textproduct: Great Falls

KEY MESSAGES

- Today through Friday there will be isolated showers and thunderstorms with some thunderstorms being strong to severe.

- It will be hot today and Tuesday with a brief cooldown on Wednesday.

- It will warm back up Thursday and Friday with a cooldown this weekend with precipitation chances.

DISCUSSION

- Meteorological Overview:

Today the upper-level ridge remains over North-central, Central, and Southwestern Montana with an upper-level trough approaching the area. This will allow temperatures to warm up due to southerly flow aloft with warm air advection. As a result of the hot temperatures there will be isolated showers and thunderstorms primarily around Southwestern Montana this afternoon and evening. On Tuesday the upper-level trough becomes a closed low and slowly moves over the Great Basin Region. This corresponds to a Pacific Cold Front moving through North-central, Central, and Southwestern Montana. This will bring another round of showers and thunderstorm to the area on Tuesday. On Tuesday across Hill, Blaine, and Choteau Counties record high temperatures will be approached. On Tuesday afternoon/evening a southeasterly jet develops which will help to bring more moisture to Montana. There remains quite a bit of uncertainty in the thunderstorms on Tuesday. See the Forecast Confidence & Scenarios section for details.

On Wednesday the closed upper-level low remains over the Great Basin vicinity. Due to the cold front that moves through on Tuesday, Wednesday will be slightly cooler but still above seasonal averages across North-central, Central, and Southwestern Montana. On Wednesday there will be enough instability and moisture for another round of showers and thunderstorms across the area. On Thursday the closed low continues to sit over the Great Basin with a very subtle and slow eastward progression. With southerly flow aloft and some warm air advection temperatures will warm back up on Thursday. This will allow instability to build and lead to another round of thunderstorms. On Friday the upper-level low slowly weakens and transitions to an upper-level trough over the Great Basin. With southerly flow aloft on Friday temperatures will be hot. On Friday there will be another round of showers and thunderstorms. On Saturday an upper-level trough associated with a surface cold front moves over North-central, Central, and Southwestern Montana. This will cool down temperatures to near seasonal averages with widespread rain. On Sunday the upper-level trough lifts northward. This allows temperatures to warm up slightly with mostly dry weather. -IG

- Forecast Confidence & Scenarios:

Today across North-central, Central, and Southwestern Montana south of the Montana Highway 200 Corridor there is a 10 - 25% chance for thunderstorms. This afternoon and evening there will be limited instability so the strongest thunderstorms will just produce gusty winds. On Tuesday there is a 20 - 35% chance for thunderstorms across North-central, Central, and Southwestern Montana. Additionally, for Tuesday the Storm Prediction Center has issued a Marginal Risk (5% chance for a 58 mph wind gust within 25 miles of a point and a 5% chance for hail with a diameter of 1 inch or greater within 25 miles of a point) for nearly all of North- central, Central, and Southwestern. On Tuesday there is currently discrepancies between individual Hi-res and long-range models on when increased moistures moves into North-central, Central, and Southwestern Montana. If the increased moisture moves into the area by the middle of the afternoon there will be widespread severe thunderstorms capable of large hail and strong winds (winds > 58 mph). If however the moisture doesn't move into the area until after 6 PM then due to the hot temperatures thunderstorms will primarily only produce strong winds and be more isolated in nature.

On Wednesday there is a 25 - 45% chance for thunderstorms across Central, and Southwestern Montana. On Wednesday the limiting factor for having the strongest and longest-lived thunderstorms is cloud cover in the morning. If skies clear or are clear Wednesday morning then that will increase the potential for severe thunderstorms across North-central, Central, and Southwestern Montana Wednesday afternoon/evening. On Thursday and Friday across most of North- central, Central, and Southwestern Montana there is a 20 - 40% chance for thunderstorms.

On Tuesday there is a 20 - 50% chance for a tenth of an inch of rain or greater across North-central, Central, and Southwestern Montana. On Wednesday there is a 15 - 40% chance for a quarter inch of rain or greater across the lower-elevations of North-central, Central and Southwestern Montana. From Thursday through Friday there is a 20 - 50% chance for a quarter inch of rain or greater across North- central, Central, and Southwestern Montana.

Today across portions of Hill, Blaine, and Choteau Counties there is greater than a 70% chance for high temperatures of 90 degrees or greater. On Tuesday there is greater than a 50% chance for high temperatures of 90 degrees or greater across North-central Montana east of I-15. On Tuesday there is greater than 60% chance for high temperatures of 95 degrees or greater across portions of Blaine and Hill Counties. Additionally with portions of Hill and Blaine Counties having lows in the mid 50s to lower 60s a Heat Advisory was considered for those areas for Tuesday afternoon/evening. Due to low confidence in impacts from this early season heat, a Heat Advisory was not issued at this time. -IG

AVIATION

25/06Z TAF Period

VFR conditions will prevail through the period. There is a chance for showers and thunderstorms to develop Monday afternoon along the Continental Divide and across Southwest Montana. Coverage is expected to remain isolated but periods of mountain obscuration are possible after 25/18Z. Any thunderstorm that develops is expected to be on the drier side, so the main concerns will be lightning and gusty, erratic winds. -thor

PRELIMINARY POINT TEMPS/POPS

GTF 88 55 89 55 / 0 10 50 60 CTB 85 52 86 52 / 0 10 60 60 HLN 85 50 85 51 / 10 30 40 70 BZN 84 48 84 46 / 20 30 60 50 WYS 78 39 75 38 / 10 10 60 40 DLN 81 47 78 44 / 40 40 40 20 HVR 91 57 96 57 / 0 0 10 60 LWT 85 52 88 51 / 0 10 10 40

TFX WATCHES/WARNINGS/ADVISORIES

None.