Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 012029
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
329 PM CDT TUE SEP 1 2015

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 329 PM CDT TUE SEP 1 2015

WATER VAPOR IMAGERY SUGGESTS WAVE PUSHING ACROSS NORTH CENTRAL
NEBRASKA IS MAKING TRACKS TOWARD SOUTHEAST SOUTH DAKOTA AT MID
AFTERNOON. SCATTERED CONVECTION HAS LACKED MUCH IN THE WAY OF
LIGHTNING FOR LAST COUPLE OF HOURS...MAINLY SCATTERED SHOWERS FROM
EAST CENTRAL TO THE LOWER JAMES VALLEY. RESULTANT CLOUDS HAVE TAKEN
THE LARGER BITE OUT OF THE WARMING POTENTIAL ACROSS THE AREA
TODAY...SO HAS NOT DESTABILIZED QUITE AS MUCH AS SOME OF THE MODELS
AND ANALYSES HAVE INDICATED. STILL...A WELL SOUPED UP LOWER
ATMOSPHERE WITH WIDESPREAD UPPER 60S TO LOWER 70S DEWPOINTS AT THE
SURFACE...AND ROUGHLY AN INCH AND A HALF PRECIPITABLE WATER ALONG
THE ELONGATED LOWER TO MID LEVEL BOUNDARY.

CONVECTIVE CHANCES GOING INTO THE EVENING ARE THE PRIMARY CONCERN
FOR THE AFTERNOON PACKAGE. A FEW LIGHT SHOWERS AND SPRINKLES ALONG
THE BOUNDARY AT MID AFTERNOON ARE EXPECTED TO FIND A TRANSITION
TO DEVELOPMENT OF SCATTERED THUNDERSTORMS AS THE LARGER SCALE LIFT
WITH THE WAVE MOVES TOWARD SOUTHEAST SOUTH DAKOTA LATE AFTERNOON.
SEEMS THAT MOST SHORT RANGE/HIGH RES MODEL SOLUTIONS CONTINUE TO
DRAG A BIT ON DEVELOPMENT AND STARTING TOO FAR WEST...SO HAVE SIDED
CLOSER TO THE LARGE SCALE FORCING WHICH SUGGESTS DEVELOPMENT THE
LAST COUPLE HOURS IN THE AFTERNOON FROM LOWER JAMES TOWARD I 29
CORRIDOR. WILL SEE GENERALLY AN EASTWARD SHIFT TO SCATTERED
PRECIPITATION AREA THROUGH THE EVENING. DIFFICULT TO PUSH POPS MUCH
PAST A CHANCE/SCATTERED LEVEL AT THIS TIME...WITH FEATURES FAIRLY
WEAKLY DEFINED. KINEMATIC AND THERMODYNAMIC PARAMETERS ARE FAR FROM
IDEAL FOR SEVERE STORMS...BUT WARMER OVERALL PROFILE AND LIKELY SLOW
MOVEMENT OF FEATURES TIED TO BOUNDARY AND LIFT FROM APPROACHING WAVE
SUGGEST THERE IS A POTENTIAL FOR SOME BRIEF PERIODS OF HEAVY
RAINFALL. HOWEVER...WITH WAVE MOVING THROUGH AND LOW LEVEL JET WINDS
VEERING AS THIS OCCURS...NOT LIKELY TO GET TOO LONG A PERIOD WITH
THE GREATER HEAVY RAIN THREAT.

ON WEDNESDAY...WILL GO FROM A WARM AND UNCOMFORTABLY HUMID DAY
EAST...TO DOWNRIGHT HOT TOWARD THE SOUTH CENTRAL. THERE IS LIKELY A
ZONE BETWEEN THE SLIGHTLY BETTER MIXED FAR WEST...AND THE HIGHLY
INVERSION DOMINANT LESS HOT AND MORE HUMID AREAS FROM THE JAMES
VALLEY EASTWARD...WHERE THE HEAT INDEX WILL GET CLOSE TO 100
DEGREES. WILL HAVE TO WATCH FOR ANY FOG POTENTIAL EARLY IN THE
DAY...BUT GRADIENT OVERNIGHT AND EARLY MORNING SHOULD KEEP FROM
GETTING TOO EXTREME.

