Area Forecast Discussion
Issued by NWS Great Falls, MT
Issued by NWS Great Falls, MT
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764 FXUS65 KTFX 122057 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 257 PM MDT Sun May 12 2024 .SYNOPSIS... Hazy conditions from wildfires in Canada continues to diminish this evening and tomorrow. Above normal temperatures continue through tomorrow and scattered showers and a few thunderstorms this evening and again tomorrow afternoon and evening. Next best chances of precipitation is Monday night into Tuesday. && .DISCUSSION... Key Points: - Haze and smoke from Canadian wildfires diminishes across North Central Montana through tonight. - General thunderstorms and rain showers this evening and again tomorrow afternoon and evening with above normal temperatures and breezy conditions. - Next weather system arrives for the area Monday night and Tuesday with cooler temperatures Tuesday and a return of near normal temperatures for Wednesday. Rest of today through Monday... Latest visible satellite imagery continues to show hazy conditions clearing out from west to east across North Central Montana this afternoon. Haze is forecasted to continue for parts of Hill and Blaine Counties tonight and clear out for late tonight into tomorrow morning. Visible satellite also shows developing cumulus clouds across the higher terrain of Central Montana and a line from the Canadian Border down to Craig. A few rain showers and general thunderstorms can develop late this afternoon and early evening across the Hi-Line and from Great Falls to Lewistown. Primary concerns with any developed thunderstorms today are a brief downpour and lightning. Low temperatures remain in the 40s and 50s, except at some higher mountain elevations with lows in the 30s. Above normal high temperatures continue tomorrow with highs in the 70s. Winds increase tomorrow afternoon across the area gusting between 20 and 30 mph, with locally higher wind gusts across the Rocky Mountain Front and adjacent Plains area. There`s going to be two primary locations to watch for tomorrow, one for the Southwest and one along the Hi-Line. For Southwest Montana, a weak upper level shortwave moves through bringing unsettled weather conditions to the surface in the form of rain showers and thunderstorms. Timing for showers and thunderstorms, is favored to be between 2 PM and 8 PM. For along the Hi-Line and Canadian Border, a low pressure system with an associated stationary front to our north is forecasted to move southeast and meet with a cold front from Pacific Northwest tomorrow afternoon. Primary shower and thunderstorm activity start time is between 3 to 5 PM that is likely (>30%) to continue into the early evening hours. Primary concerns for any developed thunderstorms tomorrow are lightning, a brief downpour, gusty erratic winds, and small/pea sized hail. Webb Tuesday...ensemble clusters all favor a secondary shortwave diving southeast over the Northern Rockies through Tuesday night, with some uncertainty in the amplitude of the shortwave as it digs from Western Montana/Idaho towards the Central Rockies. NBM probabilistic gives areas along and southeast of a Cut Bank to Lewistown line, and northeast of a Butte to West Yellowstone line, a 40-80% chance for 24hr (12z Tuesday to 12z Wednesday) precipitation amounts to exceeding 0.10", with generally between a 20-50% chance for amounts to exceed 0.25". While this precipitation will be beneficial for many lower elevations, the rain falling on top an already rotting snowpack across Central Montana mountains will lead to additional runoff into area creeks and streams. High temperatures on Tuesday in wake of Monday`s Pacific front will fall back below normal after several days of above normal temperatures, with readings in the 60s across lower elevations. Wednesday through next Sunday...an active and unsettled pattern is expected through the remainder of the work week and into the upcoming weekend as quasi zonal to northwesterly flow develops over the Northern Rockies through much of the period. While the multi- model ensemble mean favors this pattern there is still a degree of uncertainty with respect to the amplitude of the ridge over the Eastern Pacific and trough over the center of the CONUS/Canada, especially from Thursday onwards, which will have a big impact on how warm/cool temperatures end up being across Southwest through North Central Montana over this timeframe. Daily chances for showers and thunderstorms will be favored across the entire CWA within this quasi zonal to northwesterly flow regime; however, daily precipitation values will largely remain below 0.10" where precipitation is observed. - Moldan && .AVIATION... 12/18Z TAF Period VFR conditions continue for Southwest Montana airfields through the TAF period, with gusty winds developing tomorrow afternoon and probability of showers increasing after the 13/18z timeframe. Haze from Canadian wildfires continues to impact KCTB, KHVR, and KGTF. Visibility improves through 21z for KGTF and KCTB, with KHVR seeing improvement tomorrow morning based on current surface observation clearing trends and latest near-surface smoke model guidances. Haze within the KLWT vicinity has been observed on latest webcams, but based on clearing trends from visible satellite, should not impact the airfield. KLWT also has potential to see vicinity showers this evening, but confidence is not high for impacts to the airfield so it was not included in the TAF. KHVR has potential (50%) to see rain showers this evening, but visibility could continue to be impacted from haze after the showers move through. Webb Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .HYDROLOGY... The Flood Warning for Clear Creek has been cancelled as water levels have finally fallen below minor flood stage as of early this (Sunday) morning. Water levels on Clear Creek will continue to slowly fall to below action stage through Monday afternoon. The Flood Watch for the Bears Paw Mountains has also been cancelled this morning given no recent reports of flooding across the watch area. With this being said, the Big Sandy Creek gage near Havre (which is outside of the Bears Paw Mountain zone) was approaching Action Stage as of this morning. We will continue to monitor this gage through the remainder of the morning and act accordingly should water levels rise further through Action Stage towards Minor Flood Stage. - Moldan The flood watch continues for the mountain ranges of Central Montana. No new flood impacts have been reported over the past 12-24 hours. This is good news, as this means the runoff is coming off slowly or the runoff is soaking into the ground. In either case, if this trend continues, this flood watch could also be cancelled early. Brusda/Moldan && .PRELIMINARY POINT TEMPS/POPS... GTF 49 75 47 62 / 40 30 40 80 CTB 48 72 46 62 / 0 30 50 60 HLN 51 77 50 67 / 0 30 20 70 BZN 45 74 43 65 / 10 40 40 70 WYS 37 64 35 57 / 10 70 60 70 DLN 45 72 43 64 / 0 40 20 50 HVR 50 77 48 69 / 60 40 50 50 LWT 47 71 45 59 / 30 20 50 80 && .TFX WATCHES/WARNINGS/ADVISORIES... Flood Watch through Monday morning for Cascade County below 5000ft-Fergus County below 4500ft-Judith Basin County and Judith Gap-Little Belt and Highwood Mountains-Meagher County Valleys- Snowy and Judith Mountains-Western and Central Chouteau County. && $$ http://www.weather.gov/greatfalls