Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 252032
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
332 PM CDT SAT JUL 25 2015

.SHORT TERM...(THIS EVENING THROUGH SUNDAY)
ISSUED AT 332 PM CDT SAT JUL 25 2015

OCCASIONAL CONVECTION CONTINUES TO FIRE UP OFF AND THIS AFTERNOON
PRIMARILY SOUTH OF INTERSTATE 90. 700MB TEMPERATURES ARE ONLY AROUND
+8C SO THE ATMOSPHERE IS CERTAINLY NOT CAPPED WITH ABUNDANT
MOISTURE. THEREFORE IT DOES NOT TAKE A LOT TO GET STORMS GOING.
RESPONSIBLE FOR THIS...IS THE 18Z GRIDDED ANALYSIS SHOWS A 700MB
SHORT WAVE EXTENDING FROM NORTHWEST SD TO EAST CENTRAL NEB. THIS
WAVE MOVES VERY LITTLE THROUGH 00Z SUNDAY...AND IS REPLACED BY A
STRONGER WAVE MOVING INTO OUR WESTERN ZONES BY THIS EVENING.
CURRENTLY THIS SECOND AND STRONGER WAVE IS STILL OUT AROUND
NORTHWEST SD...SO IT IS DIFFICULT TO ASCERTAIN JUST HOW EXACTLY IT
WILL EVOLVE TONIGHT IN OUR AREA. ONE THING IS FOR SURE IN THE NEARER
TERM...IS THAT THE CURRENT CONVECTION HAS BASICALLY SCOURED OUT OUR
WESTERN ZONES FOR THE TIME BEING ALLOWING THEM TO HEAT UP AND BECOME
RATHER UNSTABLE. CURRENT THOUGHTS ARE THAT BECAUSE OF THIS...
SCATTERED CONVECTION MAY DEVELOP ACROSS OUR WESTERN ZONES THIS
EVENING AS THE SECOND SHORT WAVE APPROACHES...POSSIBLY BECOMING A
BIT MORE NUMEROUS IN EAST CENTRAL SD AS THE EVENING PROGRESSES. BUT
AGAIN WITH NO REAL LOW LEVEL BOUNDARIES TO KEY ON...THE EXACT TIMING
AND PLACEMENT FOR THE BEST CHANCES OF STORMS REMAIN RATHER UNCERTAIN
TONIGHT.

THE SHORT WAVE THEN PROGRESSES TO OUR EXTREME EASTERN ZONES BY 12Z
SUNDAY BEFORE EXITING. THEREFORE THE BEST STORM CHANCES SHOULD BE
EAST OF I 29 AFTER THE MIDDLE OF TONIGHT...WITH LITTLE REMAINING IN
OUR EAST BY 12Z SUNDAY. THERE COULD BE STRATUS AROUND FOLLOWING THE
RAINFALL...ESPECIALLY ALONG AND EAST OF THE JAMES RIVER VALLEY LATE
TONIGHT AND SUNDAY MORNING FOLLOWING THE GFS20. BELIEVE THE STRATUS
IS TOO FAR WEST ON THE NAM. AT ANY RATE AS THE STRATUS LIFTS...WE
ARE LOOKING AT ANOTHER WARM AND HUMID DAY ON SUNDAY WITH SOME
POSSIBLE REDEVELOPMENT OF ISOLATED STORMS EAST OF I 29 LATE SUNDAY
AFTERNOON UNDER A TOWERING CU FIELD. BELIEVE THE CURRENT SPC SLIGHT
RISK OUTLOOK IS GOOD FOR TONIGHT...PRIMARILY TARGETING THE JAMES AND
MO RIVER VALLEYS IF ONE IS TO BELIEVE THE MU CAPE AND WIND SHEAR
FIELDS. FOR INSTANCE EAST OF THE SLIGHT RISK AREA...MID LEVEL WINDS
ARE FORECAST TO BE RATHER WEAK TONIGHT AT ONLY 20 TO 25 KNOTS
COMPARED TO 30 TO 35 KNOTS IN THE SLIGHT RISK AREA. THIS FOLLOWS
SUIT ON THE 0-6KM BULK SHEAR VECTORS WHICH ARE QUITE STOUT FOR THIS
TIME OF YEAR IN THE SLIGHT RISK AREA AVERAGING 45 TO 50 KNOTS. 925-
850MB MU CAPE VALUES PER THE NAM ARE INDEED AROUND 2000-3000 J/KG
THIS EVENING AND OVERNIGHT IN THE JAMES AND MO RIVER VALLEYS WHICH
SHOULD SUPPORT ROTATING UPDRAFTS CAPABLE OF PRODUCING SOME LARGE
HAIL COUPLED WITH STRONG WIND GUSTS. ONE FINAL NOTE...LOOKED AT HEAT
INDEX VALUES FOR SUNDAY AFTERNOON AND THEY CURRENTLY DO NOT WARRANT
A HEADLINE.


