363 FXUS65 KSLC 072320 AFDSLC Area Forecast Discussion National Weather Service Salt Lake City UT 420 PM MST Sun Nov 7 2021 .SYNOPSIS...A weak cold front will bring chance for rain and snow showers for southwest Wyoming and northern Utah this evening into Monday morning. A more impactful shortwave will arrive Tuesday into Wednesday bringing accumulating mountain snow and valley rain. A ridge of high pressure will build in to allow for drier conditions forecast thereafter. && .SHORT TERM (Through 12Z/5AM MST Tuesday)...Light rain showers are noted in the Cache Valley this afternoon with light snow falling upstream around 7,000 feet. This adjusted our snow level forecast slightly for this evening but the trend is the same through the evening and overnight. Snow levels are expected to continue decreasing to ~6,000 feet by Monday morning (and around ~5,000 feet from across the Greater Salt Lake Desert and to the Cache Valley). As a result, a rain, snow or a rain/snow mix is forecast this evening into tomorrow morning depending on elevation. Look for chances of precipitation to increase from north to south heading into the overnight hours with the best chances between midnight and 6 am along the Wasatch Front. Snowfall accumulations above 7,000 feet range from 0.1 inch to 1.0 inch. One forecast uncertainty regarding the chances of precipitation tomorrow afternoon into evening for the Wasatch, Uinta Mountains and southwest Wyoming. A few higher resolution forecast models are emphasizing an additional potential shortwave during this timeframe. This would allow for additional snowfall and potential impacts along I-80 should the snow materialize. It is something to keep an eye on for consistency in tonight's forecast. .LONG TERM (After 12Z/5AM MST Tuesday)...A transient ridge following in the wake of Sunday/Monday's shortwave will quickly be replaced by yet another shortwave trough embedded in the mean longwave flow through the day on Tuesday. This next deeper trough will carry with it much more moisture as it taps into subtropical moisture before progressing inland and across the Great Basin region. A warm surge ahead of the main baroclinic zone will keep snow levels fairly high toward the onset of precipitation late Tuesday morning/ early afternoon, however, as the cold frontal boundary pushes across the CWA, snow levels will drop substantially. Current thinking is that the rain/snow line will be around the 7500-8000ft mark, dropping to ~5300-6000ft by Wednesday morning. Areal extent of the precipitation currently looks to be confined to areas from roughly Nephi northward as this is where the best dynamics look to set up, but have maintained chance PoPs into the central mountains given the broad moisture transport. As far as accumulations go, the mountainous terrain (mainly north of the intersection point of US-6 and I-15) will do fairly well, with generally 5 to 10 inches of snow accumulation (~0.75" to 1" QPF) with locally higher amounts possible. For the Wasatch Front, the event will be entirely rain, with some mixed precip possible for the bench areas. Along the Wasatch Back and for Uinta County Wyoming, thinking that accumulating snowfall will be seen, however, amounts are expected to be ~1-2 inches or less. Given the amount of snowfall in the northern mountains for this early season timeframe, considering issuing a Winter Weather Advisory (though it will be more on the low end) with main impacts anticipated across higher elevation passes that remain open... but will refrain for this current forecast package. A bulk of the precipitation looks to come to an end by the morning hours on Wednesday, however, lingering lower level moisture and cool, disturbed northwesterly flow will prevail over the area through the day on Wednesday which should keep some chances for terrain driven showers through much of the day. Additional accumulations are expected to be low, but not negligible, especially in the favored areas (upper Cottonwoods & Ogden Peak among others along the Wasatch Front). Moist northwesterly flow will continue across the northern third of the area through Thursday, with the best chances to see terrain driven precipitation across mainly the Bear River mountains and high Uintas. Little impacts are anticipated at this time. Heading into Friday, a ridge of high pressure looks to begin to build back over the region, allowing dry conditions to reestablish with a warming trend through the weekend. Across northern Utah, temperatures should rise from slightly below normal on Thursday following the storm to ~5F above average by Sunday as the ridge regains control. && .AVIATION...KSLC...Low end VFR conditions are expected to be maintained over the KSLC terminal through the overnight hours as lower stratus begin to fill in over the airfield. An area of showers will develop north of the airfield overnight, bringing little, if any, rainfall over the airfield. Main concern with this area will be a stratus layer with CIGs at, or below, 6kft AGL which will lead to mountain obscuration. Otherwise, north winds will remain in place through the overnight hours, with speeds relaxing below 10kts by ~03Z. REST OF UTAH AND SOUTHWEST WYOMING...An area of showers across northern Utah/ southwest Wyoming will gradually diminish through the evening, however, redevelopment of these showers is expected overnight. As showers redevelop, low end VFR to high end MVFR conditions will develop from ~KENV to KEVW and KSLC to KLGU. Brief IFR conditions may be possible for KLGU and KEVW between 05-13Z. Otherwise, largely clear skies across southern Utah will gradually increase in coverage overnight, though CIGs are expected to remain above 12kft AGL. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...None. WY...None. && $$ SHORT TERM...NDeSmet LONG TERM...Webber AVIATION...Webber 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