144  
FXUS65 KBYZ 201510  
AFDBYZ  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BILLINGS MT  
910 AM MDT TUE OCT 20 2020  
   
UPDATE
 
 
FAIRLY STRONG PRESSURE RISES MOVING ACROSS OUR EAST ARE STARTING  
TO PRODUCE BREEZY NW WINDS, WITH GUSTS 20-35 MPH MANY LOCATIONS.  
RAIN/SNOW SHOWER ACTIVITY IS ON THE DECREASE BUT WILL LINGER FOR A  
COUPLE MORE HOURS. BUILDING SURFACE HIGH OVER EASTERN MT WILL  
BRING A MOSTLY DRY DAY ONCE WE GET TO THE AFTERNOON. TEMPS WILL BE  
WARMER THAN THE PAST FEW, BUT STILL WELL BELOW NORMAL. HAVE  
TWEAKED POPS, SKY AND WIND PER CURRENT TRENDS...BUT OVERALL  
FORECAST IS IN GOOD SHAPE. JKL  
 

 
   
DISCUSSION
 
 
TODAY THROUGH WEDNESDAY NIGHT...  
 
WE HAVE CANCELLED THE WEATHER ADVISORY FOR CUSTER COUNTY AS LOW  
LEVEL TEMPERATURES HAVE WARMED ABOVE FREEZING IN THIS AREA. WE  
WILL LET THE OTHER ONES FOR FALLON AND CARTER RIDE FOR NOW UNTIL 6  
AM AS SOME POCKETS OF COLD AIR MAY BE LINGERING IN THIS AREA YET.  
SOME RAIN/SNOW SHOWERS ARE STILL POSSIBLE, BUT SHOULD NOT AMOUNT  
TO MUCH AS MOST OF ENERGY ALOFT EXITS TO THE EAST THIS MORNING.  
 
STRONG JET OVER THE AREA TODAY, BUT SOUNDINGS SUGGEST AN INVERSION  
WILL PREVENT THE BULK OF MID LEVEL FLOW FROM REACHING SURFACE.  
THAT SAID, STRONG PRESSURE RISES WILL LEAD TO BRISK NORTHWEST  
WINDS, ESPECIALLY IN THE FAR EASTERN SECTIONS OF THE CWA. TEMPS  
WILL BE WARMER, BUT HINDERED BY EXISTING SNOW COVER. LOOK FOR  
READINGS TO BE MOSTLY UPPER 30S TO MID 40S WHICH IS WELL BELOW THE  
SEASONAL AVERAGES.  
 
BACKING WINDS ALOFT AND ISENTROPIC ASCENT WILL INTRODUCE OUR NEXT  
CHANCE OF LIGHT PRECIP BY TONIGHT. PRECIP TYPE WILL AGAIN BE  
DIFFICULT TO CALL. WE WILL MENTION SOME LIGHT FREEZING RAIN AGAIN  
AS SURFACE TEMPS ARE LIKELY TO FALL BELOW FREEZING, BUT  
PRECIPITATION MAY BE SORTA PATCHY OVERALL WITH LITTLE ACCUMULATION  
EXPECTED.  
 
WEDNESDAY/WEDNESDAY NIGHT...WINDS CONTINUE TO BACK EARLY WEDNESDAY  
AS UPPER TROF MOVES INTO THE ROCKIES. MOISTURE SLOWLY ENCROACHES  
ON OUR AREA FROM THE WEST WITH STRONG FRONTOGENESIS ACROSS OUR  
CWA BY EVENING SUPPORTED BY OVERRUNNING AND UPSLOPE. SOME AREAS OF  
RAIN ON WEDNESDAY WILL INCREASE AND TURN TO SNOW WEDNESDAY  
NIGHT. SNOW WEDNESDAY NIGHT MAY APPROACH 6-10 INCHES OR MORE IN  
THE MOUNTAINS WITH 3-6 INCHES IN THE NEARBY WESTERN LOWER  
ELEVATIONS AND A COUPLE OF INCHES IN THE EAST. ADDITIONAL SNOWFALL  
IS THEN EXPECTED THURSDAY). WHILE THE LAST SYSTEM DID NOT HAVE  
MUCH WIND INVOLVED, IT DOES LOOK LIKE BLOWING SNOW MAY BE AN ISSUE  
WITH THIS ONE. WE WILL ISSUE A WINTER STORM WATCH FOR AREAS WE  
BELIEVE WILL BE HARDEST HIT (SW MOUNTAINS AND FOOTHILLS ALONG WITH  
A LARGE PORTION OF SOUTH CENTRAL MONTANA). THE WATCH WILL START  
AT NOON WEDNESDAY FOR THE SOUTHWEST MOUNTAINS, AND AT 6 PM  
WEDNESDAY FOR THE LOWER ELEVATIONS. END TIME FOR ALL LOCATIONS IS  
6 PM THURSDAY. WE ANTICIPATE OTHER AREAS TO THE EAST WILL  
EVENTUALLY NEED WINTER WEATHER ADVISORIES AS WELL. BT  
 
THURSDAY THROUGH MONDAY...  
 
