895 FXUS65 KVEF 070908 AFDVEF Area Forecast Discussion National Weather Service Las Vegas NV 108 AM PST Sun Nov 7 2021 .SYNOPSIS...Temperatures will remain above seasonal normals today as a dry weather pattern remains over the region. Early in the week an atmospheric river will move into central California and weaken as it moves south. This will bring the chance of high elevation snow (>8500ft) to the Sierras, as well as some minor low level rainfall in the northern Owens Valley. By the middle of the week, broad high pressure will build over the desert southwest bringing drier conditions and warmer than normal temperatures to the area. && .SHORT TERM...Today through Tuesday. The short term focus continues to be the prospect of an atmospheric river to impact the western CONUS Monday and Tuesday and what effect it will have to the Sierra, Owens Valley and overall Great Basin. What looking more certain: 1) Sierra snowfall should be rather substantial but it will be almost certainly confined to over 10000ft. Why? Because the brunt of the AR will be positioned too far north and will begin deforming as high pressure builds over the Pacific quickly after landfall. Snow levels below 8500 ft quickly rise as the parent low pushes northeast and heights begin to build. 2) Winds will be quite strong, but again confined to high elevations. This is due to strong ridgetop flow resulting in a robust mountain wave set up. This will be maximized overnight Monday into Tuesday morning as the low takes on a negative tilt and energy pushes over the Sierra. NBMv4.1 is showing max wind gust potential of over 60 mph at times as this feature pushes over but as it stands, conditions are not looking favorable, at least dynamically, for downslope winds. However, depending on how much precip is able to blow over, precip drag could bring higher winds down to the western extent of the Owens Valley. The 12Z ECMWF EFI highlight CA 519 and 523 as the zones most likely needing a wind product Tuesday of some kind, but at this time, looks advisory level. Where uncertainty is still high: 1) Snowfall totals for Aspendell (will be sitting very near the snow level). NBM 24 hour snowfall percentages show ~25% chance for greater than 2 inches but 5% of being greater than 6 inches. Either way this isn't advisory criteria but what is concerning is overall QPF values are much higher, with ~20% chance of >1" over 24 hours. While confidence is increasing that the snow levels should stay above the elevation of Aspendell, can't rule out much higher numbers if the snow level indeed stays below what is forecast. 2) QPF totals for the northern Owens Valley. WPC guidance has consistently kept values generally below a quarter inch for Bishop throughout the event, but that is falling between the 50th and 75th percentile according to the NBM. Thus, illustrating that higher values are possible (~25%). Feel the WPC number is quite fair given the fact that we'd be inheriting a deteriorating AR and it will be taking a northwest to southeast orientation by the time it reaches Bishop. To summarize, a very interesting and complex system should overall prove to be minor but chances for greater impacts are non-zero for our CWA. It's looking more like our most likely product issuance will be wind related for the Sierra and possibly San Bernardino. .LONG TERM...Wednesday through Saturday. The aforementioned trough and associated atmospheric river are forecast to be gone Wednesday, with decreasing clouds and post-frontal northerly winds expected areawide, with gusts of 20 to 30 mph possible down the Colorado River Valley. Thereafter, models agree on ridging building somewhere near or west of the Desert Southwest, meaning dry weather with above normal temperatures areawide. If the ridge builds overhead, winds would be light; if it builds farther west, northerly breezes would be felt down the Colorado River Valley. Otherwise, barring a major change in the expected pattern evolution, low impact weather is likely outside of the Colorado River Valley through the period. && .AVIATION...For McCarran...Winds around 8-12 kts will prevail into the early morning hours today favoring a south-southeasterly direction. Winds are forecast to shift back southerly and become gusty up to 25 kts during the afternoon. No operationally significant cloud cover forecast. For the rest of southern Nevada, northwest Arizona and southeast California...Another day of gusty southwest winds are expected for all terminals except KBIH. Cloud cover should remain above 15kft and remain FEW/SCT. && .SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report any significant weather or impacts according to standard operating procedures. && $$ DISCUSSION...TB3 AVIATION...TB3 For more forecast information...see us on our webpage: https://weather.gov/lasvegas or follow us on Facebook and Twitter