textproduct: Eureka

KEY MESSAGES

*Moderate to major heat risk continues through the weekend for much of the interior peaking today in most areas.

*Localized critical fire weather possible this weekend due to stronger afternoon valley winds and low relative humidity.

*Coastal stratus to continue for much of the North Coast today and tonight with continued chances for afternoon clearing.

*Temperatures diminish slightly next week, yet most inland areas remain in the upper 90s to around 100 through mid-week.

SYNOPSIS

Persistent high pressure aloft remains through the weekend. Inland areas continue to see above normal temperatures while the coast remains under marine stratus. Temperatures are expected to gradually start cooling closer to normal next week. An upper level trough off the coast may bring monsoon moisture and the slight potential for thunderstorms late next week or next weekend.

DISCUSSION

A steady ridge of high pressure remains entrenched over the west coast leading to warm to VERY hot temperatures for the inland areas. Most inland valleys can expect high temperatures above triple digits today and close to, if not slightly above 100F tomorrow. The coast continues to offer some relief from this heat. Offshore stratus is blanketing much of the California coast, yet satellite imagery shows mixing making its way from the OR boarder southward. However, slightly above average SSTs and offshore flow will contribute to limited development of prolonged overcast conditions through the rest of the weekend.

Warming continues across the interior with moderate to localized areas of major HeatRisk indicated. The heat is expected to peak on today, particularly over Lake County, where conditions were on the edge of warranting an excessive heat warning instead of only an advisory. Regardless, this persistent heat will be dangerous for anyone working outside and everyone in the interior portions of all of Northern California should be drinking plenty of fluids and taking breaks in the shade to avoid heat stroke or heat exhaustion.

The aforementioned interior heating will tighten the surface pressure gradient over NW CA forcing stronger onshore (NW) sea breezes each afternoon and evening. With very dry conditions across the interior this will result in increase fire weather concerns. For more details, see the fire weather section below.

The upper level ridge that has settled over the area should finally weaken and migrate eastward through early next week. A secondary high pressure system is forecasted to set up over the Pacific which will lead to weak troughing settling over the west coast. This should allow temperatures to cool several degrees back to around normal for this time of year and could lead to increased likelihood of afternoon clearing of coastal stratus. This may also start to bring the threat for inland thunderstorms late next week or next weekend with there is enough moisture associated with this evolving synoptic system.

AVIATION...18Z UPDATE

Coastal stratus remains across the entire western seaboard today. Expect IFR/LIFR conditions for most of the day along coastal terminals. Slight clearing is possible, yet not expected from 19Z-00Z, better changes are for areas near large river deltas compared to areas near steeper terrain. If it does clear, overcast skies will return later this afternoon between 02-04Z for most of the North Coast before developing to fog late this evening. Winds will build to 10-15kts or so and will be mostly northerly for most of the day along the coast. Wind directions this will be dictated by coastal eddies forming and migrating along the coastline.

Inland areas are expected to remain VFR with gusty afternoon winds developing during the peak heating of the day. Upslope winds will form through the morning and midday before NW winds dominate the interior areas of NW CA. Anomalously hot temperatures for the inland areas could lead to density altitude issues this afternoon as well, be aware.

MARINE

Significant wave heights have been building through the morning as northerly winds build steadily. Observations show gusts up to 15-20kts which should increase through the afternoon, especially further away from the coastline. Waves in the outer waters are likely larger and steeper than the nearshore buoys are recording due to the strongest winds expected downwind of Cape Mendocino and Point St. George, where gale force gusts are likely (>50% probability). These forecasted winds called for a Gale Warning for the outer waters through the remainder of the weekend, and likely longer into the middle of next week if long range weather models hold fast. The inner waters are more likely to see moderate to fresh breezes with steep waves due to propagation from the fetch areas in the outer waters. The very steep northerly waves have called for a small craft advisory for the inner waters this weekend.

Plan your seafaring outings accordingly and always feel free to reach out for any addition information regarding the marine forecast for NW CA.

FIRE WEATHER

Stronger afternoon winds are expected to develop for valleys this afternoon. Winds are already following the channeled terrain and should increase with gusts up to 20 or even 25mph possible through the heat of the afternoon. These breezy conditions are expected to expand to localized areas for several hours this afternoon bringing critical fire weather Trinity, northern and eastern Mendocino, and Lake Counties. While the duration of the winds and low RH values are shorter than needed for Red Flag status, it is important to remember that even a single spark could start a wildfire in these conditions. Tonight, higher elevations at or above 2,500ft can expect continued low RH recoveries at or below 20% as a thermal belt develops at midslopes. Sunday afternoon, breezy winds are expected again for several hours, yet the RH is expected to be slightly higher than today.

Next week, temperatures are expected to slight cool as the upper level ridge moves eastward. The new large scale weather set up looks to have the potential for some dry thunderstorms next Friday or Saturday. There is still a lot of uncertainty on this, (moisture, lift, stability, etc.) but it definitely will need to be watched and accounted for through the coming work week.

COASTAL FLOODING

Sea levels continue to run approximately 0.8 ft above the predicted tide level in Humboldt Bay. Tides will become more amplified early next week following the normal lunar cycle. The predicted tide at the North Spit is 7.95 ft MLLW at 10:21 pm on Monday the 10th and then 7.99 ft MLLW at 11:17 pm on Tuesday the 11th. 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.

EKA WATCHES/WARNINGS/ADVISORIES

CA... Heat Advisory until 11 PM PDT this evening for CAZ105-106.

Heat Advisory until 10 PM PDT Sunday for CAZ108-110>114- 116>120.

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 10 PM PDT Sunday for PZZ450-455.

Small Craft Advisory until 3 PM PDT this afternoon for PZZ470-475.

Gale Warning until 3 AM PDT Tuesday for PZZ470.

Gale Warning until 10 AM PDT Monday for PZZ475.