988  
FXUS65 KBYZ 312216  
AFDBYZ  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BILLINGS MT  
416 PM MDT SUN MAY 31 2020  
   
UPDATE
 
 
UPDATE TO ISSUE SEVERE THUNDERSTORM WATCH FOR CUSTER, FALLON,  
POWDER RIVER AND CARTER COUNTIES UNTIL 10PM. HOOLEY  
 

 
   
DISCUSSION
 
 
HOTTEST TEMPERATURES OF THE YEAR OCCURRING THIS AFTERNOON ACROSS  
THE FORECAST AREA. BILLINGS AIRPORT RECENTLY HIT 91 DEGREES BUT  
THE DEWPOINT DROPPED DRAMATICALLY AS DRIER AIR IS MOVING WEST TO  
EAST ACROSS THE FORECAST AREA. THIS FRONT WILL CONTINUE TO MOVE  
ACROSS EAST AND SOUTHEAST MONTANA THIS AFTERNOON INTO THIS  
EVENING. A SURFACE TROUGH IS CURRENTLY LOCATED NORTH/SOUTH FROM  
TREASURE COUNTY TO BIG HORN COUNTY AND THIS IS WHERE THE  
THUNDERSTORMS ARE CURRENTLY DEVELOPING. WEST OF THIS AREA  
DEWPOINTS HAVE DROPPED INTO THE 30S AND 40S SO WE ARE NOT  
EXPECTING ANY THUNDERSTORM ACTIVITY ACROSS THOSE AREAS.  
 
FURTHER EAST, A SOUTHEAST WIND HAS ADVECTED LOW 60 DEWPOINTS INTO  
THE AREA AND SHEAR IS MUCH BETTER AS WELL. THIS, COMBINED WITH  
PLENTY OF SUNSHINE OUT EAST, HAS RESULTED IN AN UNSTABLE  
ATMOSPHERE. SOUNDINGS SHOW SOME OF THE AREA STILL CAPPED FOR THE  
NEXT HOUR OR TWO. BUT AS THE CAP BREAKS, A FEW STRONG TO SEVERE  
THUNDERSTORMS WILL BE LIKELY LATE THIS AFTERNOON THROUGH MID-  
EVENING. THE STORMS SHOULD MOVE EAST OUT OF THE AREA INTO THE  
DAKOTAS BY AROUND MIDNIGHT.  
 
SOMEWHAT COOLER AIR WILL BE IN PLACE MONDAY AND SLIGHTLY COOLER  
YET TUESDAY. ANOTHER DISTURBANCE WILL MOVE OVER THE FORECAST AREA  
MONDAY INTO MONDAY NIGHT RESULTING IN CONTINUED CHANCES FOR SHOWER  
AND THUNDERSTORM ACTIVITY. THERE WILL REMAIN AN ISOLATED CHANCE  
FOR A SEVERE STORM NEAR THE DAKOTA BORDERS DURING THE EVENING INTO  
MONDAY NIGHT. HIGHS MONDAY WILL COOL INTO THE LOWER 80S WITH  
MAINLY UPPER 70S FOR TUESDAY. HOOLEY  
 
WEDNESDAY THROUGH SUNDAY...  
 
