textproduct: Great Falls

KEY MESSAGES

- Daily chances for thunderstorms in Southwest Montana spreading into Central Montana by Thursday.

- Temperatures will gradually warm with Thursday expected to be the hottest day of the week before a cold front brings cooler temperatures to the region.

- Cooler and breezier conditions are expected to last through the weekend.

DISCUSSION

- Meteorological Overview:

Upper-level ridging will continue to build over the region with gradually increasing surface temperatures through the middle of the week. With the position of the ridge axis, southwesterly flow aloft will maintain enough of an influx of monsoonal moisture to keep up daily chances for afternoon showers and thunderstorms, particularly in Southwest Montana. As the ridge starts to move eastward Wednesday into Thursday, the coverage for thunderstorm activity is expected to become more widespread into Central Montana with a chance for isolated strong to severe thunderstorms possible particularly on Thursday as an upper-level trough starts to push into the region. This trough will continue to make its way across Montana through the weekend bringing cool and breezy conditions to the state and daily chances for showers and thunderstorms. While some uncertainty in the extended pattern remains, there are hints that a cooler and potentially more active pattern may start to set up heading into next week.

- Forecast Confidence & Scenarios:

Thunderstorm and Precipitation Chances:

There will be daily chances for thunderstorms across Southwest Montana Tuesday 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

25/06Z TAF Period

Weak shortwaves will undercut a building ridge aloft and bring increased mid- and higher level cloudiness and a few isolated showers and thunderstorms tonight into Tuesday. Convective activity currently along the MT/ID border will slowly expand northward during the overnight hours into Tuesday morning, but will generally stay south the US highway 12 corridor. Additional showers and storms will initiate with afternoon instability over roughly the same locations between 25/18 and 26/06Z. Brief gusty winds up to 30 kts and isolated lightning will be the primary impacts with this activity, but there's a 30% chance or less for for impacts at the southwest terminals. Otherwise, surface winds will mostly be easterly over the plains and variable in southwest MT. Once again, wildfire smoke will compromise slantwise visibility upon ascent/descent.

For KGTF: Winds will be east to northeast for much of the period, with gusts mostly less than 15 kts. There is currently less than a 20% chance for crosswinds over 15 kts. VFR conditions will prevail, but wildfire smoke will compromise slantwise visibility upon ascent/descent. - RCG

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. So at this time, critical fire weather conditions are not expected. 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

PRELIMINARY POINT TEMPS/POPS

GTF 78 52 82 53 / 0 0 0 0 CTB 76 48 78 49 / 0 0 0 0 HLN 85 53 85 54 / 0 0 10 10 BZN 83 49 83 50 / 0 0 10 20 WYS 80 41 79 40 / 10 20 40 40 DLN 85 49 84 49 / 0 0 20 20 HVR 80 51 82 52 / 0 0 0 0 LWT 76 48 81 50 / 0 0 10 0

TFX WATCHES/WARNINGS/ADVISORIES

None.