769 FXUS65 KGJT 100912 AFDGJT Area Forecast Discussion National Weather Service Grand Junction CO 312 AM MDT Wed Oct 10 2018 .SHORT TERM...(Today through Thursday) Issued at 310 AM MDT Wed Oct 10 2018 Midlevel low pressure is currently located over northern Utah this morning and is expected to track eastward over the WY/CO state line today. The QC forcing associated with this system is modest and as a result widespread showers have develop in response to this ascent. Valley rain and mountain snow will continue through out the day with most of the precipitation falling this morning and early afternoon. As of now the snow levels are roughly around 7000-8500 feet across the area and are expected to lower to the valley floors in northeast Utah and northwest Colorado this afternoon. Along the highway 40 corridor the 700 mb temperatures will dip down to -6C, but highs in the valleys could manage to reach the upper 30s to lower 40s. A difference of a few degrees will dictate the snow amounts and impacts. The best chances for accumulating snow will be in the morning at these locations. Although current observations show sites in that area in the upper 30s so perhaps snow will be overall limited in the lowest elevations. The precipitation is expected to spread across most of the forecast area today with the exception of southeast Utah and southwest Colorado. Satellite imagery is showing a midlevel dry slot on the back side of the system that models are depicting will track over the forecast area this afternoon. This dry air should cause the showers to end around the same time the forcing for ascent moves east of the divide. A few showers could linger in the Park Range, Grand Mesa, Flat Tops, Elk and Sawatch Mountains into the early evening. Convection could contribute to enhanced snowfall rates at times, but breaks in the clouds and afternoon temperatures may support melting on the pavement. Most of the impacts from this snow will remain above 8000 feet with totals of 4-8 inches and localized amounts up to 10 inches. Tonight that system moves east allowing a short break in the precipitation while another trough carves out the western CONUS. As this occurs the subtropical jet lifts northward into the region and warm advection sets up over the area. In response to this and the positively tilted trough across the west a band of modest frontogenesis develops over southeast Utah and stretches into central Colorado late tonight into tomorrow. There could be some enhanced lift from a minor impulse in the southwest flow aloft otherwise given the tilt of the midlevel trough QG forcing appears weak. Precipitation rates could become modest within the band and the overall lack of progression could favor prolonged precipitation. Some models are indicating the band could develop around sunrise and last into the early evening. Although temperatures appear to recover from the previous trough as snow levels should lift through out the day. This will also translate to warmer high temperatures, which will play a role in snow accumulations. This warming trend might have not been fully represented in the snow-to-liquid ratios, which may end up lower than expected. A majority of this snowfall stays confined to the Grand Mesa, Flat Tops, Elk and Sawatch mountains. Amounts remain rather uncertain given the warmer temperatures, but as of now another 4-6 inches with localized 10 inches could be possible at these locations. .LONG TERM...(Thursday night through Tuesday) Issued at 310 AM MDT Wed Oct 10 2018 The front that set up over the Bookcliffs and Roan Plateau Thursday will slowly move south and east Thursday night as its supporting upper trough weakens and moves east. A band of precipitation stretching across NW CO and east-central UT will slowly weaken early Friday morning with precipitation ending in UT by sunrise Friday. Models show most of the moisture exiting the forecast area by 18Z Friday. Friday night through Saturday: UT and CO will be caught in the col between an old cutoff low off the southern CA coast and the general northwesterly flow aloft over the northern Rockies and the plains. Dry conditions are expected with slightly warmer temperatures. Saturday night the next trough will drop in from the north. It will push a cold front most strongly down the front range with its western trailing edge dragging through western CO Sunday. Most of the precipitation will focus over the mountains close to the Continental Divide and the northwest CO plateau from Craig east. Monday and Tuesday should see a return to drier northwest flow. The closed low off the southern CA coast will move inland Tuesday and may draw some clouds and moisture up into SW CO Tuesday afternoon. && .AVIATION...(For the 06Z TAFS through 06Z Wednesday night) Issued at 1139 PM MDT Tue Oct 9 2018 Rain in the valleys and snow in the mountains will spread east overnight then clear from west to east after about 14z Wednesday morning. All TAF sites should experience MVFR to IFR CIGS and occasional IFR VSBY in better showers. Mountains will obscured with breaks in the obscuration beginning about 18Z. Snow levels will drop to 6500 feet across the north with KHDN, KASE, and KGUC likely to see showers of snow or at least a rain/snow mix. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...Winter Weather Advisory until 6 PM MDT this evening for COZ004- 009-010-012-013. UT...Winter Weather Advisory until 3 PM MDT this afternoon for UTZ023. && $$ SHORT TERM...KJS LONG TERM...CC AVIATION...CC