textproduct: Eureka

SYNOPSIS

Generally warm and calm conditions will persist Friday with slight cooling this weekend. Friday and Saturday will see isolated thunderstorms over the interior mountains with broader and stronger storm potential Sunday.

KEY MESSAGES

-Warm and dry conditions will continue Friday with a weak marine layer near shore

-Isolated thunderstorms (10-15% chance) over the eastern interior Friday and Saturday afternoon.

-Scattered and strong thunderstorms (15-25% chance) over the the interior Sunday afternoon with some storms pushing closer to shore.

DISCUSSION

Weak high pressure has begun to peak today with interior highs in the upper 70s to low 80s under mostly clear and dry conditions. A broken marine layer has persisted near the coast thanks to a building marine inversion.

A weak shortwave approaching the area Friday and into the weekend will bring somewhat more unsettled conditions. Increased marine influence and cloud cover will slightly cool interior temperatures with highs mostly in the mid 70s by Saturday. Lower pressure will help lift the marine layer onshore, though moth models show at least some marine stratus sticking around.

The greatest impact of the shortwave will be the potential for thunderstorms over the interior. Beginning Friday afternoon, daytime CAPE values will begin to approach 1000 J/Kg over the eastern interior. Precipitable water, however, will be very marginal generally between 0.4 and 0.8 inches. Such factors will combine to create isolated thunderstorms (10 to 15% chance) over the interior. Chances will be greatest and far eastern Trinity, Mendocino, and Lake COunties along the rim of the Sacramento Valley. Very similar conditions are expected Saturday, though most convective models show a slight reduction in thunder chances (generally less than 15%).

The shortwave will morph into a cutoff low and travel down along the California coast Saturday into Sunday. Tropical air wrapping up the Sacramento valley will bring much more moisture to the area with precipitable water over 1.2 inches. Combined with increasing wind shear and still solid CAPE, the chances for thunderstorms will be much greater on Sunday. Storm chances over the interior are around 25% with greater potential for storms to push east to west into the coast (10 to 15% chance of storms along the Humboldt and Del Norte COast). Some of the storms over the interior hold the potential to be severe with strong outflow winds and isolated damaging hail. Storms are most likely to be wet, so much so that NBM currently places a 0.1 to 0.3 inches of rain all across the northern half of the area on Sunday.

Storms will likely leave behind cooler and cloudier conditions for next Monday, though moisture and clouds will generally limit any frost or freeze concerns. Generally calm and warm conditions will most likely build for the remainder of next week.

AVIATION

Satellite imagery shows coastal stratus evaporating close to coastal terminals sites. A large bank of stratus continues to exist over the Pacific. There is high confidence (>70%) of this stratus deck returning over the coastal terminals this afternoon/evening. A slight (~30%) chance of drizzle is possible for both KACV and KCEC this evening into Friday morning. Northerly winds will build through the day as well. Inland, VFR is expected with gusty winds close to ridgetops. Northerly winds are forecasted to continue inland as well, with N-S orientated valleys having strong flow compared to other protected areas.

MARINE

Low pressure over the interior interacting with high pressure in the NE Pacific is strengthening the surface pressure gradient. This setup is resulting in northerly winds strengthening over the waters, leading to large, steep seas. While the largest waves are modeled for the outer waters, steep seas of 7 to 9 ft are propagating into the inners as well. Near-gale to gale conditions will periodically develop each afternoon over the waters through Saturday. Gale strength gusts will be more persistent around and south of Cape Mendocino, yet coverage is too low to warrant a widespread gale warning for the southern waters. Hazardous Seas Warnings persist over the outer zones to account for the periods of light gales but more importantly the continued large, steep seas. Conditions hazardous to small crafts are being observed for the inner zones due winds up to 20-25 kts and steep seas of 7 to 10 ft. An area of low pressure will approach the area Saturday, allowing the northerly winds to subside through Saturday evening. This will begin an extended period of lighter winds and smaller seas which may carry into next week. The GFS global water shows a long period swell filling into the waters Saturday afternoon. As it arrives, the swell is forecasted to be around 2ft@20s before building up to 7ft@15s by Sunday evening.

BEACH HAZARDS

On Sunday, a long period northwest swell with periods between 16-19 seconds will arrive. This swell continues to be monitored as it may pose a moderate risk of sneaker waves for coastal areas. Should this swell continue as modeled, a Beach Hazard Statement is more likely than not to be hoisted. Sneaker waves are anomalously large, unexpected waves that sweep across beaches without warning. There can be up to 30 minutes of smaller waves before a sneaker wave arrives to the shoreline. Choose your recreation wisely by avoiding steep beaches and jetties as well as staying much farther back from the ocean than normal. Never turn your back on the ocean! DS

EKA WATCHES/WARNINGS/ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 9 AM PDT Saturday for PZZ450-455.

Hazardous Seas Warning until 9 AM PDT Saturday for PZZ470- 475.