textproduct: Eureka

SYNOPSIS

A warm up for the next few days will be gradual. Moisture will make its way into the area towards the end of the weekend with the arrival of a frontal boundary and dynamic forcing, light rain is likely Sunday.

DISCUSSION

Broad flat ridging will remain over the the area through the end of the week. A long fetch of southwesterly moisture with above normal PWATS will remain offshore through the end of the week. Minor short wavelength disturbances in the southwest-westerly flow aloft may result (10-20% chance for a few hundredths) in a few light showers or sprinkles mostly across Del Norte and northern Humboldt through Friday, particularly over the highest terrain. More amplified flow is forecast to occur Fri-Sat as another trough digs offshore over the northeast Pacific and precip chance along the OR/CA border is forecast to diminish.

Otherwise, dry weather with generally above normal daytime high temperature is forecast for the rest of the week. Occasional mid and high clouds cutting over the flat ridge will hamper the longwave cooling and overnight low temperatures will most likely not be as cold. A more significant counter to the longwave cooling will be abundant low cloud cover and fog in the interior valleys. High resolution mesoscale models as well as BUFKIT profiles show lower boundary layer humidity tonight and low clouds may not be as extensive after the moist air push last night. Fog and low clouds will likely form again in the valleys Thu night/Fri AM, especially in Trinity, Humboldt and northern Mendo.

Days 3-7: Global models continue to indicate another shortwave trough approaching NW California coast this weekend. Surface frontal passage appears to hold off til Sunday when most of the precip is expected. A faster scenario suggests rain arriving earlier, Sat night. With a dominant blocking pattern, this does not appear as likely as a slower progression. Multi-model ensemble (NBM QMD) continues to indicate a 40-60% chance for 0.25 inches or more in 24 hours ending 4 PM Sunday or 4 AM Monday for mainly the northern most zones. There is a 13-23% chance for 1" in 24 hours over Del Norte mountains and SW Humboldt (King Range) for the same 24 hour time periods. Generally lighter amounts of rain are forecast for eastern valleys of Trinity and southern portions of Lake and southern Mendo where chances for 0.10 inches in 24 hours are around 20-45% ending 4 AM Monday. Snow levels appear quite high when most of the precip arrives, generally above 6kt on Sunday, lowering to 5kft in the cooler air after frontal passage by Monday morning. Southerly winds may also become gusty for the higher terrain in advance of the surface front Sat night or Sun morning. Deterministic GFS 925mb winds do increase to 40-45 kt offshore Sat evening. ECMWF ensemble meteograms and EFI are not suggesting strong southerly winds with the front at this time. NBM 24 hour probabilities indicate a 10-30% chance for gusts to 40 mph or more over the ridges of Del Norte and SW Humboldt Sat Night and Sun morning. Stay tuned for fine tuning of the forecast. Lingering showers will be possible on Monday before a ridge aloft amplifies and northerly to northeasterly surface flow develops and we stay dry for a day or two and perhaps most of next week.

AVIATION

Cold air moving east of the area has helped solidly turn wind out of the east. In turn, this has helped generate mostly dry and clear VFR conditions all along the coast. There is some slight potential for fog formation tonight in interior valleys such as near Ukiah, but passing high level clouds have even reduced that to a 50% chance. Widespread VFR conditions will continue all through the day and evening Thursday. /JHW

MARINE

Currently gentle southerly winds throughout the waters will persist until Saturday with only very isolated gusts over 20 kts int he far outer waters. That said, a persistent series of long period westerly swells will maintain a steep sea state through Friday morning. COmbined sea will most likely barely drop below 10 feet Friday, but another westerly swell will build in and keep sea no shorter than about 8 feet into the weekend. Sea will most likely very briefly calm Saturday night into Sunday, but a weak front crossing the area Sunday will most likely rebuild steep short period seas. Yet another round of steep, long period swells will build behind the frost once again building over 10 feet into early next week. /JHW

EKA WATCHES/WARNINGS/ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory from 3 AM Thursday to 3 AM PST Friday for PZZ450.

Small Craft Advisory until 3 AM PST Friday for PZZ455.

Small Craft Advisory until 3 AM PST Friday for PZZ470-475.