Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 271120
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
620 AM CDT WED MAY 27 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 346 AM CDT WED MAY 27 2015

SURFACE HIGH PRESSURE CENTERED ACROSS THE CENTRAL PLAINS WILL SHIFT
EAST TODAY.  THIS WILL LEAD TO SOUTHERLY FLOW DEVELOPING ACROSS THE
PLAINS ORIGINATING IN THE GULF LEADING TO GOOD MOISTURE
RETURN...EVENTUALLY.  WITH MOSTLY CLEAR SKIES ACROSS THE AREA THIS
MORNING...SHOULD SEE STRONG MIXING...HOWEVER...STEEP LAPSE RATES
FROM 925 - 700 MB RESULTS IN A SMALL AMOUNT OF ELEVATED INSTABILITY.
FAIR AMOUNT OF DRY AIR ALOFT INITIALLY...AND WITH STRONG SOUTHERLY
FLOW AND MOISTURE TRANSPORT NOT WELL ESTABLISHED YET...EXPECT DEW
POINTS TO FALL SOME THROUGH THE MORNING.  WITH THE ELEVATED
INSTABILITY...COULD SEE AN ISOLATED STORM TRY TO DEVELOP THROUGH THE
AFTERNOON HOURS BUT REALLY SUFFERING FROM A LACK OF A TRIGGER AND
DEEP MOISTURE THROUGH THE AFTERNOON. OPERATIONAL RUN OF THE HRRR
SUGGESTS A FEW STORMS ARE POSSIBLE ALONG THE BUFFALO RIDGE IN
SOUTHWEST MINNESOTA THIS AFTERNOON WHERE UPPER LEVEL INSTABILITY IS
GREATEST.  CANADIAN CONTINUES TO POINT TO THIS AREA AS WELL...BUT
HAVE NOT ADDED ANY MENTION OF PRECIP QUITE YET DUE TO THE
AFOREMENTIONED NEGATIVES. DAY SHIFT WILL NEED TO KEEP AN EYE ON THIS
THOUGH.

EXPECT CONVECTION TO DEVELOP ACROSS WESTERN PORTIONS OF THE STATE
THIS AFTERNOON...BUT LIFT NORTHEAST THROUGH THE EVENING HOURS
FOLLOWING THE SHORT WAVE ALOFT.  MODELS SUGGEST SHORTWAVES WILL
SPLIT THE FORECAST AREA...WITH ONE WAVE MOVING INTO THE NORTHEAST
CORNER OF SOUTH DAKOTA AND THE SECOND REMAINING TO THE SOUTH ACROSS
THE CENTRAL PLAINS. COULD SEE AN ISOLATED STORM MOVE INTO CENTRAL
SOUTH DAKOTA THIS EVENING...BUT AS THE UPPER WAVE LIFTS NORTHEAST
AND WITH STORMS MOVING INTO LESS FAVORABLE ENVIRONMENT...BELIEVE
THEY WILL STRUGGLE TO MAINTAIN THEIR STRENGTH.  WITH CONVECTION
ACROSS THE CENTRAL PLAINS AFFECTING DEEP MOISTURE POTENTIAL...HAVE
CUT POPS BACK INTO THE 20 PERCENT RANGE AND CONFINED AREAL COVERAGE
TO WEST OF THE JAMES. LOWS SHOULD BE FAIRLY MILD TONIGHT WITH 30-40
KNOT LOW LEVEL JET DEVELOPING ACROSS THE PLAINS...GENERALLY IN THE
50S TO LOWER 60S.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 346 AM CDT WED MAY 27 2015

ON THURSDAY...WEDNESDAY NIGHTS SHORT WAVE QUICKLY EXITS PRIMARILY
NORTH OF OUR AREA. THE MOISTURE PROFILE IS NOT REAL DEEP. BUT
ENOUGH MOISTURE EXISTS THAT A BAND OF SCATTERED RAINFALL COULD
MOVE ITS WAY EASTWARD ACROSS THE FORECAST AREA IN THE
MORNING...LIKELY WEAKENING AS IT MOVES FROM WEST TO EAST. AT ANY
RATE NOT A LOT RAINFALL IS EXPECTED ANYWAY. FOR THURSDAY
AFTERNOON...THERE IS NO REAL FOCUSING MECHANISM...WE ARE JUST LEFT
WITH A FAIRLY UNSTABLE ATMOSPHERE WITH ML CAPES AVERAGING 1500 TO
2500 J/KG AND 925-850MB LIFTED INDEX VALUES OF -3 TO -7C. ONLY
CHANCE POPS ARE WARRANTED AT THIS TIME. THE HIGHEST INSTABILITY
EXISTS ALONG AN AXIS FROM GREGORY COUNTY TO KINGSBURY COUNTY IN
SOUTH DAKOTA. A MARGINAL SEVERE THREAT IS WORTH MENTIONING IN THE
FORTH COMING HWO BUT THIS WILL BE LIMITED BY A DISCERNIBLE LACK OF
WIND SHEAR...VERY UNIDIRECTIONAL IN THE LOWEST KILOMETER COUPLED
WITH MID LEVEL WIND SPEEDS FORECAST TO BE ONLY 15 TO 20 KNOTS. SO
NEEDLESS TO SAY THE 0-3KM AND 0-6KM BULK SHEAR VECTORS ARE WEAK
WHICH WILL SEVERELY LIMIT ROTATING UPDRAFTS. CONCERNING
HIGHS...850MB TEMPERATURES FINALLY INDICATE A WARM DAY DESPITE
WHAT COULD BE QUITE A FEW MID AND HIGH LEVEL CLOUDS. LOOKING FOR
HIGHS A COUPLE OF DEGREES EITHER SIDE OF 80. THE ECMWF AND GEM
GLOBAL TEMPERATURES HAVE BEEN PERFORMING VERY WELL LATELY...BUT
THIS TIME AROUND THEY LOOK A BIT TOO COOL.

