141  
FXUS63 KFSD 251101  
AFDFSD  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SIOUX FALLS SD  
601 AM CDT SUN JUN 25 2017  
   
SHORT TERM
 
(TODAY AND TONIGHT)  
ISSUED AT 416 AM CDT SUN JUN 25 2017  
 
THE MAIN FOCUS FOR TODAY'S FORECAST IS POTENTIAL FOR SHOWERS AND  
ISOLATED THUNDERSTORMS THIS AFTERNOON AND OVERNIGHT.  
 
IN GENERAL, MODELS ARE IN AGREEMENT IN EVOLUTION TODAY AND TONIGHT.  
WEAK UPPER LEVEL WAVE CURRENTLY ON THE SASKATCHEWAN AND NORTH DAKOTA  
BORDER IS FORECAST TO MOVE SOUTHEAST THROUGH THE DAY. AS IT DOES A  
WEAK FRONT WILL DEVELOP AROUND 850 MB. MOISTURE REMAINS VERY  
LIMITED BUT WITH 700 MB TEMPS BELOW ZERO SEVERAL CAMS AS WELL AS NAM  
SHOW NO CONVECTIVE INHIBITION WITH MUCAPE AROUND 200 J/KG. THE  
COMBINATION OF FORCING FROM THE UPPER WAVE AND FRONT SHOULD BE  
ENOUGH TO GET A FEW SHOWERS TO DEVELOP IN NORTHEAST SOUTH DAKOTA  
LATER THIS MORNING AND THEN SPREAD SOUTHEAST THROUGH THE AFTERNOON.  
MOISTURE IS VERY LIMITED AND THIS WILL LIMIT COVERAGE OF ANY  
SHOWERS AND STORMS THAT DEVELOP. AFTER DISCUSSING WITH  
SURROUNDING OFFICES, WE ALSO DECIDED TO ADD THUNDER IN THIS  
AFTERNOON AND EARLY EVENING WITH THE IDEA THAT THERE WILL BE  
STRONG ENOUGH ASCENT WITH THE LIMITED CAPE TO PRODUCE A  
COUPLE OF THUNDERSTORMS WITHIN THE AREA OF SHOWERS. THE LOSS OF  
DIURNAL HEATING SHOULD END THE THREAT FOR THUNDER. ALSO THERE  
IS STILL A LOT OF DRY AIR BELOW CLOUD BASE WHICH WILL ALLOW SOME OF  
THE RAIN TO EVAPORATE BEFORE REACHING THE GROUND. THEREFORE HAVE  
KEPT POPS LESS THAN 40 PERCENT DUE TO UNCERTAINTY ON COVERAGE. WITH  
THE BEST CHANCE ALONG AND SOUTH OF INTERSTATE 90 AFTER SUNSET WHEN  
THE 850 MB BOUNDARY AND UPPER WAVE APPEAR TO HAVE THE BEST  
INTERACTION. THE PRECIPITATION SHOULD MOVE SOUTH OF SIOUX CITY AND  
STORM LAKE BY 12Z MONDAY.  
 
OTHERWISE, IT WILL BE LESS WINDY THAN YESTERDAY AS A RIDGE OF HIGH  
PRESSURE BUILDS INTO CENTRAL SOUTH DAKOTA. THERE IS ENOUGH GRADIENT  
EAST OF I-29, ESPECIALLY IN SOUTHWESTERN MINNESOTA, THAT GUSTS COULD  
AGAIN APPROACH 30 MPH THIS AFTERNOON. HIGHS TODAY WILL BE SIMILAR TO  
YESTERDAY MID 60S ALONG THE BUFFALO RIDGE TO THE UPPER 70S IN SOUTH  
CENTRAL SD. OVERNIGHT, LOWS WILL AGAIN FALL INTO THE 40S WITH A FEW  
LOWER 50S NEAR HIGHWAY 20 WHERE MORE CLOUDS WILL INHIBIT RADIATIONAL  
COOLING.  
   
LONG TERM
 
(MONDAY THROUGH SATURDAY)  
ISSUED AT 416 AM CDT SUN JUN 25 2017  
 
ANY LINGERING THICKER MID CLOUDS AND ISOLATED SHOWERS WILL CERTAINLY  
BE ON THE WAY OUT OF THE LOWER MISSOURI RIVER VALLEY BY EARLY  
MONDAY, AS BOUNDARY CONTINUES TO PUSH SOUTHWARD AND SURFACE RIDGE  
SETTLES ACROSS THE HEART OF THE AREA THROUGH THE AFTERNOON. TEMPS  
WILL AGAIN BE SIMILAR TO EVEN A SHADE COOLER WITH MAINLY UPPER 60S  
TO MID 70S. WITH THE SURFACE RIDGE RESIDING ACROSS THE AREA THROUGH  
THE EVENING, AND LINGERING LONGEST IN NORTHWEST IOWA INTO THE EARLY  
OVERNIGHT, WOULD EXPECT TEMPERATURES WITH COOL AND DRY AIRMASS TO  
AGAIN UNDERCUT MOST GUIDANCE, AND HAVE LOWERED SEVERAL DEGREES INTO  
THE MID TO UPPER 40S FOR LOWER LOCATIONS ACROSS NORTHWEST IOWA AND  
NEARBY LOCATIONS.  
 
