710  
FXUS65 KBYZ 211525  
AFDBYZ  
 
AREA FORECAST DISCUSSION...UPDATED  
NATIONAL WEATHER SERVICE BILLINGS MT  
925 AM MDT SAT OCT 21 2017  
   
UPDATE
 
 
MAIN CHANGE TO THE FORECAST WAS TO UPGRADE THE HIGH WIND WATCH  
FROM JUDITH GAP TO BIG TIMBER. THIS AREA WILL SEE AN IMPRESSIVE  
UPPER AND MID LEVEL JET WORK OVER IT LATE TONIGHT THROUGH SUNDAY.  
STRONG DOWNWARD MOTION AND MIXING OF THE BOUNDARY LAYER SUPPORTS  
THE IDEA OF STRONG TO DANGEROUS WIND GUSTS FOR HIGH PROFILE AND  
LIGHT VEHICLES. WE STARTED THE WARNING AT 3 AM TONIGHT FOR THIS  
AREA JUST TO GIVE IT SOME ROOM AS WINDS WILL INCREASE AND PEAK  
PROBABLY AROUND MIDDAY SUNDAY. END TIME IS 9 PM.  
 
REST OF FORECAST IN GOOD SHAPE. WE DID BACK OFF POP'S A BIT FOR  
THE MOUNTAINS THE REST OF TODAY. SNOW SHOWERS WILL DEVELOP OVER  
MOUNTAINS TONIGHT. BT  
 

 
   
SHORT TERM...VALID FOR TDY AND SUN
 
 
WATER VAPOR IMAGERY SHOWS A WEAKENING TROF OVER EASTERN MT, AND A  
FAST WESTERLY FLOW UPSTREAM MOVING INTO THE PAC NW. LIGHT SHOWERS  
OVER OUR CWA HAVE MOSTLY ENDED AS SURFACE FRONT HAS PUSHED INTO  
THE CENTRAL DAKOTAS, LEAVING GUSTY WESTERLY DOWNSLOPE WINDS ACROSS  
OUR CWA. CANNOT RULE OUT A FEW SNOW SHOWERS OVER THE MOUNTAINS  
THIS MORNING, AND MAYBE AN EARLY MORNING SPRINKLE IN OUR NORTH,  
OTHERWISE IT WILL BE DRY TODAY UNDER SUBSIDENCE ALOFT AND WITH  
PERSISTENT GUSTY W-NW SURFACE WINDS. BOUNDARY LAYER WILL REMAIN  
WELL-MIXED AND GUSTS OF 35 TO 50 MPH WILL BE WIDESPREAD. TEMPS  
TODAY WILL BE COOLER WITH HIGHS IN THE 50S TO LOWER 60S.  
 
A 130-150 KT H3 WESTERLY JET WILL NOSE INTO THE NORTHERN ROCKIES  
TONIGHT INTO SUNDAY. THE COMBINATION OF MID LEVEL WARM ADVECTION  
(I.E. STABILIZING), LEE SIDE PRESSURE FALLS AND INCREASING  
WESTERLY MID LEVEL FLOW ON THE ORDER OF 65-70 KTS WILL RESULT IN  
A SIGNIFICANT INCREASE IN SW GAP WINDS AT LIVINGSTON AND NYE  
TONIGHT. CURRENT INDICATIONS ARE THAT WE'LL SEE ADVISORY LEVEL  
GUSTS BEGIN BEFORE MIDNIGHT, AND PEAK WINDS OVERALL SHOULD OCCUR  
BETWEEN 09-15Z SUNDAY. CONFIDENCE CONTINUES TO INCREASE IN A  
PERIOD OF 70+ MPH GUSTS, SO HAVE ISSUED A HIGH WIND WARNING FOR  
THE LIVINGSTON AREA AND BEARTOOTH FOOTHILLS FROM MID EVENING  
THROUGH SUNDAY. WINDS WILL GRADUALLY DECREASE THROUGH SUNDAY  
AFTERNOON AS WINDS BECOME MIXED AND DIRECTIONS VEER WESTERLY.  
 
