117  
FXUS65 KBYZ 180609 AAA  
AFDBYZ  
 
AREA FORECAST DISCUSSION...UPDATED  
NATIONAL WEATHER SERVICE BILLINGS MT  
1109 PM MST SAT FEB 17 2018  
   
UPDATE
 
 
QUICK UPDATE TO ADD IN YELLOWSTONE COUNTY TO THE WINTER WEATHER  
ADVISORY. A BAND OF MODERATE TO HEAVY SNOW WITH SOME POSSIBLE ICE  
MIXED IN HAS BEEN TRAINING OVER AREAS NORTH OF BILLINGS. 2 TO 4  
INCHES OF SNOW ARE POSSIBLE OVERNIGHT, WITH AN INCH OR TWO OF SNOW  
FOR BILLINGS AND AREAS SOUTH. WILL CONTINUE TO MONITOR THE  
FOOTHILLS FOR POTENTIAL INCLUSION INTO THE WINTER WEATHER ADVISORY  
AS WELL. STP  
 
EARLIER UPDATE: SNOW HAS FILLED IN WEST AND NORTH OF BILLINGS.  
WEB CAMS SHOWING SNOW COMING DOWN AT A PRETTY GOOD PACE FROM REED  
POINT TO BIG TIMBER TO JUDITH GAP TO ROUNDUP. HAVE ADJUSTED POPS  
AND SNOW AMOUNTS SLIGHTLY TO ACCOUNT FOR RADAR AND MODEL TRENDS.  
ADDED NORTHERN STILLWATER COUNTY TO THE ADVISORY BASED ON ABOVE.  
OTHER UPDATES MADE EARLIER THIS EVENING LOOK ON TRACK. WINDS HAVE  
PICKED UP AT LIVINGSTON AND WERE NOW JUST BELOW ADVISORY CRITERIA.  
EXPECT AN CONTINUED UPTICK IN WINDS THROUGH THE EARLY OVERNIGHT  
HOURS, THEN DROPPING OFF TOWARD MORNING. ADVISORY THERE IN GOOD  
SHAPE. TWH  
 

 
   
SHORT TERM...VALID FOR SUN AND MON
 
 
WATER VAPOR IMAGERY THIS AFTERNOON SHOWS A POTENT WAVE TRAVELING  
THROUGH NORTHERN WASHINGTON WITH FLOW ALOFT BACKING FROM  
NORTHWESTERLY TO WESTERLY OVER SOUTHERN MONTANA AND NORTHERN  
WYOMING. THIS IS PROMOTING AN ONSET OF DOWNSLOPING AND GAP FLOW  
WINDS ALONG THE MOUNTAINS AND GENERATING SOME MODERATING  
TEMPERATURES. LOWER SPOTS ALONG THE RIVERS ARE STUCK IN THE  
COLDER AIR BUT VWP IN BILLINGS SHOWS SOUTHERLY WINDS JUST ABOVE  
THE FIRST GATE AND A BOUNDARY IS SHIFTING NORTHEAST ALONG A  
LEWISTOWN TO HYSHAM LIGHT PRODUCING BRIEF SNOW SHOWERS.  
 
WAVE OVER WASHINGTON SENDS A PIECE OF ENERGY THAT TRAVELS ACROSS  
NORTHERN MONTANA WHILE MORE ENERGY LINGERS BACK OVER THE PACNW AND  
HELPS DEVELOP A SLOWER MOVING TROUGH. THIS PATTERN SETS UP A  
PERIOD OF ACTIVE WEATHER TONIGHT...FOLLOWED BY A RELATIVELY LULL  
LATE TONIGHT INTO EARLY SUNDAY...WITH ANOTHER ROUND OF WEATHER  
SUNDAY AFTERNOON INTO MONDAY. TONIGHT A STRONG SURFACE LOW  
EXPECTED TO TRACK ACROSS SOUTHERN MONTANA BUT MODEL SOLUTIONS VARY  
BY ABOUT 80 MILES IN ITS TRACK WHICH IS A HUGE DIFFERENCE BETWEEN  
A COUPLE OF INCHES OF SNOW AND NO SNOW. GFS IS FURTHEST SOUTH WITH  
THE SURFACE LOW WHICH APPEARS TO BE BIASES BY TREND TO BLEND THE  
SURFACE INFLECTION INDUCED BY THE SHORTWAVE INTO A STRONG LEE  
MOUNTAIN WAVE SIGNATURE ON THE EAST SIDE OF THE BEARTOOTH/ABSAROKA  
MOUNTAINS. RAP NAM AND SREF MODELS ALL TRACK A LOW FURTHER NORTH  
AND MAINTAIN MORE DOWNSLOPING FOR PORTIONS OF SOUTH CENTRAL  
MONTANA. MODELS DO AGREE HEAVIEST AREA OF SNOWFALL WILL BE OVER  
AND NORTH OF THE BULL MOUNTAINS EXTENDING OVER TOWARDS THE CRAZY  
MOUNTAINS. HAVE LOWERED PRECIPITATION CHANCES AND AMOUNTS FOR THE  
BILLINGS AREA AND LOCATIONS LIKE HARDIN AND HYSHAM BUT THINK THAT  
WINTER WEATHER ADVISORY IN AFFECT FOR AREAS NORTH AND WEST OF  
BILLINGS LOOKS GOOD.  
 
