textproduct: Eureka

SYNOPSIS

Heavy rain likely tonight and Sunday, now for areas south of Del Norte county. A short break is likely Monday before more rounds of rain return mid week. Minor flooding and river flooding impacts are possible this afternoon and again by the middle of the week. Strong winds and lower snow levels possible mid to late next week.

Update

A strong area of low pressure is approaching the coast this morning. It is deepening faster and moving farther north than earlier model runs were showing. So this has changed the forecast. Stronger winds are now expected and this is drawing the moisture plume farther north than previously expected. Areas around Humboldt Bay and the Eel River delta are now expected 1.5 to 2.5 inches while the mountains of Humboldt county are expected to see 3 to 6 inches of rain by Sunday evening. Gusts of 45 to 55 mph are expected over the higher terrain and coastal areas of central and southern Humboldt, Mendocino and Lake counties. So have added a wind advisory to highlight this.

AVIATION...(06z TAFs)

Rain continues after the heaviest of periods and passage of moisture plumes to the area. Sunday will continue with less intensity but steady. Wind and subsequently low level wind shear will complicate flight conditions for KACV and KUKI. With the quick onset of high winds from the south, KUKI will see shear around 05-07z, lasting into the early evening with winds out of the south around 40-45kts at 2000ft. Flight categories will toggle back and forth from MVFR to IFR as periods of rain and lower visibility keep conditions variable. Most of the rain and gusty winds will be south of the 41 latitude as the AR aims from the southwest. /EYS

MARINE UPDATE

A fast moving low pressure with a more zonal flow aloft is transporting water vapor to the southern waters along with gusts that have a quick and sudden onset. Gales have been hoisted for the southern inner and outer waters to accommodate the hazardous situation. Small craft advisories will follow the Gales after the expected easing of the AR, Sunday at 21z. Showers are expected through Sunday with a swell diminishing from the northwest around 7- 8FT at 11 seconds.

PREV DISCUSSION

/issued 126 PM PST Sat Dec 20 2025/

SYNOPSIS...Heavy rain likely again through Sunday, especially south of Cape Mendocino. A short break is likely Monday before more rounds of rain return mid week. Minor flooding and river flooding impacts are possible starting tomorrow and again mid next week. Strong winds and lower snow levels possible mid to late next week.

KEY MESSAGES...

- Several rounds of heavy rain likely for the next week.

- Both small stream and main stem river flooding, trends higher into this weekend and early next week as more rounds of heavy rainfall occur over saturated grounds.

- Strong, gusty southerly winds possible Tuesday and Wednesday.

- Snow levels gradually drop by mid next week, and could be as low as 3500 to 4500 ft by Tuesday and Wednesday.

DISCUSSION...

Today through early Monday...The next round of rain arrives this afternoon and radar imagery is already showing this rain moving into southern Humboldt and Mendocino counties. The heaviest rain will largely remain south of Cape Mendocino, but still conditions will remain wet north of the Cape. Rain rates of over 0.25 to 0.5 inches an hour are possible in the higher terrain for much of Sunday morning. Total rain amounts of 3-6 inches are forecast for Mendocino and Lake Counties. Southern Humboldt and southern Trinity could still see 1-3 inches, with localized areas seeing up to 4 inches. Minor flooding impacts are possible Sunday with this extended period of heavy rainfall. See the hydrology section below for more details. North of these areas, including coastal Humboldt and much of Del Norte are forecast to see 1-2 inches. Southerly winds will be breezy, with gusts of 20-30 mph possible tonight in Mendocino and Lake Counties. Higher terrain and exposed areas could see locally higher gusts up to 40 mph.

Monday...The main pulse of moisture moves to the south of the area with stratiform rain transiting to lingering light showers. This will allow some time for rivers and streams to recede before the additional rounds of rain. Snow levels drop to 4000 to 5000 ft at this time, so any showers may be in the form of snow at Scott Mountain Pass along Highway 3. No more than a dusting is expected.

Monday Night through Wednesday...Yet another push of moisture is forecast to move over the area, but uncertainty is higher on where the heaviest rain will occur. There is a roughly 50/50 spread on where the plume will be centered: north or south of Cape Mendocino, but regardless rain is likely to return. NBM shows around a 60-80% chance for over 3 inches of rain in 48 hours Tuesday-Thursday morning for much of Mendocino, Lake, and southern Humboldt and Trinity Counties. Chances north of these areas drop below 30%. Chances for over 2 inches increase significantly. Forecast amounts are currently 2-4 inches south of Cape Mendocino and 1-3 inches north of the Cape, but this is subject to changed based on the storm track.