THURSDAY NIGHT STILL LOOKS RAINY AS THE VARIOUS MODELS ARE POINTING
AT UPPER QG FORCING MOVING THROUGH ASSOCIATED WITH A SHORT WAVE.
HEIGHT FALLS AT 500MB ARE PRETTY IMPRESSIVE. THE BEST CHANCE FOR
SEVERE WEATHER IF IT HAPPENS WOULD LIKELY BE ONLY IN THE EVENING AND
IN OUR WESTERN ZONES JUST AHEAD OF THE ASSOCIATED SURFACE WIND
SHIFT. IN ADDITION ML CAPES IN OUR WEST AVERAGE 1500 TO 2000 J/KG
ALONG THE AXIS MENTIONED ABOVE. BUT IT DOES STABILIZE FAIRLY RAPIDLY
BETWEEN 00Z AND 03Z THURSDAY EVENING. LOOKING FORWARD BY 06Z
FRIDAY...WE ARE NOT LEFT WITH MUCH INSTABILITY AT ALL IN THE
FORECAST AREA. BUT HIGH POPS ARE WARRANTED AS THE SYSTEM MOVES
EASTWARD WITH A DEEP MOISTURE PROFILE. GFS PWAT VALUES ARE AVERAGING
1.25 TO 1.50 INCHES SO WOULD NOT BE SURPRISED TO SEE POCKETS OF
HEAVY RAINFALL. BUT WITH THE PROGRESSIVE NATURE OF THE 850MB
BOUNDARY MOVING FROM NORTHWEST TO SOUTHEAST...THERE MAY NOT BE A LOT
OF TRAINING ECHOES THURSDAY NIGHT OR FRIDAY MORNING. AND SPEAKING OF
LOW LEVEL WINDS...THERE IS SOME DISCREPANCY WITH THE WIND SHIFT/COLD
FRONTAL TIMING. THE NAM AND ECMWF ARE IN ONE CAMP WITH A SLOWER
SOLUTION...CLEARING THE COLD FRONT JUST SOUTHEAST OF OUR FORECAST
AREA BY 00Z SATURDAY. THE GFS AND GEM GLOBAL ARE IN THE OTHER CAMP
IN MOVING THE COLD FRONT JUST SOUTHEAST OF OUR AREA BY 18Z FRIDAY.
SO ABOUT A 6 HOUR DIFFERENCE. ALL MODELS ARE PROGRESSIVE WITH THE
LOW LEVEL WIND SHIFT...JUST DIFFERENT TIMING. FOR NOW...SPLIT THE
DIFFERENCE IN THE GRIDS AND HAVE A 21Z FRIDAY EXIT FROM STORM LAKE
IA. INCREASED THE NORTHERLY SURFACE FLOW ON FRIDAY BEHIND THE
FRONTAL PASSAGE WITH 925MB WINDS AVERAGING 25 KNOTS...EVEN HAVE SOME
30 KNOT VALUES...SO IT WILL BE A WINDY DAY FOR MOST LOCATIONS. AND
ALONG WITH THE HIGH POPS THURSDAY NIGHT...LIKELY POPS ARE STILL
WARRANTED FRIDAY MORNING EXCEPT ACROSS OUR NORTHERN AND WESTERN
ZONES WHO ARE DEEPER INTO THE COOLER AIR AND STABILITY. RAIN CHANCES
WILL THEN CONTINUE TO DECREASE FROM NORTHWEST TO SOUTHEAST FRIDAY
AFTERNOON THROUGH FRIDAY EVENING. THERE WILL BE NO SEVERE WEATHER
THREAT ON FRIDAY DUE TO THE SPEED AT WHICH THE COLD FRONT IS MOVING
THROUGH. HIGHS ON FRIDAY WILL VARY FROM THE MID 60S NORTHWEST...TO
MID 70S SOUTHEAST...FOLLOWED BY SEASONABLY CHILLY LOWS FRIDAY NIGHT
OF 40 NORTHWEST...TO NEAR 50 SOUTHEAST.

THE WEEKEND LOOKS DRY NOW...WITH CHILLY HIGHS OF ONLY 60 TO 65 ON
SATURDAY...MODERATING 5 TO 10 DEGREES WARMER ON SUNDAY. ONLY
SPORADIC SMALL POPS WARRANTED FOR EARLY NEXT WEEK WITH NOTHING
REALLY TO KEY ON. THE AREA SHOULD BE MOSTLY DRY MONDAY AND
TUESDAY...BUT AFTER THE EXTENDED PERIOD IT COULD BE AN ACTIVE COUPLE
OF DAYS.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING)
ISSUED AT 613 AM CDT WED MAY 27 2015

VFR CONDITIONS EXPECTED THROUGH THE PERIOD. SURFACE HIGH PRESSURE
WILL SHIFT OFF TO THE EAST AND SOUTHERLY WINDS WILL INCREASE
THROUGHOUT THE DAY. THERE IS AN OUTSIDE CHANCE OF AN ISOLATED
STORM DEVELOPING ACROSS SOUTHWEST MINNESOTA AFTER 19Z. 35-40 KNOT
LOW LEVEL JET DEVELOPS TONIGHT ACROSS THE CENTRAL PLAINS AFFECTING
KHON. FURTHER TO THE EAST...LOW LEVEL JET WILL BE LESS...AND HAVE
KEPT LOW LEVEL WIND SHEAR OUT.

&&

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

$$

SHORT TERM...
LONG TERM...MJ
AVIATION...



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