837 FXUS65 KTFX 161137 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 540 AM MDT Thu May 16 2024 .SYNOPSIS... Strong and gusty winds are expected through Friday as an upper level disturbance and associated Pacific front approach and eventually cross the Northern Rockies. Light precipitation can be expected over this timeframe, with the best chance of seeing amounts in excess of a tenth of an inch occurring over North Central Montana. Unsettled and cool conditions are then expected from the weekend through much of next week, with multiple additional chances for widespread precipitation. && .Update... Early morning update has been published to account for light rain moving across the western Hi-Line. Initial thoughts with the first iteration of the forecast was that this area of precipitation would primarily fall as virga as Hi-Res models often support PoPs beneath a Chinook Arch despite a dry sub-cloud layer being present. This has not been the case this morning per surface obs and webcams, which support the mention of low PoPS at this time as rain is reaching the surface, most recently in the Cut Bank Area. - Moldan && .AVIATION... 16/12Z TAF Period Expect VFR conditions across North Central and Southwestern Montana over the next 24 hours, even as winds increase and upper level cloud cover increases. Winds will be strongest across the plains, particularly at KCTB and KGTF during the afternoon hours, and we will have a few light rain or virga showers around, particularly around KCTB and KGTF this morning before shifting east to KLWT and KHVR during the afternoon. Ludwig Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PREV DISCUSSION... /ISSUED 318 AM MDT Thu May 16 2024/ Today through Friday... forecast concern through the period will be strong and gusty southwest to west winds ahead of and following an upper level disturbance and associated Pacific front. Main area of concern through the day today for winds will be from the Rocky Mountain Front to the Interstate 15 corridor in North Central Montana, specially along the US Hwy 2 corridor from Shelby to Marias Pass where the latest NBM probabilities supports a 60-75% chance for maximum 24hr wind gusts to exceed 48kts through this evening. Hourly wind gusts in excess of 48kts through this evening peak at between 20-40% from approximately 17z this morning through 23z this afternoon. This difference between maximum 24hr and hourly wind gusts probabilities suggests that any wind gusts approaching or exceeding high wind criteria would most likely be a one an done type of scenario. The 24hr maximum sustained probability for the aforementioned areas ranges from 80-90% for today, with the hourly probabilities once again peaking between 17-23z at between 30-60%. While High Wind criteria wind gusts and/or speeds may be realized from late this morning through the afternoon hours in the Browning and Cut Bank Areas, the overall frequency (i.e. one or two observations of 58+ mph wind gusts and/or one hour of sustained winds of 40 mph) of these values being reached are too low to warrant a High Wind Warning at this time. By Friday the upper level disturbance will begin to move over the Northern Rockies, with a Pacific front sweeping eastward and across Southwest through North Central Montana from the late morning through afternoon hours. This Pacific front will bring another period of strong and gusty winds; however, this time the winds will be experienced across all of Southwest through North Central Montana. While NBM probabilities do not support widespread High Wind criteria wind gusts/speeds, wind gusts in excess of 41kts have a 70+% chance of occurring across most of the CWA outside of a small portion of central North Central Montana. While several locations may actually realize High Winds on Friday, I do not currently expect these location to be concentrated enough in one specific area to warrant a High Wind Watch as it would be like throwing darts at a dartboard...blindfolded (i.e. high false alarm rate). None-the-less, Friday will be windy across the entire CWA and travelers will need to exercise caution, especially if operation high profile vehicles. Finally, periods of light precipitation will be possible from today through Friday, but amounts will largely remain below a 0.1" outside of the Hi-Line and Glacier National Park Area. The East Glacier Park zone has the highest probabilities for 0.5" of precipitation through the timeframe at 10-30%, with 20-60% chance for 2" or more of snow. Saturday through Sunday...ensemble clusters strongly favor longwave troughing over the Northern Rockies throughout the weekend, with the leading mode of uncertainty being the overall amplitude of the longwave trough, specifically on Sunday. A deeper longwave trough on Sunday, which is overall favored in 3 of the 4 clusters, would result in cooler and "wetter" conditions through the weekend across much of Southwest through North Central Montana. Latest NBM probabilities for a 0.25" of precipitation from 12z Sunday to 12z Monday generally range from 20-40% south of the US Hwy 2 corridor and north of the US Hwy 12 corridor. Additionally, the probability for snowfall of 2" or more along the Continental Divide and across the mountains of Central Montana over this timeframe is approximately 30%, with 48hr probabilities (including Saturday and Saturday night) ranging from 30-50% for these same areas. High temperatures on Saturday in wake of Friday's Pacific front will fall into the 60s, with Sunday only seeing highs rise into the 50s. Monday through next Thursday...an unsettled and "cooler" pattern is favored through the upcoming work week, with the multi-model ensemble cluster suggesting overall longwave troughing over the Western CONUS and Western Canada and inconsequential periods of transient shortwave ridging moving over the Northern Rockies. Some uncertainty exists with the timing, position, and amplitude of individual shortwaves troughs rotating through the longwave trough, but the main message to put forward will be that their exists multiple chances for precipitation (some of which may fall as mountain snow) and below normal temperatures through the upcoming work week. - Moldan && .PRELIMINARY POINT TEMPS/POPS... GTF 76 54 64 42 / 10 10 40 40 CTB 73 48 56 38 / 30 10 60 50 HLN 80 52 67 40 / 10 20 40 10 BZN 78 45 66 32 / 10 20 60 20 WYS 67 35 63 22 / 20 20 30 10 DLN 77 45 67 31 / 10 10 10 0 HVR 78 52 66 42 / 20 20 60 70 LWT 73 45 60 38 / 20 20 60 50 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && $$ http://www.weather.gov/greatfalls