Area Forecast Discussion
Issued by NWS Great Falls, MT
Issued by NWS Great Falls, MT
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255 FXUS65 KTFX 011144 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 544 AM MDT Wed May 1 2024 .Aviation Section Updated... .SYNOPSIS... A wintry spring storm will bring periods of rain and snow to the area through Friday morning. Temperatures will remain cool to below normal through the rest of the work week before warming up this weekend. && .DISCUSSION... Key Points: 1. The weather system has slowed a little since the last update but is generally still on track to arrive today with the greatest impacts expected tonight through Thursday afternoon. 2. Precipitation has already begun in the higher elevations of the Rockies and will become more widespread across north-central and central Montana by this afternoon. Higher elevations will have snow the entire time while lower elevations will oscillate between daytime rain and nighttime snow. 3. Cool and wet conditions will continue through the remainder of the week before warming up this weekend. Impact and Timing By Region: Glacier National Park and the Rocky Mountain front... The greatest impacts are now through Thursday. Heavy wet snow and gusty winds up to 40 mph are possible. Slippery roads and periods of reduced visibility due to blowing snow are possible which will make travel hazardous at times, especially along Marias Pass. People traveling through this area should be prepared for rapidly changing conditions and ideally avoid travel if at all possible. By Thursday evening snow is expected to decrease in intensity, however, light snow showers are expected to continue through Friday morning. Hi-Line east of Shelby... Precipitation will start off as rain and transition to snow heading into late Wednesday night/early Thursday morning. Along the Canadian border in the Sweet Grass Hills, higher snow amounts will be possible. However, along Highway 2, snow amounts are expected to be less than half an inch with most precipitation falling as rain and most snow melting quickly upon reaching the ground. Lower elevations of central Montana (including Great Falls, Helena, and Lewistown)... Precipitation will pick up this afternoon, starting off as rain and slowly transitioning to snow after sunset tonight. The heaviest precipitation is expected Thursday morning through Thursday afternoon. How much snow accumulates on the ground is a bit tricky considering how warm the ground is and depends on how much snow falls in the early morning hours before transitioning back to rain during the day. The main concern in this area will be deteriorating road conditions as slushy roads may make travel difficult at times and below freezing temperatures overnight, particularly Thursday night into Friday morning, may allow for some of the slush to freeze which will make the roads slippery. This back and forth between nighttime snow and daytime rain will start tapering off by Friday afternoon. The mountains of central Montana (including the Snowies, Judith, Big Belts, Little Belts, Highwood Mountains)... Snow will pick up this afternoon with the greatest impacts expected late tonight into Thursday morning which may make morning travel in the area very difficult at times, particularly along Highway 89. Snow showers will linger through Friday morning and taper off by Friday afternoon. There is a bit of concern with upsloping potential along the Little Belts through the duration of the event which may enhance the expected snow amounts and allow for periods of heavy snow and reduced visibility in the region. Anyone driving in the area or in the backcountry will need to be prepared for rapidly changing conditions. Southwestern Montana south of a line between Butte and Bozeman... This region will be the least impacted comparatively. Light rain showers are expected for lower elevations with mountain snow generally above 5000 feet. There are some concerns along Bozeman Pass with a slight upslope potential and slushy conditions possible but not enough to raise alarm bells at this point in time. With this weather system starting up north and moving south, southwestern Montana will not experience significant impacts until late Thursday morning into Thursday afternoon. Generally light showers will continue through Friday morning before tapering off. Advisory Update: One major change with this forecast was to expanding the winter weather advisory to include the Bears Paw Mountains. Looking at how northwesterly flow sustains itself over that section of the hi-line for most of the event, the potential for upsloping is high enough to warrant advisory-level snowfall. It is worth noting that the most significant impacts will be confined to the Bears Paw Mountains and the area immediately surrounding the mountains with otherwise minimal impacts at the lower elevations of far southern Blaine county. The start and end time for this advisory was delayed 6 hours from the other advisories in central Montana to account for the delay in precipitation arriving to this portion of the region. Extended forecast (Friday afternoon and beyond)... After this trough exits the region, ensemble guidance points towards a ridge building over the intermountain west Friday into Saturday. This will allow for much warmer conditions to return to Montana for a couple days with a lurking potential of 70 degree plus temperatures for portions of the plains. But cool weather lovers will not need to hold their breath for too long as ensemble guidance also points towards another large trough moving onshore sometime late in the weekend into early next week which will bring the potential for another round of unsettled weather and cooler temperatures. -thor && .AVIATION... 540 AM MDT Wed May 01 2024 (01/12Z TAF Period) Moist westerly flow aloft across the Northern Rockies and Montana will gradually shift more northwesterly Wednesday night as a broad upper level low gradually shifts east across southern Alberta. VFR conditions prevail through the TAF period for all terminals except KCTB and KHVR which will see prevailing MVFR/IFR conditions developing after 02/04Z. Short periods of MVFR/IFR conditions are possible for all terminals later in the afternoon into the overnight hours as showers become more widespread across the region. Periods of mountain obscuration will be a concern mainly after 01/21Z. -thor Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PRELIMINARY POINT TEMPS/POPS... GTF 51 33 43 31 / 60 80 90 60 CTB 47 31 42 29 / 80 90 90 20 HLN 51 36 50 32 / 50 50 70 40 BZN 47 26 50 28 / 50 30 60 30 WYS 40 17 44 18 / 60 40 50 40 DLN 45 25 50 28 / 40 20 20 30 HVR 54 33 45 31 / 50 70 90 50 LWT 47 28 40 28 / 40 50 90 50 && .TFX WATCHES/WARNINGS/ADVISORIES... Winter Storm Warning until noon MDT Thursday for East Glacier Park Region. Winter Weather Advisory until noon MDT Thursday for Northern High Plains-Southern Rocky Mountain Front. Winter Weather Advisory from 6 PM this evening to 6 AM MDT Friday for Bears Paw Mountains and Southern Blaine. Winter Storm Warning until 6 PM MDT Thursday for Little Belt and Highwood Mountains. Winter Weather Advisory from noon today to 6 PM MDT Thursday for Big Belt, Bridger and Castle Mountains-Snowy and Judith Mountains. && $$ http://www.weather.gov/greatfalls