124  
FXUS63 KFSD 230346  
AFDFSD  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SIOUX FALLS SD  
1046 PM CDT SAT APR 22 2017  
   
SHORT TERM
 
(THIS EVENING THROUGH SUNDAY)  
ISSUED AT 415 PM CDT SAT APR 22 2017  
 
SURFACE RIDGE OF HIGH PRESSURE WILL CONTINUE TO DRIFT OFF TO THE  
SOUTHEAST TONIGHT. THIS WILL TURN OUR WINDS AROUND TO THE SOUTH AND  
SOUTHWEST AS THE NIGHT PROGRESSES. THEREFORE LOWS ARE A BIT TRICKY  
TONIGHT. THE COOLEST LOCATION OVERALL WILL BE NORTHWEST IOWA AS THE  
WINDS WILL BE LIGHTEST THERE. IN FACT USED A BLEND OF THE ARW AND  
NMM FOR LOWS IN NORTHWEST IOWA WHICH COOLED OFF THE LOW TERRAINED  
AREAS TO BELOW CONSENSUS GUIDANCE READINGS, SUCH AS SIOUX CITY AND  
SPENCER. CONVERSELY WITH A SOUTHWEST WIND IN PLACE, RAISED MARSHALL  
AND WINDOM MN ABOVE GUIDANCE, AS WELL AS STORM LAKE IA.  
 
WINDS STILL LOOK FAIRLY STRONG ON SUNDAY BETWEEN THE DEPARTING HIGH  
TO OUR SOUTHEAST AND LOW PRESSURE MOVING INTO THE FRONT RANGE OF THE  
ROCKIES. TO THE NORTH, A STALLED FRONTAL BOUNDARY EXTENDS FROM  
CENTRAL MN THROUGH NORTHERN SD NOT IMPACTING OUR WEATHER YET.  
SURFACE WINDS WILL BE DECIDEDLY SOUTHWEST WHICH IS AN EXCELLENT  
WARMING DIRECTION. THEREFORE RAISED CONSENSUS HIGHS A FULL CATEGORY  
WHICH MIXES TEMPERATURES FROM 850MB A FULL 22 OR 23 DEGREES DOWN TO  
THE SURFACE. WIND SPEEDS WILL AVERAGE 20 TO 30 MPH IN OUR WESTERN  
ZONES, AND 15 TO 25 MPH ACROSS THE EAST. THE SOUTHWEST WIND SHOULD  
ALSO HELP TO DRY DEW POINTS MORE THEN CONSENSUS, SO USED A BLEND OF  
THE ARW AND NMM AGAIN WHICH PICKED UP ON THIS TREND. MINIMUM  
HUMIDITY VALUES ARE DRY ENOUGH TO WARRANT A FIRE WEATHER WATCH  
HOWEVER THERE ARE A COUPLE OF PROBLEMS. FIRST, OUR COOL SEASON  
GRASSES HAVE GREENED UP. WITH OUR WESTERN ZONES SHORT GRASS  
DOMINATED WHICH ARE GREEN, THEY WILL LIKELY NOT EXPERIENCE ANY FIRE  
STARTS. IN OUR EASTERN ZONES WHICH ARE MORE WARM GRASS DOMINATED,  
THE WIND SPEEDS ARE NOT QUITE STRONG ENOUGH TO WARRANT A FIRE  
WEATHER WATCH.  
   
LONG TERM
 
(SUNDAY NIGHT THROUGH SATURDAY)  
ISSUED AT 415 PM CDT SAT APR 22 2017  
 
GUSTY SOUTHERLY WINDS WILL PERSIST SUNDAY NIGHT, LEADING TO A MILD  
OVERNIGHT WITH LOWS IN THE MID 40S TO LOWER 50S. LOW-LEVEL JET  
INCREASING TO 30 TO 40 KTS AHEAD OF WAVE PUSHING INTO THE DAKOTAS  
LATER SUNDAY NIGHT, AND WILL LIKELY REMAIN STRONGEST AND MOST GUSTY  
AT/NEAR ELEVATION. APPEARS AS IF A FAIRLY STRONG ELEVATED MIXED  
LAYER WILL ADVECT NORTH THROUGH THE NIGHT, WITH GRADIENT IN LAPSE  
RATE HOVERING NEAR THE FAR WESTERN/NORTHERN BORDERS OF THE CWA BY  
MORNING. WHILE VERY UNLIKELY, A COUPLE OF ROGUE SHOWERS COULD DOT  
LOWER BRULE TO MID JAMES VALLEY LOCATIONS TOWARD DAYBREAK.  
 
OVERALL, FAIRLY LOW AMPLITUDE SYSTEM WILL BE TRAVERSING THE REGION  
ON MONDAY, WITH BULK OF UPPER DYNAMICS PASSING JUST NORTH OF THE  
AREA. ELEVATED MIXED LAYER AGAIN COULD INCITE A FEW SHOWERS DURING  
THE MORNING MAINLY TOWARD HIGHWAY 14 AND THROUGH AREAS WEST OF I-29.  
WILL HAVE SURFACE WAVE GENERALLY TRACK FROM CENTRAL SD TOWARD  
CENTRAL MN BY EVENING, DRAGGING A COLD FRONT ACROSS THE AREA. WITH  
MOISTURE RETURN TO INTERACT WITH WAVE FAIRLY MEAGER, BOUNDARY  
REMAINS FAIRLY CAPPED TO SURFACE OR NEAR SURFACE DEVELOPMENT,  
ESPECIALLY FURTHER SOUTH TOWARD THE MISSOURI RIVER. POTENTIAL FOR A  
COUPLE OF LATE DAY THUNDERSTORMS LIMITED TO NEAR THIS BOUNDARY, BUT  
EXPECT A FAIRLY SPARSE COVERAGE OF ANY PRECIPITATION, AND MUCH LESS  
SOUTH THAN NORTH.  
 
