textproduct: Eureka

SYNOPSIS

The possibility of interior thunderstorms increases Friday into Sunday as an area of low pressure begins to organize by the end of the week.

DISCUSSION

Marine stratus filling in overnight into Wednesday morning as low level inversion is further enhanced behind high pressure and subsidence, albeit a weak ridging pattern with gaps not encouraging vorticity. The gradient will not be particularly steep across isobars until a more uniformed and defined system begins to form Saturday, strengthening Sunday. That said, GFS is highlighting MUCAPE and RH with an embedded shortwave late Friday afternoon into the early evening for the interior areas of Siskiyou, western Trinity and in a linear succession down to northeastern Mendocino and western Lake county. The mean surface CAPE from NBM is highlighting most of the interior starting Friday which could be attributed to surface heating and parcel buoyancy but with increasing humidity there could be implications for thunderstorm activity. Ensembles also show a rise in PWAT values rising into the weekend for what could be thunderstorms with the chance of lightning Friday through Monday at least. NBM begins to include Del Norte Saturday early evening for 15% and greater chances of thunder which also coincides with high CAPE values in the 700-800j/kg range. /EYS

AVIATION...00Z TAFs

Stratus expanded out from Humboldt Bay Tuesday evening. Confidence is growing on southerly return flow from a coastal eddy to advect stratus up to CEC through Wednesday morning. MVFR to IFR CIGS expected at ACV (53% chance for IFR). There is a lesser chance (20%) for LIFR in the 13-16Z Wednesday timeframe at ACV. CIGS at CEC will mainly range in MVFR levels for a chance (26%) for IFR. UKI is expected to remain VFR with very little indications for a surge push of stratus up the Russian River Valley. Chances for this occurrence and resulting MVFR CIGS are 21%.

MARINE

Northerly winds will continue their strengthening trend through Friday. Gale to near gale conditions will be possible in the waters by Thursday. The inner water buoys are recording up to 8 ft short period seas Tuesday night, with propagation from the outer zones where the stronger northerlies continue. Small Craft advisories remain in all zones to cover the wind and steep sea threat to smaller vessels.

A brief period of lower seas is possible Wednesday morning and early afternoon so the advisories end early Wednesday morning. However, winds and seas will build further by Wednesday afternoon and advisories will need to once again be issued for those areas starting as early as mid afternoon on Wednesday. Persistent winds over the outer waters will keep seas elevated and winds in small craft criteria to near gale Wednesday into Wednesday night. As the pressure gradient further strengthens, gale force gusts will become likely Thursday afternoon through Friday night in the outer zones. Gale conditions may linger into Saturday before winds begin substantially easing late Saturday afternoon.

EKA WATCHES/WARNINGS/ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 5 AM PDT early this morning for PZZ450.

Small Craft Advisory until 6 AM PDT early this morning for PZZ455.

Small Craft Advisory until 3 PM PDT Thursday for PZZ470.

Gale Watch from Thursday afternoon through late Friday night for PZZ470.

Small Craft Advisory until 11 PM PDT this evening for PZZ475.

Gale Watch from this evening through late Friday night for PZZ475.