textproduct: Eureka

KEY MESSAGES

* An early season storm is on track to bring moderate to heavy rainfall, slick roads, and strong southerly winds Wednesday.

* There is a slight chance of thunderstorms, mainly in Trinity County, this afternoon and evening.

*Another low will bring additional light rainfall and colder temperatures late in the week, with a chance for interior frost.

SYNOPSIS

A strong area of low pressure will move in Wednesday. Strong southerly winds develop with this storm system, along with moderate to locally heavy rainfall. A disturbance ahead of it will bring chances for isolated thunderstorms through the overnight hours for Trinity County and potentially some areas closer to the coast.

DISCUSSION

Instability associated with a shortwave disturbance brought showers and chances for isolated thunderstorms Tuesday afternoon. Forcing and instability will increase through the evening and overnight hours as the trough passes through.

A secondary, deeper upper low will then swing in Wednesday. Southerly winds aloft will be strong for an early season storm, with 44 to 55 kts down to 925 mb (around 2000 ft). Winds advisories have been issued for elevations above 1000 ft for Humboldt and Del Norte counties for gusts of 40 to 50 mph. Stronger gusts up to 60 mph will be likely for interior ridges of Del Norte. Despite the strong southerly flow aloft, little to no instability and a persistent low level inversion should inhibit mixing near the coast and in sheltered valleys. As a result, the strongest gusts are expected to remain elevation dependent, mainly above 1000 to 1500 ft, with lower elevations likely underperforming. NBM still holds moderate chances (40 to 55%) for wind gusts over 35 mph for the lower elevation coastal areas.

Expected rainfall totals continue to trend higher with this atmospheric river type storm system. Rates will be moderate to locally heavy, up to 1/2 inch per hour for select ridges. A broad area of the Northern CA will see 0.5 to 1.5 inches of total rain. The King Range and south to southwest oriented ridges of Humboldt to Del Norte have moderate to high chances (50 to 70%) of seeing over 2.5 inches.

As the first significant storm system of the season, as few early- season hazards are worth noting. Strong southerly winds may bring down more than typical weakened limbs and branches, particularly those stresses during the dry summer months. Additionally, accumulated oil and other roadway residue will result in slick driving conditions as rain initially develops.

A much colder and unstable area of low pressure looks to then dive down from the north Thursday through Friday. There will be a shot for thunderstorms, overnight interior frost, and additional light rainfall.

AVIATION

18Z TAFs.Strengthening southerly flow aloft will increase chances for low level wind shear and turbulence. Wave and lenticular type clouds have been identified already Tuesday afternoon. Chances for isolated thunderstorms will end overnight for areas around Cape Mendocino and mainly Trinity County. A strong front will quickly increase southerly winds after 12Z Wednesday. Southerly winds of 45 to 55 kts at 1500 to 2000 ft AGL will create a threat for low level wind shear into Wednesday evening. Moderate to heavy rainfall will lower VIS while CIGs generally hover in the MVFR to IFR levels.

MARINE

Southerly winds increased Tuesday afternoon with a passing trough. Chance for thunderstorms in the southern waters will end this evening. An early season, strong storm system will then move through, bringing strong southerly winds starting early Wednesday morning. Areas of sustained gale strength winds to 34 kts can be expected to sweep through the northern waters Wednesday morning through Wednesday afternoon. Winds will quickly ease Wednesday night. A mid period northwest swell will then fill in Thursday, potentially creating advisory level 10 ft seas.

FIRE WEATHER

Some lightning has been detected over the coastal waters as a shortwave trough moves in. Chances for isolated thunderstorms (10-15%) for mainly trinity county and perhaps around Cape Mendocino or coastal Mendocino will continue into tonight for quickly ending. Another area of low pressure will bring widespread wetting rainfall and areas of moderate to locally heavy rainfall Wednesday. Southerly winds will quickly increase starting Wednesday morning with the low, and will become strong through Wednesday evening. Gusts of 40 to 50 mph are forecast for the ridges from Cape Mendocino and northward, with higher gusts over the interior Del Norte ridges. Additional light rainfall and chances for thunderstorms are likely Thursday, while temperatures turn much cooler.

EKA WATCHES/WARNINGS/ADVISORIES

CA... Wind Advisory from 5 AM to 8 PM PDT Wednesday for CAZ101- 102.

Wind Advisory from 7 AM to 8 PM PDT Wednesday for CAZ104>106.

NORTHWEST CALIFORNIA COASTAL WATERS... Gale Warning from 9 AM to 6 PM PDT Wednesday for PZZ450.

Small Craft Advisory from 2 PM to 10 PM PDT Wednesday for PZZ455.

Gale Warning from 6 AM to 6 PM PDT Wednesday for PZZ470.

Small Craft Advisory from 9 AM to 10 PM PDT Wednesday for PZZ475.