Area Forecast Discussion
Issued by NWS Great Falls, MT
Issued by NWS Great Falls, MT
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373 FXUS65 KTFX 231554 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 954 AM MDT Thu May 23 2024 .SYNOPSIS... Precipitation that has prompted Winter Storm Warnings and Winter Weather Advisories will end from northwest to southeast through the day today. Additional showers and a few thunderstorms look to develop across primarily North-central Montana this afternoon. Unsettled weather lasts into the weekend before a warming and drying trend starts late Sunday into early next week. && .Update... Morning update has been published, with no major changes made to the on-going forecast. Widespread precipitation, which was associated with an upper level disturbance moving over Northwest Wyoming, was slowly decreasing in areal coverage from the north and west across Central and Southwest Montana. This trend is expected to continue through the early afternoon hours across these areas, with most if not all of the precipitation pulling away prior to 3 PM MDT. The one exception will be across eastern portions of Southwest Montana where northerly upslope flow will help to maintain rain and snow showers across the Gallatin, Madison, and Bridger Ranges and surrounding foothills through the early evening hours tonight. Additionally, clearing skies across North Central Montana this morning will allow the boundary layer to warm, which combined with moist and cool northwesterly flow aloft will lead to increasing instability. This instability combined with embedded waves diving southeast within the northwesterly flow aloft will help to promote the development of showers and thunderstorms over North Central and northern portions of Central Montana by the early afternoon, with these showers/storms persisting through the overnight hours. - Moldan && .AVIATION... 23/06Z TAF Period A mix of rain and snow across Southwest through Central Montana will slowly decrease in areal extent and eventually diminish late morning or early afternoon. Expect mountain obscuration through the morning across most areas. Showers and a few thunderstorms look to develop across western portions of North-central Montana early this afternoon, with limited confidence that a thunderstorms impacts any TAF sites. Fog will be a concern late tonight where clearing skies overlap with areas that will see precipitation today. -AM Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .HYDROLOGY... A Flood Watch remains in effect for areas near creeks and streams over in the Little Belt Little mountains through Friday morning. Current probabilistic forecasts support one to two inches of rainfall/liquid equivalent precipitation through Friday. Snow levels will fluctuate with this weather system. However, there are concerns for flooding on area creeks and streams given recent precipitation/saturated soils and at least a portion of the upcoming precipitation falling as rain at all elevations. Those near water should be vigilant and ready to seek higher ground if flooding occurs. && .PREV DISCUSSION... /ISSUED 506 AM MDT Thu May 23 2024/ Through tonight...The upper level disturbance that has been advertised the past several days has finally made its appearance, currently across southern ID. Cool temperatures aloft resulted in numerous showers and a few thunderstorms late yesterday that eventually resulted in a congealed stratiform rain across the plains, which is now stretching southwestward across the Continental Divide (With snow falling in the mountains). High resolution guidance drifts this area of precipitation southeastward through the remainder of the night as the responsible upper level disturbance and associated forcing also shifts in that direction. Meanwhile a somewhat narrow corridor of H7-H6 frontogenesis will develop across Southwest Montana this morning north/northwest of an easily identifiable upper level low presently near Monida, resulting in another band of precipitation. The two bands eventually consolidate across Central and Southwest Montana this morning before shifting southeastward and dissipating late this morning and into the afternoon. Snow levels are generally around 5500ft as of ~230 AM, and will continue to fall through around mid morning. Lower elevation snow continues to looks likely at times in Southwest Montana valleys through the late morning or early afternoon once precipitation diminishes or moves away from the region. Consideration was given toward an upgrade to the lower elevation Winter Weather Advisory in the Bozeman area. The concern is for higher amounts on the far south side of the Gallatin Valley where snow looks to begin a bit earlier than the remainder of the Gallatin Valley. Localized snow amounts on the order of 6 inches or so would not surprise me in this area. Given the limited areas extent of these higher snowfall amounts, I elected to stick with the going Winter Weather Advisory. Meanwhile further north, partly cloudy skies across the northern plains late morning will combine with cool air aloft to result in showers and a few thunderstorms this afternoon and evening. An upper level disturbance across South-central Canada will retrograde back west a bit, with a wave pivoting around its western periphery tonight in the vicinity of North-central Montana. This will allow for scattered showers to continue into the overnight in this area. Friday through Sunday morning... The northern Rockies will be between systems on Friday, though cool northwesterly flow aloft will promote late morning through early evening showers and thunderstorms. Another system this weekend looks to take a similar track as the last system (Drop south from BC, shift east across southern ID, finally exiting eastward across WY), but this system has trended to be less organized in nature compared to the first. Hence, an unsettled periods still looks likely Saturday afternoon into Sunday morning, with confidence in more widespread impacts decreasing at this time. Sunday afternoon into the middle of next week... Ensembles favor a return to upper level ridging late Sunday into early next week. A warming trend looks likely, with limited chances for an afternoon shower or thunderstorm. There is uncertainty how long the ridging lasts, as most ensemble members bring an upper level disturbance and Pacific cold front across the region mid week at some point. -AM && .PRELIMINARY POINT TEMPS/POPS... GTF 53 39 63 39 / 70 20 30 20 CTB 53 39 61 37 / 60 70 40 20 HLN 54 37 66 42 / 100 10 20 20 BZN 48 26 62 36 / 100 10 20 20 WYS 41 23 55 29 / 100 20 20 20 DLN 48 27 61 36 / 100 10 20 20 HVR 55 42 63 40 / 30 60 60 20 LWT 47 33 59 36 / 90 20 40 20 && .TFX WATCHES/WARNINGS/ADVISORIES... Winter Storm Warning until noon MDT today for Elkhorn and Boulder Mountains-Northwest Beaverhead County-Ruby Mountains and Southern Beaverhead Mountains-Southern Rocky Mountain Front- Upper Blackfoot and MacDonald Pass. Winter Weather Advisory until noon MDT today for Gates of the Mountains. Flood Watch through Friday morning for Little Belt and Highwood Mountains. Winter Storm Warning until 6 PM MDT this evening for Big Belt, Bridger and Castle Mountains-Gallatin and Madison County Mountains and Centennial Mountains-Little Belt and Highwood Mountains-Snowy and Judith Mountains. Winter Weather Advisory until 3 PM MDT this afternoon for Beaverhead and Western Madison below 6000ft-Gallatin Valley- Madison River Valley-Missouri Headwaters. && $$ http://www.weather.gov/greatfalls