textproduct: Eureka

SYNOPSIS

Moderate to major HeatRisk will continue across the interior through Tuesday, though coastal areas will still see marine influence and cooling. The heat wave will break down beginning Wednesday.

KEY MESSAGES

- Temperatures begin to slightly ease but remain above average Tuesday. - Cooling trend beginning to build in Wednesday.

- Slight (15%) thunderstorm chances over the eastern interior Thursday and Friday afternoons.

DISCUSSION

High pressure ridging continues to dominate across the area with the strongest focus persisting over Humboldt and Trinity Counties today with valley high temperatures again around 100. High temperatures will continue to be above average, though not record breaking. High temperatures rebound again today for the southern half of the area thanks to weakened south wind. Ukiah returned to near 100 Monday afternoon. Conditions will ease by just a couple degrees Tuesday, but these temperatures still constitute a generally moderate HeatRisk with some areas of major risk for the warmest valleys. Heat has made for a robust but very shallow marine layer that has blanketed the immediate coast, though clearing Monday was slight better than Sunday.

High pressure will begin to weaken more by Wednesday with interior highs pulling back into the mid 80s. Most deterministic models show weak trough pushing onshore around Thursday. This trough will definitely cool conditions and help deepen marine influence along shore, creating a more persistent and further reaching marine layer. Compared to previous runs, more high resolution models show a weak moisture plume moving up the Sacramento valley. Interacting with the trough, this could (20% chance) produce elevated, mostly dry thunderstorms in eastern Mendocino and Trinity Counties on Thursday and Friday afternoons. /JHW

AVIATION

Though brief, the coastal stratus showed the first signs of weakness Monday with periods of scattering. Southerly return flow over the coastal waters continues to replenish stratus mass from the unlimited supply being generated over the Pacific. LIFR conditions and areas of fog remained over the coastal terminals Monday night.

High pressure overhead strengthens overnight, and the marine layer will further compress to very shallow levels through Tuesday morning. High pressure then weakens Tuesday, and the northerly winds increase. This will finally allow for turbulent mixing to scour out the stratus throughout day north of Cape Mendocino, though a quick return is expected going into Tuesday evening. Weaker northerly winds south of the cape will create and southerly eddy which will keep the stratus over or along the Mendocino coast Tuesday.

MARINE

Northerly winds have entered a strengthening trend. Near gale to gale conditions will develop over portions of the waters Tuesday, mainly over the outers Tuesday. The northerly winds will strengthen through Wednesday. Though winds will be lighter, short period and occasionally large seas around 9 to 11 feet will enter the inner waters around and north of Cape Mendocino Tuesday through Thursday morning. Thereafter, seas trend lower after the stronger northerlies likely pull farther offshore.

FIRE WEATHER

An ongoing heat wave has helped rapidly dry fuels. Interior high temperatures have been reaching near 100 with RH generally between 15 and 25 percent. Overnight RH recovery has also been poor with thermal belts with mid and upper elevation nighttime RH only around 50 percent. ERC has rapidly increased across the board with most RAWS already reaching near the 90th percentile, even close to shore. That said, the general lack of wind will continue to suppress the risk of any fast moving fires. Hot and dry conditions will weaken beginning Wednesday.

The pattern late week is coming more into focus. Some longer range high resolution models show a more well formed though weak moisture plume moving up the Sacramento Valley late week. Combined with the the passing upper level trough, such a setup is likely to create Thunderstorms over high terrain Thursday and Friday afternoons and evenings. The greatest potential will be in NE Trinity County (20% chance) with lower chances (10%) around the Yolla Bollys. Any storms that form will be mostly dry. Given the preceding heat wave, any lightning is likely to be efficient with possible new fire starts.

COASTAL FLOODING

Another high astronomical tide is predicted just at 1:15 am, Wednesday, June 17 for Northwest California. High tides have been reaching 9.1 to 9.3 ft. Tides will trend lower starting Wednesday. High tides will cause minor coastal flooding round Humboldt Bay, including King Salmon and low- lying roads near Arcata Bottoms.

EKA WATCHES/WARNINGS/ADVISORIES

CA... Heat Advisory until 10 PM PDT Tuesday for CAZ102-105-108- 111-114-116-117.

Coastal Flood Advisory until 2 AM PDT Tuesday for CAZ103.

Coastal Flood Advisory from 11 PM Tuesday to 3 AM PDT Wednesday for CAZ103.

NORTHWEST CALIFORNIA COASTAL WATERS... Coastal Flood Advisory until 2 AM PDT Tuesday for PZZ415.

Coastal Flood Advisory from 11 PM Tuesday to 3 AM PDT Wednesday for PZZ415.

Small Craft Advisory from noon Tuesday to 3 AM PDT Wednesday for PZZ450.

Small Craft Advisory until 8 AM PDT Tuesday for PZZ470.

Gale Warning from 8 AM Tuesday to 9 AM PDT Wednesday for PZZ470.

Small Craft Advisory from 3 AM Tuesday to 9 AM PDT Wednesday for PZZ475.