TOWARD SOUTH CENTRAL SD, RETURN FLOW WILL STRENGTHEN CONSIDERABLY  
POST 06Z MONDAY NIGHT, AND WILL LIKELY START THE DAY ON THE BREEZY  
SIDE AT MORE EXPOSED SITES IN LOWER BRULE AREA. SOUTHERLY WINDS WILL  
INCREASE RAPIDLY AND EXPAND THEIR REACH EASTWARD THROUGH THE DAY,  
WITH 25 TO 35 KNOTS IN THE MIXED LAYER MOST AREAS WEST OF I-29 AT  
SOME TIME DURING THE DAY. FAIRLY DRY LOWER LEVELS WITH TRAJECTORY  
OUT OF EXITING RIDGE LINGERING THROUGH NW IA AND SW MN, BUT SHOULD  
BEGIN TO SEE INCREASING LOW LEVEL MOISTURE BELOW THE STRONGLY  
WARMING TEMPERATURES ALOFT INTO SOUTHEAST SD. CONCERN IN THAT WITH  
700-500 HPA LAPSE RATES OF 7.5-8.5 C/KM, THERE COULD BE SOME  
TENDENCY FOR MID-LEVEL ACCAS TYPE SHOWERS/ISOLATED T DEVELOP DURING THE  
AFTERNOON ACROSS SOUTHEAST SD, BUT REALLY DO NOT SEE A GREAT DEAL OF  
LARGER SCALE SUPPORT TO LIFT ALONG THE ADVANCING INSTABILITY  
GRADIENT.  
 
AT THIS TIME, PERIOD OF GREATEST CONCERN IN THE FORECAST WILL ARISE  
ON TUESDAY NIGHT, WHEN THERE WILL BE A MUCH IMPROVED PROSPECT FOR  
CONVECTION. UNLESS SOME MID-LEVEL CONVECTION DEVELOPS LATE AFTERNOON  
INTO EARLY EVENING AS ELEVATED MIXED LAYER SHOVES EASTWARD TO I-29  
BY EARLY EVENING. WARM LAYER ALOFT WILL MEAN FOCUS FOR CONVECTION  
WILL LIKELY BE CLOSER TO THE LOW-LEVEL CONVERGENCE BOUNDARY ACROSS  
WESTERN SD AND IN LEE OF BLACK HILLS LATE AFTERNOON INTO VERY EARLY  
EVENING AS UPSTREAM TROUGH APPROACHING FROM THE WEST WILL FLATTEN  
THE FLOW ALOFT AND KNOCK BACK WARMER TEMPS ALOFT FROM WEST TO EAST,  
ALSO INCREASING DIRECTIONAL SHEAR OVERNIGHT. 45 TO 55 KNOT SOUTH TO  
SOUTHWEST LOW-LEVEL JET AND WESTERLY FLOW PUNCHING ACROSS IN THE MID  
TO UPPER LEVELS DOES GENERATE A FAIRLY POTENT DEEP-LAYER SHEAR,  
ALTHOUGH MOST GUIDANCE SUGGESTS WILL HAVE SOME WEAKNESS TO WINDS  
AROUND THE MIDDLE OF THE 0-6KM PROFILE. NONETHELESS, THERE IS  
SUFFICIENT SHEAR TO SUPPORT STORM ORGANIZATION. SHEAR IS HIGHLY  
BOUNDARY PARALLEL, SO EXPECT WESTERN DISCRETE STORMS TO EVOLVE  
FAIRLY QUICKLY TOWARD A MORE LINEAR AND WIDESPREAD STRUCTURE, WHICH  
WILL ALSO BE SUPPORTED BY GOOD DYNAMICAL SUPPORT TO LIFT WITH PV  
ANOMALY PUSH, MEANING MOST AREAS WILL BE LIKELY TO SEE AT LEAST SOME  
PRECIPITATION AS THE LINE MOVES EAST. ELEVATED INSTABILITY CENTERING  
ON GENERALLY 1000-2000 J/KG, AND PROVIDED STORMS CAN ABANDON MORE  
SURFACE-BASED ROOTS HEADING LATER INTO THE NIGHT, SHOULD SEE A  
FAIRLY DECENT MCS PRESS EASTWARD ACROSS THE AREA FROM THE MID  
EVENING TOWARD SOUTH CENTRAL SD, INTO SOUTHWEST MN AND NORTHWEST IA  
AFTER MIDNIGHT. POTENTIAL THREATS WOULD GENERALLY BE LARGER HAIL AND  
DAMAGING WIND GUSTS.  
 
