textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Cold front tonight into Monday bringing cooler, showery and breezy conditions.

- Closed low impacting the region late Wednesday into Friday.

A trough and associated surface cold front approaching the region are causing showers this afternoon. Overnight tonight, The cold front will cause snow levels to come crashing down to the valley floors, but the precipitation will stop around the same time, so minimal snow impacts are expected in the valleys. Mountain locations will pick up a few inches of snow, though only minimal impacts are expected, with the exception of over Marias Pass in northwest Montana.

By Wednesday, a trough is digging off the Pacific Northwest coast to eventually become a closed low. This will set up southwest flow into the northern Rockies region, and it will also bring more precipitation. By Thursday, the cold air associated with this low is over the region and the snow levels lower to near the valley floors, causing a good Spring snow in many places. Portions of the lower elevations of central Idaho, including Grangeville, have about a 50% chance of seeing accumulating snow while the median forecast for the mountains of central Idaho is closer to the 5 to 7 inch range. The valley snow in western Montana will be much more variable from location to location with 90th percentile forecasts coming in at 1-2 inches in the valleys and median forecasts of no accumulating snow. Further south in Lemhi County, ID, median snow forecasts by Thursday evening are around 1 inch of new snow with the 90th percentile forecast coming in at 2-3 inches. Whether in central Idaho, Lemhi County, or western Montana, the foothills and higher elevations around the valleys will pick up more snow, potentially 4-6 inches. But snow amounts in the terrain will be highly variable from location to location.

By next weekend, models have very poor agreement on any kind of pattern. Some clusters show a ridge, and others a trough. The overall message to take from this pattern is that the pattern will remain very active with troughs and short lived ridges every couple of days, which is a very typical situation for the Spring.

AVIATION

An approaching trough and cold front will cause minimal impacts to aviation across the region through tomorrow. Lower ceilings with the moisture moving into the region are only expected to briefly touch on MVFR conditions, if at all. Falling snow levels tonight will coincide with the arrival of drier air, so minimal snow impacts are expected as well. Even though valley terminals will only see minor impacts, expect frequent mountain obscurations through Monday night due to the precipitation.

Unstable conditions on Monday afternoon will cause some convection with a chance for snow showers to affect area terminals. Current model forecasts are showing very low chances for snow showers, but past experience has been that models often under forecast the shower potential behind a cold front in the Spring.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Winter Weather Advisory from 8 PM this evening to 10 AM MDT Monday for West Glacier Region.

ID...None.