Winds will also start to increase starting as early as Tuesday afternoon, however this will be dependent on the position of the surface low developing off the northern California coast and there is high uncertainty. The "worst-case" scenario could produce wind gusts in excess of 50-60 mph with locally higher gusts in channeled terrain and higher terrain. However, the probabilities for this are relatively low. NBM gives around a 30-40% chance for much of Mendocino and Lake Counties to see peak gusts greater than 40 mph. This will need to be watched as this has the potential to bring strong, damaging winds.

Snow levels are forecast to drop Wednesday to between 3500 and 4500 ft. This is low enough to bring heavy snow to the high mountain passes including Scott Mountain Pass at Highway 3 and the highest passes along Highway 36. There is still some uncertainty on snow levels and where the precipitation will be focused, so exact snow amounts are uncertain. This cold system could support small hail showers along the coast as well, so this will need to be watched.

Thursday through Saturday...Uncertainty remains with the storm track late next week, but additional rain is likely through Thursday. NBM maintains a 30-50% chance for 2 inches in 48 hours Wednesday-early Friday from Cape Mendocino and southward. Small hail showers and interior snow may continue through Friday if precipitation continues. A break in precipitation may finally arrive by Saturday. JB

AVIATION...(18z TAFs)...Doppler radar depicts showers moving onshore across Mendocino and southern Humboldt counties late this morning. IFR ceilings around 500 feet have been impacting UKI, with VCSH. This is expected to improve to VFR during the next hour. While VFR conditions are observed at the coastal terminals along the North Coast. Otherwise, conditions are expected to deteriorate this afternoon and evening from south to north, with rain increasing in coverage. Expect VFR to MVFR conditions at all TAFs terminal, dropping to IFR/LIFR conditions in periods of heavy rain this evening and tonight. Surface winds from S-SW increasing to 5-15 kts late tonight, with occasional higher gusty winds at UKI. Winds aloft are expected to increase as well tonight into Sunday. Low level wind shear (LLWS) from 35 to 45 kts around 2000 feet is expected to develop at KUKI and KACV as a result tonight. /ZVS

MARINE...Light to gentle winds gradually shifting from north to south this afternoon, while scattered to numerous showers are moving across the waters as the next storm system approaches. Southeast wind are expected to rapidly increases to strong gusts winds around 25 kts this evening into tonight, especially south of Cape Mendocino. Wind waves will build to around 6-8 feet at 6-7 seconds across the southern waters on Sunday morning, promoting hazardous conditions for small crafts. Have to issued a Small Craft Advisory for the southern waters in response the steep waves from Sunday morning through Sunday night. Winds gradually diminish and shift to west- southwest throughout the day on Sunday, with gentle to moderate breezes into Monday.

Monday, another storm system is expected to move north of the area. This will bring moderate to strong southerly winds north of Cape Mendocino, while generally light to moderate breezes across the southern waters. Monday night into Tuesday, winds are expected to weaken. A larger mid-period westerly swell around 9-11 feet at 12-13 seconds arrives Monday night into Tuesday.

The next storm system likely to bring gales on Wednesday through Thursday. There is a 75-85% chance for wind gusts exceeding 34 kts south of Cape Mendocino on Wednesday and Thursday, while chances increase to 70% across the northern outer waters on Thursday. A larger mid-period south-southwest swell build across the waters on Thursday. /ZVS

HYDROLOGY...Additional rain continuing through Sunday has the potential to bring minor flooding impacts. The heaviest rain is expected to be from about Cape Mendocino and southwards. This will again pose a threat for quick rises in streams and creeks along with rock and mudslides. Risk for rock and mudslides will again increase and could impact travel on area highways. At this time, only the Russian River at Hopland is forecast to exceed flood stage, and is expected to peak Sunday afternoon. The Eel is forecast to hit monitor stage Sunday night, but remain well below flood stage. While no other rivers are forecast to reach flood stage, heavy rain focused on the Eel, Navarro, and Mad, river basins could support some or all of these basins to run higher than forecast.

The next weather system on Tuesday and Wednesday will have a higher potential for main stem rivers to reach flood stage. The Russian River at Hopland has a 55 percent chance of exceeding flood stage Tuesday night. The Navarro River has a 40 percent chance. The Eel River has a 30 percent chance of reaching flood stage on Wednesday. These mid-week systems have a particularly high level of uncertainty in the location and amounts of rainfall so these river levels will need to be watched.

EKA WATCHES/WARNINGS/ADVISORIES

CA... Flood Watch through late Sunday night for CAZ108.

Flood Watch through Monday morning for CAZ109>115.

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory from 6 AM to 9 PM PST Sunday for PZZ455-475.