Area Forecast Discussion
Issued by NWS Missoula, MT

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000
FXUS65 KMSO 231017
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
417 AM MDT Wed May 23 2018

.DISCUSSION...

The afternoon/evening shower and thunderstorm routine is expected
to continue across the Northern Rockies today and Thursday. The
most significant threat from thunderstorms will be brief, heavy
rainfall, lightning, and erratic winds. Daytime temperatures will
remain seasonally mild during this time, however overnight
temperatures will be on the warm side. These warm overnights will
be key for increasing the rate of melting snow at high elevations.
High flowing streams and rivers will continue.

A ridge of high pressure will pass over the Northern Rockies on
Friday, with the warmest afternoon temperatures of the next week
anticipated. Despite the ridge, moisture will still be streaming
through the upper level flow and allowing showers and
thunderstorms to develop. A weak front is projected to move across
north central Idaho and northwest Montana Friday evening through
late Friday night, enhancing and focusing thunderstorm activity
in those areas. Some models suggest intense rain threat from any
thunderstorms that develop. This Friday night period will need to
be watched closely for any excessive rain runoff and fast
increases in the flow of area small streams (however not mainstem
rivers).

This weekend through at least early next week, a closed low
pressure circulation over the Great Basin will resume the daily
shower/thunderstorm activity each afternoon for the Northern
Rockies. The presence of clouds and precipitation will keep
temperatures from varying greatly between day and night. Again,
warm overnights will keep the snow melting at an accelerated pace.
Streams and rivers will continue to flow high and fast.

Forecast model solutions for the Northern Rockies diverge greatly
from the middle the next week onward. In the face of large
discrepancies, persistence and climatology are dominating the
forecast at this time. In other words, there is little to suggest
that the daily shower and thunderstorm circuit will be ending
anytime soon under a predominantly southwest flow aloft.

&&

.AVIATION...There is a 30% of LIFR fog occurring at KBTM between
1000 UTC and 1500 UTC. VCSH and increased cloud cover will limit
fog potential after 15 UTC at KBTM. Expect another round of
afternoon and evening showers/thunderstorms across the Northern
Rockies Wednesday afternoon and evening. KMSO and KSMN will have
the best chance of being impacted by the storms. These storms are
expected to be slow moving and fairly terrain locked, so terrain
obscurations are highly likely. Storms will be capable of
producing heavy rainfall reducing VSBY and CIGS. The convection
will diminish shortly after sunset by 03-04 UTC.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Flood Watch until 3 PM MDT this afternoon Kootenai/Cabinet
     Region.

ID...None.
&&

$$



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