textproduct: Great Falls

KEY MESSAGES

- Daily chances for showers and thunderstorms with higher rainfall amounts through the weekend, with the potential for some minor mountain snow at ridge tops on Sunday.

- Breezy and gusty winds on Sunday, especially along the Rocky Mountain Front and Crazy Mountains.

- Below normal temperatures for Sunday and Monday.

DISCUSSION

- Meteorological Overview: Closed upper level low off the coast of British Columbia and associated upper level trough will dig south over the Pacific Northwest by Saturday morning before tracking east along the Canadian border through the day on Sunday. Southwesterly flow aloft ahead of the approaching upper level trough will continue to transport Pacific moisture north and east over the Northern Rockies through the timeframe. Stratiform rain and showers are the predominant precipitation drivers currently however isolated embedded and air mass thunderstorms could develop this afternoon as mid level stratiform dries out and daytime heating reaches its max. High temperatures in the upper 70s to upper 80s today will fall to the 60s to low 70s by Sunday as the trough propagates through the CWA and exits Monday morning. Mid level winds will shift westerly by Sunday afternoon and create strong and gusty surface winds for most of the CWA as the low tracks eastward. Areas along the northern Rocky Mountain Front will see the highest winds due to pressure gradient forcing and cross-barrier downsloping.

Synoptic pattern next week will be primarily under the influence of longwave troughing over the Pacific Coast keeping southwesterly flow over the CWA bringing above normal PWAT's and warmer temperatures until Friday when the long wave trough propagates eastward. - Akins

- Forecast Confidence & Scenarios: EFI's indicate elevated winds above climate norms for the northern Rocky Mountain Front as well as higher than normal QPF's for the Southwest of Montana for Saturday and Sunday. NBM signals of 80%+ probabilities for wind gusts over 35 KT for Northern RMF and leeside of Crazy Mtns along Hwy 191. Confidence is lower but still worth mentioning for gusts over 50 KT with NBM signaling 30% probability in the same areas. Probabilities could increase or decrease depending on latitudinal position of the upper low's track as well as timing of the jet streak position during maximum mixed layer times on Sunday. For QPF's on Saturday, NBM is indicating a 40% probability for rainfall over 1" for the West Yellowstone area from noon Saturday until 6pm Sunday as well as 30% probabilities of over 1" in the Little Belts and Bridger Mtns. - Akins

AVIATION

29/00Z TAF Period

Scattered showers/thunderstorms will affect the CWA through this evening. A few storms could produce strong wind gusts. Expect lower ceilings on Saturday, with another chance for showers/thunderstorms. Some storms could produce strong wind gusts over Southwest MT. Mountains/passes will be obscured across much of the CWA by clouds/precip through the period.

For KGTF: Expect some gusts between 15 and 20 knots through about 0130z this evening, then lighter surface winds are expected the rest of tonight through Saturday. There is the potential for stronger wind gusts with the thunderstorms on Saturday afternoon, but the probability looked to low at this time to include the gusty thunderstorm wind gusts in the TAF. Brusda

PRELIMINARY POINT TEMPS/POPS

GTF 58 79 50 67 / 20 60 80 60 CTB 50 74 46 62 / 10 40 60 30 HLN 54 78 48 70 / 10 90 80 50 BZN 52 77 46 69 / 20 60 80 70 WYS 40 65 35 65 / 60 90 90 80 DLN 51 75 43 71 / 50 70 70 40 HVR 56 86 50 70 / 20 40 70 60 LWT 55 79 47 67 / 20 70 60 80

TFX WATCHES/WARNINGS/ADVISORIES

None.