000
FXUS63 KFSD 200355
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1055 PM CDT WED JUN 19 2013

.SHORT TERM...(THIS EVENING THROUGH THURSDAY)
ISSUED AT 315 PM CDT WED JUN 19 2013

SHORTWAVE CONTINUES TO WORK ACROSS THE AREA THIS AFTERNOON. MODIFIED
SOUNDINGS SUGGEST CAP SHOULD BE BROKEN BY THIS POINT. HOWEVER
CURRENT CU FIELD IS CLEARLY BEING CHOKED OFF. GUESS IS THAT DRY AIR
ALOFT ENTRAINING INTO THE UPDRAFT...COMBINING WITH SLIGHTLY WARMER
MID LEVEL TEMPS THAN MODELED IS THE CULPRIT. ALSO THE LACK OF ANY LOW
LEVEL FOCUS FOR STORMS TO GET GOING. STILL THINK THE THREAT WARRANTS
ISOLATED TO SCATTERED MENTION IN THE GRIDS THROUGH THIS EVENING...AS
STILL COULD GET SOMETHING AS WE CONTINUE TO DESTABILIZE AHEAD OF THE
COOLING MID LEVEL TEMPERATURES ASSOCIATED WITH THE WAVE. SMALL HAIL
AND WIND GUSTS TO 45 MPH CONTINUE TO BE THE MAIN THREATS WITH ANY
STORM THAT IS ABLE TO FORM. LOW LEVEL JET REALLY PICKS UP TONIGHT
RESULTING IN STRONG THETAE ADVECTION AND ELEVATED THUNDERSTORM
THREAT. MODEL CONSENSUS IS THAT MOST LIKELY AREA FOR THIS CONVECTION
TO FORM WOULD BE NORTH OF OUR CWA CLOSER TO THE NOSE OF THE JET AND
COOLER MID LEVEL TEMPERATURES. IF THIS CONVECTION BECAME ORGANIZED
AND WAS ABLE TO ESTABLISH A SURFACE CONNECTION...IT WOULD FOLLOW THE
CORFIDI VECTORS SOUTH SOUTHEAST INTO OUR CWA. WHILE IF OT STAYS
MAINLY ELEVATED IT WILL FOLLOW MORE OF THE MEAN LAYER WIND AND GO
NORTHEAST. WILL HAVE TO WATCH WHAT CA FORM IN NORTHWEST OR NORTH
CENTRAL SOUTH DAKOTA AS THE LOW LEVEL JET KICKS IN AND HOW IT STARTS
MOVING. BEST CHANCE OF SEEING SOMETHING APPEARS TO BE SOUTHWEST
MINNESOTA BASED ON THE ABOVE POTENTIAL STORM MOTIONS...AND WILL KEEP
THE HIGHER CHANCE POPS THERE.

UNCERTAINTY CONTINUES INTO THURSDAY. SEEMS LIKE WE WILL HAVE TO
DEAL WITH SOME LEFTOVER CLOUD COVER FROM WHATEVER HAPPENS
TONIGHT...AND POSSIBLY SOME STRATOCU THAT FORMS WITH OUR STRONG
SOUTHEAST FLOW. COMBINED THIS WITH A PRETTY DECENT CAP...AND
CONVECTION DURING THE AFTERNOON SEEMS UNLIKELY. 12Z NAM WAS REALLY
THE ONLY MODEL AGGRESSIVE WITH QPF ON THURSDAY...AND EVEN THE NAM HI
RES VERSION IS DRY. THUS WENT AHEAD AND LOWERED POPS. WILL KEEP THE
SLIGHT CHANCE TO CHANCE GIVEN UNCERTAINTY. CAP DOES WEAKEN AS YOU
GET EAST...SO THAT APPEARS TO BE THE AREA THAT WOULD HAVE THE BEST
SHOT. CAPE AND SHEAR PROFILES APPEAR FAVORABLE FOR SEVERE WEATHER IF
A STORM IS ABLE TO FORM...BUT AGAIN THIS SEEMS LIKE A LOWER
PROBABILITY EVENT AT THIS TIME...AT LEAST THROUGH 0Z. HIGHS ARE
TRICKY...AND WILL DEPEND ON CLOUD COVER. OUR PREVIOUS FORECAST WAS
ABOVE CONSENSUS...AND WHILE THIS MAKES ME A LITTLE UNCOMFORTABLE
GIVEN CLOUD COVER CONCERNS...IT DOES NOT TAKE MUCH SUN FOR OUR TEMPS
TO JUMP RAPIDLY. THUS ENDED UP NOT CHANGING THE GOING FORECAST MUCH
AT ALL WITH REGARDS TO TEMPERATURES.

.LONG TERM...(THURSDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 315 PM CDT WED JUN 19 2013

THURSDAY NIGHT SHOULD SEE A FEW THUNDERSTORMS DEVELOP IN ACROSS THE
AREA WITH THE BETTER CHANCE IN SOUTHWEST MINNESOTA. CAPPING WILL
LIKELY PLAY A ROLE IN KEEPING THUNDERSTORMS AT BAY SO ONLY LOW POPS
OVER THE WESTERN AND SOUTHERN PARTS OF THE CWA. PARTS OF SOUTHWEST
MINNESOTA MAY BE FIGHTING OFF A WORKED OVER ATMOSPHERE BUT IF SOME
DECENT HEATING CAN OCCUR CAPE...AROUND 2000 J/KG AND SFC TO 3 KM
BULK SHEAR VALUES OF ABOUT 30 TO 35 KNOTS WOULD SUPPORT A FEW SEVERE
THUNDERSTORMS. OTHERWISE BREEZY AND A BIT HUMID WITH LOWS FROM THE
UPPER 60S TO LOWER 70S.

