668 FXUS65 KTFX 271038 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 335 AM MST Fri Jan 27 2017 UPDATED AVIATION SECTION .DISCUSSION... Today through Sunday...This will be a period of dry and warming conditions for much of the forecast area, but gusty westerly winds will increase through the weekend, especially along the Rocky Mountain Front. Clear skies and light winds will allow patchy freezing fog to develop this morning again in the southwest valleys, with a few flurries also possible in the West Yellowstone area. Otherwise, a northerly flow aloft ahead of a high pressure ridge approaching from the west will keep a chance of snow in the western mountains into Saturday. The remainder of the area will remain dry. A strong pressure gradient along the Rocky Mountain Front will also continue strong westerly downslope winds there; wind gusts will mostly be in the 40 to 60 mph range through Saturday. A weaker gradient out onto the plains of North Central Montana will continue breezy, but not nearly as strong, winds there. An approaching shortwave trough will then start to break down the upper level ridge, causing westerly winds aloft to increase significantly. The strongest mid-level (700 mb) winds of 55-70 kt winds will stay right along the Rocky Mountain Front on Sunday, but the surface pressure gradient is forecast to spread out more so onto the plains, causing increasing winds there. Although the mid level winds do not indicate potential for High Wind highlights over the plains on Sunday, the situation looks a little better for possible highlights along the Rocky Mountain Front. Fellow forecaster notes, though, that the overall trend from the forecast models has been to decrease them. Will therefore continue to monitor the situation and hold off on highlights for now. Regarding temperatures, they will generally warm through the period, especially associated with the winds over the plains, where highs in the 35 to 40 degree range could approach 50 by Monday with mild overnight lows. The southwest will be much slower to warm up, as winds will have a harder time mixing down into the valleys there due to continued temperature inversions. Coulston Sunday Night through Friday...Zonal mid- to upper-level flow over our CWA looks to be the rule through this period. However, both the ECMWF and GFS suggest a pronounced shortwave trough embedded within this flow will overspread the Pac NW Friday and near our CWA late in the day. The aforementioned zonal flow aloft looks to include 50 knot+ 700 mb westerly flow across the Rocky Mountain Front Sunday night into Monday. Thus, strong downslope winds are expected along the Rocky Mountain Front during this period, but confidence in the occurrence of warning-criteria surface winds remains low. Compared to 24 and especially 48-hours ago, the latest few runs of model data now suggest these strong downslope winds will be confined to the Rocky Mountain Front and may not easily overspread most of the North- Central MT Plains. Thus, the surface wind forecast for the plains has been adjusted downward. The GFS continues to prog a surface cold front diving southward across our CWA Monday morning into afternoon, while the Canadian and ECMWF models suggest the frontal passage will transpire Monday afternoon through Tuesday morning. This forecast update leans on the Canadian and ECMWF guidance due to multi-model support. Showers, mainly in the form of snow, are still expected to accompany the front. In addition, it looks like the cold front will stall somewhere over Southwest MT on Tuesday as the cold, dense air behind it has trouble traversing the higher terrain. The resulting stationary front then looks to reside over Southwest MT through Thursday, before potentially advancing northward as a warm front on Friday due to warm air advection ahead of the aforementioned shortwave trough. Lift along the frontal boundary should trigger periods of snow Tuesday through Friday across our CWA. In addition, this lift and snowfall rates may be enhanced by the right entrance region of a mid- to upper-level jet streak Tuesday into Wednesday. Still too early to talk specific snow amounts, but this time period will continue to be monitored closely. Near to slightly above normal temperatures are expected Monday. An overall cooling trend will follow. By Thursday and Friday, readings look to generally be about 5 to 10 degrees below normal in most places. Jaszka && .AVIATION... Updated 1035Z. VFR conditions will continue over the forecast area for at least the next 24 hours, unless otherwise specified. High pressure aloft over the Pacific coast will keep the area under a northerly flow aloft that will keep lower VFR ceilings along and west of the Continental Divide. Low clouds will also keep flurries in the West Yellowstone area through around 18Z. Patchy fog may also develop this morning elsewhere across the southwest valleys, but it will likely not directly impact the terminals. Otherwise, only some high cloudiness will pass over the area. However, westerly winds will remain gusty at times over the North Central Montana plains. This will be especially so close to the Rocky Mountain Front, where gusts in the 35 to 55 kt range will be common through the period. Coulston && .PRELIMINARY POINT TEMPS/POPS... GTF 37 25 41 30 / 0 0 0 0 CTB 38 25 41 30 / 0 0 0 0 HLN 31 12 31 15 / 0 0 10 0 BZN 26 6 30 11 / 0 0 0 0 WEY 17 -8 21 -3 / 0 10 10 10 DLN 27 11 36 16 / 0 0 10 0 HVR 35 19 38 25 / 0 0 0 0 LWT 36 21 39 27 / 0 0 0 10 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && $$ weather.gov/greatfalls