I29.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 1152 AM CDT MON AUG 24 2015

VFR CONDITIONS ARE ANTICIPATED ACROSS THE REGION INTO TUESDAY.
BREEZY NORTHWEST WINDS WILL TURN LIGHT AND VARIABLE BY THE EVENING
AND OVERNIGHT HOURS AS SURFACE RIDING MOVES THROUGH. HIGH-RES
MODELS ARE HINTING AT POTENTIAL RIVER/VALLEY GROUND FOG AROUND
DAYBREAK...WITH KSUX HAVING THE HIGHEST POTENTIAL. WILL NOT
INCLUDE ATTM...BUT LATER SHIFTS MAY NEED TO MONITOR.


&&

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

$$

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



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