Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 022034
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
334 PM CDT SAT MAY 2 2015

.SHORT TERM...(THIS EVENING THROUGH SUNDAY)
ISSUED AT 334 PM CDT SAT MAY 2 2015

A LITTLE MORE COMPLEX FORECAST OVER THE NEXT 24 HOURS...PRIMARILY
DEALING WITH CONVECTIVE CHANCES AS A COLD FRONT PUSHES THROUGH THE
REGION LATE TONIGHT AND SUNDAY. UNSEASONABLY WARM AIR MASS IN PLACE
AHEAD OF THE BOUNDARY TODAY...WITH LATE AFTERNOON TEMPERATURES IN
THE MID 70S TO MID 80S OVER THE FORECAST AREA. SCATTERED CU WHICH
HAS DEVELOPED THIS AFTERNOON EXPECTED TO DIMINISH WITH LOSS OF
HEATING TOWARD SUNSET. HIGH-RES MODELS TRYING TO DEVELOP ISOLATED
SHOWERS/THUNDERSTORMS ALONG THE BOUNDARY IN SOUTH-CENTRAL SOUTH
DAKOTA/NORTH-CENTRAL NEBRASKA IN THE NEAR TERM...PROPAGATING THIS
ACTIVITY INTO THE MISSOURI RIVER VALLEY THIS EVENING. UNSURE WHETHER
THIS WILL HOLD TOGETHER AS FAR EAST AS MODELS DEPICT...AS MOISTURE
IS QUITE LIMITED IN FORECAST SOUNDINGS THIS FAR EAST...SO OPTED TO
ONLY CARRY AN ISOLATED POP INTO CHARLES MIX COUNTY THROUGH 03Z. DEEP
DRY SUB-CLOUD LAYER COULD RESULT IN MARGINALLY STRONG WIND GUSTS...
BUT HAIL THREAT LOOKS MINIMAL.

ADDITIONAL ELEVATED ACTIVITY POSSIBLE IN AREA OF WEAK CONVERGENCE
AND ENHANCED MOISTURE TRANSPORT OVER THE NORTHERN PORTIONS OF THE
CWA...MAINLY TOWARD MIDNIGHT AND LATER. BETTER SUPPORT FOR THIS
DEVELOPMENT MAY BE JUST NORTH OF THE CWA...BUT WILL CONTINUE WITH A
LOW POPS NORTH OF SD HIGHWAY 34/MN HIGHWAY 30 OVERNIGHT INTO EARLY
SUNDAY. DO NOT EXPECT ANYTHING SEVERE WITH THESE STORMS.

MAIN FOCUS FOR SUNDAY WILL BE ALONG THE COLD FRONT AS IT MOVES EAST
ACROSS THE FORECAST AREA. GFS HAS SLOWED EASTWARD PROGRESSION OF THE
FRONT A BIT FROM PREVIOUS FORECAST...BUT OTHER MODELS SIMILAR TO THE
EARLIER TIMING AND THUS HAVE STUCK PRETTY CLOSE TO THIS LINE OF
THINKING. THIS BRINGS THE FRONT THROUGH YKN-FSD-MML BY NOON...THEN
SLOWLY TRACKS IT THROUGH THE SOUTHEAST 1/3 OF THE CWA THROUGH 00Z.
EXPECT MORNING HOURS TO BE FAIRLY QUIET...WITH THE FRONT BECOMING
THE PRIMARY FOCAL POINT FOR DEVELOPMENT IN THE AFTERNOON. SOUNDINGS
SHOW FAIR CAPPING INVERSION IN PLACE AHEAD OF THE FRONT...BUT
CONVERGENCE ALONG THE BOUNDARY ALONG WITH A WEAK MID LEVEL WAVE
SHOULD BE ABLE TO TRIGGER ISOLATED DEVELOPMENT AFTER 19-20Z.
COVERAGE SHOULD INCREASE ALONG THE BOUNDARY THROUGH THE LATE
AFTERNOON HOURS. MOST AGGRESSIVE MODELS INDICATE SBCAPE VALUES AS
HIGH AS 3000J/KG...THOUGH LOWER END OF THE SPECTRUM NEAR 1500J/KG IS
LIKELY MORE REALISTIC. DEEP LAYER SHEAR IS ON THE WEAK SIDE...AROUND
30KT OR LESS AHEAD OF THE FRONT...THOUGH COULD BE LOCALLY ENHANCED
RIGHT ALONG THE BOUNDARY. INSTABILITY SHOULD BE SUPPORTIVE OF
MARGINAL HAIL THREAT AS HIGHLIGHTED BY SPC...THOUGH WEAKER SHEAR
SHOULD LIMIT HAIL GROWTH SOMEWHAT.

BEHIND THE FRONT...INCREASING NORTHERLY FLOW AND DRYING AIR MASS
WILL LEAD TO ANOTHER HIGH TO VERY HIGH FIRE DANGER THREAT...WITH
VERY HIGH MOST LIKELY NORTHWEST OF BROOKINGS-LAKE ANDES LINE WHERE
DRY AIR AND STRONGEST WINDS WILL BECOME BETTER ESTABLISHED BY MID-
LATE AFTERNOON.