MOST OF THE EXTENDED PERIOD LOOKED ACTIVE WITH WEATHER. HOWEVER,  
FOR WEDNESDAY INTO THURSDAY, WEST FLOW WILL BE OVER THE AREA N OF  
A RIDGE, AND THE FORECAST AREA WILL BE MAINLY DRY. WARM ADVECTION  
AND MOISTURE INCREASE OVER THE SW MOUNTAINS THU. AFTERNOON WHICH  
WILL BRING A CHANCE OF SHOWERS AND THUNDERSTORMS TO AREAS MAINLY W  
OF KBIL. WARM ADVECTION AND MOISTURE WILL CONTINUE MOVING NE INTO  
THE AREA AROUND A NW TO SE ORIENTED UPPER RIDGE ON FRIDAY FOR  
CONTINUED CHANCES OF SHOWERS AND THUNDERSTORMS. ON SATURDAY, SW  
FLOW WILL BE OVER THE AREA, AND MODELS SHOWED PRECIPITABLE WATERS  
POSSIBLY OVER AN INCH OVER EASTERN AREAS. ENSEMBLES SHOWED THAT  
QPF AND TEMPS HAD FAIR AMOUNT OF UNCERTAINTY FROM SATURDAY ONWARD.  
ON SUNDAY, UNCERTAINTY INCREASED FURTHER DUE TO THE DIFFERENCES IN  
LOCATION OF THE UPPER LOW/TROUGH OVER W CANADA/PACIFIC NW. GIVEN  
THE ABOVE, CHANCES FOR SHOWERS AND STORMS WERE STILL WARRANTED  
OVER MUCH OF THE AREA THROUGH SUNDAY. EC ENSEMBLES SHOWED HIGH  
CAPES OVER THE E FRIDAY AND FRI. NIGHT. GIVEN THE GENERAL PATTERN,  
THERE WILL BE CHANCES FOR STRONG TO SEVERE STORMS FRIDAY THROUGH  
SUNDAY. TEMPS WILL BE MOSTLY IN THE 80S THROUGH THE PERIOD. ARTHUR  
 

 
   
AVIATION
 
 
MAINLY VFR CONDITIONS WILL PREVAIL THROUGH TONIGHT AND ON MONDAY.  
HOWEVER, ISOLATED TO SCATTERED THUNDERSTORMS THIS AFTERNOON WILL  
PRODUCE LOCALIZED MVFR OR LOWER CONDITIONS, MAINLY OVER AREAS EAST  
OF KBIL WHERE HEAVY RAIN, LARGE HAIL AND STRONG DAMAGING WINDS  
ARE POSSIBLE. THIS INCLUDES KMLS, KBHK, K4BQ AND KSHR GENERALLY  
FROM 20Z TO 04Z. THERE WILL BE LOCALIZED MOUNTAIN OBSCURATIONS  
OVER THE NE BIGHORNS THIS AFTERNOON. ISOLATED THUNDERSTORMS WILL  
MOVE INTO WESTERN AREAS, FROM KLVM TO HARLOWTON, MONDAY  
AFTERNOON. ARTHUR  
 

 
   
PRELIMINARY POINT TEMP/POPS
 
 
MON TUE WED THU FRI SAT SUN  
-----------------------------------------------------------  
BIL 055/082 057/078 055/085 056/080 055/085 060/083 055/083  
00/U 22/W 11/B 12/T 22/T 34/T 34/T  
LVM 050/079 052/077 050/081 052/078 050/081 054/077 049/075  
02/T 43/W 11/U 14/T 34/T 46/T 56/T  
HDN 054/084 055/078 054/086 055/082 055/088 060/084 055/085  
00/U 11/B 11/B 12/T 32/T 44/T 33/W  
MLS 055/082 056/078 054/085 056/082 055/085 061/084 057/085  
20/U 21/B 10/U 11/B 31/B 44/T 22/W  
4BQ 055/083 055/078 053/084 054/083 054/086 059/084 055/086  
30/U 21/U 11/U 11/B 31/B 44/T 22/W  
BHK 054/080 054/077 050/082 052/080 053/082 058/081 055/083  
40/U 21/U 11/U 11/B 32/T 45/T 22/W  
SHR 054/086 053/077 053/083 053/082 053/087 058/083 052/084  
00/U 02/W 10/U 12/T 22/T 44/T 22/W  
 

 
   
BYZ WATCHES/WARNINGS/ADVISORIES
 
 
MT...SEVERE THUNDERSTORM WATCH 238 IN EFFECT UNTIL 10 PM MDT THIS  
EVENING FOR ZONES 32-33-36-37.  
WY...NONE.  
 

 
 

 
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