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000
FXUS63 KFSD 140219
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
919 PM CDT THU JUN 13 2013

.UPDATE...
ISSUED AT 919 PM CDT THU JUN 13 2013

MAIN CHANGE TO FORECAST INVOLVES PRECIPITATION CHANCES. FOR THIS
EVENING...DO EXPECT LIGHT SHOWERS/THUNDERSTORMS TO PERSIST IN NW
IA UNTIL ABOUT MID NIGHT. THIS IS ASSOCIATED WITH A WEAK 700 MB
FRONT.

FARTHER WEST...AM GOING TO DELAY CONVECTIVE CHANCES WEST OF I29
UNTIL AFTER 06Z AND REALLY NOT GO ABOVE A 20 PERCENT UNTIL AFTER
09Z. THE UPPER LEVEL WAVE IS WELL TO THE WEST YET AND AS A RESULT
THE STEEPER LAPSE RATES DO NOT ARRIVE INTO THE JAMES VALLEY UNTIL
06Z. OF EVEN GREATER CONCERN THE LOW LEVEL JET DOES NOT REALLY
INCREASE UNTIL AFTER 06Z. AS A RESULTS THE BEST THETA-E ADVECTION
IS NOT UNTIL ALMOST 12Z. BOTH RAP AND HRRR ARE MUCH SLOWER IN
DEVELOPING CONVECTION. IN FACT THE RAP HAS ALMOST NO CONVECTION
UNTIL AFTER 12Z. THAT MAY BE A LITTLE TOO SLOW GIVEN MUCAPES OF
1000 TO 1500 J/KG AND CIN NEAR ZERO AT KFSD BY 12Z AND APPROACHING
WEAK WAVE. CURRENT MENTION OF NICKEL TO HALF-DOLLAR SIZE HAIL IN
HWO FOR LATE TONIGHT AND TOMORROW SEEMS REASONABLE GIVEN AMOUNT OF
CAPE AVAILABLE TO STORMS...EVEN WITH EFFECTIVE SHEAR AROUND 20 KTS
FOR MORNING CONVECTION. TEMPERATURES LOOK ON TRACK FOR TONIGHT.

GRIDS UPDATED AND WILL UPDATE HWO SHORTLY TO SLOW DOWN TIMING OF
CONVECTION.

&&

.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 405 PM CDT THU JUN 13 2013

ISOLATED SHOWERS AND THUNDERSTORMS THIS AFTERNOON WILL PASS OVER THE
AREA FROM SIOUX CITY TO STORM LAKE AND SOUTH WITH LITTLE FANFARE.
LATER TONIGHT IN AXIS OF INCREASING MOISTURE AND
INSTABILITY...ISOLATED STORMS ARE EXPECTED TO DEVELOP OVER MORE OF
THE AREA AND MOVE FROM WEST TO EAST...PROBABLY BECOMING SCATTERED BY
DAYBREAK IN THE EAST. AIR STILL DOES NOT LOOK UNSTABLE ENOUGH GIVEN
AVAILABLE MOISTURE AND MEAGER LIFT TO PRODUCE SEVERE WEATHER...BUT
SOME LATE COULD PUT DOWN SOME SMALL HAIL. THIS ACTIVITY WILL BE ONLY
SLOWLY INCREASING AS IT MOVES EAST INTO BETTER AREA OF THERMAL LIFT.
HOWEVER...INSTEAD OF DECREASING FRIDAY MORNING AS NOCTURNAL ACTIVITY
OFTEN DOES...EXPECT A CONTINUED SLOW INCREASE IN COVERAGE BECAUSE OF
INCREASING DYNAMIC SUPPORT AS WAVE AND SURFACE BOUNDARY APPROACH.
NIGHTTIME ACTIVITY HAS LITTLE SUPPORT FROM LOW LEVEL JET WHICH
DEVELOPS STRONGLY TO THE WEST OF OUR AREA...BUT EVEN THOUGH EXPECTED
TO DECREASE FRIDAY...IT WILL THEN BE MOVING INTO OUR AREA...SO
EXPECT SCATTERED ELEVATED STORMS TO CONTINUE DEVELOPING AT A TIME
WHEN THEY WOULD NORMALLY BE DECREASING. THE QUESTION REMAINS AT WHAT
TIME LATE IN THE DAY THE STORMS COULD BECOME MORE SURFACE BASED OR
WHETHER THEY EVEN WILL. HOWEVER...INSTABILITY SEEMS ENOUGH BY MIDDAY
FRIDAY FOR EVEN THESE ELEVATED STORMS TO PRODUCE ISOLATED SEVERE
HAIL REPORTS. TEMPERATURES TONIGHT AND FRIDAY WILL BE KEPT CLOSE TO
WHAT WE HAVE BEEN GOING FOR...A LITTLE COOLER THAN GUIDANCE IN THE
EAST DUE TO THE EXPECTED CLOUD COVER AND SCATTERED CONVECTION. WINDS
WILL INCREASE TO BREEZY LEVELS IN THE EAST FOR A WHILE FRIDAY AHEAD
OF SURFACE TROUGH/OCCLUDED FRONT.

