Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 170356

Area Forecast Discussion...Updated
National Weather Service Billings MT
856 PM MST Fri Feb 16 2018

Fine tuned the forecast, but this update feeds off the update
earlier this evening. Unstable atmosphere sitting over the area
with 850-500mb lapse rates around 8c/km over southern Montana and
northern Wyoming. This instability will lead to an area of snow
showers tonight, mainly east of Billings. Radar was filling back
in as shortwave energy moves in from north central Montana. Models
have not had a great track record at being consistent on the
exact position of the strongest showers, but have been consistent
on the general placement east of Billings. Snow showers were
pretty quick moving, but reports of impressive snow rates over
north central Montana have come in this evening. Have adjusted
PoPs and snow amounts slightly to try and time the snow showers.
Believe the heaviest snow showers will set up from Treasure to
Rosebud to northern Big Horn to western Custer and western Powder
River counties, but the latest GFS has shifted this projection
east of these locations for the time being. Models do not project
the bands to set up in any one locations, but shift them through
quickly. Will have to watch this closely as some locations in the
general area mentioned earlier could pick up 3-4 inches of new
snow overnight, but does not appear to be a widespread thing. TWH


.SHORT TERM...valid for Sat and Sun...

Today through Monday...

Stronger flow aloft through the weekend with a series of
disturbances bringing periods of unsettled weather. Biggest chance
at present time is the track of a potent wave Saturday night
looks to be much further north which will lower precipitation
amounts and lower overall expected snowfall amounts for the lower

Disturbance moving southward through western Montana is followed
by another wave moving into BC. Pressure rises this afternoon
moving into northwest Montana indicating the leeside trough will
start moving off of the continental divide. This will allow gap
flow winds to subside around sunset but breezy conditions persist
through much of the evening. Cold front crosses the region late
this evening overnight but lift looks limited for the western half
of the region due to downslope off of Snowies and Belts. Mountains
will see accumulations due to orographic flow and further into
southeast Montana there limited downslope will help snowfall
accumulate a bit better.

Approach of next system brings warm air advection but downslope
component will limit most precipitation to the mountains as mid
level blow backs around to the west and southwest. Temperatures
will again be in 20s with some 30s along the foothills. Saturday
night the disturbance tracks across the area but is progged to
track further north with each model run. This puts the area into a
mixing and downslope scenario through most of the night with an
increase of gap flow winds. This trajectory lowers snowfall
chances overnight for lower elevations and have reduced
accumulations for Saturday night into early Sunday. Exception is
north of Billings along the Musselshell River where the north side
of a surface low will combine with upslope to generate a chance
to accumulate especially along the Bull Mountains. Temperatures
Saturday night are likely to climb up until midnight and could
reach the 40s in some areas along the foothills before falling
sharply by daybreak.

Sunday cold air surges strongly back into the region and flow
aloft becomes southwesterly by late Sunday afternoon. This allows
a more persistent light snow pattern to evolve which is the best
chance for accumulations in the Billings area. Biggest question is
how much moisture will be available as cold air gets really deep
and best ascent region could be closer to the foothills. Have
trended lower with overall low level elevation snowfall amounts
given the trends in the forecast today. borsum

.LONG TERM...valid for Mon...Tue...Wed...Thu...Fri...

A generally drier period was in store for the extended, but it
will start out very cold. There were fairly large ensemble spreads
in the GEFS minimum temperatures during the period, but all
ensemble members were cold. The GEFS also showed some uncertainty
with the pattern from midweek on, and this was also reflected in
the deterministic models.

Upper trough associated with the weekend system will move over the
area through Tuesday, then deamplify as it shifts E Tue. night.
Kept a chance of snow with little accumulation over the area
Monday, then dropped it to slight chance Mon. night. Monday will
be very cold with 850 mb temperatures around -20 degrees C,
resulting in highs in the single digits. Lows Mon. night will be
in the teens below zero. Record low high temperatures are possible
Monday and record low min temperatures are possible Mon. night.
Tuesday will be drier with highs in the single digits and teens.

The GFS brings some energy into the area in NW flow on Wednesday,
while the ECMWF had weak ridging over the area. Despite these
differences, Wed. will be dry and warmer. Expect increasing winds
in the gap areas Wed. and Wed. night. Next trough starts to affect
the area on Thursday with the ECMWF moving the trough faster to
the E than the GFS. Model blends gave some low PoPs N and W of
KBIL Thu. night. The trough remains over the area Friday with low
chances for precipitation. Temperatures will reach the mid 20s to
mid 30s Thu. and Friday. Arthur



Gusty WSW surface winds will continue to decrease at KLVM through
this evening. Winds will shift to the N and NW with a cold
frontal passage across the area after 06Z tonight. Scattered snow
showers will move S through the area tonight into Saturday morning
with MVFR/IFR conditions. Widespread mountain obscurations are
expected through the TAF period. More snow will move into the
area after 18z on Saturday, mainly affecting areas N and W of
KBIL. Arthur/Dobbs



    Sat     Sun     Mon     Tue     Wed     Thu     Fri
BIL 015/031 008/014 906/006 914/014 903/027 010/031 013/032
    54/S    66/S    74/S    21/B    10/U    11/B    12/S
LVM 021/038 014/020 906/006 909/015 002/026 014/033 016/034
    76/S    77/S    74/S    21/B    11/N    12/S    22/S
HDN 013/030 008/016 905/007 916/012 907/024 007/029 009/030
    74/S    56/S    74/S    21/B    11/U    11/B    12/S
MLS 009/022 004/011 906/004 916/006 909/016 001/023 004/024
    75/S    74/S    64/S    21/B    10/U    11/B    12/S
4BQ 014/027 010/017 903/007 914/011 909/021 004/028 008/029
    72/S    45/S    75/S    21/B    10/U    11/B    11/B
BHK 011/020 005/012 907/004 915/006 910/016 002/024 003/025
    63/E    63/S    65/S    21/B    10/U    11/B    11/B
SHR 016/032 013/020 906/006 916/012 910/023 005/031 008/032
    52/S    56/S    65/S    21/B    11/U    00/B    11/B


MT...Winter Storm Warning in effect until 9 AM MST Sunday FOR
      ZONES 67-68.


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