textproduct: Great Falls

KEY MESSAGES

- Unseasonably mild, dry, and breezy conditions continue today.

- A Pacific weather system brings mountain snow, lower elevation rain and snow showers, and slightly cooler temperatures Wednesday and Thursday.

- Windy conditions with periods of mostly mountain snow are in the forecast for the weekend into early next week while temperatures generally remain above average.

DISCUSSION

Meteorological Overview:

Dry westerly flow aloft begins to turn more southwesterly today in response to an approaching Pacific trough. There will be continued unseasonably mild temperatures and dry conditions today while southwesterly surface winds gust in the 15 to 30 mph range for most locations. The notable exception to this will be along the Rocky Mountain Front where gusts will exceed 40 mph at times.

Higher level clouds associated with the aforementioned trough begin increasing as early as this afternoon before deepening moisture brings lower clouds and light mountain snow along the Continental Divide and southwest mountains late tonight into Wednesday. Mountain snow expands late Wednesday into Thursday while lower elevations see a more scattered variety of rain and snow showers. Most of the energy with this system looks to shear off and head into the Great Basin/SW CONUS, but there's sufficient cold air aloft for accumulating snow in the mountains and at least a brief period of snow at lower elevations amid convective banding, especially over southwest MT on Thursday. This system will exit the Northern Rockies by early Friday and will be replaced by strong westerly flow aloft this weekend into next week.

This will bring periods of strong, gusty winds that look to peak in coverage and strength during the early to mid- next week timeframe. Hazard concerns will initially be fire weather conditions and wind impacts, mostly over the central/north-central MT before lobes of colder air introduce mountain accumulating snow, convective lower elevation precipitation, and perhaps more expansive periods of strong winds next week. -RCG

-Forecast Confidence & Scenarios:

Snow Wednesday and Thursday

Mountain snow slowly expands eastward off the Continental Divide on Wednesday and peaks in coverage and intensity early Thursday. Newer model guidance has been trending the liquid precipitation and snow amounts higher over the last few runs, especially for the mountains south of 190. There's a bit of a mismatch comparing this to the meteorological setup given a majority of the energy with this system looks to split off to our south, leaving an open wave over the Northern Rockies. Instability and convective banding will be more heavily relied on to overcome the weaker forcing. Nonetheless, areas south of 190 will be monitored for localized heavier bands of snow, particularly over or near mountain passes. Current probabilistic guidance supports 4 to 8 inches of snow over these southwest mountains with 70% confidence, heaviest over the Madison and Gallatin Ranges. The Bozeman area will be closely monitored for accumulating snow in this scenario given their proximity to the mountains.

Periods of strong winds this weekend into next week

The stronger westerly flow aloft will bring multiple periods of t strong, gusty winds this weekend into early next week. The winds will initially be strongest along the Rocky Mountain Front and the plains on Saturday and Sunday before becoming more expansive and including much of the forecast area during the early and mid portion of next week. Above normal temperatures continue Saturday through Monday and do raise fire weather concern, though there will be moisture aloft that looks to prevent minimum humidities from outright crashing into the critical range, see the fire weather section for more information. Probabilities for 55 mph+ gusts increase above 50% for most locations by Monday with similar probabilities for gusts over 75 mph + along the Rocky Mountain Front. Lobes of colder air begin to move in Tuesday and beyond which will add mountain snow and lower elevation convective precipitation. At this time its uncertain whether Canadian cold fronts will undercut the northern periphery of stronger winds aloft and and bring periods of lighter winds over the plains. - RCG

AVIATION

03/12Z TAF Period

VFR conditions prevail during this TAF period. Diurnally driven breezy to windy conditions will be most pronounced along the Rocky Mountain Front and the plains this afternoon before decreasing around sunset. Clouds and mountain obscuration gradually increase along the Continental Divide tonight. -RCG

FIRE WEATHER

Another day of unseasonably mild temperatures will be accompanied by breezy and dry conditions today. Minimum relative humidity values will fall to critical levels over the grasslands of central and north-central MT. A passing Pacific weather system will bring cooler temperatures and scattered areas of precipitation for temporary relief for the second half of the workweek.

Well above normal temperatures, dry conditions, and strong to very strong winds move in this weekend and may lead to elevated fire weather conditions over the grasslands of central and north- central MT again; most notably along and west of the Interstate 15 corridor and along the Montana Hwy 200 and US 87 corridors between Rogers Pass and Lewistown where winds look to be strongest. Additionally, HDWI indices will climb to between the 90th and 95th Percentile of climatology Saturday through Monday across Fire Weather Zones 113, 115, and 117. Given the mild and overall dry winter season across much of the Northern Rockies, and with grass remaining dormant/pre- greenup, fire weather concerns will be elevated. - RCG/Moldan

PRELIMINARY POINT TEMPS/POPS

GTF 65 37 58 34 / 0 0 10 50 CTB 60 34 53 27 / 0 0 10 10 HLN 61 31 55 33 / 0 0 20 80 BZN 61 29 58 30 / 0 0 0 80 WYS 48 18 44 23 / 0 0 10 80 DLN 57 30 53 33 / 0 0 10 90 HVR 63 33 59 27 / 0 0 0 40 LWT 61 35 58 32 / 0 0 0 60

TFX WATCHES/WARNINGS/ADVISORIES

None.