UPSTREAM JET, MUCH STRONGER, WILL BE CLOSE ON THE HEELS OF THIS  
SYSTEM, AND IS LIKELY TO BRING SOME LIGHT RAINFALL INTO SOUTH  
CENTRAL SD BY LATER MONDAY NIGHT, WHILE NORTHERLY FLOW OF COOLER AIR  
WILL WORK THROUGH THE CWA. WHILE LIKELY THAT DRY AIR WILL IMPEDE  
NORTHWARD PROGRESSION TO PRECIP DEVELOPMENT, WOULD BE POSSIBLE THAT  
A LITTLE ADDED WET BULB EFFECT COULD POTENTIALLY INTRODUCE A CHANCE  
FOR A LITTLE MIX OF SNOW TOWARD K9V9 EARLY DAY TUESDAY. A VERY  
FRONTOGENETIC SETUP ON TUESDAY SUGGESTS A WIDESPREAD THREAT FOR  
RAINFALL, ESPECIALLY NEAR/SOUTH OF I-90 AND NORTHEAST THROUGH  
SOUTHWEST MN BY LATER IN THE DAY. FAIRLY NEUTRAL MID-LEVEL THERMAL  
PROFILES SPILL NORTHWARD THROUGH AREAS SOUTH OF I-90 DURING THE  
LATER MORNING THROUGH EARLY AFTERNOON, AND ALMOST TAKES ON LOOK OF  
POTENTIALLY STRONGER BANDING OF SHOWERS FROM KYKN TO KMJQ, AND WOULD  
NOT BE SHOCKED FOR A ROGUE RUMBLE OR TWO ALONG SOUTHERN EDGE OF  
PRECIP SHIELD WITH POTENTIAL FOR SLANTWISE INSTABILITY. WITH UPPER  
WAVE TO YET MOVE THROUGH, STILL A STRONG CHANCE FOR RAINFALL INTO  
THE EVENING EAST OF I-29, THEN DROPS OFF FAIRLY QUICKLY AFTER 06Z.  
INCREASING NORTHERLY FLOW WILL CONTINUE TO BRING COOLER AIR INTO  
AREA AS SURFACE WAVE DEVELOPS ACROSS IOWA AND THE MISSISSIPPI  
VALLEY. LIKELIHOOD OF TEMPERATURES COOL ENOUGH TO FORCE AT LEAST A  
MIX TO SNOW APPEAR POSSIBLE ON BACK EDGE OF PRECIPITATION FROM EAST  
CENTRAL SD INTO SOUTHWEST MN. COULD BE DEALING WITH SOME NEAR  
FREEZING TEMPERATURES, EVEN WITH WINDS OF 10 TO 20 MPH CONTINUING  
BY WEDNESDAY MORNING.  
 
WEDNESDAY INTO EARLY THURSDAY BRINGS THE ONLY LIKELY DRY PERIODS,  
BUT TEMPERATURES WILL REMAIN BELOW NORMAL, AND WILL BE WATCHING FOR  
A POTENTIAL FREEZE WEDNESDAY NIGHT. QUITE A BIT OF VARIANCE ON  
EAST/WEST LOCATION ON WRAP-AROUND CLOUDINESS AND POTENTIAL FOR  
PERSISTENCE OF NORTHERLY WINDS. UNLIKELY TO SURPASS THE MID 50S FOR  
HIGHS ON ANY ACCORD.  
 
FINAL PORTION OF THE EXTENDED RANGE FORECAST IS WROUGHT WITH  
UNCERTAINTY, BUT GENERALLY INDICATES A POTENTIAL FOR RAINFALL AT ONE  
TIME OR ANOTHER FROM LATER THURSDAY INTO SATURDAY. ENOUGH VARIANCE  
THAT MADE NO ATTEMPT TO ALTER GRIDS FROM BLENDED INITIALIZATION,  
OTHER THAN TO SHADE TOWARD A LITTLE LESSER PRECIP THREAT FRIDAY  
ACROSS PARTS OF SOUTHWEST MN. TRENDS HAVE BEEN FOR THE GFS TO  
BECOME A BIT MORE ECMWF-LIKE AND LESS OF AN ENSEMBLE OUTLIER FROM  
YESTERDAY TO TODAY, BUT STILL HAVE A MUCH MORE AGGRESSIVELY TIMED  
PATH THAN OTHER SOLUTIONS. CERTAINLY NOTHING MILD ABOUT THE WEATHER  
PATTERN THROUGH AT LEAST NEXT WEEKEND.  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)  
ISSUED AT 1037 PM CDT SAT APR 22 2017  
 
VFR CONDITIONS CONTINUE THROUGH THE TAF PERIOD. LOW-LEVEL WIND  
SHEAR OF 40 KNOTS AT AROUND 1400 FT WILL BE POSSIBLE ACROSS KHON  
EARLY SUNDAY MORNING. MODELS SUGGEST LOW-LEVEL WIND SHEAR AGAIN  
BY THE END OF THE TAF PERIOD, BUT CONFIDENCE IS TOO LOW TO  
INCLUDE IN TAFS AT THIS TIME.  
 

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

 
 

 
 
SHORT TERM...MJ  
LONG TERM...CHAPMAN  
AVIATION...DUX/05  
 
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