textproduct: Great Falls

KEY MESSAGES

- Periods of light snow continue along the Continental Divide from Rogers Pass north through Glacier National Park through the weekend.

- A few light rain and snow showers will track east across north- central and southwest Montana Sunday morning with overall mild conditions prevailing through Monday.

- Widespread snow is likely to accompany a transition to a colder and more active weather pattern beginning Tuesday.

DISCUSSION

- Meteorological Overview:

Flat upper level ridging remains in place across the Northern Rockies and MT through the rest of the weekend in between a split upper level trough offshore of the west coast and deeper trough shifting across northern Canada. A plume of Pacific moisture streaming out of the offshore trough across the Northern Rockies will support some periods of mainly mountain precipitation, with measurable precip/accumulating snowfall primarily focused along the continental divide. A few light rain/snow showers may accompany an embedded disturbance moving east across north-central MT Sunday morning. Otherwise, the overall mild conditions persist across the area through Monday with breezy to locally windy conditions along the Rocky Mtn Front and portions of north-central MT diminishing this evening. Meanwhile, gusty southwest winds will persist across southwest MT, mainly over ridgetops and valleys with N-S alignment, where winds will increase further on Monday as southerly flow increases ahead of the incoming upper level trough.

A significant transition in our overall weather pattern occurs on Tuesday as the offshore trough moves inland and deepens in response to upper level energy diving south out of the Gulf of AK. Models are in reasonable agreement with a wave of energy lifting out of the trough and across the area Tuesday, supporting a period of widespread precipitation/snow. Cooling aloft arrives initially beneath the upper level trough before a lower level cold airmass surges south from AB into the area later Tuesday through Tuesday night. Colder (near to below seasonal) temperatures are likely to follow through the remainder of the week with additional energy moving through the trough maintaining chances for at least some localized snowfall. Hoenisch

- Forecast Confidence & Scenarios:

Periods of snow across the continental divide this weekend will create some winter driving conditions at times on portions of US-2 over Marias Pass and MT-200 from Lincoln to Rogers pass. While total weekend snow accumulation over these passes of 2 -4 inches is expected, snow intensity looks to be periodic and light with temperatures near freezing. Still, travelers should anticipate some changing visibility and road conditions over these areas.

Confidence is increasing in widespread/measurable snow across much of the area Tuesday, though there is still considerable uncertainty in the timing/duration and amounts of precipitation at this point. Latest blended model guidance gives areas along and west of I-15 across north central MT (including Great falls and Cut Bank) a 70% or higher risk of snowfall exceeding 2 inches with similar probabilities over the southwest MT mountains but lower probabilities across eastern portions of north-central MT and the SW MT valleys.

Temperature forecasts are trending colder for the Wednesday through Friday period as an increasing number of model ensemble members support of colder airmass surging south across the area by Wednesday. Additional cooling is possible if trends continue and considering potential for snow-cover following the Tuesday system. A reasonable low-end (25th percentile) scenario would have daytime temperatures as cold as the single digits across north-central MT Wednesday and Thursday. Hoenisch

AVIATION

14/18Z TAF Period

Mountain snow will continue over mostly the Continental Divide during the TAF period. It will be breezy along the North-Central MT plains this afternoon, with winds decreasing this evening. Sunday morning, a front will move through North-Central MT and will bring slight chances for light rain/snow. However, there remains a little uncertainty in the timing and exact location of precipitation along the front. -Wilson

PRELIMINARY POINT TEMPS/POPS

GTF 33 51 31 57 / 20 30 10 10 CTB 25 46 23 50 / 10 10 10 10 HLN 30 51 28 53 / 20 30 20 10 BZN 29 53 27 53 / 10 10 20 10 WYS 18 40 17 40 / 10 20 10 30 DLN 30 52 26 51 / 0 10 0 0 HVR 28 47 25 53 / 20 20 20 10 LWT 29 45 27 52 / 10 30 20 10

TFX WATCHES/WARNINGS/ADVISORIES

None.