High Wind in Montana, January 29 to 30, 2018

Area Forecast Discussion
National Weather Service Great Falls MT
1040 AM MST Mon Jan 29 2018

Aviation Section Updated

.SYNOPSIS...
A mild airmass originating over the Pacific will overspread the
region today with temperatures warming well above seasonal
averages by this afternoon. Winds increase today with strong and
potentially damaging winds likely to develop by late this
afternoon along the Rocky Mountain Front, then spreading east
across the north central Montana plains tonight through Tuesday
morning with the passage of a cold front. Cooler and continued
unsettled conditions are anticipated for the second half of this
week into the weekend.

&&

.MORNING UPDATE...

The main changes for the morning update were to up winds some
tonight over the plains and adjust afternoon highs based on current
obs/trends.

Water vapor imagery this morning continues to show a stream of
moisture coming into the Pac NW at this time, leading to widespread
cloudiness and a narrow Chinook Arch. However, lower levels remain
generally dry and echoes showing up on radar are likely virga. What
also shows up nicely on water vapor is the incoming, strong jet that
will lead to the high wind event over the plains. The jet is just
now approaching the WA coast. The high wind event still looks on
track and for now, no changes are planned for the High Wind Warning.
Of note, the gusty winds right along the Rocky Mtn Front this
morning may actually decrease some into about mid-afternoon or so,
before really ramping up by early this evening. Given the potential
of stronger winds for at least a part of the Rocky Mtn Front this
afternoon, we'll hold off on adjusting the start time of the
Warning, but again, the main impact period with this wind event
looks to be after 7pm along the Rocky Mtn Front and after 11pm or so
for the plains east of I-15.

With moisture continuing to run into the Continental Divide, steady
snow is expected at/above pass level there this evening/tonight.
Impacts should mostly be confined to recreationalists, but some
blowing and falling snow may cause travel impacts over Marias Pass
and we'll continue to evaluate this potential for any future winter
weather highlights. For now, though, the lighter snowfall
amounts/rates look to limit the impacts. MARTIN

&&

.AVIATION...
Updated 1740Z.

Strong winds, LLWS, and mtn wave activity to impact much of the
forecast area through Tuesday.

A strong jet, just now reaching the WA coast, will move across
Montana this evening/tonight and will be accompanied by a cold front
passage. The combination of the front, mtn wave activity, and steep
lapse rates will allow a period of strong winds and possible LLWS
across the area, especially this evening through Tuesday morning. Of
note, wind gusts may reach 50-60kt in the vicinity of CTB late this
evening/tonight. Across SW MT, the peak of the wind may hold off
until Tuesday or even Tuesday afternoon as the front moves through.
A few SHRA/SHSN will accompany the front on Tuesday, mainly
in/around the mountains and possibly impacting HLN/EKS/BZN. MARTIN

&&

.PREV DISCUSSION...
/ISSUED 420 AM MST Mon Jan 29 2018/

Today through Wednesday...Warmer airmass of Pacific origin will
continue to overspread the region today eroding the cold airmass from
north central MT from SW to NE through early this afternoon.
Overrunning precipitation across n-central MT has been very light and
spotty with still some potential for light freezing
drizzle/sprinkles, but impact and coverage will be very low.
Afternoon temperatures should reach mid 40s to mid 50s across much
of the forecast area this afternoon with increasing winds. Strong
and potentially damaging winds are on track to develop late this
afternoon and evening along the Rocky Mtn front where favorable
conditions for Mountain wave wind enhancement may produce some
gusts in excess of 80 mph locally along the immediate east slopes
this evening. Late this evening through Tuesday morning, strong
winds spread east onto the plains where gusts may exceed 70 mph
in the Cut Bank area with 55-65 mph gusts likely across a good
coverage of the north-central MT plains late tonight through
Tuesday morning. A high wind warning is in effect for areas with
the greatest potential for strong winds and will continue to
monitor potential for more isolated strong wind gusts possible
with the frontal passage further into SW MT Tuesday morning.
Remnant of atmospheric river pushing into NW WA today will sag
south with the cold front and shortwave tonight, brining a period
of widespread precipitation to areas along the continental divide
late tonight with a broken/scattered area of showers likely to
accompany and follow the cold front passage through SW MT on
Tuesday. Colder conditions under NW flow aloft in place over the
region Wednesday with a colder surface airmass nudging south into
the region from Canada by Wednesday afternoon. light snow will
increase over the mountains on Wednesday as well as along the
leading edge of colder air moving south. Hoenisch

Wednesday Night through Monday...Although unorganized, chances for
light snow continue Wednesday night and Thursday. A stationary front
will separate cold air over North-central MT from seasonally mild
temperatures over southwest MT. Areas of light snow are likely to
redevelop Thursday night as the surface front briefly moves
northeast with weak warm advection aloft. A strong cold front brings
a new surge of Arctic air into North-central MT sometime on Friday.
Widespread snow develops Friday night into Saturday, possibly
continuing into Sunday. This weekend system will need to monitored
closely with the potential for 3-6 inches of new snow and the
possibility for significant winter weather related impacts.
Temperatures return to near average on Monday as Chinook winds help
bring warmer air into the region. PN

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  54  39  45  25 /  10  10  10  10
CTB  49  33  41  22 /   0  10  10  10
HLN  46  30  40  19 /   0  10  30  10
BZN  43  37  41  16 /   0  20  40  10
WEY  34  29  33   7 /  10  30  60  40
DLN  44  35  41  16 /   0  10  30  10
HVR  28  28  38  15 /  10   0   0  10
LWT  45  34  40  21 /  10  10  10  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Warning from 11 PM this evening to 11 AM MST Tuesday
Blaine...Cascade...Central and Southern Lewis and Clark...
Chouteau...Eastern Pondera...Eastern Teton...Fergus...Hill...
Judith Basin...Liberty...Toole.

High Wind Warning from 2 PM this afternoon to 8 AM MST Tuesday
Eastern Glacier...Northern Rocky Mountain Front...Southern Rocky
Mountain Front.

&&

http://www.weather.gov/greatfalls

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
723 AM MST MON JAN 29 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0621 AM     NON-TSTM WND GST DEEP CREEK RAWS         48.36N 113.11W
01/29/2018  M71 MPH          GLACIER            MT   MESONET

            MESONET STATION DCRM8, DEEP CREEK RAWS.

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
1142 AM MST MON JAN 29 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0921 AM     NON-TSTM WND GST DEEP CREEK RAWS         48.36N 113.11W
01/29/2018  M76 MPH          GLACIER            MT   MESONET

            MESONET STATION DCRM8, DEEP CREEK RAWS.

&&