430  
FXUS63 KFSD 181728  
AFDFSD  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SIOUX FALLS SD  
1128 AM CST TUE DEC 18 2018  
   
SHORT TERM
 
(TODAY AND TONIGHT)  
ISSUED AT 249 AM CST TUE DEC 18 2018  
 
TEMPERATURES EARLY THIS MORNING STILL NEAR THEIR CLIMATOLOGICAL  
HIGHS FOR THIS TIME OF YEAR, IN THE UPPER 20S AND 30S. GOES EAST  
SATELLITE IMAGERY SHOWS A BROAD UPPER LOW SPINNING OVER THE  
DESERT SOUTHWEST WITH HIGH LEVEL CLOUDS CURRENTLY FILTERING OVER  
OUR AREA. THRU THE DAY, A WEAK PIECE OF ENERGY FROM THIS BROAD  
TROUGH WILL SLIDE THROUGH THE AREA LARGELY JUST BRINGING AN  
INCREASE IN MID/UPPER LEVEL CLOUD COVER. WITH SURFACE FLOW OUT OF  
MORE OF A SOUTHWESTERLY TO WESTERLY DIRECTION, ALONG WITH  
SEASONABLY WARM AIR ABOVE THE SURFACE, ANOTHER MILD AFTERNOON IS  
EXPECTED. EVEN WITH THE INCREASING CLOUD COVER, CONTINUED THE  
TREND OF LEANING ON THE UPPER ENDS OF GUIDANCE VALUES FOR  
AFTERNOON HIGH TEMPERATURES AS MIXING POTENTIAL MAY HELP TO  
COMPENSATE FOR ANY LOSS OF RADIATIONAL HEATING, ESPECIALLY GIVE  
THE TIME OF YEAR/SUN ANGLE.  
 
BY TONIGHT, THE MAIN UPPER LEVEL TROUGH BEGINS TO SLIDE EASTWARD.  
ANY BREAKS IN THE UPPER LEVEL CLOUDS FROM TODAY WILL BE FILLED IN  
WITH INCREASING CLOUD COVER ALONG WITH PERHAPS A BIT OF FOG IN NW  
IOWA. THIS WILL ALSO WORK TO KEEP OVERNIGHT LOWS ON THE WARM SIDE  
OF NORMAL AGAIN, OR GENERALLY IN THE 20S.  
   
LONG TERM
 
(WEDNESDAY THROUGH MONDAY)  
ISSUED AT 249 AM CST TUE DEC 18 2018  
 
WEDNESDAY: MODELS CONTINUE TO ADVERTISE A NARROW BAND OF LIGHT  
PRECIP SLIDE THROUGH WITH THIS TROUGH PASSAGE. WHILE SEVERAL  
OPERATIONAL MODELS, ALONG WITH THEIR RESPECTIVE ENSEMBLE MEMBERS,  
SHOW SOME VERY LIGHT QPF AMOUNTS, GIVEN A DRY LAYER IN THE LOWER  
LEVELS OF THE ATMOSPHERE EXHIBITED IN THE FORECAST SOUNDINGS, AM  
SKEPTICAL THAT WE SEE A WHOLE LOT MORE THAN SOME SPRINKLES. IN  
EITHER CASE, WILL STILL MAINTAIN SOME LOW SLIGHT CHANCE POPS OVER  
PORTIONS OF THE AREA FOR THE POTENTIAL THAT A FEW LOCATIONS PICK  
UP A HUNDREDTH OF AN INCH OR TWO OF RAIN. IF THIS BAND OF PRECIP  
CAN MAKE IT INTO OUR FAR WESTERN ZONES EARLIER ENOUGH IN THE  
MORNING BEFORE TEMPERATURES WARM ABOVE FREEZING, CAN'T COMPLETELY  
RULE OUT A VERY LIGHT WINTRY MIX BUT CONCERN AT THIS TIME IS  
PRETTY LOW.  
 
HIGH TEMPERATURES WEDNESDAY WILL BE SOMEWHAT TRICKY WITH CLOUD COVER  
IN PLACE BUT ALSO WARMER 925 MB TEMPERATURES SURGING IN FROM THE  
WEST. IF WE CAN MIX DOWN SOME OF THIS AIR WITH INCREASING WESTERLY  
WINDS, TEMPERATURES COULD EASILY MAKE IT INTO THE 50S NEAR AND WEST  
OF THE JAMES RIVER.  
 
THURSDAY AND FRIDAY: AFTER THE MINOR SYSTEM ON WEDNESDAY, UPPER  
LEVEL RIDGE BEGINS BUILDING TO OUR WEST BY THURSDAY AND SLIDES  
EASTWARD BY FRIDAY. QUIET AND COOLER WEATHER EXPECTED, ALTHOUGH  
TEMPERATURES STILL RUNNING 5-10 DEGREES ABOVE THEIR SEASONAL  
NORMALS.  
 
WEEKEND: A QUICK MOVING SHORTWAVE(S) WILL MOVE THROUGH THE REGION  
ALTHOUGH MODELS IN DISAGREEMENT WITH THE DETAILS. THE GFS IS QUICKER  
AND SOMEWHAT MORE ROBUST WITH AN INITIAL WAVE, PERHAPS BRINGING SOME  
VERY LIGHT PRECIP TO MAINLY OUR NORTHERN COUNTIES SATURDAY, WHILE  
THE EC/CANADIAN ARE SLOWER IN THE SATURDAY NIGHT/SUNDAY TIMEFRAME.  
HAVE OPTED TO KEEP THE SLIGHT CHANCE BLENDED GUIDANCE UNTIL MORE  
CONSISTENCY IS REALIZED. WHILE THE PRECIP CHANCES LOOK FAIRLY SLIM  
CURRENTLY WITH THIS SYSTEM, WHAT LOOKS MORE CERTAIN IS THAT THIS  
WILL DRAW IN SOME COOLER TEMPERATURES, MAINLY BACK INTO THE 30S FOR  
AFTERNOON HIGHS.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)  
ISSUED AT 1120 AM CST TUE DEC 18 2018  
 
VFR CONDITIONS ARE EXPECTED THROUGH THE PERIOD. MID TO HIGH CLOUDS  
WILL BE ON THE INCREASE THIS AFTERNOON INTO WEDNESDAY AS A WEAK  
SYSTEM MOVES THROUGH. A FEW SPRINKLES TO VERY LIGHT RAIN WILL BE  
POSSIBLE ON WEDNESDAY THROUGHOUT THE DAY FROM WEST TO EAST.  
 
ALTHOUGH CONFIDENCE REMAINS LOW TO MODERATE, AREAS OF FOG LOOK  
POSSIBLE ACROSS NORTHWEST IOWA AND ADJACENT COUNTIES EARLY  
OVERNIGHT INTO MID WED MORNING.  
 

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

 
 

 
 
SHORT TERM...KALIN  
LONG TERM...KALIN  
AVIATION...05  
 
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