textproduct: Eureka

SYNOPSIS

A cutoff low is approaching the region. Rain showers, mountain snow and breezy winds are expected tonight through Wednesday. There is also a chance for thunderstorms, mainly on Tuesday afternoon. A stretch of drier weather is then expected to begin late in the week.

DISCUSSION

A frontal boundary ahead of the approaching upper level low brought a round of rain today. Snow levels were around 6000 feet aside from northeastern Trinity with locally lower snow levels around 5000 feet. Some areas will see a short break in the rain behind the front this afternoon. Generally showers are expected to continue tonight and Tuesday as the upper level low slowly approaches the area and then moves overhead. Tuesday afternoon as the upper low moves overhead the potential for thunderstorms increases through the afternoon. The HREF is showing 200 to 400 j/kg of surface CAPE and lapse rates aloft of around 7C/KM. This should be be enough to develop some thunderstorms. A few of them could be strong with around 30 to 35 kt of deep shear. They will be the most likely in Mendocino and Lake counties in the afternoon. This is also expected to lower snow levels to around 4000 to 5000 feet Tuesday morning. Snow levels are expected to rise in the afternoon. For now just have the winter weather advisory out for the far northern portion of Trinity county. Showers are expected to linger into Wednesday as a shortwave moves down the back side of the low.

Thursday and Friday high pressure is expected to build into the area bringing dry weather to the area. For the weekend mainly dry weather is expected, but there is an upper level low to the northeast of the area. The ensemble clusters are showing different positions of this low. If the solution with low closer to the area verifies this may allow a few convective showers over the mountains each afternoon. MKK

AVIATION

Conditions will vary through the TAF period. A frontal boundary will continue to funnel showers over the area for the next few hours before wavering. These showers could lead to IFR/MVFR conditions due to degraded visibilities and locally lower ceilings. High resolution data shows a break in the rain for North Coast terminals from around 20Z - 08Z. Inland terminals can expect stubborn low clouds to remain through the TAF period and gustier winds that could mix down to terminal spaces. A 925mb jet is weakening, yet LLT is still possible until around 21Z as well. Conditions will degrade after 08Z through the end of the TAF period as another push of storms materializes over NW CA. Expect a return of IFR/MVFR conditions for Tuesday morning. DS

MARINE

Southerly winds continue as a surface low pressure system circulates off the coast of California. This low pressure to our west will continue to force southerly winds for the coastal waters through the evening. As this low advances close the coastline, winds will become variable and light. Winds after the storm system migrates eastward will become northerly. Small (<3ft) short period seas are expected with these wind shifts. A NW swell of around 9- 11ft@13s will diminish through the evening into Tuesday. There is also a 10-15% chance for thunderstorms this afternoon into Tuesday. This increases the likelihood for Special Marine Warnings to be issued near storms. sporadic gusty winds are possible near storms as downdrafts accelerate along the ocean surface.

Seas are to remain relatively low through Wednesday before northerly winds increase later this week, especially in the afternoons of Thurs., Fri., and Sat. These winds will force larger, steep period seas and are currently at around a 20% probability of gale force winds in the usual windy spots along the coast- downwind of Cape Mendocino and Point St. George. This northerly wind pattern is expected to last into Saturday. DS

EKA WATCHES/WARNINGS/ADVISORIES

CA... Winter Weather Advisory until 11 AM PDT Tuesday for CAZ117.

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 2 PM PDT this afternoon for PZZ455-470-475.