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FXUS65 KREV 031004 AFDREV

Area Forecast Discussion National Weather Service Reno NV 204 AM PST Sun Dec 3 2023

SYNOPSIS

Showers near the Sierra crest, far northeast CA and northwest NV and breezy winds will wind down today, with high pressure bringing a few days of drier and warmer conditions and lighter winds to the region. Additional fast moving storm systems will bring periods of breezy winds and additional chances for rain and mountain snow showers for mid to late week.

DISCUSSION

The southern edge of a Pacific moisture flow produced periods of showers across the northern Sierra, northeast CA and northwest NV from Saturday through the overnight hours. Some minor snow accumulations occurred with chain restrictions for upper sections of the main Sierra/Tahoe area passes including Donner, Echo, Mt.
Rose, and Carson Pass. Snow levels have continued to rise to at least 7000 feet as an upper level ridge advances toward CA/NV, bringing a warmer air mass. The wettest area was the northern Surprise Valley, where almost 0.80" rainfall occurred at Ft.
Bidwell. Winds were also pretty gusty with 50-60 mph gusts in the Surprise Valley, in the foothills near Verdi, and even briefly at the Reno airport. Ridge top gusts peaked in the 80-100 mph range, and some gusts near 40 mph were still occurring outside the NWS Reno office between midnight and 1 AM.

As the high pressure ridge continues building into CA-NV today, the lingering shower activity will end as the day progresses, and winds will ease up. This ridge will also bring the start of a warming trend with highs today climbing into the lower-mid 50s for lower elevations, and 40s for Sierra communities. Highs will have a reasonable chance of reaching 60 degrees for several western NV valleys Monday-Wednesday, the warmest levels since mid-November.
Lighter winds could bring minor haze to urban valleys again on Monday-Tuesday, although the inversions won't be as strong compared to last week. Potential for freezing fog increases in the typical fog prone valleys of northeast CA and parts of I-80 around Truckee for late Monday night-Tuesday AM.

The next weather system is projected to arrive Wednesday with increasing winds, and precip chances returning to the Sierra and northeast CA-northwest NV, and a few passing showers across western NV. This system will be relatively warm, with projected snow levels generally near or above 8000 feet for the Sierra during the bulk of the storm, possibly dipping to near 7000 feet as the precip tapers off late Wednesday night.

On the heels of the midweek system is a secondary shortwave passage most likely for Thursday-Thursday night, with shower chances possibly lingering into early Friday. This system looks to be notably colder with projected snow levels dropping from near 6000 feet at the onset to near 4500 feet behind the front early Friday morning. The majority of the GFS/ECMWF ensemble guidance has trended weaker overall with this system's precip potential with the most likely scenario keeping Sierra snowfall below 6".
However, the Canadian ensemble guidance shows a more promising snowfall potential for the Sierra, and a couple of ECMWF outliers produce Sierra snow totals of 1 foot or more from Thursday-early Friday. Given this variance, there is some reduced confidence for the late week system in terms of rain/snow amounts, although there is notably higher confidence for temperatures cooling to near or below average for Friday into next weekend. MJD

AVIATION

* Gusty west-northwest flow aloft will keep wind ridge gusts of 50+ kts going through this morning, with continued turbulence and periods of LLWS. Surface wind gusts of 20-25 kt at the far western NV terminals will diminish after daybreak, with lighter winds across all areas from later today through Tuesday.

* Widespread cloud cover will continue today and much of tonight, although CIGS will generally remain at VFR levels for most of the main terminals. The only exceptions are periodic MVFR cigs thru 18Z today at KTRK/KTVL, and if enough clearing occurs late tonight, patchy FZFG could develop at KTRK for early-mid morning Monday (about 20% chance). With clearing skies Monday and most of Monday night, the FZFG potential at KTRK increases to at least 70%.

* Additional weather systems will bring increasing winds and clouds across the region, and chances for showers mainly for the Tahoe area terminals Wednesday-Friday. MJD

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

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