368 FXUS65 KSLC 082207 AFDSLC Area Forecast Discussion National Weather Service Salt Lake City UT 407 PM MDT Fri Oct 8 2021 .SYNOPSIS...An active weather pattern will prevail with one storm system impacting the region tonight into Saturday afternoon and then another storm system Monday into Wednesday. A ridge returns for the end of next week. && .SHORT TERM (Through 12Z/6am Monday)...The atmospheric river which brought widespread and beneficial rain to southern and eastern Utah today will be peeling off the east overnight as the leading shortwave of the main trough over Nevada this afternoon moves into Utah tonight. Meanwhile, showers and isolated thunderstorms will continue under the diffluent region of the incoming trough. As the trough axis itself moves into northern Utah this evening, showers will become more numerous along the Wasatch Front and Wasatch Mountains, especially after midnight as the 700mb trough axis passes and the flow becomes west northwest. Rain intensity should increase for several hours as orographics enhance the lift. Snow levels currently are near 9500 ft but will lower to near 7500 ft by late Saturday morning. Accumulations in the Wasatch Mountains, central mountains, and southern mountains above 8500 should be about 1-4 inches but locally higher amounts are possible. The NBM point for Alta forecast about 5 inches which looked reasonable. The Uintas will have the highest amounts where a snow advisory remains in effect through Saturday for 4 to 12 inches of snow above 9000 ft. The 700mb trough axis will move into eastern Utah by Saturday afternoon, which means the moist NW flow will continue over the I-15 corridor from about Beaver northward to the Idaho border through mid afternoon Saturday. Therefore, scattered showers and isolated thunderstorms have been extended into the afternoon in these areas and for all mountains. The trough pulls away Saturday evening and skies are expected to become partly cloudy or even clear. Although not in the current forecast, if showers linger into the evening in some mountain valleys and then clearing occurs, patchy fog is quite likely by Sunday morning. Despite the ridge moving in Sunday, the NW flow will remain rather cool with little change from Saturday. Therefore, temperatures will remain about 10-15 degrees below normal in the north and about 5-10 degrees below normal in the south. .LONG TERM...(After 12Z/6AM Monday)...A potent and unseasonably cold Pacific Northwest storm system remains on track to impact Utah and southwest Wyoming Monday into Tuesday. Guidance remains in very good agreement with regard to the timing of the system, bringing the initial front into northwest Utah Monday morning, with the front and associated trough continuing southeast across the state during the day Monday. Most significant precip will initially be in association with the front, with deterministic models showing good fgen forcing. Precip will then transition to a cold pool dominated regime Monday night into Tuesday before the precip tapers off with the exit of the trough Tuesday night/early Wednesday. There still seems to be noticeable ensemble spread with regard to the strength of the system, with the various ensemble systems not favoring a particular strength. Regardless, this system will bring the coldest temperatures of the year so far, with temperature more typical of mid-November than early October. There will be widespread valley frost with hard freeze conditions possible for many valleys. Given the good amount of moisture and instability anticipated with this system along with the relatively large period of heavier precip, significant snow is looking more and more likely for the mountains of Utah and potentially the mountain valleys as well. Overall, models are trending just slightly warmer with temperatures so the potential for valley snow is decreasing, but snow will be possible down to the benches. Behind the exiting system, a much weaker system is expected to follow behind it for late Wednesday into Thursday. Progressive in nature, this system is expected to primarily act to limit warming of the airmass but cannot rule out a small amount of precip for northern portions of the forecast area. Behind that system, high pressure will bring drier and more stable conditions along with a warming trend for the end of the forecast period. && .AVIATION...KSLC...Widespread showers and thunderstorms are expected to continue through 04Z before transitioning to widespread showers with an occasional thunderstorm. Although VFR conditions will dominate, brief MVFR conditions will be possible with heavier shower/thunderstorm activity. A secondary window for MVFR CIGs is forecast to be in the 03-09Z period when precipitation is forecast to be most persistent. Low confidence in wind speed and direction forecast through the period as showers and storms will modulate these forecast parameters. In general, S-SE winds of 10-20kts with occasionally higher gusts expected through about 06Z, with winds generally turning to the NW thereafter. Models do indicate winds may be rather variable through the night. REST OF UTAH AND SOUTHWEST WYOMING...Widespread showers and thunderstorms will impact the terminals this evening before southern terminals dry out overnight. Showers will continue overnight impacting mainly terminals north of I-70. Additionally, mountain top obscurement will be possible across the central mountain spine from KCDC to KEVW through the period. Gusty southwesterly flow will develop at the surface across the airspace this afternoon. Wind gusts will be in the 20-25kt range. Winds will gradually shift to the W-NW from north to south overnight through Saturday as a cold front moves south and east. VFR conditions will prevail most sites, although temporary reductions to MVFR will be possible in heavier convective activity. An exception will be KLGU and KBCE where the potential exists for prolonged IFR stratus to build into both sites after 06Z. && .FIRE WEATHER...A good moisture tap along with a trough slowly moving across the Great Basin will result in widespread to numerous showers and isolated thunderstorms tonight into Saturday. Snow levels are currently above 9500 ft but will lower to near 7000 feet across northern Utah and to near 8000 feet across the southern mountains by Saturday morning. General snow accumulations of less than 4 inches below 8500 feet but higher amounts will occur at higher elevations. Wetting rains are expected across all valleys, with locally over an inch snow water equivalent in the mountains. A weak ridge will move over the region Sunday for sunny and dry conditions, but this will be short lived as a cold trough and associated cold front move into northern Utah Monday morning and then spread to a western Uinta Basin to Saint George line by Monday evening. Cold and unstable conditions will prevail behind the front with snow levels lowering to some western valley floors by Monday night. Dry weather is expected late Wednesday into the weekend with warming temperatures. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...Flood Watch until midnight MDT tonight for UTZ103-107-110. Flood Watch until 6 PM MDT this evening for UTZ124. Winter Weather Advisory until 6 PM MDT Saturday for UTZ112. WY...None. && $$ SHORT TERM...Struthwolf LONG TERM...Traphagan AVIATION...ADeSmet FIRE WEATHER...Struthwolf 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