Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 201147
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
647 AM CDT SUN APR 20 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 403 AM CDT SUN APR 20 2014

THUS FAR SEEING LITTLE MORE THAN VERY LIGHT ECHOES DEVELOP ALONG
STATIONARY BOUNDARY IN OUR FAR SOUTHEAST CWA...INDICATIVE OF MEAGER
LIFT IN SPLIT FLOW PATTERN ALOFT. AS A RESULT...HAVE TRIMMED BACK
POPS TO JUST 20-30 PERCENT THROUGH THE EARLY MORNING HOURS...THEN
ENDING ALTOGETHER MID-LATE MORNING AS MID LEVEL RIDGING DIMINISHES
LIFT EVEN FURTHER. BOUNDARY REMAINS IN THE SOUTHEAST THROUGH THE
AFTERNOON...BUT BECOMES MORE DIFFUSE AS IT LIFTS A BIT FURTHER TO
THE NORTHWEST AHEAD OF SUBTLE LOW PRESSURE AND NORTH-SOUTH TROUGH
PUSHING INTO CENTRAL DAKOTAS. MOISTURE INCREASING ALONG THE BOUNDARY
IN NORTHWEST IOWA ALONG WITH STRONG HEATING INTO THE 70S WILL RESULT
IN INCREASED INSTABILITY/WEAKENING 850MB CAP THIS AFTERNOON...AND
SHOULD SEE AT LEAST SCATTERED SHOWERS/ISOLATED THUNDERSTORMS DEVELOP
ACROSS SOUTHEAST PORTIONS OF THE CWA BY MID-LATE AFTERNOON. DESPITE
BETTER INSTABILITY...FORECAST SOUNDINGS SHOW THIN/TALL CAPE PROFILES
AND MINIMAL SHEAR...SO NO SEVERE THREAT WITH ANY STORMS THAT DEVELOP.

TOWARD EARLY EVENING...ALSO START TO SEE WEAK EXTENSION OF NORTHERN
STREAM WAVE SWING INTO CENTRAL SD...INTERACTING WITH AFOREMENTIONED
LOW LEVEL BOUNDARY THERE. WORTH A MENTION OF SHOWERS AND MAYBE A FEW
THUNDERSTORMS AS THE BOUNDARY TRACKS EAST ACROSS SOUTHEAST SD DURING
THE EVENING...THOUGH THIS AREA HAS LESS LOW LEVEL MOISTURE TO WORK
WITH...SO WILL LIMIT POPS TO 20-30 PERCENT FOR NOW. BOUNDARY SHOULD
BE CLOSE TO EXITING FAR SOUTHEAST CORNER OF THE DAY BY EARLY MONDAY
MORNING...AND ANY THREAT OF SHOWERS/THUNDERSTORMS SHOULD DIMINISH AS
WELL...WITH STRONG DRYING BEHIND THE BOUNDARY.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 403 AM CDT SUN APR 20 2014

THE SYSTEM WILL PULL OFF TO THE EAST BY MONDAY MORNING WITH SURFACE
HIGH PRESSURE BUILDING SOUTHWARD INTO THE REGION. THIS WILL RESULT
IN CLEARING SKIES...AND BREEZY CONDITIONS THROUGH THE AFTERNOON WITH
COLD AIR ADVECTION/STEEP LOW LEVEL LAPSE RATES BEHIND THE DEPARTING
SYSTEM. MODELS HAVE BEEN COMING IN TOO HIGH WITH RESPECT TO DEW
POINTS OF LATE...SO WENT ON THE LOW SIDE OF GUIDANCE WITH DEW POINTS
ON MONDAY. THIS RESULTED IN AFTERNOON RELATIVE HUMIDITY PERCENTAGE
VALUES IN THE LOWER TO MID 20S OVER OUR ALL BUT OUR NORTHEASTERN
AREAS...AND WITH THE AFOREMENTIONED WINDS WILL SEE AN ENHANCED FIRE
DANGER ACROSS THE AREA. AS FOR HIGHS...IN A COLD AIR ADVECTION
REGIME HIGHS IN THE MID 60S TO LOWER 70S STILL SEEMS APPROPRIATE.
THE SURFACE RIDGE AXIS SLIDES OVERHEAD ON MONDAY NIGHT...AND WITH
CLEAR SKIES AND WINDS BECOMING VERY LIGHT WENT ON THE LOW SIDE OF
GUIDANCE WITH RESPECT TO LOWS...MID AND UPPER 30S ACROSS THE CWA.

