textproduct: Great Falls

KEY MESSAGES

- Dry weather persists today.

- A cold front Tuesday will bring rain/snow for mostly near the Continental Divide and a slight cooldown for the Hi-line.

- Strong winds develop for the Rocky, Mountain Front, Hi-line, and Southwest MT Wednesday.

- Drier conditions towards the weekend, with near to slightly above normal temperatures.

DISCUSSION

- Meteorological Overview:

This zonal flow aloft pattern persists through most of the work week. Dry weather is expected to persist Monday. Tuesday, a weak trough develops along the Pacific coast. As a result Pacific moisture advection moves in. A weak surface low moves into Montana, bringing mountain rain/snow along the Continental Divide, and light rain everywhere else. Stronger winds aloft increases Wednesday as that upper-level waves moves inland. The low pushes south throughout the day Wednesday, developing a strong pressure gradient behind. A combination of strong mid level jet and pressure gradient will mix strong winds down to the surface, particularly along the Hi-line and Southwest MT.

A brief cooldown is expected behind this system Thursday. The weak shortwave trough still in influence keeps light rain/snow for Thursday. Friday through the weekend has the upper-level ridge build in, keeping the weekend drier and temperatures warming up back to slightly above normal.

- Forecast Confidence & Scenarios:

Mountain Snow Tuesday and Wednesday:

Snow levels are expected to rise Tuesday into Wednesday, especially in Southwest MT. Southwest MT mountains are expected to see light rainfall, but light rainfall amounts will make additional snowmelt difficult. Farther north towards the Northern Continental Divide, above freezing Tuesday afternoon temperatures and mid 30s low temperatures Wednesday will make snow struggle to accumulate at pass level during most of the event. Any impacts from snow will likely be above Marias pass.

Winds Wednesday:

The stronger 700mb winds move in Wednesday morning, with winds still at 60-70kts by mid morning and early afternoon. Therefore daytime mixing should help translate these winds to the surface across the Rocky Mountain Front and Hi-line. The strong pressure gradient will also bring a concern for strong sustained winds as well. This will likely be the main driver for winds across Southwest and portions of North-Central MT. There's a 60-80% chance for 58 mph wind gusts along the Rocky Mountain Front and Sweet Grass Hills. Beaverhead Valleys and the Missouri Headwaters region have a 40-60% chance for 58 mph wind gusts. Ensembles show similar probabilities for sustained winds of 40 mph, with 20-50% chances spreading farther east along the Hi-line and MT Highway 200 corridor. High wind watches have been issued for the Hi-line and parts of the Southwest Valleys have been issued for Wednesday. Depending on how far south the mid level jet develops, further expansions to the watch may be needed.-Wilson

AVIATION

23/12Z TAF Period.

Overall VFR conditions are expected across the CWA through the period. Other than some passing mid/high level clouds, little to no aviation impacts are expected at this time. The next chance for precipitation generally arrives along the divide on Tuesday morning. Brusda

FIRE WEATHER

There is a concern on Wednesday for at least elevated fire weather conditons over Southwest MT because of low humidity, mild temperatures and the potential for strong winds. It is possible that fire weather statements might be needed for portions of Southwest MT on Wednesday. Brusda

PRELIMINARY POINT TEMPS/POPS

GTF 59 39 60 47 / 0 0 10 20 CTB 55 30 51 39 / 0 0 20 30 HLN 61 37 64 43 / 0 0 10 30 BZN 63 37 68 46 / 0 0 10 20 WYS 55 29 55 37 / 0 0 10 20 DLN 64 39 67 45 / 0 0 0 10 HVR 55 32 55 38 / 0 0 10 40 LWT 56 35 61 44 / 0 0 10 30

TFX WATCHES/WARNINGS/ADVISORIES

High Wind Watch from late Tuesday night through Wednesday afternoon for Eastern Glacier, Western Toole, and Central Pondera-Eastern Toole and Liberty.

High Wind Watch from Wednesday morning through Wednesday evening for Beaverhead and Western Madison below 6000ft-Hill County- Missouri Headwaters-Northern Blaine County-Ruby Mountains and Southern Beaverhead Mountains.