textproduct: Great Falls

KEY MESSAGES

- Trending warmer the next couple days, warmest Thursday.

- Thunderstorms increase in coverage the next couple days.

- Cooler this weekend, particularly Sunday.

DISCUSSION

- Meteorological Overview:

Upper level ridging continues to build in across the region ahead of troughing meandering off the Pacific NW coast. Although the ridging is building in, lingering moisture aloft will combine with daytime heating and deep mixing to result in widely scattered showers and thunderstorms this afternoon and early evening, mainly near and south of I-90.

Heading into Wednesday the ridge axis looks to sit firmly overhead, with influence from the troughing from the west beginning to sneak in, particularly near the Continental Divide. Coverage of showers and thunderstorms increases further near the Continental Divide. Given the drier low-levels, precipitation amounts don't look particularly high, which would raise concern for potential lightning ignitions.

Ridging begins to slip eastward Thursday, which looks to lead to both the warmest day of the week, as well as the day with greatest coverage of showers and thunderstorms. Inverted-V profiles suggest strong wind gusts will be the greatest concern for thunderstorms Thursday.

Uncertainty increases toward the weekend, though at least initially confidence remains modestly high that a west-southwest flow will be in place Friday. Breezy winds look to be the most likely outcome from this setup, with lower confidence in any precipitation. As for the weekend, there looks to be a broad upper level disturbance over BC/AB and vicinity, which looks to send a smaller embedded wave toward the Northern Rockies by Sunday. Timing and track of this system will play a large role in whether precipitation will be more localized or a bit more widespread this weekend. Nonetheless, the weekend and particularly Sunday look to be cooler. -AM

- Forecast Confidence & Scenarios:

Thunderstorm and Precipitation Chances:

There will be daily chances for thunderstorms across Southwest Montana through Thursday that will slowly spread north as the week continues. Looking at model soundings, there are deep inverted-v profiles which increases confidence in these thunderstorms being on the drier side. This means the main threats will be lightning and gusty/erratic winds which will provide little relief to the current fire situation. For more on the expected fire weather concerns, see the FIRE WEATHER section.

As the thunderstorm potential spreads into Central Montana, there is still an expectation that most of these thunderstorms will be on the drier side with a hint that some isolated strong to severe weather is possible Thursday afternoon. Current model runs indicated around 1000-1500 J/kg CAPE with around 20-35kts of bulk shear. There is still a bit of uncertainty with where the greatest threat for severe weather will be but the main concern with any thunderstorm that develops will be strong wind gusts.

Extended Forecast:

There is decent agreement amongst the models on a strong upper-level trough moving through this weekend which will bring cooler and breezy conditions to the region. Looking towards next week, there is an interesting potential with cluster guidance hinting towards potentially multiple troughs moving through the area. It is far too early to pin down the finer details of what is to occur but there is hope of fall-like conditions on the more distance horizon. -thor

AVIATION

25/18Z TAF Period

The main concern for the TAF period is isolated drier showers and thunderstorms in Southwest MT this afternoon and evening (25/21z to 26/03z). Gusty winds and lightning are the main concerns with thunderstorms. Other than that, light to slightly breezy southeast to northeast winds across North-Central MT. Wildfire smoke will continue to effect slantwise visibility for take offs/descents.

For KGTF: East-northeast/northeast winds prevail through the evening. Winds prevail less than 15 kts throughout the day, but a few gusts of 18 kts can't be ruled out in the evening. The probability for crosswinds exceeding 15kts is 20% from 26/01z to 26/03z. -Wilson

FIRE WEATHER

Through Wednesday, there are only marginal concerns for elevated fire weather with temperatures gradually warming and winds generally expected to be on the calmer side. The only wild card that could potentially create difficult conditions will be the daily chances for dry thunderstorms. The primary focus on Tuesday will be Southwest Montana with the threat for dry thunderstorms spreading into portions of Central Montana by Wednesday. With this being the only mode of concern for fire weather, no products will be issued at this time. But given how dry the fuels are folks should continue to take all measures to prevent sparks from occurring.

Thursday currently looks the most concerning for potential elevated fire weather conditions. Gusty conditions in Southwest and portions of Central Montana, combined with a more robust chance for dry thunderstorms, and temperatures ranging from the upper 80s to mid 90s could make things difficult for ongoing fire operations. Right now the HDWI is only highlighting the probability of exceeding the 75th percentile with about a 20% chance for some locations to exceed the 90th percentile. Additionally, a few thunderstorms may be on the dry side across portions of SW MT Thursday. So at this time, critical fire weather conditions are not high confidence. But this will need to be monitored closely as the wild card of dry thunderstorm coverage and intensity may act as a nudge factor towards more critical conditions. -thor/AM

PRELIMINARY POINT TEMPS/POPS

GTF 55 90 58 92 / 0 10 10 20 CTB 50 86 53 88 / 0 0 10 10 HLN 55 90 55 89 / 10 20 20 50 BZN 52 88 52 88 / 20 20 20 30 WYS 42 81 41 81 / 30 20 20 20 DLN 51 86 50 85 / 20 30 20 40 HVR 53 92 59 96 / 0 0 0 0 LWT 52 88 55 91 / 0 10 10 20

TFX WATCHES/WARNINGS/ADVISORIES

None.