THE UPPER TROUGH THAT IS EXPECTED TO MOVE INTO THE NORTHERN  
ROCKIES WEDNESDAY-WEDNESDAY NIGHT LOOKS TO PRODUCE MORE SNOW ON  
THURSDAY. MUCH OF THE AREA COULD RECEIVE ANOTHER 1 TO 4 INCHES OF  
SNOW DURING THE DAY. THE SNOW WILL GRADUALLY LIGHTEN IN THE  
AFTERNOON AS THE LARGE SCALE ASCENT WEAKENS. NORTHERLY LOW LEVEL  
WINDS WILL KEEP TEMPERATURES NEARLY STEADY IN THE 20S.  
 
CONDITIONS SHOULD DRY OUT THURSDAY NIGHT AS THE UPPER TROUGH MOVES  
AWAY FROM MONTANA AND A 1036 MB SURFACE HIGH MOVES INTO MONTANA.  
TEMPERATURES WILL DROP TO THE SINGLE DIGITS ABOVE ZERO BY FRIDAY  
MORNING.  
 
ON FRIDAY, THE SURFACE HIGH PRESSURE WILL MOVE EASTWARD AWAY FROM  
MONTANA AS ANOTHER UPPER TROUGH MOVES INTO THE PACIFIC NORTHWEST.  
THIS UPPER TROUGH SHOULD BEGIN TO SPREAD SNOW OVER SOUTH CENTRAL  
MT IN THE AFTERNOON AND OVER THE WHOLE AREA FRIDAY NIGHT. SNOW  
LOOKS TO CONTINUE THROUGH SATURDAY AND POSSIBLY SATURDAY NIGHT.  
MODEL DATA ARE SUGGESTING A 70%+ CHANCE OF AT LEAST 4 INCHES OF  
SNOW OVER SOUTH CENTRAL MT AND NORTH CENTRAL WY FROM THIS SYSTEM.  
 
STRONG SURFACE HIGH PRESSURE OVER ALBERTA SHOULD SUPPLY PLENTY OF  
COLD AIR FOR THIS WINTER STORM, KEEPING PRECIPITATION AS SNOW,  
AND TEMPERATURES FRIDAY NIGHT IN THE TEENS AND SINGLE DIGITS AND  
TEENS AND 20S ON SATURDAY. SATURDAY NIGHT LOOKS REMARKABLY COLD  
WITH LOW TEMPERATURES BELOW ZERO NORTHWEST OF BILLINGS, AND SINGLE  
DIGITS ABOVE ZERO FOR THE REST OF THE AREA.  
 
SUNDAY, UPPER RIDGING AND THE SURFACE HIGH WILL SLIDE  
SOUTHEASTWARD INTO MONTANA AND CAUSE SNOW TO TAPER OFF FROM NORTHWEST  
TO SOUTHEAST. TEMPERATURES WILL CLIMB TO THE TEENS TO LOWER 20S  
IN THE AFTERNOON. THE SURFACE HIGH WILL MOVE SOUTHEASTWARD FURTHER  
INTO THE CENTRAL PLAINS ON MONDAY, WHICH SHOULD CAUSE LOW LEVEL  
WINDS TO TURN SOUTH/SOUTHWESTERLY AND BRING INCREMENTALLY WARMER  
AIR INTO THE REGION WITH HIGH TEMPERATURES WELL INTO THE 20S. RMS  
 

 
   
AVIATION
 
 
MVFR-IFR IN AREAS OF RAIN/SNOW AND LOW CEILINGS WILL IMPROVE TO  
VFR FROM NORTH TO SOUTH TODAY AS DRIER AIR MOVES IN. NORTHWEST  
WINDS GUSTING TO 25-30 KT ARE EXPECTED OVER SOUTHEAST MT AND NORTH  
CENTRAL WY THIS MORNING INTO THE AFTERNOON, WITH LOCALLY HIGHER  
GUSTS AIDED BY RAIN SHOWERS. GILSTAD  
 

 
   
PRELIMINARY POINT TEMP/POPS
 
 
TDY WED THU FRI SAT SUN MON  
-------------------------------------------------------  
BIL 041 028/040 021/027 008/024 013/020 005/018 001/022  
2/W 36/O +8/S 22/S 88/S 74/S 21/B  
LVM 049 031/047 017/029 007/029 011/022 000/020 901/029  
2/W 47/O 96/S 14/S 89/S 63/S 21/B  
HDN 040 026/043 021/029 007/027 013/023 004/019 901/022  
3/J 34/O 98/S 21/E 77/S 74/S 21/B  
MLS 041 023/044 022/029 010/025 013/023 008/020 001/020  
2/W 23/O 97/S 11/E 67/S 64/S 21/B  
4BQ 041 026/046 023/031 011/028 016/026 009/021 001/022  
3/W 22/O 88/S 31/E 67/S 74/S 21/B  
BHK 041 021/042 021/028 007/025 010/023 007/020 001/020  
3/W 05/O 98/S 21/B 56/S 64/S 21/B  
SHR 044 025/048 018/030 008/030 013/027 004/020 901/025  
5/W 22/R 99/S 31/B 57/S 85/S 32/S  
 

 
   
BYZ WATCHES/WARNINGS/ADVISORIES
 
 
MT...WINTER STORM WATCH IN EFFECT FROM WEDNESDAY EVENING THROUGH  
THURSDAY AFTERNOON FOR ZONES  
34-40-42-56-57-63>66-138-139-141-169>172-228-235.  
WINTER STORM WATCH IN EFFECT FROM WEDNESDAY AFTERNOON THROUGH  
THURSDAY AFTERNOON FOR ZONES 67-68.  
WY...NONE.  
 

 
 

 
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