textproduct: Eureka

KEY MESSAGES

* Slight chance of interior thunderstorms today into Saturday.

* Smokey conditions likely from the MP18 Fire, focused in the Trinity River Valley and Trinity County.

* Cooler temperatures are likely through next week.

SYNOPSIS

A troughing pattern has set up over the region. Inland areas can expect cooler temperatures with the coast continuing to have overcast conditions and brief afternoon clearing. Passing shortwave disturbances increase the chance for storms inland.

DISCUSSION

The approach of an upper level trough has and will have dynamic effects on short term weather through the weekend. The extent of what those effects are is still uncertain as the axis of the broader open wave system swings over the CWA. From model soundings there are a few moisture signatures at 7k feet and way up high in the 33k feet range or 300mb which confirms the high clouds seen in the IR satellite observation you can see there. The lightning detection network has not shown any cloud to cloud or cloud to ground strikes as of 21z which could mean weak updraft helicity. Most of the components that would give us confidence in warning of a highly probable-dangerous system just are'nt there but at least within a 10-15% chance of lightning this late afternoon and into the evening. Areas that are being highlighted for HREF lightning probabilities > 10% include Trinity county near Hayfork and along the Yolla Bolly district- neighboring Tehama and Glenn Counties. Of particular focus would also be the border of Siskiyou with Trinity and Del Norte, which skew-T soundings show CAPE values in the 740 J/kg range with similar lightning probabilities > 10%. If any convective activity starts, it will be over by 06-07z. Other features from the troughing pattern will be cooler temperatures and the increased chance for rainshowers and thunderstorms for the interior. While moisture flow is not too impressive, these shortwave disturbances could have enough of an impact to promote convective activity through Saturday. Global ensembles show this synoptic feature continuing through next work week. Expect relatively repetitive weather conditions for the next several days. /EYS

AVIATION

18Z TAFs. A shortwave trough is moving through the region through Saturday morning. The marine layer has further deepened with light winds in response. Afternoon and evening MVFR to IFR ceilings at the coastal terminals will transition to IFR to LIFR through Saturday morning. Light coastal drizzle would further lower VIS and bring chances for fog. Ceilings will lift Saturday, but the deep marine layer will likely lock coverage in again to limit clearing along the coast. Farther south, abundant stratus in place through the Russian River Valley is expected to transport back into UKI before late morning clearing in the 17-18Z Saturday period.

MARINE

A relatively weak trough has set up over the region. This has caused a decrease in overall wind speeds. Waves remain steep, yet they should continue to decay through the end of the week. A southerly swell of ~3ft will build into the region by the weekend and will mix with northerly shorter period waves. However, the overall sea state should remain mixed with these two wave groups through the start of next week. Light to moderately breezy (~20kt) winds are expected through the extended forecast as of right now.

FIRE WEATHER

A troughing pattern has set up over the region. This will result in lower daytime temperatures, increased RH values, and stronger winds due to increased mixing. A deeper marine layer will reach further up river valleys through the night as well, possibly impacting any Rx burning operations.

This evening, there is a low chance (10-15%) of highly impactful thunderstorms forming over the interior specifically for the Klamath, Salmon, and Yolla Bolly Mountains. Forecast confidence is very low due to decreased instability and relatively normal moisture, however lifting will be amplified due to a shortwave disturbance flowing over the region. Any storms that do form will have motions towards the NE which should decrease the chance of any impacts. However, DCAPE values remain amplified enough create gusts capable of traveling down river valleys.

EKA WATCHES/WARNINGS/ADVISORIES

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