Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 100422

Area Forecast Discussion...Updated
National Weather Service Billings MT
922 PM MST Mon Dec 9 2019


The cold front has backed its way westward as far as Columbus
this evening as a northeast wind is noted there. The front is
expected to push a bit further west but not make it as far as
Livingston where a southwest wind is expected through the night.
Radar late this afternoon had a band of snow across Musselshell
County to Treasure and Rosebud Counties. This activity has slowly
drifted south and west but has not quite made it to Billings, but
it has enhanced over Big Horn County and most of Carbon County
where it looks to currently be snowing in Red Lodge. The back edge
of this snow has decreased in intensity and has become more
scattered in nature to the north and northeast of Billings. We are
still expecting some light snow across the Billings area this
evening, but accumulations are expected to be light. No changes
were made to the previous forecast as we are still expecting the
heavier snow accumulations over the southern half of Big Horn
County. Hooley



Today through Tuesday Night...

21z surface analysis shows a Canadian cold front dropping through
northeast Montana, with pressure falls and gusty west winds
continuing along our foothills. Light snow is currently fairly
widespread across our east, with increased NW (frontal) winds
likely producing some blowing snow. Satellite imagery shows
northerly flow aloft with a shortwave dropping out of Alberta.

As cold front continues to push southward we will see snow shift
west along low level baroclinic zone this evening. High res models
continue to push this baroclinicity further west, and we should
see snow not only develop in Billings early this evening, but we
now expect it to spread westward through Columbus and Joliet and
quite possibly Red Lodge. Downslope westerly winds should persist
at Livingston, but a light east wind may get close to Big Timber.
Will be interesting to watch the fropa this evening. As for snow
amounts, still looks like good ascent thru a deepened dendritic
layer, as we`ve seen upstream in Canada earlier today where cloud
tops made it as cold as -30C. This gives credence to what RAP/HRRR
soundings are showing in our cwa this evening. As a result, we
will see fairly high snow ratios with some NW-SE banded snow.
Amounts should range largely from 1-4 inches but could see locally
higher amounts especially along the north side of the Pryors and
northern Bighorn Mountains. Also, if the front gets to Red Lodge,
they could see more than a forecasted inch of snow tonight. Again,
this is something to watch closely. For the Billings metro area,
expect 1-2" of snow mainly between 6 pm and 2 am, but could be
more if a convergent band lingers for any length of time. Snow
will diminish and shift back to the east as wave departs early
Tuesday. Have already issued a winter weather advisory for the
Bighorn Canyon and Southern Bighorn county. Will let the evening
shift decide if expansion of this highlight is needed.

Gradual height rises and shift back to anticyclonic flow aloft
will induce lee side pressure falls on Tuesday, resulting in
increasing winds along the foothills again. Mid level winds back
westerly and this should favor the gap areas for 50+ mph gusts by
Tuesday night.

Another weaker Canadian front will slide back into our far east
tomorrow night, bringing another period of easterly winds and
potentially some light overrunning snow. Have raised pops near
Miles City, Baker and Ekalaka...locations which could see
something like a half inch of snow Tuesday night.

Western areas will see temps getting to 40 degrees on Tuesday
while our east stays colder.


Wednesday though Monday...

Made several changes to the extended forecast period this
afternoon. Increased gusty winds in gap flow areas from
Livingston to Big Timber to Harlowton to high subadvisory type
winds. Also made significant changes to pops levels and coverage
through the period.

Flow aloft will be zonal to start Wednesday, but transitions back
to unsettled northwesterly flow with a passing disturbance. The
disturbance will move southeast across the CWA Wednesday, but
looks relatively weak. Expect best chance of accumulating snow in
high terrain, with a little help from orographics. The east will
also see a chance for precip Wednesday evening, as the trof
deepens a bit, digging south, and a little upper level jet
support becomes available. Upper flow transitions back to zonal
flow quickly Wednesday night.

Meanwhile, lee troffing develops Wednesday, tightening the
pressure gradient over the Paradise Valley and up through Judith
Gap. Have increased winds to just below highlight level, from
Livingston to Big Timber, and up to Harlowton. This pattern
persists until the next disturbance moves into the region late
Thursday into Friday. This system should bring the next widespread
chance for precip across the region. Temps will remain above
normal for this time of year, with highs in the 40s, which will
switch any snow to rain during the day over the lower elevations.
Winds will remain breezy Thursday and Friday, but should remain
below advisory criteria.

The pattern remains unsettled over the weekend, as a backdoor
cold front slides into the region late Friday, setting up upslope
flow into the foothills, and some potential for overrunning type
snow elsewhere. Temps through the period will be back to around
seasonal normal, in the mid to upper 30s, so all precip with this
system should be snow. Currently accumulations look somewhat
limited, with highest amounts over foothills regions.

Winds will be on the rise in gap areas again Sunday, as the front
recedes eastward. Lee troffing will redevelop again by late
Sunday as well, bringing another round of strong and gusty,
subadvisory type, winds to start the work week.




Light snow is possible east of and along a line from Billings to
Red Lodge with the greatest impacts along the east slopes of the
Pryor and Big Horn mountains and adjacent plains, including KSHR.
MVFR is possible with areas of IFR particularly south and east of
Billings. Most of the region will improve to VFR on Tuesday, with
the exception being lingering MVFR in periodic light snow east of
KMLS through the day. Westerly winds gusting 20-30 kts will
persist along the western foothills including KLVM tonight. KLVM
will see gusts increase to 40 kts tomorrow. JKL/Borsum



    Tue     Wed     Thu     Fri     Sat     Sun     Mon
BIL 018/038 023/041 026/044 030/044 025/038 021/035 019/034
    71/E    01/B    11/E    33/O    33/O    22/S    11/B
LVM 024/041 027/041 026/043 029/041 024/035 017/032 016/032
    00/N    02/R    15/O    65/O    42/S    22/S    11/N
HDN 013/038 016/040 020/043 026/044 020/038 016/035 014/036
    82/S    01/E    11/E    33/O    32/O    21/B    11/B
MLS 008/030 012/034 019/043 029/042 021/034 017/033 018/034
    22/S    21/E    20/B    12/R    21/B    12/S    10/B
4BQ 010/033 012/035 020/041 027/042 021/034 016/032 015/033
    52/S    01/E    10/B    22/R    21/E    12/S    10/B
BHK 902/024 006/027 016/039 026/038 016/029 013/029 015/031
    12/S    31/E    20/B    11/B    21/E    12/S    10/B
SHR 014/037 016/040 019/045 024/042 018/036 014/032 010/034
    63/S    01/B    10/B    24/O    32/S    22/S    11/B


MT...Winter Weather Advisory in effect until 9 AM MST Tuesday FOR
      ZONES 138-169.


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