AS THE SURFACE LOW MOVES INTO THE REGION THIS WILL SUPPORT A  
PERIOD OF STRONG GAP FLOW WINDS TRANSITIONING TO A WESTERLY  
MOUNTAIN WAVE WIND SITUATION FOR THE LIVINGSTON AREA AND BEARTOOTH  
FOOTHILLS. HAVE BEEN WATCHING TO SEE IF THIS WILL TRANSLATE TO A  
WAVE SETTING UP ALONG THE BIG HORN MOUNTAINS BUT SUSPECT THAT LOW  
LEVEL AIRMASS WILL COOL OFF ENOUGH EARLY THIS EVENING TO KEEP IT  
FROM MIXING DOWN AND IMPACTING SHERIDAN. DO HAVE STRONG WINDS AT  
BURGESS JUNCTIONS. WINDS WILL LET UP AS THE SURFACE LOW PASSES BY.  
 
COLD FRONT PROGGED TO CROSS THE REGION BETWEEN 9 PM AND 2 AM WHICH  
WILL BRING THE BEST CHANCE OF SNOW FOR AREAS NOT IN WEATHER  
ADVISORIES BUT ANY SNOW WITH THIS FRONT WILL BE SHORT LIVED.  
EXCEPTION WILL BE OVER NORTHERN PORTIONS OF SOUTHEAST MONTANA  
WHERE SURFACE FRONT MAY NOT PASS AS QUICKLY SUPPORTING A BIT  
LONGER SNOW. ADVISORY FOR THIS AREA STILL LOOKS GOOD BUT WATCHING  
TO SEE IF THE SNOW MAY NOT LAST THAT LONG DEPENDING ON LOW TRACK.  
 
SUNDAY MORNING SEES A BREAK IN THE SNOWFALL BUT BY AFTERNOON  
BACKING FLOW ALOFT BECOMES MORE SOUTHWESTERLY AND PUSHES MOISTURE  
OVER THE AREA WHILE THE ARCTIC AIRMASS DEEPENS. THIS ALLOWS A  
LIGHT SNOWFALL TO DEVELOP MAINLY FOR SUNDAY NIGHT INTO MONDAY  
MORNING WHICH IS THE GREATEST PERIOD OF SNOWFALL FOR AREAS LIKE  
BILLINGS. THE UPPER FLOW IS SHOWING A BIT STRONGER TROUGH PASSING  
ACROSS MONTANA AND MOVING A BIT SLOWER AND THIS SETS UP BETTER  
PRECIPITATION AMOUNTS FOR SOUTHEAST MONTANA. WILL HAVE TO WATCH  
THAT AREA FOR A POSSIBLE ADVISORY MONDAY.  
 
OTHER BIG STORY IS THE COLD WHICH WILL BE NEARLY 40 DEGREES BELOW  
NORMAL FOR MONDAY. THE HIGH TEMPERATURE IS GOING TO STRUGGLE TO  
BREAK ZERO. BORSUM  
   
LONG TERM...VALID FOR TUE...WED...THU...FRI...SAT
 
 
THE GEFS SHOWED UNCERTAINTY WITH THE PATTERN BEGINNING MIDWEEK,  
WHILE THE ECMWF ENSEMBLES SHOWED HIGH CONFIDENCE WITH THE PATTERN.  
THAT BEING SAID, THE DETERMINISTIC MODELS WERE NOT IN PHASE  
BEGINNING ON WEDNESDAY, SO USED BLENDED GUIDANCE FOR THE POPS.  
 
