808
FXUS63 KFSD 181155
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
655 AM CDT TUE SEP 18 2018
SHORT TERM
(TODAY AND TONIGHT)
ISSUED AT 321 AM CDT TUE SEP 18 2018
THIS MORNING WILL BRING INCREASING THUNDERSTORM COVERAGE AS A
DISTINCT SHORTWAVE MOVES ALONG THE ELEVATED BOUNDARY DRAPED ACROSS
THE REGION. MOISTURE FOR THESE STORMS IS PRIMARILY LOCATED IN THE
800 TO 900 HPA LAYER, AND STORMS ARE EXPECTED TO BUILD TO THE SOUTH
OVER TIME AS THE WEAK LOW-LEVEL JET PROVIDES ADDITIONAL MOISTURE
ADVECTION. PRECIPITABLE WATER VALUES ARE UNSEASONABLY HIGH IN THE
INCOMING AIR MASS, SO HEAVY RAIN WILL BE POSSIBLE UNDER STORMS;
THANKFULLY, THIS CLUSTER OF CELLS LOOKS TO REMAIN FAIRLY
PROGRESSIVE. THE PRIMARILY THREAT FROM THESE STORMS WILL BE ABUNDANT
LIGHTNING, BRIEF HEAVY RAINFALL, AND LOCALIZED HAIL.
DURING THE AFTERNOON AND EARLY EVENING, ANOTHER SUBTLE UPPER-LEVEL
WAVE HAS THE POTENTIAL TO FIRE OFF ADDITIONAL STORMS AS THE
STATIONARY FRONTAL BOUNDARY REMAINS OVER THE REGION. OVERALL, SHORT-
RANGE MODELS FAVOR LOCATIONS SOUTH OF I-90 FOR THIS ACTIVITY, SO
HAVE INCREASED POPS AROUND THE SIOUX CITY VICINITY.
LATE THIS EVENING INTO THE OVERNIGHT HOURS, COOLER AIR FROM THE
NORTH IS FORECAST TO PUSH THE BOUNDARY SLIGHTLY FARTHER TO THE
SOUTH, ESPECIALLY OVER SOUTHWEST MN AND NORTHWEST IA. THIS WILL
BRING THE NORTHERN TERMINUS OF THE LOW-LEVEL JET INTO THE TRI-STATE
AREA, AND INCREASE THE THREAT FOR TRAINING THUNDERSTORMS CAUSING
HEAVY RAIN AND LOCALIZED FLASH FLOODING ISSUES. THE ULTIMATE
LOCATION OF WHERE THIS BOUNDARY SETS UP IS STILL UNCERTAIN, GIVEN
LITTLE CONSENSUS AMONG CAMS; HOWEVER, TODAY WOULD BE A GOOD TIME TO
MAKE SURE THE SUMP PUMP IS WORKING WELL, ESPECIALLY IF YOU LIVE
ALONG AND EAST OF I-29. FLASH FLOOD WATCHES MAY STILL BE NEEDED
DURING THIS TUESDAY NIGHT INTO WEDNESDAY MORNING TIMEFRAME, BUT HAVE
AGAIN HELD OFF DUE TO A LACK OF CONFIDENCE ON WHERE THIS BAND OF
HEAVIEST RAINFALL WILL END UP. FOR NOW, WILL CONTINUE TO MONITOR
TRENDS TO DETERMINE WHERE THE INGREDIENTS BEST LINE UP.
LONG TERM
(WEDNESDAY THROUGH MONDAY)
ISSUED AT 321 AM CDT TUE SEP 18 2018
WEDNESDAY INTO WEDNESDAY NIGHT, THUNDERSTORMS CONTINUE TO BE A
THREAT AS DYNAMICS INCREASE AHEAD OF AN INCOMING LONGWAVE TROUGH.
WEDNESDAY EVENING IN PARTICULAR LOOKS TO BE A FAVORABLE TIME FOR
ADDITIONAL HEAVY RAIN, GIVEN THE INTENSIFYING SURFACE LOW
PRESSURE SYSTEM. ON THURSDAY, THE STRONG UPPER TROUGH STILL LOOKS
TO PUSH THROUGH THE NORTHERN PLAINS. THIS WILL BRING A DRIER
CANADIAN AIRMASS INTO THE REGION BY THE AFTERNOON. FRIDAY THROUGH
THE WEEKEND LOOKS DRY AND COOLER WITH SEASONAL AUTUMN CONDITIONS.
AVIATION
(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)
ISSUED AT 650 AM CDT TUE SEP 18 2018
THUNDERSTORMS WILL BE POSSIBLE THROUGHOUT THE DAY. A STATIONARY
FRONT OVER THE REGION WILL BRING VARYING WIND DIRECTION, WITH ABUNDANT
CLOUDS, AND LOW CLOUDS POSSIBLE IN THE VICINITY OF STORMS. HIGH
RESOLUTION MODELS CURRENTLY HIGHLIGHT THE MID- AFTERNOON AND
EVENING AS BEING RELATIVELY THUNDERSTORMS FREE, BUT MODELS HAVE
ALSO BEEN VERY INCONSISTENT RUN-TO-RUN, SO CONFIDENCE ON
THUNDERSTORM TIMING IS LOW. ONE TREND THAT HAS BEEN STEADY
OVERNIGHT IS A BAND OF HEAVY RAIN DURING THE EARLY AM HOURS
WEDNESDAY. CURRENTLY, THESE STORMS LOOK TO FOCUS NORTH OF I-90,
AND COULD AFFECT KFSD AND KHON OVERNIGHT INTO WEDNESDAY MORNING.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
SHORT TERM...VANDENBOOGART
LONG TERM...VANDENBOOGART
AVIATION...VANDENBOOGART
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