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

Last weeks high pressure center has migrated over east TX and has become what seems to be a steady standing wave. This is resulting in pronounced light troughing over the western seaboard. Monsoonal moisture continues to flow northward through the Great Basin area with some moisture reaching the Central Valley of California. Shortwave disturbances are predicted to wobble their way downstream of the upper level flow, increases vorticity and lift for the west as well.

One result of this troughing besides cooler temperatures inland due to less compressional heating is 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. Thursday afternoons storm chances failed to materialize in NW CA, yet tomorrow the atmospheric set up will be different.

High resolution models are starting to grasp a passing shortwave disturbance tomorrow afternoon into the evening. The NAM12km model shows the shortwave setting up with its axis directly off the North Coast's coastline. In addition, the HRRR Simulated IR model shows a band of light convection racing through NW CA later Friday. That said, there is limited moisture in the environment with approx. 0.2- 0.3" above normal PWAT values. In addition, smoke and cooler temperatures will decrease instability. This means that while it is likely that atmospheric forcing will be present, there is just not enough "juice" in the atmosphere to really get any convection started. However, any storms that DO form, will likely produce dry lighting and should be taken seriously if spotted. Lightning probability have been capped a "Slight Chance" for the area to capture this unlikely, yet highly impactful, weather event.

Global ensembles show this synoptic feature continuing through next work week. Expect relatively repetitive weather conditions for the next 7 days.

AVIATION

Coastal terminals can expect IFR with periodic LIFR through the end of the week. Winds will remain light (<10kts) for the coast as well. Inland areas will experience enhanced terrain forced winds with potential increased cloud coverage within river valleys. Smoke continues for the Trinity River Valley and much of Trinity County.

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. Inversion are forecasted to be weaker and break earlier in the day. A deeper marine layer will reach further up river valleys through the night as well, possibly impacting any Rx burning operations.

This afternoon, 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 through the evening. 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... Small Craft Advisory until 3 AM PDT early this morning for PZZ455.

Small Craft Advisory until noon PDT today for PZZ470.

Small Craft Advisory until 6 PM PDT this evening for PZZ475.