Area Forecast Discussion
Issued by NWS Salt Lake City, UT
Issued by NWS Salt Lake City, UT
853 FXUS65 KSLC 131044 AFDSLC Area Forecast Discussion National Weather Service Salt Lake City UT 344 AM MST Wed Nov 13 2024 .SYNOPSIS...High pressure over the area will track east of the area later this afternoon. A weakening storm system will act to curb the warming trend over the area through Friday. Another relatively weak storm system will impact the area over the upcoming weekend. && .SHORT TERM (Through 12Z Friday)...As yesterday`s quick hitting storm system rapidly makes its way into the central United States, high pressure is moving over Utah and southwest Wyoming this morning, with the ridge axis nearly overhead. As this happens, another storm system is approaching the Pacific coast, and a few high clouds associated with the system are streaming into the area. The ridge will continue east today, with the ridge axis moving over western Colorado during the afternoon hours. This will be in response to the Pacific trough moving onshore as it weakens. What is left of the system is expected to move over the top of the ridge tonight into early tomorrow, bringing a rather weak and dry front into far northern Utah, acting to curb the warming trend just a bit. Thus, we`ll see maxes near climo today and up to 5F above seasonal normals for Thursday, making it the warmest day of the week. Southerly winds will be on the increase during the day Thursday as yet another Pacific storm system makes its way onshore. .LONG TERM (After 12Z Friday)...Two storm systems will cross the area during the long-term period, with the first bringing mountain snow and even minor valley snow accumulations late Friday into Saturday. More uncertainty lies with the second system, though this one has the potential to be colder and wetter than the first. The first storm system will take the shape of a longwave trough diving south into the western US, becoming split over the Great Basin with the parent trough moving eastward across Utah and a closed low forming well to our southwest. This closed low will track far to our south even as it eventually moves eastward, thus will not have any impact on our area. The parent trough, however, will bring precipitation chances and cooler temperatures to much of the area, particularly across northern UT and southwest WY where the best dynamics will be located. Cold air will filter into the area late Friday through Saturday morning, dropping 700-mb temperatures to around -10C and thus increasing snow chances down to valley floors (the exception being St. George). Any valley accumulations (<5000ft) should be minor as it will take time to transition from rain to snow overnight, with a 15% chance of seeing >1" of snow at KSLC (~4200ft). Currently, northern mountain accumulations are likely to remain sub-advisory, though we could see this change a bit more in the coming days due to shifts in the longwave pattern or mesoscale effects. Central and southern Utah will see less precipitation, likely less than 0.1" of water equivalent even in the mountains. After a brief break in the action on Sunday, another storm system is likely early next week, though there is plenty more uncertainty surrounding this one. We can generalize this uncertainty by grouping the forecast into two separate scenarios, where the main difference is the amplitude of the trough and thus how far south into southern UT it reaches. Scenario 1 (56% of ensemble members) favors a deeper trough, which would bring much colder temperatures and modest precipitation to much of the state. For example, 700-mb temperatures could drop to around -14C across northern UT, which would likely produce the coldest temperatures of the season so far. Chances for accumulating northern valley snow are higher with this scenario; currently, the NBM suggests a 40% chance of >1" in Salt Lake City (6% chance of >6"). Scenario 2 (44% of ensemble members) features a shallower trough that grazes across northern UT. This would likely limit impacts to northern areas, with 700-mb temperatures still dipping down to -10C across the north. In contrast, southern UT wouldn`t see much of a cooldown, if at all. Heading into mid-week, nearly all ensemble members favor a ridge setting up over the western US, though it`s unclear how long this ridge could potentially last. && .AVIATION...KSLC...Southeasterly winds are likely to last through the valid TAF period, with occasional gusts to 20kts through the afternoon (20-01z). VFR conditions will prevail. REST OF UTAH AND SOUTHWEST WYOMING...Winds will remain largely light and terrain-driven, with occasional gusts to 20-25kts out of the south this afternoon at many sites. VFR conditions will prevail at nearly all locations. Fog may develop at KLGU (60% chance) and KHCR (30% chance) early this morning before 15z, which could produce periods of LIFR conditions. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...None. WY...None. && $$ SHORT TERM...Traphagan LONG TERM/AVIATION...Cunningham For more information from NOAA`s National Weather Service visit... http://weather.gov/saltlakecity