Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 311131
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
631 AM CDT TUE MAR 31 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 421 AM CDT TUE MAR 31 2015

NOT A LOT GOING ON IN THE NEAR TERM...AS WE SEEM TO BE IN BETWEEN
DAYS OF FIRE WEATHER CONCERNS AND WITH PRECIPITATION NOT A THREAT
YET. TODAY AND TONIGHT...AN UPPER RIDGE OF HIGH PRESSURE WILL MOVE
FROM THE SPINE OF THE ROCKY MOUNTAINS THIS MORNING...EASTWARD TO
ALONG THE I 29 CORRIDOR BY 12Z WEDNESDAY. AT THE SURFACE...LOW
PRESSURE WILL MOVE INTO THE FRONT RANGE OF THE ROCKIES BY LATE
TODAY...AND NUDGE EASTWARD INTO THE CENTRAL DAKOTAS BY 12Z
WEDNESDAY. THEREFORE A SOUTHERLY FLOW OF AIR WILL INCREASE TODAY...
BUT NOT ENOUGH TO WARRANT ANY SORT OF FIRE WEATHER HEADLINES IN OUR
WESTERN ZONES. IT WILL BE DRY HOWEVER...AND MOST DEW POINT VALUES
ARE AGAIN TO HIGH. THEREFORE USED THE DEW POINT DEPRESSION OFF OF
THE NAM FOR DEW POINT VALUES. FOR HIGHS...WARMED UP READINGS
SLIGHTLY THIS AFTERNOON GIVEN 900-850MB TEMPERATURES...WITH
WIDESPREAD UPPER 60S TO UPPER 70S EXPECTED. BIAS CORRECTED VALUES
WERE IN THE BALL PARK...ESPECIALLY FROM THE ECMWF.

TONIGHT...ESPECIALLY AFTER EVENING...SOUTH WINDS WILL CONTINUE TO
INCREASE AND WILL BECOME QUITE WINDY AS THE GRADIENT TIGHTENS. IN
ADDITION...ALL OF THE VARIOUS MODELS ARE SHOWING 25 TO 40 KNOTS AT
925MB FROM 06Z TO 12Z WEDNESDAY. THE WARMEST GUIDANCE VALUES ARE
CERTAINLY PRUDENT UNDER THESE CONDITIONS. BOTH THE NAM AND GFS
SOUNDINGS LOOK TOO DRY TO SUPPORT ACCAS DEVELOPMENT...THEREFORE LEFT
CONDITIONS DRY.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 421 AM CDT TUE MAR 31 2015

WEDNESDAY IS A DAY FULL OF WEATHER CONCERNS...FROM MORNING WIND...
TO FIRE WEATHER...TO SEVERE WEATHER POTENTIAL LATER IN THE DAY. AS
VERY STRONG WAVE CURRENTLY OFF THE PACIFIC NORTHWEST COAST MOVES
THROUGH THE NORTHERN ROCKIES...LOW LEVEL JET OF 45 TO 55 KNOTS IN
PLACE ACROSS THE CWA ON WEDNESDAY MORNING. INVERSION AND CROSS RIDGE
COMPONENT SUGGESTS THAT GUSTS MAY BE ENHANCED ALONG THE DOWNSTREAM
OF THE BUFFALO RIDGE...WHERE COULD SEE SOME 45 TO 50 MPH GUSTS
THROUGH MID MORNING BEFORE MIXING AND EASTWARD SHIFT OF WIND MAXIMUM
ALOFT STARTS A DECREASING TREND. NORMAL SYNOPTIC GRADIENT STRONG
ENOUGH ON ITS OWN TO SUPPORT A GUSTY 25 TO 35 MPH FLOW.

