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FXUS65 KREV 301030 AFDREV

Area Forecast Discussion National Weather Service Reno NV 230 AM PST Thu Nov 30 2023

SYNOPSIS

A series of weak weather systems will bring periods of light showers and increased higher elevation breezes today through Saturday night. The best chance for light snowfall arrives this evening through late tonight, creating some travel issues in the Sierra and possible slick valley roads for the Friday morning commute. Next week starts out drier with a gradual warming trend.

DISCUSSION

Divergent mid-upper level flow ahead of a shortwave trough approaching the Pacific Northwest coast is spreading increased cloud cover into northern CA-western NV. Low level moisture will also increase through this morning, with latest guidance spreading very light snow showers into northeast CA, northwest NV and the Tahoe basin during the day today. Snow amounts with this initial moisture push are looking quite modest, generally up to 2" near the Sierra crest but less than 1" for the main Sierra passes and higher elevations of Lassen/Plumas/Sierra counties. Snowfall rates look to be insufficient to allow much accumulation on paved surfaces during the daytime hours.

For this evening into the late night hours, the main shortwave moves inland across Oregon with a trailing cold front sliding across northeast CA/northwest NV. The boost in forcing will bring some increase in snowfall rates, with the latest blended guidance indicating around a 50% chance of at least 2" around the Tahoe basin, but less than a 20% chance of 4". Although these are not substantial snow amounts, it will be the first of the winter season at lake level for the Tahoe basin. For the Sierra crest above 7000 feet, additional snowfall this evening/night is most likely to range from 3-6". Elsewhere, there is a 60-70% chance of at least a dusting of snow for the foothills around Reno/Carson City/Virginia City, dropping to less than 40% for the valley floors. A few foothill sites and portions of northeast CA/far northwest NV could receive an inch or two of snowfall before the trough exits to the east with snow diminishing after midnight.
Winds will increase in higher elevations with ridge level gusts up to 50 mph tonight, while the front's passage may kick up the winds a bit for lower elevations with gusts 20-25 mph.

Road conditions could be patchy slick even in lower elevations for late tonight into the Friday AM commute. While many streets have been pre-treated across the urban areas, just the mere presence of snow for the first time this winter season can lead to an increase in travel delays. Higher resolution guidance shows more gaps in the snow coverage over far western NV compared to the standard resolution of the GFS/NAM 12km guidance, but with these weaker systems the higher resolution data can underestimate the coverage of light precip across lower elevations.

Another shortwave is on track to bring additional showers late Friday afternoon into Saturday, with warm advection aloft bringing one more chance of light snow and rain late Saturday night and Sunday. At this time, areas north of Susanville-Lovelock are more favored to receive this precip, with potential for a couple inches of snow across the Surprise Valley and far northwest NV Friday night-early AM Saturday. Elsewhere including the Sierra/Tahoe regions and the remainder of western NV, the snow chances are minimal, except possibly sparse accumulations up to a couple inches in close proximity to the Sierra crest west of Tahoe. Winds will increase further in higher elevations Friday- Friday night, with ridge level gusts up to 75 mph. There should be enough warming and mixing on Saturday followed by cloud cover to keep temps above freezing Saturday night for lower elevations, with snow levels rising to at least 5500 feet. However, if a few sheltered valleys in northeast Pershing County don't scour out the near-surface cold air, a bit of freezing precip could occur at the onset of the warm advection early Sunday morning. This is a low probability (~10%) scenario.

For early-mid next week, an upper level ridge will build overhead, shifting the storm track north of the Oregon border with light winds bringing some inversions and urban valley haze, although not as strong compared to this week. Daytime highs will rise to about 5-10 degrees above average--not an unusually big warmup, but after our current lengthy stretch of temperatures below 50 degrees, projected highs rising into the 50s and even near 60 by Wednesday will feel much less like early December weather. This ridge isn't likely to last long with an active Pacific jet stream prevailing and weakening the ridge later next week, although the resulting weather systems coming to the Sierra/western NV currently aren't projected to generate a significant precip event. MJD

AVIATION

* A series of weak weather systems are expected to track across the region today through the weekend, bringing increasing chances for showers and occasional breezy winds, mainly for higher elevations.

* While a few light snow showers may reach KTRK/KTVL this morning, the best chances for accumulating snow will occur this evening between 00-08Z. Snowfall rates this evening will be generally 1/2" or less per hour but will still produce IFR conditions with about 50% chance of at least 2" on runways at KTVL/KTRK, while KMMH has about 40% chance of at least 1". Western NV terminals could see a light dusting of snow (1/4" or less) between 04-08Z this evening, although it may not readily stick on all paved surfaces.

* Winds will increase at ridge level this afternoon and continue to increase with peak gusts of 55-65 kt by Friday night. Winds will be notably lighter for lower elevations so a zone of speed shear is likely to set up, but may occur above the LLWS definition of within 2000 feet AGL. These winds will still be capable of producing periods of turbulence and mountain wave activity from this afternoon into this weekend. MJD

REV Watches/Warnings/Advisories
NV...None.
CA...None.

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