Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 012056

Area Forecast Discussion
National Weather Service Missoula MT
256 PM MDT MON JUN 1 2015


.DISCUSSION...A disturbance moving into the Pacific Northwest has
caused the upper level flow to become southwesterly over the
region. This flow pattern has allowed moisture to stream into the
area. The moisture combined with afternoon instability will cause
widespread showers and thunderstorms. The strongest thunderstorms
are expected across Lemhi county into southwest Montana this
afternoon, and could produce large hail and damage winds. During
the early evening hours, more strong thunderstorms could develop
across the Grangeville/Orofino area and move through west central
Montana during the overnight hours. All showers and thunderstorms
will be capable of very heavy rainfall, which could cause water
issues in flood-prone areas.

The system at the coast will continue to move up and through the
northern Rockies tonight into Tuesday causing ample moisture to be
ushered into northwest Montana. Areas from Libby to Glacier
National Park are anticipated to receive fairly steady
precipitation with heavier rainfall expected under embedded
thunderstorms. A flash flood watch has been issued for the Glacier
National Park due to the amount of precipitation that is expected
through Tuesday morning.

The trough is expect to dig along the Pacific coast Wednesday into
Thursday causing the upper level flow to become southwesterly once
again. The instability and strong thunderstorm potential does not
appear to be as great as Monday, but afternoon and evening
showers and thunderstorms are still anticipated.

The models are indicating that the trough will become a cut off
low over southern California by late in the week. The northern Rockies
will be between systems with temperatures steadily rising each
day. Moisture will be limited but afternoon and evening showers
and thunderstorms will be still possible.


.AVIATION...Terminals should expect an active day of
showers and thunderstorms, which may continue overnight into
Tuesday. Along with frequent lightning, bouts of heavy rainfall,
gusty and erratic winds, and hail are all possible, if not likely,
with storms that develop today. The time frame of biggest concern
for all terminals will be between the hours of 01/2000Z and
02/0300Z for the above-mentioned impacts. More convection and
disruptions from associated impacts is expected Tuesday.


.HYDROLOGY...The biggest concern today with thunderstorms
affecting the Northern Rockies will be the potential for flash
flooding and urban flooding. We expect thunderstorms to produce
torrential downpours in very brief periods of time, leading to the
threat for flash flooding. Amounts of 0.30 to 0.50 inches in as
little as 30 minutes is not out of the question.

IMPACTS: Rock slides and/or washouts over roadways are possible.
Those living near wildfire burn scar areas should prepare for
impacts from heavy rainfall in the form of mud and debris flows.
For urban areas, poor drainage will only exacerbate the amount of
rain that thunderstorms produce, causing localized flood
concerns. Have a plan in place to help alleviate any flash
flood/urban flood issues that could arise throughout the day


MT...FLASH FLOOD WATCH through Tuesday morning West Glacier


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