.LONG TERM...(FRIDAY NIGHT THROUGH THURSDAY)
ISSUED AT 405 PM CDT THU JUN 13 2013

QUESTION FOR FRIDAY EVENING INTO THE OVERNIGHT IS WHETHER SURFACE
BASED CONVECTION FIRES ALONG THE APPROACHING FRONT...AND IF IT
DOES...WHEN AND WHERE. ELEVATED ACTIVITY ONGOING ACROSS OUR EAST
DURING THE AFTERNOON WILL LIKELY HINDER SURFACE HEATING SOMEWHAT.
ALSO A STRONG CAP IS FORECAST TO BE IN PLACE...ALTHOUGH THIS SHOULD
GRADUALLY BE ERODED AS COOLER MID LEVEL TEMPERATURES MOVE INTO THE
AREA. BEST UPPER FORCING WITH THE MAIN WAVE WILL STAY WELL TO OUR
NORTH. MEANWHILE BEST FRONTOGENETICAL FORCING LOOKS TO BE FOCUSED
ACROSS CENTRAL NEBRASKA. GIVEN THIS...COMBINED WITH UNCERTAINTY ON
HOW MUCH HEATING WE GET DURING THE DAY...SEEMS LIKE MOST LIKELY
SOLUTION HAS ONE AREA OF SHOWERS AND STORMS FORM NORTH OF OUR CWA
WITH THE BETTER UPPER LEVEL FORCING. AND ANOTHER AREA FORM IN SOUTH
CENTRAL NEBRASKA ALONG THE STRONGER PORTION OF THE
BOUNDARY...LEAVING OUR CWA IN THE MIDDLE. SUBTLE SIGNS THAT A
SECONDARY WAVE MAY EJECT OUT OF THE COLORADO ROCKIES DURING THE
AFTERNOON...WHICH MAY AID IN THE NEBRASKA DEVELOPMENT. EXPECT THIS
ACTIVITY TO THEN POTENTIALLY INCREASE NORTHEAST ALONG THE FRONT...AS
THE SECONDARY WAVE EJECTS EAST AND CAPPING WEAKENS DUE TO HEATING
AND COOLING ALOFT. QUESTION IS HOW FAR NORTH THIS CONVECTION GETS.
INDIVIDUAL STORM MOTION WILL TEND TO BE ALMOST DUE EASTERLY...THUS
THE BEST CHANCE WILL PROBABLY END UP ACROSS NORTHWEST IOWA AND
EXTREME SOUTHEAST SOUTH DAKOTA IN THE EVENING INTO THE OVERNIGHT.
STORMS WOULD INITIALLY BE SUPERCELLS BEFORE PROBABLY BECOMING MORE OF
A CLUSTER...WITH LARGE HAIL AND STRONG WINDS THE MAIN THREAT...BUT
GIVEN LOW LEVEL WIND FIELDS AN ISOLATED TORNADO WOULD ALSO BE
POSSIBLE IF STORMS GET INTO OUR AREA EARLY ENOUGH. FURTHER NORTH THE
THREAT SEEMS LOWER. HOWEVER WILL HAVE TO KEEP AN EYE ON THINGS...AS
IF AN ISOLATED STORM IS ABLE TO FORM ALONG THE FRONT NEAR THE JAMES
RIVER...IT WOULD LIKELY BECOME SUPERCELLUAR WITH CAPE AROUND 2000
J/KG AND DEEP LAYER SHEAR OF 40 OR MORE KTS.

