textproduct: Eureka

SYNOPSIS

Above normal warmth is forecast to continue early next week in the interior and then trend cooler later in the week. Chance for showers and interior thunderstorms will arrive on Wednesday and continue on Thursday and Friday.

DISCUSSION

Visible satellite imagery showed stratus and potential fog building offshore over the outer coastal waters this afternoon. Mesoscale model ensemble (HREF), BUFKIT time-height sections of temperature and humidity as well as model output statistics all point to a return of stratus and fog tonight into Monday morning for coastal land areas. Typically, after a warm up in the interior and along the coast, stratus and fog will come back hard with low visibilities of 1/4SM or less. HREF chances for dense fog are around 30-50% later tonight and Monday morning. Some areas of dense fog are possible by early Mon. The shallow marine layer and stratus should clear out in the afternoon on Mon, but areas of fog and low cloud may linger near or meander about near the shoreline through the day as winds remain light and variable. Precipitation chances are minimal Mon through Tue, though spats of coastal drizzle or a few sprinkles over the mountain tops are possible.

Otherwise, dry weather and above normal high temperatures are forecast to prevail across the interior through at least Tuesday as a ridge aloft springs back up after the passage of a weak transient wave embedded in southwesterly flow aloft. Above normal 500mb heights and 850mb temps may even last into the end of the week. High temperatures may not cool down much in the interior. Marine air and low clouds pushing into the coastal river valleys could also bring significant cooling around mid week if northwest winds increase offshore over the waters.

Precipitation chances return around mid-week (Wed) as a cut-off low centered near 35N and west 140W slowly burrows eastward into a dominant ridge. NBM and WPC have slowed down the arrival of the highest precip chances and amounts til Thu. Overall not much rain is expected over 3 days (Wed-Fri), generally less than 0.25 inches with locally higher amounts due convection in the interior. Potential for interior convection/thunderstorms increases as early as Wed with long CAPE profiles around 150-300j/kg, lifted indices near -1C and PWATS over 200% of normal in the afternoon/early evening over eastern Trinity, NE Mendo and northern Lake where low level convergence of upslope winds occur. Wrap around moisture with above normal precipitable water (PWATS > 200% of normal) and greater CAPE Thu and Fri should yield stronger storms that may result in heavy downpours and perhaps some small hail. Profiles are not too favorable to strong and gusty outflow winds (inverted-V profiles), however a few deterministic models, namely the ECMWF, indicate higher surface-to-500mb S-SE bulk shear around 35-40kt and strong multi-cell storm clusters seem possible in the interior.

Beyond Fri into next weekend, wrap around moisture with interior showers and thunder remains possible on Fri and Sat if the eastward progression of cut-off low slows down or stalls over the area. Another trough may come barreling down from the NW bringing considerable cooling and perhaps more light precip. Or the ridge will come back and leave the area in dry stable weather with a warm up for the interior.

AVIATION

VFR conditions at all terminals through the day. Inland terminals to experience up-valley/up-slope, terrain-driven winds through the daylight hours. This evening, there is moderate to high probabilities of coastal stratus developing along the North Coast. This could set in between 03-06Z with a chance (20-40%) for fog development by 08Z. Expect IFR to LIFR categories from this evening through the monring as models show this cloud deck persisting through the 04/06/1800Z. Inland remains VFR through the TAF period. DS

MARINE

Weak atmospheric forcing over the coastal waters will keep winds light (<10kts) today through Tuesday. Beginning Tuesday, a surface low pressure center currently at ~145W will finally have moved close enough to force northerly winds. There remains uncertainty as to how strong these winds will be, as it depends on where this low pressure center ends up off the coast of California. As for right now however, the outer waters can expected winds between 10-20kts and the inner waters can expect winds between 5-15kts from Wednesday through the end of the week. The higher end of these winds could produce steeper seas.

In terms of swell, expect a small, long period swell through the coming week. Today through Wednesday a small, short-to-mid period swell out of the NW. The sea state later in the week will be dominated by the waves from our developing northerly winds. DS

EKA WATCHES/WARNINGS/ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... None.