textproduct: Eureka

SYNOPSIS

A mainly dry day is expected Saturday. More heavy rainfall returns Saturday night into Sunday. Monday is expected to be relatively dry, however the active storm track continues to bring additional heavy rainfall and a flooding threat, strong winds, and lowering snow levels much of next week.

DISCUSSION

Saturday morning is expected to see dry weather with more rain starting to moving into the area in the afternoon and evening. This is expected to arrive in Mendocino and Lake counties first where the focus of the rain is expected to be. This rain is expected to continue through Sunday afternoon. IVT Values from the GFS and EC ensembles show nearly 24 hours of over 500 kg/m/s. There are still some differences in the ensembles, but confidence is fairly high that there will be quite a bit of rain. The current forecast is showing 3 to 6 inches in Mendocino, Lake and southern Trinity. Farther north 1 to 3 inches is expected in Humboldt, Del Norte and northern Trinity counties. Have expanded the flood watch north into southern Trinity county. For now it looks like southern Humboldt will see around 2 to 3.5 inches which isn't expected to be enough to cause much flooding. The NBM does show the potential for close to 6 inches in southern Humboldt if there was a shift north with the event. So this will need to be watched as it gets closer. See hydrology section for more details.

Gusty winds are also expected with this event over southern Mendocino and Lake counties. 850MB winds on the NAM over southern Mendocino and Lake counties are expected to be near 45 to 50 kt. However, the strongest winds are expected to remain aloft with a fairly stable layer near the surface. This stable layer is also expected to limit the potential for thunderstorms. Snow levels with this next system are expected to remain high through the event, but start to come down as early as Monday.

Sunday night into Monday the main system is expected to move out of the area, however southwest flow continues and this is expected to keep skies clouds and some rain showers around. Snow levels are expected to be around 4,000 to 6,000 feet, but any snow that does fall should be fairly light.

Monday night into Tuesday the next weather system is expected to move into the area from the south. However, there is still quite a bit of uncertainty on when exactly this will move in. Heavier rain is expected initially in southern Mendocino and Lake counties gradually spreading north on Tuesday. Snow levels currently are expected to be around 4,000 feet in the north and 6,000 feet in the south. This will likely bring snow to Scott Mountain Pass on Hwy 3. There is certainly the potential for this colder air to move slightly north or south and impact hwy 199 and hwy 299. So this will need to be watched as it gets closer. Rainfall amounts are expected to be lighter with this colder system, but with the previous rainfall this may cause some flooding. See the hydrology section for more details. There is also the potential for some stronger winds with this system in Mendocino and Lake counties, but there is a high level of uncertainty with this still.

Wednesday may see a break in the rain or least a break in the heavier rain. However snow levels may be lower if there is any precipitation and there could be some light snow. Heavier rain is expected to return Wednesday night and Thursday. Again, this looks like a colder system. Currently the NBM is showing snow levels around 4,000 feet, but this could easily end up a thousand feet higher or lower. This will also bring the potential for some small hail. Additional rain and snow is possible on Friday with generally drier conditions possible by Saturday. MKK

AVIATION...(06z TAFs)

Upper level winds are quite strong but have not mixed down to effect landing approach with low level wind shear. The recently departed Atmospheric river has left standing water and flooded streams and could have standing water on runways or taxi. Post frontal showers have eased but another integrated water vapor plume is due by late Saturday afternoon or evening. This round will be focused on Mendocino and Lake county terminals. UKiah will likely have reduced visibility on the backside of the front with showers and ceilings at or below 15,000ft. Otherwise expect an unsettled weather pattern for the next few days with flight categories variable. /EYS

MARINE

A west to northwest swell has been building, and has reached around 8-10 feet at 11 seconds -per the latest buoy reporting. This will slowly diminish Saturday.

Another weather system is expected Saturday night into Sunday yet there is wide variability in the model solutions. The models are currently struggling to resolve the location of a strong area of low pressure and where it will exactly track. The locations of this storm will dramatically impact the strength of the coastal winds, so looking at multiple models can give a better idea of the potential winds formation. The NAM is now showing weaker winds more like the GFS, yet the ECMWF seems to capture the influence of the coastal terrain the best so a 2:1 blend has been made with the previous forecast. This yielded winds of around 20 kt. This seems reasonable for now, as confidence remains low, yet there is still the potential for a stronger winds with only a slight variation in the forecasted strength and/or track of the low.

Monday and Tuesday the winds look to generally remain fairly light with the next storm system likely to bring gales on Wednesday or Thursday. MKK/EYS

HYDROLOGY

Additional rain starting Saturday evening and continuing through Sunday has the potential to bring flooding. The heaviest rain is expected to be south of Cape Mendocino. It may extend into southern Trinity county so have added a flood watch there. 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, none of the main stem rivers are forecast to exceed action/monitor stages with this next system, although the Russian river likely will get the closest. 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 35 percent chance of exceeding flood stage Tuesday night. The Navarro River has a 20 percent chance. The Eel River has a 35 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 from Saturday afternoon through Monday afternoon for CAZ108>115.

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 3 AM PST Saturday for PZZ470.