DEEP ELEVATED MIXED LAYER WILL BE IN PLACE TO START THE
MORNING...MARKED BY 700-500 HPA LAPSE RATES OF 8 TO 9.5 C/KM. VERY
LITTLE MOISTURE EARLY ON SHOULD MEAN LACK OF ACCAS...OR AT LEAST
PRECIPITATION PRODUCTION. PERHAPS BY LATER MORNING WILL GET ENOUGH
MOISTURE ALOFT AND LEADING LIFT TO START TO SEE A BIT BETTER CLOUD
DEVELOPMENT ALONG AXIS THROUGH THE HEART OF THE CWA TO WARRANT AN
ISOLATED THUNDER THREAT. WILL START TO GET MORE INTERESTING AS THE
BOUNDARY PUSHES EASTWARD TOWARD NORTHWEST IOWA AND NORTHEAST
NEBRASKA DURING THE AFTERNOON. MOISTURE WILL BE GRADUALLY INCREASING
BENEATH THIS PLUME OF STEEP LAPSE RATES THROUGH THE DAY AHEAD OF THE
BOUNDARY...WITH DEWPOINTS REACHING AT LEAST THE LOWER TO MID 50S.
THESE REMAIN CAPPED FOR MUCH OF THE DAY...BUT WILL BE WORKED ON BY
BOTH THE LIFT FROM DEEPER LOW LEVEL FRONTAL FORCING...AND COOLING OF
THE AIRMASS ALOFT THROUGH DIABATIC PROCESSES. INEVITABLY...APPEARS
THAT WILL BE ABLE TO OVERCOME THE CAP NEAR AND JUST BEHIND THE
BOUNDARY FOR RAPID THUNDERSTORM DEVELOPMENT BY MID TO LATE
AFTERNOON...MAINLY ALONG AND EAST OF A SLAYTON TO VERMILLION LINE.
SHEAR IS FAIRLY UNIDIRECTIONAL BUT LOOKING A BIT DEEPER NOW...
SUGGESTIVE OF EARLY DISCRETE AND QUICKLY BECOMING LINEAR STRUCTURES.
WITH CAPE OF 1000-1500 J/KG...DECENT ENOUGH UPDRAFTS TO SUGGEST A
LOWER END SEVERE THREAT WITH HAIL TO HALF DOLLAR AND WIND TO 65 MPH
FOR STRONGER STORMS SOUTHEAST OF A WINDOM TO VERMILLION LINE. STORMS
SHOULD MAINTAIN SEVERE THREAT TO AROUND OR SHORTLY AFTER SUNSET...
WHICH WILL NOT BE TOO FAR FROM WHEN BEST OF COVERAGE WOULD BE
LEAVING THE FAR SOUTHEAST.

BEHIND FRONT IN THE WEST LATE MORNING...AND SPREADING THROUGH MOST
OF SE SD BY LATE AFTERNOON...RELATIVE HUMIDITY WILL CRASH FAIRLY
QUICKLY WITH INCREASING MIXING ON NORTHWEST FLOW...WITH FIRE DANGER
LIKEWISE ENHANCING.

THURSDAY WILL BE A CLASSIC MIXING DAY SOUTH OF UPPER WAVE PASSING
NORTH OF THE CWA. COLD AIR ADVECTION INCREASING LATER IN DAY WILL
ONLY AID IN DEEPER MIXING...WITH WINDS 25 TO 35 KNOTS AND VERY LOW
HUMIDITY. TEMPS WITH MIXING WOULD FAVOR UPPER 50S NORTH TO MID 60S
FAR SOUTHEAST.  FRIDAY A QUITE DAY...ALBEIT COOLER AND DRY...WITH
TEMPS RETURNING TO A BIT BELOW NORMAL AS MAIN UPPER TROUGH SWINGS
THROUGH...AND HEIGHTS ALREADY BEGIN TO BUILD BACK THROUGH THE HIGH
PLAINS.

SOLUTIONS FOR THE WEEKEND HAVE MOVED MUCH CLOSER TO AN ECMWF
WEIGHTED CONSENSUS...WITH A BACKDOOR FRONT PUSHING SOUTHWARD INTO
THE CWA FRIDAY NIGHT AND SATURDAY AS QUICK MOVING WAVE PUSHES
THROUGH THE NORTHERN GREAT LAKES. IMPACT WILL BE FOR WINDS TO BE
DOWN...WHICH WILL BE GOOD FOR LIMITING THE HIGHER END OF FIRE
DANGER. THERE WILL LIKELY BE A FAIRLY STRONG LOWER LEVEL THERMAL
GRADIENT...AND DESPITE INCREASING THE NORTH TO SOUTH TEMPERATURE
DIFFERENCE OVER THE INITIALIZATION...WOULD NOT BE SHOCKED TO SEE
THIS MANY DEGREES HIGH IN THE SOUTH IF THE BOUNDARY HANGS UP JUST A
BIT MORE TO THE NORTH. NEVERTHELESS...FLATTENING FLOW ALOFT WILL
ALLOW WARM FRONT TO WOBBLE SATURDAY NIGHT/SUNDAY...WITH SOME
DIABATIC HEATING DIFFERENCE WITH CLOUDS NORTH OF THE BOUNDARY AGAIN
SUGGESTING A STRONGER NORTH TO SOUTH DIFFERENCE THAN GUIDANCE
SUGGESTS.

