textproduct: Eureka

SYNOPSIS

Wet and unsettled weather with showers and c thunderstorms will continue Thursday through Friday. Significant cooling, more rain, possible thunderstorms and high mountain snow are anticipated for this upcoming weekend.

DISCUSSION

A closed low approaching N CA brought and active thunderstorm day Wednesday. SPC mesoanalysis depicted surface CAPE up to 1500 J/kg through the afternoon, and as a result some thunderstorms approached marginally severe criteria with gusts likely near 50 mph. This places the forecast on track.

A greater risk for thunderstorms is on track for Thursday afternoon and evening across NW CA, with a focus of stronger storms likely over northern Humboldt, Del Norte, and Trinity counties. Forecast soundings indicate sufficient buoyancy and steep midlevel lapse rates to support scattered thunderstorms capable larger hail and strong wind gusts. Marginally severe hail in the 1/2 inch to 3/4 inch range and wind gusts of 40 to 50 mph will be possible with stronger storms. Locally higher-end impacts, including hail up to 1 inch and wind gusts approaching 60, may occur with the more vigorous discrete cells. Training cells and a localized flash flooding threat may become a standout threat, especially with precipitable water values of 0.8 to 0.9 inch, locally near 1.0 inch. CAMS are outputting some higher end rainfall amounts locally where training may occur.

As the low pushes closer to the coast in the afternoon, effective shear in the 30 kt and up to near 40 kt range may allow for some organized clusters as outflow interactions increase. While the overall tornado signal remains weak (less than 5% chance), localized enhancements in low-level shear near the surface low may support a brief, weak funnel, particularly across far northern Humboldt and eastern Del Norte County where terrain and boundary interaction could locally augment rotation. Quicker storm organization would further limit this threat. The progressing low will generate some breezy southerly winds Friday afternoon for the southern zones through south Mendocino and Lake Counties.

Beyond Friday into next weekend, wet and cooler weather returns on Saturday as an upstream and much colder trough and closed low comes barreling down from the NW and kicks/absorbs the first low. Most all the models have trended much wetter for this storm system, which will include high mountain snow and a period of gusty to perhaps locally strong southerly winds around and south of Cape Mendocino and through Lake County. NBM chances for over an inch of rainfall in 24 hours are high for much of the region (60-80%). Chances for over 2 inches are also high in the King Range and the mountains of Del Norte and southern Trinity. This low looks to be quite dynamic regarding forcing and associated instability. A convective band or line of moderate to locally heavy rainfall and some thunderstorms will be possible, especially given the preceding saturated column and high precipitable water values.

Snow levels drop to around 3500 to 4000 ft by Saturday night. NBM is showing around a 50% chance for over 4" of snow on Highway 3 at Scott Mountain Pass and a 25% chance on Highway 36 at South Fork Mountain. Cold temperatures aloft could support instability near the coast, bringing showers with thunderstorms and possibly some small hail. This will need to be watched as we get closer to this event. NBM has moderate chances (45%) for snow levels below 3500 ft late Saturday through Sunday. Colder levels are possible depending on the track of the low.

Much colder temperatures are likely during and and behind this frontal passage. Near-freezing to sub-freezing temperatures are forecast, especially Sunday and Monday mornings. Stay tuned to our latest forecast for more details and possible watches, warnings and advisories. JJW

AVIATION

Isolated showers continue to move through the area early this morning. Some of the heavier showers may bring MVFR conditions. There is quite a bit of moisture around so it is possible some fog or low clouds will form early this morning. However, either these scenarios are expected to be fairly shortlived. A around of stronger showers and possible thunderstorms is expected starting midday on Thursday. Some of these thunderstorms could bring gusty winds and possible hail. Tonight, expect the showers will diminish both in strength and coverage. MKK

MARINE

An area of low pressure is approaching the area and this is starting to switch the southern waters to southerly winds while farther north they remain northerly. This generally continues through Thursday night. Friday southerly winds start to increase to around 5 to 10 kt across the area. Both days there is the potential for thunderstorms bringing locally stronger winds and possibly small hail.

There are some small swells moving through the waters, but these are generally

For the weekend a stronger area of low pressure is expected and this has the potential to bring stronger winds. The strength, timing and location remain highly uncertain due to low confidence on the track of the low. Monday high pressure starts to build into the area and moderate to strong northerly winds return. MKK

EKA WATCHES/WARNINGS/ADVISORIES

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