Marine Weather and Tide Forecast for Upper Lake, CA

DISCUSSION

Today through Wednesday
Early afternoon radar shows a band of light to moderate rain showers moving through portions of the Coastal Range and central/northern Sacramento Valley, mainly west of the I-5 corridor. Some RAWS sites are picking up around 0.10 to 0.25" inches of rain over the last 6 hours, so mostly light beneficial rain has been observed. Precipitation is expected to continue through the rest of the day, gradually spreading eastward with more widespread coverage by late afternoon/early evening. IVT values of 250 kg/ms with a southerly flow, and synoptic support of a closed low will help the Valley see beneficial rains and snow accumulations to the Sierra Nevada, southern Cascades, and Coastal Range.

Recent hi-resolution model trends have increased snow totals above 5000 feet slightly through Wednesday night. Overall impacts have remained the same however, and with increased confidence of at least Moderate winter weather impacts we have upgraded the Winter Storm Watch to a Winter Storm Warning, effective at 2 AM Tuesday through 5 PM PDT Wednesday. Heaviest snow, with potential snowfall rates of 1-2" per hour, will be Tuesday through Tuesday night, where some convective snow bands may develop. Any convective snow bands that develop may also lowering snow levels briefly, so some brief, heavy wet snow showers may be possible below 5500 feet on Tuesday. Wednesday snow levels will fall to roughly 4500-5500 feet, with mostly light lingering snow showers with 1-4 inches expected. Overall, snow accumulations of 12-18 inches above 5000 feet, 2 feet or more at the highest peaks, and Minor accumulations of 2 inches down to 4500 feet are in the forecast today through Wednesday.

Rain totals for most of the Valley and foothills increased with this afternoon's forecast run, but overall impacts look to remain unchanged. Minor rain impacts today, then Moderate rain impacts to the Valley and Foothills are expected tomorrow. The HRRR suggests the heaviest rain will move onshore with the 250 kg/ms IVT plume and closed low supporting moisture advection early Tuesday, where moderate to heavy at times rain will be possible in the Valley before moving into the Foothills by the late morning and afternoon. As the main energy moves inland, that is where our greatest chance for thunderstorms will also be across the region.
Looking at some forecast soundings across the area, shear values at 0-1 and 0-6km are not overly impressive, nor is forecast CAPE values at this time, however with the closed low over the area the potential for some weak rotation exists. Main threats with thunderstorms will be brief heavy rain, dangerous lightning, small hail, and a brief funnel/weak tornado. Valley rain will begin to taper off by Wednesday afternoon with light lingering rain showers possible through the evening.

Thursday through Sunday
By Thursday, mostly clear and dry conditions will overtake the area and continue into the weekend. A trough will build in the EPAC however, which will introduce a light shower chance to our higher terrains in the Sierra and southern Cascades Saturday and Sunday. Overall precipitation impacts look to be little to none at this point, as the trough will eventually move inland in SoCal by early next week. High temperatures will fluctuate Thursday- Sunday, with gradual warming Thursday and Friday then gradual cooling by the weekend. Highs will be in the 70s through this period, with cooler low to mid 40s - low 50s for the higher elevations.

AVIATION

A weather system is moving through interior NorCal this afternoon and will bring widespread Valley rain showers and mountain snow next 24 hours. Scattered MVFR/IFR conditions expected to develop around 00z at most TAF sites, then as we move into Tuesday morning around 06z widespread MVFR/IFR conditions at all TAF sites. Snow levels next 24 hours generally 6000-7000 feet; falling to 5500-6500 feet by 12z Tuesday. Surface winds gusting from south- southwest up to 25 knots in Valley; 35 knots in higher terrain beginning around 00z Tuesday.

STO WATCHES/WARNINGS/ADVISORIES
Winter Storm Warning from 2 AM Tuesday to 5 PM PDT Wednesday for Lassen Volcanic NP-Sierra (Cal-Tuo) Above 5000 ft-Sierra (El Dorado-Amador) Above 5000 ft-Sierra (Sierra-Placer) Above 5000 ft-Sierra (Tehama-Plumas) Above 3000 ft.