Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 142339
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
639 PM CDT TUE APR 14 2015

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 400 PM CDT TUE APR 14 2015

BRISK SOUTHERLY WINDS WILL CONTINUE WEST OF INTERSTATE 29 TONIGHT.
ALREADY HAVE ISSUED A WIND ADVISORY FOR OUR CENTRAL SD ZONES WHICH
LASTS THROUGH WEDNESDAY MORNING TO ACCOUNT FOR THESE WINDS. VERY
TIGHT PRESSURE GRADIENT EXISTS ALL NIGHT FOR THOSE LOCATIONS...AND
WINDS JUST OFF THE SURFACE ARE AN ASTOUNDING 40 TO 45 KNOTS.
OBVIOUSLY SOME DECOUPLING WILL EXIST AFTER SUNSET WHICH WILL NOTCH
DOWN THE GUSTS. BUT IN CENTRAL SD WOULD NOT BE SURPRISED TO SEE 25
TO 35 MPH LAST ALL NIGHT IN EXPOSED TERRAIN WHICH OF COURSE IS MOST
AREAS. CONCERNING LOWS...THE WINDS WILL KEEP TEMPERATURES MILD. BUT
WITH THE LIGHTER WINDS A FEW LOWER LOCATIONS IN NORTHWEST IA MAY DIP
A LITTLE BIT INTO THE 30S SUCH AS SPENCER.

ON WEDNESDAY...TOOK OUT THE POPS. THERE IS A SOLID MOISTURE INCREASE
AT LEAST ALONG AND WEST OF INTERSTATE 29. BUT THIS WAVE HAS
VIRTUALLY NO ASCENT WITH IT TO STRAIN ANY RAINFALL OUT OF THE
MOISTURE DECK IN THE 850-700MB LAYER. HIGHS ARE TRICKY HOWEVER IN
THAT IT WILL LIKELY BE PRETTY CLOUDY. SO MUCH HOW MUCH THE CLOUDS
HOLD TEMPERATURES DOWN BEING COUNTER BALANCED BY A CONTINUING SOUTH
TO SOUTHEAST WINDS MAKES THE HIGHS A CHALLENGE. SOME OF THE BIAS
CORRECTED VALUES LIKE FROM THE MAV AND GFS LOOK AWFULLY WARM GIVEN
THE DEGREE OF CLOUD COVER. THEREFORE HAD A TENDENCY TO GO WITH MORE
OF THE NON BIAS CORRECTED READINGS WHICH STANDS TO REASON AS WE HAVE
NOT HAD A LOT OF CLOUD COVER RECENTLY...AND THAT COULD INFLUENCE THE
BC READINGS.

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 400 PM CDT TUE APR 14 2015

FULL LATITUDE TROUGH THROUGH THE INTERMOUNTAIN WEST WILL BE IN THE
PROCESS OF BREAKING OFF SOUTHERN ROCKIES CLOSED CIRCULATION EARLY IN
THE PERIOD...TRANSLATING EASTWARD INTO THE PLAINS IN PARTS THROUGH
THE WEEKEND. MAIN ISSUES IN THE INTERMEDIATE TERM DEAL WITH THE
POTENTIAL FOR PRECIPITATION AS THIS SYSTEM SLIPS EASTWARD.
OVERALL...OUTSIDE THE GFS WHICH RETAINS A TREMENDOUSLY AND
ANOMALOUSLY GREATER TIE BETWEEN THE CLOSED PORTION OF THE LOW AND
NORTHERN STREAM...THERE IS A GREATER CONSENSUS TO A MUCH MORE
SEPARATED SOLUTION. RESULT OF THIS IS A LOWER THREAT OVERALL FOR
PRECIPITATION ACROSS THE AREA.

WEAK WAVE LIFTING ACROSS THE AREA DURING THE EVENING WITH A DOSE OF
800-600 HPA MOISTURE...DURING WHICH TIME LOWER LEVELS WILL STILL
REMAIN QUITE DRY. INSTABILITY IN THIS LAYER IS MEAGER AT BEST... SO
CONSIDERING THERMODYNAMIC PROFILE AND WEAKNESS OF MID/UPPER FORCING
WOULD WOULD DO WELL TO GET A FEW SPRINKLES...AND HAVE TRIMMED BACK
EVENING POPS...WHICH COORDINATES IDEAS WITH SHORT TERM AS WELL.
SHEARING VORTICITY AXIS DOES BEGIN TO CREEP TOWARD SOUTHWESTERN CWA
LATE NIGHT...AND AREA ON NORTHERN EDGE OF MID LEVEL TRAJECTORY
AROUND THE UPPER LOW COULD FIND A COUPLE OF SHOWERS OR RUMBLES BY
LATE WED NIGHT OR THURSDAY MORNING. AS WE GO THROUGH THE DAY...
WOULD SEEM TO KEEP A MINIMAL THREAT FOR SHOWERS/ROGUE THUNDER ALONG
THE MISSOURI VALLEY...AS INCREASING IMPACT OF THE PROGRESSIVE
NORTHERN STREAM PORTION OF WAVE STARTS TO AGEOSTROPHICALLY REINFORCE
DRYING AT LOWER LEVELS.  ALSO SUPPORTIVE OF LESS GEOGRAPHIC COVERAGE
OF POPS WOULD BE WEAK STEERING FLOW IN COL BETWEEN NORTHERN AND
SOUTHERN SYSTEMS...LIKELY THAT PROGRESSION OF ANY DEVELOPED
PRECIPITATION OUTSIDE THE AREA WILL BE CHALLENGED TO ACTUALLY MOVE
ACROSS A GREATER AREA.

