Sunrise 5:42 AM   Sunset 9:25 PM Moonrise 2:07 AM   Moonset 2:49 PM

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FXUS65 KMSO 010816 AFDMSO

Area Forecast Discussion National Weather Service Missoula MT 216 AM MDT Sat Jun 1 2024

...Widespread moderate to heavy rain, with rises to small streams and increased risk for rock and mudslides, Sunday night into Monday...

DISCUSSION
GOES Satellite and regional radar imagery early this morning shows a trough of low pressure moving onshore in Washington. This trough will move across the Northern Rockies by mid-afternoon, with scattered showers developing through the evening hours. The best axis of mid-level moisture and instability will set up across Idaho and Lemhi Counties and in southwest Montana, where isolated thunderstorms will be capable of producing outflow winds of 30-40 mph.

An atmospheric river remains on track to bring widespread moderate to locally heavy rain Sunday night into Monday night. Ensemble forecast systems suggest Pacific moisture will reach into the 99-99.5 percentile for this time of year, with integrated water vapor transport values seeing return intervals of a once in 10 year event for early June! As with previous forecasts, the heaviest rainfall is expected across Idaho and Clearwater Counties, with probabilities of 1.00" or more of rainfall reaching 80-90 percent along the Highway 12 corridor, Clearwater Mountains, and portions of the Camas Prairie near Grangeville.
Probabilities for 2.00" of more reach 20 percent south and east Grangeville and US Highway 12. Notable rises on small streams and rivers are anticipated. There will also be an increased threat for rock and debris onto roadways and in flood prone areas. Embedded isolated thunderstorms within the atmospheric river precipitation shield Sunday afternoon may lead to locally heavy rain and enhanced precipitation totals. If high end precipitation totals (2.00-3.00"+) are achieved, the risk for minor flooding will increase, particularly for small streams.

Further east in western Montana, precipitation is largely anticipated to be beneficial. Most locations have a 60-80 percent chance of seeing at least 0.25" of rainfall, with the exception across southwest Montana and eastern Lemhi County where rainfall amounts will be lighter. Heavier amounts (0.50-1.00") are forecast across far northwest Montana near the Idaho panhandle, where ponding of water may occur in poor drainage areas.

A strong ridge will build over the western U.S. Wednesday into next weekend, leading to an extended period of warmer, summer- like temperatures. Highs are expected to reach into the 80s to lower 90s for valleys. Ensembles continue to show uncertainty with the orientation of the ridge, thus a day or two of thunderstorms may be mixed in. /Lukinbeal



AVIATION
GOES Satellite and regional radar imagery as of 01/0830Z shows a Pacific trough moving onshore in Washington.
This trough will move across the Northern Rockies by 01/2000-2200Z, with scattered showers developing thereafter. Activity will push east of the divide by 02/0600Z. The best axis of mid-level moisture and instability will set up across Idaho and Lemhi Counties and in southwest Montana, where isolated thunderstorms will be capable of producing outflow winds of 25-35kt. /Lukinbeal

MSO WATCHES/WARNINGS/ADVISORIES
MT...None.
ID...None.

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