textproduct: Eureka

SYNOPSIS

Isolated light showers and sprinkles will be possible across Del Norte and far northern Humboldt through Thursday. Otherwise, dry weather, variable cloud cover and slightly warmer daytime temperatures are forecast through Saturday. Chance for light to moderate rain will increase Saturday night and 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 tonight-Fri, 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 ORCA 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...18Z TAFs

With daytime clearing of inland valley stratus, VFR conditions developed. High to mid level clouds will continue moving in through today while winds remain light from the south.

The recent rainfall will encourage in inland valley fog formation overnight and through Thursday morning, with impacts likely through UKI. The oceanic southerly flow will drive a band of stratus northward overnight and Thursday. Current impacts to the coast look limited at this time. A closer brush is possible along the Mendocino coast. Patchy fog is possible, but HREF visibilities do not depict VIS values under 3SM for the Mendocino coast at this time. Stratus may push closer to the Del Norte coast at times Thursday, with low confidence on CEC terminal impacts. Radiational fog development is always a concern after rainfall. The mid to high level cloud deck should limit coverage over the coastal terminals. JJW

MARINE

Mid to long period W to WSW swells add to the combined sea height of 8 to 10 ft Wednesday. Short period southerly seas of 6- 8 ft remain in the northern outer waters where southerly winds of 15 to 18 kts remain through Friday. Winds out to 10 nm and over most of the souther outer waters will remain light and generally from the south.

Stronger south winds and steep seas return for the weekend. NBM is showing around a 53% chance for gale force gusts north of Cape Mendocino.

Seas will quickly increase after midnight as a large, long period westerly swell builds in. The swell will peak Thursday at 12-14 ft at 15 to 16 seconds Thursday, then will gradually begin to subside into Friday. Combined seas may briefly fall below 10 ft Friday, but an additional mid period swell will keep seas elevated.

Combined sea heights are forecast to rise above 10 ft later Saturday from an additional long period westerly swell. A larger, long period west swell builds in Sunday when seas will reach 12-14 ft.

Seas and winds currently look to be much lower going into next week. NBM does show a 54% chance for an isolated area of gale strength gusts from northerly winds around and south of Cape Mendocino. JJW

COASTAL FLOODING

Chance for minor high tide flooding of low-lying areas around Humboldt Bay will increase during the latter portion of the week, primarily on Friday and Saturday. Highest chance (40%) for salt water inundation of normally dry areas will be on Saturday, Jan 31st. Impacts are not expected to be as severe as the King Tide flooding observed in early January. More nuisance road flooding is likely in areas like King Salmon. Strong southerly winds and large surf will increase the risk for coastal flooding.

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 from 10 PM this evening to 3 AM PST Friday for PZZ455.

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