textproduct: Eureka

KEY MESSAGES

* Moderate to major heat risk continues for much of the interior areas today.

* Stronger afternoon valley winds and low relative humidity will elevate fire danger this weekend.

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

* Heavy smoke is expected within the Trinity River Valley due low mixing heights at to the MP 18 fire.

SYNOPSIS

High pressure aloft remains through the daytime before finally weakening to start the coming work week. Inland areas continue to see above normal temperatures with moderate to locally major heat risk and afternoon gusty winds near channeled terrain. Coastal areas will remain mostly overcast with brief clearing possible this afternoon and breezy northwest winds.

DISCUSSION

The seemingly immovable upper level ridge that has dominated the weather for the past week or so will finally begin to give way to more zonal flow aloft this evening. However, through today, NW CA can expect continued warm to VERY hot temperatures for the inland areas. Most inland valleys and Lake County can expect high temperatures between at or near 100F today.The ongoing heat will be dangerous for anyone working outside. 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 coast continues to offer some relief from this heat due to a strong marine layer and its associated stratus blanketing much of the Californian coastline. The aforementioned mentioned daytime interior heating will continue to tighten the surface pressure gradient each afternoon forcing stronger onshore (NW) sea breezes. In NW-SE situated river valleys (Trinity River Valley, Eel River Valley, areas near Clear Lake, etc.) these winds will have a higher chance to mix down to the surface. These increased winds in addition to hot and dry conditions will cause very localized critical fire weather conditions over the region. For more details, see the fire weather section below.

Despite the increased surface winds, the smokey conditions within the Trinity River Valley will likely remain through midweek as the fire activity increase each afternoon. The HRRR smoke model shows smoke moving along upvalley flow before settling into valleys each night. This pattern is expected to remain through Wednesday at the earliest.

Global ensemble models and 500mb clusters suggest that the midweek, zonal flow aloft will likely evolve into weak to moderate troughing by late next week. The troughing will force a cooling trend with inland temperatures struggling to break 90F by Friday. Troughing could also create an environment capable of supporting afternoon thunderstorms over the interior mountains. A lot of variability remains regarding this weather threat, such as moisture available, if the air will be stable vs unstable, or if there will be enough lift at the surface to create updrafts. Stay aware of forecast changes as more details become available through the week.

AVIATION

Coastal stratus is continuing to dissipate across most of the North Coast. Terminals close to the shoreline will remain IFR/LIFR with minimal clearing expected this afternoon. Northerly winds are expected through the afternoon with gusts up to 15kts or so at KACV and up to 20-25kts are KCEC. Model probabilities show that more likely than not, IFR/LIFR conditions will return around 03Z (+/- 1hr) with low ceilings and degraded visibilities due to haze/mist.

Inland areas are expected to remain VFR with gusty afternoon winds developing during the peak heating of the day. NW winds will likely dominate the interior areas of NW CA. Anomalously hot surface temperatures could lead to density altitude issues this afternoon as well, be aware. Finally, the Trinity River Valley and its surrounding areas will likely have IFR/IMC due to very heavy FU from the near by MP 18 Fire. Expect extremely degraded slant and surface visibilities as well as mountain obscuration near terrain for those areas.

MARINE

Significant wave heights have been steadily building since Saturday with buoys recording widespread 8ft @ 8sec. Satellite imagery of the marine stratus and surface winds observations shows northerly nearshore winds of around 15-20kts with gusts p to 25kts. near the inner waters. The wind speeds are likely to increase further away from the coastline in the outer coastal waters. Most model data shows continued sustained winds near 30kts and gusts of 40kts possible through early this coming work week, especially for the northern outer waters. Very steep waves are to be expected leading to hazards such a blowing foam in addition to the very large seas. The biggest area of concern for the strongest winds is downwind of Cape Mendocino and Point St. George. WHile the winds will likely continue to be lighter in the inner waters with moderate to fresh breezes, waves will still be steep due to propagation from the large short period seas in the outer waters heading towards shore. These stronger northerly winds are likely to last through most of the coming work week.

FIRE WEATHER

This afternoon, localized critical fire weather is expected for the Trinity River Valley, interior Mendocino County, and areas on the direct eastern shore of Clear Lake. This short lived threat will be due to low afternoon RH values in the low teens to single digits and increased afternoon winds with NW gusts up to 20mph or so. While winds and area coverage lack the official criteria for a Red Flag warning, it is important to remember that even a single spark could start a wildfire in these conditions. The aforementioned areas have the greatest risk due to the NW-SE oriented valleys and basins that will enhance winds mixing down to the surface through the channeled terrain and over Clear Lake. The hot, dry, and windy conditions will likely cause conditions that could fuel explosive fire growth from around 3pm - 7pm today.

A slight cooling trend is expected through the coming work week. High pressure will move away from the area and very weak troughing is likely to fill in its place, setting up over the area. This troughing has the potential to funnel moisture into the area. The moisture, if it materializes over NW CA, could cause some afternoon thunderstorms for Friday and Saturday. Details on this set up are minimal now as the high pressure is still over the area, yet updates are expected through early week due to the dangerously dry fuels over the interior.

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 this week following the 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. The tide anomaly will continue to be watched this evening to warn of the possible hazard.

EKA WATCHES/WARNINGS/ADVISORIES

CA... Heat Advisory until 10 PM PDT this evening for CAZ108- 110>114-116>120.

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 3 AM PDT Tuesday for PZZ450-455.

Gale Warning until 3 AM PDT Wednesday for PZZ470.

Gale Warning until 10 AM PDT Monday for PZZ475.