578  
FXUS63 KFSD 261716  
AFDFSD  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SIOUX FALLS SD  
1216 PM CDT MON JUN 26 2017  
   
SHORT TERM
 
(TODAY AND TONIGHT)  
ISSUED AT 417 AM CDT MON JUN 26 2017  
 
SCATTERED SHOWERS AND A FEW THUNDERSTORMS WILL CONTINUE TO DRIFT  
SOUTHEASTWARD ACROSS OUR SOUTHERN ZONES THROUGH THE EARLY MORNING  
HOURS. THERE IS CLEARLY A VORT FILAMENT EXTENDING ACROSS THE  
FORECAST AREA, ESPECIALLY THROUGH OUR EASTERN ZONES FROM NORTH TO  
SOUTH IN THE MORNING HOURS. IN ADDITION, MID LEVEL QG FORCING  
IS EVIDENT FROM 700-500MB DEPARTING NORTHWEST IA BY 18Z, AS WELL AS  
SURFACE TROUGHING EXTENDING EASTWARD ACROSS FAR NORTHERN NEBRASKA.  
AS THE MORNING PROGRESSES, MID LEVEL MOISTURE WANES IN OUR SOUTH  
ENDING THE RAIN THREAT, AND SURFACE HIGH PRESSURE OOZES SOUTHWARD  
KEEPING THE AIR MASS SEASONABLY CHILLY. WILL WATCH FOR THE FORMATION  
OF PATCHY FOG AS SURFACE DEW POINT DEPRESSIONS ARE VERY SMALL EARLY  
THIS MORNING NORTH OF THE CLEARING LINE. IF ANY FOG DEVELOPS, IT  
WILL GENERALLY BE ALONG AND NORTH OF I 90. TEMPERATURES WILL MIX TO  
ABOVE 850MB THIS AFTERNOON, BUT SOUNDINGS SHOWING A FAIR AMOUNT OF  
CUMULUS POPPING FROM THE JAMES EASTWARD, THEREFORE HIGHS WILL MAINLY  
BE IN THE UPPER 60S TO MID 70S.  
 
NOT A LOT GOING ON TONIGHT. WINDS WILL SHIFT TO THE SOUTHEAST AND  
SOUTH, INCREASING A BIT WEST OF THE JAMES VALLEY LATER TONIGHT.  
PREFERRED BIAS CORRECTED MOS LOWS WHICH SHOWED A TREND OF CHILLY  
LOWS IN OUR EAST WHERE WINDS WILL BE THE LIGHTEST, BUT MILDER  
READINGS IN OUR WEST WITH THE STRONGER SOUTHERLY WINDS.  
   
LONG TERM
 
(TUESDAY THROUGH SUNDAY)  
ISSUED AT 417 AM CDT MON JUN 26 2017  
 
MAIN CONCERN WITHIN THE MEDIUM RANGE THIS MORNING IS THE THREAT FOR  
SEVERE STORMS ON TUESDAY NIGHT AND EARLY WEDNESDAY.  
 
INCREASING SOUTHERLY JET WILL BRING STRONG SOUTH WINDS TO THE AREA  
ON TUESDAY, LIKELY GUSTING IN EXCESS OF 30 MPH FOR MOST LOCATIONS.  
THIS WILL BRING AN INCREASED TRANSPORT OF MOISTURE INTO THE REGION,  
SLOWEST IN THE EAST WHERE TRAJECTORY REMAINS A BIT MORE OUT OF THE  
EXITING LOW-LEVEL RIDGE INTO EARLY EVENING. WITH RIDGING ALOFT,  
PUSH OF WARMER TEMPERATURES AND STEEPER 7-500HPA LAPSE RATES WILL  
KEEP CHANCES FOR STORMS MINIMIZED THROUGH THE DAY. HOWEVER, STILL  
WILL HAVE TO WATCH FOR A BIT MORE ELEVATED MOISTURE TO BECOME  
INVOLVED, FOR THIS COULD INCREASE THREAT OF A FEW MID-LEVEL  
SHOWERS/STORMS DURING THE AFTERNOON AS LAPSE RATES IN EXCESS OF  
8C/KM PUSH THROUGH SOUTHEASTERN SD. SOMEWHAT LIMITED MIXING DEPTH  
WITH WARMING ALOFT MAKES FOR HIGHS FROM UPPER 70S EAST OF I-29 TO  
PERHAPS THE MID 80S WEST OF THE JAMES RIVER.  
 
