Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 180358
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1058 PM CDT SUN AUG 17 2014

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 339 PM CDT SUN AUG 17 2014

SEEING TWO AREAS OF CONVECTION OVER THE AREA THIS AFTERNOON. THE
FIRST AREA RESIDES THROUGH PORTIONS OF OUR SOUTHWESTERN MINNESOTA
ZONES IN THE VICINITY OF A SURFACE TROUGH SITUATED THROUGH THAT
AREA. THIS CONVECTION HAS BEEN ISOLATED UP TO THIS POINT. MODELS
HAVE BEEN OVERDOING THIS ACTIVITY ALL DAY...BUT COULD SEE HIT AND
MISS STORMS THROUGH OUR FAR EASTERN ZONES THROUGH THE REMAINDER OF
THE AFTERNOON. A MORE WIDESPREAD AREA OF CONVECTION IS LOCATED OVER
CENTRAL SOUTH DAKOTA IN ASSOCIATION WITH AN IMPULSE OVER THAT AREA.
SOME OF THIS ACTIVITY IS BEGINNING TO ENCROACH ON OUR SOUTH CENTRAL
SOUTH DAKOTA/WESTERN MISSOURI RIVER CORRIDOR ZONES. MODELS HAVE NOT
BEEN HANDLING THIS CONVECTION WELL EITHER...HAVING IT FARTHER WEST
THEN CURRENT TRENDS AND THEN HAVING IT WEAKEN...SO SOMEWHAT PUZZLING AS
TO HOW FAR EAST IT WILL GET. SUPPOSE SOME EASTWARD MOVEMENT...THOUGH
MOST LIKELY DIMINISHING A BIT AS IT OUTRUNS THE BETTER LOW LEVEL
MOISTURE TRANSPORT.

A MORE SIGNIFICANT SHORTWAVE IS BEGINNING TO PUSH OUT OF EASTERN
WYOMING AT THIS TIME...AND ADDITIONAL CONVECTION IS EXPECTED TO
DEVELOP WITH THIS THROUGH WESTERN SOUTH DAKOTA OVER THE NEXT FEW
HOURS...THEN PUSH ACROSS OUR AREA OVERNIGHT. THIS AIDED BY A LITTLE
BETTER LOW LEVEL JET DYNAMICS THAN CURRENTLY SEEN...ESPECIALLY
THROUGH THE LOWER JAMES/MISSOURI RIVER VALLEYS DURING THE FIRST HALF
OF THE NIGHT. DEPENDENT ON WHEN THIS CONVECTION MOVES INTO OUR
WEST...CANNOT RULE OUT A COUPLE ISOLATED SEVERE STORMS WITH ELEVATED
INSTABILITY AND AN INCREASINGLY SHEARED ENVIRONMENT...WITH MAIN
THREATS BEING LARGE HAIL/STRONG WINDS. AS MENTIONED ABOVE...ANY
CONVECTION THAT DEVELOPS IS EXPECTED TO PUSH ACROSS THE AREA
OVERNIGHT AS THE WAVE MOVES EASTWARD...THEN TAPER OFF BY LATE MONDAY
MORNING IN OUR EAST.

FOR THE REMAINDER OF MONDAY...THINK THAT THERE WILL BE A BREAK IN
CONVECTION UNTIL AT LEAST AFTERNOON...WITH POSSIBLE REDEVELOPMENT IN
OUR EAST LATER IN THE AFTERNOON IN ASSOCIATION WITH A WEAK FRONTAL
BOUNDARY SLIDING ACROSS THE AREA. CONVECTIVE PARAMETERS WOULD
SUGGEST THAT A COUPLE OF SEVERE STORMS WOULD AGAIN BE POSSIBLE
THROUGH PORTIONS OF OUR LOWER NORTHWESTERN IOWA ZONES ON MONDAY
AFTERNOON.

.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 339 PM CDT SUN AUG 17 2014

THE WEAK FRONTAL BOUNDARY/UPPER TROUGH EXITS SLOWLY EASTWARD MONDAY
NIGHT TAKING THE PRECIP THREAT WITH IT. A FEW SHOWERS OR ISOLATED
STORMS MAY LINGER IN OUR FAR EASTERN ZONES THROUGH MID EVENING
MONDAY...BUT THEN WENT DRY AFTERWARD AS MODELS SHOW A TREMENDOUS
AMOUNT OF DRYING. WITH WINDS LIGHT NORTHWESTERLY AND CLEARING
SKIES...LOWS WILL FALL TO NEAR 60 DEGREES. TUESDAY WILL FOLLOW
WITH A PLEASANT DAY WITH NORTHWESTERLY WINDS CONTINUING AND HIGHS
SEASONAL IN THE LOWER TO MID 80S.

