textproduct: Eureka

SYNOPSIS

High pressure continues over NW California resulting in warm and dry conditions this week. Nocturnal valley fog is possible for northern valleys along the Trinity and Klamath rivers.

DISCUSSION

An upper level ridge has situated itself over the West Coast leading to consistent high pressure. High pressure conditions will result in cold mornings through the week as cold air drains to lower elevation spots, such as the coast and inland valleys. There is high forecast confidence that this trend will continue through the work week.

The previously mentioned cold air draining can also lead to inland valley fog, especially for east-west oriented valleys that are more sheltered from sunlight. As this cold air settles in valleys, the air will become stagnant. With stagnate air, there is an increased possibility of smoke and other pollutants remaining in valleys for multiple days leading to the potential for air quality hazards. Stagnate air in these valleys will also keep inland valley high temperatures lower. As a result, the forecasted high temperatures have been decreased from the National Blend of Models to align more with observations from previous days and, also, future expectation of trends. Along the ridges and inland valleys that remain relatively clear, warmer than average daytime temperatures are expected this week.

Relative humidity values will remain high in the valleys where air is cooler with ridgetops above the cold air layer experiencing much dryer conditions each night and day this week. This weather pattern will continue until the middle of next week, when the high pressure overhead is forecast to move out of the area and a frontal weather system may begin to return to NW California. DS

AVIATION...6Z TAFs

High pressure strengthens over Northern California. The biggest forecast challenge is if the marine layer will saturate the boundary layer enough to create fog/ low stratus around coastal terminals. HREF model data shows a 70% probability of stratus occupying after 11Z, especially for the Humboldt Bay area. TAF LAMP guidance supports this with a 50% probability of ceilings below 1000 ft AGL. Stratus and some radiational fog is expected, with only the coverage in question. Models have been trending later Tuesday morning for development. Soundings saturate the lower levels and are pessimistic with drying Tuesday. With the building ridge and strengthening inversion, whatever manages to form may be pesky along the coast today. There is some indication a weak southerly return eddy will form off the North Coast late Tuesday morning. This would keep the stratus closer to ACV and CEC. DS/JJW

MARINE

Coastal water conditions remain dominated by a fading northwesterly, mid period swell. This northwest swell will decrease in size through mid-week before another, somewhat smaller, northwest swell arrives Wednesday morning.

Northerly winds turn light on Tuesday. Come Wednesday, winds increase speed again, with the strongest winds remaining mostly in the outer waters. Winds will increase throughout the day Wednesday peaking at speeds of near gale force gusts in the northern outer waters. Steep wind waves up to 10 feet are expected to form with these winds. The steep waves will likely warrant Small Craft Advisory Wednesday afternoon through Thursday if the forecast remains on track. Stronger winds and steep seas up to 12 feet are possible in the far northern outer waters, and this may exceed advisory level conditions if the forecast increases the coverage of near gale winds and steep seas.

EKA WATCHES/WARNINGS/ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 3 AM PST Tuesday for PZZ470-475.