McArthur, CA 96056 Weather

Key messages

* Dry and mild conditions with light winds continue through this afternoon.

* Chances of light rain and mountain snow return this evening through Friday for the Sierra.

* A storm system on Saturday and Sunday brings colder temperatures along with valley rain and impactful mountain snow above 7000 ft.

Discussion

Current satellite imagery shows partly to mostly cloudy skies over the region which expects to be the case through the rest of today. The latest model guidance shows an upper low off the coast of WA today moving south slowly along the coast today and Friday. The models also show a shortwave disturbance traveling around this low later today which then moves through our area tonight. This shortwave feature will cause the dry conditions currently seen in the region to end as light rain and mountain snow chances begin to move into the Sierra this evening. The Tahoe Basin continues to have a 10-20% chance of showers this evening that will increase to around 15-40% overnight. Sierra portions south of US-50 see around a 25-60% chance for showers with the higher end chances at the Sierra crest. Spillover continues to look limited, but portions of the Sierra Front will see 5-15% shower chances as well. The shower chances continue through Friday before gradually tapering off by Friday night. When looking at the NBM snowfall probabilities, portions of the Sierra above 8000 ft now see a 20-50% chance of 3+ inches with a 70-100% chance of 1+ inches of snow by Friday night. The latest QPF values show the higher elevations of the Sierra having up to 0.25 inches of liquid. Elevations below 6500 ft that see showers continue to see a trace up to around 0.05 inches of liquid. Snow levels do look to stay above 7000 ft tonight, but some snowflakes with showers in areas around 7000 ft are possible.

Going through the weekend, models are continuing to show a wintry weather system impacting the region on Saturday through Sunday afternoon. Forecast guidance shows the aforementioned low opening into a trough on Saturday and joining with another Pacific low as it passes over our region Saturday night into Sunday. This setup will bring around a 50-80% chance for valley rain and mountain snow to the Sierra and Sierra Front on Friday afternoon. These chances then increase to around 60-90% and spread into the NV Basin and Range in the evening and continue into Sunday. Precipitation chances begin to taper off Sunday afternoon and completely leave the region by Sunday night as the system moves farther east. Daytime high temperatures may reach to around 10-20 degrees below seasonal normals on Sunday with Sunday night lows around or below freezing in W NV and in the mid-teens to low 20s in Sierra communities.

When looking at the snow levels for this system, the Tahoe Basin has snow levels dropping to between 6500-7500 ft on Saturday evening before lowering to around 5750-6250 by Sunday morning. Mono County snow levels are between 7500-8000 ft on Saturday evening and then drop to between 6750-7500 ft by Sunday morning. When looking at the NBM snowfall probability for the duration of this system, Donner Pass has a 50% chance of 3+ inches of snow while elevations of above 8000 ft in Mono County see a 30-45% chance for 6+ inches of snow. The highest elevations of the Sierra do see around a 15-25% chance for at 12+ inches of snow as well. Due to this incoming impactful weather, a Winter Weather Advisory has been issued for Saturday morning through Sunday morning for Tahoe areas above 7000 ft and for elevations above 8000 ft in Mono County (See the Advisory for more details including snowfall amounts). Checking with CalTrans and NDOT (for Mt. Rose Highway) for the latest road conditions is recommended as travel through these areas will be hazardous. Other areas that see snowfall in the Tahoe area and Mono County that are not in these elevation based advisories may see between a trace to around 2 inches of snow. While snow may mix in with rain in portions of the Sierra Front, the NV Basin and Range mostly sees light to moderate rain through the duration of the system, with a 10% chance for thunderstorms on Saturday evening that could yield periods of heavier rainfall. Please continue to watch for forecast updates as there is still some uncertainty with this system as forecast models still are not in the best agreement in their solutions to this complex pattern.

By Monday, an upper ridge moves over the area, signaling drier conditions with slightly milder temperatures at least through Wednesday. Longer range guidance continues to hint at another system moving into the area late week, but there isn't too much more to say about it at this time as models are in great disagreement on details this far out. -078

Aviation

VFR conditions expect to continue through at least 30/00Z underneath a broken to overcast cloud deck over the region. While KREV/KCXP/KMEV will still have VFR conditions beyond 30/00Z, there is currently a 5-15% chance for isolated light rain showers around these terminals between 30/06Z-31/00z. As for the Sierra terminals, forecast guidance shows rain/mountain snow chances beginning as early as 03/03Z at the Sierra crest. KTRK/KTVL/KMMH will see around a 30-60% chance for showers going through the night and into Friday, which may cause MVFR conditions. Little to no snowfall accumulation is expected at the the Sierra terminals as measurable snowfall is expected to stay in higher elevations of the Sierra. With Sierra ridge winds increasing after 30/00Z, periods of mountain wave turbulence and LLWS may be possible.

Increased rain and mountain snow shower chances are forecast over the weekend within the region as an impactful storm system moves through. -078

.REV Watches/Warnings/Advisories: NV: Winter Weather Advisory from 8 AM Saturday to 7 AM PDT Sunday NVZ002.

CA: Winter Weather Advisory from 8 AM Saturday to 7 AM PDT Sunday CAZ072-073.