000
FXUS63 KFSD 130346
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1046 PM CDT WED JUN 12 2013

.SHORT TERM...(THIS EVENING THROUGH THURSDAY)
ISSUED AT 409 PM CDT WED JUN 12 2013

SCATTERED TO NUMEROUS SHOWERS ASSOCIATED WITH UPPER LOW PULLING
ACROSS THE NORTH SIDE OF OUR AREA WILL DECREASE STEADILY THE REST OF
THE AFTERNOON AND EARLY EVENING. THEY REACH DOWN TO THE FSD AREA AND
INTO PART OF NORTHWEST IA WHERE THY ARE ISOLATED. THE LOW WILL PULL
OUT STEADILY DURING THE EVENING AND AFTER THE SHOWERS ARE TOTALLY
OUT...BY SHORTLY AFTER SUNSET...STEADY CLEARING SHOULD TAKE PLACE
FROM THE WEST. NORTHERLY WINDS WILL SLOWLY BUT STEADILY DECREASE AND
TEMPERATURES WILL COOL INTO THE LOW TO MID 50S. AT THIS TIME DO NOT
EXPECT WINDS TO LIGHTEN UP LONG ENOUGH BEFORE DAYBREAK TO MENTION
ANY FOG...ESPECIALLY CONSIDERING SOME LOW LEVEL DRYING WILL BE
TAKING PLACE. THURSDAY SHOULD BE MOSTLY SUNNY...WITH PERHAPS THE
BEGINNINGS OF INCREASING CLOUDS WEST LATE IN THE DAY. NEAR SEASONAL
TEMPERATURES AND LIGHT WINDS WILL MAKE THURSDAY A PLEASANT OUTDOOR
DAY.

.LONG TERM...(THURSDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 409 PM CDT WED JUN 12 2013

INCREASING THETAE ADVECTION AND ISENTROPIC LIFT THURSDAY NIGHT WILL
LEAD TO AN INCREASE IN CLOUDINESS AND PRODUCE ISOLATED TO SCATTERED
ELEVATED SHOWERS AND THUNDERSTORMS. STILL SOME UNCERTAINTY ON THE
AMOUNT OF ELEVATED INSTABILITY THAT WILL BE AVAILABLE. THE NAM IS ON
THE HIGH END...SUGGESTING AROUND 2000 J/KG. THIS COMBINED WITH
EFFECTIVE SHEAR AROUND 30 TO 40 KTS WOULD PROBABLY BE ENOUGH FOR
MARGINAL SEVERE HAIL PRODUCING STORMS. HOWEVER GIVEN
UNCERTAINTY ON AMOUNT OF INSTABILITY...BEST CALL AT THIS POINT IS
PROBABLY THAT WE WILL SEE AN INCREASING CHANCE OF STORMS OVERNIGHT
INTO FRIDAY MORNING...WITH A FEW POTENTIALLY PRODUCING MARGINALLY
SEVERE HAIL.

FRIDAY IS A BIT TRICKY WITH ELEVATED CONVECTION LIKELY ONGOING IN
THE MORNING...ESPECIALLY ACROSS OUR EAST. ATTENTION THEN TURNS TO AN
APPROACHING COLD FRONT. STRONG CAPPING WILL EXIST OVER THE CWA...SO
THE QUESTION BECOMES CAN HEATING AND THE APPROACHING FRONT BREAK THE
CAP. MOST MODEL SOLUTIONS CURRENTLY HOLD THE CAP ACROSS OUR CWA.
SHORTWAVE SEEMS TO LAG THE FRONT...NOT ADDING MUCH IN THE WAY OF
SUPPORT. BEST LOW LEVEL FRONTOGENESIS SEEMS TO FOCUS SOUTH OF US AS
WELL. THUS MOST THINGS SUGGEST THE ATMOSPHERE MAY STAY CAPPED.
HOWEVER IF SOMETHING IS ABLE TO FORM NEAR THE JAMES RIVER THEY WOULD
LIKELY BE SEVERE...WITH SHEAR AND CAPE SUPPORTIVE OF SUPERCELLS.
WILL KEEP IN CHANCE POPS FOR NOW GIVEN UNCERTAINTY. BY FRIDAY NIGHT
DRIER AIR BEGINS TO WORK INTO OUR AREA ALOFT...WITH THE BEST THETAE
ADVECTION OFF TO OUR EAST. THUS ITS LOOKING MORE LIKELY THAT ANY
NOCTURNAL CONVECTION WOULD GET GOING IN OUR EAST AND QUICKLY MOVE
OUT OF OUR CWA.

