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000
FXUS63 KFSD 151022
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
522 AM CDT WED MAY 15 2013

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 428 AM CDT WED MAY 15 2013

LINGERING MID LEVEL BOUNDARY AND SOME WEAKLY UNSTABLE 700-500 HPA
LAPSE RATES CREATING SOME ISSUES WITH THE FORECAST EARLY THIS
MORNING. WAVE TOPPING DEVELOPING RIDGE ALOFT AND NUDGING UP AGAINST
NORTHWEST SOUTH DAKOTA ACTING TO INDUCE SOME CROSS FRONTAL FLOW...
AND WEAK REGION OF HIGH BASED LIFT FROM NORTHWEST TO SOUTHEAST ACROSS
THE STATE. MID LEVEL FRONTOGENETIC FORCING REMAINS FAIRLY STRONG
MAINLY ALONG AND NORTH OF I90 THROUGH THE DAY... WEAKENING SOME BY
AFTERNOON AS WAVE MOVES PAST. VERY DRY LOWER ATMOSPHERE IS CERTAINLY
IMPACTING THE POTENTIAL EASTWARD SPREAD AND OVERALL COVERAGE OF
WETTING RAINFALL. THE HRRR KEEP SLIPPING AWAY ON DEVELOPING
PRECIP...PUSHING IT BACK AT LEAST AN HOUR OR TWO WITH SUCCESSIVE RUN
DESPITE THE INCREASING PRESENCE ON RADAR OVER THE LAST HOUR OR TWO.
HIGH RES MODELS SEEM TO HAVE THE RIGHT IDEA...AND SUPPORT FROM LARGER
SCALE DYNAMICS MENTIONED ABOVE. INDICATIONS ON VARIOUS FORECAST
SOUNDING FROM 100 TO 300 J/K ELEVATED INSTABILITY...SO WOULD NOT BE
SURPRISED TO GET A FEW RUMBLES OF HIGH BASED THUNDER...EVEN WITH THE
OVERALL PROBABILITY/ COVERAGE OF PRECIPITATION LIKELY LACKING...AND
AT THIS POINT NOT WARRANTING MUCH MORE THAN A LOWER SCATTERED
MENTION.

SOME CONCERN THAT LINGERING CLOUDS AND ANY EVAPORATIVE EFFECTS WOULD
HAVE AN IMPACT ON TEMPERATURES TODAY...BUT SHOULD START TO GET AT
LEAST A DECENT AMOUNT OF SUNSHINE AFTER MAIN WAVE SHEARS BY TO THE
NORTH...AND LINGERING DIV Q ACROSS THE SOUTH WEAKENS AS WELL. MIXING
CENTERS AROUND THE MID TO UPPER 70S...AND DID NUDGE THIS JUST A BIT
HIGHER FOR THE FAR WEST.

TONIGHT LOOKS TO BE QUIETEST PERIOD OF THE FORECAST...WITH WEAK MID
TO UPPER LEVEL RIDGING OVER THE AREA TONIGHT AHEAD OF NEXT WAVE. NAM
AND GEM ACTUALLY A BIT FASTER IN BRINGING PRECIP CHANCE BACK INTO
OUR SOUTHWEST LATE TONIGHT...HOWEVER BEST FORCING WITH WARM ADVECTION
AND ADVANCING WAVE APPEARS TO REMAIN FOCUSED JUST WEST OF OUR AREA
THROUGH 12Z AND WILL LEAVE TONIGHT DRY AS A RESULT. LIGHT WINDS AND
RELATIVELY DRY AIR MASS WILL ALLOW FOR FAIR AMOUNT OF RADIATIONAL
COOLING...AND LOWS IN THE LOWER 50S LOOK REASONABLE FOR MOST AREAS.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 428 AM CDT WED MAY 15 2013

MESSY PATTERN THROUGHOUT THE LONG TERM PERIOD OF THIS FORECAST...WITH
DIFFICULTY PINPOINTING ANY PERIOD WHICH COULD BE SIGNIFICANTLY DRIER
THAN ANOTHER.

PERIOD STARTS WITH WARM FRONT AND ASSOCIATED WAVE MOVING ACROSS THE
FORECAST AREA THURSDAY/THURSDAY NIGHT. NAM/GEM/ECMWF QUITE BULLISH IN
PRODUCING FAIR AMOUNT OF PRECIP WITH THIS SYSTEM...WHILE THE GFS IS
MUCH DRIER THOUGH STILL INDICATIVE OF SOME PRECIP CHANCE. 15/00Z NAM
SEEMS TO BE SLIGHT OUTLIER IN SPEED WITH WHICH IS TRACKS THE WAVE AND
ASSOCIATED PRECIP TO THE NORTHEAST ON THURSDAY...AND HAVE GENERALLY
FOLLOWED SLOWER IDEA FOR NOW...KEEPING OUR NORTHEAST COUNTIES DRY
UNTIL THURSDAY EVENING. PERSISTENT WARM ADVECTION WILL THEN LEAD TO
INCREASING PRECIP CHANCE THROUGH THE OVERNIGHT HOURS THURSDAY NIGHT.
TEMPERATURES SHOULD BE SEASONABLE WITH HIGHS THURSDAY IN THE MID TO
UPPER 70S. INCREASING MOISTURE/CLOUD COVER WILL HOLD TEMPERATURES UP
IN THE UPPER 50S THURSDAY NIGHT.

