369  
FXUS63 KABR 182327 AAA  
AFDABR  
 
AREA FORECAST DISCUSSION...UPDATED  
NATIONAL WEATHER SERVICE ABERDEEN SD  
627 PM CDT SAT AUG 18 2018  
   
UPDATE
 
 
ISSUED AT 622 PM CDT SAT AUG 18 2018  
 
FORECAST IS ON TRACK THIS EVENING AS A LOW PRESSURE SYSTEM MAKES  
ITS WAY EAST INTO CENTRAL SOUTH DAKOTA. SOME OF THESE STORMS ARE  
STRONG WITH OUTFLOW WINDS GUSTING TO 45 MPH. INDIVIDUAL CELLS ARE  
STILL HAVING A DIFFICULT TIME INTENSIFYING DUE TO THE LACK OF  
SHEAR, BUT WILL CONTINUE TO WATCH FOR AN ISOLATED SEVERE CELL WEST  
OF THE MISSOURI.  
 

 
   
SHORT TERM
 
(THIS EVENING THROUGH SUNDAY)  
ISSUED AT 242 PM CDT SAT AUG 18 2018  
 
MAIN FORECAST CHALLENGE IN THE SHORT TERM WILL BE THE EVOLUTION OF  
THE SLOW MOVING LOW PRESSURE SYSTEM AND ASSOCIATED PRECIP ONSET/  
AMOUNTS.  
 
WITH TEMPS IN THE UPPER 80S AND DEWPOINTS IN THE 60S, CAPE VALUES  
HAVE RISEN TO 2000+ J/KG ACROSS THE CENTRAL PART OF SOUTH DAKOTA  
THIS AFTERNOON. EFFECTIVE SHEAR HOWEVER, IS QUITE LACKLUSTER,  
GENERALLY LESS THAN 20 KTS ACROSS THE REGION. THEREFORE EXPECT  
SEVERE STORMS TO BE OF THE MULTICELL PULSE TYPE. MANY OF THE CAMS  
DO SHOW CONVECTION SNEAKING INTO THE SOUTHWEST CWA AROUND THE 00Z  
TIME FRAME, THEN GRADUALLY SPREADING EASTWARD. MAY ALSO SEE SOME  
ENHANCEMENT IN STORM COVERAGE DUE TO A 20 KT LLJ DEVELOPING LATER  
TONIGHT. THEN THERE WILL PROBABLY BE A BREAK ACROSS THE EASTERN  
CWA BETWEEN OVERNIGHT CONVECTION AND WHEN THE DEFORMATION ZONE  
INDUCED PRECIPITATION REALLY GETS GOING SUNDAY AFTERNOON. PWATS  
TOP OUT OVER 1.5 INCHES AND HEAVY RAIN IS POSSIBLE WITH ANY  
STORMS. THE MAIN CHANGE WITH THE CURRENT MODEL RUNS HAS JUST BEEN  
TO SLOW DOWN THE ONSET OF PRECIPITATION.  
 
THE SURFACE PRESSURE GRADIENT WILL TIGHTEN UP ON THE BACKSIDE OF  
THIS SYSTEM ON SUNDAY. USED CONSMOS TO HIGHLIGHT THE STRONGER WINDS  
ANTICIPATED.  
   
LONG TERM
 
(SUNDAY NIGHT THROUGH SATURDAY)  
ISSUED AT 242 PM CDT SAT AUG 18 2018  
 
WHEN THE PERIOD OPENS, THE DEFORMATION ZONE OVER THE REGION IS  
SLOWLY WORKING SOUTHEAST TOWARD IOWA. THERE SHOULD BE SOME  
DEFORMATION-FORCED PRECIPITATION ONGOING MAINLY OVER THE EASTERN  
HALF OF THE FORECAST AREA SUNDAY NIGHT, PROBABLY LINGERING FOR A FEW  
HOURS INTO MONDAY MORNING ALONG/EAST OF THE I-29 CORRIDOR. AT THAT  
POINT, THE FORECAST GOES DRY AS NORTHWEST FLOW ALOFT DEVELOPS OVER  
THE NORTHERN PLAINS. BY THURSDAY, MODELS ARE STILL SUGGESTING THE  
FLOW PATTERN NEARLY FLATTENS OUT, WITH THE ECMWF REMAINING THE MOST  
CONSISTENT MODEL BRINGING A MODERATELY STRONG/TRANSIENT UPPER WAVE  
ACROSS THE NORTHERN TIER STATES, AND SOME PRECIPITATION POTENTIAL  
THURSDAY NIGHT INTO FRIDAY MORNING. BEYOND FRIDAY, THE 12Z GSM  
FAMILY OF SOLUTIONS INDICATES A ZONAL/NEARLY ZONAL PATTERN WILL  
REMAIN ACROSS THE REGION.  
 
STILL LOOKS UNSEASONABLY COOL TO START THE PERIOD, ESPECIALLY WITH  
THE NAEFS S.A. TABLE OUTPUT HIGHLIGHTING ANOMALOUSLY COLD 850HPA AIR  
AROUND (1 TO NEARLY 2.5 STANDARD DEVIATIONS BELOW CLIMO NORMAL) TO  
START THE WEEK OFF. THE COOLISH AIR IS FORECAST TO STICK AROUND  
THROUGH MID-WEEK BEFORE AIRMASS MODERATION AND SOME RETURN FLOW LOW  
LEVEL SOUTHERLY FLOW HAS A CHANCE TO GET GOING WEDNESDAY INTO  
THURSDAY. THERE COULD BE ANOTHER NOTABLE COLD FRONT SWEEPING THROUGH  
THE REGION BY NEXT WEEKEND. BUT, AT THIS POINT, THE MORE PROBABLE  
SCENARIO IS WARMER AIR STICKS AROUND THROUGH SATURDAY.  
 

 
   
AVIATION
 
(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)  
ISSUED AT 622 PM CDT SAT AUG 18 2018  
 
VFR CONDITIONS WILL PREVAIL OVERNIGHT EXCEPT IN THE VICINITY OF  
THUNDERSTORMS WHERE CIGS OR VSBY MAY FALL TO MVFR. BEHIND THE LOW,  
IN THE DEFORMATION ZONE, ON SUNDAY MVFR CIGS WILL BE MORE  
WIDESPREAD, AFFECTING ALL THE TAF SITES.  
 

 
   
ABR WATCHES/WARNINGS/ADVISORIES
 
 
SD...NONE.  
MN...NONE.  

 
 

 
 
UPDATE...WISE  
SHORT TERM...SERR  
LONG TERM...DORN  
AVIATION...WISE  
 
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