textproduct: Eureka

KEY MESSAGES

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

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

* Slight chance of interior thunderstorms late in the week and into Saturday

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

SYNOPSIS

Interior temperatures trend below normal late in the week. 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 and into Saturday.

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 low level inversion is showing signs of weakening as more of a troughing pattern develops, and this will help clear out the smoke more efficiently over the coming afternoons.

The troughing will continue to lower interior daytime highs. Temperatures will be near or below climatological normals Wednesday, followed by continued lowering to below normals through the extended forecast. The marine layer is deepening and extending farther inland, and will be conducive to producing light drizzle over the coming days.

The broad troughing and embedded disturbances will also bring low chances for some showers or perhaps thunderstorm activity. A weak surge of monsoon moisture associated with a shortwave disturbance may clip portions of the southern zones Thursday, but even the most aggressive modes keep the moisture SE of Lake County at this time. This day will still be watched regarding any dry lightning potential through Trinity County (5%), especially if the moisture flux nudges northwest at all.

A secondary wave will move NE over Northern California Friday into Saturday morning. This disturbance will carry higher instability and moisture (though still meager), giving a slightly higher chance for some thunderstorm activity (5-10% over Trinty County northward through far eastern Del Norte County, and 10-15% over Siskiyou County and far northeast Del Norte). There would be a potential for nocturnal activity late Friday as well if storms occur at all. precipitable water values will be on the higher side, and precipitation reaching the ground would be possible. That said, this is still a very low confidence forecast; however, it will still be watched very closely due to historical poor model handling of the setup type and the impact even a little lightning would have regarding fire potential over the very dry vegetation.

AVIATION

Marine stratus is forcing LIFR/IFR conditions for most of California this morning. Southerly winds are present along most of the Lost Coast and should be expected through the morning as well. Stronger NW winds are likely to develop between 20Z (+/- 1 hr) for the Del Norte and Humboldt coastlines which should increase the likelihood of mixing and VFR conditions. Overnight LIFR/IFR is expected to return to the coastline with light, southerly winds.

Inland terminals can expect VFR (away from smokey areas). Afternoons winds are expected to follow the terrain with upvalley flows that are likely to be gusty. Smoke from wild fires could pose localized areas of mountain obscuration in addition to sfc/slant visibility issues, especially for the Trinity River Valley and the Humboldt Bay areas.

MARINE

Strong northerlies with gale conditions continue in the outer waters. These winds are generated steep and hazardous seas up to 12 ft at 10 to 11 seconds. These larger seas will periodically migrate into the inner waters following the afternoon/evening stronger wind surges. Seas of up to 11 ft have occasionally been observed at the North Spit buoy. Northerly winds will drop below 25 kts Thursday afternoon as troughing enters the region. The northerlies will drop more substantially Friday and especially through the weekend as troughing weakens the pressure gradient.

FIRE WEATHER

Elevated fire weather conditions continue within the mountains of Del Norte and in the King Range as 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.

Minimum RH and overnight recoveries will continue to improve 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.

A weak surge of monsoon moisture associated with a shortwave disturbance may clip portions of the southern zones Thursday, but even the most aggressive modes keep the moisture SE of Lake County at this time. This day will still be watched regarding any dry lightning potential through Trinity County (5%), especially if the moisture flux nudges northwest at all.

A secondary wave will move NE over Northern California Friday into Saturday morning. This disturbance will carry higher instability and moisture (though still meager), giving a slightly higher chance for some thunderstorm activity (5-10% over Trinty County northward through far eastern Del Norte County, and 15% over Siskiyou County and far northeast Del Norte). There would be a potential for nocturnal activity late Friday as well if storms occur at all. Storm movement would be to the north/northeast at just over 20mph.

COASTAL FLOODING

Measured sea levels continue to run approximately 0.7 to 0.8 ft above the predicted tide level in Humboldt Bay. 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, the possible sea level could result in minor coastal flooding around Humboldt Bay with minor impacts in King Salmon and possibly a few other localized areas around the bay. Additional minor coastal flooding is possible for the 12:10 AM high tide early Thursday morning. However, 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 which would push more water into Humboldt Bay. That said, any flooding will be very minor if it occurs.

EKA WATCHES/WARNINGS/ADVISORIES

CA... Coastal Flood Advisory from 10 PM this evening to 1 AM PDT Wednesday for CAZ103.

NORTHWEST CALIFORNIA COASTAL WATERS... Coastal Flood Advisory from 10 PM this evening to 1 AM PDT Wednesday for PZZ415.

Small Craft Advisory until 9 AM PDT Thursday for PZZ450-455.

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