DISCUSSION
The marine layer will begin deepening with an approaching upper trough and frontal system, lessening the chances for fog development along the coast tonight. With the dropping heights, inland temperatures are trending to below average levels.
Daytime highs will sharply drop by 15 to up to 19 degrees Wednesday with the passing of the cold trough. There is a high probability (70- 95%) for a wetting rain of at least a tenth of an inch from N Humboldt through Del Norte Wednesday. Del Norte County, including its interior, has a 50 to 75% chance for a quarter inch of greater in a 6 hour period early Wednesday morning. Forcing, steepening lapse rate and weak instability may allow for convective showers, although latest model soundings are not supportive of thunderstorm development. Chances for a wetting rain quickly drop off going south into Mendocino County.

This system will begin increasing northwesterly to westerly winds this afternoon, and especially tonight through Wednesday night.
There is a solid signal for maximum wind gusts around or over 30 mph Wednesday morning through Wednesday night in far SE Mendocino and Lake counties (70-80%). There is also a moderate chance (53-63%) for wind gusts to exceed 35 mph late Wednesday in far south Lake County.
There will be fire weather concerns in Lake County during the transition to a more moist airmass. Deterministic models have been well aligned for the pattern to persist with additional troughing and precipitation chances into the weekend, and there is robust ensemble and cluster support for this scenario. /JJW



AVIATION
Coastal stratus brought LIFR TO IFR conditions to many coastal airfields through the day with minimal improvement and only isolated areas observing scattering ceilings. Some scattering is still possible early this evening, especially along the Mendocino coast. Otherwise ceilings and visibilities are expected to deteriorate after sunset for coastal airfields like KCEC and KACV.
As the cold front will crosses through the region early Wednesday morning, the marine layer is expected to deepen with the potential for light rain showers, mostly for areas north of Mendocino County.
Additionally, a slight chance for a thunderstorm is possible across Del Norte County Wednesday morning. Interior areas will most likely see VFR through the TAF period. /kmz



MARINE
North winds will ease slightly this evening as a frontal boundary weakens the pressure gradient and then brings a brief round of south/southwest winds across the northern waters early Wednesday morning. That said, gusty winds near 30 kt will persist across the southern waters this evening before frontal passage. As a result, a shortlived small craft advisory was hoisted for the southern inner waters as gusts near 30 kt impact nearshore. Some isolated gale force gusts will even be possible near Cape Mendocino. Otherwise marine winds decrease briefly on Wednesday before north winds ramp up to 15 to 25 kt again late in the work week. As for the sea state, steep seas around 5 to 7 feet this evening will subside slightly into Wednesday as a northwest wave system dominates the marine environment. Steep seas will build again in response to the winds later this week with wave heights peaking near 7 to 9 feet across the outer waters. /kmz



FIRE WEATHER
An upper trough will begin approaching the region late Tuesday. There is a high probability (70-95%) for a wetting rain of at least a tenth of an inch from N Humboldt through Del Norte Wednesday. Del Norte County, including its interior, has a 50 to 75% chance for a quarter inch of greater in a 6 hour period early Wednesday morning. Chances drop below 15% in northern Mendocino County Wednesday. The cold trough will drop inland daytime highs by a solid 15 to 19 degrees Wednesday. Thunderstorms may also be possible in Del Norte Wednesday, although guidance has been trending away from development.

Northwest winds will begin to increase Tuesday afternoon, and will peak on Wednesday when gusts over 30 mph are likely (70-80%), mainly in Lake County, but also southern Mendocino County. RH values have dropped in the mid teens to upper 20s this afternoon, and winds are expected to mildly tick up over the next few hours. There is some uncertainty as to how fast this environment can moisten up Wednesday in Lake County with the peak winds, but minimum RH values in the mid to upper 30s are forecast. This will be sufficient for critical fire weather conditions to occur...but there is low confidence on the duration. /JJW

EKA WATCHES/WARNINGS/ADVISORIES
CA...
None.
NORTHWEST CALIFORNIA COASTAL WATERS...
Small Craft Advisory until 3 AM PDT Wednesday for PZZ455.

Small Craft Advisory until 3 PM PDT this afternoon for PZZ470.

Small Craft Advisory until 9 AM PDT Wednesday for PZZ475.