935 
FXUS65 KMSO 092043
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
243 PM MDT Fri Aug 9 2019

.DISCUSSION...Widespread rain showers and isolated thunderstorms
will continue to spread from the south to north across the
Northern Rockies through the evening hours. Brief heavy rain and
occasional lightning will be the main threats this evening.  

We continue to watch for the potential for strong to severe
thunderstorms developing across west-central and southwest
Montana, as well as north-central Idaho tomorrow afternoon and
evening. Thunderstorms will begin to form in north-central Idaho
in the late morning, and strengthen as they move north into 
western Montana later in the afternoon. Storms that become severe 
in nature will have the potential to produce strong damaging wind 
gusts in excess of 50 mph. Winds gusts of these speeds may topple
trees and power lines. These strong storms can also produce large
hail in excess of 1 inch in diameter. Another impact from these
storms will be very heavy rain. Area burn scars will be 
susceptible for rock and mudslides, along with flooding in some 
urban locations and other flood prone areas. A Flash Flood Watch 
has been issued for certain locations with these vulnerabilities. 
Details can be found at our website www.weather.gov/mso. Scattered
thunderstorms will continue to move across the region through 
midnight Saturday night, but these storms that move overhead after
sunset are not expected to be severe in nature.

As the upper level trough moves through the area on Sunday,
widespread rain will develop, particularly across the Idaho
panhandle and northwest Montana. Precipitation amounts of a
quarter of an inch or more will be possible in these areas.
Thunderstorms will also be possible in the afternoon, and will be
capable of brief heavy rain and small hail. Temperatures will run
roughly 15 degrees cooler than normal for this time of year. 

A weak ridge of high pressure is expected over the region to start
next week, with temperatures slowly warming though still running
somewhat below seasonal normals. As the flow becomes more
southwesterly by mid week, the chance for showers and
thunderstorms will increase.


&&

.AVIATION...Rain will dissipate at KGPI, KMSO, and KBTM by 
10/0200Z and a short break in unsettled weather will last through 
Saturday morning. The exception will be KSMN as some isolated 
storms overnight are not out of the question. Saturday will bring 
active weather to all terminals in the afternoon as many 
ingredients come together for strong convection. Expect a decrease
in visibility as widespread showers and thunderstorms bring heavy
rain, lightning, gusty winds, and a chance of hail to all 
terminals. Storms will start at KSMN by about 10/2000Z, spread 
north and northeast to KBTM and KMSO, then continue to KGPI by 
about 10/2200Z. 

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Flash Flood Watch from Saturday afternoon through Saturday 
     evening Bitterroot/Sapphire Mountains...Butte/Blackfoot 
     Region...Missoula/Bitterroot Valleys...Potomac/Seeley Lake 
     Region.

     Flash Flood Watch from Saturday afternoon through Saturday 
     evening Flathead/Mission Valleys...Kootenai/Cabinet 
     Region...West Glacier Region.

ID...     Flash Flood Watch from Saturday morning through Saturday 
     afternoon Lower Hells Canyon/Salmon River Region...
     Orofino/Grangeville Region...Southern Clearwater Mountains.

&&

$$