textproduct: Great Falls

KEY MESSAGES

- On Wednesday there will be showers and thunderstorms around with gusty to strong winds.

- It be warm through Wednesday with a cool down Thursday through Saturday.

- It will be windy across Southwestern Montana on Wednesday and across North-central Montana on Thursday.

DISCUSSION

/Issued 239 PM MDT Tue May 12 2026/

- Meteorological Overview:

This afternoon there is an upper-level ridge over North-central, Central, and Southwestern Montana. This will allow temperatures to warm up with mostly dry weather. On Wednesday the upper-level ridge remains over North-central, Central, and Southwestern Montana with an upper-level trough approaching the area. This upper-level trough is associated with a Pacific cold front. On Wednesday due to southerly flow aloft and the upper-level ridge it will be hot. Due to the approaching upper-level trough combined with an increasing pressure gradient it will be windy on Wednesday in Southwestern Montana. Due to increasing moisture combined with warm air advection due to southerly flow aloft instability will build across North-central, Central, and Southwestern Montana. This will bring scattered showers and thunderstorms to the area. The primarily risk with any thunderstorm will be strong winds and lightning. Wednesday evening/night the upper-level trough and cold front begin to move through the area. Due to a strong pressure gradient and strong low and mid-level winds there will be windy conditions across North-central Montana Wednesday evening into Wednesday night. On Thursday the upper-level trough remains over North-central, Central, and Southwestern Montana. On Thursday there remains a strong pressure gradient. This combined with strong low and mid-level winds will bring windy conditions to North-central Montana. On Thursday due to cold temperatures aloft and at the surface there will be snow at some mountain locations.

Friday through Sunday upper-level troughing remains present with a few shortwaves moving through the upper-level flow. This will keep cooler temperatures around with isolated showers and thunderstorms at times Friday through Sunday. -IG

- Forecast Confidence & Scenarios:

On Wednesday the Storm Prediction Center (SPC) has issued a Slight Risk (15% chance for wind gusts of 58 mph or greater within 25 miles of a point) for severe weather across a portion of North-central Montana. Additionally across the rest of North-central, Central, and Southwestern Montana the SPC has issued a Marginal Risk (5% chance for wind gusts of 58 mph or greater within 25 miles of a point) for severe weather. There is a 15 - 25% chance for thunderstorms across North-central, Central, and Southwestern Montana.

On Wednesday there is a 40 - 80% chance for wind gusts of 55 mph or greater. Some of those wind gusts will be from thunderstorms while some will be driven by the low and mid-level winds. As a result for Wednesday afternoon a High Wind Watch was issued for Southwestern Montana. On Thursday there is greater than an 80% chance for wind gusts of 55 mph or greater across most of North-central Montana. On Thursday there is an 80% chance for wind gusts of 75 mph or greater along the Rocky Mountain Front. As a result a High Wind Watch remains in effect for most of North-central Montana for Thursday. On Thursday across lower-elevations of Glacier National Park there is a 20 - 40% chance for 2 inches of snow or greater. -IG

AVIATION

13/00Z TAF Period

VFR conditions will prevail through the start of the period with increasing cloud cover overnight ahead of a storm system passing through on Wednesday. Winds will be generally light overnight but pick up out of the west/southwest after 13/18Z with widespread gusts up to 35kts possible through the remainder of the TAF period. The strongest winds will be found along the Rocky Mountain Front and across Southwest Montana where gusts up to 50kts are possible at times.

By 13/20Z, isolated to scattered showers and thunderstorms start form across the region generally moving southwest to northeast across the region. The main concerns will be lightning and gusty, erratic winds. CIGs will generally prevail VFR towards the end of the TAF period but high MVFR CIGs are possible, particularly across Southwest Montana. -thor

FIRE WEATHER

UPDATE: FWZ113 and Southwest Montana have been upgraded to a Red Flag Warning for Wednesday.

Elevated to critical fire weather conditions are expected on Wednesday as temperatures soar well above normal and into the mid- 80s to low 90s, with the potential for numerous locations to set new daily record highs for May 13th across Southwest through North Central Montana. The warm temperatures will be accompanied by dry conditions, with relative humidity values in the teens across much of the lower elevations of North-Central, Central, and Southwest Montana.

Strong and gusty south to west winds are expected starting Wednesday afternoon; most notably along and south of the I-90 corridor within the north-south orientated valleys of Southwest Montana, west of the I-15 corridor over the plains of Central and North Central Montana, and across Hill and Blaine Counties. Further enhancement of winds are likely beneath and/or near shower and thunderstorm activity. There is a marginal risk for severe thunderstorms across the entire region on Wednesday but the greatest risk for dry thunderstorms extends east of the I-15 corridor and north of Highway 200. For this portion of North-Central Montana, the main concerns will be frequent lightning and gusty, erratic winds that might not only start new fires but make existing fires difficult to contain.

Probabilities for the Hot-Dry-Windy Index (HDWI) rising to within the 95Pct of Climatology has increased to a 80% or greater chance across most lower elevations across Southwest Montana south of the I- 90 and across Hill and Blaine Counties in North Central Montana, with Fire Weather partners indicating that fuels would be receptive to fire, especially across Southwest Montana. Thus, the decision was made to upgrade these areas to a Red Flag Warning. Additional areas across the region are still running a 20-40% chance of exceeding the 95Pct but there is not enough confidence in thunderstorm coverage to help nudge any additional zones into a Red Flag Warning at this time.

-Moldan/thor

PRELIMINARY POINT TEMPS/POPS

GTF 50 89 47 64 / 0 50 60 0 CTB 46 82 40 59 / 0 40 60 10 HLN 50 89 44 64 / 10 50 40 0 BZN 45 89 40 68 / 10 30 50 0 WYS 42 81 30 64 / 0 30 30 0 DLN 50 84 38 68 / 20 40 30 0 HVR 47 93 44 68 / 0 30 80 40 LWT 46 88 43 64 / 0 30 60 10

TFX WATCHES/WARNINGS/ADVISORIES

High Wind Watch from Wednesday evening through Thursday evening for East Glacier Park Region-Eastern Glacier, Western Toole, and Central Pondera-Northern High Plains-Southern High Plains- Southern Rocky Mountain Front-Upper Blackfoot and MacDonald Pass.

Red Flag Warning from noon to 9 PM MDT Wednesday for Hill and Blaine Counties.

High Wind Watch from late Wednesday night through Thursday evening for Bears Paw Mountains and Southern Blaine-Fergus County below 4500ft-Hill County-Northern Blaine County-Snowy and Judith Mountains-Western and Central Chouteau County.

High Wind Watch from late Wednesday night through Thursday afternoon for Cascade County below 5000ft-Eastern Toole and Liberty-Helena Valley-Judith Basin County and Judith Gap.

High Wind Watch from Wednesday afternoon through Wednesday evening for Beaverhead and Western Madison below 6000ft-Canyon Ferry Area-Gallatin Valley-Gallatin and Madison County Mountains and Centennial Mountains-Madison River Valley-Missouri Headwaters-Northwest Beaverhead County-Ruby Mountains and Southern Beaverhead Mountains.