textproduct: Great Falls

KEY MESSAGES

- Mild, dry, and breezy conditions continue today.

- A cold front will bring mountain snow with lower elevations rain and snow showers late Wednesday into Friday.

- Windy conditions return for the weekend and the beginning of next week.

DISCUSSION

- Meteorological Overview:

High pressure in the area today will keep things dry and unseasonably mild through the rest of the day today. Wednesday, an upper-level trough begins to approach the area. Light snow will begin to fall along the Northern Rockies Wednesday morning. Better chances for precipitation will arrive along a Pacific front late Wednesday into Thursday morning. This front will bring moderate to heavy mountain snow with lighter rain/snow across lower elevations. Although most of the snow will fall along the front, there will be lingering mountain snow through Friday as the trough passes through. The cold front will bring a slight cool down in temperatures, before the chinook winds during the weekend warms them up again.

Behind this system, high pressure builds over the Great Basin, while low pressure builds in farther north into Alberta, Canada. This will create a strong pressure gradient Saturday through Monday. There will be a few instances of a stronger mid level jet moving through. This will create periods of strong winds over the weekend. During this time period, there will be elevated grassland fire weather concerns given the unseasonably mid, dry, and windy conditions over the plains.

Monday, another cold front will pass through, cutting off the strong winds through the forecast period. There will be mostly mountain snow during the weekend through the beginning of next week, but the cold front will bring slight chances for rain/snow Monday.

- Forecast Confidence & Scenarios:

Snow Wednesday Through Friday:

There remains some uncertainty in the system passing through Wednesday through Friday. The cold front passing through late Wednesday through Thursday morning will bring impactful snow to mainly the Southwest MT mountains. Forecast soundings show little instability along the front to bring a concern for convective snow bands. This combined with some frontogenesis due to decent cooling behind the front will bring some moderate to heavy snow bands while passing through. The main uncertainty lies in how much snow falls along the front, and how much snow lingers behind the front. Hi-res and medium range guidance keeps snow mostly to the frontal passage and dries out quicker behind the front, only keeping light additional snow accumulations through Friday. Some of the longer range deterministic guidance have higher moisture amounts along and behind the front. This brings a slight concern for heavier snow along US 191. There is a 60%+ probability for 8" of snow in the Southwest MT mountian, and since most of the forcing will be along the front, I am a bit skeptical on the higher end amounts. Since right now I am mostly confident heavy snow will impact above pass level, I have held off on a Winter Storm Watch. However, if the uncertainty in the snow amount spread decreases, and trends towards the higher end amounts, than a watch may be needed down the road.

The other place to watch for will be the Southwest MT valleys. Temperatures will be rather marginal Thursday morning, but enough forcing along the front can crash temps/road temps and allow for up to a couple of inches of snow accumulations. Depending on how quickly this front moves through, it may affect the morning commute as well.

Winds Late Friday Through Monday:

Models are still trending towards a windy weekend. Most of the winds look to be pressure gradient driven Saturday and Sunday. There will be a few instances of a stronger mid level jet coming through of up to 60-70kts at times, but these waves will generally be quicker. Stronger sustained winds will mainly be the concern during the weekend with a few periods of stronger wind gusts as these 700mb waves move through. Late Sunday into Monday, a more persistent, stronger, mid level jet moves into the region. This will bring better chances for more scattered to widespread strong wind gusts to the region. Saturday, there's an 80%+ chance for 75 mph wind gusts along the Rocky Mountain Front foothills and a 50-80% chance for 58 mph wind gusts along the Montana Highway 200 corridor. -Wilson

AVIATION

03/18Z TAF Period

Expect increasing clouds over the CWA through the period. VFR conditions will occur through about 03z Wed, then expect lowering ceilings across the CWA as well. Mountains will become obscured after 03z, especially along the Rocky Mountain Front. Also, light precip will develop over the northern Rockies after 06z Wed, gradually spreading southward along the divide through 18z Wed. Brusda

FIRE WEATHER

Unseasonably mild temperatures, afternoon humidities dropping into the teens, and breezy winds have already set up this afternoon and will continue for the rest of the day. A cold front Wednesday evening into Thursday will bring a slight relief in mild temperatures and will bring scattered precipitation through Friday.

Concerns for elevated grassland fire weather conditions increases Saturday through Monday. Windy chinook winds will bring back unseasonably dry, mild, and windy conditions to the north-central plains. The Hot, Windy, and Dry index reaches back into the 90th-95th percentile of climatology across the region Saturday through Monday. Areas of concern will be along and west of the Interstate 15 corridor and along the Montana Highway 200 and US 87 corridors between Rogers Pass and Lewistown where the windiest conditions will set up. A combination of these factors and it being ahead of the greenup period, will bring an elevated fire risk for grassland fires. -Wilson

PRELIMINARY POINT TEMPS/POPS

GTF 37 58 34 47 / 0 10 60 40 CTB 34 53 27 46 / 0 20 20 20 HLN 32 55 33 44 / 0 20 90 60 BZN 28 57 31 44 / 0 0 80 80 WYS 19 43 23 36 / 0 0 80 90 DLN 29 52 32 43 / 0 10 90 60 HVR 34 58 28 46 / 0 10 40 30 LWT 36 57 31 43 / 0 0 50 60

TFX WATCHES/WARNINGS/ADVISORIES

None.