318  
FXUS63 KBIS 312359  
AFDBIS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BISMARCK ND  
659 PM CDT SUN MAY 31 2020  
   
UPDATE
 
 
ISSUED AT 647 PM CDT SUN MAY 31 2020  
 
THE FORECAST FOR THIS EVENING REMAINS ON TRACK. SEVERE  
THUNDERSTORM WATCH NUMBER 238 REMAINS IN EFFECT FOR THE  
SOUTHWEST.  
 
THUNDERSTORMS CONTINUE TO MOVE NORTHEAST ACROSS SOUTHEASTERN  
MONTANA, AND ARE PROJECTED TO ENTER SOUTHWEST ND BETWEEN 00-01Z.  
AT THIS TIME, ONE SEVERE STORM TRACKING EAST OF MILES CITY,  
SHOWING SIGNS OF BEING SUPERCELLULAR, TAKING A RIGHT MOVER TRACK  
MORE EASTERLY VERSUS NORTHEAST. STILL SOME UNCERTAINTY ON THE  
OVERALL STORM COVERAGE ACROSS WESTERN ND WITH FORCING ALOFT NOT  
THAT IMPRESSIVE.  
 
WILL MAINTAIN THE WIND ADVISORY AS IS BUT SHOULD BE ABLE TO LET IT  
EXPIRE WITHIN THE NEXT HOUR.  
 
 
UPDATE  
ISSUED AT 511 PM CDT SUN MAY 31 2020  
 
SEVERE THUNDERSTORM WATCH NOW IN EFFECT FOR PORTIONS OF SOUTHWEST  
NORTH DAKOTA. WILL UPDATE ALL PRODUCTS TO REFLECT THIS.  
 

 
   
SHORT TERM
 
(THIS EVENING THROUGH MONDAY)  
ISSUED AT 247 PM CDT SUN MAY 31 2020  
 
THE MAIN CONCERN FOR THE SHORT TERM PERIOD IS THE POTENTIAL FOR  
STRONG TO SEVERE THUNDERSTORMS IN WESTERN NORTH DAKOTA THIS EVENING.  
 
AN UPPER LEVEL RIDGE AXIS SITS OVER THE NORTHERN PLAINS EARLY THIS  
AFTERNOON, WITH A 30-40 KT LOW LEVEL JET UNDERNEATH. SURFACE  
ANALYSIS SHOWS HIGH PRESSURE OVER THE GREAT LAKES AND A DEEPENING  
LOW IN SOUTHERN ALBERTA. THIS SETUP HAS RESULTED IN WINDY CONDITIONS  
ACROSS THE REGION. THE STRONGEST WINDS HAVE BEEN IN NORTHWEST NORTH  
DAKOTA, WHERE SUSTAINED WIND SPEEDS OVER 30 MPH HAVE ROUTINELY BEEN  
REPORTED. A WIND ADVISORY IS IN EFFECT FOR THAT AREA UNTIL 8 PM CDT.  
 
