118  
FXUS65 KBYZ 181437  
AFDBYZ  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BILLINGS MT  
837 AM MDT SAT AUG 18 2018  
   
UPDATE
 
 
SHOWERS AND THUNDERSTORMS HAVE FILLED IN OVER CENTRAL ZONES WITH  
AREAS OF MODERATE RAIN FROM THE BIGHORN BASIN THROUGH YELLOWSTONE  
COUNTY REPORTED THE MORNING. SHOWERS AND THUNDERSTORMS WILL  
CONTINUE THROUGH THE DAY AS A SLOW MOVING UPPER LOW SLIDES ACROSS  
SOUTHERN MONTANA. RAISED POPS TO ACCOUNT FOR RADAR COVERAGE AND  
LATEST MODEL GUIDANCE. KEPT THE MENTION OF STRONG THUNDERSTORMS  
OVER THE SOUTHEAST TODAY. CAPE HIGH, BUT SHEAR LOW, SO WOULD  
EXPECT PULSING TYPE OF STORMS. CLOUD COVER GETTING IN THERE SOONER  
THAN EXPECTED COULD INHIBIT DEVELOPMENT, BUT AREA LOOKS MOSTLY  
CLEAR AT THIS POINT. UPDATE ALREADY SENT. TWH  
 

 
   
SHORT TERM...VALID FOR TDY AND SUN
 
 
NO MAJOR CHANGES NEEDED TO THE GOING SHORT-TERM FORECAST. GUST  
FRONT WITH SHOWERS AND THUNDERSTORMS CROSSED THE W AND CENTRAL  
PARTS OF THE FORECAST AREA EARLIER IN THE NIGHT, BEFORE THE GUST  
FRONT WEAKENED OVER ROSEBUD COUNTY. THE COLD FRONT WAS DIFFICULT  
TO DISCERN, BUT APPEARED TO BE OVER THE WESTERN PART OF THE AREA  
BASED ON W WINDS AND PRESSURE RISES. UPPER LOW WAS OVER ID AT  
0730Z PER WATER VAPOR IMAGERY. PLENTY OF MOISTURE WAS SEEN MOVING  
N INTO THE AREA AHEAD OF THE LOW. THE LOW WAS PROGGED TO BE OVER  
SE MT/NE WY BY 00Z SUNDAY AND WILL BE ACCOMPANIED BY STRONG  
Q-VECTOR CONVERGENCE. PRECIPITABLE WATERS WILL BE AROUND AN INCH  
TODAY AND THE BEST INSTABILITY WILL BE OVER SE MT WITH NOT MUCH  
SHEAR. HREF SHOWED A 10 PERCENT NP OF UPDRAFT HELICITY IN THE SE  
CORNER OF MT THIS AFTERNOON. SPC PLACED THIS AREA IN A MARGINAL  
RISK FOR SEVERE STORMS WHICH LOOKED REASONABLE AHEAD OF THE  
APPROACHING COLD FRONT. FOR POPS, THERE WERE TWO SCHOOLS OF MODEL  
SOLUTIONS. THE GFS/WRF HAD A MORE CONVECTIVE SOLUTION ALONG THE  
COLD FRONT, WHILE THE ECMWF/CANADIAN PAINTED A SYNOPTIC PICTURE OF  
WIDESPREAD QPF AROUND THE UPPER LOW. WENT WITH A BLEND OF BOTH  
SOLUTIONS GIVEN THE NATURE OF THE PATTERN TODAY, WHICH RESULTED IN  
SCATTERED TO LIKELY POPS OVER THE ENTIRE AREA EXCEPT FOR SE MT  
THIS MORNING, THEN HAD MAINLY LIKELY POPS ACROSS THE AREA THIS  
AFTERNOON. ADDED MENTION OF HAIL/GUSTY WINDS TO THE MARGINAL RISK  
AREA. IT WILL BE WARM IN THE MID TO UPPER 80S AHEAD OF THE FRONT,  
OTHERWISE TEMPERATURES WILL BE IN THE 70S.  
 
