textproduct: Eureka

SYNOPSIS

Northerly breezes will persist along the coastline into the weekend, but be noticeably lighter than the last few days. Seasonably warm to below average temperatures are expected through Thursday before temperatures warm up Friday and through the holiday Weekend.

KEY MESSAGES

- Northerly breezes near the coastline through the weekend.

- Hotter temperatures over the holiday weekend.

DISCUSSION

A very typical summer pattern is in-store for Northwest California over the next week as troughing over the inter- mountain west is replaced by a building ridge and heat builds toward the region over the weekend. Temperatures will begin around normal to slightly below normal Thursday into Friday and then warm generally above normal Saturday and Sunday across the interior. Highs Thursday will mostly be in the 80s and low 90s in interior valleys, warming to the mid to upper 90s by Sunday. Coastal areas will likely see an increase in moisture due to a compacting of the marine layer, which should result in more stratus and the potential for drizzle each morning Friday through Sunday, especially in the Humboldt Bay area. The ridge may break down some early next week as a trough strengthens over British Columbia. This could decrease 850mb temperatures over the region resulting in a slight decrease in temperatures early to mid next week. This outcome remains highly uncertain as the exact location of the trough/ridge axes will determine the end result over our area.

Details specific to July 4th: Temperatures are forecast to be around 60 at the coast and in the lower to mid 90s inland. Cloud cover may be more extensive along the coastline with moisture increasing in the boundary layer and a stronger marine layer inversion due to the building ridge. Low stratus and fog may be a concern during the evening hours for coastal areas depending on the strength of the coastal winds and the mixing they can provide. Drizzle may develop during the morning hours and late evening.

Broad southerly flow will spread over the region Sunday with a weak disturbance ahead of a trough. Moisture and instability currently look limited with this system Sunday and perhaps Monday, but there is a better signal for convective activity than has been observed in a stretch. Currently looks like Siskiyou County would have a better chance at thunderstorms, but Trinity County may have a chance if the modeled quality of elevated moisture improves. Though there is currently under 10% chance for thunderstorms at this time, this type of pattern bears a close watch during fire season. RPA/JJW

AVIATION

Northerly winds subsided overnight. Extensive marine stratus is observed offshore and increasing in coverage from the north. Soundings point to a shallower inversion than observed over the previous nights when MVFR to TEMPO IFR occurred Wednesday morning. MOS and LAMP guidance lowers ceiling to IFR and perhaps into LIFR territory (300 to 400 ft AGL). There is currently only a 30% chance for LIFR levels, but the chances has been nudging higher. The coastal winds will be light and from a more northwesterly direction Thursday, a setup favorable to lock the ceiling in longer or backbuild stratus against the higher inland terrain. For the 6Z TAFS, have introduced LIFR CIGS and extended the duration of ceilings Thursday based on the preponderance of evidence.

MARINE

The end of the persistent northerly gale is finally in sight. Hazardous seas have certainly been observed in the inner waters with the Humboldt Bay North Spit buoy reading up to 12 ft at 9 seconds as of Wednesday evening. The gales in the outer water and portions of the inners responsible for these seas will wind down into Thursday morning. A conversion to Small Craft Advisories will be required to cover the remaining northerly winds and steep seas. Winds and seas will be lowest through Friday, with 5 to 8 ft short period seas. Northerly winds and short period seas will increase again through the weekend.

EKA WATCHES/WARNINGS/ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Hazardous Seas Warning until 6 AM PDT early this morning for PZZ450-455.

Small Craft Advisory until 9 PM PDT this evening for PZZ450.

Small Craft Advisory until 9 AM PDT Friday for PZZ455.

Gale Warning until 6 AM PDT early this morning for PZZ470- 475.

Small Craft Advisory until 9 PM PDT Friday for PZZ470-475.