textproduct: Eureka

KEY MESSAGES

* A couple more days of high temperatures with bring Moderate HeatRisk across the interior through the week.

* A developing trough will bring much cooler conditions by Friday and the weekend.

* No wetting rain forecast for the next 10 days.

SYNOPSIS

Much warmer and drier than normal conditions will persist for a couple more days with shallow marine influence along shore. Much more seasonable cooler and moister conditions arrive by the weekend alongside strong north winds near shore. Chances for wetting rain remain near zero.

DISCUSSION

Much warmer than normal conditions continue to linger under the influence of weakening high pressure. Many interior valleys again hit 100 on Tuesday with similar temperatures again most likely Wednesday and Thursday. Such conditions will continue to support moderate to isolated major HeatRisk across the interior but especially Mendocino and Lake Counties. Meanwhile, an especially shallow but strong marine layer will remain along shore with low marine fog and clouds and scattering out in the afternoon.

By Friday, weak low pressure moving over the eastern Pacific will weaken heat and bring generally much more seasonable conditions. On Friday, highs will drop back into the lower 90s with a deeper marine layer along shore. A broad trough and associated surface cold front will further cool conditions by Saturday and into Sunday. High temperatures will drop back into the 70. Despite the front, essentially no models show any moisture associated with trough. Very light coastal drizzle will be the only precipitation potential as the marine layer gets lifted.

As the trough dips south, there is strong model agreement that there is potential for unusually (EFI values of 0.75) strong north winds Saturday and Sunday. Winds could be particularly enhanced by low pressure detaching from the trough and moving south, though this scenario is uncertain. NBM shows most likely wind gusts along shore of 35 mph on Sunday. The strongest winds would be on coastal ridges and headlands. There is a 60% chance of gusts over 45 mph over the King Range and in the coastal waters, though that chance is only 10 to 20% for more populated areas like Crescent City and Humboldt Bay. Winds will most likely keep marine air scattered out along the coast, especially as winds turns slightly easterly into early next week.

Ensembles remain dry throughout the extended forecast period (next 10-14 days), though much weaker high pressure will generally result in more normal temperatures. /JHW

AVIATION...06z TAF

A very shallow marine layer is again impacting the coast, bringing a thin band of LIFR fog and ceilings to near coastal terminals. LIFR conditions will most likely persist overnight before slowly pulling back by late morning Wednesday. The pattern will most likely persist one more day with LIFR conditions resurging Wednesday evening, though ceilings are slightly started to lift with weaker high pressure. VFR conditions will continue across the interior. /JHW

MARINE

As high pressure stalls and weakens Wednesday, moderate winds in the outer waters will generally become gentle Wednesday. That said, stronger winds just outside the waters will continue to generate some steep mid period seas up to 9 feet. These seas will mostly effect the outer waters with much calmer conditions close to shore. There continues to be be very minor, southerly longer period swells from distant tropical storms.

North winds will quickly increase Friday and push closer to shore as low pressure pushes east of the areas. Gusts will most likely be near gale conditions with a 40% chance of proper gales south of Cape Mendocino by Friday evening. Of course, steep short period seas will rise in response. Winds will continue to strengthen Saturday as broad trough dips north of the area. By Saturday, there as 80% chance of gusts over 40 kts in the southern outer waters with gale conditions in the inner waters. Very windy conditions will then persist until at least next Monday. Around Sunday a long period swell around 5 feet at 22 seconds will augment the sea state. If short period seas were not so steep, such a swell would create a significant sneaker wave risk. /JHW

FIRE WEATHER

Prolonged much hotter and drier than normal conditions have had a significant affect on observed fire danger. ERC values are currently above the 80th percentile across interior NW California. With a couple more days of warming and drying and due to the lagging nature of heavier fuels, ERC values will crest near the 90th percentile on Friday and Saturday. Such values will most likely be record breaking for October. At the same time, strong north winds gusting 30 to 40 mph will build near shore and along exposed ridges. Although by Saturday, conditions will be much more seasonably cool and moist (highs in 70s and RH around 30 percent), the lack of any rain chances and recent drying will still support near record breaking Burning Index values for October around Saturday. All that said, there is potential for much above average fire activity through the weekend. /JHW

EKA WATCHES/WARNINGS/ADVISORIES

CA... Heat Advisory until 11 PM PDT Thursday for CAZ110>114- 118>120.

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 4 PM PDT Wednesday for PZZ470- 475.