Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 020853
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
353 AM CDT SUN AUG 2 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 353 AM CDT SUN AUG 2 2015

A COLD FRONT WILL DROP SOUTHWARD ACROSS THE REGION THROUGH
TODAY...MAKING IT THROUGH OUR CWA BY 00Z THIS EVENING. IN THE
ABSENCE OF ANY SIGNIFICANT FORCING OR MOISTURE...THE MAIN EFFECTS
FOR OUR AREA FROM THIS SYSTEM WILL BE INCREASING NORTHWESTERLY WINDS
DURING THE DAY AND LOWERING DEWPOINTS BY AFTERNOON. IN SPITE OF LOW
LEVEL COLD AIR ADVECTION BEHIND THE FRONT...IT WILL BE ANOTHER VERY
WARM DAY WITH GOOD MIXING. HIGHS WILL TOP OUT IN THE MID 80S THROUGH
THE HIGHWAY 14 CORRIDOR TO LOWER 90S THROUGH THE MID AND LOWER
MISSOURI RIVER VALLEY.

HIGH PRESSURE BEGINS TO BUILD INTO THE REGION TONIGHT. THIS WILL
BRING MOSTLY CLEAR SKIES THROUGH MUCH OF THE NIGHT ALONG WITH LIGHT
NORTHERLY WINDS. THIS ALONG WITH THE COLD AIR ADVECTION BEHIND THE
FRONT WILL RESULT IN A COOLER NIGHT WITH LOWS IN THE MID 50S TO
LOWER 60S.


.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 353 AM CDT SUN AUG 2 2015

MONDAY WILL BE ANOTHER PARTLY TO MOSTLY SUNNY DAY. AS THE NEXT WAVE
APPROACHES FROM THE WEST...EXPECT TO SEE SOME INCREASE IN CLOUDS IN
THE MISSOURI VALLEY. HOWEVER...ANY RAINFALL IS EXPECTED TO HOLD OFF
UNTIL AFTER 00Z. INSTEAD...WITH A RIDGE OVER THE EASTERN
DAKOTAS...EXPECT ANOTHER FAIRLY EFFICIENT MIXING DAY EVEN THOUGH
WINDS WILL BE LIGHTER THAN TODAY. MIXING WILL RESULT IN DEW POINTS
FALLING INTO THE LOWER 50S NORTH OF I90 WITH MID TO UPPER 50S IN THE
MISSOURI VALLEY. HIGHS ON MONDAY WILL GENERALLY BE FROM 80 TO 85.

A VERY SLOW MOVING WAVE WILL BEGIN TO AFFECT THE AREA ON MONDAY
NIGHT AND IS EXPECTED TO BE AROUND THROUGH WEDNESDAY. BECAUSE THIS
WAVE IS WITHIN RELATIVELY WEAK FLOW ALOFT AS IT MOVES ACROSS THE
LARGE SCALE RIDGE...THERE IS SOME SPREAD IN MODEL SOLUTIONS.
FIRST...WITH THE EXCEPTION OF THE NAM...ALL MODELS SHOW A PIECE OF
THIS WAVE MOVING ACROSS KANSAS TUESDAY AND TUESDAY NIGHT WHICH WILL
RESULT IN CONVECTION BETWEEN I70 AND I80 AND MAY DELAY OR LIMIT
MOISTURE RETURN INTO THE AREA. THIS LEADS TO THE CANADIAN GEM
KEEPING MOST OF THE PRECIPITATION IN NEBRASKA THROUGH TUESDAY NIGHT.
MODEL SOLUTIONS ALSO DIFFER ON THE SPEED OF THE SYSTEM ALTHOUGH THE
ECMWF AND GFS ARE FAIRLY SIMILAR SHOWING THE WAVE MOVING ACROSS LATE
TUESDAY AFTERNOON AND EVENING. WITH THE UNCERTAINTY IN BOTH MOISTURE
RETURN AND TIMING GENERALLY KEPT THE HIGHEST POPS AT 50 PERCENT OR
LESS.

