textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Stable conditions cause valley fog and low clouds through Friday.

- A pattern shift on Saturday will bring some atmospheric river remnants to northwest Montana with higher snow levels and minimal impacts expected.

- Cooling early next week with lowering snow levels.

Clearing overnight may allow for some radiational cooling and reintroduction of valley fog this morning. Satellite is already showing decent coverage of fog and stratus in some valleys in central Idaho between the cloud breaks, and cameras are showing fog near Missoula and Kalispell this morning.

Pacific moisture wraps around a powerful Pacific low pressure system as it drops south along the west coast Friday. While it will bring a warm southerly flow, it will also increase clouds which in turn will limit warming Friday and Saturday (even limited warming will run 10 degrees above normal in many locations). A little light precipitation is expected in north-central Idaho and Lemhi County, ID Saturday with no impacts expected.

The next push of moisture arrives late Monday affecting the region through Wednesday morning. Precipitation amounts are light in most ensemble members but, there is a minority of members that have very high precipitation amounts exceeding 1 inch in the mountains. As is typical for this time of year, snow levels are very uncertain with recent model trends going higher. As a result, ensembles are now showing a less than 10% chance for 6-inches or more of snow in the Anaconda Pintlar mountains by Wednesday morning. While impacts should be limited to near the passes, they will also dissipate rapidly as the sun rises Wednesday. If precipitation amounts continue to trend up, impacts could increase and expand, stay updated on future forecasts, especially if you plan to head into the back country next week.

AVIATION

A dirty ridge over the region is increasing the high level clouds, but despite this the saturated boundary layer and stable conditions beneath are still producing valley fog. Occasional breaks in the upper level clouds reveal the valley fog and stratus in satellite imagery showing the most widespread impacts across central and northern Idaho. Cameras and ASOS also show significant impacts across northwest Montana including terminal KGPI while more marginal conditions exist at terminal KMSO. The upper level cloud cover and continued stable conditions today make timing the breakout of the fog difficult, but generally improved aviation conditions are expected around 12/17Z or 12/18Z, especially at terminal KMSO.

MSO WATCHES/WARNINGS/ADVISORIES

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