220 FXUS65 KSLC 060418 AFDSLC Area Forecast Discussion National Weather Service Salt Lake City UT 1018 PM MDT Sat Nov 5 2022 .UPDATE...Updated aviation section below. The remainder of the forecast remains in good shape and thus the previous discussion follows below (with the exception of the updated aviation section). && .SYNOPSIS...A series of winter storms will impact the region, with the first ending tonight into early Sunday. The next winter storm will begin with strong winds Monday and then widespread precipitation later Monday through late Wednesday. && .SHORT TERM (Through 12Z Thursday)...An eventful November continues to unfold with two separate, significant winter storms in the short term forecast period. Afternoon upper air and satellite analysis indicates a broad ridge remains in place across the eastern Pacific while an aggressive and active northern stream continues to impact the PacNW and the Interior West. Afternoon mesoanalysis indicates a cold front is approaching the Utah/Idaho border at this time. RADAR imagery depicts a broad band of moderate to at times heavy precipitation associated with this front. Blowing dust and strong winds associated with this front closed I-15 near Idaho Falls earlier this afternoon. Reviewing the latest CAMS runs, much of the CAM guidance suggests this band of moderate to at times heavy precipitation will maintain coherence into northern Utah, reaching the Cache Valley near 4 PM and gradually shifting south along the Wasatch Front, reaching northern Utah County by 8 PM or so. This may bring a period of moderate to heavy rain/snow mix or even snow to the valleys during some of the higher travel times as large events are ongoing or let out. As far as heavy, dense mountain snow, this will continue into the evening and overnight period. Winter Storm Warnings remain in effect for the Wasatch Mountains, with winter weather advisories for the western Uintas (with the heaviest accumulations restricted to western portions of the chain). Winter weather advisories also remain in effect for the Bear River Valley, Bear Lake area and the Uinta County, WY area. Winds have gusted as high as 55 mph in light snow at the Evanston airport. Attention then turns to what is looking like the most significant winter storm of the fall season. A deepening upper level trough will gradually shift south along the Canadian Pacific Coast through early Monday. As this trough deepens, multiple jet maxes will be rotating around the base of the trough. This will help to set up the first part of the storm...strong winds across western Utah Monday afternoon and evening. With 700mb winds in excess of 50kts to some guidance indicating as high 70kts across western Utah, the bulk of guidance supports widespread gusts in excess of 60 mph across the western valleys of Utah. These values are near to outside the CFSR climatology, or to put it another way, anomalous even for November, in a normally windy location. Given all of this, issue a high wind watch for the western valleys including the Tooele Valley Monday afternoon and evening. Additional locations will need wind advisories, but for now wanted to highlight where the threat is the highest to exceed 58 mph. As this strong, deep trough with a landfalling atmospheric river around the southern Sierras begins to shift eastward toward the California Coast, a band of moderate to heavy precipitation will cross into western Utah. Expect precipitation to begin as early as Monday afternoon across far northwestern Utah, gradually shifting south and east through Monday night. By Tuesday afternoon, a well forced band of moderate to heavy precipitation is expected to be located from roughly Logan to west of Cedar City. This band is going to be slow to move through much of the Tuesday/Wednesday period. While the coldest temperatures at 700mb lag behind the main band, expect through a combination of dynamic cooling and heavy precipitation, that rain may mix with or change to snow in valley locations under the band as early as 18Z Tuesday. This is an area of lower confidence as some of the guidance suggests even with these processes, snow levels will remain above valleys until Wednesday morning. The current forecast represents a blend toward this colder range of guidance given the well forced, moderate to heavy banding represented in the bulk of the model guidance. This band of moderate to heavy precipitation only intensifies in the guidance Tuesday night into Wednesday as a 160kt+ jet max with attendant diffluence aloft sets up right over Utah. If this heavy band is snow at this point, valleys under the band could see heavy snow accumulations. As the 500mb low ejects crosses northern Utah Wednesday afternoon, moderate to heavy precipitation will likely continue across much of Utah. Flow is expected to turn west to northwest in the wake of this feature and much colder 700mb temperatures will build into the state. This will usher in the last round of orographically enhanced precipitation from Wednesday evening into Thursday morning. Either way, the potential for 1-2 inches of snow water equivalent/rain/snow looks likely for the western valleys from St. George to the Wasatch Front to the Cache Valley. East of the mountain spine will see significant less. The northern mountains are currently expected to see on the order of 1.5-3.0 inches of snow water equivalent with this storm. Similarly the western portion of the southern mountains looks to see somewhere between 1.5-2.5". We don't want to get our snow lovers too excited, but confidence is growing quickly that 1 to 2 feet to perhaps some locations seeing 30 inches + is looking more and more likely for the northern mountains. Confidence is quite high this will be a significant mountain storm...however whether some areas will see 30 inches + is something that is too early to tell. .LONG TERM (After 12Z Thursday)...The extended forecast period looks to turn quiet behind the extensive trough pattern effecting the CWA during the short term. By Thursday morning the trough axis will be through the region but could leave some lingering mountain precipitation for the northern mountains of Utah and into SW Wyoming. Any lingering showers will likely shut off by the afternoon hours as the backside of the trough will promote northwesterly flow and subsidence over the region. This will drive back in very cold and dry air back into the region which will bring clearing skies and dry conditions through the end of the extended. The deep cold pool behind the trough is expected to bring some of the coldest temperatures of the season so far as most valley highs are in the 30s and 40s while overnight temperatures fall into the teens and even single digits for a majority of the CWA. Deterministic models show potential for a shortwave to move through towards the very end of the extended that could bring back some precipitation for northern Utah and SW Wyoming but there is much uncertainty at this time with the timing among both models and ensemble guidance. && .AVIATION...KSLC...Surface cold front has moved through the area. Band of precipitation associated with this boundary expected to persist through 06Z per his-res models, however radar trends suggest precipitation will linger beyond 06Z. Rain is expected through around 06Z, with a 40 percent chance snow will mix in. No snow accumulation is expected. CIGs expected to largely remain VFR with a 30 percent chance for MVFR CIGs. Low confidence in wind speed and direction forecast through 06Z. Thereafter, models are in good agreement that winds will ultimately shift to the SSE. Gusty S winds of 15-25kts expected to develop after 21Z as the frontal boundary moves back north as a warm front. .REST OF UTAH AND SOUTHWEST WYOMING...Snow with IFR or LIFR visibility and ceilings will last through around 05Z in southwest Wyoming. Much of northern Utah will have rain that tapers off from north to south during the evening and overnight. Rain may mix with snow at valley locations in northern Utah, but no snow accumulation is expected. Elsewhere, conditions will stay dry. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...High Wind Watch from Monday morning through Monday evening for UTZ101-102-115-122. Winter Weather Advisory until 2 AM MST Sunday for UTZ109. Winter Storm Warning until 4 AM MST Sunday for UTZ110. Winter Storm Warning until 9 AM MST Sunday for UTZ111. Winter Weather Advisory until 9 AM MST Sunday for UTZ112. WY...Winter Weather Advisory until 5 AM MST Sunday for WYZ021. && $$ ADeSmet/Kruse/Selbig/Wilson For more information from NOAA's National Weather Service visit... http://weather.gov/saltlakecity For frequently asked questions about the Area Forecast Discussion visit... http://weather.gov/saltlakecity/general/afd_faqs.php