OVERALL...EXPECT THE 850 MB THETA-E GRADIENT TO SLOWLY MOVE NORTH
TOWARD THE MISSOURI RIVER ON MONDAY NIGHT. THE BEST CHANCE FOR RAIN
MONDAY NIGHT WILL BE IN SOUTH CENTRAL SD WHERE THERE WILL BE THE
GREATEST INSTABILITY AND FORCING FOR ASCENT. THE CHANCE FOR RAIN
WILL SLOWLY MOVE NORTHEAST ON TUESDAY BUT WITH THE SLOW MOVEMENT OF
THE UPPER WAVE AND FRONT AS WELL AS DRY LOW LEVEL AIR IN PLACE...THE
CHANCE FOR RAIN WILL BE PRIMARILY SOUTHWEST OF A LINE FROM HURON TO
STORM LAKE WITH THE GREATEST CHANCE FOR RAIN ON TUESDAY AFTERNOON IN
SOUTH CENTRAL SOUTH DAKOTA. WITH THE WAVE MOVING INTO EASTERN SOUTH
DAKOTA AND NEBRASKA TUESDAY NIGHT...THE CHANCE FOR RAIN WILL FINALLY
REACH SOUTHWESTERN MINNESOTA AFTER MIDNIGHT. THE GREATEST CHANCE FOR
RAIN WILL REMAIN SOUTH OF I90 IN SOUTHEAST SOUTH DAKOTA. AT THIS
TIME...THERE LOOKS TO BE THE POTENTIAL FOR A HALF INCH OF RAIN OR
MORE IN THE MISSOURI VALLEY...WHILE IN SOUTHWEST MINNESOTA LITTLE IF
ANY RAINFALL IS EXPECTED.

WITH INCREASING CLOUDS FROM MONDAY NIGHT THROUGH TUESDAY NIGHT...THE
DIURNAL RANGE WILL DECREASE. LOWS ON MONDAY NIGHT WILL BE IN THE MID
50S IN SOUTHWEST MINNESOTA WHERE DRY AIR AND CLEAR SKIES WILL RESULT
IN RADIATIONAL COOLING. IN THE MISSOURI VALLEY...WITH INCREASING
CLOUDS LOWS WILL BE IN THE LOWER 60S. THE CLOUD COVER AND POSSIBLE
RAINFALL WILL KEEP HIGHS IN THE MISSOURI VALLEY AROUND 80 WHILE
LOWER 80S ARE EXPECTED FARTHER NORTH ALONG I90 AND INTO EAST
CENTRAL SD. LOWS ON TUESDAY NIGHT WILL BE A FEW DEGREES WARMER
WITH MORE CLOUD COVER...FROM THE UPPER 50S IN SOUTHWEST MINNESOTA
TO THE MID 60S IN THE MISSOURI VALLEY.

IN THE EXTENDED...WEDNESDAY THROUGH SATURDAY...THE GFS AND ECMWF
BEGIN TO DIVERGE ON THE TIMING AND LOCATION OF WEAK WAVES MID TO
LATE WEEK. BUT BOTH MODELS DO AGREE ON BELOW NORMAL TEMPERATURES
THROUGH SATURDAY DUE TO BOTH CLOUD COVER AS WELL AS COOLER AIR
ADVECTING IN BEHIND THE SYSTEM LATER WEDNESDAY AND THURSDAY. AS A
RESULT...HAVE HIGHER POPS...30 TO 50 PERCENT...ON WEDNESDAY.
THEN...WITH TIMING DIFFERENCES...BEGIN TO GRADUALLY DECREASE POPS
THROUGH THURSDAY NIGHT DUE TO BOTH INCREASED UNCERTAINTY AND BOTH
MODELS BEGIN TO SHOW THAT LARGE SCALE FORCING FOR ASCENT DECREASES.
AT THIS POINT...FRIDAY THROUGH SATURDAY GENERALLY LOOK DRY ALTHOUGH
DID KEEP A SLIGHT CHANCE OF THUNDERSTORMS EAST OF I29 FRIDAY AS THE
FIRST WAVE EXITS AND THEN WEST OF THE JAMES RIVER FRIDAY NIGHT AND
SATURDAY AS ANOTHER WAVE APPROACHES.


&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1204 AM CDT SUN AUG 2 2015

VFR CONDITIONS EXPECTED THROUGH THE TAF PERIOD.


&&

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

$$

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


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