textproduct: Eureka

SYNOPSIS

Moderate to locally heavy rain will arrive for Del Norte and Humboldt Counties Monday into Monday night. 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

The long stretch of unseasonably dry weather will come to an end this upcoming week as a series of frontal systems impacts NW CAL with bouts of moderate to locally heavy rain.

The first round of rain will build in Monday afternoon into Monday night. This round will be almost exclusively focused on Del Norte and Humboldt with rainfall rates of 0.10-0.25 inches per hour and locally heavier rates over 0.50in/hr for SW facing aspects of Del Norte and Humboldt Counties. HREF ensemble extreme has over 1 inch/hour which seems execessive. 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 only a 20% 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 Thu or Thu 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

Widespread VFR conditions today with light winds will continue through the evening before a frontal system approaches our area late tonight and tomorrow morning. The marine layer is expected to deepen tonight with lower clouds and rain arriving bringing conditions down to MVFR/IFR for the North Coast tomorrow. Gusty southerly winds are expected with this passage tomorrow morning as well increasing the threat of low level turbulence and mountain wave formation with winds aloft up to 40kts at 2500-3000ft. Valley fog inland tonight is not expected, yet still possible with about a 40% probability of ceilings under 500ft from 10Z to 14Z.

MARINE

Winds will strengthen this evening into Monday as an approaching cold front moves through the coastal waters. Gusts from 20-30 kts are expected across the northern waters, with the strongest across the northern outer waters with gusts of 15-25kts in the southern waters. Strong winds and steep-short period seas will promote hazardous conditions prompting for the hoisting of a small craft advisory across zone 470 from 11 P.M. this evening through 11 A.M. tomorrow. Winds diminish in the wake of the front tomorrow afternoon into Tuesday, becoming light to gentle southerly breezes. A mid- period westerly swell around 8 to 10 feet is expected to build in Monday night into early Tuesday morning. A series of frontal system are expected to bring strong southerly winds and steep seas mid- to late next week.

HYDROLOGY

Minor rises expected on North Coast rivers early to mid week. 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.

EKA WATCHES/WARNINGS/ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory from 11 PM this evening to 11 AM PST Monday for PZZ470.