000
FXUS63 KFSD 181141
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
641 AM CDT TUE JUN 18 2013

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 403 AM CDT TUE JUN 18 2013

STRONG SHORT WAVE ENERGY MOVING DOWN THE NW FLOW ALOFT WILL BE
DEPARTING OUR EASTERN ZONES SHORTLY. HOWEVER OUR MISSOURI RIVER
VALLEY ZONES WILL NEED TO BE WATCHED IN THE NEAR TERM AS ELEVATED
INSTABILITY WILL FIRE OFF SOME ISOLATED TO SCATTERED ACCAS. THERE
MAY BE BETTER CHANCES OF THIS HAPPENING SOUTH OF OUR FORECAST
AREA. BUT CERTAINLY LOW POPS ARE WARRANTED IN OUR MISSOURI RIVER
VALLEY ZONES EARLY TODAY. OTHERWISE THE WEATHER SHOULD BE QUIET
FOR MUCH OF THE DAY...GOING WITH THE WARMER GUIDANCE READINGS AS
THE BIAS CORRECTED STILL LOOKS TOO COOL.

CONVECTION CHANCES TONIGHT ARE UNCERTAIN. A COUPLE OF THE HIRES
MODELS WERE BRINGING RAINFALL CHANCES LATE TONIGHT ALMOST THROUGH
OUR ENTIRE FORECAST AREA WHICH DID NOT SEEM REASONABLE GIVEN THE
AMOUNT OF STABILITY EAST OF I 29. BUT AS THE LOW LEVEL JET
INCREASES WEST OF I 29 AND THETAE ADVECTION...WOULD NOT BE
SURPRISED TO SEE AN ELEVATED SHOWER OR THUNDERSTORM GET GOING FROM
I 29 WESTWARD LATE TONIGHT. BUT THE BETTER RAIN CHANCES WILL HOLD
OFF UNTIL WEDNESDAY.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 403 AM CDT TUE JUN 18 2013

A VERY LARGE UPPER LOW BEGINS TO SET UP SHOP OVER THE WESTERN U.S.
ON WEDNESDAY AND THURSDAY. THIS LOW WILL SEND PERIODIC SHORT WAVES
EASTWARD THROUGH THE PLAINS...PRIMARILY AT NIGHT IN OUR FORECAST
AREA. AS LONG AS THE UPPER LOW IS MAINTAINED OVER THE WESTERN U.S...
SHORT WAVE ENERGY WILL BE A COMMON FEATURE AHEAD OF IT.

WEDNESDAY STILL LOOKS UNSETTLED. RIDGING THROUGHOUT THE LOW
LEVELS CONTINUES TO PRESS EASTWARD GIVING OUR FORECAST AREA AN
INCREASING LOW LEVEL JET AND PLENTY OF THETAE ADVECTION. NAM SHOWS
DEEP ASCENT AND VEERING PROFILES. HOWEVER AT THIS TIME THE WIND
SPEEDS LOOK STRONGER IN THE LOW LEVELS THAN IN THE MID LEVELS...
AND SHORT WAVE ENERGY IS VERY WEAK. BUT CAPPING DOES NOT LOOK TO
BE IN PLACE...SO MULTICELLULAR CONVECTION SHOULD BE AROUND
THROUGH THE ENTIRE DAY. ALMOST WENT LIKELY POPS IN AN AREA BOUNDED
BY HURON...TO MITCHELL...SIOUX FALLS AND BROOKINGS. HOWEVER THERE
IS SOME DISAGREEMENT BETWEEN THE VARIOUS HIRES MODELS ON EXACT
PLACEMENT AND BEST TIMING. IN FACT THE WRF ARW IS NOTICEABLY
ABSENT OF ANY QPF AT ALL WHICH WAS AN OUTLIER WITH THE REST OF THE
HIRES MODELS AND ALSO THE GLOBAL MODELS. BUT DID OPT TO GO
CERTAINTY WORDING IN THE SCATTERED CATEGORY. THIS TIME AROUND...
WITH ANTICIPATED CLOUD COVER...THE COOLER GUIDANCE VALUES SUCH AS
THE MET AND BIAS CORRECTED READINGS LOOKED BETTER THEN THE WARMER
GUIDANCES.

SCATTERED THUNDERSTORMS ARE STILL WARRANTED WEDNESDAY NIGHT AS A
STRONGER SHORT WAVE IS FORECAST TO MOVE RIGHT ACROSS OUR FORECAST
AREA. THIS WAVE WILL INTERACT WITH A VERY STOUT LOW LEVEL JET...30
TO 40 KNOTS...AND INCREASING LOW LEVEL MOISTURE. WIND PROFILES ARE
VERY STRONGLY VEERING...AND WILL MENTION A POSSIBILITY OF LOW END
SEVERE IN THE FORTHCOMING HWO. WITH THE SOUTH WIND FIRMLY IN
PLACE...LOWS WILL BE WARM WITH MANY GUIDANCE VALUES LOOKING TOO
COOL. THE MET...MAV AND ECMWF LOOKED TO HAVE THE BEST HANDLE ON
TEMPERATURES.

