River Flood Advisory 2, NWS Missoula, MT

Area Forecast Discussion
National Weather Service Missoula MT
258 AM MDT Wed May 20 2020

.DISCUSSION...Lingering embedded thunderstorms remain within the
spinning low pressure centered around the Northern Rockies this
morning. Moderate to heavy rainfall that occurred overnight across
west central Montana has moved into northwest Montana and north
central Idaho. These areas will continue to see the best focus of
rainfall throughout the day. A brief drying period may occur
across southwest Montana into portions of west central Montana (in
and around the Missoula/Bitterroot valleys) for a period of time
this afternoon, but will eventually fill back in with more
rainfall by this evening.

With widespread moderate to heavy rainfall expected through
Thursday, our main concern continues to be rapid rises on small
streams and creeks and mainstem rivers rising above flood stage.
Particular emphasis is given to small streams/creeks across north
central Idaho, as this is where the heaviest rainfall will exist
today. Loose soil, sloughing of land, rock fall over highways, etc
should also be anticipated due to persistent heavy rainfall.

Mainstem rivers across the entire region will continue
to rise as well, albeit somewhat slower though not any less
significant. Flood Watches and Warning(s) remain in effect across
west central Montana and north central Idaho, however additional
Watches/Warnings may need to be issued as this system evolves
further.

Rain will remain somewhat consistent in the forecast through
Friday, with periodic breaks finally happening thereafter.
While rainfall will become less widespread, it will still remain
a fixture going into the weekend.

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.AVIATION...Moderate to heavy rainfall will plague KMSO, KGPI, and
KGIC throughout the day today, with breaks in precipitation
occurring for KBTM and KSMN through this afternoon. With the low
pressure center expected to revolve around the Northern Rockies
over the next 24-48 hours, persistent rainfall should be expected.
Low ceilings will be commonplace, with periodically lowered
visibility in areas of particularly heavy rain. Mountain
obscurations will exist henceforth under this unsettled and wet
pattern.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Flood Watch through late tonight Bitterroot/Sapphire Mountains...
     Missoula/Bitterroot Valleys.

ID...Flood Watch through late tonight Lower Hells Canyon/Salmon River
     Region...Northern Clearwater Mountains...
     Orofino/Grangeville Region...Southern Clearwater Mountains.

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