Key messages
- Rain showers are expected to continue to taper off this afternoon and evening.
- Dry, cooler and breezy conditions are expected Friday with frost or freezing temperatures possible Friday night/Saturday morning.
- There is the potential for a pattern change to cooler and wetter weather. This may start as early as Sunday or more likely hold off until early or mid next week.
Synopsis
Rain showers continue through this afternoon and finally move out this evening and overnight. This will set up a cool and dry Friday with frost likely Friday night. Warm and dry conditions are expected Saturday. The next chance for rain for Humboldt and Del Norte is expected by late this weekend/early next week.
Discussion
An upper level low pressure system will continue its journey east through Central California today with associated rain showers continually diminishing this afternoon/evening for Northwest California. Light to moderate rain occurred this morning for the North Coast. In particular, there has been a multi hour almost continual band of moderate rainfall over mostly Humboldt County with widespread rain totals of 0.55 to 0.90 inches between about Orleans, Slate Creek, and Notchko down to School House Ridge through the cities around Humboldt Bay, and the hills east of Humboldt Bay down to Bridgeville. While rain showers are diminishing and ending along the North Coast, showers will continue through Trinity, Mendocino, and Lake counties into later this evening.
The low quickly moves east of the area this evening with much drier air filling in behind. The areas that do manage to clear are expected to see valley fog. The chilly airmass could allow some areas to drop into the mid 30s and see localized frost, but with widespread rainfall, valley fog will limit cooling. Closer to the coast and above a couple thousand feet, the ridges are expected to clear out and see breezy easterly winds. Friday is expected to see quite a bit of drying, but temperatures are expected to remain in the 60s to low 70s. This drier air will set up the area for a chilly night Friday into Saturday morning. Easterly winds will likely keep the coast clear and the ridges dry.
Sunday and into early next week, the forecast remains highly uncertain. The models have backed off from the wettest solutions. However, some of the model clusters continue to show a tenth to a quarter of an inch of rain on Sunday, mainly in the evening. NBM shows around a 35% chance for a tenth of an inch of rain Sunday night into Monday for Northern Humboldt and Del Norte. The models are still showing a fairly even split between a large ridge and trough over the area. This could mean a difference in interior high temperatures in the 50s in the trough or over 75 under the ridge. By Tuesday or Wednesday an increasing number of the cluster members showing a trough moving into the area bringing the potential for some rain. This will definitely be a time period to watch and may be the early signs of a more significant pattern change. JB/MKK
Aviation
Showers continue to taper off for coastal terminals as they linger in Mendocino, Trinity and Lake. IFR to MVFR conditions will dominate into the evening. Later this evening, winds will begin to trend offshore. This will aid in the gradual scattering and lifting of lower clouds at area terminals overnight.
Marine
Elevated northerly winds and steep seas are anticipated through Saturday with a very high chance for widespread gale force gusts by very late today/early Friday and continuing into very early Saturday. Seas will be dominated by these steep and hazardous wind waves. Winds diminish Saturday into Sunday as a low pressure system approaches north of the area. JLW/JB
Fire Weather
After this upper low exits the area this evening, a much drier airmass arrives Friday into Saturday. Breezy offshore winds over the ridges will develop this evening in Del Norte and Siskiyou and over much of the interior ridges Friday night. Lake County, especially, could see more widespread offshore winds over the higher terrain. Overnight recoveries outside the valley floors are likely to be poor given these offshore winds with Maximum RHs in the 20s and 30s. While critical conditions are possible, wetting rains today may limit the impact of these conditions somewhat. There is also some uncertainty on how long and how widespread these winds will be. This will need to be watched for potential fire weather headlines. JB
Coastal Flooding
High astronomical tides associated with the full moon will bring chances for coastal flooding around Humboldt Bay starting as early as Sunday with chances continuing through next week. Astronomical tides at the North Spit tide gauge reaches 7.49 ft MLLW on 11:26 AM Sunday. With the tidal anomaly currently running 1.0 to 1.5 ft above forecast, minor coastal flooding is possible at these levels. The highest astronomical tides, and highest chances for coastal flooding, are forecast to be on Tuesday and Wednesday of next week at 8.04 ft and 8.06 ft, respectively. JB
Eka Watches/Warnings/Advisories
CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory from 6 PM this evening to 9 PM PDT Friday for PZZ450-455.
Small Craft Advisory until 6 PM PDT this evening for PZZ470.
Gale Warning from 6 PM this evening to 9 PM PDT Friday for PZZ470.
Small Craft Advisory until 9 PM PDT this evening for PZZ475.
Gale Warning from 9 PM this evening to 9 PM PDT Friday for PZZ475.
NOTE: The full forecast discussion is now regularly issued between 10 am/pm and 1 pm/am. Additional updates will be issued as needed.
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