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 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

Stratus and fog has redeveloped along the coast and continues to expand into areas not yet cloudy as of this hour. Only the Shelter Cove area north to Cape Mendocino may remain clear overnight. LIFR ceilings and visibilities falling to below a half mile will be possible into the morning hours with visibility occasionally falling to a quarter mile or less. A weak marine inversion should allow for the coastal clouds to mix out through the morning hours, bringing a return to VFR by around midday. Farther inland VFR will prevail through the forecast period. /RPA

MARINE

Northerly winds will increase over the next few days as a trough moves inland and heat builds into the weekend. This will result in an expansion of the small craft advisories into additional areas Saturday into Sunday, particularly in the outer waters. Some gusts to gale force will be possible late in the weekend but at this time the gusts appear to be limited enough to not require early heads-up of gale potential. Thus, small craft advisories will only be issued at this time. The northerly winds will decrease quickly early next week as another trough approaches the area.

EKA WATCHES/WARNINGS/ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory from 9 AM Friday to 9 PM PDT Saturday for PZZ455.

Small Craft Advisory from 3 PM this afternoon to 9 PM PDT Saturday for PZZ475.