Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 240923
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
423 AM CDT FRI JUL 24 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 422 AM CDT FRI JUL 24 2015

HEAT...HUMIDITY AND THUNDERSTORMS WILL BE THE MAIN FOCUS THE NEXT 24
HOURS. UPPER LEVEL SUPPORT PUSHING EAST OF THE AREA WITH THE TAIL END
REMAINING OVER PARTS OF MAINLY NORTHWEST IOWA THROUGH THE MORNING
INTO THE EARLY AFTERNOON. BEHIND THIS UPPER LEVEL SUPPORT MID LEVEL
LAPSE RATES ARE PRETTY STEEP AND GRADUALLY SINK SOUTH THROUGH THE
MORNING. WILL HAVE TO KEEP AN EYE ON THIS AS SOME WEAK SHOWERS AND
THUNDERSTORM ACTIVITY WAS DEVELOPING JUST NORTH OF THE AREA WITHIN
THIS AXIS. BY MID TO LATE AFTERNOON A WEAK COOL FRONT IN CENTRAL
SOUTH DAKOTA EARLY THIS MORNING WILL BE IN SOUTHERN PARTS OF
NORTHWEST IOWA AND COULD PROVIDE THE FOCUS FOR ISOLATED
THUNDERSTORMS...OF FEW OF WHICH COULD BE SEVERE. WHILE THE CAP WILL
LIKELY HOLD IF SOMETHING CAN DEVELOP 4000 J/KG CAPE WOULD SEE
POTENTIAL FOR HEN EGG HAIL AND WIND GUSTS TO 70 MPH.

BY TONIGHT THE AXIS OF INSTABILITY AND LOW LEVEL BOUNDARY WILL BE
IN THE FAR SOUTHERN CWA AND WILL CONTINUE THE THREAT FOR
THUNDERSTORMS MAINLY ALONG THE MISSOURI RIVER VALLEY. INSTABILITY
NOT TOO IMPRESSIVE AT THIS TIME SO NOT EXPECTING SEVERE WEATHER
AFTER DARK.

AS FOR HEAT...WITH DEW POINTS IN THE MID 70S EXPECTED OVER NORTHWEST
IOWA AND TEMPERATURES INTO THE 90S WILL CONTINUE THE HEAT ADVISORY
IN THAT AREA.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 422 AM CDT FRI JUL 24 2015

WILL LIKELY SEE A FEW STORMS WANDERING THE ELEVATED INSTABILITY
GRADIENT ON SATURDAY MORNING ALONG THE MISSOURI RIVER CORRIDOR.
INSTABILITY IS NOT TREMENDOUS...AND EFFECTIVE SHEAR FOR THE
START OF THE DAY REMAINS SOMEWHAT MEAGER. HOWEVER...BROAD FLAT
RIDGE WILL FIND ITSELF FLATTENED MORE WITH FLOW IN THE LOWER TO
MID LEVEL STRENGTHENING TOWARD THE END OF THE DAY BY APPROACH OF
WAVE. ECMWF/NAM ARE A BIT FASTER THE WAVE COMPARED TO GFS...WHICH
HELP TO IGNITE MORE IN THE WAY OF CONVECTION ALONG THE BOUNDARY
THROUGH THE SOUTHWEST HALF OF THE AREA DURING THE LATER MORNING
AND EARLY AFTERNOON. LESSER CONVECTION FOUND IN GFS AND END OF
WRF-ARW RUN...ALLOWING THE INCREASE IN NEAR SURFACE MOISTURE TO
INCREASE POTENTIAL INSTABILITY TO NEAR 2000 J/KG. DEEP LAYER SHEAR
IS FORMIDABLE FOR LATE JULY STANDARDS...40 TO 50 KNOTS...AND
EXHIBITS POTENTIAL FOR A WELL DISTRIBUTED SHEAR PROFILE. POTENTIAL
FOR THIS COMBINATION OF PARAMETERS SUGGESTS CONCERN WARRANTED FOR
A HIGHER END SEVERE WEATHER THREAT...HIGHLY ORGANIZED STORMS
DRIVEN BY A WELL DEFINED WAVE MOVING THROUGH THE RIDGE. ABOUT THE
ONLY REASON THAT CANNOT BE MORE DEFINITIVE ON SEVERE THREAT IS THE
VARIOUS TIMING ON WAVE...AND THE POTENTIAL IMPACT FROM CONVECTION
IN THE MID LEVEL BOUNDARY TO THE SOUTH THROUGH THE MORNING HOURS.
IF THIS CONVECTION PERSISTS OR BECOMES MORE WIDESPREAD...IMPACT OF
CLOUDS AND COOLING WILL KEEP MAIN LOWER LEVEL BOUNDARY TO THE
SOUTH...AS WELL AS THE BETTER LOWER LEVEL SHEAR. SEVERAL SOLUTIONS
INDICATE THIS TO BE THE POSSIBILITY...LEAVING THE BETTER FORCING
TO COME IN WITH THE DEEPER CONVERGENCE FROM THE NORTH/WEST LATER
IN THE EVENING AND THE OVERNIGHT...POSSIBLY EVOLVING AS ANOTHER
LATER NIGHT HIGHER END WIND EVENT. IT WILL DEFINITELY WARRANT SOME
ATTENTION AS THE MANY SUBTLE DETAILS WORK OUT OVER THE NEXT 24
HOURS...BUT THE UPGRADE TO AT LEAST THE SLIGHT RISK IS WELL
WARRANTED.

