Sunrise 6:23 AM   Sunset 8:43 PM Moonrise 12:00 AM   Moonset 7:07 AM

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FXUS65 KMSO 270818 AFDMSO

Area Forecast Discussion National Weather Service Missoula MT 218 AM MDT Sat Apr 27 2024

DISCUSSION
The Northern Rockies sits under a deep trough of low pressure extending south through the Great Basin this morning. This trough is one in a series of disturbances lined up over the northeastern Pacific Ocean and moving towards the northwestern U.S. In the near-term, rain will grace the forecast for today, with the highest probability for precipitation being across southwest Montana and Lemhi County due to a midlevel circulation to the southeast sending moisture back up from the south. Snow levels this morning will be around 5000 to 6000 feet, so expect slushy or snowpacked roads over Lost Trail and Homestake Passes. Winter Weather Advisories are in effect for elevations above 6000 ft in the affected areas. Snow showers will occur at lower elevations also, but if there's any accumulation at all below 6,000 ft it won't be enough to warrant an advisory.

As today’s trough of low pressure moves east overnight tonight, upper level flow becomes westerly as the next disturbance moves down the Canadian coast on Sunday. As it does, it will push Pacific moisture onshore into the Pacific Northwest and, eventually, into the Northern Rockies. Expect valley rain and high elevation snow to continue into Sunday morning with an increase in westerly winds in the afternoon with the passing of a weak cold front. Chances for precipitation will again increase on Monday as this next wave moves through the northwestern U.S. and into the Northern Rockies, bringing pacific moisture, a cold front, and a favorable position of the upper level jet.

The Northern Rockies will remain under an unsettled pattern through the middle of next week. Ensemble solutions show good agreement for cool, wet weather to continue through Wednesday.
Agreement starts to waver later in the week, when some solutions begin to show a shift towards a drier pattern while others keep the Northern Rockies under a strong trough.



AVIATION
A deep trough of low pressure will keep rain showers in the forecast throughout the day today. The southeasterly nature of the midlevel flow will result in increasing rainfall intensity at KBTM, further dropping visibility and ceilings by about 27/1500Z this morning and lasting through about 27/2000Z.
Elsewhere, expect light rain for most of the day today. Snow over the higher elevations will obscure terrain over the Continental Divide and the Bitterroot and Clearwater Ranges.



MSO WATCHES/WARNINGS/ADVISORIES
MT...Winter Weather Advisory until 6 PM MDT this evening for Bitterroot/Sapphire Mountains...Butte/Blackfoot Region.

ID...Winter Weather Advisory until 6 PM MDT this evening for Eastern Lemhi County...Western Lemhi County.

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