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KEY MESSAGES

* Gusty northeast to east ridge winds return late Friday through Saturday night, with chilly breezes for lower elevations. * Saturday will be the coldest day of the upcoming week, with hazardous wind chills near or below zero degrees for Sierra backcountry areas. * A slow warming trend with valley inversions resumes next week, then a weak weather system brings chances for light showers mainly near the Sierra by mid-late next week.

DISCUSSION

Today continues a similar quiet weather pattern, although a thinning of this morning's thick cloud cover should allow temperatures to warm up by a few degrees compared to yesterday. For the first time in about 2 weeks, much of the freezing fog around Mono Lake has diminished, with weather stations around the Lee Vining area climbing above freezing for the first time since the early January snow event.

Most of the region remains between weather systems through the rest of today, except for far southern Mono County being clipped by the outer edge of a closed low off the southern CA/Baja coast. The effects will be minimal, with 10-20% chances for a few snow flurries and sprinkles from Mammoth Lakes/Mammoth Mountain southward through early this evening. This low will eventually move inland across Baja/northwest Mexico this weekend with no further weather impacts to the eastern Sierra.

Meanwhile, a back-door cold front will march southward across eastern CA-western NV Friday afternoon and night. This will be accompanied by an uptick in N-NE breezes across lower elevations, followed by stronger NE-E Sierra ridge top winds overnight through Saturday night, with peak gusts near 50 mph projected during the day Saturday. When combined with the colder air mass, wind chills for higher backcountry elevations could dip to near or below zero degrees at times from Saturday morning through Saturday night. Anyone planning recreation activities in the high Sierra this weekend should have plenty of winter weather gear handy to avoid frostbite or hypothermia.

For lower elevations, the main effect of this front will be on Saturday with a notable temperature drop as daytime highs only reach the lower-mid 40s, slightly below late January averages. Lows for Saturday night plunge into the teens and single digits for typically cooler valleys. N-NE winds won't be particularly strong with gusts generally 15-20 mph, but will add some extra chill especially for the US-95 and US-6 corridors of Mineral/SE Mono counties, where these winds will be more persistent. These winds should mix out most of the haze and inversions Saturday, but this will be short-lived.

From Sunday through the early next week, we'll see a return of valley inversions as light winds prevail, although this high pressure ridge is less amplified compared to the mid-January pattern, limiting the inversion strength. Temperatures slowly rise each day starting Sunday, returning to the lower-mid 50s for western NV valleys and 40s for Sierra communities by Tuesday.

The next weather system is projected to reach CA/NV around the late Wednesday-Thursday time frame, but the majority of the ensemble guidance favors a weaker system with light precip amounts. Shower chances for the eastern Sierra/Tahoe regions (leaning toward snow) and northeast CA (mainly rain) are currently around 15-25%, dropping to less than 15% for western NV. MJD

AVIATION

VFR conditions and light winds will continue through much of Friday with valley haze reducing slantwise visibility around the western NV terminals. Dry conditions prevail except for a low 10-20% chance for -SHRA/-SHSN at KMMH thru 02Z this evening. Most of the thicker mid-high level cloud cover thins out this afternoon, but another band of clouds sweeps through tonight. This will limit freezing fog chances to about 20% around KTRK mainly between 10-15Z Friday, more of the patchy and shallower type.

A cold front brings a slight increase in N-NE breezes into western NV Friday afternoon with gusts remaining below 20 kt. For Friday night, a band of lower cloud cover may bring MVFR CIGS to Sierra/Tahoe terminals and obscuration of higher terrain around the western NV terminals. Sierra ridge wind gusts increase Friday night with peak gusts to 45 kt on Saturday, producing areas of turbulence near and west of the Sierra crest. MJD

REV Watches/Warnings/Advisories

NV...None. CA...None.