Area Forecast Discussion
Issued by NWS Salt Lake City, UT
Issued by NWS Salt Lake City, UT
091 FXUS65 KSLC 212106 AFDSLC Area Forecast Discussion National Weather Service Salt Lake City UT 306 PM MDT Sat Sep 21 2024 .SYNOPSIS...An area of low pressure will move through the Four Corners region through the weekend, bringing some threat for modest canyon winds Saturday night across prone areas of northern Utah. A mostly dry front and grazing system then move through Monday, followed by high pressure and mostly quiet conditions thereafter. && .SHORT TERM (Through 12Z/6AM Monday)...Afternoon GOES-W water vapor and visible satellite loop both show clear evidence of upper level low centered south of the UT/AZ border. This feature will continue to shift northeastward through the Four Corners region today and gradually eject through the Central Plains Sunday. Through the remainder of Saturday, the forecast region will remain placed more on back side of the cyclonic flow associated with the upper low. While moisture is far from prolific (PWAT values around 0.5 to 0.7 inches), in combination with modest diurnal destabilization and energy associated with the low it will be sufficient to help trigger continued redevelopment of isolated to scattered convection. Available CAM guidance suggests highest coverage of such convection will generally be along and east of Utah`s spine up into the Uintas or so, with activity beginning to wane fairly quickly through the late evening hours. Given the drier characteristics to the airmass, biggest threat from any convection appears to still be some gusty outflow winds. That said, while instances of more moderate to heavy rain will be limited to a handful of the strongest cells, can`t entirely rule out seeing something slip through a more rain sensitive and quick responding basin. While the airmass will continue to dry moving into Sunday, there may be enough lingering moisture to result in seeing a few widely isolated showers develop, primarily along the higher terrain. Aside from the precipitation associated with the upper low, its movement also looks to place it in a favorable area to bring a brief period of stronger gradient driven canyon winds tonight to some of the typically prone areas across northern Utah. Given the lack of other components for a more typical downslope style setup (little to no cold air advection or critical layer noted), anticipate the winds to be fairly modest. Mean HREF wind gusts generally fall in the 25 to 35 mph range, with ensemble maximum values noted in the 40 to 45 mph range. The latter max range especially seems like a reasonable number for some of the locally gustier canyon mouths. High resolution guidance suggests the most favorable time window for these winds is just prior to midnight on through around 4am or so, but likely will see some modest gusts hang on through at least sunrise. Given the continued departure of the low, a repeat of strong canyon winds Sunday night looks quite unlikely. .LONG TERM (After 12Z/6AM Monday), Issued 358 AM MDT... Deterministic global and ensemble system agreement has improved through midweek, with consensus favoring broad northerly flow through Wednesday, with Utah and SW Wyoming residing on the eastern periphery of a building PacNW ridge. Enough lingering moisture and cyclonic flow remains to support an isolated shower across southern Utah Monday and Tuesday afternoon/early evening, but this activity will be few and far between. Such a pattern also allows for largely seasonable to slightly above normal temperatures into midweek. Heading into the second half of the workweek, upstream PacNW ridge is shown cresting across the Great Basin, ensuring dry, stable and outstanding early Autumn weather with high temperatures ranging 5F to 15F above normal. As we head into the later portion of the week and into next weekend, there is some uncertainty introduced regarding the strength and timing of shortwaves progressing through the southwestern Canadian provinces and International Border region. Solutions range from keeping the ridge firmly in place to those with stronger grazing troughs that may offer a slight cooldown along with locally breezy conditions. Even members with the strongest troughs offer little in the way of precipitation as we head into next weekend, with only ~10% of the solution space offering light precipitation amounts by next weekend. && .AVIATION...KSLC...VFR conditions will persist for the KSLC terminal through the period. Cumulus buildups are expected into the early evening over nearby terrain, especially southeast of the terminal. There is a very low, or less than a 15% chance for a late afternoon/early evening shower approaching the terminal vicinity from the east. WNW winds, occasionally gusty up to 20kts, will continue through 1-3Z before diminishing and turning southeast. There is a 30% chance of volatility in winds after 03Z Sunday due to the presence of easterly canyon winds near the terrain east of the terminal. .REST OF UTAH AND SOUTHWEST WYOMING...An area of low pressure will move through southern Utah into Saturday evening, providing showers and thunderstorms, especially over the higher terrain east of I-15 and south of I-80, with coverage increasing as one approaches the CO and AZ borders. Largely VFR conditions expected, however can`t rule out brief mountain obscuration in briefly heavier convection, along with gusty and erratic winds. Canyon winds expected to develop along the lee of the Wasatch between KSLC and KBMC after 06Z Sunday, with local gusts near 30kts through mid-morning Sunday. && .FIRE WEATHER...A trough of low pressure currently centered near the UT/AZ border will shift northeastward through the weekend. Ongoing activity Saturday will diminish through the evening. While the atmosphere will begin to dry Sunday, lingering moisture will be sufficient for a widely scattered afternoon shower or two primarily across high terrain, but additional wetting rain chances remain minimal. On Monday a mostly dry cold frontal boundary will push through northern and central UT, and while some modest increase to winds and gusts are expected with this frontal passage, critical fire weather conditions are not anticipated. Thereafter on through the upcoming week high pressure is favored to settle into the region. This will promote a drying trend with daily minimum relative humidity values and overnight recovery trending downwards accordingly. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...None. WY...None. && $$ SHORT TERM...Warthen LONG TERM...Cunningham AVIATION...Van Cleave FIRE WEATHER...Warthen For more information from NOAA`s National Weather Service visit... http://weather.gov/saltlakecity