textproduct: Eureka

SYNOPSIS

DISCUSSION

Satellite imagery shows areas of stratus and fog in many of the coastal and interior valleys late this morning. Low cloud cover will gradually lift and scatter out today, giving way to a fairly pleasant December afternoon. The main exception will be at the northern Humboldt and Del Norte coasts, where stratus and drizzle is likely to return this afternoon and evening one last day. Precipitation amounts are very minimal with up to a few hundredths of an inch of drizzle possible in Del Norte. High pressure moving over the area will disrupt any further drizzle after today.

The persistent ridge of high pressure responsible for blocking Pacific storm systems will strengthen and nose eastward through the week. Significant warming for the interior will occur as a result. The current forecast yields interior high temperatures reaching 10-20F above climatological norms midweek through the weekend. NBM shows a high probability (70% or higher) for the warmer interior valleys, including Ukiah and much of Lake County, to exceed 70F Thursday and Friday. NBM probabilities for exceeding 75F around Ukiah is around 20% for Thursday and Friday. This would break the high temperature record of 72F from 1958 for Ukiah on Friday if the forecast holds. NBM data shows around a 40% chance of a new record for Friday.

Ensembles and clusters are hinting at the weakening of the stubborn ridge through the weekend. Precipitation chances start to increase through the latter portion of the weekend. However, any meaningful breakdown of the ridge or zonal flow may not occur until early next week. A more likely situation is fairly steady light rain compared to heavy downpours.

AVIATION...(06Z TAFs)

Ceilings have come down as of 04z for KCEC as IFR conditions are likely to prevail until Wednesday afternoon. With light drizzle, accumulated precipitation presents another hazard as radiational cooling produces fog at ground level. Tempo groups for such the occasion accompany the 06z TAFs. Light wind is an additional supporting factor for fog development which is in play for all terminals through the night. Ceilings at KCEC will hover under 1000ft or so, with lower visibility into Wednesday morning. KACV has similar conditions, lifting ceilings out by 18z Wednesday. KUKI is also susceptible to fog from a different source, likely to be advection from a cardinal direction. The area profiler shows shallow fog south of KUKI, so not likely to advect up the valley but possible from other directions. /EYS

MARINE

Northerly winds are forecast to ramp up south of Cape Mendocino and persist through at least Friday. Wind gusts peak around 20-30 kts in the lee of Cape Mendocino, with breezy winds reaching nearshore areas at times. Steep wind waves of 5-7 ft are possible with these winds. North of Cape Mendocino, winds remain light and southerly through at least Thursday. North winds return late Thursday into Friday and could be breezy in the outer waters. The sea state remains dominated by mid-period northwest swells, with additional swells filling in Wednesday and again Thursday. These will keep the sea state elevated and combined seas could exceed 10 ft at times, especially south of the Cape where the swell will combine with the steep wind waves. Winds ease this weekend as high pressure weakens. JB

BEACH HAZARDS

An increased threat of sneaker waves is expected for the Del Norte, Humboldt, and Mendocino coastlines this Thursday. A mid-period westerly swell generated by a storm currently located near 45N,155W will enter the coastal waters early Thursday (tomorrow) morning. A lack of local wind waves along the North Coast will allow this swell to dominate the sea state over an existing, yet decaying, swell, creating beach conditions that could look deceivingly calm. Forecast confidence will grow as the swell passes NOAA/NDBC buoys Wednesday morning. Remember to never turn your back to the ocean, and to avoid steep beaches, jetties, outcroppings, and rocks during these events. DS

EKA WATCHES/WARNINGS/ADVISORIES

CA... Beach Hazards Statement from Thursday morning through Thursday evening for CAZ101-103-104-109.

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory from 3 PM this afternoon to 10 AM PST Thursday for PZZ455.

Small Craft Advisory from 3 PM this afternoon to 2 AM PST Friday for PZZ475.