textproduct: Eureka

SYNOPSIS

Diurnal, shallow coastal stratus is anticipated for coastal and near coastal areas with better chances for scattering or clearing each afternoon through the end of the week. Inland areas will remain dry and hot under a building upper-level ridge.

DISCUSSION

The fringes of an upper level trough centered over British Columbia and an upper level ridge over the Southwest US are interacting with each other over Northwest California. Last night and this morning, the upper level low brought more zonal flow to the region which aided in deepening coastal stratus and then led to clearing/scattering stratus this afternoon for most coastal areas due to atmospheric mixing. Inland areas will experience heating as the upper ridge strengthens and moves westward late this week and into the weekend. High temperatures in the mid to upper 90s will become widespread across the interior valleys of Trinity, Mendocino, and Lake counties by Thursday. Subsidence will compress the marine layer, keeping it shallow and confined to the coast and immediate valleys.

Late this weekend and into next week, the placement of the upper ridge over the Southwest will determine the path of monsoonal moisture over the western US. Next week has the potential to heat up and dry out more than the end of this week, as well. The monsoonal moisture could cause instability in the atmosphere, mainly over northeastern Trinity County early next week. As of now, chances for isolated thunderstorms look low, but this pattern will be monitored for any potential impacts to Northwest California. /JLW

AVIATION

Chances for longer periods of cleared or scattered low clouds are expected to continue this afternoon and evening for coastal terminals. As high pressure becomes more dominant in the region late this week, coastal stratus is expected to be less widespread and more shallow. IFR/LIFR conditions are expected to redevelop for terminals in the Humboldt Bay area and nearshore areas of the Eel River Valley. Along the Del Norte Coast, coastal stratus development could be staved off as northerly winds increase closer to shore. VFR conditions are forecast for inland terminals throughout the TAF period. /JLW

MARINE

The pressure gradient between the offshore lower level high and the inland thermal low is tightening across the waters. Winds south of Cape Mendocino are sustained at 20 to 25 knots, producing steep, wind-driven seas in the southern marine zones. A Gale Watch has been hoisted for the southern outer waters for Thursday as widespread frequent gusts over 34 knots seems to be increasingly likely.

In the northern outer waters, wind speeds are modeled to increase to 20 to 25 knots with wave heights reaching 9 feet at a short 8- second dominant period late tonight. Throughout the northern marine zones, steep seas will create hazardous conditions for small craft. As a result, small craft advisories have been added for the northern marine zones, as well, for Thursday and Friday.

EKA WATCHES/WARNINGS/ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory from 11 PM this evening to 11 AM PDT Friday for PZZ415-450.

Small Craft Advisory until 10 PM PDT Friday for PZZ455.

Small Craft Advisory until 10 PM PDT Friday for PZZ470.

Small Craft Advisory until 5 AM PDT Thursday for PZZ475.

Gale Watch from late tonight through Thursday evening for PZZ475.