High Wind and Strong Wind in Montana, June 13, 2020

Area Forecast Discussion
National Weather Service Missoula MT
926 AM MDT Sat Jun 13 2020

.UPDATE...We upgraded the Butte/Blackfoot Region to a high wind
warning for late this morning through this afternoon. Our high
resolution models continue to indicate wind gusts to near 60 mph
are possible early this afternoon, generally along and south of
Interstate 90 from Homestake Pass to the Anaconda cut off
(including the Butte area). Tree fall and power outages are
anticipated, with dangerous cross winds for high profile
vehicles traveling along east/west oriented portions of
Interstate 90.

In addition, we have issued a lake wind advisory for Flathead Lake
this afternoon and early evening. High resolutions models indicate
the potential for strong thunderstorms to move over the lake
between roughly 2pm and 6pm this afternoon. Damaging wind gusts
over 50 mph will be possible with these storms and could create
dangerous conditions for small craft on the lake. These storms
have the potential to reach up into the Flathead valley and
Glacier National Park as well. Damaging winds, hail and brief
heavy rain are all potential threats. If you live or are
recreating in northwest Montana today, keep an eye to the sky and
have a plan to take shelter, if necessary.

&&

.AVIATION...Cloud cover and showers are moving toward the region,
associated with disturbances in southerly flow. The main low
pressure center and shortwave trough are approaching from NV,
which will cause showers and thunderstorms in north-central Idaho
during this morning, and showers and thunderstorms in western
Montana during this afternoon. A cold front is also expected to
pass through the Northern Rockies, which will tighten the pressure
gradient and cause gusty winds. Gusts near 40 knots will be
common today and there may even be gusts over 50 knots with
thunderstorms and also in the vicinity of KSMN to KBTM. Wind
highlights remain in effect for Lemhi County through southwest
Montana. Northwest Montana and especially the Glacier Park Region
have the highest potential for strong thunderstorms this
afternoon, but the vigorous trough passage will bring the
potential for widespread thunderstorms today. Snow levels will
lower tonight to around 5500 feet with accumulations expected.

&&

.PREV DISCUSSION... /ISSUED 343 AM MDT Sat Jun 13 2020/

DISCUSSION...Active weather is still expected today due to an
approaching shortwave trough and cold front. The pressure gradient
will tighten today and winds will become breezy to windy with
gusts commonly 30-40 mph but some will have gusts over 50 mph.
The strongest winds are most likely to be in Lemhi County through
southwest Montana. Confidence is high for gusty winds today.

Thunderstorms are expected today but there are questions on how
widespread they will be and who will have the strongest storms.
Surface-based lift appears to be limited, which is causing
convective allowing models to struggle with their thunderstorm
forecasts, ranging from widespread thunderstorms to only isolated
thunderstorms. The cold front and trough will provide lift, which
will be enough for thunderstorms and at least a few strong
thunderstorms this afternoon, so the forecast has been trended
toward higher chances for thunderstorms. Northwest Montana, and
especially the Glacier Region are expected to have the most
favorable conditions for thunderstorms, and the Storm Prediction
Center continues to highlight GNP for a threat of strong
thunderstorms.

As today's shortwave moves off to the north, the main trough and
low pressure system will move into the Pacific Northwest. Snow
levels are still expected to lower down to around 5500 feet with
the next low tonight. Latest models guidance show the coldest air
arriving during Sunday afternoon so this may limit some of the
snow accumulation potential, either way, snow can be planned for
in the high terrain.

Sunday's low is forecast to quickly move through the region, and
Sunday night is showing fairly dry. The next weather system
arrives on Monday, in the form of a broad trough, that will be
the dominate weather feature for much of the week. Temperatures
will be below average and there may be showers each day this week.

AVIATION...Cloud cover and showers are moving toward the region,
associated with disturbances in southerly flow. The main low
pressure center and shortwave trough are approaching from NV,
which will cause showers and thunderstorms in north-central Idaho
during this morning, and showers and thunderstorms in western
Montana during this afternoon. A cold front is also expected to
pass through the Northern Rockies, which will tighten the pressure
gradient and cause gusty winds. Gusts near 40 knots will be
common today and there may even be gusts over 50 knots with
thunderstorms and from KSMN to KBTM. Wind highlights remain in
effect for Lemhi County through southwest Montana. Northwest
Montana and especially the Glacier Region have the highest
potential for strong thunderstorms this afternoon, but the
vigorous trough passage will bring the potential for widespread
thunderstorms today. Snow levels will lower tonight to around 5500
feet with accumulations expected.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...High Wind Warning until 6 PM MDT this evening Butte/Blackfoot
     Region.

     Lake Wind Advisory from 1 PM this afternoon to 6 PM MDT this
     evening Flathead/Mission Valleys.

ID...Wind Advisory until 6 PM MDT this evening Eastern Lemhi County.

&&