THE SHORT WAVE DEPARTS THURSDAY MORNING...GIVING AREAS EAST OF I
29 THE BEST CHANCE FOR RAINFALL BEFORE NOON. THERE DOES NOT APPEAR
TO BE A LOT GOING ON THURSDAY AFTERNOON OTHER THAN REAL SPOTTY
RAIN CHANCES DUE TO PURE INSTABILITY. THE HIGHEST POPS BARELY IN
THE CHANCE CATEGORY ARE WARRANTED IN SOUTHWEST MN WHERE THE 700MB
TEMPERATURES ARE THE COOLEST...AT ABOUT +12C. BUT WEST OF THERE IT
COULD BE REAL TOUGH TO GET ANYTHING GOING DESPITE WARM AND MUGGY
LOW LEVEL AIR. THE SECOND HALF OF THURSDAY NIGHT WILL SEE YET
ANOTHER SHORT WAVE MOVE EASTWARD WHICH WILL GIVE OUR AREA ANOTHER
SHOT AT CONVECTION...POSSIBLY LOW END SEVERE HERE AND THERE.

IN THE EXTENDED PORTION OF THE FORECAST FRIDAY THROUGH MONDAY...IN
GENERAL THE VARIOUS MEDIUM RANGE MODELS ARE IN PRETTY GOOD AGREEMENT
WITH THE LARGE SCALE. THEY CONTINUE TO PLACE THE VERY LARGE UPPER
LOW FOR THIS TIME OF YEAR OVER THE WESTERN U.S. ON FRIDAY...THEN
MOVE IT NORTHEASTWARD AND WEAKEN IT THROUGH THE WEEKEND. WITH A
SOUTHWEST FLOW ALOFT AHEAD OF THE UPPER TROUGH...THE PATTERN DOES
LOOK UNSETTLED AND UNSTABLE. HOWEVER THUNDERSTORM CHANCES WILL
CERTAINLY DEPEND ON THE DEGREE OF CAPPING...WHICH COULD BE PRETTY
SIGNIFICANT IN OUR AREA AT LEAST EARLY IN THE EXTENDED. THE ECMWF
HAS A STOUT +14C AT 700MB OVER OUR FORECAST AREA ON
FRIDAY...THEREFORE LOWERED POPS. THEN THE NEXT SHORT WAVE WHICH
HAS BEEN WELL ADVERTISED BY THE VARIOUS MODELS MOVES ACROSS THE
NORTHERN PLAINS ON FRIDAY NIGHT. THE ECMWF TAKES THE WAVE UP AND
OVER THE CAPPING...GIVING OUR AREA ONLY A GLANCING BLOW THROUGH
OUR NORTHWEST AND NORTH CENTRAL ZONES. THE GFS DIVES IT FURTHER
EASTWARD IMPACTING OUR AREA A LITTLE MORE...WHILE THE GEM GLOBAL
IS WELL TO THE NORTHWEST. IF WE ARE CAPPED...THE RAINFALL WILL
HINGE OF COURSE ON LOW LEVEL BOUNDARIES...WHICH AT THIS TIME LOOK
TO BARELY NUDGE INTO OUR WESTERN ZONES BEFORE STALLING. SO FOR
NOW...KEEPING POPS BELOW THE LIKELY THRESHOLD IS WARRANTED... WITH
DECREASING POPS HEADING SOUTHWARD.

THE ECMWF THEN BRINGS A MORE SIGNIFICANT SHORT WAVE ACROSS OUR
AREA SATURDAY NIGHT AND BELIEVE THIS IS THE MAIN ONE TO WATCH. AS
THE PARENT UPPER LOW EJECTS INTO THE NORTHWESTERN HIGH PLAINS...
MID LEVEL TEMPERATURES COOL IN OUR FORECAST AREA TO +10C TO +12C
AT 700MB...MUCH MORE CONDUCIVE FOR CONVECTION. NOW IF THIS WAVE
QUICKLY EJECTS AS ADVERTISED BY MANY OF THE 00Z MEDIUM RANGE
MODELS...THE CHANCES FOR THUNDERSTORMS WILL DWINDLE SUNDAY THROUGH
MONDAY. SO A GRADUAL LOWERING OF POPS FOR THOSE TWO DAYS MAY BE IN
ORDER WITH UPCOMING FORECASTS.

THEN BEYOND THE EXTENDED...THE GFS AND ECMWF DEVELOP A LARGE UPPER
RIDGE WHICH COULD VERY WELL GIVE US QUIETER WEATHER FOR A WHILE...
QUICKLY LOOKING MORE LIKE A SUMMERTIME PATTERN. THE TEMPERATURES
AND HUMIDITY WILL CERTAINLY FEEL MORE SUMMERLIKE FRIDAY THROUGH
MONDAY...WITH WIDESPREAD 80S TO AROUND 90 COMMON FOR HIGHS...WARM
MUGGY LOWS...AND DEW POINT VALUES WELL INTO THE 60S AND LOWER 70S.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)
ISSUED AT 637 AM CDT TUE JUN 18 2013

VFR SHOULD CONTINUE OVER THE AREA THROUGH 19/12Z. SCATTERED TSRA
MAY AFFECT THE AREA AFTER THAT TIME.

&&

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

$$

SHORT TERM...MJF
LONG TERM...MJF
AVIATION...