textproduct: Great Falls

KEY MESSAGES

- Another cold night will occur, but not as cold as the previous night.

- Snow showers will bring another round of light, accumulating snow to the mountains tonight through Friday night.

- Temperatures moderate over the weekend, with all locations warming well above normal by early next week.

DISCUSSION

- Meteorological Overview:

Longwave troughing over the Western CONUS/Canada, with a closed low over Alberta, will gradually shift east and over the Central CONUS through Friday night as longwave troughing over the Pacific builds eastward and amplifies over the Northern Rockies through this weekend. Prior to this occurring a compact shortwave, embedded within the aforementioned longwave trough, will dive southeast from Southern British Columbia and over Montana from late tonight through Friday night. This shortwave and the subsequent northwest flow aloft in its wake will help to support predominately mountain snow showers across Southwest through North Central Montana; with the strongest and most persistent showers occurring over the Continental Divide and Island Ranges of Central Montana. With that being said a few snow showers can't be ruled out over lower elevations, especially northerly upslope favored areas like Lewistown, Great Falls, and Bozeman.

At the surface strong high pressure over the Prairie Provinces this afternoon will weaken slightly and move further northeast, with an a weak area of low pressure moving southeast across Western Montana to Central Montana through Friday morning. This will result in increasing southerly flow across the region, which combined with increasing cloud cover associated with the shortwave will lead to a slightly "warmer" night across most areas tonight; however, most locations will still fall into the teens below to single digits below zero. Highs on Friday will warm back into the 20s to low 30s above zero along and south of the MT Hwy 200 corridor, with the teens above zero over the plains.

Continued moderation in temperatures will occur over the weekend and the upper level ridge amplifies over the Northern Rockies, with the stubborn cold prone valleys of North Central and Central Montana being the slowest to moderate initially. By early next week increasing southwesterly flow and subsequent downsloping will lead to further warming, with all location warming well above normal. While this southwesterly flow will usher in warmer temperatures it will also support daily chances for precipitation, especially over the mountains. - Moldan

- Forecast Confidence & Scenarios:

Accumulating Snow from Tonight through Friday Night...

NBM probabilities with respect to snowfall accumulations of 1" or greater generally range from a 5-10% chance across lower, northerly upslope elevations in Central and Southwest Montana to a 40-70% chance along the Continental Divide and Island Ranges of Central Montana. The probability for 3" or more of snow mainly ranges from a 10-30% chance along the Continental Divide. These low probabilities and overall amounts gives confidence in little to minor impacts occurring through the timeframe, especially across lower elevations. - Moldan

AVIATION

19/18Z TAF Period

VFR conditions prevail this TAF period under clearing skies. Looking toward tonight and Friday morning, there is a non-zero risk for some fog in areas where skies remain relatively clear. Given this remains lower confidence at this time range, mention of fog has been withheld for the time being. -AM

PRELIMINARY POINT TEMPS/POPS

GTF -6 25 5 25 / 0 20 20 0 CTB -8 16 -2 20 / 10 30 10 0 HLN 1 29 8 33 / 0 30 10 0 BZN -2 29 7 36 / 10 20 20 0 WYS -17 21 0 25 / 20 30 30 10 DLN 2 30 4 34 / 10 10 10 0 HVR -13 15 -6 19 / 0 10 10 0 LWT -5 28 4 28 / 10 20 60 0

TFX WATCHES/WARNINGS/ADVISORIES

None.