968
FXUS63 KFSD 071938
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
238 PM CDT TUE JUL 7 2020
SHORT TERM
(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 237 PM CDT TUE JUL 7 2020
A BAND OF SHOWERS AND ISOLATED THUNDERSTORMS MAINLY ALONG AND NORTH
OF I-90 EARLIER TODAY WAS IN RESPONSE TO STRENGTHENING MID LEVEL
WARM ADVECTION. HOWEVER AS WE MOVE INTO THE LATE AFTERNOON AND
EVENING THAT WARM ADVECTION WILL SEE SOME DRYING IN THE LAYER AND
THUS THIS BAND DIMINISHED. THE FOCUS OF THIS WARM ADVECTION WILL
SHIFT NORTH THROUGH THE EVENING AND OVERNIGHT AS MORE DRY AIR IN THE
MID LEVELS DEVELOPS, SO LOOKING AT A QUIET NIGHT WITH VERY WARM
OVERNIGHT TEMPERATURES WHILE A SOUTH WIND INCREASES. EXPECTING LOWS
MAINLY IN THE MID 70S.
AS UPPER LEVEL LOW PRESSURE WRAPS UP OVER SOUTH CENTRAL CANADA ON
WEDNESDAY A MID LEVEL TROUGH WILL SWING INTO CENTRAL SD. THIS TROUGH
SHOULD APPROACH THE MISSOURI RIVER BY LATE AFTERNOON AND WILL LIKELY
SPARK SOME SHOWERS AND THUNDERSTORMS FROM CENTRAL SD INTO NORTHEAST
SD AND POSSIBLY SOUTHWEST MN. THIS WILL BE DEPENDENT UPON THE
LOCATION OF THE SURFACE OR NEAR SURFACE COOL FRONT. SOUNDINGS
SUGGEST LITTLE IN THE WAY OF MID LEVEL MOISTURE OR INSTABILITY SO
LOCATIONS SHOULD REMAIN DRY UNTIL THE CAPPING CAN BE BROKEN, WHICH
WILL LIKELY BE SOMETIME BETWEEN 21Z AND 23Z. CAPE VALUES WILL BE
MODERATE TO HIGH, LIKELY 2750 TO 3500 J/KG NEAR THE FRONT. THE SHEAR
WILL BE DECENT, LIKELY RUNNING ABOUT 30 KNOTS IN THE SURFACE TO 3
KM, WITH THE DEEPER SHEAR LIKELY RUNNING ABOUT 40 KNOTS. SO, THIS
SHOULD SUPPORT A FEW VERY STRONG UPDRAFTS AND WITH THE EXPECTED
SHEAR AND FAIRLY DRY ENVIRONMENT ISOLATED SUPERCELLS WILL BE
POSSIBLE. THE STRONGEST OF WHICH COULD PRODUCE TENNIS BALL SIZED
HAIL AND WIND GUSTS TO 75 MPH. BY VERY LATE AFTERNOON INTO THE EARLY
EVENING IT IS LIKELY THE STORMS WILL BECOME A BIT MORE LINEAR AND
POSSIBLY COLD POOL DOMINANT WHICH WOULD ALLOW FOR MORE OF A SOUTH
SOUTHEAST MOTION. TAKING INTO ACCOUNT THAT THE UPPER LEVEL LOW
PRESSURE MIGHT BE A BIT SLOWER THAN FORECAST, THIS MEANS THAT THE
MID LEVEL WAVE AND SURFACE FRONT COULD BE A BIT FARTHER WEST IN THE
LATE AFTERNOON WHICH SUGGESTS THAT THE NAM COULD BE A TOUCH ON THE
QUICK SIDE. AT 7 PM WEDNESDAY THE GFS, CANADIAN AND EC ALL HAVE THE
925MB TO SURFACE FRONT NEAR AND WEST OF THE JAMES VALLEY WHILE THE
NAM IS MORE BETWEEN I-29 AND THE JAMES RIVER. WHILE THIS IS NOT A
HUGE DIFFERENCE WITH STRONG/SEVERE THUNDERSTORMS 20 TO 40 MILES WILL
MAKE ALL OF THE DIFFERENCE. SO CONFIDENCE NOT SUPER HIGH ON THIS BUT
WILL LEAN A BIT WEST ON BEST CHANCES FOR LATE AFTERNOON AND EARLY
EVENING DEVELOPMENT, WHICH SHOULD BE WHEN SOME OF THE STRONGEST
UPDRAFTS OCCUR. THE LATEST HREF OUTPUT PUTS THE FRONT CLOSER TO THE
NAM, BUT OF COURSE THE HREF IS NAM HEAVY SO NOT SURE HOW USEFUL THAT
INFORMATION IS?
LONG TERM
(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 237 PM CDT TUE JUL 7 2020
ONCE THIS WAVE PASSES UPPER LEVEL FLOW TURNS MORE WESTERLY AS THE
UPPER LEVEL LOW PRESSURE MOVES ALONG THE U.S/CANADIAN BORDER. FLOW
ON THURSDAY WILL TURN WESTERLY. THERE IS A WEAK CONVERGENT BOUNDARY
THAT WILL WORK THROUGH AS WINDS TURN A BUT MORE NORTHWEST IN THE
AFTERNOON BUT FOR NOW CONDITIONS LOOK DRY AND STABLE SO NOT
EXPECTING AN THUNDERSTORMS. NORTHWEST IA DOES SHOW SOME BRIEF
WEAKNESS IN THE CAP IN THE LATE AFTERNOON. WILL LEAVE SOME LOWER
POPS IN THE SOUTH IN CASE AN MCS IS STILL EXITING ON THURSDAY
MORNING AND IN CASE AN ISOLATED CELL DEVELOPS IN THE AFTERNOON.
THURSDAY NIGHT INTO FRIDAY WEAK MID LEVEL RIDGING AND DRIER WESTERLY
FLOW SHOULD KEEP MOST LOCATIONS DRY. BY LATE FRIDAY AFTERNOON THIS
RIDGE TRIES TO BREAK DOWN A BIT IN CENTRAL SD THEN A WEAK WAVE MOVES
THROUGH THE AREA ON FRIDAY NIGHT WHICH WILL BE OUR NEXT BETTER
CHANCES FOR SHOWERS AND THUNDERSTORMS. BOTH THURSDAY AND FRIDAY
TEMPERATURES WILL MODERATE AND BE BACK TO AROUND NORMAL. HUMIDITY
LEVELS WILL ALSO BE ON THE SEASONAL SIDE WITH DEW POINTS IN THE
60S.
SATURDAY THROUGH TUESDAY SHOULD BE A BIT MORE ON THE QUIET SIDE AS
BROAD UPPER LEVEL RIDGING BUILDS INTO THE AREA. TEMPERATURES MAINLY
80S TO LOWER 90S. A BIT BETTER CHANCE FOR THUNDERSTORMS BY TUESDAY
AS A WAVE MOVES INTO THE WESTERN HIGH PLAINS BUT THAT'S FAR ENOUGH
OUT TO NOT HAVE MUCH CONFIDENCE IN.
AVIATION
(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1207 PM CDT TUE JUL 7 2020
OTHER THAN A WEAKENING AREA OF SHOWERS AND ISOLATED LIGHTNING
STRIKES JUST WEST OF FSD THROUGH 18-19Z TODAY, VFR CONDITIONS ARE
EXPECTED. AFTER 21Z WEDNESDAY STRONG TO SEVERE THUNDERSTORMS WILL
BE POSSIBLE, ESPECIALLY BETWEEN FSD AND HON.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
SHORT TERM...08
LONG TERM...08
AVIATION...08
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