NORTHERN SWEET GRASS AND WHEATLAND COUNTIES WILL ALSO SEE  
INCREASED SW-W WINDS LATE TONIGHT AND SUNDAY, WITH PEAK GUSTS  
BEGINNING ONCE PRESSURE FALL AXIS MOVES EAST OF NORTH CENTRAL MT,  
I.E. STARTING 09-12Z. CANNOT RULE OUT SOME MOUNTAIN WAVE  
ACTIVITY, BUT MOST WIDESPREAD AND CONSISTENT GUSTS WILL OCCUR  
DURING THE DAY ON SUNDAY WITH MIXING INTO CORE OF STRONG MID LEVEL  
FLOW. WILL KEEP THE HIGH WIND WATCH IN EFFECT FOR THESE AREAS AND  
LET DAY SHIFT MAKE A FINAL DECISION ON A POTENTIAL WARNING.  
 
FURTHER EAST, STRONG MIXED WEST WINDS WILL SPREAD ACROSS THE LOWER  
ELEVATIONS ON SUNDAY, WITH EXPECTATION OF WIDESPREAD 40-55 MPH  
GUSTS. DO NOT SEE A SYNOPTIC MECHANISM TO BRING THE STRONGER MID  
LEVEL WINDS DOWN, BUT IF ANY LIGHT SHOWERS DEVELOP A CONVECTIVE  
GUST WILL NEED TO BE WATCHED. IN ANY EVENT, SUNDAY WILL BE QUITE  
WINDY ACROSS THE CWA AND THOSE WITH OUTDOOR/TRAVEL PLANS WILL NEED  
TO TAKE NOTE.  
 
PASSAGE OF PACIFIC SHORTWAVE OCCURS LATE SUNDAY AND SUNDAY NIGHT,  
AND WE SHOULD SEE SOME LIGHT SHOWERS ALONG MID LEVEL BAROCLINIC  
ZONE. OUR WESTERN MOUNTAINS WILL SEE A FEW INCHES OF SNOWFALL THE  
NEXT COUPLE DAYS, BEGINNING TONIGHT WITH A PERIOD OF MOIST  
ISENTROPIC ASCENT AND THEN LATE SUNDAY AND SUNDAY NIGHT WITH  
SHORTWAVE/INSTABILITY.  
 
TEMPS WILL BE WARMER SUNDAY WITH HIGHS IN THE 60S TO NEAR 70  
DEGREES. COLD ADVECTION AND BREEZY NW WINDS CAN BE EXPECTED SUNDAY  
NIGHT.  
 
JKL  
   
LONG TERM...VALID FOR MON...TUE...WED...THU...FRI
 
 
SOME UNCERTAINTY HAS CREPT INTO THE EXTENDED FORECAST AS THE  
GEFS/ECMWF ENSEMBLES SHOWED LOWER CONFIDENCE WITH THE MIDWEEK  
SYSTEM AND THE 00Z ECMWF WAS DIFFERENT THAT IT'S PREVIOUS RUN FROM  
THURSDAY ONWARD. IN ADDITION, SUPER TYPHOON LAN, SEEN ON WATER  
VAPOR SOUTH OF JAPAN EARLY THIS MORNING, WAS FORECAST TO MOVE NE  
AS IT BECOMES EXTRATROPICAL. THIS SYSTEM ADDS UNCERTAINTY TO THE  
DOWNSTREAM PATTERN THAT WILL AFFECT OUR REGION.  
 
ON MONDAY, MODELS WERE CONSISTENT WITH SHOWING THE PACIFIC JET  
BECOMING ORIENTED N-S AS IT SHIFTS E OF THE AREA. SOME MOISTURE  
LINGERS OVER THE SOUTHERN MOUNTAINS EARLY IN THE DAY FOR A SLIGHT  
CHANCE OF SNOW SHOWERS, OTHERWISE IT WILL BE DRY. HIGH  
TEMPERATURES WILL BE AROUND NORMAL. WINDY CONDITIONS WILL CONTINUE  
WITH THE GFS SOUNDINGS SHOWING WINDS IN THE 30S THROUGH THE  
COLUMN. UPPER RIDGING, DRY WEATHER AND A WARMING TREND THEN MOVE  
THROUGH THE AREA THROUGH WEDNESDAY. EXPECT PERIODS OF GUSTY WINDS  
W OF KBIL. HIGHS WILL TOP OUT AROUND 70 DEGREES ON WEDNESDAY.  
 
