433 FXUS65 KPIH 160310 AFDPIH Area Forecast Discussion National Weather Service Pocatello ID 810 PM MST Tue Jan 15 2019 .UPDATE...A few minor tweaks made to the forecast for overnight and Wednesday morning. Have introduced a little more confidence with short term models, as they are in good agreement with NAM this evening. Snowfall expected to push into Idaho from the south between 09z-12z, spreading north into the Snake Plain/Magic Valley region right around commute time. South flow just above the surface appears likely to impact the I-86 corridor with downsloping, despite very weak north/northeast gradient at the surface. This should keep precip held off until after the height of the commute for this region. Highlands south to the Utah border, and including the I-84 region from Burley south to Utah state line, and I-15 Pocatello south to Utah state line, and Idaho Cache Valley likely to see the heaviest precipitation start just before the commute and last through the morning. Timing looks similar to previous forecast and will leave headline intact for travel impacts despite snowfall expectations remaining 1-3" in lower elevations and 2-5 at pass level. DMH && .PREV DISCUSSION... /issued 148 PM MST Tue Jan 15 2019/ SHORT TERM...Tonight and Wednesday. Today's band of snow continues to shift northeast and should be out of our hair by early evening. Under that band, roads are slick but not terrible. We are seeing conditions improve fairly quick behind that band. Slick spots may remain overnight as traffic dies down and we lose any type of heating associated with daytime hours. The question before the next band moves in toward morning will be stratus and fog. We are expecting low clouds to reform across the Snake Plain, across Island Park and the Teton Valley. We could easily see that in other valleys as well., depending on how long they clear out. Fog COULD be an issue as well, but decided to leave it out of the forecast for now. The next band of snow begins to push across the Utah border around Midnight, shifting northward through the morning. The models are waffling a bit on the northern extent of this main band of snow, but seem to be honing in on a general "line in the snow" from around Galena Summit to Atomic City to Wayan...and points south. The snow really looks to be confined across the southern highlands, especially in the corridor between I-84 and US-91. We issued a WINTER WEATHER ADVISORY for those areas in the morning, with travel impacts for the morning commute. Once you get to the 84/86 corridor northward, snow amounts look to be light. There is low confidence in the potential for an area of 1-2 inches of snow across the lower Snake Plain, Shoshone/Lava Beds and Craters area of 1-2". A couple of models have it, a couple don't and a few have and inch or less in those areas. We went with the "middle of the road forecast" which is around 1". For the afternoon and evening hours, snow will be mostly confined to east of I-15 (another 1-3" possible) and across the Sawtooths and Wood River Valley. Pockets of light snow remain possible elsewhere. Keyes MEDIUM TERM...Thursday and Friday...There are several impacts due to winter weather hazards anticipated throughout the day Thursday to mention. Beginning very early Thursday, freezing rain will be possible across the Eastern Magic Valley, through Shoshone, along the interstate corridor and toward Pocatello, Fort Hall and Blackfoot by sunrise. This would crease hazardous travel conditions before the morning commute. Conditions in these areas should switch over to a rain/snow mix near sunrise and continue throughout the day. This rain/snow mix line will continue tracking along the interstate corridor to Idaho Falls by late morning. Additionally, Thursday morning will bring the potential for freezing drizzle and flash freeze potential for the Island Park and Teton areas. Rapidly deteriorating road conditions and slick hazardous travel are possible. The snow activity is forecast to increase in intensity during the afternoon and evening hours in these areas and continue into Friday. Looking at the Central Mountains, Snow will be underway already Thursday morning and will be at peak intensity and will continue to snow throughout the day but weaker intensity. An additional snow band is expected for Friday in this region. Across all of Southeast Idaho, blowing and/or drifting snow is forecast on occasion where snow is already on the ground and/or where snow falls both Thursday and Friday. NP/Keyes LONG TERM...Saturday through Tuesday...Forecast models have changed from the last model run and are now showing some showers overtop the high pressure ridge in the northern portion of the forecast area. For now, we will wait for some model consistency before we increase POPS over the weekend. Models continue to indicate snow for late Sunday into Monday as the next system moves through the region from the northwest. Models are keeping more of the energy with that system further north today, which gives us a better shot for snow. NP/Valle AVIATION...As today's band of snow shifts north and east, conditions will rapidly improve. The question through tonight will be stratus and fog. We do have ceilings dropping to MVFR/IFR at IDA, PIH and DIJ. As for fog, we will don't have the included in the forecast but is certainly to watch out for. After 9z and through the rest of the morning, the next band of snow moves into eastern Idaho. We are expecting MVFR to IFR conditions through the morning hours with this band, even with some downslope component at BYI and PIH. Conditions will improve in the afternoon, with DIJ dealing with at least VCSH and low ceilings the longest. Keyes && .PIH WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 2 AM to 11 AM MST Wednesday for IDZ057>060. && $$