BY FRIDAY THE BETTER CHANCES FOR THUNDERSTORMS WILL BE IN THE FAR
EASTERN CWA NEAR THE INSTABILITY AXIS AND THE VEERED LOW LEVEL JET
WHILE ANOTHER CHANCE WILL EXIST NEAR AND BEHIND THE FRONT IN THE FAR
WESTERN CWA. BY LATE AFTERNOON AND EARLY EVENING THE ATMOSPHERE
BECOMES FAVORABLE FOR SEVERE THUNDERSTORMS...ESPECIALLY IN THE
NORTHERN CWA WHERE THE CAP IS MUCH LOWER. CAPE VALUES LIKELY TO
APPROACH 3000 J/KG WITH SHEAR VALUES NOT OVERLY IMPRESSIVE.
REGARDLESS EXPECT A FEW SEVERE STORMS NORTH OF INTERSTATE 90 LATE
FRIDAY AFTERNOON AND FRIDAY NIGHT AS +14 AT 700MB LIKELY TO BE A
LITTLE TOO WARM IN THE SOUTH TO ALLOW ANY UPDRAFTS TO GET GOING.
HIGHS FRIDAY FROM NEAR 95 IN SIOUX CITY TO THE MID 80S ALONG HIGHWAY
14. LOWS FRIDAY NIGHT AGAIN VERY WARM AND MAINLY UPPER 60S TO LOWER
70S.

WILL CONTINUE THE THOUGHTS THAT MOST OF THE ACTIVITY WILL BE NORTH
AND WEST OF THE AREA ON SATURDAY WITH A BURLY CAP IN PLACE AND THE
AREA BEGINNING TO GET INTO MORE OF A DEEP SOUTHERLY FLOW REGIME WITH
LITTLE CONVERGENCE. THE BETTER CHANCES WILL BE ALONG A FRONT IN
CENTRAL SOUTH DAKOTA. WILL GO WITH HOT AND BREEZY CONDITIONS...HIGHS
FROM THE MID 80S T MID 90S...THEN LOWS AGAIN SATURDAY NIGHT UPPER
60S TO LOWER 70S.

FOR THE PERIOD SUNDAY THROUGH WEDNESDAY...AN UPPER LEVEL WAVE WILL
PASS NORTH OF THE AREA SUNDAY NIGHT INTO MONDAY WHICH WILL CONTINUE
THE THREAT FOR A FEW THUNDERSTORMS. AFTER THIS THE MODELS BEGIN TO
DIVERGE A BIT BUT STILL SUPPORT A RELATIVELY FAST WEST TO SOUTHWEST
FLOW ALOFT ACROSS NORTH DAKOTA INTO SOUTHERN CANADA. THIS SHOULD
START TO DECREASE THE THREAT FOR THUNDERSTORMS A BIT AS THE AREA
COULD GET DEEPER INTO THE WARM AND DRY AIR ALOFT. HOWEVER THE GFS
AND ECMWF BOTH BRING A WAVE THROUGH MONDAY NIGHT...MORE VIGOROUS ON
THE GFS...SO NO GREAT CERTAINTY THAT IT WILL BE DRY.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 1055 PM CDT WED JUN 19 2013

ISOLATED THUNDERSTORMS WILL BE POSSIBLE ACROSS THE AREA THROUGH THE
PERIOD...WITH BETTER CHANCES FAVORING AREAS ALONG AND EAST OF THE
JAMES RIVER. MVFR-IFR VISIBILITY WILL BE POSSIBLE WITH ANY STORMS
THAT DO DEVELOP...WITH MVFR CEILINGS ALSO POSSIBLE WITH STORMS
DURING THE DAY THURSDAY. HOWEVER CONFIDENCE IN TIMING/COVERAGE OF
STORMS AFFECTING SPECIFIC TAF LOCATIONS IS TOO LOW TO INCLUDE TSRA
MENTION IN TAFS AT THIS TIME.

MODELS SHOWING SOME INCREASE IN SUB-3000FT MOISTURE THROUGH THE
EARLY MORNING HOURS THURSDAY...BUT WITH NO HINT OF STRATOCU WITHIN
THIS LAYER CURRENTLY UPSTREAM...WILL GO WITH JUST SCATTERED 2-3KFT
LAYER THROUGH THE MORNING. BY AFTERNOON...BROKEN CEILING MAY DEVELOP
WITH ADDITIONAL HEATING...BUT CURRENTLY EXPECT THIS TO BE JUST ABOVE
3KFT.

FINALLY...LOW LEVEL JET ACROSS THE AREA TONIGHT COULD LEAD TO A
PERIOD OF LLWS BETWEEN SOUTHEAST SURFACE WINDS AND MORE SOUTHERLY
WINDS ABOVE INVERSION. WILL HAVE LLWS AT KHON WHERE THE CORE OF THE
LOW LEVEL JET WILL BE STRONGEST THROUGH THE FIRST FEW HOURS OF THE
TAF PERIOD.

&&

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

&&

$$

SHORT TERM...CHENARD
LONG TERM...08
AVIATION...JH