THE ECMWF AND GFS BOTH BRING A TROUGH SE INTO THE AREA WED. NIGHT  
WITH AN ACCOMPANYING COLD FRONT. GFS ALSO SHOWED AN ATMOSPHERIC  
RIVER MOVING THROUGH THE AREA. THERE WAS GOOD MODEL AGREEMENT IN  
DROPPING 850 MB TEMPERATURES BELOW ZERO DEGREES C AS WELL. THE  
ABOVE SUPPORTED A GOOD CHANCE OF RAIN SHOWERS MIXING WITH AND  
CHANGING TO SNOW SHOWERS OVERNIGHT. THE MODELS THEN FALL OUT OF  
AGREEMENT ON THURSDAY WITH THE ECMWF CUTTING OFF A LOW OVER NE  
MT/W ND, WHILE THE GFS MAINTAINS A PROGRESSIVE SYSTEM AND ENDS THE  
PRECIPITATION FROM NW TO SE. GIVEN THE PREVIOUS RUN OF THE ECMWF  
WAS VERY SIMILAR TO THE CURRENT RUN OF THE GFS, HAVE FOLLOWED THE  
GFS CLOSELY. WILL BE WATCHING FUTURE MODEL RUNS FOR A CONSENSUS  
FOR THURSDAY. MODEL BLENDS GAVE HIGHS IN THE 40S FOR THURSDAY.  
KEPT THU. NIGHT/FRIDAY DRY PER THE GFS. THE GFS BRINGS A SHORTWAVE  
DOWN IN NW FLOW FOR SATURDAY, WHILE THE ECMWF PIVOTS THE MIDWEEK  
SYSTEM OUT OF THE REGION. GIVEN THE GREAT DEAL OF UNCERTAINTY,  
USED MODEL BLENDS AND CLIMO FOR THE END OF THE PERIOD. ARTHUR  
 

 
   
AVIATION
 
 
GUSTY WNW WINDS 30 TO 40 KTS THROUGH THE AFTERNOON TODAY AT ALL  
TERMINALS. EXPECT DECREASING WINDS OTHER THAN AT LVM WHERE WINDS  
WILL INCREASE WITH GUSTS TO 65 KTS AFTER 06Z. STRONG WINDS  
EXPECTED TO PERSIST THROUGH THE DAY SUNDAY AT LVM. GUSTY WINDS  
WILL BE THE ONLY HAZARD TO AVIATION, AS CLOUD DECKS AND VISIBILITY  
ARE EXPECTED TO REMAIN VFR AT ALL SITES THROUGH THE PERIOD. WALSH  
 
 

 
   
PRELIMINARY POINT TEMP/POPS
 
 
TDY SUN MON TUE WED THU FRI  
-------------------------------------------------------  
BIL 058 042/069 045/060 037/067 045/070 036/045 029/050  
0/N 21/N 21/N 00/U 01/N 42/W 11/B  
LVM 052 045/063 043/058 036/067 044/068 033/045 027/049  
1/N 33/W 51/N 00/N 01/N 72/J 11/B  
HDN 059 036/070 042/062 033/067 039/071 033/046 025/050  
0/N 21/N 21/N 00/U 01/U 52/W 10/B  
MLS 058 035/069 043/059 032/064 040/069 033/044 024/046  
2/W 11/N 21/N 00/U 01/U 32/J 11/B  
4BQ 057 033/070 043/058 032/063 040/071 033/044 025/046  
1/N 01/N 21/N 00/U 00/U 42/W 11/B  
BHK 056 033/067 040/056 031/060 038/066 031/042 023/043  
1/N 01/N 21/N 00/U 01/U 33/W 11/B  
SHR 056 031/069 039/058 032/065 036/072 031/043 023/046  
0/N 11/B 21/N 00/U 00/U 63/W 11/B  
 

 
   
BYZ WATCHES/WARNINGS/ADVISORIES
 
 
MT...HIGH WIND WARNING IN EFFECT FROM 3 AM TO 9 PM MDT SUNDAY FOR  
ZONES 28-41-63.  
HIGH WIND WARNING IN EFFECT FROM 9 PM THIS EVENING TO 6 PM  
MDT SUNDAY FOR ZONES 65-66.  
WY...NONE.  
 

 
 

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

The Nexlab MT Page
The Nexlab WY Page Main Text Page