TUESDAY NIGHT AND WEDNESDAY WILL USHER IN A RAPID CHANGEOVER IN THE
WEATHER. ALL DETERMINISTIC MODELS ARE NOW SHOWING DECENT RAINFALL
CHANCES AS STRONG WARM AIR ADVECTION AND THETAE ADVECTION...BOTH IN
THE LOW AND MID LEVELS...LIFTS NORTHWARD ALONG AN 850MB BOUNDARY.
THE VARIOUS MODELS ARE REMARKABLY SIMILAR WITH THE TIMING AND
PLACEMENT OF THE 850MB BOUNDARY...AND IN PLACING A LEADING SHORT
WAVE MOVING INTO OUR SOUTH CENTRAL SD ZONES BY LATE NIGHT. SO
ESPECIALLY AFTER MIDNIGHT...HAVE STRONG CHANCE POPS IN OUR MO
RIVER VALLEY ZONES...LIFTING NORTHWARD ALONG THE 850MB SHEAR ZONE
AND ADVANCING SHORT WAVE DURING THE DAY ON WEDNESDAY. FOR
TEMPERATURES...AFTER LOWS IN THE 60S AGAIN...HIGHS ON WEDNESDAY
COULD BE HELD DOWN BY WHAT SHOULD BE A FAIR AMOUNT OF CLOUD
COVER...WITH MID 80S IN SOUTH CENTRAL SD WHERE THE MOST CLEARING
SHOULD TAKE PLACE...AND ONLY NEAR 80 IN OUR EASTERN ZONES.

AS THE CRUX OF THE SHORT WAVE MOVES INTO OUR EASTERN ZONES WEDNESDAY
NIGHT...IT IS ACCOMPANIED BY STRONG DIRECTIONAL WIND SHEAR IN THE
LOW LEVELS OFF THE SURFACE...AS A STRONG LOW LEVEL JET FROM A
SOUTHWESTERLY DIRECTION COLLIDES WITH WEAK WINDS FROM THE SOUTH.
PLENTY OF LOW LEVEL SPEED AND DIRECTIONAL CONVERGENCE THEREFORE
EXISTS WITH THE SHORT WAVE...PRODUCING LIKELY POPS OVER OUR ENTIRE
NORTHEAST QUARTER OF THE FORECAST AREA. CHANCES FOR RAIN THEN TAPER
OFF HEADING WESTWARD. IN TIME...WILL HAVE TO MONITOR THE POTENTIAL
FOR SEVERE WEATHER MAINLY IN THE FORM OF HAIL ACROSS EXTREME
NORTHWEST IA AND SOUTHWEST MN. A LOT OF IT WILL HINGE ON THE
STABILITY FACTOR IN HOW MUCH HEATING OCCURS PRIOR TO THIS ON
WEDNESDAY. THAT IS A HUGE QUESTION MARK RIGHT NOW.

THINGS QUIET DOWN AGAIN ON THURSDAY WITH A WARM AND HUMID DAY IN
STORE. THEN THE EVER PRESENT DETERMINISTIC MODEL VARIANCE BEGINS
AGAIN BY FRIDAY. THE ECMWF DIGS A COLD UPPER TROUGH IN CENTRAL
CANADA A BIT SOUTHWARD THROUGH THE PACIFIC NORTHWEST...AND
EVENTUALLY INTO THE NORTHERN PLAINS. THE GFS KEEPS UPPER RIDGING
PRESENT ALONG THE GULF COAST STATES...AND TROUGHING UPSTREAM IN THE
INTERMOUNTAIN WEST. THAT WOULD GIVE THIS AREA AN UNSTABLE SOUTHWEST
FLOW ALOFT AND MUCH WARMER TEMPERATURES WHEN COMPARED TO THE ECMWF.
THE GEM GLOBAL IS IN BETWEEN THOSE TWO SOLUTIONS. THEREFORE PRECIP
CHANCES ARE HARD TO PREDICT. BUT IN GENERAL...THERE LOOKS TO BE
CONSENSUS FOR STRONG CHANCE POPS FIRST IN OUR WESTERN ZONES ON
FRIDAY...THEN THROUGHOUT THE FORECAST AREA FRIDAY NIGHT. EVEN THE
COLDER ECMWF SHOWS UNSTABLE SOUTHWEST FLOW ALOFT AND A CORRESPONDING
SURFACE COLD FRONT FRIDAY NIGHT BEFORE THE COLDER AIR SETS IN FOR
THE WEEKEND. RIGHT NOW...NOT TOTALLY BUYING THE CHILLIER ECMWF
SOLUTION FOR THE WEEKEND AS THIS MODEL HAS BEEN VARYING WILDLY THE
PAST FEW DAYS. THE GFS HAS ALSO NOT BEEN TERRIBLY CONSISTENT BUT AT
LEAST IT HAS SHOWN SOME SEMBLANCE OF THE UPPER RIDGE CENTERED NEAR
THE GULF COAST FOR QUITE SOME TIME NOW. SO WENT WITH MILD
TEMPERATURES ON SATURDAY...WITH SOME COOLER READINGS ON SUNDAY.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 1053 PM CDT SUN AUG 17 2014

CONVECTION CONTINUES TO FAIL TO DEVELOP UPSTREAM...SO HAVE REMOVED
CONVECTION FROM THE TAFS THROUGH THE PERIOD. MAINTAIN VFR
CONDITION WITH SOUTHERLY WINDS TRANSITIONING TO NORTHWEST. COULD
SEE SOME SHALLOW FOG DEVELOP MONDAY MORNING...OTHERWISE EXPECT
CONDITIONS TO REMAIN VFR.

&&

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

$$

SHORT TERM...JM
LONG TERM...MJ
AVIATION...






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