Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 191707

Area Forecast Discussion
National Weather Service Billings MT
1007 AM MST Thu Jan 19 2017


Only a minor update to the inherited forecast this
clean up a few border inconsistencies. Inherited high pops low
qpf and mixed precip potential look good at this time. AAG


.SHORT TERM...valid for Tdy and Fri...

Gap winds continue to gust to around 50 mph at the western
Livingston DOT station, but have decreased significantly at the
airport and at Nye. Pressures are falling at a pretty good clip in
the northern great basin as amplified Pacific trof moves inland,
so winds will continue to decrease through the day. Have cancelled
the wind advisory for the Livingston area and Beartooth

Main forecast issue in the short term involves the aforementioned
trof and what is shaping up to be a period of rain/snow for our
west and central parts tonight and Friday morning. Ascent will
exist in RRQ of 100 kt southerly H3 jet lifting to our north, as
stronger dynamics associated with southern split of trof move thru
the southern Rockies. There will also be some mid level
frontogenesis ahead of the trof axis, but models remain quite
different with this and where exactly the greatest pcpn will fall.
Will continue to side with the EC which has been most consistent
with its QPF and is more in line with the jet forcing than low
level upslope, such as is the case with the NAM. The 00z GFS also
sided with the EC here. Precipitation on the order of a 0.10-0.25
is expected in an area from Livingston to Billings, greatest in
central parts, with less as you move further east as forcing
weakens through Friday.

This will not be a cold system and precipitation type seems to
favor rain to a rain/snow mix at lower elevations. Surface temps
should be above freezing as pcpn begins this evening, and 850mb
temps are expected to remain a little above 0C through the
duration of the event, with boundary layer wet bulb temps right
around freezing. So this creates a difficult snowfall forecast at
lower elevations, and accumulation will likely vary and be
greatest over the hills, with the expectation that some QPF will
be wasted as rain. Upslope enhancement does not look to be a
factor along the Beartooth Absarokas as low level winds should
stay westerly, but southern Big Horn County could see some with a
shift to NW winds on Friday. Overall have painted snow amounts of
2 inches or less in west/central parts, with 3-5 over the
mountains. Will need to monitor surface temps and potential areas
of enhanced frontogenesis with this event, again stressing the
model differences at this time. The Friday morning commute could
be affected, including at Billings.

Light pcpn will taper off as forcing weakens and shifts east late
Friday and Friday night, as weak shortwave ridge builds in from
the west.

Temperatures will trend cooler the next couple of days, with mid
30s to mid 40s today and 30s on Friday. Snow cover will continue
to be a factor in holding down temperatures, especially as
downslope winds decrease.


.LONG TERM...valid for Sat...Sun...Mon...Tue...Wed...

There continues to be a fair amount of uncertainty among the
models as we move into the extended portion of the forecast.
Perhaps some lingering snow over the far eastern Plains on
Saturday as a low exits over the Dakotas. Strong low approaches
the California coastline by Saturday night. As this system evolves
eastward, southern stream of the jet becomes enhanced over the
southwestern US. GFS keeps more energy over Wyoming and
subsequently more precip over MT/WY than the other models. For now
trending closer to the ECMWF and CMC models with the best precip
chances confined to northern Wyoming and extreme southern Montana
on Monday/Tuesday.

ECMWF and GFS both indicate northwest upper-flow pattern by the
end of next week. GFS brings ridging and warmer temps into
western MT while the ECMWF keeps a cooler temperature profile. For
now, keeping a blend of temperatures which keeps us near climo
for this time of the year. Will have to watch for possible wind
issues from Livingston to Big Timber by the end of next week if
models continue to show tight pressure gradient from Idaho through
the Dakotas. Walsh



Winds at LVM will continue to decrease through the night. Expect
precip to move in from the west this afternoon, with MVFR
conditions possible at LVM and BIL. Possible transition from rain
to snow during the late afternoon at LVM and BIL. Snow moves into
SHR during the nighttime hours. Walsh



    Tdy Fri     Sat     Sun     Mon     Tue     Wed
BIL 043 031/036 019/031 020/032 017/029 016/026 013/029
    0/E 77/W    21/U    11/U    12/S    33/S    21/B
LVM 043 028/039 014/034 018/036 018/035 013/029 011/030
    3/W 65/W    21/B    21/N    23/S    32/S    21/N
HDN 037 027/035 013/030 009/030 007/026 010/024 006/026
    0/B 57/W    21/B    11/U    11/B    34/S    22/S
MLS 036 020/032 019/030 015/029 009/024 012/025 009/025
    0/U 12/J    32/J    21/B    11/B    22/S    22/S
4BQ 038 018/034 017/032 014/031 006/028 011/026 008/026
    0/U 14/W    32/J    21/B    11/B    44/S    22/S
BHK 038 017/033 020/031 018/030 009/025 012/023 010/023
    0/U 02/W    23/J    32/J    11/B    23/S    22/S
SHR 038 020/034 012/032 010/032 009/031 011/025 008/027
    0/U 36/W    31/B    11/U    12/S    54/S    22/S




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