textproduct: Eureka

SYNOPSIS

The first of a series of frontal systems will bring strong to damaging south winds, a period of moderate to heavy rain and mountain snow this weekend. Another frontal system is expected to bring a prolonged period of moderate to heavy rain, and mountain snow early into mid next week.

KEY MESSAGES

* Strong to damaging southerly winds will bring an increased risk of downed trees and power outages tonight through Sunday. Strongest winds expected Saturday evening into Sunday.

* Periods of moderate to heavy rain Sunday through Tuesday.

* Increased risk for minor flooding of small creeks and streams and urban areas with poor drainage early next week.

DISCUSSION

Wet and unsettled weather returns this weekend and will continue through early next week as a series of frontal systems impact northwestern California with strong to damaging winds, heavy rain, and heavy mountain snow.

A broad closed upper-level trough continues to drop from the Gulf of Alaska and settle over the Northeast Pacific (NEPAC). Southerly winds have started to increase in Del Norte and Humboldt Counties as a warm front approaches the area. The strongest winds will be over the exposed ridges and coastal headlands, where gusts of 40 to 60 mph are possible. Mainly light rain is expected through Sunday morning.

Winds are expected to steadily increase Saturday into Sunday, with strong to damaging south-southeast winds over the coastal headlands and exposed ridges. A broad surface low will develop well off the California Coast this morning, and track north-northeast through Sunday. This will favor a strong pressure gradient and a long- duration low level jet at 925 mb from 65 to 75 kts along the NW California Coast Saturday into Sunday. It will be more unstable and strong winds aloft most likely mix down to the surface starting this afternoon and continuing into Sunday, especially near or along the surface front. The strong winds are expected to develop from north to south, beginning tonight for Del Norte and Humboldt counties and spreading southward into Mendocino Coast by this afternoon, and persist through Sunday morning. Gusts up to 50 mph is expected for the Humboldt Coast, Mendocino Coast and northern Mendocino Interior. Up to 70 mph gusts are forecast for the coastal headland and exposed ridges in Del Norte and Humboldt County, with locally up to 80 mph possible over the more prominent exposed ridges. Even Del Norte Coast is expected to be impacted by damaging winds up to 60 mph Saturday evening into Sunday. A High Wind Warning is in effect for interior Humboldt, the King Range, and Del Norte County, including the coast. A Wind Advisory is in effect for the Humboldt Coast, Mendocino Coast, and portions of northern Mendocino County.

CAMs are suggesting a narrow line of organized convection activity with moderate to heavy rain moving from northwest to southwest early Sunday. A few thunderstorms are possible with this line with shallow instability Sunday morning, especially over the coastal waters and nearshore coast. Total rainfall amounts forecast up to 2.5 inches for Del Norte County from 4 AM Sunday through 4 AM Monday, and 0.75 to 1.50 inches for Humboldt County. Locally up to 3 inches is anticipated over the southwest windward facing terrain. Elsewhere, around 0.5 to 1.0 inches is expected for Humboldt, Trinity, and northern Mendocino counties. Locally higher amounts up to 2 to 3 inches are possible in the King Range. Southern Mendocino and Lake are expected to see a quarter to a half inch of rain.

Snow levels start out around 2000 to 2500 ft this morning, meaning there may be some light snowfall to lower elevations in Trinity County over some of the passes on Highways 3, 36, and 299, and perhaps a few snowflakes down to Weaverville. This is a warm system, so snow levels are likely to gradually rise up to 4000 to 4500 ft by this evening. This will limit snow impacts mainly to Highway 3 at Scott Mountain Pass. A Winter Storm Warning is now in effect for the potential of up to a foot of snow through Sunday. Snow levels continue to rise and are likely to be above 6000 ft by Sunday night. Snow levels continue to rise to above 8000 ft into early next week.