BY SATURDAY THE FRONTAL BOUNDARY SHOULD BE TO OUR SOUTH. HOWEVER LOW
LEVEL MOISTURE SEEMS TO LAG BEHIND THE FRONT. SO AGAIN THE QUESTION
IS WHETHER THE CAP BREAKS. NOT MUCH IN THE WAY OF A WAVE...BUT UPPER
LEVEL DIVQ SUGGESTS AN ENVIRONMENT THAT IS MORE SUPPORTIVE THAN NOT
FOR DEVELOPMENT...PROBABLY DUE TO DECENT POSITIONING IN THE RIGHT
ENTRANCE REGION OF AN UPPER JET. THE BETTER CHANCE FOR STORMS WILL
PROBABLY END UP TO OUR SOUTH CLOSER TO THE VICINITY OF THE FRONT.
HOWEVER THE EC AND GFS BOTH KEEP AT LEAST 1000 J/KG OF CAPE OVER ALL
BUT OUR FAR NORTH. THE NAM IS QUICKER WITH THE DRY AIR
INTRUSION...PRETTY MUCH ELIMINATING ANY INSTABILITY. WITH A WEAKER
CAP WE MAY BE ABLE TO BREAK IT...BUT THE LACK OF A TRIGGER
MECHANISM WOULD MAKE ME WORRIED. ALL SAID...WILL KEEP IN SLIGHT TO
CHANCE POPS. AGAIN SHEAR WOULD SUGGEST SUPERCELLS WOULD BE POSSIBLE
IF ANYTHING DOES FORM. SO WILL HAVE TO WATCH TRENDS. HIGHS NEAR
AVERAGE EXPECTED...UPPER 70S TO LOW 80S.

STRONGER WAVE MOVES THROUGH ON SUNDAY. WILL KEEP CHANCE
POPS...ALTHOUGH LATEST INDICATIONS ARE THAT THE BEST FORCING WILL
SPLIT US. WITH ONE AREA OF SHOWERS WITH THE MAIN WAVE NEAR THE
CANADIAN BORDER...AND AN AREA OF THUNDERSTORMS CLOSER TO THE GREATER
INSTABILITY OVER NEBRASKA. SEVERE THREAT AGAIN SEEMS POSSIBLE WITH
THESE SOUTHERN STORMS...BUT IF TRENDS CONTINUE THIS WOULD END UP
SOUTH OF OUR CWA. TEMPS MAY END UP A FEW DEGREES WARMER THAN
SATURDAY.

DRYING AND A QUICK COOL SHOT BEHIND THE WAVE ON MONDAY...ALTHOUGH
ONLY TO A FEW DEGREES BELOW NORMAL...MID 70S TO LOW 80S. RIDGING
THEN BEGINS TO BUILD BACK IN TUESDAY INTO WEDNESDAY...WITH HIGHS
RETURNING INTO THE THE NEAR AVERAGE RANGE. FOR NOW WILL KEEP THE
FORECAST DRY...ALTHOUGH AS THE RIDGE AXIS GETS CLOSER WE MAY GET
INTO A SMALL ELEVATED THUNDERSTORM RISK BY LATER TUESDAY INTO
WEDNESDAY...BUT PROBABILITIES TOO LOW TO PUT IN FORECAST THIS FAR
OUT.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 1046 PM CDT WED JUN 12 2013

VFR CONDITIONS ARE EXPECTED TO PREVAIL THROUGH THE TAF PERIOD.
HIGH PRESSURE WILL CONTINUE TO BUILD ACROSS THE EASTERN THIRD OF
SOUTH DAKOTA. PATCHY RADIATIONAL FOG MAY DEVELOP ACROSS SOUTHEAST
SOUTH DAKOTA DESPITE THE DRY AIRMASS IN PLACE...AND HAVE
INTRODUCED SOME LIGHT FOG TO THE KHON TAF FOR LATE TONIGHT WHERE
WINDS WILL BE THE LIGHTEST. WINDS WILL INCREASE OUT OF THE EAST
FOR THURSDAY AHEAD OF AN APPROACHING WARM FRONT. SOME VFR CUMULUS
DEVELOPMENT IS EXPECTED DURING PEAK HEATING AS WELL THURSDAY.

&&

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

$$

SHORT TERM...
LONG TERM...CHENARD
AVIATION...