LIKELY GENESIS REGION FOR CONVECTION WILL OCCUR ACROSS WESTERN  
PORTIONS OF SD DURING THE LATE AFTERNOON INTO VERY EARLY EVENING, IN  
LEE OF THE BLACK HILLS AND ALONG THE FRONTAL CONVERGENCE AS WAVE/JET  
BEGINS TO PUNCH INTO THE RIDGE IN THE HIGH PLAINS. ENVIRONMENT  
HEADING INTO THE EVENING SUGGESTS ELEVATED CAPE FROM 1500-2000 J/KG,  
AND THE 45-55KT LOW-LEVEL JET STRETCHING OUT LOW-LEVELS IN FAIRLY  
NICE TURNING HODOGRAPH. ROOTING OUT USEFUL SHEAR, LOOKS LIKE  
EFFECTIVE VALUES OF 30-40 KT. AS LONG AS STORMS CAN WORK TOWARD A  
MORE ELEVATED NATURE, SHOULD SEE MAXIMIZED SEVERE THREAT FOR LARGE  
HAIL AND DAMAGING WIND WEST OF THE JAMES VALLEY THROUGH THE EVENING  
HOURS, ALTHOUGH THE HAIL SIZE WILL BE INCREASINGLY LIMITED BY THE  
WARM TEMPERATURES ALOFT AS WELL AS LIKELIHOOD OF MORE LINEAR  
STRUCTURES/COMPETING UPDRAFTS DEVELOPING THROUGH THE EVENING AS  
SHEAR VECTORS REMAIN ALIGNED MAIN ALONG BOUNDARY. PRESENCE OF THE  
WARM AND DRY LAYER ALOFT WILL LIKELY IMPEDE THE STRONGEST STORM  
POTENTIAL HEADING EASTWARD TOWARD I-29 AND BEYOND, AND SHEAR BEING  
LARGELY LINE-PARALLEL WILL ALSO LEAD TO A DECREASING THREAT OF  
SEVERE WIND GUSTS AS LIKELY MCS WORKS EASTWARD. MARGINAL THREAT  
SEEMS APPROPRIATE.  
 
SOME CONVECTION WILL LIKELY BE LINGERING INTO THE MORNING AROUND  
NORTHWEST IA AND SOUTHWEST MN AS LOW-LEVEL JET CONTINUES TO VEER, AND  
PRECIPITATION COULD COME TO A SLIGHTLY MORE RAPID END WITH EFFECTIVE  
OUTFLOW BOUNDARY PROGRESSING ALONG WITH WAVE AND WELL AHEAD OF MAIN  
SYNOPTIC BOUNDARY. WITH PASSAGE OF WAVE, MORE WESTERLY COMPONENT  
SHOULD QUIET DOWN CONVECTIVE THREAT MOST AREAS, WITH PERHAPS A  
LIMITED CHANCE THROUGH THE AFTERNOON ACROSS MAINLY NORTHWEST IOWA AS  
THE BOUNDARY OF MORE LIMITED CONVERGENCE PRESSES THROUGH, BUT FAIRLY  
UNLIKELY TO MODIFY AIRMASS IN WAKE OF OVERNIGHT/EARLY MORNING  
STORMS. BEHIND THE FRONT, READINGS LIKELY TO REACH WELL INTO THE  
80S THROUGH THE WESTERN MISSOURI RIVER CORRIDOR.  
 
BOUNDARY WILL CONTINUE TO PUSH SOUTHWARD THROUGH EARLY THURSDAY,  
SOUTH OF I-80, BUT AS ANOTHER WAVE DROPS OUT OF THE CANADIAN ROCKIES  
AND INTO THE NORTHERN PLAINS LATER THURSDAY INTO THURSDAY NIGHT,  
THIS SHOULD WANDER A BIT MORE NORTHWARD AS LOW PRESSURE ORGANIZES TO  
THE SOUTH. WHILE IMPACTS IN TERMS OF SEVERE WEATHER ARE LIKELY TO  
REMAIN SOUTH OF THE AREA LATER THURSDAY/THURSDAY NIGHT, THERE SHOULD  
BE AN INCREASE IN POTENTIAL FOR THUNDERSTORMS STARTING LATER  
THURSDAY AFTERNOON IN THE MISSOURI AND JAMES RIVER AREAS, SPREADING  
NORTH AND EAST ACROSS THE AREA OVERNIGHT.  
 
LESS CONFIDENT IN THE OVERALL PATTERN FROM FRIDAY ONWARD, AS MODELS  
TAKE CLOSED WAVE THROUGH THE NORTHERN PLAINS IN SOME WAY, SHAPE AND  
FORM THROUGH SATURDAY. RUN TO RUN CONTINUITY COULD BE CHARACTERIZED  
AS SHAKY AT BEST. PRECIPITATION IS LIKELY OVERDONE SATURDAY AND  
SUNDAY, AT LEAST IN COVERAGE. TEMPERATURES SHOULD START FRIDAY AS  
THE COOLEST DAY, THEN SLIGHT DAY TO DAY WARMING THROUGH SUNDAY.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)  
ISSUED AT 1214 PM CDT MON JUN 26 2017  
 
VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD. THE MAIN  
IMPACT WILL BE INCREASING SOUTHERLY SURFACE WINDS AFTER MIDNIGHT  
FROM WEST TO EAST. GUSTY WINDS UP TO 35 MPH ARE EXPECTED EAST OF  
I-29 ON TUESDAY.  
 

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

 
 

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