THE LOW WILL MOVE SE OUT OF THE AREA TONIGHT WITH HIGHEST POPS  
E AND SE OF KBIL. THE FLOW WILL BECOME MORE NNE TONIGHT WHICH WILL  
HELP CLEAR OUT THE SMOKE. A BACK DOOR FRONT WILL SAG INTO THE AREA  
ON SUNDAY, BRINGING SOME UPSLOPE SHOWERS TO AREAS OVER AND NEAR  
THE MOUNTAINS, AS WELL AS COOLER CONDITIONS. HIGHS WILL BE IN THE  
70S. UPSLOPE FLOW CONTINUES SUN. NIGHT AHEAD OF THE NEXT SYSTEM  
OVER THE PACIFIC NW. EXPECT SHOWERS AND A FEW EVENING  
THUNDERSTORMS OVER AND NEAR THE MOUNTAINS. ARTHUR  
   
LONG TERM...VALID FOR MON...TUE...WED...THU...FRI
 
 
NO MAJOR CHANGES IN THE EXTENDED AS RIDGING TRIES TO BUILD INTO  
THE NORTHERN ROCKIES. SOME SUBTLE DIFFERENCES IN THE THE MODELS  
REMAIN, BUT THE OVERALL PICTURE CONTINUES. ENOUGH SHORTWAVE ENERGY  
IS STILL EXPECTED TO MOVE OVER THE BUILDING RIDGE TO KEEP SOME  
ISOLATED TO SCATTERED POPS GOING THROUGH AT LEAST MID WEEK. THE  
MOUNTAINS ARE STILL MORE LIKELY TO SEE THE SHOWERS AND  
THUNDERSTORMS THAN THE LOWER ELEVATIONS. TEMPERATURES WILL STILL  
BE ON THE COOLER SIDE OF NORMAL FOR MONDAY WITH HIGHS GENERALLY IN  
THE UPPER 70S. TUESDAYS WILL SEE MOST OF THE AREA INTO THE 80S,  
WITH THE REST OF THE FORECAST IN THE UPPER 80S TO LOWER 90S FOR  
HIGHS. REIMER  
 

 
   
AVIATION
 
 
SHOWERS WITH SOME EMBEDDED THUNDERSTORMS WILL IMPACT THE ENTIRE  
REGION TODAY. VFR WILL GENERALLY PREVAIL, BUT MVFR IS POSSIBLE IN  
AREAS OF HEAVIER RAIN, AND MOUNTAINS WILL BE OCCASIONALLY  
OBSCURED. HEAVIEST RAIN WILL SHIFT EAST OF KBIL TONIGHT. WESTERN  
AREAS COULD SEE A RISK OF FOG TONIGHT. JKL  
 

 
   
PRELIMINARY POINT TEMP/POPS
 
 
TDY SUN MON TUE WED THU FRI  
-------------------------------------------------------  
BIL 076 057/078 056/074 053/080 057/090 060/088 057/086  
+/T 41/B 23/T 21/B 11/U 21/U 00/U  
LVM 078 049/079 048/075 048/082 050/090 051/087 048/086  
7/T 41/B 34/T 32/T 11/U 21/U 01/U  
HDN 081 055/079 054/077 052/082 055/092 057/090 055/089  
9/T 52/W 23/T 21/B 11/U 21/U 00/U  
MLS 082 058/079 051/077 053/083 057/091 061/091 058/089  
5/T 52/W 12/T 11/U 01/U 21/U 00/U  
4BQ 081 057/077 047/078 052/081 055/091 058/090 056/089  
7/T 73/W 12/T 21/B 11/U 21/U 00/U  
BHK 086 057/076 046/076 049/081 054/090 057/088 055/088  
7/T 62/W 02/T 11/U 00/U 11/U 10/U  
SHR 073 053/075 049/078 052/082 052/090 055/088 053/087  
8/T 74/T 24/T 32/T 11/U 21/U 00/U  
 

 
   
BYZ WATCHES/WARNINGS/ADVISORIES
 
 
MT...NONE.  
WY...NONE.  
 

 
 

 
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