textproduct: Eureka

SYNOPSIS

Shower activity and the chance for thunderstorms increase today through Thursday. Breezy NW winds will blow over the entire forecast area through midweek.

DISCUSSION

A cold front passage yesterday forced a few sprinkles for the lower elevations with some light rain recorded in the higher terrain of Del Norte and Humboldt counties. The upper-level trough associated with this cold front will settle over the area as a closed low. This will force an influx of moisture to the area as well as creating breezy west-southwest winds are expected over the exposed ridges and channeled terrain through the week.

Thunderstorms are expected each afternoon this week as the upper-lvl low continues to impact the area. Colder air aloft will create some shallow instability this morning. If storms do form, they will be capable of produce brief, heavy downpours and a slight chance (10- 20%) of thunderstorms in Del Norte, Humboldt and northern Trinity counties. Breezy W-NW winds increase today along the coast and interior ridges Tuesday and Wednesday as the low flows southward. Gusts between 20 to 30 mph are most likely, yet localized gusts up to 40mph are definitely possible across the interior exposed ridges and channeled terrain. Come Thursday, the back side of the closed low will impact by increasing the chance of convective showers and thunderstorms. There is a 15-25% chance of thunderstorms across the interior on Thursday, with the highest chance over the northern Trinity County.

Ensembles and deterministic model guidances suggest a weak shortwave ridge building briefly filtering dry air across the area. High temperatures are expected to increase and become more seasonably for this time of the year. A series of shortwave trough may bring an increasing cloudiness and some isolated mountain showers this weekend. /ZVS

AVIATION

A frontal passage has disrupted the marine layer along the coast. Multiple cloud layers are being observed across the CWA. Valley fog is possible, especially for the North Coast. Rainshowers and weak thunderstorms are possible through the morning, yet minimal impacts are expected. Ceilings are forecasted to remain above IFR through the evening with scattered clearing and NW winds developing Tuesday morning. Gusty winds across all of NW CA extent vertically with North winds of 25-35kts at 2.5kft AGL. Low Level Turbulence is possible through the week, especially during the afternoons. Offshore flow aloft Tuesday will promote a higher chance of clearer skies overnight.

MARINE

A weak cold front passed over the area. Seas will rise sharply through the morning as a NW swell fills into the waters. Due to the cold front's past storm track, there was ample fetch and winds to create multiple NW large steep waves. This is particularly notable for the inner waters where steep seas will build before winds begin to build. This will force moderate to strong northwest breezes with frequent gusts to 25-35kts in the outer waters by this afternoon.

Moderate north winds persist during the day before strengthening and pushing closer to shore late this afternoon and evening. Steep, short period seas will persist during this time. North winds will peak Wednesday with near gale to gale force gusts developing. Gale watches have been issued to mark this hazard. There is high confidence that at least some of the area in the outer marine zones will have gale force winds (>=35kts), yet the extent of the area coverage of these winds is less confident as of right now. These strong winds will force steep, short period seas that will mix with the NW swell creating a hazardous sea state through the week. Calmer conditions will gradually arrive late week before northerly winds build again this coming weekend.

FIRE WEATHER

Breezy NW winds with gusts from 25 to 35 mph is expected Tuesday night through Wednesday over the exposed ridges and channeled terrain across the interior, then shifting to the coastal headlands Wednesday afternoon. Enhanced fire weather threat exists for zones 418 and 421 due to gusts up to 40 mph and low daytime RH values around 35 percent and overnight recovery values around 70 percent. Winds are the expected to diminish throughout the day on Wednesday for the interior. /ZVS

BEACH HAZARDS

Large mid-period seas will fill into the coastal waters early this morning. Steep sea will precede stronger north winds on area beaches, particularly those in Humboldt and Del Norte County. Seas build over 12 feet at 14 seconds early Tuesday may provide for some moderate sneaker wave conditions before north winds also push into the inner waters Tuesday evening. /JHW

EKA WATCHES/WARNINGS/ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 3 AM PDT Thursday for PZZ450-455.

Small Craft Advisory until 3 PM PDT Wednesday for PZZ470.

Gale Watch from Wednesday afternoon through late Wednesday night for PZZ470.

Small Craft Advisory until 3 AM PDT Wednesday for PZZ475.

Gale Watch from late tonight through late Wednesday night for PZZ475.