textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- A transition to colder and blustery conditions continues today as an Arctic boundary slides into western Montana.

- Freezing Spray Potential (Flathead Lake): Gusty northeast winds and high lake levels may generate freezing spray along the south and west shores of Flathead Lake this morning.

- Weekend Uncertainty: A sneaky round of light snow cannot be ruled out with a disturbance dropping out of Canada this weekend.

The primary story for today is the arrival of the cold front and the associated winds gusting 20-30 mph in favored valleys including Missoula and Flathead.

Flathead Lake: East and northeast wind gusts of 15-25 mph are interacting with unseasonably high lake levels creating wave heights sufficiently high to generate freezing spray. There is an increased risk for ice accumulation on docks and shoreline property. There is also an isolated risk for slick spots to develop on roadways immediately adjacent to the lake (such as Hwy 93 through this morning. Winds and wave heights will taper off this afternoon.

Water Vapor satellite imagery reveals a swath of moisture currently rotating around the ridge in the Northern Territories of Canada, aiming south toward the Northern Rockies. Models often handle these northerly flow disturbances poorly, and there is little consensus on the timing, or depth of this moisture as it arrives this weekend. If the moisture holds together and is deep enough, there is potential for a surprise light snow Saturday or Saturday night. If the moisture shears apart upon encountering the ridge, we will simply see increased cloud cover and perhaps a few flurries along the Continental Divide.

Bottom Line: While snow is not in the forecast, don't be surprised if Saturday ends up grayer and flakier than the raw model output suggests.

We expect a return to drier conditions as the weekend disturbance exits. Temperatures will remain below normal, with highs in the 20s. If skies clear Sunday night, Monday morning lows could plunge well into the single digits or below zero in the colder valleys.

Monday through Thursday: The forecast remains low confidence regarding the next pattern shift. The models continue to diverge on how a Pacific trough will interact with the cold air established over the continent. Current model trends favor a drier solution, suggesting the high pressure will block most of the Pacific moisture. However, should the Pacific energy override the cold dome, a period of overrunning light snow or freezing rain remains possible mid to late week. We have maintained low-end PoPs to account for this possibility.

AVIATION

Gusts of 20-30 kts will be common in favored valleys including KMSO and KGPI into this afternoon. KBTM and KHRF begin the period with MVFR ceilings, but the influx of dry, easterly downslope flow will effectively scour the valley stratus, transitioning all terminals to VFR by this afternoon. Mountain obscurations currently affecting north-central Idaho through west- central Montana, and low ceilings in north-central Idaho are expected to improve rapidly this afternoon as ceilings lift and scatter with incoming drier air.

MSO WATCHES/WARNINGS/ADVISORIES

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