533 FXUS65 KSLC 101648 AFDSLC Area Forecast Discussion National Weather Service Salt Lake City UT 1048 AM MDT Wed Oct 10 2018 .SYNOPSIS...The upper level low pressure system over extreme southwest Wyoming will continue east away from the forecast area this afternoon. A second weather disturbance will reach far southern Utah by late tonight, and impact southern and central Utah through Thursday. && .SHORT TERM (THROUGH 12Z SATURDAY)...The upper low currently positions over extreme southwest Wyoming will move east out of the forecast area by early afternoon. The wraparound northwest flow on the back side of this feature along with the moist and somewhat unstable air mass has maintain mostly light/moderate precip over the northern mountains and adjacent valleys this morning. This precip has shown a decreasing trend in the areal coverage and intensity the past couple of hours. This trend will continue into early afternoon, with most if not all precip ending by late afternoon. Southern Utah will see a chance for precip late tonight through Thursday. A shortwave diving south along the northern California coast will turn east later this evening, reaching extreme southwest Utah by early Thursday morning. Anticipating a gradual increase in clouds overnight, with showers holding off until late tonight. Precip should expand north and east as dynamic support from the now weakening shortwave moves east along the Utah/Arizona border Thursday. Building heights Thursday night/Friday bring an end to precip across the region. The next shortwave diving south out of western Canada will bring some increase in clouds Friday night, with any precip holding off until after 12Z Saturday. Issued an earlier update to remove headlines and make a few adjustment to the forecast narrative. .LONG TERM (AFTER 12Z SATURDAY)... The synoptic pattern over the West at the start of the long term period will be characterized by a mid-level ridge centered over the Pacific with a cut-off low pinned to its south off the southern California coast. A shortwave is progged to dive southward along the eastern periphery of the Pacific ridge Saturday into Sunday. Unfortunately 00Z guidance has diverged on the track of this wave with the EC/FV3 favoring a more western track while the CMC/GFS(and majority of GEFS) favor a more eastern track. The further west solutions would both advect a cooler airmass into the area (H7 temps around -10C in northeastern parts of the area) and also come with chances of snow for northeastern parts of the area. Conversely only modest cooling is advertised in the GFS/CMC solutions with almost no precipitation chances as the wave's dynamics are focused well to our east. To account for these discrepancies went with a blended solution slightly weighted towards the cooler EC/FV3 camp this package. The potential for a frost/hard freeze in valley locations Sunday and/or Monday AM remains although this will be dependent on how cold the airmass gets (which is a bit more uncertain). Additionally the northerly pressure gradient and cold advection in the wake of this wave could result in gusty canyon winds in SW Utah Sunday into Monday AM. The pattern trends warmer and drier next week as the Pacific ridge builds inland. Although a general pattern change looks likely, one caveat would be the cutoff low mentioned at the start of this discussion. This is progged to more or less meander around the southwestern US next week, bringing cooler and more unsettled weather wherever it happens to track. However, given the decaying nature of this feature and guidance's typical struggles with cut-off lows more or less ignored it for this forecast package. && .AVIATION...Periodic MVFR ceilings will persist in the moist/unstable air mass through 18Z-19Z. Looking at a gradual increase in ceilings/visibilities as the center of the upper level low pressure system over southwest Wyoming moves east away from the area. Winds out of the east this morning will turn to the north-northwest as precipitation ends behind the exiting low pressure system. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...None. WY...None. && $$ CONGER 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