Area Forecast Discussion
Issued by NWS Salt Lake City, UT
Issued by NWS Salt Lake City, UT
859 FXUS65 KSLC 211009 AFDSLC Area Forecast Discussion National Weather Service Salt Lake City UT 409 AM MDT Tue May 21 2024 .SYNOPSIS...A cooler and more stable airmass will reside across much of the area today as a trough begins lifting out of the region. Increasing southwesterly flow will bring a brief warming and drying trend Wendesday, before the next cold front pushes through the region late Wednesday through Thursday. The pattern will remain active through the upcoming weekend. && .SHORT TERM (Through 12Z/6AM Thursday)...A broad upper trough continues to slowly swing through the region early this morning. The associated surface front has pushed south and east of the forecast area, while the trailing 700mb baroclinic zone currently stretches across southern Utah. A weak shortwave trough embedded within the mean cyclonic flow is currently riding along this boundary, and resulting in an area of showers spreading into southwest Utah at the present time. This area will quickly spread east, likely exiting the forecast area near or shortly after sunrise. In the wake of the frontal boundary, a much cooler airmass resides across the forecast area this morning, and will keep max temperatures confined to the low-mid 60s across northern/western valleys including the Wasatch Front (roughly 10F below climo), and near 80 around St George. In the wake of this wave, southwesterly flow will quickly develop across the forecast area by early Wednesday, and then strengthen throughout the day. This will result in a brief warming and drying trend area-wide, as max temps trend roughly 8-12F warmer. This warmup is in advance of the next cold front, which will reach northwest Utah late Wednesday afternoon, then sweep across much of northern and central Utah Wednesday night. The associated shortwave trough digging into the Snake River Plain/northern Great Basin will interact with the frontal boundary to bring a chance for precipitation across northern Utah Wednesday evening into Wednesday night. .LONG TERM (After 12Z/6AM Thursday)...Long term forecast period begins with a shortwave trough moving east into the Northern Rockies, with an associated cold frontal boundary moving southward through Utah. This front continues to appear fairly dry in nature, with most guidance (including what limited high res CAM guidance is now available) suggesting just some light showers along/near the front, and largely remaining north of US-40 or so. Boundary still looks to stall somewhere near to a bit south of the I-70 corridor as the parent shortwave continues eastward, with much cooler postfrontal temperatures settling. To that point, Thursday afternoon highs for locations behind the front look to be around 5 to 15 degrees cooler than that of Wednesday. Aside from temps/precip, still seeing potential for some prefrontal wind gusts ~25-40 mph, generally across southern and eastern Utah, as well as some gusty postfrontal winds in portions of the southwest Wyoming. For Friday, remnant boundary will likely remain draped somewhere across central Utah, and help trigger some isolated to scattered diurnal showers as weaker trailing energy advects through overhead. Airmass will moderate during the day as well, so will see temperatures begin to rebound back upwards. Warming temperatures continue into Saturday as the old baroclinic zone washes out and H7 temperatures increase. As a result, expect daytime highs Saturday near to maybe a bit below climatological normal for late May. Continued energy advecting through in advance of another approaching shortwave will once again trigger some isolated to scattered showers across the forecast region. General consensus amongst guidance is that this shortwave and associated cold front take a similar progression to the prior system Saturday evening into Sunday, with the fairly dry front moving south and stalling/washing out across central Utah Sunday. The exception to this scenario appears to be something akin to the deterministic Canadian model (and supported by ~30% of ensembles) where shortwave is more disjointed/weaker, and thus any surface reflection is much more muted. That would likely be a drier and more mild scenario, but for now kept NBM guidance for Sunday which includes a cooldown of several degrees from central Utah northward in addition to some continued isolated to scattered showers. A bit of uncertainty remains for Memorial Day, with around 55% of ensemble membership supporting a quick building ridge, and the other 45% maintaining some sort of weak lingering trough influences. For the ridge scenario, dry conditions and normal to slightly above normal temperatures would be expected. For the weak/lingering trough, a more muted warmup and maybe some isolated precipitation chances (generally further north in the forecast region) would be a bit more likely. In any case, little suggests anything of a washout type of day or much in the way of anything substantial at this time, but those with outdoor plans may want to keep an eye on the forecast all the same. Almost all guidance then supports further building of a ridge moving into midweek, with dry conditions and warm temperatures favored. While out just beyond the general time period of this forecast (and subject to change being over a week out), current NBM guidance even carries a 25% chance for KSLC to see its first 90 degree day on Wednesday 5/29. For context, the mean first 90+ degree day for KSLC specifically is 6/3, so not too far off all things considered. && .AVIATION...KSLC...Very isolated lake enhanced showers possible through mid morning or so. Winds fairly light and variable, likely becoming NW between ~15-17Z. Isolated afternoon showers anticipated to remain east of the terminal, though if showers manage to develop/collapse over the terrain just to the east, could see some brief periods of easterly winds try to push in. NW winds largely favored to persist though, with a shift back to SE ~03-04Z Wed. .REST OF UTAH AND SOUTHWEST WYOMING...System will continue to depart the area through the TAF period. Some isolated afternoon showers possible at northern terminals, primarily at terminals east of Utah`s high terrain (e.g. LGU/HCR/EVW). VFR conditions largely expected to persist, though brief MVFR possible with any heavier showers. These showers could also produce brief gusty/erratic outflow winds. Otherwise, expect most terminals (excluding ENV) to carry a more northerly wind component during the day, with some modest gusts possible (primarily at southern terminals). && .FIRE WEATHER...A cooler and more stable airmass has settled across the region in the wake of Monday`s cold front, keeping daytime temperatures roughly 10 degrees below normal. Lingering moisture across northern Utah will maintain a chance for showers mainly east of I-15 while the remainder of the area remains generally dry. Despite the cooler airmass, drier air will quickly mix down across central and southern Utah, resulting in RH values falling near or below 15 percent this afternoon across lower elevations, and low to mid 20 percent range over the higher terrain of southern Utah. Increasing southwesterly flow Wednesday will bring a warming and drying trend across the area. Daytime temperatures will trend 8-12 degrees warmer state-wide, while RH values trend 4-8 percent lower. A cold front will reach far northwest Utah Wednesday afternoon, then push through the state Wednesday night through Thursday. Temperatures will trend 8-12 degrees cooler across northern and central Utah Thursday, while the airmass ahead of the front remains warmer across southern Utah. Any precipitation with this system looks to remain confined to northern Utah. The unsettled pattern looks to continue into the upcoming weekend, before a more pronounced warming and drying trend sets up beginning early next week. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...None. WY...None. && $$ Seaman/Warthen For more information from NOAA`s National Weather Service visit... http://weather.gov/saltlakecity