textproduct: Eureka

KEY MESSAGES

* Interior areas continue to see near to slightly below normal temperatures through this weekend.

* Coastal areas continue to see overnight stratus with afternoon clearing.

* Tropical moisture may bring a few showers to Mendocino and Lake Counties Friday morning.

SYNOPSIS

Generally mild, seasonable weather continues today and Thursday. Tropical moisture arrives to the area Thursday night and Friday, bringing a slight chance for rain showers to Mendocino and Lake Counties.

DISCUSSION

An upper-level trough remains in place over the Pacific Northwest. This has moderated interior temperatures with highs in the high 80s to low 90s for most interior valleys. A weak marine inversion in place has allowed for coastal stratus to clear into the afternoons, but stratus will likely reform each evening and continue overnight for the coming days. Coastal high temperatures are forecast to be in the low to mid 60s as northwesterly afternoon breezes return. A deep marine layer also brings overnight stratus farther inland, which is moderating some fire weather concerns, especially closer to the coast.

Thursday into Friday, moisture from the remnants of Tropical Storm Iselle, currently off the coast of Mexico, will arrive to central and northern California. Models are coming into better agreement on the position and timing of the moisture. Precipitable water values hover around 0.8" to around 1.0". Dry lower levels will limit potential for any of this to reach the ground, but a few sprinkles are possible in southern Mendocino and Lake Counties Friday morning and early afternoon. Instability is limited and thunderstorm chances are low (less than 5%). That said, there are a couple models that do show stronger cells with slightly more instability, so thunderstorm chances are nonzero but still very low. Recent model runs have moved this moisture plume to be in a more north-south orientation, which is also limiting moisture coverage over the area in general and also limiting moisture to from Thursday evening to Friday morning. By Friday afternoon, moisture moves eastward. This will be watched closely as any increase in instability could bring more confidence in thunderstorms.

This weekend, a trough in the Pacific Northwest rebuilds and is modeled to be slightly stronger and farther south. This will continue the moderated interior temperatures (high temperatures in the 80s to low 90s), and possibly bring coastal drizzle overnight and more persistent coastal stratus into the afternoons. Coastal high temperatures are also forecast to drop into the high 50s to low 60s with this more cloudy pattern. Early next week, a stronger trough drops from the Pacific Northwest. This is expected to bring cooler temperatures across the area with most interior areas 5 to 10 degrees below average. Coastal drizzle or light rain is possible for the Humboldt and Del Norte Coasts as well, but recent model runs have been trending this moisture northward. /JB

AVIATION

18Z TAFs.A weakened inversion allowed the stratus to clear out and VFR conditions to take hold by Wednesday morning. Winds will be generally light, with occasional gusts from afternoon northwesterly winds. Marine stratus currently observed offshore will spread back over the coast overnight. Similarly to the previous 24 hours, ceilings will lower to IFR and LIFR levels late Wednesday and into Thursday, with some periods of fog possible. VFR conditions will remain inland.

MARINE

Light winds continue today outside of breezy northerlies in the lee of Cape Mendocino. Outside the lee of the Cape, seas are dominated by a mid period southerly swell at around 3 to 4 ft. Though winds will be generally lighter for the nearshore waters south of the cape, steep seas of 6 to 8 ft will likely periodically propagate in. Northerly winds increase Thursday through Friday with widespread gusts of 20 to 30 kts likely for the outer waters. The northerlies further strengthen through the weekend, with near gale to gale conditions likely. JJW/JB

EKA WATCHES/WARNINGS/ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory from 3 PM Thursday to 9 PM PDT Friday for PZZ475.