304  
FXUS63 KFSD 241139  
AFDFSD  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SIOUX FALLS SD  
639 AM CDT THU MAY 24 2018  
   
SHORT TERM
 
(TODAY AND TONIGHT)  
ISSUED AT 340 AM CDT THU MAY 24 2018  
 
ANOTHER DAY OF CONVECTIVE UNCERTAINTY, AS WE DEAL WITH INTERACTIONS  
OF WEAK FORCING WITH CONVECTIVE REMNANTS THROUGHOUT THE DAY. EARLY  
THIS MORNING, HI-RES GUIDANCE SIMILAR IN DEPICTING DEVELOPMENT  
THROUGH THE PRE-DAWN HOURS AS LOW LEVEL JET INTERACTS WITH OUTFLOW  
FROM DYING COMPLEX IN SOUTH CENTRAL SOUTH DAKOTA/CENTRAL NEBRASKA.  
THIS SCATTERED ACTIVITY EXPECTED TO MOVE TOWARD THE I-29 CORRIDOR IN  
TIME FOR THE MORNING COMMUTE, THEN WEAKEN AFTER 15Z AS THE LOW LEVEL  
JET DIMINISHES.  
 
QUESTIONS THEN BECOME HOW PERSISTENT LINGERING CLOUD DEBRIS WILL BE,  
AND WHAT EFFECT THIS WILL HAVE ON HEATING/DESTABILIZATION POTENTIAL  
LATER TODAY AS SUBTLE WAVES SLIDE NORTHEAST ACROSS THE FORECAST  
AREA. MODEST CONSENSUS POINTS TO MID-LATE AFTERNOON RE-DEVELOPMENT  
IN OUR EASTERN CWA, BUT RUN-TO-RUN CONSISTENCY IN HRRR IS SEVERELY  
LACKING, SO CONFIDENCE IN FAVORED TIMING/LOCATION IS LOW. SOMEWHAT  
HIGHER CONFIDENCE IN SCATTERED DEVELOPMENT IN OUR NORTHWEST CWA  
TOWARD EVENING, AS TAIL END OF A WAVE MOVING ACROSS THE DAKOTAS  
INTERACTS WITH PRE-FRONTAL TROUGH/DRYLINE WEST OF THE JAMES RIVER.  
 
DESPITE THE UNCERTAINTY IN HEATING, SHOULD BE LOOKING AT DECENT  
INSTABILITY THIS AFTERNOON, WITH EVEN WEAKEST MODELS SHOWING MIXED  
LAYER CAPE VALUES IN 1-2KJ/KG IN OUR EASTERN CWA. PROBLEM IS DEEP  
LAYER SHEAR IS QUITE WEAK AT LESS THAN 20KTS, SO MAY BE TOUGH TO  
SUSTAIN ORGANIZED STORMS. STRONGER INSTABILITY IN OUR WESTERN AREAS  
THANKS TO STEEPER MID-LEVEL LAPSE RATES, THOUGH EVEN THERE SHEAR IS  
LIMITED, SO STILL LOOKING FOR PULSY, MULTI-CELL CLUSTERS TRACKING  
ACROSS THE CWA THROUGH THE EVENING/OVERNIGHT HOURS. GIVEN THE LACK  
OF GOOD SHEAR, CANNOT ARGUE WITH MARGINAL OUTLOOK FROM SPC FOR OUR  
AREA TODAY, KEEPING SLIGHT RISK JUST NORTH OF OUR CWA WHERE SHEAR IS  
SLIGHTLY BETTER.  
   
LONG TERM
 
(FRIDAY THROUGH WEDNESDAY)  
ISSUED AT 340 AM CDT THU MAY 24 2018  
 
STRETCH OF CALMER WEATHER EXPECTED TO DOMINATE MUCH OF THE UPCOMING  
HOLIDAY WEEKEND, AS UPPER RIDGE BUILDS INTO THE REGION. THIS WILL  
BRING WELL ABOVE NORMAL TEMPERATURES FRIDAY INTO EARLY NEXT WEEK,  
WITH SATURDAY STILL LOOKING TO BE THE WARMEST OF THE BUNCH WITH  
HIGHS IN THE 90S MOST AREAS. DEW POINTS CURRENTLY EXPECTED TO BE IN  
THE UPPER 50S-LOWER 60S FRIDAY/SATURDAY, POSSIBLY CREEPING A LITTLE  
HIGHER SUNDAY AS LOW LEVEL FLOW TURNS MORE SOUTHERLY AGAIN, SO MAY  
HAVE TO WATCH FOR SOME AREAS REACHING HEAT ADVISORY CRITERIA, THOUGH  
READINGS REMAINING A FEW DEGREES SHY AT THIS TIME. WILL CONTINUE TO  
HIGHLIGHT THE UPCOMING WARMTH ONLINE, AND WILL ADD A MENTION TO THE  
HWO AS WELL. WHILE CANNOT RULE OUT A STRAY SHOWER OR STORM AT SOME  
POINT THROUGH SUNDAY, PRECIPITATION CHANCES ARE MINIMAL WITH THE  
WARM RIDGE IN CONTROL, SO WILL MAINTAIN THE DRY FORECAST FOR NOW.  
 
SUNDAY NIGHT/MONDAY, THE UPPER RIDGE AXIS SHIFTS EAST AS A PIECE OF  
ENERGY LIFTS NORTHWARD THROUGH THE CENTRAL HIGH PLAINS. THIS COULD  
BRING SPOTTY SHOWERS/STORMS TO THE AREA FOR THE MEMORIAL DAY HOLIDAY  
ITSELF, BUT PRECIPITATION CHANCES SHOULD GROW THROUGH MIDWEEK AS THE  
BROAD WESTERN TROUGH SHIFTS EAST INTO THE NORTHERN PLAINS. FAIRLY  
GOOD CONSENSUS IN THE 00Z MODELS FOR A WET PERIOD LATE TUESDAY INTO  
TUESDAY NIGHT, BUT CONFIDENCE NOT QUITE HIGH ENOUGH TO GO WITH A  
LIKELY POP THAT FAR OUT, SO WILL STICK TO JUST HIGH CHANCE RANGE FOR  
NOW. THIS SHOULD BRING SOME RELIEF FROM THE WEEKEND HEAT, THOUGH AT  
THIS POINT STILL LOOKING LIKE TEMPERATURES WILL REMAIN A BIT ABOVE  
NORMAL AS MAY COMES TO A CLOSE.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z FRIDAY MORNING)  
ISSUED AT 637 AM CDT THU MAY 24 2018  
 
PRIMARILY VFR CONDITIONS THROUGH THE TAF PERIOD. THERE WILL BE  
PERIODIC THUNDERSTORM CHANCES THROUGH THE PERIOD, FOCUSED EARLY  
THIS MORNING, AND AGAIN LATE THIS AFTERNOON INTO TONIGHT.  
CONFIDENCE IS LOW IN TIMING/LOCATION OF LATE DAY DEVELOPMENT, SO  
OPTED TO ONLY CARRY A MINIMAL MENTION OF EVENING THUNDER/VCTS IN  
THE TAFS AT THIS TIME.  
 

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

 
 

 
 
SHORT TERM...JH  
LONG TERM...JH  
AVIATION...JH  
 
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