HEIGHTS WILL REBUILD ON SUNDAY ACROSS THE AREA...WITH TEMPS ALOFT
CONTINUING TO WARM. LINGERING MAINLY EARLY DAY RUMBLES EXITING
EASTERN CWA DURING THE MORNING. IN THE WAKE...MAY HAVE A LITTLE
ISSUE WITH LOW LEVEL MOISTURE TRAPPED TO PRODUCE A CAPPED
STRATOCUMULUS FIELD...BUT EVEN WITH LIMITED SUNSHINE SHOULD SHAKE
OUT TO BE A STEAMY DAY WITH HIGHS IN THE UPPER 80S TO LOWER 90S.
INCREASING MID LEVEL LAPSE RATES AND LOW LEVEL JET BY LATER
SUNDAY NIGHT...FOR EVER SO SMALL CHANCE OF A THUNDERSTORM ALONG
THE NORTHWEST PERIPHERY OF THE CWA. BREEZY...HOT AND HUMID THE
MAIN MESSAGE FOR MONDAY...WITH HIGHS UP A FEW DEGREES...AND THE
HEAT INDEX CLOSING ON 100 DEGREES MANY AREAS.

HARD TO PICTURE MUCH OF A POTENTIAL FOR CONVECTION EVEN YET ON
MONDAY NIGHT...AS WILL BE RESIDENT IN THE WARMEST LAYER ALOFT...
AND ANY MEANINGFUL CONVERGENCE OF THE LOWER TO MID LEVEL WIND
FIELD DISPLACED WELL TO THE NORTH. FRONT MAY BE KNOCKING ON THE
DOOR OF THE FAR WESTERN CWA...AND PERHAPS JUST ENOUGH THREAT FOR
HIGH PLAINS DEVELOPMENT TO BE CLOSE ENOUGH FOR A FAR WESTERN CWA
SMALL THUNDER THREAT LATER AT NIGHT.

TUESDAY...WILL START TO SEE THE IMPACTS OF AN UNSEASONABLY STRONG
WAVE MOVING ALONG THE INTERNATIONAL BORDER. AS A RESULT OF THIS
SYSTEM...A FAIRLY STRONG FRONTAL BOUNDARY WILL SWEEP THROUGH THE
PLAINS. WILL SEE LOW LEVEL WINDS TAKE ON A SOUTHWEST DIRECTION
WITH GOOD PREFRONTAL WARM SURGE. GUIDANCE IS FAR TOO COOL FOR THIS
REGIME...AND HAVE COORDINATED A 5 TO 8 DEGREE RISE FOR THE
SOUTHEAST HALF OF THE AREA...TAPERING OFF BACK TO THE NORTHWEST
WHERE THE FRONT WILL ARRIVE EARLIER IN THE DAY. BOUNDARY IS
PUSHING OUT WELL AHEAD OF THE MID LEVEL COOLING THUS VERY
CAPPED...WITH ONLY A SMALL PROBABILITY OF BREAKING TOWARD THE
SOUTH AND EAST LATE DAY...A BIT BETTER EARLY EVENING. COOLER AND
MUCH DRIER CONDITIONS TO FOLLOW FOR WEDNESDAY AND THURSDAY.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1138 PM CDT THU JUL 23 2015

TSRA THROUGH 12Z EXPECTED TO STAY NORTH AND NORTHEAST OF FSD AND
NOT AFFECT TAF SITES. OTHERWISE AREAS OF CEILINGS AOB 1K FEET AND
VISIBILITIES 3-5SM IN FOG WILL BE OVER SOUTHEAST HALF OF AREA 09Z
THROUGH 15Z...POSSIBLY AFFECTING KSUX AND KFSD. A FEW CEILINGS
1-3K FEET WILL LINGER IN THE SAME AREA THROUGH 18Z. GENERALLY VFR
NORTHWEST HALF OF AREA THROUGH THE PERIOD...AND OVER ALL OF THE
AREA AFTER 18Z...EXCEPT FOR ISOLATED TO SCATTERED TSRA IN
NORTHWEST IA 22Z-25/06Z.


&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...HEAT ADVISORY FROM 2 PM THIS AFTERNOON TO 7 PM CDT THIS EVENING
     FOR SDZ070-071.

MN...NONE.
IA...HEAT ADVISORY FROM 2 PM THIS AFTERNOON TO 7 PM CDT THIS EVENING
     FOR IAZ012>014-020>022-031-032.

NE...HEAT ADVISORY FROM 2 PM THIS AFTERNOON TO 7 PM CDT THIS EVENING
     FOR NEZ013-014.

&&

$$

SHORT TERM...08
LONG TERM...CHAPMAN
AVIATION...



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