Area Forecast Discussion
Issued by NWS Great Falls, MT
Issued by NWS Great Falls, MT
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893 FXUS65 KTFX 040543 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 1143 PM MDT Fri May 3 2024 ...AVIATION SECTION UPDATED... .SYNOPSIS... Lingering showers and snow showers will be around through the early evening ahead of a mild and dry Saturday. Precipitation chances will return Sunday into much of next week, with potential for an impactful spring system over the middle of next week. && .UPDATE... Surface high pressure is dominant across the state this evening. Rain showers have dwindled down as skies continue to clear. No major changes were made to the update as dry weather stays overnight. Patchy fog will be limited due to drier air at the surface. -Wilson && .AVIATION... 1143 PM MDT Fri May 3 2024 (04/06Z TAF Period) Lingering clouds from isolated shower activity earlier this evening are quickly giving away to mostly clear skies. Aside from some isolated fog patches later tonight/early Saturday over the far southwest valleys and portions of the plains, VFR conditions associated with high pressure over the Northern Rockies are expected for most if not all of the 04/06Z to 05/06Z TAF period. However, keep in mid that higher clouds do increase later tonight into Saturday, and a few light showers may lift northward into far Southwest Montana around 04/00Z and beyond. Light east to southeasterly surface winds increase on Saturday and may gust up to 25 mph at times. - RCG Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PREV DISCUSSION... /ISSUED 255 PM MDT Fri May 3 2024/ Through Saturday...Transient shortwave ridging is beginning to build in across the Northern Rockies between one upper disturbance exiting eastward across Southern Canada and another approaching the Pacific NW. Lingering northwesterly flow aloft will combine with daytime heating to result in rain and snow showers the remainder of this afternoon and early evening, primarily across the plains. Clearing skies and light winds tonight will allow for patchy fog formation into Saturday morning, but is not expected to pose many impacts at this time. Saturday looks to be a pleasant day as the aforementioned ridge moves overhead, with the only potential blemish being breezy easterly to southeasterly winds across the plains in the afternoon. Daytime highs look to rise to near to a touch above average in most areas. -AM Saturday night into next week...Deep southerly flow aloft develops over Southwest MT Saturday night ahead of a closed low moving onto the Pacific NW coast. This system will trek eastward into S ID on Sunday, placing the Northern Rockies on the ascent side of the system for northward expansion of shower and isolated thunderstorm activity, though temperatures will remain near average for one more day. H700 flow slows down by Sunday afternoon and MU CAPE looks to be around 100 to 300 J/kg (highest southwest MT), so not expecting anything beyond general thunderstorm risks at this time. Ensembles remain in decent agreement with the aforementioned closed low swinging NE into E MT and slowing down some Monday through early Thursday. Although, there are differences on the precise path of the low, most favor cool, wet, and windy periods during this timeframe. According to the NAEFS Standardized Anomaly, H700 temperatures are forecast to be around -8C for much of this event, which would support mountain accumulating snow, but mostly rain at lower elevations. Current probabilistic forecasts for rainfall highlight the eastern portions of North-central MT with the highest chances (50 to 70%) for 1 inch of rainfall during the 72 hr period ending next Thursday at 6 am, with nearly all locations in the CWA standing at least a 50% for a quarter inch of rainfall for the same time period. The one drier exception looks to be southwestern valleys from Dillon to the Three Forks area. As mentioned earlier, thermodynamic profiles should confine accumulating snow to mountain areas, with the Little Belts and the Madison/Gallatin ranges seeing 60% + chances for 8 inches of snow or more Monday through Thursday, with most of it falling Tuesday night into Wednesday. H700 flow on the backside of this low will be at or above the 30 to 40 kt range for an extended period, resulting in gusty to at times strong northwesterly surface winds. While all days Monday through Wednesday look to be on the windier side, Tuesday is being singled out by the EC Extreme Forecast Index and NBM probabilistic forecasts as the windiest day overall, with many locations seeing 70% + chances for wind gusts above 40 mph. Drier and milder conditions move in for Thursday and Friday of next week, though around 50% of the ensembles support weaker troughing remaining in place for non-zero chances for precipitation and near average temperatures heading into next weekend. - RCG && .PRELIMINARY POINT TEMPS/POPS... GTF 29 64 42 63 / 0 0 10 40 CTB 28 60 37 59 / 0 0 10 30 HLN 32 69 44 69 / 0 0 10 60 BZN 27 67 42 65 / 0 0 10 70 WYS 21 60 36 52 / 0 0 30 90 DLN 30 66 43 60 / 0 10 40 70 HVR 27 64 39 71 / 0 0 0 20 LWT 25 59 36 65 / 10 0 10 30 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && $$ http://www.weather.gov/greatfalls