textproduct: Eureka

KEY MESSAGES

* High confidence (85 to 100 percent probability) in at least widespread moderate heat risk continuing across interior valleys today, where maximum afternoon temperatures will reach 100 to 108 degrees.

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

* There is the potential for thunderstorms late next week or over the weekend in the interior.

* Strong northerly winds will sustain steep, hazardous seas and gale- force gusts up to 40 knots across outer waters through at least Monday.

SYNOPSIS

An expansive upper-level high, centered over the Great Basin will maintain hot, dry conditions across interior Northwest California through early week. Offshore, a sharp cross-coast zonal pressure gradient between east Pacific high pressure and the interior thermal trough will drive gale-force northerly winds and steep waves. Inland temperatures will begin a slight 3 to 6 degree cooling trend by mid-to-late week as the upper ridge gradually weakens.

DISCUSSION

Strong mid-level subsidence beneath a Great Basin ridge dominates regional atmospheric stability, keeping sky cover clear and promoting rapid daytime surface heating across inland valleys. At the surface, the persistent zonal pressure gradient between the Eastern Pacific High and the interior thermal trough continues to generate strong coastal northerlies while compressing the marine boundary layer below 800 feet AGL along the immediate shoreline.

Model ensemble guidance indicates around a 90-100 percent probability of many interior valley temperatures rising above 100 degrees this afternoon. Afternoon relative humidity values will drop to 814 percent across much or the interior valleys, maintaining localized elevated fire weather concerns. Mid-level height falls early next week will support a gradual cooling trend by Thursday as a broad trough approaches the Pacific Northwest.

Late in the week with the broad trough approaching there is the potential for thunderstorms. The current NBM is showing a 10 to 20 percent chance of thunderstorms across Trinity county and northeastern Mendocino county on Friday with a similar potential on Saturday. The ensemble clusters show some variations on how much moisture there will be, but they will likely be fairly dry. It is still possible there will not be enough moisture for any thunderstorms at all. This will need to monitored as it gets closer.

AVIATION

A shallow marine layer compressed below 1500 feet AGL will help promote a return of IFR to LIFR ceilings along the immediate coast through late morning, although confidence is waning on how much of a rebound that stratus will have. Boundary layer saturation will favor lower surface visibilities to 1 to 3 statute miles at KCEC and KACV before daytime mixing restores VFR conditions generally between 18Z and 20Z. KUKI will remain prevailing VFR under clear skies, with afternoon northerly gusts reaching 15 to 18 knots.

MARINE

A tight zonal pressure gradient will maintain gale- force northerlies across outer waters. Gale Warnings remain active for the Northern Outer Waters and Southern Outer Waters into Monday, where gusts to 40 knots and steep seas of 10 to 12 feet at 8 to 9 seconds will persist due to localized cornering accelerations downwind of Cape Mendocino and Point St. George. Small Craft Advisories remain in effect for the Northern Inner Waters and Southern Inner Waters for gusts to 30 knots and steep 7 to 8 foot seas. May need further extensions or upgrades to hazard coverage for at least the Northern Outer Waters beyond Monday.

FIRE WEATHER

Strong subsidence under the Great Basin upper ridge will maintain hot and dry conditions across interior valleys today. Ensembles indicate an 85 to 90 percent probability of minimum afternoon relative humidity values falling into the 8 to 14 percent range across parts the interior valleys. Expect many interior valley highs reaching 101 to 108F.

The zonal pressure gradient between the offshore Eastern Pacific High and the interior thermal low will drive gusty afternoon breezes through interior valleys and across exposed ridges. Model guidance shows a probability of west-northwest wind gusts reaching 20 to 25 mph through at least some wind-prone gaps and mountain passes. Poor nocturnal relative humidity recovery of 20 to 35 percent along some midslopes and ridges above the shallow marine inversion will maintain elevated fire weather concerns overnight.

There is the potential for dry thunderstorms Friday and/or Saturday this week. Confidence remains low on the details of how much moisture and the exact location of the storms. The current NBM has a 10 to 20 percent chance of thunderstorms across Trinity county and down in the Yolla Bollas.

COASTAL FLOODING

Sea levels have backed off slightly and are currently running 0.7 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 increases just slightly to run 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 10 PM PDT this evening for CAZ108- 110>114-116>120.

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

Gale Warning until 3 AM PDT Tuesday for PZZ470.

Gale Warning until 10 AM PDT Monday for PZZ475.