MID LEVEL SHORTWAVE TROUGHING WILL MOVE INTO EASTERN MONTANA LATE  
THIS AFTERNOON AS A SURFACE TROUGH SHARPENS ATTENDANT TO THE  
SOUTHERN ALBERTA SURFACE LOW. THE PRESENCE OF ADDITIONAL FORCING IN  
THE FORM OF LOW LEVEL FRONTOGENESIS IS FORECAST ACROSS EASTERN  
MONTANA. MOST GUIDANCE AGREES THAT CONVECTIVE INITIATION WILL OCCUR  
IN EASTERN MONTANA LATE THIS AFTERNOON, THOUGH SOME OF THE FORCING  
MECHANISMS APPEAR A BIT DISJOINTED SPATIALLY. ADDITIONALLY, RECENT  
GUIDANCE SUGGESTS CONVECTIVE INHIBITION WILL BE MUCH WEAKER ACROSS  
EASTERN MONTANA THAN ORIGINALLY THOUGHT, OWING TO A GREATER  
LIKELIHOOD OF CONVECTIVE INITIATION GIVEN THE FORCING THAT IS  
FORECAST TO BE PRESENT. THERE IS STILL SOME ON UNCERTAINTY ON  
EXACTLY WHERE CONVECTIVE INITIATION MAY OCCUR, BUT THERE IS A  
NOTABLE TREND IN MORE RECENT GUIDANCE TO SHIFT LOW LEVEL FORCING AS  
FAR EAST AS THE ND/MT BORDER BY LATE AFTERNOON. THIS CAN BE SEEN,  
FOR EXAMPLE, IN RAP 0-1 KM MOISTURE FLUX DIVERGENCE AND THETA-E  
FIELDS. HOWEVER, THERE IS GREATER CONVECTIVE INHIBITION AND LESS MID  
LEVEL FORCING THE FARTHER EAST YOU GO. THIS FURTHER CONTRIBUTES TO  
THE UNCERTAINTY IN THE OVERALL OUTCOME OF THIS EVENT.  
 
SURFACE BASED STORMS THAT DEVELOP WILL BE IN AN ENVIRONMENT  
CHARACTERIZED BY DEWPOINTS AROUND 60 F, CAPE AROUND 2000 J/KG, AND  
30-40 KTS OF EFFECTIVE BULK SHEAR, ACCORDING TO THE HREF ENSEMBLE  
MEAN. SHEAR VECTORS ORIENTED NEARLY PERPENDICULAR TO THE SURFACE  
TROUGH SUGGEST A DISCRETE MODE WILL BE FAVORED INITIALLY, THOUGH  
COLD POOL PROCESSES AND SUSTAINED FORCING MECHANISMS MAY EVENTUALLY  
LEAD TO UPSCALE GROWTH INTO LINEAR CLUSTERS DOWNSTREAM. A LARGE HAIL  
THREAT IS SUPPORTED BY THE AFOREMENTIONED INSTABILITY AND SHEAR,  
STORM MODE, AND RELATIVELY DRY MID LEVELS. A DAMAGING WIND THREAT IS  
SUPPORTED BY HIGH LCLS AND INVERTED-V THERMODYNAMIC PROFILES, AS  
WELL AS BY ANY TRANSITION TO A LINEAR MODE.  
 
THERE IS GENERAL MODEL CONSENSUS THAT AT LEAST ISOLATED SHOWER AND  
THUNDERSTORM ACTIVITY WILL CONTINUE TO MOVE ACROSS NORTH DAKOTA  
OVERNIGHT AS THE SURFACE TROUGH AND MID LEVEL SHORTWAVE TRACK  
EASTWARD, THOUGH SOME OF THE MORE RECENT CAM RUNS HAVE BACKED OFF ON  
THIS SOLUTION, LIKELY DUE TO INCREASING MLCIN. QUIET AND WARM  
WEATHER IS EXPECTED ON MONDAY AS SUBSIDENCE REBOUNDS OVER THE  
NORTHERN PLAINS. HIGHS WILL MAINLY BE IN THE 80S.  
   
