textproduct: Great Falls

KEY MESSAGES

- Mainly light snow develops tonight along the Rocky Mountain Front and persists through much of the weekend.

- Additional light mountain precipitation makes further inroads east of the Continental Divide Sunday.

- Cooler temperatures with intermittent precipitation moves in Tuesday through much of the remainder of next week.

DISCUSSION

- Meteorological Overview:

A westerly to southwesterly flow aloft will persist through the weekend. Waves of moisture will accompany this persistent flow aloft, resulting in periods of snow along the Continental Divide at times through Sunday. Given daytime highs at pass level approaching or exceeding the freezing mark this weekend, persistent impacts are not forecast at this time. The pass most likely to see intermittent minor impacts from the snow looks to be Marias Pass, most likely to occur during the overnight hours.

A brief reprieve looks to develop Monday as the region is between systems. Heading into Tuesday, deep upper level troughing with several embedded waves moves further inland across the west. There appears to be several embedded waves that will track across the region next week, the first of which looks to move across the region Tuesday. Temperatures trend much closer to average and perhaps a touch below average by Tuesday evening, particularly over the plains. A period of precipitation accompanies this system, most of which looks to fall as snow at lower elevations.

Heading into the rest of the week there looks to be several additional waves moving across the region. Confidence in timing each wave remains low, but the main takeaway is that temperatures remain on the cooler side, with persistent opportunities for mainly light precipitation. -AM

- Forecast Confidence & Scenarios:

Snow this weekend along the Rocky Mountain Front:

The main snow accumulations look to be above pass level this weekend. That said, over 48 hours ending Sunday evening the probability for 4 inches of snow is roughly 60% at Marias Pass. Given this snow looks to fall over an extended period, and that some will fall during the day when some melting will occur, we are holding off on a Winter Weather Advisory for the time being.

Tuesday and beyond:

There continues to be large spread in guidance with respect to precipitation amounts, timing, and location Tuesday through the remainder of the week. The main takeaway continues to be a trend toward seasonably cold temperatures, with snow at times in most areas. At lower elevations the probability for 3 inches of snow between Monday evening and Thursday evening sits between 20 and 40% for the most part. -AM

AVIATION

13/18Z TAF Period

Aside from a few areas of low clouds near West Yellowstone, the primary concern this TAF period will be for mountain snow developing along the Rocky Mountain Front tonight into the day Saturday. Mountain obscuration around areas of precipitation is forecast.

Otherwise the only other concern will be for breezy winds across portions of the plains today. A weak wind shift to a more northwesterly direction across North-central Montana this afternoon is in the cards, but is low probability at this time. -AM

PRELIMINARY POINT TEMPS/POPS

GTF 34 54 33 50 / 0 0 10 20 CTB 27 49 25 45 / 0 10 0 10 HLN 26 50 30 50 / 0 10 20 40 BZN 23 49 30 52 / 0 0 10 20 WYS 16 36 18 40 / 0 10 10 20 DLN 24 49 30 52 / 0 0 0 10 HVR 27 54 28 48 / 0 0 10 10 LWT 24 45 29 45 / 0 0 20 40

TFX WATCHES/WARNINGS/ADVISORIES

None.