textproduct: Eureka

SYNOPSIS

Moderate to locally heavy rain will arrive for Del Norte and Humboldt Counties today into tonight. Rain is forecast to spread southward by Tuesday for Mendocino and Lake. More rain is forecast for the remainder of this week. Strong gusty winds will also be possible with each storm, especially late week and next weekend.

DISCUSSION

A strong low pressure over the the NERN Pacific, just in the Gulf of Alaska, will drive a series of frontal system to impact Northwest California today and into Wednesday, with moderate to heavy rain and gusty winds.

Satellite and Doppler radar imagery depicts the first of a series of frontal systems approaching Northwest California. As of 12 AM, light rain showers are observed moving northeast across Del Norte County, while a narrow band light to moderate rainfall approaches the northern coastal waters. A frontal boundary, along with a long plume of subtropical moisture ingested in the southwesterly flow will continue to approaches the area today into tonight bringing increasing chance of precipitation and gusty winds over the high elevations. This round will be almost exclusively focused on Del Norte and Humboldt counties. Cold air aloft will spread across the northern portion of the area today bringing increasing instability late this morning and afternoon, especially for areas north of Trinidad. CAMs show moderate to strong returns over Del Norte and far northern Humboldt late this afternoon. Hourly max rainfall rates of 0.10-0.25 inches is expected, with locally heavier rates over 0.50in/hr for SW facing aspects of Del Norte and Humboldt Counties. Much lighter rain rates are expected for Mendocino and Lake til perhaps Tue when moist plume sags southward and stalls out.

Another, stronger round of rain rain will begin to arrive and spread further South Tuesday into early Wednesday. This round will most likely have some periods of moderate to heavy rain Tuesday night, which may generate very minor urban flooding. This second round will spread further south with only a slight focus on the North Coast. Low elevation amounts with this round will most likely be between 0.5 and 1.5 inches with upper elevation amounts of 2 to 4 inches of rain. In this rain, even the southern most part of the area is nearly guaranteed to see wetting rain.

Southeast winds will also be gusty through the week. Peak wind gusts at lower elevations will most likely be 20 to 35 mph, with a 30% chance of impactful gusts over 45 mph on high coastal ridges. Winds gusts will most likely be strongest with the second round of rain Tuesday into Wednesday. ECMWF ensemble indicates potential for strongest winds Thursday or Thursday night, though there continues to be large spreads. Above average warmth and fairly high snow levels will severely limit all prospects for significant snowfall except over the highest mountain peaks.

There remains generally high confidence (80% of ensemble members) that a wetter pattern will continue through the end of December. Long range forecasts have placed a higher risk for a moderate to strong atmospheric river near the end of next week and next weekend. This could translate into heavy rainfall and wind gusts over 50 mph. Ensemble spread remains high but has gradually increased in confidence for a period of heavy rain. With preceding rain, some minor flooding will become possible. Lending support for wet and stormy weather through the end of December is CPC's 8-14 day outlook which has NW CA in a high risk for heavy precip, a moderate to high risk for mountain snow and a moderate risk for high winds.

AVIATION...06z TAFs

Generally MVFR conditions have built across the area even along the coast as an approaching storm system has lifted ceilings and inhibited any fog formation. Showers will most likely begin to build along the far northern coast before sunrise Monday. Showers will increase in strength and move south through the day with the strongest showers during the afternoon. MVFR ceilings with brief period of IFR are most likely through the day near the coast. More VFR to MVFR conditions are most likely for the southern half of the area that will remain more dry. Showers will linger overnight Monday into Tuesday with ensembles showing greater potential (50% chance) for more consistent IFR ceiling and some patchy fog overnight. /JHW

MARINE

After a long period of calm conditions, southerly winds have begun to increase in the northern waters as a storm system approaches the area. Winds will peak in the northern outer waters later Monday morning with gusts over 25 kts. Other zones will see some moderate southerly wind gusts but will generally remain calmer. Winds will be just strong enough to build short period seas over 6 feet int he northern outer waters through Monday night.

Winds will generally weaken for much of Tuesday, but a mid period westerly swell building over 10 feet will maintain moderately steep seas at least for the the northern waters through much of Tuesday. Another storm system will cross the area late Tuesday into early Wednesday. Southerly winds will again only briefly increase over 20 kts and be mostly restricted to the northern waters.

Calmer conditions will arrive again Wednesday though, once again, a mid period westerly swell up to 10 feet will likely maintain very moderately steep sea in the northern waters. A stronger storm system is expected later in the week. this will spread stronger south winds more into the southern waters with near gale gusts in the norther waters around Friday, though the potential for proper gales remains low (around 20 percent). /JHW

HYDROLOGY

Minor rises are expected on North Coast rivers from Monday through Wednesday. All main stem rivers are forecast to remain below Monitor or Action Stage. Minor flooding of smaller rivers, creeks and streams with poor drainage will be possible. Soil moisture is expected to continue increase or saturate late in the week with additional rain, increasing the risk of rockslides and mudslides, and minor flooding.

EKA WATCHES/WARNINGS/ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory from 1 AM to 11 AM PST Tuesday for PZZ450.

Small Craft Advisory until 11 AM PST Tuesday for PZZ470.