.LONG TERM...(SUNDAY NIGHT THROUGH SATURDAY)
ISSUED AT 332 PM CDT SAT JUL 25 2015

THE ACTIVE WEATHER PATTERN WILL CONTINUE INTO EARLY NEXT
WEEK AS A SERIES OF WAVES LIFTS INTO THE REGION. WITH THE UPPER
RIDGE AXIS CENTERED OVER THE HIGH PLAINS AND VERY SLOWLY SHIFTING
EASTWARD ACROSS THE PLAINS THROUGH TUESDAY...HOT AND HUMID
CONDITIONS WILL PERSIST. EXPECT DEWPOINTS HOVER NEAR 70 AND HIGHS TO
REACH 85 TO 95 ON MONDAY. WITH A WAVE LIFTING INTO THE CENTRAL HIGH
PLAINS SUNDAY NIGHT...WILL LEAVE LOW END CHANCES OF THUNDERSTORMS
NEAR THE MISSOURI RIVER WHERE MOISTURE RETURN IS A BIT BETTER
OVERNIGHT. THE GFS IS MORE ROBUST WITH THIS ACTIVITY SPREADING
ACROSS MUCH OF THE FORECAST AREA...HOWEVER THE GENERAL CONSENSUS
FOCUSES THE CONVECTION AROUND I80 WITH A FEW STRAY STORMS WORKING
INTO OUR EXTREME SOUTH AND WEST.

BREEZY SOUTHERLY WINDS DEVELOP ON MONDAY AND MONDAY NIGHT AHEAD OF A
MORE SUBSTANTIAL WEATHER SYSTEM DEEPENING OVER THE NORTHERN ROCKIES.
SCATTERED THUNDERSTORMS WILL AGAIN BE POSSIBLE MONDAY NIGHT...BUT
WITHOUT MUCH CONVERGENCE/SUPPORT...WILL STICK WITH CHANCE POPS FOR
NOW. THE BEST POTENTIAL LOOKS TO BE NORTH OF I90 CLOSER TO WHERE A
MID LEVEL BOUNDARY/WAVE POTENTIALLY TRACKS. A FRONT STILL LOOKS
LIKELY TO DROP THROUGH THE REGION ON TUESDAY. STILL SOME TIMING
CONCERNS...BUT IT STILL LOOKS LIKE IT MAY SET UP OVER THE EASTERN
FORECAST AREA LATER IN THE DAY AND BECOME THE FOCUS FOR ADDITIONAL
THUNDERSTORM ACTIVITY IN THE AFTERNOON AND INTO EARLY WEDNESDAY.
DEPENDENT ON EARLY MORNING CONVECTION ON TUESDAY...NORTHWEST IOWA
AND ADJACENT AREAS POTENTIALLY WILL SEE ENOUGH INSTABILITY AND SHEAR
FOR SEVERE WEATHER CONCERNS.

SOME RELIEF TO THE HEAT AND HUMIDITY RETURNS WEDNESDAY AND THURSDAY
WITH SLIGHTLY COOLER NORTHWEST FLOW ALOFT. LOOK FOR DRY CONDITIONS
AND HIGHS IN THE 80S. THE UPPER RIDGE BEGINS REBUILDING TO THE WEST
LATE IN THE WEEK...WITH HIGHS AGAIN REACHING 85 TO 95. THE GFS AND
ECMWF CONTINUE TO BOTH INDICATE THAT A SUBTLE BOUNDARY SLIDES
THROUGH THE AREA AROUND FRIDAY OR FRIDAY NIGHT...SO WILL KEEP SOME
LOW END POPS GOING.


&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1227 PM CDT SAT JUL 25 2015

WATCHING A CLUSTER OF THUNDERSTORMS MOVING INTO FAR SOUTHEAST
SOUTH DAKOTA THROUGH THE NEXT HOUR. THESE STORMS WILL CONTINUE TO
DISSIPATE AS THEY MOVE EAST OF I29. EXPECT BRIEF MVFR CEILINGS AND
VISIBILITY IN THE STORM AT KFSD...HOWEVER RIGHT NOW IT LOOKS LIKE
THE CELL IN NORTHEAST NEBRASKA WILL TRACK NORTH OF KSUX. LATER
THIS EVENING...ANOTHER ROUND OF STORMS ARE EXPECTED TO DEVELOP IN
CENTRAL SD AND TRACK SOUTHEAST ACROSS SOUTHEAST SD. EXPECT ALL 3
SITES TO POTENTIALLY BE IMPACTED BY THESE STORMS AFTER 00Z. SOME
MVFR LOW CLOUDS AND VISIBILITY MAY ALSO DEVELOP BEHIND THESE
STORMS LATE TONIGHT BUT SHOULD DISSIPATE BY MIDDAY.


&&

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

$$

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


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