ON TUESDAY THE HIGH BEGINS TO MOVE OFF TO THE EAST...WITH A
SOUTHEASTERLY SURFACE FLOW RETURNING TO THE AREA DURING THE DAY. IT
WILL BECOME BREEZY IN OUR WEST THROUGH THE DAY IN A TIGHTENING
GRADIENT AS A SURFACE TROUGH NUDGES OUT OF THE ROCKIES. THERMAL
PROFILES CONTINUE TO COOL A BIT IN OUR EAST...SO LOOKING AT HIGHS IN
THE LOWER 60S OVER EAST CENTRAL SOUTH DAKOTA AND SOUTHWESTERN
MINNESOTA...WHILE READINGS WILL CLIMB INTO THE LOWER 70S THROUGH
SOUTH CENTRAL SOUTH DAKOTA. BY TUESDAY NIGHT A WESTERN U.S. UPPER
LEVEL TROUGH BEGINS TO NUDGE TO THE EAST...AND WILL SEE
PRECIPITATION CHANCES INCREASE ACROSS THE AREA OVERNIGHT AS THETA E
ADVECTION RAMPS UP AS A 40 TO 50 KT LOW LEVEL JET STREAMS OUT OF
CENTRAL/EASTERN NEBRASKA. WHILE THERE COULD BE ISOLATED
THUNDERSTORMS IN OUR WEST IF ANYTHING DEVELOPS EARLY IN THE
NIGHT...INSTABILITY LOOKS TO BE WEAK...AND BECOMING INCREASINGLY SO
THROUGH THE NIGHT...SO THINK THAT MOST OF THE ACTIVITY THAT DEVELOPS
WILL BE IN THE FORM OF SHOWERS.

SHOWER AND THUNDERSTORM CHANCES WILL CONTINUE FOR WEDNESDAY...AND
ESPECIALLY WEDNESDAY NIGHT AS THE MAIN UPPER LEVEL DYNAMICS LIFT
ACROSS THE REGION AS THE TROUGH MOVES INTO THE NORTHERN PLAINS. IT
APPEARS THAT THE BETTER INSTABILITY WITH THE SYSTEM WILL REMAIN
SOUTH OF OUR CWA...SO AM NOT ANTICIPATING ANY SEVERE STORMS. WITH A
WARM FRONT LIFTING UP ACROSS PORTIONS OF THE AREA ON
WEDNESDAY...HIGHS WILL CLIMB INTO THE LOWER TO MID 70S THROUGH SOUTH
CENTRAL SOUTH DAKOTA AND THE MISSOURI RIVER CORRIDOR...WHILE IT WILL
REMAIN COOL BACK THROUGH SOUTHWESTERN MINNESOTA WITH HIGHS IN THE
LOW 60S.

FARTHER INTO THE EXTENDED...A GENERAL COOLING TREND FOR THURSDAY
THROUGH SATURDAY AS THE UPPER LEVEL TROUGH SLOWLY PUSHES EASTWARD
INTO THE GREAT LAKES/OHIO VALLEY REGION BY THE END OF THE WEEK. WILL
CONTINUE TO HAVE A FEW SHOWERS INTO THURSDAY...THOUGH THE GENERAL
TREND WILL BE FOR TAPERING OFF FROM WEST TO EAST THROUGH THURSDAY
NIGHT...POSSIBLY LINGERING IN OUR FAR NORTHEAST INTO FRIDAY AS THE
MAIN UPPER LEVEL LOW TRACKS THROUGH THE UPPER MISSISSIPPI VALLEY.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)
ISSUED AT 646 AM CDT SUN APR 20 2014

VERY HIGH BASED SHRA/TSRA IN FAR SOUTHEAST CORNER OF THE FORECAST
AREA AT THE START OF THE PERIOD. TSRA MAY STILL BE CLOSE TO KSUX
RIGHT AT 12Z...BUT EXPECTED TO MOVE EAST SHORTLY THEREAFTER...SO DID
NOT INCLUDE TSRA MENTION IN 12Z KSUX TAF. THIS ACTIVITY EXPECTED TO
SHIFT EAST OF THE FORECAST AREA BY AROUND 15Z...AND EXPECT DRY
CONDITIONS THROUGH THE EARLY AFTERNOON WITH CHANCE OF SHRA/TSRA
INCREASING ACROSS NORTHWEST IOWA AGAIN AFTER 20Z. NOT A HIGH DEGREE
OF CONFIDENCE IN TIMING TSRA THREAT AT ANY ONE LOCATION...BUT DID
INCLUDE A BRIEF WINDOW OF TSRA POTENTIAL AT KSUX DURING PERIOD OF
MORE FAVORABLE INSTABILITY IN THE LATE AFTERNOON. SPOTTY SHRA/TSRA
ALSO POSSIBLE IN SOUTHEAST SD/SOUTHWEST MN AS WEAK BOUNDARY MOVES
ACROSS THE REGION TONIGHT...BUT EXPECT ISOLATED COVERAGE AT BEST AND
OPTED TO NOT INCLUDE IN KHON/KFSD TAFS AT THIS TIME DUE TO LOW CHANCE
OF OCCURRENCE. VFR CONDITIONS SHOULD BE GENERAL RULE THROUGHOUT THE
PERIOD...THOUGH BRIEF MVFR VISIBILITY POSSIBLE IN HEAVIER SHOWERS.

&&

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

$$

SHORT TERM...JH
LONG TERM...JM
AVIATION...JH








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