textproduct: Eureka

KEY MESSAGES

* Rain showers possible Wednesday afternoon through Thursday morning, mainly in the south and interior areas.

* Seasonable temperatures, with a higher chance for frost and subfreezing temperatures for the interior late in the week.

* Very high uncertainty by the weekend with equal chances for moderate rain or warm and dry weather.

SYNOPSIS

A passing area of low pressure will stall off the California coast, brining periods of rain showers Wednesday afternoon through Thursday to the region. Behind this there is a chance for frost and some interior freezes Friday and into the weekend.

DISCUSSION

An upper level low to the southwest of the area is expected to bring some clouds to the area this afternoon and cooler temperatures. A shower or two is possible in southern Mendocino county, but generally dry weather is expected. Tonight a few showers may push into southern Mendocino and Lake counties, but coverage on the CAMS is very spotty so confidence is low on this. Wednesday afternoon the models show coverage increasing. However there is some pretty significant disagreement in where these showers will end up. Generally the models agree there is a higher probability of the heavier showers in Mendocino and Lake counties as well as up into Trinity county. Some of the models do show some showers making it out to the Humboldt county coast. Probabilities do drop off more by the time you get up to Del Norte county. The showers are expected to continue to move to the north and west Wednesday night into Thursday. The probability of a wetting rain for the 24 hour period ending at 18Z Thursday is 40 to 60 percent for the higher terrain of Trinity, Mendocino and Lake counties.

Thursday afternoon and evening the back edge finally moves through and drier air starts to moves in. This should end the rain showers, but it is uncertain if it will be enough to clear out the clouds in the interior valleys. Any valleys that do clear out Thursday night will likely see frost or freezing temperatures. For now removed fog from most of the Trinity county valleys, but most other areas still have fog in them. This will need to be monitored as it gets closer. The coast may clear out enough to see some frost develop as well. Friday afternoon is expected to see some warming and drying and this may help dry things out for Friday night and this may end up being the colder night in many of the valleys. Saturday afternoon may see highs return to the upper 70s to low 80s.

Sunday and into early next week the models continue to struggle with a solution. 50 percent of the members show a wet pattern while 50 percent show a ridge. The most recent run has trended slightly drier, but this will need to be watched. Currently the deterministic GFS and ECMWF are on the warm and dry side of the solutions. MKK

AVIATION...(18Z TAFs)

A deep marine layer and recent rains brought stratus and fog into the sheltered river valleys early this morning, which has been slow to clear. All TAF sites mostly remained VFR through the night with only minor disruptions along the coast. There is high uncertainty with the return of stratus tonight, but should it return, it is likely to be much shallower and confined to the coast and nearby river valleys. REFS hints at around a 40% chance for ceilings under 1000 ft at ACV and a 60% chance at CEC. Light offshore winds remain present tonight, which may limit stratus impacts at the coastal terminals. Impacts are likeliest around sunrise Wednesday. Otherwise, VFR conditions are expected outside the coast for the next 24 hours. Rain showers from an upper low may bring a few light rain showers to UKI early Wednesday morning. Chances for rain increases Wednesday afternoon and overnight. /JB

MARINE

Winds remain relatively light and turn northerly today, however seas remain elevated at around 9 to 12 ft from a mid period westerly swell. This swell has peaked and will gradually subside over the coming days. An upper low off the coast, which is generating this swell, will move southeastward closer to the central CA coast. This is bringing some uncertainty on the winds on Wednesday, with some models pushing stronger northerlies in the outer waters. A few models are also showing a southerly wind surge near the Humboldt and Del Norte Coasts Wednesday morning. Most models show this as fairly weak, peaking around 10 to 15 kts, however the CANSAC model does show locally stronger winds over 20 kts from Cape Mendocino to the Del Norte Coast. This scenario is unlikely and very dependent on the track of the low, but it is something to watch.

As this low exits the area Wednesday night into Thursday, stronger and more widespread northerly winds return across the waters. Gale force gusts are likely for the outer waters and the lee of Cape Mendocino by Thursday evening. Strong winds continue through Friday evening. Much lighter winds are expected this weekend. /JB

FIRE WEATHER

Dry weather is expected to continue through tonight. Wednesday a isolated showers are possible in southern Mendocino and Lake counties with the showers expanding through the afternoon and evening. Temperatures and humidity are expected to be similar on Wednesday. There is also the potential for a few thunderstorms Wednesday afternoon and evening, although confidence is low this. These are expected to be accompanied by at least some rain if they occur. Showers are expected to continue to expand north Wednesday night and Thursday morning. These are finally expected to push out of the area Thursday afternoon. Breezy north winds are expected to pick up in the afternoon as well. However temperatures are expected to remain in the 60s with RH over 50 percent in many areas. Cold dry air Friday will help bring RH back closer to 20 percent during the day. Uncertainty remains for the weekend regarding chances for precipitation, with an equal split for moderate rain or unseasonably warm conditions. MKK

EKA WATCHES/WARNINGS/ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 8 PM PDT this evening for PZZ450- 455-470-475.