GENERALLY, THE EXTENDED PERIOD WILL BE QUIET WITH A WARMING  
TREND. HIGH AMPLITUDE TROUGH FROM THE SHORT-TERM PERIOD WILL  
BE OVER THE REGION ON TUESDAY. 850 MB TEMPERATURES WILL BE A FEW  
DEGREES HIGHER THAN THEY WILL BE ON MONDAY, BUT HIGHS WILL STILL  
BE IN THE SINGLE DIGITS. LINGERING MOISTURE WILL BE OVER THE SE  
ZONES AND MOUNTAINS FOR A SLIGHT CHANCE OF SNOW IN THESE AREAS.  
MODELS STILL HAVE TROUGHINESS OVER THE AREA ON WEDNESDAY, BUT ARE  
OUT OF PHASE WITH THE ENERGY IN THE TROUGH. GFS SHOWED A SLIGHT  
CHANCE OF SNOW OVER THE SW MOUNTAINS, OTHERWISE THE FORECAST WILL  
BE DRY. TEMPERATURES WILL CLIMB INTO THE 20S IN THE W WITH TEENS  
E. LEE TROUGHING WED. NIGHT INTO THURSDAY WILL SUPPORT POSSIBLE  
ADVISORY WINDS IN THE GAP FLOW AREAS. GFS SHOWED A REINFORCING  
TROUGH FOR THURSDAY, WHILE THE ECMWF HAD BRIEF UPPER RIDGING.  
BLENDS GAVE LOW POPS N AND W OF KBIL, AND HIGHS IN THE 20S TO LOW  
30S. GENERAL TROUGHINESS CONTINUED ON BOTH MODELS FRIDAY THROUGH  
SATURDAY WITH CHANCES FOR SNOW SHOWERS, MAINLY IN THE MOUNTAINS,  
AND HIGHS IN THE 20S AND 30S. ARTHUR  
 

 
   
AVIATION
 
 
EXPECT STRONG SOUTHWEST WINDS WITH GUSTS TO 50KTS AROUND KLVM WILL  
CONTINUE THROUGH AROUND 09Z. AROUND KSHR COULD SEE STRONG GUSTS  
TO 45 KTS BRIEFLY AS A FRONT MOVES THROUGH AFTER 04Z. EXPECT SNOW  
TO CONTINUE OVERNIGHT AT ALL TERMINALS WITH MVFR TO IFR CONDITIONS  
EXPECTED. HEAVIER SHOWERS COULD PRODUCE LOCALIZED LIFR  
CONDITIONS. EXPECT IMPROVING CONDITIONS AT ALL TERMINAL EXCEPT  
KSHR AFTER 12Z. REIMER  

 
   
PRELIMINARY POINT TEMP/POPS
 
 
SUN MON TUE WED THU FRI SAT  
-----------------------------------------------------------  
BIL 012/013 906/002 918/009 906/021 008/031 011/031 014/033  
77/S 74/S 21/B 11/U 11/B 11/B 11/B  
LVM 017/020 910/003 917/010 901/023 013/032 015/033 018/034  
77/S 84/S 22/J 11/N 22/J 22/J 22/J  
HDN 013/014 902/005 921/010 909/021 004/028 007/029 010/031  
76/S 74/S 22/J 11/U 11/B 11/B 11/B  
MLS 009/012 905/004 915/005 911/015 001/021 002/022 005/026  
72/S 64/S 22/J 11/U 11/B 12/J 11/B  
4BQ 016/018 903/005 916/007 911/018 002/027 006/028 009/030  
64/S 76/S 32/J 11/U 11/B 11/B 11/B  
BHK 010/012 905/003 914/004 912/015 000/022 002/023 004/027  
92/S 65/S 22/J 11/U 11/B 12/J 11/B  
SHR 020/025 906/005 919/008 914/020 000/028 007/030 010/033  
56/S 76/S 32/J 11/U 11/B 11/B 11/B  
 

 
   
BYZ WATCHES/WARNINGS/ADVISORIES
 
 
MT...WINTER WEATHER ADVISORY IN EFFECT UNTIL 9 AM MST SUNDAY FOR  
ZONES 28>35-41-42-63.  
WIND ADVISORY IN EFFECT UNTIL 2 AM MST SUNDAY FOR ZONES  
65-66.  
WINTER STORM WARNING IN EFFECT UNTIL 9 AM MST SUNDAY FOR  
ZONES 67-68.  
WY...NONE.  
 

 
 

 
WEATHER.GOV/BILLINGS  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab MT Page
The Nexlab WY Page Main Text Page