textproduct: Eureka

SYNOPSIS

Drier and colder weather is expected to last through Tuesday. Light rain return from south to north Wednesday into Thursday, followed by a frontal system with moderate to locally heavy rain, high mountain snow and gusty winds on Friday. Bouts of rain and gusty winds are forecast to continue into the weekend.

DISCUSSION

Dry offshore flow and adiabatic warming will keep NW California in fine weather through Tue. Fog and low clouds have been reforming again Sunday evening and early Monday morning in the interior valleys. Fog should clear out by early afternoon. Meanwhile, coastal areas have been largely clear of the persistent valley fog. We did issue another frost advisory even with a warmer airmass. With only thin high clouds to counteract longwave cooling, it may take only a few hours of calm winds for temps to plummet into the mid 30's.

Out short 4 day break in the wet and stormy weather will once again be coming to an end later this week. Latest operational model guidances shows the ridge will begin to weaken and shift eastward on Wednesday as a trough from Gulf of Alaska interacts with a subtropical cut-off low. A large swath of moisture in advance of the trough will spread northward from Central California on Wednesday (New Year's Eve). Some light rain or sprinkles will be possible as early Wednesday afternoon and evening for Mendocino, Lake, southern Humboldt and southern Trinity counties. The light rain will expand northward into early Thu (News Year's Day). 6-hourly rain rates increase to 0.10-0.20 inches with localized maximums up to 0.30 inches in the King Range. Higher rain rates will likely occur with frontal passage Thu night into into Fri morning. The CW3E tools for GEFS and ECMWF EPS are showing an increasing chance (50-75%) of IVT greater than 250 kg/m/s arriving on Friday across the area. Probabilities for AR1 and AR2 are still 50% or less from both the GEFS and EPS. ECMWF is higher with a 20% chance for AR3 in SW Humboldt and NW Mendo. NBM probabilities of 24-hours precipitation exceeding 1 inch range from 30-45% for areas south of Cape Mendocino 4AM Thursday to 4AM Friday, with up to 60% for the King Range. While chances increase to 40-60% from 4 AM Friday to 4 AM Saturday, with 25-35% chances for northern Humboldt, northern Trinity and Del Norte counties. Some localized urban and small stream is not completely out of the question with 6 hourly rates near 1 inch.

With 925mb winds around 65-75 kt ramping by Fri, winds are sure to crank up over the higher terrain and coastal headlands by Friday morning. A warning for winds will likely be necessary. Another potent frontal boundary will follow over the weekend and once again provide strong and damaging wind gusts.

CPC has a large area along the entire west coast in a slight risk for heavy precip and high winds Jan 5-8, so stay tuned.

AVIATION

Interior valley fog is expected overnight with LIFR conditions at interior terminals, including UKI. There is some uncertainty regarding westerly wind aloft that could result in less overnight fog development than the previous two nights. Other than the overnight interior and morning fog, VFR will prevail with light winds across Northwest California. /RPA

MARINE

Winds and seas will continue to subside this morning as ridging builds over the west coast. Light winds and relatively low seas will persist for the next several days. Winds will turn out of the south on Tuesday into Wednesday as the next storm system begins to develop south and west of the waters. What was looking like a rather weak system yesterday in the model guidance has transitioned to a more potent storm in the 2nd half of the week with potentially 2-3 fronts moving through the region into the weekend and early next week. Each front could bring strong south winds with gales. Steep seas will develop in response to the strong winds along with the potential for nearby developed westerly, steep, large swells. /RPA

COASTAL FLOODING

Another round of very high tides is coming up the 31st through 4th. At the North Spit Tide gauge on Humboldt Bay these are expected to be peak around 8.7 above MLLW on January 2nd and 3rd. There is still a lot of uncertainty on the winds, bu there is the potential for gale force southerly winds during this time period. The storm surge models are already showing nearly a foot of surge, but higher amounts are possible if the winds line up with the highest tides. This could yield quite a bit of flooding in the low lying areas around Humboldt Bay. Rain may also be occurring which exacerbate flooding surrounding Humboldt as creeks and low areas may not be able to drain during high tide. There are still a lot of variables, but this could bring 1 to 2 feet of saltwater onto to normally dry ground around Humboldt Bay. The impacts are less clear outside of Humboldt Bay and will be more driven by the wave size and running up much farther than normal. MKK

EKA WATCHES/WARNINGS/ADVISORIES

CA... Frost Advisory from 2 AM to 9 AM PST Monday for CAZ101-103- 109.

NORTHWEST CALIFORNIA COASTAL WATERS... None.