Area Forecast Discussion
Issued by NWS Great Falls, MT
Issued by NWS Great Falls, MT
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247 FXUS65 KTFX 192335 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 535 PM MDT Thu Sep 19 2024 .Aviation Section Updated... .SYNOPSIS... Breezy and gusty winds will continue through Friday in wake of a fast moving disturbance, with a chance for showers over the plains of Central and North Central Montana on Friday. Temperatures will be below normal on Saturday, but warm back near to above normal from Sunday through early next week. && .DISCUSSION... Rest of today through tonight...primary forecast concern throughout the period is the potential for fog, mainly in the valleys of Southwest and Central Montana and in the Milk River Valley in North Central Montana where the combination of light winds and clearing skies will be favorable for the development of fog. Showers have largely come to an end over the plains of Central and North Central Montana; however, and isolated (rogue) shower can`t be ruled out through the remainder of the afternoon over or downstream of the Sweet Grass Hills and Bears Paw Mountains. Otherwise, breezy and gusty west to southwest winds will gradually decrease through the early evening hours, but remain "strong" enough (near 10-15 mph) over the plains of Central and North Central Montana to keep the boundary layer mixed and limit the development of fog tonight despite recently saturated soils. With this being said, a few fog prone valleys in Southwest and Central Montana and the Milk River Valley in North Central Montana are expected to see favorable wind speeds for the development of fog, with the latest HREF and/or NBM guidance giving these areas a 10-20% chance for visibilities of 6 miles or lower. While dense fog is not currently anticipated, given the abundance of low level moisture from recent precipitation it is not out of the realm of possibility for a few low-lying spots within these valley locations to see visibilities of 1 mile or less during the overnight hours and into Friday morning. - Moldan Friday through next Thursday...A progressive weather pattern develops through Monday with a series of lower amplitude troughs in the upper level flow moving east across western Canada. The first trough and its associated low at the surface already move east across southern AB tonight with a cooler airmass sliding south in its wake across north-central MT on Friday, expanding into southwest MT Saturday. Breezy west winds this afternoon and overnight tonight on the plains will shift to the north and northwest on Friday with a few showers possible near Glacier NP and along the US/Canadian border but most areas will remain dry. While afternoon temperatures are only slightly below seasonal averages, the cooler airmass and clearing skies later Friday night and again Saturday night will allow temperatures to fall to the 30s at many locations and bring the risk of frost to some areas. Dry and warmer conditions develop Sunday as upper level ridging transits the area before breezy conditions develop with the arrival of the next upper level wave Sunday night and Monday. There is some uncertainty still with precipitation associated with the wave moving through the area Sunday night and Monday, but this is a fast moving system with current probabilities around 20-30% for showers on Monday. Medium range model ensembles seem to be in reasonable agreement in the depiction of upper level ridging building across the western US by the middle of next week, likely resulting in a return to near and above average temperatures. - Hoenisch && .AVIATION... 20/00Z TAF Period VFR conditions will prevail during this TAF period with mostly few to scattered clouds at all terminals. For the overnight hours, there is a 20% chance of fog development around KWYS which may produce brief periods of MVFR to IFR ceilings around the terminal. But confidence in impacts was not high enough to include in this round of TAFs. Winds will start to pick up by 20/14Z with gusty winds expected across north-central and central Montana through the remainder of the TAF period with mountain wave turbulence possible during this time. -thor Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PRELIMINARY POINT TEMPS/POPS... GTF 49 70 38 62 / 0 10 20 0 CTB 46 61 34 61 / 0 60 70 0 HLN 48 73 39 64 / 0 0 10 0 BZN 41 71 32 63 / 0 10 0 0 WYS 26 62 25 62 / 0 0 10 0 DLN 42 69 31 62 / 0 0 0 0 HVR 49 66 37 61 / 0 30 30 0 LWT 47 66 36 58 / 0 10 20 0 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && $$ http://www.weather.gov/greatfalls