textproduct: Eureka

KEY MESSAGES

* Slightly cooler, but still hot, interior temperatures are forecast through Wednesday.

* Smokey conditions likely from the MP 18 Fire in the Trinity River Valley.

* Slight chance of interior thunderstorms late this week or over the weekend.

* Minor coastal flooding is possible around Humboldt Bay at the evening high tide tonight and Wednesday night.

SYNOPSIS

Slightly above normal temperatures in the interior are expected through Wednesday. Coastal areas continue to have near normal temperatures with overnight stratus clearing in the afternoons along with breezy northwest winds. There is a slight chance for dry thunderstorms in the interior late this week.

DISCUSSION

Smoke from the MP 18 fire continues to impact air quality over Northern California, particularly in the interior valleys of Humboldt and Trinity counties. Depending on fire containment, expect a similar pattern to carry through the week.

The high pressure ridge responsible for the extended period of hot temperatures is finally beginning to weaken. Temperatures will trend cooler as a result, but will still be hot through Wednesday. The heat has greatly dried out the region and fire weather concerns will be elevated with any increase in winds. See the fire weather section below.

There will be a more noticeable drop in interior temperatures Thursday as a troughing pattern settles over the region. High temperatures in the interior valleys will struggle to break 90 by Friday, and will continue to lower through the weekend. Clusters show a potential brief rebound in the ridge late in the weekend before a deeper area of low pressure potentially develops.

There is some potential for thunderstorm formation under this troughing pattern, including from various shortwave disturbances that pass through. Models are showing an uptick in moisture moving in Wednesday, however instability is meager. This could result in a few virga showers in the higher terrain, but lightning risk seems very low. Thunderstorm risk rises slightly (to 5 to 10%) during the afternoons Thursday through Saturday, with the highest chances on Friday afternoon. Most activity, if any, seems regulated to Trinity County, Siskiyou County, and the Yolla Bollys. This pattern will continue to be closely monitored for deviations in modeled trends.

AVIATION...(06Z TAFs)

Stratus has formed around Humboldt Bay late Monday evening bringing IFR ceilings. LIFR to IFR ceilings are likely at ACV early this morning with visibility reductions possible near sunrise. CEC may see stratus, as well, with gusty south winds advecting stratus northward. Interior areas are likely to remain VFR outside the river valleys of Trinity and interior Humboldt County where smoke can lead to visibility reductions. Stratus is likely to lift late morning into the afternoon. Gusty north winds are possible again at the coast this afternoon. JB

MARINE

Strong northerly winds continue in the outer waters. The largest fetch area being in the Northern outer waters with gusts over 40 kts in localized areas. South of Cape Mendocino, the wind field will be wide as it fans out into the southern outer waters with gusts up to 40 kts or so. Wind wave action from the northerlies will give 10-12ft wave heights and periods in as many seconds, creating steep and dangerous sea conditions. The Gale Warning for the northern and southern outer waters is extended through Thursday. In addition to the Gale Warning there is also a small craft advisory (SC.Y) for the inner coastal waters for steep seas. Otherwise, a long period southerly swell of around 1 ft wave height is due to arrive overnight into early morning Tuesday. Conditions improve late this week into next weekend. /EYS

FIRE WEATHER

Elevated fire weather conditions continue within the mountains of Del Norte and in the King Range as overnight relative humidity recoveries remain poor to moderate and winds remain gusty. In Del Norte, easterly winds gusts of up to 30 mph are possible overnight through Wednesday night. Similarly in the King Range there will be gusty afternoon northerly winds with poorer overnight recoveries in the higher elevations. Relative humidities will trend upwards over the coming days which will mitigate fire risk.

Minimum RH and overnight recoveries will improve today, especially in Humboldt, Del Norte, and much of Mendocino Counties, with moistening westerly flow and lower daytime highs from the breakdown of the ridge of high pressure. A troughing pattern then takes shape, which will maintain good recoveries and also increases chances for a deepened marine layer to infiltrate farther into the interior.

Monsoonal moisture moves into northern California Wednesday which may support a few virga showers to develop. There is a low chance (5-10%) for thunderstorms each afternoon from Thursday through Saturday, with the best chances on Friday with Trinity and Siskiyou Counties would be the most likely to see activity. With cloud bases modeled to be 20k ft or higher, little to no precipitation is expected to reach the ground. This will continue to be watched over the coming days.

COASTAL FLOODING

Sea levels continue to run approximately 0.7 to 0.8 ft above the predicted tide level in Humboldt Bay. Tides will become more amplified early this week following the lunar cycle. The predicted tide at the North Spit tide gauge is 7.99 ft MLLW at 11:17 pm on tonight. If the tide continues to run at around 0.8 ft above predicted, this could result in minor coastal flooding around Humboldt Bay with minor impacts in King Salmon and possibly a few other locations around the bay. Additional minor coastal flooding will be possible for the 12:10 AM high tide early Thursday morning, although astronomical tides are only 7.84 so the the anomaly would need to increase to nearly a foot. This is possible as northerly winds will be diminishing and may locally become southerly. Still any flooding will be very minor if it occurs.

EKA WATCHES/WARNINGS/ADVISORIES

CA... Coastal Flood Advisory until 1 AM PDT Tuesday for CAZ103.

NORTHWEST CALIFORNIA COASTAL WATERS... Coastal Flood Advisory until 1 AM PDT Tuesday for PZZ415.

Small Craft Advisory until 9 AM PDT Thursday for PZZ450.

Small Craft Advisory until 3 AM PDT Wednesday for PZZ455.

Gale Warning until 9 AM PDT Thursday for PZZ470-475.