615  
FXUS63 KFSD 240406  
AFDFSD  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SIOUX FALLS SD  
1106 PM CDT THU MAR 23 2017  
   
SHORT TERM
 
(THIS EVENING THROUGH FRIDAY)  
ISSUED AT 354 PM CDT THU MAR 23 2017  
 
A COUPLE OF ELEVATED WAVES HAVE GENERATED SMALL COMPLEXES OF  
THUNDERSTORMS ACROSS FAR SOUTHEAST SD AND NORTHWEST IA TODAY, THE  
FIRST OF WHICH PRODUCED SOME ISOLATED SEVERE HAIL AS IT TRACKED FROM  
NEAR YANKTON INTO AREAS SOUTH OF THE IOWA GREAT LAKES. THE SECOND,  
WEAKER COMPLEX IS LIFTING NORTHEAST INTO NORTHWEST IOWA AS OF 20Z.  
MOVEMENT ON BOTH WAVES HAS BEEN QUITE FAST, ON THE ORDER OF 50-60KT.  
 
FOR TONIGHT, WATCHING A LINE OF ENHANCEMENT DEVELOPING ON IR AND  
WATER VAPOR SATELLITE IMAGERY FROM WEST OF KONL INTO FAR NORTHWEST  
KANSAS LATE THIS AFTERNOON. AS UPPER TROUGH OVER THE ROCKIES BEGINS  
TO KICK EASTWARD AND INTERACT WITH THIS FEATURE, EXPECT THUNDERSTORM  
DEVELOPMENT IN WESTERN NEBRASKA, EXPANDING NORTHEAST INTO SOUTHEAST  
SOUTH DAKOTA THROUGH THE EARLY-MID EVENING AS A 40-50KT LOW LEVEL  
JET DEVELOPS IN EASTERN NEBRASKA AND ENHANCES CONVERGENCE ALONG AN  
INVERTED TROUGH, PROGGED TO LIE FROM CENTRAL NEBRASKA, TOWARD KYKN  
AND KFSD, AND INTO SOUTHWEST MN BY 03Z. UNLIKE ACTIVITY EARLIER  
TODAY, FOR WHICH THE MOST HIGH-RES MODELS WERE PLAYING CATCH UP, THE  
HRRR/ARW/NAMNEST, AND EVEN LOWER-RES GFS/CMCREG ARE SIMILAR IN THEIR  
DEPICTION OF DEVELOPMENT THROUGH THE EVENING. GIVEN THE INCREASING  
ELEVATED INSTABILITY AHEAD OF THE WAVE, AND INCREASED SUPPORT FROM  
THE LOW LEVEL JET, CANNOT RULE OUT ANOTHER ISOLATED STRONG-SEVERE  
STORM. HOWEVER, WITH DEEPER MOISTURE BECOMING AVAILABLE, LOCALLY  
HEAVY RAIN MAY BE A GREATER CONCERN.  
 
THUNDER THREAT EXPECTED TO WANE AFTER 06Z AS COLUMN BECOMES MORE  
MOIST-ADIABATIC, BUT WIDESPREAD SHOWERS SHOULD CONTINUE WITH DEEP  
MOISTURE FEEDING INTO WHAT BECOMES A NEARLY STATIONARY LOW-MID LEVEL  
FRONT ACROSS THE FORECAST AREA. SURFACE FRONT DOES EVENTUALLY PUSH  
SOUTHEAST OF THE AREA BY 12Z-15Z, WITH 850MB FRONT LINGERING NEAR  
KSUX-KSLB LINE INTO THE AFTERNOON. THIS WILL KEEP POTENTIAL FOR A  
FEW THUNDERSTORMS OVER THE FAR SOUTHEAST PART OF THE FORECAST AREA  
ON FRIDAY, WITH WIDESPREAD RAIN ACROSS AT LEAST THE SOUTHEAST HALF  
OF THE AREA AS DEEP MOISTURE CONTINUES TO ROTATE NORTHWARD AROUND  
THE SLOWING SYSTEM SHIFTING EAST THROUGH THE PLAINS. WITH RAIN BAND  
LIKELY TO PERSIST OVER THE SAME AREA, CERTAINLY POTENTIAL FOR SOME  
RAINFALL AMOUNTS IN EXCESS OF AN INCH SOUTHEAST OF LAKE ANDES-SIOUX  
FALLS-WINDOM LINE JUST TONIGHT AND FRIDAY. THAT COMBINED WITH THE  
MORE LOCALIZED RAINFALL FROM TODAY'S ACTIVITY COULD RESULT IN SOME  
RIVER RISES FOR THE LOWER BIG SIOUX AND OUR RIVERS ACROSS NORTHWEST  
IOWA.  
   
