Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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941 FXUS65 KSLC 191649 AFDSLC Area Forecast Discussion National Weather Service Salt Lake City UT 1049 AM MDT Mon Apr 19 2021 .SYNOPSIS...A trough will graze northern Utah with a few showers today, while an associated cold front will bring gusty winds. Another chance of showers is expected midweek. && .DISCUSSION...Satellite imagery this morning readily shows increased northwest flow around ridgetops with cirrus cloud streaming off of the Raft Rivers downstream for around 100 miles. Surface observations just upstream of our area in the eastern Snake River plain are starting to show the elevated winds reaching the surface, with Burley ID recently reaching ~60 mph gusts. Will need to monitor observations closely in our area to see if overperforming winds will merit a High Wind Warning for any areas. This cold front will continue to push southward through our area, reaching the Wasatch Front by the early to mid afternoon and central Utah by the later afternoon. More details in the previous discussion. No significant forecast updates today, just bringing in some recent observations and latest guidance for today. .PREVIOUS DISCUSSION...ISSUED 414 MDT... .SHORT TERM (Through 12Z Thursday)...Early this morning, the mid- level ridge axis is shifting southeastward across the forecast area with mostly clear skies and light winds in place. However, just upstream an approaching storm system can be seen in the Northern Rockies. This fast-moving progressive trough will clip across northeast Utah and southwestern Wyoming this afternoon, pushing a cold front across the region through this evening. Winds will be the main impact across the forecast area ahead of and behind the cold front passage today. Most locations will see wind gusts in the 30-40 mph range with the frontal passage, however orographically favored downslope areas like Northwest Utah downstream of the Raft Rivers and out across the Salt Flats, the Uintah Basin and Castle Country to the San Rafael Swell, will see slightly stronger winds into the 45-55 mph range. Wind Advisories are in effect for these favored areas. Also, the strong cold front passage is likely to pick up some dust from the Snake River Plain, but also more locally the Salt Flats given the very dry soil conditions in drought conditions. Have included some patchy blowing dust in the forecast for most of western Utah behind the cold front passage. While the bulk of the forcing and moisture with this trough passage will favor locations to our northeast, expect some scattered showers to develop along the cold front. Rapidly steepening mid-level lapse rates with the PV max tracking through northeastern Utah will provide support for strongly forced but widely scattered convective showers during peak surface heating. Thus expect any stronger showers that can develop today will be capable of producing graupel and some rumbles of thunder. Best chance of any measurable precipitation will remain over the mountains, particularly the Uintas. High pressure will settle in over Wyoming tonight through Tuesday morning. Winds will decrease, particularly over northern Utah in closer proximity to the surface high tonight allowing for optimal radiational cooling conditions. With the growing season now underway in lower elevations of northern Utah, a Hard Freeze Warning is in effect northern portions of Box Elder Country and the Cache Valley for tonight as temperatures are expected to fall into the mid to upper 20s. Mainly quiet weather will prevail on Tuesday, but a decaying trough will approach southwest Utah by late Tuesday into Wednesday. Some scattered showers are possible ahead of this trough, especially Wednesday afternoon with peak heating. Otherwise, increasing easterly pressure gradient with light easterly 700 mb flow across the northern Wasatch will likely support some enhanced canyon winds, which currently look to remain below advisory levels, but enough to be noticeable in the prone areas, thus have added into the forecast. .LONG TERM (After 12Z Thursday)... Subtle troughiness into Friday, then ridging into the weekend. It`s a rather interesting large scale set up over the western CONUS for the majority of the long term period, with lower than normal heights dominating the late week period, primarily aided by maintenance of a long wave trough downstream, and weak energy undercutting the mean ridge position over the PacNW. the latter reinforces lower than norm heights locally through Friday, but provides minimal support for much more than a few showers over largely the higher terrain each day. None of the guidance supports much in the way of forcing or thermal change, so chances for precip remain largely in the slight chance to chance range, with QPF on the light side. Heading into the weekend ensemble means continue to depict building heights locally as low amplitude ridging translates in from the west, this in response to another undercutting (and more consolidated) trough approaching the Pac coast. With roughly 80% of ensemble members latching on to a similar outcome as just relayed, H7 temps climbing up to some +5 to +7 degrees by Sunday PM suggest temps pushing 10+ degrees above normal is likely Sunday, with modest southwesterly flow aloft driving gusty southerly winds across the area. It`s too far out for much detail, but the takeaway hedges towards warm/windy for Sunday. Thereafter (into and through Monday) the evolution and inland translation of the trough is a lower confidence forecast with a variety of outcomes regarding detail...especially QPF. The latter being tied most closely with the orientation of the trough and associated trajectories of IVT transport inland/locally. It`s something to watch moving forward. && .AVIATION...Southerly winds currently in place at the KSLC terminal are expected to switch to the northwest between 17-18z behind a dry cold front. The strongest northwest winds with gusts over 30kts will occur between 20 and 23Z. Although decreasing in speed, northerly winds are expected to persist through the evening prior to shifting back to the southeast between 06-07z tonight. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...Red Flag Warning until 9 PM MDT this evening for UTZ489-492-494- 495-497-498. Wind Advisory until 9 PM MDT this evening for UTZ114-120-121. Hard Freeze Warning from midnight tonight to 10 AM MDT Tuesday for UTZ101-103-107. Wind Advisory until 9 PM MDT this evening for UTZ101. Red Flag Warning until 9 PM MDT this evening for UTZ482>484. WY...None. && $$ UPDATE...Van Cleave SHORT TERM...Church LONG TERM...Merrill AVIATION...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

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