textproduct: Eureka

SYNOPSIS

Strong and gusty south winds are expected to ease today. Light to moderate and locally heavy rain, and mountain snow for elevations above 4500 feet today. Another frontal system is expected to bring a prolonged period of moderate to heavy rain and gusty winds late Monday through Tuesday night.

KEY MESSAGES

* Strong to damaging southerly winds will bring an increased risk of downed trees and power outages through this morning.

* Light to moderate and locally heavy rain today, with the heaviest amounts in Del Norte and Humboldt counties. Snow levels beginning about 4500 feet, rising to above 6000 feet Sunday evening.

* Another frontal system will bring moderate to heavy rainfall, mountain snow above 6000 feet, and strong gusty winds Monday through Tuesday night.

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

DISCUSSION

Strong gusty S-SE winds continued overnight. Peak wind gusts were generally around 40-50 mph for most lower elevations. Some higher elevation sites gusted over 60 mph. Wind sensor at Crescent City Harbor reported a peak gusts of 62 mph. There have been some power outages reported and reports of tree debris on the roads. Ensemble mean peak wind gusts from the mesoscale scale models are a bit too heavy with the gusts while ECMWF ensemble seemed slightly more in line with observations. All models have winds diminishing below criteria today. Our current wind warnings and advisories are set to expire at 10 AM Sunday morning and see no reason to extend these at this point.

It will remain breezy and locally windy today as an incoming frontal boundary moves onshore this morning and stalls this afternoon. Mesoscale model guidance continue to depict a thin high reflectivity line approaching the North Coast this morning. Locally heavy rain rates, 0.25-0.50in/hr, are highly probable (60-80% chance) for mainly Del Norte and higher elevations of Humboldt, particularly SW Humboldt. A few embedded elevated cells seem possible as well with HRRR indicating reflectivity cores over 50dBZ over the coastal waters with a thin wavy line. 500mb temps seem too warm and freezing levels too high for thunder. however.

Snow is also a distinct concern for elevations above 4500 feet and may result in hazardous driving conditions on highway 3 over Scott Mountain pass this morning. Snow levels will increase above pass level (5,400 feet) this afternoon.

The next frontal system with IVT's spiking up above 500 kg/m/s is expected to impact the area Monday through Tuesday night. Ensemble means and control members continue to indicate a longer period of moisture flux or a moderate AR conditions. Confidence is reduced by dry antecedent conditions and pre-existing low flows NBM 72-hour chance of exceeding 3 inches is above 80% for Del Norte and portions of Humboldt, southern Trinity and northern Mendocino counties from 4 AM Sunday through 4 AM Wednesday. Chances are lower 25-40% chance for around Humboldt Bay and lowest elevations in southern Mendocino and Lake counties. In addition, this system is expected to bring another round of gusty to strong south winds Monday night into Tuesday morning, especially for the coastal headlands and exposed ridges along the North Coast. The strong southerly winds will likely limit rain amounts for the Humboldt Bay areas. A broad brush flood watch has been issued for this next this longer duration AR. Once again dry antecedent conditions and low flows will limit the risk for flooding unless deep convection develops and rain rates exceed 1 inch/hour and sustain for a long duration over the same spot.

AVIATION...06Z TAFs

Main threats are low level wind shear and turbulence with strong winds mixing down to the surface. A frontal boundary will bring periods of moderate rainfall to isolated and brief heavy rainfall after 12Z. VFR to MVFR CIGs and VIS will be maintained outside of PROB30 heavier precipitation rates.

A passing strong area of low pressure and frontal system will maintain elevated southerly winds. Wind gusts of 40 to 55 kts are occurring over much of Del Norte and Humboldt counties. Winds aloft near 2000 ft AGL of 50 to 70 kts will create a high risk for dangerous low level wind shear and turbulence. Winds aloft and through the surface will slowly begin weakening after 14Z Sunday, but southerly winds of 35 to 45 kts near 2000ft AGL will remain a hazard into Monday morning. Downsloping southeasterly winds are raising ceiling heights. Chances for MVFR ceilings increase to 65 percent after 16Z Sunday. JJW/JLW

MARINE

Storm conditions are underway over the outer waters and around Cape Mendocino, wile solid Gale gusts and localized Storm gusts continue in the inners. Southerly winds will be particularly strong in the northern outer water (zone 470) where high end storm conditions with gusts up to 60 kts will likely continue into very early this morning. Seas are very steep, large, and hazardous. Seas will be particularly large in zone 470, up to 25 ft through Sunday morning. Winds and seas will slowly subside Sunday, but gale strength gusts will linger over portions of the waters through Sunday.

A secondary front will begin increasing southerly winds to better coverage of 34 kt gusts Sunday night through Monday. There has been an extension of the Gale Warning in zone 470 until early Monday morning. A Hazardous Seas Warning would most likely be required for multiple zones for steep seas of 13 to 15 ft.

Another strong front will crank up the southerly winds Monday night through Tuesday, with sustained winds up to 34kts. A Gale Warning can be expected through that period. Winds and seas will finally begin to subside late Tuesday. This break in large seas and strong winds looks to carry through much of next week as a shift to northerly wind direction develops. JJW/JLW

HYDROLOGY

A second atmospheric river is expected to impact NW Californian late Monday through Tuesday night. Moderate to heavy rainfall is expected for a durations of 24 to 36 hours and will bring the potential for rapid rises on rivers, streams and creeks across the region. The Weather Prediction Center (WPC) continues to include Del Norte County, Humboldt, Trinity, Mendocino and Lake counties in the Marginal Risk (at least 5%) of excessive rainfall for Monday and Tuesday. There is a moderate to high chance (75 to 95%) for 24-hr probability of precipitation exceeding 1 inch from 4 PM Monday through 4 PM Tuesday for most of the area, with highest chance in the higher terrain of Humboldt and Del Norte. Convective allow models will likely shed more light on hourly rates. Risk for urban and small stream flooding will increase on Tuesday. At this point, all main stem rivers are forecast to remain below minor flood stage. Stay tuned as forecasts, particularly river stage forecasts, can and do change.

EKA WATCHES/WARNINGS/ADVISORIES

CA... High Wind Warning until 10 AM PST Sunday for CAZ101-102- 104>106.

Flood Watch from Monday evening through Tuesday evening for CAZ101>115.

Wind Advisory until 10 AM PST Sunday for CAZ103-109-110-112.

Winter Storm Warning until 3 PM PST Sunday for CAZ107.

NORTHWEST CALIFORNIA COASTAL WATERS... Gale Warning until 11 AM PST Sunday for PZZ450.

Gale Warning until 1 PM PST Sunday for PZZ455.

Storm Warning until 4 AM PST Sunday for PZZ470-475.

Gale Warning from 4 AM to 11 AM PST Sunday for PZZ470-475.