.LONG TERM...(SUNDAY NIGHT THROUGH SATURDAY)
ISSUED AT 334 PM CDT SAT MAY 2 2015

BY SUNDAY EVENING THE FRONTAL BOUNDARY FINALLY EXITS OUR CWA WITH ANY
LINGERING CONVECTION IN OUR FAR SOUTHEASTERN IOWA ZONES WINDING
DOWN. EXPECT THE REMAINDER OF THE NIGHT TO BE MAINLY DRY ACROSS THE
AREA. WITH WEAK COLD AIR ADVECTION BEHIND THE DEPARTING SYSTEM IT
WILL BE A LITTLE COOLER ON SUNDAY NIGHT WITH LOWS IN THE MID 40S TO
LOWER 50S.

ON MONDAY THE FRONTAL BOUNDARY STALLS OVER SOUTHERN NEBRASKA AND
SOUTHERN IOWA...AND AS A SHORTWAVE LIFTS OUT OF COLORADO WILL SEE
RAIN CHANCES INCREASE SOUTH OF INTERSTATE 90 BY THE
AFTERNOON...BECOMING LIKELY ON MONDAY NIGHT WITH MODELS SHIFTING
PRECIPITATION FARTHER NORTH THAN PREVIOUS RUNS. MONDAY WILL BE A
COOLER DAY IN A NORTHEASTERLY TO EASTERLY LOW LEVEL FLOW WITH HIGHS
JUST EITHER SIDE OF 70 ACROSS THE ENTIRE AREA.

ON TUESDAY THE BOUNDARY LIFTS BACK TO THE NORTH AS A WARM FRONT...AND
WHILE THERE ARE SOME MODEL DIFFERENCES WITH TIMING...IT WILL KEEP
CONVECTIVE CHANCES GOING...ESPECIALLY IN THE AFTERNOON. MODELS THEN
POINT TOWARD A REPRIEVE FOR MUCH OF TUESDAY NIGHT. HIGH TEMPERATURES
ARE A LITTLE TRICKY FOR TUESDAY DEPENDING ON WHERE THE FRONTAL
BOUNDARY ENDS UP...BUT AT THIS POINT GOING FOR HIGHS MOSTLY LOWER
70S...WITH MID AND UPPER 70S POSSIBLE THROUGH OUR FAR SOUTHERN ZONES
WHERE WARM AIR ADVECTION WILL BE BETTER REALIZED.

THE REMAINDER OF THE WEEK LOOKS TO BE UNSETTLED AS SHORTWAVES ARE
EJECTED OUT OF AN UPPER LEVEL TROUGH OVER THE WESTERN CONUS. THE
BETTER CHANCES FOR PRECIPITATION LOOK TO BE IN THE WEDNESDAY TO
EARLY THURSDAY TIME FRAME AS A MORE SIGNIFICANT SHORTWAVE LIFTS INTO
THE NORTHERN PLAINS. HIGHS THROUGH THE PERIOD WILL REMAIN ABOVE
NORMAL...IN THE 70S...WITH LOWS MOSTLY 50S.


&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1255 PM CDT SAT MAY 2 2015

VFR CONDITIONS SHOULD DOMINATE ACROSS THE AREA THROUGH THE TAF
PERIOD. WINDS WILL REMAIN SOUTH-SOUTHWEST THROUGH THE DAY WITH
AREAS OF GUSTS NEARING 25KT...MOST LIKELY ACROSS NORTHWEST IOWA.

COLD FRONT IN WESTERN SD WILL TRACK TOWARD THE FORECAST AREA
TONIGHT...AND PUSH INTO AREAS WEST OF INTERSTATE 29 AFTER DAYBREAK
SUNDAY. ISOLATED ELEVATED SHOWERS/THUNDERSTORMS POSSIBLE AHEAD OF
THE FRONT...MAINLY NORTH OF INTERSTATE 90...DURING THE PRE-DAWN
HOURS...BUT WITH SPOTTY COVERAGE HAVE OPTED TO NOT INCLUDE IN KHON
TAF AT THIS TIME.

SOUTHWESTERLY LOW LEVEL JET DEVELOPING AHEAD OF THE FRONT WILL
CREATE POTENTIAL FOR AREAS OF LOW LEVEL WIND SHEAR IN NORTHWEST
IOWA. ADDED THIS INTO KSUX TAF LOCATION...WHERE DECOUPLED SURFACE
WIND WILL TEND TO FAVOR MORE OF A SOUTHEAST DIRECTION...CREATING
DIRECTIONAL SHEAR IN ADDITION TO SPEED SHEAR.


&&

.FIRE WEATHER...
ISSUED AT 334 PM CDT SAT MAY 2 2015

INCREASING NORTH WINDS BEHIND A COLD FRONT WILL AID IN MIXING DRY
AIR TO THE SURFACE AGAIN FRIDAY AFTERNOON. WINDS GUSTING INTO 25
TO 30 MPH RANGE WILL COMBINE WITH MINIMUM HUMIDITY VALUES OF 25
TO 35 PERCENT IN POST-FRONTAL AIR MASS...TO PUSH GRASSLAND FIRE
DANGER INTO VERY HIGH RANGE ALONG AND NORTHWEST OF LAKE ANDES TO
BROOKINGS LINE SUNDAY AFTERNOON.

&&

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

$$

SHORT TERM...JH
LONG TERM...JM
AVIATION...JH
FIRE WEATHER...JH



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