946 FXUS65 KSLC 201248 AFDSLC Area Forecast Discussion National Weather Service Salt Lake City UT 547 AM MST Wed Feb 20 2019 .SYNOPSIS...A potent winter storm will settle into the Great Basin today, then remain over the region through late in the week. Heavy snow associated with this storm will concentrate mainly across the southern two-thirds of Utah late today through early Friday. && .SHORT TERM (THROUGH 00Z SUNDAY)...The large-scale pattern this morning consists of a weak shortwave ridge over Utah while upstream, a trough centered over the PacNW is tracking SSE. Ahead of said trough, moisture has increased over northern Utah as warm advection strengthened over the area. This has resulted in an area of snow across northern Utah. At the surface, pressure falls over Idaho and Nevada has led to a tightening southeasterly pressure gradient across northwest through west-central Utah. As such, enhanced south/southeast winds are noted across northwest Utah. Accumulating snow across northern Utah is expected to continue impacting area roadways through the morning commute, and as such, Winter Weather Advisories remain in place for the northern Wasatch Front and Cache Valley and adjacent mountains, as well as the northwest deserts (areas favored in southwest flow). New with the morning package was the addition of the Ogden Valley where favorable southwest flow should allow that area to also do well in terms of accumulation. Snow across northern Utah should decrease this afternoon as the warm advection weakens and the upstream trough dives south. The trough is progged to end up closing off over Nevada tonight. Snow is expected to begin developing across southern Utah this afternoon as an embedded vort max dives into southern Nevada and towards southwest Utah while warm advection strengthens in southwesterly flow aloft. The upper low will remain over Nevada into tomorrow before filling and tracking east on Friday. Until that time, a moist upslope south to southeast flow will persist for an extended period of time as a 700mb circulation tracks slowly east along the Utah/Arizona border. As a result, expect significant accumulations across southern through east-central Utah. Even Utah's Dixie is expected to see significant (for that area) accumulations. Winter Weather Warnings and Advisories are in place for the most impacted areas. Additional areas may eventually need to be added later depending on how the storm evolves. For example, the western Uinta Basin could potentially see significant accumulations tomorrow afternoon/night as moisture wraps around the low in an easterly upslope flow. West-central Utah may also see significant accumulations particularly along the I-15 corridor late tomorrow afternoon into Friday with the northerly flow on the backside of the trough as it starts to exit east. Otherwise, most of the Wasatch Front area is expected to see little in the way of snow tonight through the duration of the storm due to an easterly downslope flow tonight through tomorrow night. Besides the snow, another thing to watch will be canyon winds along the Wasatch Front due to said easterly flow. An easterly pressure gradient will set up across the Wasatch tonight. However, with weak flow aloft, these winds will likely remain localized to the canyons with gusts in the 30-40mph range. The gradient is progged to remain more or less in place through tomorrow night. However, the latest models are now indicating stronger 700mb flow (20-30kt) tomorrow through tomorrow night with cold advection (though not particularly strong) across the terrain. If this trend continues, there will be some potential for stronger and more widespread downslope winds. The storm will finally exit the area by Friday evening. After that, the pattern will start to trend more zonal for the weekend. On Saturday, warm advection across northern Utah ahead of a weak, low- amplitude trough passing by to the north could allow some snow to develop near the Idaho border. .LONG TERM (After 00Z Sunday)...An active pattern will continue with a couple of systems impacting the forecast area through the middle of next week. Global models are in general agreement with a broad trough of low pressure from the Pacific Northwest through the Northern Rockies early in the period, reinforcing cold air over the region. A glancing upper level disturbance rotating through the base of the trough could produce some light snow activity over the northern portions of the forecast area Saturday night and Sunday. The primary change to this forecast period was to scale back on precipitation potential for central Utah, as bulk of upper level support remains to the north of the forecast area. Global models all indicate a strong shortwave will swing through the northern Great Basin Sunday night and Monday, though with some differences. In general, the GFS indicates a compromise between more shallow solution of ECMWF and deeper Canadian solution. Experimental FV3 GFS favors the Canadian solution. With ample moisture and strong upward lift generated by shortwave and significant jet energy, boosted chances for precipitation. Global models all indicate some mid level ridging for Tuesday and Wednesday, with significant warming of temperatures aloft. Models, in particular GFS, may be a bit aggressive in generating QPF, though will hold on to chance wording for northern portions of forecast area, with precipitation type in valleys looking to be a mix of rain and snow. && .AVIATION...With winds backing to the southwest, snow showers will remain well north of KSLC early in the TAF period, with VFR conditions prevailing, with ceilings at or above 6,000 feet AGL. Still expect light snow to develop mid to late morning, then continue into the afternoon, with MVFR ceilings and visibilities. Southerly winds will prevail into tonight. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...Winter Storm Warning from noon today to 4 PM MST Friday for UTZ518. Winter Storm Warning from 5 PM this afternoon to 9 AM MST Friday for UTZ012-013-016-019>021. Winter Weather Advisory until noon MST today for UTZ001-002- 005>007. Winter Weather Advisory from noon today to 9 AM MST Friday for UTZ014. Winter Weather Advisory from noon today to 4 PM MST Friday for UTZ010-517. WY...None. && $$ Cheng/Barjenbruch 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