textproduct: Great Falls

KEY MESSAGES

- Isolated showers continue along Central MT/Hi-line through the evening, with a storm or two capable of producing gusty winds, small to large hail, and localized flash flooding.

- Better chances for scattered showers and thunderstorms arrive Wednesday afternoon, with gusty winds, large hail, and heavy rainfall as the primary hazards.

- Dry and hot conditions build in towards the weekend.

DISCUSSION

- Meteorological Overview:

The small shortwave will continue to track across Central MT/Hi- line this afternoon. Isolated showers and thunderstorms continue to develop as a result through the evening hours. Current mesoanalysis shows CAPE building towards 1,000 j/kg. Bulk shear around 20kts at the time suggests thunderstorms could struggle to become strong to severe at first, before better shear moves in late this afternoon. With the shortwave tracking east across the state, the thunderstorm threat will mainly be across Hill, Blaine, and Fergus Counties. One or two strong to severe thunderstorms will be capable of producing strong winds and small to large hail. Very high PWATs of 1 to 1.2" across North-Central MT also brings a localized flash flooding threat for any storm that produces heavy rainfall.

Behind this shortwave, a stable airmass settles in for the night and Wednesday morning. Hi-res models show ample low level moisture for the development of patchy fog across the Golden Triangle Region tonight into the morning. Though, this will largely depend on how much rain the areas receives today.

Weak southwest flow aloft tomorrow will continue to bring in moist and unstable air into the region. Scattered showers and thunderstorms develop along a cold frontal passage Wednesday afternoon and evening. Overall forcing and shear are better which gives better chances for strong to severe thunderstorms. Severe wind gusts will be the primary hazard due to deep mixing and 1,000+ j/kg of DCAPE. However, these high based storms have all the instability being at the mid levels so I can't rule out isolated large hail. PWATs nearing an inch will also bring another heavy rainfall threat with a low end chance for localized flash flooding over burn scars and urban areas.

Thursday through the weekend, an upper-level ridge will build in across the state, bringing drier weather and hot temperatures. Current forecast temperatures reach the mid to upper 90s this weekend. The stress impact from this ridge will largely depend on how much we cool off at night. Currently there's a 40-70% chance minimum temperatures of 65 degrees and higher Sunday and Monday. Ensembles hint at monsoonal moisture could come back next week with ridging, bringing a return for precipitation.

- Forecast Confidence & Scenarios:

One concern earlier today for the thunderstorm potential was the small lingering mesoscale convective vortex system this morning will limit surface heating and instability. Though it looks to be areas that got a little sun was able to rebuild instability quickly. However, the chances for strong to severe storms this afternoon will be isolated. For thunderstorm chances Wednesday, the north Central MT plains look to be the best corridor for strong to severe thunderstorms. -Wilson

AVIATION

07/18Z TAF Period

Isolated to widely scattered showers and thunderstorms were on- going across portions of North Central and Central Montana late this morning, generally along and east of a KLWT, to KGTF, to KCTB line. These showers and storms will continue to develop and move east through 21-03z this evening, with the KLWT and KHVR terminals having the best opportunity of seeing reduced VIS and low CIGS due to precipitation. Beyond 06z Wednesday focus and concerns will shift to the potential for fog/mist developing over the plains of Central and North Central Montana, but confidence was not high enough to mention with this TAF package. - Moldan

PRELIMINARY POINT TEMPS/POPS

GTF 55 91 56 88 / 0 30 20 0 CTB 53 87 56 82 / 10 10 0 0 HLN 56 88 56 87 / 0 50 30 0 BZN 54 87 52 86 / 10 10 40 0 WYS 46 82 45 81 / 10 10 20 0 DLN 52 85 50 86 / 10 20 20 0 HVR 53 91 57 86 / 10 10 30 0 LWT 51 86 53 84 / 10 10 50 0

TFX WATCHES/WARNINGS/ADVISORIES

None.