The next frontal system along with a moderate to strong Atmospheric River (IVT's greater than 500 kg/m/s) is expected to impact the area Monday through Tuesday next week. This have the potential to bring widespread moderate to heavy rainfall early next week. There still uncertainties on exact timing of the breaks in rain will be a big factor in the level of impacts. 48 HR NBM probability indicates there is a 50-75% chance of precipitation exceeding 2 inches across Del Norte, Humboldt, southern Trinity and northern Mendocino counties from 4 AM Monday through 4 AM Wednesday, and a 15-30% chance for around Humboldt Bay and lowest elevations in southern Mendocino and Lake counties. Stay tuned! /ZVS/JB

AVIATION

A compact surface low pressure system, associated with a broad closed upper low in the NEPAC, continues toward Northwest California. An associated coastal jet will develop along the coast early this morning, bringing gusty south to southeasterly winds across the region. The highest winds are expected for higher elevation terminals that may be around coastal headlands or exposed ridges. Before the winds mix down to lower elevations later this morning, LLWS will be an issue, especially for coastal terminals. Gusts from 35 to 45 knots are expected for most coastal terminals with slightly lower gusts expected for lower elevation terminals further south and east of the coast. This system will bring showery conditions across the region into the afternoon. Overcast skies will dominate with elevated winds keeping conditions VFR. /JLW

MARINE

Winds have turned southeasterly and will continue to increase through the day. Widespread gale conditions will spread through all the marine zones by early to mid morning. Conditions have reached the northern waters and will slowly spread south and closer to shore through the day. Confidence is high that storm conditions (gusts over 48 Kts) will effect the outer waters (90% of ensemble members) by early Saturday afternoon. Though gale conditions will build into the inner waters around this time, wind speeds will likely stall during the day before surging later in the evening. There is a 50% chance of at least isolated storm gusts in the inner waters Saturday evening. Very steep short period seas will build in excess of 22 feet in the northern waters, though the Cape will partially protect the inner waters and keep seas closer to 8 to 12 feet. Seas in the southern waters will also be slightly lower.

Strong gale to storm force winds will persist into Sunday. Winds will remain gale force but likely fall below storm force during the day Sunday with short period seas gradually falling closer to 12 feet. Short period seas and winds will gradually decline early next week with only a very minor mid period northwest swell up to 6 feet mixing with the short period seas. /JHW

HYDROLOGY

An Atmospheric River event is expected to impact NW California this weekend and into mid next week. A prolonged period of moderate to heavy rainfall will bring the potential for rapid rises on rivers, streams and creeks across the region. The Weather Prediction Center (WPC) included Del Norte County, Humboldt, Mendocino and Lake counties in the Marginal Risk (at least 5%) of excessive rainfall for Day 4 and 5 (Monday and Tuesday). There is a 60 to 80% chance for 24-hr probability of precipitation exceeding 1 inch from 4 PM Monday through 4 AM Tuesday, with up to 90% chance in the higher terrain of Humboldt and Del Norte.

Rapid rises of the main stem rivers is expected Sunday night through mid next week. At this point the CNRFC is forecasting all main stem rivers remain below flood stage during this event. There is a 30% chance for the Eel River at Fernbridge reaching or exceeding action/monitor stage on Wednesday. Meanwhile, there is a less of 10% chance for reaching or exceeding action/monitor stage for Mad River at Arcata. There is around a 10% chance for the Russian River at Hopland and the Navarro River at Navarro to reach flood stage. All other rivers have less than a 10% chance to reach monitor or flood stage. /ZVS

EKA WATCHES/WARNINGS/ADVISORIES

CA... High Wind Warning until 10 AM PST Sunday for CAZ101.

High Wind Warning until 10 AM PST Sunday for CAZ102-104>106.

Wind Advisory from 7 AM this morning to 10 AM PST Sunday for CAZ103.

Winter Storm Warning from 10 PM this evening to 4 PM PST Sunday for CAZ107.

Wind Advisory from 10 AM this morning to 10 AM PST Sunday for CAZ109-110-112.

NORTHWEST CALIFORNIA COASTAL WATERS... Gale Warning until 7 AM PST Sunday for PZZ450.

Small Craft Advisory until 7 AM PST this morning for PZZ455.

Gale Warning from 7 AM this morning to 1 PM PST Sunday for PZZ455.

Gale Warning until 7 AM PST this morning for PZZ470.

Storm Warning from 7 AM this morning to 4 AM PST Sunday for PZZ470.

Small Craft Advisory until 1 AM PST early this morning for PZZ475.

Gale Warning until 1 PM PST this afternoon for PZZ475.

Storm Warning from 1 PM this afternoon to 4 AM PST Sunday for PZZ475.