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

Warmer and drier than normal conditions will persist for a spell longer with shallow marine influence along shore. Much more seasonable cooler and moist 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 earlier this week with similar temperatures again most likely Thursday. Such conditions will continue to support moderate to isolated major HeatRisk across the interior but especially Mendocino and Lake Counties. Meanwhile, the shallow marine layer will remain along shore with low marine fog and clouds while scattering out in the afternoon as the strength of the inversion weakens ahead of the inbound low.

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/EYS

AVIATION...(18Z TAFs)

LIFR stratus is being observed along the Humboldt and Del Norte coasts early this morning. Some partial clearing and lifting is possible for a few hours this afternoon, but a consistent light onshore breeze is likely to keep any improvements brief. Regardless, LIFR stratus with dense fog is likely again this evening and overnight. As high pressure begins to weaken Thursday, stratus may finally clear more solidly in the afternoon with around a 70% chance of clear skies. Interior areas are likely to remain VFR for the next 24 hours. /JB

MARINE

Winds in the outer waters gradually diminish and pull farther offshore today. While winds diminish, seas remain steep in the outer waters through this evening. While the small craft advisories will be allowed to expire, the hazard for steep seas is still likely 40-60 nm offshore. Along with the decaying wind waves, there continues to be be very minor, southerly longer period swells from distant tropical storms.

North winds will quickly increase Thursday night into Friday and push closer to shore. Confidence is growing in gale force gusts in the lee of Cape Blanco moving close to shore and bringing gale force northerlies to the northern outer waters Thursday night into Friday morning. A Gale Watch has been issued for this time period, however there is still some uncertainty on how close to shore these gales will reach. Regardless, these strong winds in the northern waters diminish slightly Friday morning. Winds will instead increase significantly in the lee of Cape Mendocino Friday. Gale force gusts are likely for much of the outer waters. Steep short period seas will rise in response. Winds will continue to strengthen Saturday, both in the northern and southern waters, as a 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. Localized storm force gusts are likely in the immediate lee of Cape Mendocino. 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 large and steep, such a swell would create a significant sneaker wave risk. /JHW/JB

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 6 PM PDT Thursday for PZZ470.

Gale Watch from Thursday evening through Friday morning for PZZ470.

Small Craft Advisory until 9 PM PDT this evening for PZZ475.

Gale Watch from Friday morning through Saturday morning for PZZ475.