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Area forecast discussion 
National Weather Service Billings Montana
838 PM MST Thursday Jan 29 2015

Update...
we will remain dry tonight under the influence of upper level
ridging. Weak shortwave to our north will allow for a barely
noticeable frontal passage later tonight. Given a shift to more
westerly winds across our east by early tomorrow...and some degree
of high cloudiness for much of the night...do not see much of a
fog risk across our east. The hrrr agrees...so have adjusted early
Friday weather grid to remove patchy fog. Otherwise some eastern
valleys are already near forecast lows so have tweaked these down
a bit. Overall very quiet weather tonight and tomorrow as we await a
pattern shift this weekend. Jkl

&&

Short term...valid for Friday and Sat...

Just another day or two of relatively benign weather before we
transition back to a colder and unsettled weather pattern. For
this package I have raised probability of precipitation quite a bit for Saturday
evening/night as models are in good agreement for that time
frame. The fact the models all have a jet nosing across our region
combined with the signals on the cross sections makes ME think
there will be significant banding of precipitation by Saturday
evening. The main forecast issue is if and how deep upslope flow
makes it into Red Lodge and the other foothill locations. Models
are tending to keep the flow northwesterly in the foothills and
not hit them too hard. This strict demarcation is probably due to
the position of the upper jet oriented northwest to southeast directly over
Billings keeping the cold air mainly east of the foothills. If
the jet position trends further SW then snowfall will be more
likely and heavier in the foothills. For now...kept probability of precipitation and quantitative precipitation forecast
a bit lower in the foothills than in the Yellowstone County area.
That said...it still does not look right now to warrant any
highlights based on snowfall amounts with only around an inch or
two snowfall in the hardest hit areas. However...the one impact
that does concern ME is the fact we will have warm Road temperatures yet
Saturday ahead of the weather system...and temperatures may plummet
quickly resulting in icy Road conditions. So cannot rule out an
advisory yet for Billings and surrounding areas. We will analyze
this more closely tomorrow while beginning to advertise this
possibility in other products such as our website weather story
and hazardous weather outlook. Bt

Long term...valid for sun...Mon...Tue...Wed...Thu...

Made some large adjustments to the extended forecast with
confidence increasing in a colder and wetter period. Northwest flow will
be over the region through Wednesday. Channeled vorticity will move out
of the area on sun taking precipitation with it. The next surge of
Pacific moisture will move quickly into the region bringing
another chance of precipitation to mainly the mountains. A low
pressure wave will then move into the area Sun night bringing more
precipitation to the area. Have raised mountain probability of precipitation for this
period. The wave will move southeast of the area during Monday and will be
followed by another wave which will continue the chances of
precipitation.

On Monday night...models were in good agreement in the timing of a
shortwave wrapping around the Hudson Bay low which will reinforce cold
air over the area and form a strong wave along the southward
moving front. Pacific moisture will accompany the system and the
flow will turn upslope. The combination of these factors will
result in the likelihood of snow over central and western portions
of the area. The Hudson Bay shortwave rotates through the region
Tuesday and Tuesday night continuing a good chance of snow over the area
for Tuesday...before the moisture moves out of the area Tuesday night.
Have raised probability of precipitation across the entire area Monday night and Tuesday...and
had likely probability of precipitation over the central and western zones. Note that the
timing of the best precipitation chances will be subject to change
as the models notoriously have difficulty in the timing of
shortwaves in northwest flow.

Tapered off the precipitation chances Tuesday night...then went mostly
dry for Wednesday into Thursday as upper ridging builds into the area. Flow
becomes more progressive on the GFS on Thursday while the European model (ecmwf)
maintains an upper ridge. Both models warmed up the airmass
considerably on Thursday.

Regarding temperatures...readings will be slightly below normal on
sun under the continued cold airmass from Sat. Temperatures will
be challenging on Monday which looks to have a warm start before
colder air filters back into the area later in the day. Expect
below normal temperatures on Tuesday with the system over the area.
Temperatures will then moderate for Wednesday into Thursday. Arthur

&&

Aviation...

Skies will be partly cloudy this evening and throughout the
overnight hours as some middle and high level clouds move across the
forecast area. VFR conditions are expected to prevail. Hooley
&&

Preliminary point temp/pops...

Friday Sat sun Monday Tuesday Wednesday Thursday
-----------------------------------------------------------
bil 031/050 027/039 019/032 028/045 021/023 009/027 021/043
00/b 02/west 63/j 43/west 66/S 21/b 11/north
lvm 027/049 024/044 020/037 031/047 025/027 017/035 027/046
00/b 01/b 43/west 43/west 66/S 21/b 22/west
hdn 026/047 022/037 015/030 022/043 017/019 007/025 012/040
00/b 02/west 42/j 43/west 56/S 21/b 01/b
mls 027/044 023/032 011/025 019/035 013/015 902/018 006/038
00/u 05/j 32/j 33/j 54/S 21/b 01/b
4bq 025/049 023/039 015/028 023/043 019/021 006/023 012/042
00/u 02/west 32/j 33/west 34/S 21/b 01/b
bhk 025/043 020/027 007/021 014/033 011/013 905/014 004/032
00/u 15/j 42/j 23/j 44/S 11/b 11/b
shr 022/045 018/039 015/029 022/044 018/020 006/028 015/041
00/b 01/b 32/j 22/west 35/S 21/b 11/b

&&

Byz watches/warnings/advisories...
Montana...none.
Wyoming...none.

&&

$$
Weather.Gov/Billings

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