textproduct: Great Falls

KEY MESSAGES

- Cooler, drier, and less windy conditions move in for the next couple of days, but there will be lingering gusty winds in the Milk River Valley area today.

- Temperatures warm back above average and shower and thunderstorm activity increases in coverage by mid-week.

- A Pacific weather system looks to bring more shower and thunderstorm activity, cooler temperatures, and gusty westerly winds this weekend into early next week.

DISCUSSION

- Meteorological Overview:

The closed low responsible for yesterdays wind, thunderstorms, and elevated fire weather conditions is now moving eastward into the Canadian Prairies. Cooler, drier, and less windy conditions will be left in its wake, but there will be some lingering gusty northwesterly winds over plains east of I15. These winds will be most impactful over the Milk River Valley where winds will routinely gust in the 20 to 30 mph range.

Although mostly dry conditions will prevail today, subtle shortwave energy and lingering instability may bring isolated shower and thunderstorm activity to areas along the MT/ID/WY borders in far southwest MT today. There may also be some passing low and mid- level clouds along the Hi-Line on the backside of the aforementioned closed low.

Ridging aloft begins to build in over the interior west for the mid- week period, but another trough approaching the Pacific NW will gradually bring an increasingly southwesterly flow aloft over the Northern Rockies. This will warm temperatures back above average and bring a slow northward expansion of scattered shower and thunderstorm activity as the week progresses.

The Pacific NW trough looks to send stronger shortwaves into an environment with ML CAPE running in the 300 to 900 J/kg range and Wednesday and Thursday. These should be the busiest convective days if this set up occurs. Dry sub-cloud layers will make localized gusty winds and lightning the primary concerns with this activity.

The trough eventually ejects eastward towards the Northern Rockies sometime this weekend into early next week. While there are some timing and depth discrepancies among ensemble members, the most likely scenario looks to be more scattered more shower and thunderstorm activity, cooler temperatures, and periods of gusty westerly winds. -RCG

AVIATION

24/06Z TAF Period

Wildfire smoke from the Camp Creek Fire will impact portions of North Central and Central Montana through the overnight hours. For most locations this will only impact slantwise visibility but surface-level visibility impacts are possible at KGTF and KLWT. Once northerly winds start to pick up after sunrise the plume of smoke is expected to be pushed further south which will help clear out KGTF/KLWT but may bring some slantwise visibility reductions towards KHLN. Breezy winds are expected again on Monday afternoon across the northern plains.

Overnight there is a slight chance for fog developing around KWYS but confidence was not high enough to include it in the TAF. Isolated thunderstorms are possible across portions of Southwest Montana late Monday into early Tuesday but confidence in any impacts to the terminals is low.

Mountain obscuration will remain a concern where wildfire smoke is present and around any potential thunderstorm activity.

For KGTF: Calm winds will continue through the night with periods of MVFR conditions expected through 24/17Z when the latest smoke models start pushing smoke away from KGTF as more northwesterly winds start to set up. Crosswinds are expected through the afternoon but the risk of seeing crosswinds over 15kts is currently at 20%. While slantwise visibility is expected to improve somewhat after 24/17Z, there is a possibility that smoke aloft may start to return later in the day depending on how the Camp Creek Fire behaves. Greater impacts to slantwise visibility may start to return after 24/22Z and last through the remainder of the evening. -thor

PRELIMINARY POINT TEMPS/POPS

GTF 80 52 83 54 / 0 0 0 0 CTB 76 48 78 50 / 0 0 0 0 HLN 83 53 85 56 / 0 10 10 10 BZN 82 49 84 50 / 0 10 20 10 WYS 79 40 78 40 / 0 20 30 30 DLN 84 49 84 49 / 0 20 20 20 HVR 82 51 83 53 / 0 0 0 0 LWT 78 48 81 51 / 0 0 0 0

TFX WATCHES/WARNINGS/ADVISORIES

None.