LONG TERM
 
(MONDAY NIGHT THROUGH SUNDAY)  
ISSUED AT 247 PM CDT SUN MAY 31 2020  
 
ANOTHER MID LEVEL SHORTWAVE WILL APPROACH WESTERN NORTH DAKOTA  
MONDAY NIGHT. THERE IS DECENT MODEL CONSENSUS FOR OVERNIGHT SHOWER  
AND THUNDERSTORM DEVELOPMENT AHEAD OF THIS WAVE, WITH FORCING  
POSSIBLY BEING AIDED BY INCREASING LOW TO MID LEVEL MOISTURE  
TRANSPORT. IF UPDRAFTS CAN TAKE ADVANTAGE OF 1000-2000 J/KG MUCAPE  
OVER SOUTHWEST NORTH DAKOTA, ALONG WITH AT LEAST 40 KTS EFFECTIVE  
BULK SHEAR, STORMS COULD BECOME SEVERE, WITH LARGE HAIL BEING THE  
MAIN THREAT. THERE IS UNCERTAINTY ON HOW MUCH MLCIN WILL BE PRESENT  
THOUGH, WHICH WILL BE LARGELY DEPENDENT ON INFLOW LAYER RH. THIS  
CONDITIONAL SEVERE THREAT MAY EXPAND INTO SOUTH CENTRAL NORTH DAKOTA  
TUESDAY MORNING AS THE SHORTWAVE CONTINUES TO PROPAGATE EASTWARD,  
BUT INSTABILITY LOOKS MORE MARGINAL THERE. FARTHER NORTH, SCATTERED  
SHOWERS ARE POSSIBLE TUESDAY MORNING IN ASSOCIATION WITH STRONGER  
HEIGHT FALLS, BUT THERE IS EXPECTED TO BE LITTLE TO NO INSTABILITY.  
 
MODEL GUIDANCE HAS TRENDED AWAY FROM BROAD UPPER LEVEL RIDGING TO  
MORE OF A ZONAL FLOW PATTERN LATE TUESDAY THROUGH THURSDAY, WITH  
VARIOUS DISTURBANCES PASSING THROUGH. THIS PATTERN SHIFT HAS  
RESULTED IN A SLIGHTLY COOLER TEMPERATURE FORECAST THROUGH  
THURSDAY, THOUGH STILL NEAR TO ABOVE NORMAL. LONG RANGE GUIDANCE  
APPEARS TO BE CONVERGING ON A SOLUTION THAT QUICKLY BUILDS UPPER  
LEVEL RIDGING OVER THE NORTHERN PLAINS HEADING INTO THE WEEKEND  
AHEAD OF DEEPENING LONGWAVE TROUGHING OVER THE PACIFIC COAST. THIS  
COULD SIGNAL THE BEGINNING OF AN ACTIVE PERIOD NEXT WEEKEND,  
THOUGH DETERMINISTIC MODELS ARE EXHIBITING THEIR KNOWN BIASES IN  
THE PROGRESSIVENESS OF THE PATTERN, WITH THE GFS BEING MUCH  
QUICKER TO BRING SHORTWAVE ENERGY INTO THE NORTHERN PLAINS THAN  
THE ECMWF.  
 

 
   
AVIATION
 
(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)  
 
ISSUED AT 647 PM CDT SUN MAY 31 2020  
 
VFR CONDITIONS ARE EXPECTED THROUGH THE FORECAST PERIOD. THERE IS  
A CHANCE OF THUNDERSTORMS IN WESTERN ND THIS EVENING. THIS  
POTENTIAL SHIFTS INTO CENTRAL ND OVERNIGHT, BUT WITH DECREASING  
PROBABILITY. LEFT VCTS IN THE FOR KDIK, BUT OPTED TO REMOVE AND  
GO WITH VCSH FOR KXWA, KMOT, KBIS AND KJMS. IF A STORM DOES  
HAPPEN TO PASS OVER A TERMINAL, A BRIEF PERIOD OF MVFR/IFR  
VISIBILITY AND SPORADIC WIND GUSTS WOULD BE POSSIBLE. STRONG  
SOUTHEAST WINDS AROUND 20-25 KTS GUSTING TO 30-40 KTS WILL  
GRADUALLY DECREASING THIS EVENING AND OVERNIGHT, WITH WINDS  
SHIFTING TO THE NORTHWEST FOR MONDAY.  
 

 
   
BIS WATCHES/WARNINGS/ADVISORIES
 
 
WIND ADVISORY UNTIL 8 PM CDT /7 PM MDT/ THIS EVENING FOR NDZ001-  
002-009-010-017.  
 

 
 

 
 
UPDATE...NH  
SHORT TERM...HOLLAN  
LONG TERM...HOLLAN  
AVIATION...NH  
 
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