389 FXUS65 KSLC 090439 AFDSLC Area Forecast Discussion National Weather Service Salt Lake City UT 939 PM MST Tue Jan 8 2019 .SYNOPSIS...High pressure will dominate midweek, with a weak weather system moving through during the latter portion of the week. && .DISCUSSION...Evening water vapor and H5 analysis depict a high amplitude ridge axis becoming displaced downstream of the local area (axis stretches negatively from New Mexico NW to coastal BC). Meanwhile a deep trough remains largely in place off the pac coast with only a slow northeasterly jog over the last few hours. That track/trend will continue moving forward. In place overhead remains a mild airmass dominated by the ridge, with H7 temps 7C warmer than 24 hours ago. This can be noted in the 00z KSLC RAOB with H7 temps peaking now near 0C, and a descending subsidence inversion falling to just below crest level. Below that gets a bit more complicated in the northern valleys, as snow pack and the previously strong radiational cooling from last night's clear skies created another modestly strong inversion below 6kft, which is still maintained down through the boundary layer attm. Anticipating these two inversions will largely couple overnight. Would have anticipated a higher likelihood of rapid stratus development over the next 12-24 hours once again across the valley basins, this if not for the noted low level drying apparent in the aforementioned RAOB. Somewhat surprising really as some stratus/sprinkles developed below the lower inversion earlier today. Elevated flow in the mixed layer between said inversion levels just may have provided enough turbulent flow for some low level evacuation, as did increased high clouds potentially aiding similar above the subsidence inversion. It would take more analysis to peg down the reason, but it occurred. Shying away from redevelopment of stratus for now, with overnight cloud cover remaining fairly thin and high (cirrus) as such. Bottom line through the next 24hrs...dry and tranquil, mild with periodic high clouds. Will continue to monitor the evolution of the inversion through that time, but presence of CAA aloft beginning tomorrow should preclude an overly strong one from forming, even though it will be present. No updates at this time... PREVIOUS DISCUSSION...The next trough is expected to move through the forecast area Thursday evening with little impacts expected ATTM. The upper level pattern appears to be loosely organized with a majority of the jet influence remaining north and south of the forecast area. This will place Utah in a shear axis between the strongest energy remaining to the north and south of Utah. Any precipitation Thursday night and Friday morning is expected to remain light and short-lived with little to no accumulation expected, even in the higher elevation areas. Despite continued cooling aloft, the inversion is not expected to dissipate with this trough's passage either, leaving poor air quality in place through the week. In the wake of the trough, a building ridge is expected to develop over the northern Rockies Friday. A large scale blocking pattern is expected to be in place across the region at the beginning of the long term period, characterized by a highly amplified ridge centered across the northern Rockies. A weak shortwave trough is forecast to undercut the ridge and traverse the Desert Southwest Saturday, but should remain well south and as such have gone with a dry forecast. Eventually both the GFS and ECMWF break down the ridge and bring a shortwave trough into the Great Basin Monday, before lifting this wave through the forecast area Tuesday. Have increased POPs by 10-20 percent across the south Monday night, then area-wide Tuesday. accordingly. Temperature forecast is fairly low confidence across the valleys and will be dependent on how much mixing occurs in the short term, in addition to fog/stratus development. As such trended toward guidance for now but included haze through the upcoming weekend. && .AVIATION... Light and variable winds currently in place at the KSLC terminal are expected to become a prevailing southeast by 05z. Light south winds will persist into early Wednesday afternoon before shifting to the west- northwest around 19-20Z. A 30 percent chance exists that MVFR haze will develop Wednesday night. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...None. WY...None. && $$ DISCUSSION/AVIATION...Merrill PREVIOUS DISCUSSION...Bonnette/Seaman 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