IN THE LONGER RANGE...PRETTY MUCH HAD TO JETTISON THE GFS LINE OF
REASONING WITH HICCUP IN SHORTER TERM...AND SIDED TOWARD
ECMWF/CANADIAN. STRONGER WAVE WILL DROP SOUTHWARD INTO THE NORTHERN
PLAINS LATER IN THE WEEKEND...DRIVING A STRONGER CONVERGENCE
BOUNDARY ACROSS THE AREA AS SYSTEM INTERACTS TO SOME DEGREE WITH
SOUTHERN PLAINS CLOSED SYSTEM. HAVE INCREASED PRECIPITATION CHANCE
ON SATURDAY NIGHT AND SUNDAY WITH MOISTURE TRANSPORT AND FRONTAL
FORCING. THIS SYSTEM IS MUCH MORE PROGRESSIVE AND ENDS PRECIPITATION
AS MUCH AS 12-18 HOURS EARLIER THAN PREVIOUS GUIDANCE. QUICK DRYING
INTRODUCED BY SUNDAY EVENING AS WAVE CONTINUES TO DIG/CONGEAL TOWARD
THE GREAT LAKES. VARIATION OF HOW STRONGLY CLOSED NORTHERN STREAM
SYSTEM IS DEFINES HOW MUCH POTENTIALLY COOLER MONDAY COULD BE... BUT
STRONG MIXING SHOULD KEEP AT LEAST NEAR NORMAL TO SLIGHTLY BELOW
TEMPS IN PLAY WITH THE COOLDOWN.

NOT CRAZY ABOUT A GREAT PRECIPITATION THREAT FOR TUESDAY...GIVEN THE
REMAINING DRY AIR AT LOWER LEVELS...BUT WITH SEVERAL SOLUTIONS
DIVING A WEAK JET THROUGH THE REGION WITH MID LEVEL FRONTAL BOUNDARY
HANGING AROUND...HELD ON TO THE LOWER CHANCE FOR RAINFALL. MUCH ON
TEMPERATURES WILL DEPEND ON THE RECONNECTION OF THE NORTHERN AND
SOUTHERN STREAMS...HOW QUICKLY THIS OCCURS...AND HOW DEEP TROUGH
BECOMES TO THE EAST. WITH THE RANGE OF UNCERTAINTY...HAVE NOT
STRAYED APPRECIABLY FROM SUPERBLEND GUIDANCE...WITH EXCEPTION OF
ADDING A FEW DEGREES FOR MIXING ON TUESDAY.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)
ISSUED AT 638 PM CDT TUE APR 14 2015

VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD. THE BIGGEST
AVIATION CONCERN IS STRONG SOUTHERLY WINDS GENERALLY WEST OF
INTERSTATE 29. IN FACT APPROACHING CENTRAL SD...WINDS WILL GUST
FREQUENTLY TO AROUND 35 KNOTS INTO EARLY EVENING...AND WILL REMAIN
QUITE WINDY IN THAT AREA ALL NIGHT.

&&

.FIRE WEATHER...
ISSUED AT 400 PM CDT TUE APR 14 2015

THE CURRENT RED FLAG WARNING SHOULD BE ABLE TO EXPIRE AT 8 PM
WHICH IS CLOSE TO SUNSET. AT THAT POINT WINDS WILL DECREASE A BIT
ALONG WITH RISING HUMIDITY VALUES. THE ONE EXCEPTION WILL BE OUR
FIRE WEATHER ZONE IN CENTRAL SD WHO WILL PROBABLY HAVE RED FLAG
WINDS THROUGH THE NIGHT. BUT THE HUMIDITY WILL RECOVER TO OVER 40
PERCENT BY LATE EVENING.

AT THIS TIME...THERE IS NO NEED TO ISSUE A FIRE WEATHER WATCH FOR
ANY OUR OF ZONES FOR WEDNESDAY. THIS IS DUE TO INCREASED HUMIDITY
VALUES WEST OF INTERSTATE 29 WHEN COMPARED TO TODAY...OR WIND SPEEDS
NOT STRONG ENOUGH EAST OF INTERSTATE 29.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...RED FLAG WARNING UNTIL 8 PM CDT THIS EVENING FOR SDZ255>258.

     WIND ADVISORY UNTIL 1 PM CDT WEDNESDAY FOR SDZ050-052-057-058-
     063-064.

MN...RED FLAG WARNING UNTIL 8 PM CDT THIS EVENING FOR MNZ900.

IA...NONE.
NE...RED FLAG WARNING UNTIL 8 PM CDT THIS EVENING FOR NEZ249.

&&

$$

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



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