SATURDAY SEES THE FRONT LIKELY TO OUR SOUTH. BUT DECENT UPPER
SUPPORT IN THE RIGHT ENTRANCE OF A STRONG UPPER JET IS EXPECTED.
MODELS ALSO SUGGEST THAT LOW TO MODERATE INSTABILITY MAY LINGER
ALONG AND SOUTH OF INTERSTATE 90. THUS WHILE IT WOULD SEEM LIKELY
THAT THE GREATEST THUNDERSTORM COVERAGE WILL REMAIN SOUTH IN THE
VICINITY OF THE FRONT...CAN NOT RULE OT ISOLATED TO SCATTERED
ACTIVITY SOUTH OF INTERSTATE 90. AGAIN SHEAR PROFILES WOULD SUPPORT A
LARGE HAIL AND WIND THREAT WITH ANY STORM THAT DOES FORM. HIGHS
DEPENDENT ON CLOUD COVER AND COVERAGE OF SHOWERS AND STORMS...BUT
NEAR SEASONABLE READINGS IN THE UPPER 70S TO LOW 80S SEEM PROBABLE.

ON SUNDAY A STRONGER WAVE WILL EJECT SOUTHEAST OUT OF CANADA AND
INTO THE FAR NORTHERN PLAINS. STILL UNCERTAINTY ON AVAILABLE
MOISTURE AND WHERE THE BEST FORCING ENDS UP. WIND FIELDS WOULD
SUGGEST A SEVERE THREAT WITH ANY STORMS THAT COULD FORM...BUT AGAIN
LATEST INDICATIONS ARE THAT THE BEST THREAT MAY END UP SOUTH OF US.
BUT SOMETHING TO KEEP AN EYE ON. HIGHS PROBABLY A COUPLE DEGREES
WARMER ON SUNDAY...BUT STILL AROUND OR JUST SLIGHTLY ABOVE AVERAGE.

DRIER AND COOLER AIR MOVES IN ON MONDAY BEHIND THE WAVE. MODELS
COMING IN A BIT COOLER ALOFT...AND THUS HIGHS LOOK LIKE THEY WILL
END UP AT LEAST A FEW DEGREES BELOW SEASONABLE NORMALS...WITH MID TO
UPPER 70S EXPECTED. RIDGING THEN BEGINS TO BUILD IN TUESDAY INTO
THURSDAY. ALTHOUGH LATEST RUNS SLOW THIS DOWN A BIT...SUGGESTING
SLIGHTLY COOLER HIGHS POSSIBLE. EITHER WAY EXPECTING READINGS
AROUND AVERAGE THROUGH THURSDAY...WITH A SLOW WARMING TREND EACH
DAY. RIDGE AXIS SHOULD MOVE OVERHEAD AROUND WEDNESDAY. UNCERTAINTY
ON TIMING AND PLACEMENT OF SUBTLE WAVES RIDING OVER THE RIDGE...BUT
THE SETUP WOULD SUGGEST AT LEAST THE MENTION OF A RETURN OF ISOLATED
SHOWERS AND THUNDERSTORMS ANYTIME LATER WEDNESDAY INTO THURSDAY.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z FRIDAY EVENING)
ISSUED AT 633 PM CDT THU JUN 13 2013

THUNDERSTORMS IN THE VICINITY OF KSUX AT 23Z WILL BE MOVING
SOUTHEAST OF THERE BY 01-02Z. OTHERWISE VFR CONDITIONS THROUGH EARLY
FRIDAY MORNING. EXPECT SCATTERED SHOWERS AND THUNDERSTORMS...MAINLY
SOUTH OF INTERSTATE 90 FROM AROUND 09Z-15Z...AND THEN ANOTHER ROUND
OF THUNDERSTORMS TO DEVELOP FRIDAY AFTERNOON...BUT THESE WILL BE
MAINLY EAST OF INTERSTATE 29.


&&

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

$$

UPDATE...SCHUMACHER
SHORT TERM...
LONG TERM...CHENARD
AVIATION...MG