textproduct: Missoula

This forecast discussion was created in the public domain by the National Weather Service. It can be found in its original form here.

DISCUSSION

KEY MESSAGES:

- Record Warmth (through Sat): High pressure brings well above normal temperatures. Daily record high potential with considerable sunshine, some high clouds.

- Pattern Shift (Sun-Mon): A transition to cooler, unsettled weather begins Sunday. Expect breezy southwest winds ahead of the system.

- Winter Impacts (Mon-Mon Night): Moderate pass level snow impacts. Snow levels return to valley floors by early Tuesday but limited precipitation is expected at that point.

Satellite imagery this afternoon is showing an amplifying ridge of high pressure building over the western US and high clouds over northwest Montana. Some moisture is riding up and over the ridge, resulting in those high and mid-level cloud decks. High pressure will persist through Friday before flattening on Saturday. In the meantime, expect daytime high temperatures to remain well above normal. The warm temperatures will threaten daily records across the Northern Rockies. One challenge to the forecast will be the extend of cloud cover, which would suppress high temperatures.

Flow aloft turns westerly by Saturday evening as a trough of low pressure moves east out of the Gulf of Alaska. This feature will send Pacific moisture onshore, increasing chances for precipitation for northwest Montana on Saturday night. Those chances will spread east on Sunday. Temperatures will initially stay warm enough to support rain in the valley bottoms. A cold front on Monday will bring snow levels down to valley floors. Snow accumulation will still be limited to the higher terrain and mountain passes. While temperatures drop after Sunday, daytime highs still stay about 5 to 10 degrees above normal.

AVIATION

The primary forecast challenge is the disconnect between dryer model guidance in the boundary layer and saturated ground conditions across western Montana and north-central Idaho (early "mud season") from recent thaw period without much for drying winds. Expect this low-level moisture to drive radiational fog development at KGPI, KMSO, an KSMN overnight tonight as skies continue to clear and winds decouple.

MSO WATCHES/WARNINGS/ADVISORIES

MT...None. ID...None.

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