LONG TERM
 
(FRIDAY NIGHT THROUGH THURSDAY)  
ISSUED AT 354 PM CDT THU MAR 23 2017  
 
PRIMARILY CONTINUED TO FOLLOW A BLEND OF THE GFS AND ECMWF FOR THE  
TRACK OF THE SURFACE AND UPPER LOW, AND THEIR CORRESPONDING  
PRECIPITATION TRENDS FOR FRIDAY NIGHT AND SATURDAY. HIGH POPS ARE  
STILL WARRANTED FRIDAY NIGHT GENERALLY ALONG AND SOUTHEAST OF A LAKE  
ANDES SD TO WINDOM MN LINE AS A DEEP TROWAL CENTERED IN THE 290-310K  
LAYER BECOMES THE DOMINANT PLAYER TO THE NORTH OF THE WRAPPED UP  
UPPER LOW. THAT SAID, THE QPF TREND ON THE NAM LOOKS TOO HEAVY NEAR  
THE I 90 CORRIDOR GIVEN THE DEGREE OF DRY AIR WHICH IS BEGINNING TO  
NUDGE INTO THE MID LEVELS IN THAT AREA. THEREFORE TRENDED CLOSER TO  
GFS/ECMWF/WPC VALUES FOR FRIDAY NIGHT RAIN AMOUNTS. THE  
AFOREMENTIONED TROWAL STILL HANGS AROUND IN NORTHWEST IA ON  
SATURDAY. HOWEVER WITH EVER INCREASING DRY AIR ADVECTING IN, POPS  
WILL WILL SLOWLY WIND DOWN IN THAT AREA. ALL TOLD FOR THE RAIN  
EVENT, LOOKING AT A ONE INCH TO INCH AND A HALF BAND THROUGHOUT THE  
SOUTHEAST HALF OF OUR FORECAST AREA, LETS CALL IT ALONG AND SOUTH OF  
LAKE ANDES SD TO WINDOM MN. AMOUNTS THEN RAPIDLY TAPER OFF NORTH OF  
THERE TO JUST VERY MINIMAL AMOUNTS IN OUR NORTHWEST AROUND HURON.  
THIS IS BECAUSE THE TRACK OF THE LOW ACROSS THE SOUTHERN AND CENTRAL  
PLAINS IS NOT FRIENDLY TO THAT AREA, TOO MUCH DRY AIR IN THE MID  
LEVELS CUTOFF FROM THE DEEP MOISTURE SUPPLY.  
 
BY SUNDAY AND THROUGH THE REST OF THE FORECAST, THE UPPER FLOW IS  
VERY WAVY. ONE WAVE MOVES THROUGH SUNDAY AND SUNDAY NIGHT BUT WILL  
ONLY GIVE MINIMAL CHANCES FOR MEASURABLE RAINFALL. THEN ANOTHER  
STRONG UPPER LOW DIGS INTO THE DESERT SOUTHWEST BY TUESDAY. AFTER  
THAT SOME MODERATE DISCREPANCIES STILL EXIST IN THE TRACK OF IT  
SIMILAR TO YESTERDAYS MODEL RUNS. IN THE LARGE SCALE, THE  
DETERMINISTIC ECMWF AND GFS ARE NOT HORRIBLY DISSIMILAR AT 500MB. BUT  
BY MID WEEK THE ECMWF IS MORE CUTOFF WITH THE LOW PLACING THE  
NORTHERN PLAINS IN A DOMINANT NORTHERN JET. THE GFS IS ALSO WRAPPED  
UP BUT DOES BRING UP A GREATER INFLUENCE OF MOISTURE INTO OUR AREA  
FROM THE GULF. INTERESTINGLY, BOTH MODELS BRING IN ANOTHER STRONG  
UPPER TROUGH ON ITS HEELS ALONG THE PACIFIC COAST BY DAY 7 THURSDAY.  
CHANCE POPS FOR MAINLY RAIN BROUGHT ON BY WARM AIR ADVECTION AHEAD  
OF THE AFOREMENTIONED UPPER LOW ARE STILL WARRANTED TUESDAY NIGHT  
AND WEDNESDAY. CHANCE POPS ARE CONTINUED TO BE WARRANTED INTO  
THURSDAY AS THE LOW GETS CLOSER. BUT TAKEN LITERALLY THE ECMWF WOULD  
BE DRY BY THEN. AT ANY RATE, A TYPICAL SPRING LIKE ACTIVE PATTERN.  
BECAUSE OF THIS, TEMPERATURES WILL BE ABOVE NORMAL BUT NOT GREATLY  
ABOVE NORMAL, AS THE PERIODIC WAVES CONTINUALLY KNOCK BACK DAYTIME  
HIGHS. HIGHS IN THE MID 40S AND 50S WILL DOMINATE SATURDAY THROUGH  
NEXT THURSDAY.  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)  
ISSUED AT 1054 PM CDT THU MAR 23 2017  
 
SHOWERS AND THUNDERSTORMS OVER NEBRASKA WILL CONTINUE TO MOVE  
NORTHEAST INTO THE AREA DURING THE OVERNIGHT HOURS. A FEW OF  
THESE STORMS MAY BECOME STRONG TO SEVERE WITH LARGE HAIL AND HEAVY  
RAINFALL; PRODUCING LOW CEILINGS AND REDUCED VISIBILITY.  
THEREFORE MVFR/IFR CONDITIONS WILL BE PERSISTING FOR MOST OF THE  
TAF PERIOD. RAIN SHOWERS WILL CONTINUE THROUGHOUT THE DAY, AND  
WILL GRADUALLY DIMINISH FROM THE WEST THROUGH LATE FRIDAY NIGHT.  
 

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

 
 

 
 
SHORT TERM...  
LONG TERM...MJ  
AVIATION...05/JM  
 
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