VERY PROGRESSIVE MID-LEVEL FEATURE WILL KEEP CONVECTION MOVING  
ALONG, AND MAY EXIT EVEN FASTER THAN FORECAST ON WEDNESDAY MORNING,  
ABANDONING THE SYNOPTIC FRONTAL BOUNDARY PUSHING TOWARD THE JAMES  
RIVER VALLEY EARLY MORNING. WHILE HAVE MAINTAINED SOME LOWER CHANCE  
POPS ON WEDNESDAY THROUGH NORTHWEST IOWA DURING THE AFTERNOON, THERE  
IS UNCERTAINTY IF THE MODIFICATION OF ATMOSPHERE BY EARLIER STORMS  
CAN BE OVERCOME IN TIME TO PRODUCE AFTERNOON STORMS ALONG THE  
BOUNDARY IN NORTHWEST IOWA. MIXING BEHIND THE FRONT SHOULD PUSH  
READINGS WELL INTO THE 80S, ESPECIALLY THROUGH LOWER BRULE AREAS  
WHICH COULD APPROACH 90.  
 
BEYOND WEDNESDAY, FORECAST BECOMES A BIT MORE MUDDLED WITH VARIOUS  
IMPULSES TIMING THROUGH THE WEST/NORTHWEST FLOW INTO NEXT WEEKEND.  
ONE SUCH SERIES OF WAVES MOVES ACROSS ON THURSDAY INTO FRIDAY,  
DRAGGING DYNAMIC LIFT FORCING ACROSS THE AREA MAINLY AFTERNOON AND  
OVERNIGHT. WHILE MOST SOLUTIONS KNOCK THE MAIN SYNOPTIC BOUNDARY  
WELL SOUTH BY THURSDAY NIGHT ALONG WITH THE LIONS SHARE OF  
INSTABILITY AND MOISTURE, THE ECMWF DOES ATTEMPT TO DIG A SHARPER  
NORTHERN STREAM TROUGH, PICK UP A PIECE OF SOUTHERN ENERGY AND WRAP  
BACK NORTHWARD TOWARD NORTHWEST IOWA ON THURSDAY NIGHT WITH A MUCH  
HIGHER CHANCE FOR CONVECTION. FOR NOW, HAVE SETTLED ON MODEST CHANCE  
POPS TO SEE HOW INTERVENING CONVECTION AFFECTS THE PATTERN. AFTER  
SHARP TROUGH PASSES FRIDAY, SHOULD BE GENERALLY DRY THROUGH  
SATURDAY, ALTHOUGH HINTS THAT RETURN FLOW COULD INITIATE BY LATER  
SATURDAY TOWARD SOUTH CENTRAL SD ALLOWING FOR A LOW CHANCE OF STORMS  
BY LATE DAY ALONG ADVANCING MID-LEVEL INSTABILITY ONCE AGAIN. TEMPS  
SHOULD SETTLE OUT FAIRLY CLOSE TO NORMAL AGAIN BY THE WEEKEND.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)  
ISSUED AT 557 AM CDT SUN JUN 25 2017  
 
MAIN CONCERN IS SHOWERS LATER THIS AFTERNOON AND OVERNIGHT. THERE  
IS A SLIGHT CHANCE OF A THUNDERSTORMS AT KHON AND KFSD PRIOR TO  
02Z MONDAY. HOWEVER, THE RISK OF BOTH STORMS AND SHOWERS IS  
30 PERCENT OR LESS SO DID NOT INCLUDE IN TAF AT THIS TIME. THE  
RISK OF A SHOWER IS A LITTLE HIGHER IN SUX AFTER MIDNIGHT BUT  
TIMING REMAINS UNCERTAIN AND THERE IS NOT EXPECTED TO BE THUNDER.  
SO ALSO DID NOT INCLUDE IN SUX TAF AT THIS TIME. CEILINGS AND  
VSBYS ARE EXPECTED TO BE VFR THROUGH THE PERIOD. WINDS WILL BE  
AROUND 10 KTS AT KHON AND 10-15 KTS AT KFSD AND KSUX DURING THE  
DAY BECOMING LIGHT AND VARIABLE OVERNIGHT.  
 

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

 
 

 
 
SHORT TERM...SCHUMACHER  
LONG TERM...CHAPMAN  
AVIATION...SCHUMACHER  
 
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