textproduct: Eureka

SYNOPSIS

Shower activity and the chance for thunderstorms continue late this afternoon and evenin. Potential for thudnesrtorms increase across the interior on Thursday. Breezy NW winds over coastal headlands and exposed ridges through this evening. A warming and drier trend expected Friday through mid- next week.

KEY MESSAGES

- Breezy nort-nortwest winds along the coastal headlands and exposed ridges through this evening. - Showers and occassional thunderstorms continue late this afternoon and evening.

- Potential of thunderstorms increase (15-30% chance) across the interior on Thursday, capable of produce dangarous lightning strikes, brief heavy downpours, small hail, and gusty, erratic winds.

- Drier with a gradual warming trend this weekend through early next week, with interior Minor HeatRisk potentially on Monday.

DISCUSSION

Showers are rotating west-northwest around a low- pressure system centered over the Sierra this afternoon. As of 1 PM PDT, radar imagegry depicts thunderstorms with frequent lighting strikes just right the northern Humboldt Coast, between Orick and Klamath, before the steering flow pushed them westward over the waters. This development is driven by a sharp, mesoscale convergence zone where synoptic northeasterly flow associated with the afforementioned low- pressure is effectively undercutting and colliding with the gusty northwesterly wind flowing down the immediate coastline. In addition, northwesterly winds peack up along the coastal headland and exposed ridges this afternoon, where gusts from 25 to around 40 mph are observed. Winds are expected to diminish this evening into Thursday.

An uptick in precipitation is expected late this afternoon and evening, with stronger showers and occassional thunderstorms. CAMs suggest organized convective showers moving westward across Trinity County. HRRR and HiRes-ARW model sounding guidances are suggesting elevated instability and steep mid-level lapse rates over Trinity County. There remain a 10-20% chance of thunderstorms over the high terrain in Trinity County, with a non-zero probability elsewhere. Frequent lightning, brief heacy downpours and gusty, erratic winds are possible with the strongest storms.

On Thursday, isolated to scattered thudnerstorms are forecast to developed in the back side of the closed low Thursday afternoon. Cold air aloft and higher instability (MUCAPE value around 200-300 J/kg) will increase the chances (15-30%) of thunderstorms across the interior on Thursday, with the highest chance in Trinity County. Occassional cloud-to- ground lightning, brief heavy downpours, small hail, and gusty, erratic winds will be possible.

A weak ridge builds in briefly on Friday, while the low exits the area shifting eastward. This will bring dry air across the area. However, some lingering moisture will yield in isolated mountain showers across the eastern portion of the area the on Friday. Although the chances of thundertorms are lower (less than 10%),a non-zero chances remains in place. High temperatures are expected to increase and become more seasonal for this time of the year.

Saturday, a weak disturbance will move across the area and trigger another chance of isolated mountain thunderstorm development over NE Trinity County in the afternoon. The NBM has a chance of thunderstorms up to 15% in Trinity County for Saturday afternoon. While most model soundings depict a well- defined cap that could inhibit convection over most of our CWA.

The 500 mb ridge appears to slowly build back Sunday through mid- next week, resulting in drier weather with a gradual warming trend. Minor HeatRisk will likely resturn on Monday, especially across the interior valleys. High uncertainties are for mid to late next week. Ensemble clusters suggest the ridge weakening and flattening by mid next week with a broad upper level trough developing over the Gulf of Alaska./ZVS

AVIATION

Passing showers have brought brief periods of IFR along the coast but otherwise gusty north winds under high overcast ceilings have generated mostly VFR conditions all along the coast. Most high resolution models show another line of showers crossing the area between 5 and 10 PM this evening, which is likely to again bring sporadic IFR conditions. Otherwise, most models (70%) show largely VFR conditions overnight, though there is slight potential for low coastal fog and clouds. VFR conditions are most likely Friday with showers over the interior but less likely near the coast. /JHW

MARINE

Strong north winds persist in all waters this afternoon with some gale conditions focused in the northern outer waters. Short period seas remain very steep up to 12 feet. North winds will begin to weaken and pull further offshore into Thursday. Just as short period seas begin to fall, however, a unusually long period northwest swell will build up to around 7 feet. Such a swell is unusual for May and will brining at least a moderate risk of sneaker waves to area beaches. Otherwise, Winds will be mostly calm by Thursday afternoon alongside falling short period seas. Moderate north winds will begin to return to all waters Friday and into the weekend. Some marginal gale conditions are possible by Saturday. /JHW

BEACH HAZARDS

Shorter period seas and winds will calm Wednesday evening into Thursday. At the same time, an unusually long period northwest swell will build Wednesday evening and through the day on Thursday. The forerunners of this swell will begin to build in at just couple feet around 24 seconds. The swell will peak Thursday around 8 feet at 16 seconds. Though falling short period waves will somewhat mask the swell, there will be a moderate risk of sneaker waves on area beaches. The greatest risk will be in areas of mostly calm winds on beaches that are exposed to the northwest. /JHW

EKA WATCHES/WARNINGS/ADVISORIES

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

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 5 AM PDT Thursday for PZZ450-455.

Small Craft Advisory until 3 PM PDT this afternoon for PZZ470.

Gale Warning until 11 PM PDT this evening for PZZ470.

Small Craft Advisory until 11 AM PDT Thursday for PZZ475.