BY LATER SUNDAY NIGHT AND MONDAY...MAY SEE A PRECIPITATION THREAT
GRADUALLY EVOLVE. HOWEVER...WILL NOT SEE MUCH DEEPER SATURATION
START UNTIL AT LEAST MONDAY WHEN NOTABLE SURGE OF SUB 850 HPA
MOISTURE STREAMS NORTHWARD...SO FOR NOW THE ABUNDANCE OF LOWER
LEVEL MOISTURE AND EASTERLY FLOW APPEARING ON MODELS WOULD SUGGEST
A LOT OF LOWER CLOUDS AROUND...WITH PERHAPS SOME ROGUE ELEVATED
CONVECTION AS WEAK WAVES RIDE PAST...AND GET SOME PERIODS OF
ENHANCED THETA E ADVECTION/CONVERGENCE.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)
ISSUED AT 629 AM CDT TUE MAR 31 2015

VFR CONDITIONS WILL PREVAIL TODAY AND TONIGHT. ONE THING TO WATCH
FOR IS NON CONVECTIVE LOW LEVEL WIND SHEAR CONDITIONS...ESPECIALLY
AT THE KFSD AND KSUX TAF SITES OVERNIGHT TONIGHT. REASON IS A VERY
STRONG LOW LEVEL JET SETS UP JUST OFF THE SURFACE FROM THE
SOUTH...COUPLED WITH RELATIVELY LIGHT WINDS AT THE SURFACE AT
THESE TWO LOCATIONS. LATE TONIGHT WHEN A TIGHTER SURFACE GRADIENT
MOVES TOWARD INTESTATE 29...STRONGER SURFACE WINDS WILL ENSUE
HELPING TO BALANCE OUT THE WIND SHEAR BETWEEN THE SURFACE AND 1000
FEET AGL.

&&

.FIRE WEATHER...
ISSUED AT 420 AM CDT TUE MAR 31 2015

FIRE DANGER IS LIKELY TO BE ELEVATED...VERY HIGH TO EXTREME...
WEDNESDAY WITH THE DRY CONDITIONS AND STRONG WINDS. RED FLAG
POTENTIAL ALONG AND WEST OF THE JAMES RIVER WITH PLUNGING POST
FRONTAL HUMIDITY AND GUSTY NORTHWEST WINDS. NOT THERE WITH THE
HIGHER HUMIDITY EAST. HAVE ISSUED A FIRE WEATHER WATCH FOR ZONES
255 AND 256 THROUGH THE AFTERNOON AND EARLY EVENING.

DEEP MIXING ON THURSDAY WILL ALSO CREATE FIRE WEATHER CONCERNS
AS HUMIDITIES DROP TO A VERY LOW 15 TO 25 PERCENT...AND WINDS
LIKELY TO GUST TO AT LEAST 25 TO 30 KNOTS.

WILL HAVE TO KEEP AN EYE ON THE MISSOURI VALLEY FOR FIRE CONCERNS
OVER THE WEEKEND. IF BOUNDARY ENDS UP A BIT MORE NORTHWARD...THIS
WOULD YIELD WARMER TEMPERATURES AND MUCH LOWER HUMIDITY. HOWEVER...
WINDS WOULD LIKELY REMAIN BELOW ANY CRITERIA FOR CRITICAL BEHAVIOR.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...FIRE WEATHER WATCH FROM WEDNESDAY AFTERNOON THROUGH WEDNESDAY
     EVENING FOR SDZ255-256.

MN...NONE.
IA...NONE.
NE...NONE.
&&

$$

SHORT TERM...MJ
LONG TERM...CHAPMAN
AVIATION...MJ
FIRE WEATHER...CHAPMAN



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