Area Forecast Discussion
Issued by NWS Great Falls, MT
Issued by NWS Great Falls, MT
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502 FXUS65 KTFX 121126 CCA AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 530 AM MDT Sun May 12 2024 .SYNOPSIS... Above normal temperatures will continue through Monday across all of the Northern Rockies, with increasing westerly winds on Monday as a Pacific front sweeps eastward across the region. This front will also bring more widespread chances for showers and even a few thunderstorms on Monday afternoon and evening, with better chances for rain on Tuesday across portions of the region. && .DISCUSSION... Today through Monday...above normal temperatures will prevail throughout the period, with temperatures ranging from the 70s to low 80s across lower elevations. Morning showers over eastern portions of North Central Montana will gradually depart to the east through the mid-morning hours today, with additional showers and even a few thunderstorms developing this afternoon along and northeast of a Kings Hill Pass, to Great Falls, to Sweet Grass line. With "drier" air in the low to mid-levels (i.e. inverted-V soundings) this afternoon and evening, any initial shower or thunderstorm will be capable of producing gusty and erratic winds. By tonight a shortwave and associated Pacific front will begin to move from over the Pacific Northwest and towards the Northern Rockies. This shortwave and Pacific front will then move over/across the Northern Rockies during the afternoon/evening hours on Monday, leading to additional chances for showers and thunderstorms across all of Southwest through North Central Montana. In addition to increasing precipitation chances, westerly surface winds will be on the increase across all of Southwest through North Central Montana with and behind the passage of the Pacific front. While probabilistic data does not support the threat for High Winds on Monday afternoon/evening, wind gusts of between 30-40kts will be common across most locations. 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... 12/12Z TAF Period VFR and MVFR conditions are expected today, as some smoke from Canadian wildfires pushes into North Central Montana. Smoke will be most noticeable along the US 2 corridor, with KCTB and KHVR being the most impacted with periods of visibility at or below 3SM at times. KLWT and KGTF will see some reductions, but should remain VFR for the most part. Watch for a few TSRA around KLWT this afternoon, otherwise expect dry conditions today. Ludwig 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 78 49 78 49 / 20 10 20 40 CTB 78 48 77 47 / 10 10 30 60 HLN 80 49 78 49 / 0 0 20 20 BZN 76 45 74 42 / 0 10 40 30 WYS 68 36 64 34 / 10 20 70 40 DLN 75 46 72 42 / 0 10 30 20 HVR 75 49 78 50 / 20 50 40 50 LWT 70 46 72 47 / 40 50 30 50 && .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