textproduct: Great Falls

KEY MESSAGES

- After a hot day today, temperatures trend cooler into Sunday behind a cold front.

- Critical fire weather conditions develop this afternoon, persisting into Sunday.

- After a briefly cooler stretch behind the cold front, temperatures trend back warmer mid-week.

DISCUSSION

- Meteorological Overview:

Strong upper level ridging in place across the region will quickly be ushered eastward through the day today as an upper level trough slides east near the International Border. Ahead of the approaching trough temperatures rise well into the 90s across the region, reaching as high as 110F or so in typically heat prone areas. The ongoing Extreme Heat Warnings and Heat Advisories are unchanged with this update. Those with plans outside today should plan for numerous breaks and for plenty of hydration.

A dry cold front arrives as the upper level troughing moves eastward this afternoon. Ahead of the front, breezy southwesterly winds look to develop in many areas, transitioning to a more northwesterly direction behind the front late afternoon and into the evening. The strongest cross barrier flow aloft holds off til this evening and tonight, peaking in excess of 60 kts along the Northern Rocky Mountain Front. The combination of cooling temperatures near the surface behind the front and still mild temperatures aloft will result in some ridgetop stability tonight along the Rocky Mountain Front. This will aid in translating the aforementioned stronger winds aloft to the surface in these areas via mountain wave activity. The strongest winds aloft fade quickly after sunrise Sunday, though the continued brisk westerly flow aloft will keep gusty winds around through the day Sunday.

A quick moving trough in wake of the initial troughing that will be exiting eastward by Sunday afternoon moves across the area Sunday night. This trough looks to have enough moisture associated with it to result in a brief stretch of light precipitation along the Northern Rocky Mountain Front Sunday evening and overnight. Temperatures aloft look to be quite cool, which will yield the risk for some light snow near mountain peaks in Glacier NP over this timeframe.

A cooler northwesterly flow aloft persists into the early week across the region, resulting in a below average temperatures across the region for a couple days. This trend looks to be short-lived however, as temperatures begin to trend warmer by mid-week. -AM

- Forecast Confidence & Scenarios:

Strong winds tonight:

Ridgetop stability will yield a good setup for translating stronger winds to the surface tonight near the Rocky Mountain Front. Given the strongest winds aloft continue to take aim at the Northern Rocky Mountain Front, and largely only nick the Southern Rocky Mountain Front, no changes are being made to the ongoing High Wind Warning. Should the stronger winds aloft trend much further southward, additional High Wind Warnings may become necessary near the Southern Rocky Mountain Front. -AM

AVIATION

01/06Z TAF Period

VFR conditions will prevail across all terminals during this TAF Period. However, smoke from wildfires has been periodically reducing visibility at the KCTB and KHVR terminals this evening and will continue to do so through at least 01/10Z. Across all terminals after 01/18Z winds will begin to increase with the strongest winds being at the KCTB terminal. At the KCTB terminal by the end of this TAF Period winds will gust in excess of 40 kt. Across most of the TAF sites smoke from wildfires will reduce slantwise visibility during this TAF Period. At the KCTB terminal there will be isolated instances of low-level wind shear at the very end of this TAF Period. -IG

For KGTF: Winds will be light through 18Z. Between 18Z and 23Z winds will increase and shift from the southwest to the west. Between 21Z and 00Z there is a 70% chance for a 15 kt crosswind. -IG

FIRE WEATHER

Critical fire weather conditions are forecast this weekend across all fire weather districts. Gusty winds developing this afternoon ahead of a dry cold front will combine with relative humidities approaching single digits to result in critical fire weather conditions in most areas. Winds shift to a more northwesterly direction this afternoon and evening behind the cold front. While gusty winds diminish somewhat out over the plains tonight, strong winds will develop along the Rocky Mountain Front this evening, slowly expanding over the plains through the night and into the day Sunday. Overnight humidity recovery is forecast to be nearly non-existent where these winds are persistent overnight near the Rocky Mountain Front.

Although cooler temperatures will be moving in behind the cold front for Sunday, very low relative humidity will persist (Approaching single digits once again). Combine this with forecast breezy winds, and critical fire weather conditions will be around once again for Sunday. -AM

PRELIMINARY POINT TEMPS/POPS

GTF 103 63 85 50 / 0 0 0 0 CTB 97 55 75 45 / 0 0 0 0 HLN 100 60 84 50 / 0 0 0 0 BZN 101 57 90 49 / 0 0 0 0 WYS 91 48 86 40 / 0 0 0 0 DLN 95 55 88 47 / 0 0 0 0 HVR 106 62 86 48 / 0 0 0 0 LWT 101 61 85 49 / 0 0 0 30

TFX WATCHES/WARNINGS/ADVISORIES

Red Flag Warning from noon today to 9 PM MDT Sunday for Central and Eastern Lewis and Clark National Forest Areas-Chouteau and Fergus Counties-Eastern Glacier/Toole/Central/Eastern Pondera/Liberty-Helena and Townsend Ranger Districts of the Helena National Forest-Hill and Blaine Counties-Lewis and Clark National Forest Rocky Mountain District-Rocky Mountain Front- Lincoln Ranger District of the Helena National Forest.

Heat Advisory from noon today to 3 AM MDT Sunday for Beaverhead and Western Madison below 6000ft-Canyon Ferry Area-Eastern Glacier, Western Toole, and Central Pondera-Eastern Pondera and Eastern Teton-Eastern Toole and Liberty-Elkhorn and Boulder Mountains-Gates of the Mountains-Helena Valley-Hill County- Meagher County Valleys-Missouri Headwaters-Northern Blaine County-Snowy and Judith Mountains.

High Wind Warning from 6 PM this evening to noon MDT Sunday for East Glacier Park Region-Eastern Glacier, Western Toole, and Central Pondera-Northern High Plains.

Extreme Heat Warning from noon today to noon MDT Sunday for Bears Paw Mountains and Southern Blaine-Fergus County below 4500ft-Western and Central Chouteau County.

Extreme Heat Warning from noon today to 3 AM MDT Sunday for Cascade County below 5000ft-Gallatin Valley-Judith Basin County and Judith Gap-Madison River Valley.