MUCH OF FRIDAY/FRIDAY NIGHT COULD AGAIN BE BETWEEN PERIODS OF MORE
WIDESPREAD/ORGANIZED PRECIPITATION...THOUGH EASTERN AREAS COULD SEE
A FEW THUNDERSTORMS LINGER INTO THE MORNING...WHILE THE WEST HAS A
CHANCE OF DEVELOPMENT FRIDAY NIGHT AS RETURN FLOW OF MOISTURE MOVES
INTO CENTRAL SOUTH DAKOTA. WITH WARM FRONT EXPECTED TO BE NORTH OF
THE AREA BY FRIDAY AFTERNOON...AND GENERAL LACK OF PRECIP ALONG WITH
BREEZY SOUTH WINDS...SHOULD SEE DECENT MIXING TO HELP WARM TEMPS INTO
THE MID 80S ACROSS THE WEST. DESPITE WARMER TEMPS AND POTENTIAL FOR
SOME GUSTY WINDS...DO NOT EXPECT SIGNIFICANT FIRE DANGER FRIDAY AS
WE SHOULD HAVE MUCH HIGHER BOUNDARY LAYER MOISTURE WITH EVEN MIXED
OUT DEW POINTS HOLDING IN THE UPPER 50S TO AROUND 60. THAT MOISTURE
ALONG WITH WEAK LOW LEVEL JET WILL HOLD OVERNIGHT LOWS IN THE LOWER
TO MID 60S FOR FRIDAY NIGHT.

SATURDAY INTO SATURDAY NIGHT CONTINUES TO LOOK LIKE MOST FAVORED
PERIOD FOR ORGANIZED PRECIPITATION ACROSS THE REGION...AS BROAD
WESTERN CONUS TROUGH BEGINS TO SHIFT EASTWARD INTO THE PLAINS.
PRECIP SHOULD INITIALLY BE FOCUSED NEAR BOUNDARY ACROSS CENTRAL
SOUTH DAKOTA BY SATURDAY AFTERNOON...WITH THUNDERSTORMS THEN
EXPANDING EASTWARD ACROSS OUR FORECAST AREA SATURDAY NIGHT. THIS
PERIOD CONTINUES TO BE GREATEST THREAT FOR SEVERE WEATHER FOR OUR
FORECAST AREA...WITH STEEP MID LEVEL LAPSE RATES AND DEEP FORCING
AHEAD OF TROUGH BRINGING POTENTIAL FOR HAIL/WIND.

AS IS TYPICAL IN CONVECTIVE SEASON...MODELS NOT SHOWING A GREAT DEAL
OF AGREEMENT IN TIMING/LOCATION OF BOUNDARIES FROM THIS POINT
FORWARD. HOWEVER...THEY HAVE TRENDED TOWARD A FAVORED SOLUTION IN
CLOSING OFF THE UPPER LOW SOMEWHERE IN THE CENTRAL/NORTHERN PLAINS
BY SUNDAY NIGHT/MONDAY...WITH THE LOW THEN PERSISTING ACROSS THIS
REGION THROUGH MUCH OF EARLY NEXT WEEK. THIS LEADS TO POTENTIAL FOR
AT LEAST SCATTERED PRECIPITATION SUNDAY THROUGH TUESDAY...AND HAVE
NOT STRAYED FAR FROM CONSENSUS GRIDS WHICH HOLD ONTO CHANCE RANGE
POPS FOR THE LONGER RANGE. TEMPERATURES SHOWING LESS AGREEMENT LATE
IN THE PERIOD...WITH LATEST ECMWF WRAPPING MUCH COLDER AIR AROUND THE
BACK SIDE OF THE UPPER LOW BY MONDAY AND ESPECIALLY TUESDAY. FOR NOW
WILL STICK WITH SOMEWHAT MORE MILD GFS/CONSENSUS SOLUTION WHICH...
ALTHOUGH COOLER THAN THE MILD TEMPERATURES EXPECTED THROUGH THE
WEEKEND...WILL KEEP HIGHS IN THE 60S.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING)
ISSUED AT 521 AM CDT WED MAY 15 2013

ELEVATED INSTABILITY AND A DISTURBANCE MOVING ACROSS FAR NORTHERN
SOUTH DAKOTA THIS MORNING WILL CONTINUE TO PRODUCE ISOLATED TO
SCATTERED SHOWERS AND A FEW THUNDERSTORMS ACROSS THE AREA. OTHER
THAN THE IMMEDIATE SHORT TERM AROUND KHON...NOT LIKELY TO HAVE A
HIGH ENOUGH PROBABILITY OF THUNDER TO WARRANT MENTION IN THE TAFS.
DESPITE PRECIPITATION...VERY HIGH BASED NATURE WILL MEAN THAT
CONDITIONS SHOULD REMAIN VFR. THE PRECIPITATION SHOULD MOVE OUT
OF THE IMMEDIATE AREA BY 18Z...AND DRY CONDITIONS ARE EXPECTED
THROUGH 12Z THURSDAY. HOWEVER...SCATTERED THUNDERSTORMS SHOULD BE
POISED SOUTHWEST OF THE KHON AREA TOWARD 12Z MOVING FROM ORIGINS
IN WESTERN NEBRASKA AND SOUTHWEST SOUTH DAKOTA.

&&

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

$$

SHORT TERM...CHAPMAN/JH
LONG TERM...JH
AVIATION...CHAPMAN