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.

SYNOPSIS

High pressure starts to weaken this week, but 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.

DISCUSSION

The seemingly immovable upper level ridge that has dominated the weather for the past week or so has finally begun to give way to more zonal flow aloft. This will begin the "cooling" trend starting today, though interior temperatures will still remain hot with the warmest valleys breaking 100. Still, most areas will see highs a couple degrees cooler today. This trend continues with interior valleys seeing highs in the high 90s to just over 100 through Wednesday. Coastal areas remain in 60s for much of the week with stratus forming each night and clearing, at least partially, in the afternoons.

Daytime heating in the interior 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 winds along with hot and dry conditions will continue elevated fire weather conditions this afternoon. 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, depending on fire containment, through midweek as the fire activity increases 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 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, instability, 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...(06Z TAFs)

Coastal stratus has started to reform around Humboldt Bay and IFR to MVFR conditions are likely around ACV early this morning. Confidence is lower on stratus impacts at CEC as northerly winds increase near Pt St George this morning. This may be just far enough off shore and/or above the surface inversion to prevent stratus from making it to the airport, despite southerly surface winds being observed currently. Regardless, IFR to MVFR stratus is likely to lift and scatter shortly after sunrise. Interior areas outside the near-coastal river valleys will remain VFR through the night. However, smoke impacts in the Trinity River Valley may bring low visibilities until winds pick up in the afternoon. VFR conditions (outside of smoke) are likely by the afternoon with gusty northerly winds likely at the coastal terminals.

MARINE

Gale force northerly winds remain persistent in the outer waters and are likely to continue through Wednesday. Despite lighter winds nearshore (peaking at 10 to 20 kts each afternoon), steep seas of 7 to 9 ft are likely through Wednesday. High pressure begins to weaken mid to late this week which will bring relief to the strong northerlies. Steep seas will gradually ease Thursday into Friday, which will give way for very mild conditions across the waters Friday into the weekend.

FIRE WEATHER

A slight cooling trend is expected this week as high pressure moves out of the area while weak troughing sets in. Still, hot and dry conditions continue early this week. Afternoon winds will not be as strong as this weekend's but still is likely to be locally elevated in channeled terrain. Gusts up to 20 to 25 mph are possible in the Trinity River Valley and around Clear Lake this afternoon. Additionally, the higher elevations of Del Norte will see gusty overnight east winds, which will lead to poor to moderate overnight relative humidity recoveries. However, relative humidity is expected to remain high enough outside the highest ridges to avoid widespread critical conditions.

Troughing has the potential to funnel moisture into the area later this week. The moisture, if it materializes over NW CA, could result in some afternoon thunderstorms for Thursday, Friday, and Saturday. Confidence remains low at this time and NBM probabilities currently hover around 5 to 10% in Trinity and Siskiyou Counties. This will be watched closely over the coming days.

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 tonight 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... None.

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 10 PM PDT Wednesday for PZZ450.

Small Craft Advisory until 3 AM PDT Wednesday for PZZ455.

Gale Warning until 10 PM PDT Wednesday for PZZ470-475.