textproduct: Eureka

SYNOPSIS

A frontal system will continue to produce moderate to heavy rain and a threat for minor flooding through this evening. Showers tonight are forecast to diminish on Wednesday.

KEY MESSAGES

* Increased risk for urban and small stream flooding through this evening as a moderate atmospheric river brings widespread moderate to heavy rain.

* The Russian River at Hopland is forecast to reach or exceed flood stage this afternoon. The Eel River at Fernbridge is forecast to reach/exceed flood stage this evening.

* Wet and unsettled weather possible this weekend.

DISCUSSION

A strong atmospheric river storm impacting NW California will continue through through late this afternoon and early evening with moderate to heavy rainfall .

Satellite imagery depicts a slow-moving frontal boundary coupled with subtropical moisture streaming across the area this today. Rain amounts over the last 24 hours (12PM Monday to 12PM Tuesday) ranged from 2 to 4 inches from Del Norte County to Northern Mendocino County, with localized higher amounts up to 7.5 inches over the west-southwest windward facing terrain in southwest Humboldt, southern Trinity and northern Mendocino counties. Southern Mendocino and Lake counties saw 0.5 to 1.5 inches. Rainfall intensity will continue to increase for Mendocino and Lake counties this afternoon as the steady stream of subtropical moisture proceeds southward along the surface front. Urban and small stream flooding has been reported across portions of Humboldt and northern Mendocino counties. Flood Advisory remain in effect for Del Norte, Humboldt, southern Trinity and northern Mendocino counties.

Widespread moderate to heavy rain will likely decrease to showers this evening. A flood watch remains in effect until 10 PM this evening as it will take at least that long for water to drain and rivers to recede. Additional amounts of 0.5 to 1.5 inches are expected through early Wednesday morning across much of the region, with the heaviest rain rates focused over the west- southwest windward facing terrain.

Forecast from the river forecast center has all stages below minor flood stage, with the following exceptions:

* Russian River at Hopland: forecast to reach minor flood stage (15.0 feet) this afternoon.

* Eel River at Fernbridge: forecast to reach minor flood stage (20.0 feet) this evening. * There is a low (10-20%) chance for South Fork Eel River at Miranda to get close or exceed minor flood stage.

Conditions will begin to settle down on Wednesday. Considerable low level moisture will linger in the wake of the front and with warm air aloft, expect considerable low cloud cover and fog in the interior valleys and along the coast. Otherwise, we are looking dry until Friday when the stalled out upper low over the central Pacific edges closer to the coast. Timing and location of trough passage remains uncertain. Moisture transport under 250kg/m/s is forecast while PWATS increase. It not looking like any major precip at this time. There is a subtle hint for some convection or thunder as a mid level speed max noses toward the North Coast on Saturday in advance of the 500mb cold core. Surface temperatures should remain mild and above normal as we head into the last week of February and the first few days of March. /ZVS&DB

AVIATION...18Z TAFs

Rainfall rates will continue transitioning lighter, with lingering light showers Tuesday night. The downsloping and warming southeasterly winds ended with a shift to south- southwesterly. CIGs and VIS were able to lower to the IFR to LIFR levels response. As winds turn lighter to calm overnight, the chances for LIFR conditions, including fog formation, will remain. There is a broad 60 70% chance for continued CIGs below 1000 ft AGL and 40 to 50% for ceilings below 500 ft AGL. Probabilities for LIFR lessen to 30-40% after 7Z Wednesday when the front finally pushes through. JJW

MARINE

Southerly winds and steep seas continue to subside through the afternoon hours as a frontal system passes through. A small, mid period southwest swell is also moving in today. Winds will turn light to gentle overnight. There will be a brief surge of northerly winds Wednesday through Thursday morning, mainly over the outer waters beyond 10 nm and around Cape Mendocino. Speeds will remain below 20 kts with short period seas of 4 to 6 ft through Thursday morning. Northerly winds increase slightly stronger Friday afternoon. An area of low pressure approached Sunday with likely little impacts unless it takes a more northern track. The pressure gradient will increase behind it early next week with strengthening northerlies. There is currently a 45% chance for some gale strength gusts Monday with the northerlies. JJW

HYDROLOGY

Additional moderate to heavy rainfall with a moderately-strong atmospheric river is forecast to continue impacting NW California through late this afternoon and early evening. More minor flooding impacts are likely late this afternoon mainly across Humboldt and Mendocino counties due to additional rain falling in a short amount of time. Soils are are about 55-70% saturated and streamflow are running higher. Some impacts include urban and small stream flooding. In addition, small rock and mud slides are possible in areas of steep terrain that are already saturated. The Russian River at Hopland is still forecast to reach minor flood stage (15.0 feet) this afternoon. The Eel River at Fernbridge: forecast to reach minor flood stage (20.0 feet) this evening. There is a low (10-20%) chance for South Fork Eel River at Miranda to get close or exceed minor flood stage. The reminder of the main stem rivers are expected to remain below minor flood stage through this event. Our prolonged dry spells this wet season and low flows will reduce the threat for major or severe flooding. /ZVS

EKA WATCHES/WARNINGS/ADVISORIES

CA... Flood Watch until 10 PM PST this evening for CAZ101>115.

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 4 PM PST this afternoon for PZZ450-455-470-475.