textproduct: Eureka

KEY MESSAGES

* Periodically unsettled weather through late week.

* Seasonable tempertures, with a higher chance for frost and subfreezing temperatures for the interior late in the week.

* Very high uncertainty by the weekend with equal chances for moderate rain or warm and dry weather.

SYNOPSIS

A passing area of low pressure will stall off the California coast, brining periods of unsettled weather to the region through late week. A cold front will bring I broader chance for frost and some interior freezes late in the week.

DISCUSSION

An area of low pressure moving southward off N CA is evident on mid level water vapor imagery. A persistent deformation line off this feature brought some light rain and drizzle across an isolated sections of N CA Monday. The increased cloudcover will largely prevent colder temperatures capable of frost formation Tuesday night.

The low will continue progressing southward off the CA coast, eventually pulling east into S CA late in the week. The low will tap into some deeper moisture Wednesday, sending some wrap around moisture back northward. Showers will be likely Wednesday, but coverage is highly uncertain, particularly from the SW trajectory and over the higher terrain. Of note, there will be modest CAPE with the moisture arrival, and some thunderstorms will be possible. Chances are low, up to 10% for mainly southern Trinity to Lake County.

How the moisture evolves for Thursday is in question, but more showers for at least the far southern zones will be again possible Thursday. A dry cold front then sweeps the remaining moisture east Thursday afternoon. Conditions will quickly dry out overnight Thursday, allowing for temperatures to drop to chilly values, with some interior freezes through Friday morning and likely again Saturday morning.

By the weekend, ensemble and models show a remarkable amount of divergence. Roughly 50% show a strong, moist low dipping across the area with potential for 1-2 inches of rain along the North Coast. The other 50% show high pressure building generating warmer and drier than normal conditions. This makes the deterministic official forecast unusually uncertain for anytime beyond Friday. Historically, models tend to overdue Pacific storm strength in the extended forecast through this earlier transitional period to the rainy season.

AVIATION...6Z TAFs

Nearby low pressure cleared out the shallow stratus leaving persistent VFR conditions. Some isolated interior valleys may see some localized early morning fog, especially where light rainfall was recorded Monday. Otherwise, there is a low chance, up to 30% for some MVFR level stratus to reform through Tuesday morning. Winds remain light from the nearby low. Some high resolution guidance depict fog formation in the Ukiah valley Tuesday morning, but current observations show a dry environment non- conducive for fog formation.

MARINE

Generally gentle north winds will persist through Wednesday with some weak southerly winds in the inner waters. Weak winds will keep short period seas calm, but a mid period swell will quickly build up to 12 feet Tuesday, generating some marginally steep seas during the day. The swell will mostly decay below 8 feet by early Wednesday. Moderate north winds will gradually build in the outer waters Thursday. Winds will push closer to shore Friday as cold front passed by with some near gale gusts likely by Friday in the lee of Cape Mendocino. /JHW

FIRE WEATHER

Offshore winds Tuesday and Wednesday will bring a return of moderately dry conditions, but even then RH recovery will remain high with daytime RH struggling to get below 30 percent. High temperatures will broadly remain in the 70s. Weak instability Tuesday will bring higher mixing heights and more effective ventilation. Higher instability will arrive Wednesday when moisture from an area of low pressure wraps in. Isolated showers will be possible, or even a chance for a thunderstorm (10%) from the moisture surge Wednesday. Coverage of showers is highly uncertain, and the forecast will likely evolve as Wednesday nears. More precipitation is possible Thursday as the low slowly weakens and departs the the east. Cold dry air Friday will help bring RH back closer to 20 percent during the day. Uncertainty remains for the weekend regarding chances for precipitation, with an equal split for moderate rain or unseasonably warm conditions.

EKA WATCHES/WARNINGS/ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 8 PM PDT this evening for PZZ450- 455-470-475.