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 329 PM CDT TUE SEP 1 2015

FOR NOW LOOKING DRY WEDNESDAY NIGHT INTO THURSDAY NIGHT AS TROUGH TO
THE WEST KEEPS UPPER LEVEL RIDGING IN PLACE. A WAVE IS EXPECTED TO
SWING NORTH ON THE EAST SIDE OF THIS TROUGH WITH SLIGHTLY BETTER
CHANCES FOR SHOWERS AND THUNDERSTORMS TO THE WEST OF THE AREA. WITH
STRONG SOUTHERLY FLOW IN PLACE THE EVENINGS AND OVERNIGHTS WILL BE
VERY WARM AND BOTH THURSDAY MORNING LOWS AND FRIDAY MORNING LOWS
HAVE THE POTENTIAL TO REACH OR EXCEED RECORD WARM LOW TEMPERATURES
FOR EARLY SEPTEMBER. VERY WARM AND HUMID ON THURSDAY WITH A LITTLE
LESS WARM CONDITIONS ON FRIDAY WITH AN INCREASE IN CLOUDS AND A
HIGHER THREAT FOR SHOWERS AND STORMS.

IN THE OUTER PERIODS (SATURDAY THROUGH TUESDAY)...FAIRLY DEEP TROUGH
OVER THE WESTERN UNITED STATES IS PROJECTED TO START LIFTING TOWARDS
THE NORTHERN PLAINS ON SUNDAY. FLOW ALOFT WILL TURN FROM SOUTHWEST
TO WEST WITH HINTS THAT TROUGHING COULD AGAIN DEVELOP OVER THE
WESTERN UNITED STATES TUESDAY INTO WEDNESDAY. OVERALL THIS PATTERN
STILL HINTING AT A VERY GOOD CHANCE FOR SHOWERS AND THUNDERSTORMS
THROUGH THE PERIOD...ESPECIALLY OVER THE WEEKEND. TEMPERATURES
SHOULD REMAIN ABOVE NORMAL SATURDAY AND SUNDAY THEN BACK TO AROUND
NORMAL TO START THE WEEK. SEVERE WEATHER IS NOT LOOKING LIKE A MAJOR
THREAT OVER THE WEEKEND AS THE MID AND UPPER LEVEL WIND FIELD IS A
LITTLE WEAK AND THE LOW LEVEL WIND FIELD HAS LITTLE DIRECTIONAL
SHEAR. WHILE SUNDAY COULD POSE THE GREATER THREAT FOR SEVERE
THUNDERSTORMS...TIMING OF THE WAVE AS WELL AS WHAT HAPPENS WITH
CONVECTION SATURDAY INTO SUNDAY MORNING WILL PLAY BIG ROLES. WILL
ALSO NEED TO KEEP AN EYE ON THE HEAVY RAIN THREAT AS PRECIPITABLE
WATER COULD BE ABOUT 1.67 TO 1.75 INCHES AND CORFIDI VECTORS HINTING
AT POTENTIAL FOR SLOW MOTION.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1252 PM CDT TUE SEP 1 2015

HIGH BASED SHOWERS AND ISOLATED THUNDERSTORMS FROM EAST CENTRAL TO
SOUTH CENTRAL SD AT MIDDAY SHOULD REFOCUS/REDEVELOP LATE AFTERNOON
ACROSS SOUTHEAST SOUTH DAKOTA...WHICH ARE LIKELY TO PROGRESS EAST
AND NORTHEAST THROUGH THE EVENING AND EARLY OVERNIGHT. DEVELOPMENT
SHOULD REMAIN EAST OF KHON...WITH A FEW HOURS OF THREAT FOR KFSD
AND KSUX FROM LATE AFTERNOON TO MID EVENING. HAVE NARROWED MENTION
A BIT IN TAFS FOR THESE SITES...WITH HIGH RESOLUTION MODEL TIMING
SOMEWHAT ERRATIC...AND HAVE TIMED CLOSER TO LARGER SCALE FORCING.
AFTER PRECIPITATION SHIFTS EAST TONIGHT WITH WAVE AND VEERING LOW
LEVEL JET...THERE IS SOME GRADIENT OVERNIGHT WHICH SHOULD KEEP
VISIBILITY REDUCTIONS CLOSER TO THE MVFR RANGE LATE TONIGHT/EARLY
WEDNESDAY MORNING. LOW LEVEL WIND SHEAR LOOKS TO BE MAINLY A
PROBLEM FOR KSUX IN PROXIMITY TO VEERED LOW LEVEL JET.

&&

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

$$

SHORT TERM...CHAPMAN
LONG TERM...08
AVIATION...CHAPMAN


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