textproduct: Great Falls

KEY MESSAGES

- Another round of showers and thunderstorms move from south to north this afternoon and evening with a few stronger storms capable of producing localized strong winds over 50 mph, brief heavy downpours, and hail.

- There will be a period of general rain and embedded thunderstorms over Central and North-central Montana tonight into Thursday.

- Clouds and precipitation will cool temperatures closer to average today and on Thursday.

- Slightly above average temperatures and daily showers and thunderstorms are expected heading into the weekend, with some storms on the stronger side.

DISCUSSION

- Meteorological Overview:

Showers and thunderstorms over the Central Montana have diminished, but will continue along the Hi-Line of Hill and Blaine counties through mid- morning thanks to a weak perturbation within the westerly flow aloft. Another area of showers and thunderstorms, associated with a stronger shortwave, moves into Southwestern Montana later this morning before heading into Central and North- central Montana this afternoon and evening. Although wind shear will be on the lower side, precipitable water values between 0.75 and 1 inch and CAPE in the 600 to 1,200 J/kg range will be sufficient for a few stronger storms with localized wind gusts over 50 mph, brief heavy downpours, and marginally severe hail (0.25 to 1 inch in diameter).

As the shortwave lifts northeastward tonight into Thursday, a closed low begins to develop with the showers and thunderstorms over Central and North-central Montana transitioning to more of an area of general rain and embedded thunderstorms. Low level east to northeasterly flow will also work to maintain periods of light to moderate rain. The heaviest precipitation will be over the northerly/easterly upslope areas along the Rocky Mountain Front and the Central Montana island ranges where probabilistic guidance supports rainfall totals in the 0.25 to 1 inch mark through Thursday afternoon. The clouds and precipitation will cool temperatures closer to average, coolest on Thursday.

Southwesterly flow aloft strengthens heading towards the weekend and early next week all while CAPE and precipitable water values more or less remain roughly similar to those of previous days. The additional shear will increase overall storm intensity and lifespan. - RCG

- Forecast Confidence & Scenarios:

Stronger showers and thunderstorms today and this weekend...

Showers and thunderstorms will be most concentrated over the southwest this morning into the early afternoon hours before moving northward into Central/North-central Montana later in the afternoon and evening. The areas with the highest CAPE values will be south of a weak frontal boundary situated just south of the Hi-Line. Slightly cooler temperatures today does work against stronger storm development, but increased moisture should make up the difference. Localized wind gusts over 50 mph, brief heavy downpours, and marginally severe hail (0.25 to 1 inch in diameter) will be the primary hazards in addition to lightning. Improved shear does increase storm intensity and storm life cycle Friday through early next week. Friday and Saturday look to be the busiest days as of right now, but this will be dependent on the timing of shortwaves and frontal boundaries.

Rain over Central and North-central Montana tonight into Thursday...

A closed looks to develop over Central and Eastern Montana tonight into Thursday which will work to maintain areas of rain and embedded thunderstorms over the plains and the northern/eastern slopes of the Rocky Mountain Front and the Central Montana island ranges. Probabilistic guidance supports rainfall totals between 0.25 and 1 inch in these areas with a 40 to 80% chance for a half inch or more of rainfall, highest over Central Montana island ranges and their northerly foothills. Localized areas may see amounts exceeding an inch, particularly areas that are hit localized heavier downpours from thunderstorms earlier in the day. Flooding is generally not expected, but those outdoors near waterways and or low lying areas should be aware of their surroundings. - RCG

AVIATION

11/06Z TAF Period

Scattered showers and thunderstorms over Central and Southwest Montana will continue to move eastward and slowly diminish and end through 11/09Z. Variable cloudiness and a few showers are expected near the Canadian border later tonight before another round of showers and thunderstorms moves into Southwest Montana after 11/12Z. This shower and thunderstorm activity will expand northward/eastward into Central and North-central Montana during the afternoon and evening hours. Haze from Canadian wildfire smoke will continue to impact KHVR over the next 24 hours and is expected to expand westward in KCTB by Wednesday afternoon. - RCG

Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information.

PRELIMINARY POINT TEMPS/POPS

GTF 80 55 74 52 / 50 90 80 30 CTB 75 52 71 49 / 50 90 90 30 HLN 79 57 79 54 / 60 70 60 40 BZN 77 50 77 49 / 70 80 40 30 WYS 72 39 71 39 / 80 90 30 30 DLN 72 46 75 48 / 90 80 30 20 HVR 80 52 70 49 / 40 90 90 30 LWT 76 52 64 47 / 60 90 90 30

TFX WATCHES/WARNINGS/ADVISORIES

None.