textproduct: Eureka

KEY MESSAGES

* A few 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.

* Not much precipitable rain expected other than drizzle.

SYNOPSIS

An upper level trough along with isolated low pressure areas from the south will breakdown the persistent upper level ridge pattern by the end of the week. A few more mornings of dense fog are likely until the trough swings down from B.C. and interrupts the stable layer inversion.

DISCUSSION

As the work week progresses, the strong area of high pressure that has kept a Heatrisk advisory in play for the southern areas of the CWA, will get a reprieve as the high pressure over the four corners gets overwhelmed. Several low pressure areas from the active ENSO equatorial reversal, approach from the southeastern Pacific. This upcoming set up will have these lows absorbed into the upper wave trough which will be stretching down the west coast at the end of the week - Friday and Saturday, according to the ECMWF and GFS. Despite plenty of moisture being sourced, there are'nt any signs of precipitable amounts greater than a few hundredths of an inch for our area in the next several days other than occasional drizzle or condensed low cloud vapor from overnight cooling dynamics.

Otherwise, there is a definite drop off in temperatures from Thursday to Friday and even more of a diminish of daytime high temperatures into the weekend. The previously mentioned areas of low pressure begin to interact with the upper wave pattern Friday morning as the larger upper trough amplifies over British Columbia bringing cooler air masses with the frontal boundary. Chances for any rain are less than 10% and, if anything, would manifest in enhanced coastal drizzle. This inside slider pattern would still bring much cooler temperatures with highs this weekend 10 to 20 degrees cooler. Low temperatures also have high chances to be the coldest yet of the fall with 20 to 50% chances for freezing temperatures this weekend into early next week in the coldest valleys of Trinity and eastern Mendocino Counties.

Along with the cooler temperatures, breezy northerly winds are also becoming more likely, especially along the coast. NBM is showing 30% chances for gusts over 40 mph on the Humboldt and Del Norte coasts on Saturday, with locally higher probabilities over the King Range and mountains of Del Norte. Chances for gusts over 30 mph are much higher and more widespread at 70% along the coast and 20-50% for much of the interior. While winds are likely to be strongest Saturday, breezy winds are likely again Sunday.

As of now, the extended forecast remains dry. Long range ensembles show little chance for any precipitation with much of the storm track moving north of the area. CPC also has high chances for below normal precipitation in the 8-14 day outlook.

AVIATION...18Z TAFs

A very shallow marine layer continues to impact the coastal terminals. Visibilities lowered to less than 1/4SM at times from the shallow stratus. Daytime heating is allowing for scattering and improvement at ACV and CEC, but at least TEMPO periods of fog and LIFR conditions are possible as light NW winds pool the stratus against the coast, particularly around Humboldt Bay and ACV. Expect LIFR conditions and fog to quickly redevelop through the later afternoon and evening hours for the coastal areas. The fog is expected to become locally dense once again, with visibilities than than 1/4SM. The interior will remain VFR with generally light winds.

MARINE

North winds remain elevated in the outer waters today with widespread sustained winds of 15 kt to 20kts. Seas steepen in response to these winds bringing combined seas of 6 to 10 ft across the waters, including in the nearshore waters where winds remain much lighter. Areas of dense fog with visibilities at times less than 1/4 miles will remain over the waters Seas remain dominated by these wind waves through the week with only small south- southwesterly mid period swells in addition to the wind waves. Winds begin to ease Wednesday, especially in the southern waters, as high pressure strengthens further. Stronger northerlies return Friday into the weekend. Widespread gale force gusts to areas of sustained gale strength winds are likely this weekend. Storm force gusts are possible in the lee of Cape Mendocino.

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 11 PM PDT this evening for PZZ450.

Small Craft Advisory until 4 PM PDT Wednesday for PZZ470- 475.