textproduct: Eureka

KEY MESSAGES

* Above normal temperatures continue today for the interior with high temperatures in the 90s to around 100.

* There is a 20 percent chance of thunder mainly in Trinity County this afternoon and evening. Dry lightning and gusty winds will elevate fire risk. There is a 10 percent chance of other areas seeing thunder as well.

* Coastal flooding: Minor coastal flooding around Humboldt Bay possible at the evening high tide through Wednesday night.

SYNOPSIS

Hot temperatures continue across much of the interior today. Isolated thunderstorms or showers are possible today in the interior. Slightly cooler temperatures are expected Wednesday through Friday with warming again for the weekend.

DISCUSSION

An upper level trough in British Columbia continues to inch eastward while an upper ridge over the Rockies continues to expand westward. This ridge will bring above normal temperatures to the interior with 90s likely for most valleys and the warmest areas slightly exceeding 100. Minor to locally moderate HeatRisk is expected.

A shortwave moving up the west side of the ridge is approaching the area from the southwest this morning. The monsoon moisture has started moving in with the 00Z MFR sounding already showing 0.80 inches of PWAT. Late this morning and into the afternoon as the shortwave approaches, combined with the daytime heating is expected to develop some instability. The NAM and the GFS are both showing 300 to 400 j/kg of surface CAPE in Trinity county with the 700 to 500 mb lapse rates up around 8c/km. The model soundings are showing a deep inverted V increasing the potential for strong downburst winds. There is still quite a bit of uncertainty on coverage of the storms, however the CAMS generally show storms forming in the afternoon in Trinity county.

Drier air returns midweek as the Pacific Northwest trough moves southwestward. A deeper marine layer will likely bring interior temperatures down by a few degrees, while bringing more widespread, and possibly persistent, coastal stratus. High pressure returns late week, returning warmer interior temperatures. Models have slowed down the next period of monsoonal moisture with the most recent NBM showing PWATS not increasing until Monday and Tuesday. The instability looks weak and the thunder probabilities are now only showing a max of 10 percent. This will still need to be watched as it gets closer but for now it looks less threatening. /JB/MKK

AVIATION

Model soundings show a deeper marine layer but the trend overnight for the past few TAF periods has had a compressed cloud layer underneath. It is expected and already verifying somewhat, that 500 foot ceilings are beginning to transition from Scattered to Broken at the coastal terminals as of 04z. GFS suggest light southerly winds and overcasts down to 100 feet which follows recent trends although visibility is not likely to get down to 1/4 mile overnight into Tuesday early morning as the marine layer lifts. Westerly winds will prevail by sunrise at KACV with a bit more southwesterly bearing at KCEC. IFR categories will transition to MVFR categories by the afternoon at the coastal terminals with winds just under 10 knots and eventually VFR by the late afternoon. Prevailing VFR conditions at KUKI are expected with light to calm winds most of the morning and northerlies gusting up by the late afternoon. /EYS

MARINE

Northerly winds will continue over the waters, strongest over the southern zones, particularly around Cape Mendocino. Afternoon and evening wind pulses will create gale conditions along and south of Cape Mendocino, with gusts nearing 40kts at times in a confined expansion fan around the cape. Steep seas up to 9ft will be generated in response. These seas will likely propagate into inner coastal waters and coast farther south of the cape where lighter winds are.

The northern zones north of the cape will see lighter winds and seas, especially inside of 10 nm. Steep seas up up to 6 ft will periodically make in into the northern inner zones from the stronger offshore winds however.

A trough of low pressure will establish itself well offshore the N. CA coast Friday. This will greatly ease the winds and seas throughout the day Saturday. This feature looks remain around through the weekend to continue much calmer conditions.

COASTAL FLOODING

High astronomical tides and the basin wide warmth in the ocean is creating higher than normal water levels despite light northerly winds. The water levels were close to 0.7 feet over the astronomical tide Monday evening resulting in a high tide of 9.1 feet. This will likely put water levels close to 9 feet again at the North Spit in Humbodlt causing and cause minor flooding again Tuesday late evening. The tide will begin to diminish Wednesday night/Thursday morning. MKK/EYS

Fire Weather

For thunder information see general discussion above. Wednesday afternoon stronger northwest winds are expected in Mendocino and Lake counties. Mendocino county is expected to see afternoon RH only drop into the 20s due to the northwest winds. Farther inland in Lake county there is elevated fire danger. RH is expected to be in the teens both Wednesday and Thursday afternoons. This will be especially true in eastern Lake county. For now conditions don't look severe enough to warrant a red flag warning, but have added a headline to the FWF to highlight this. MKK

EKA WATCHES/WARNINGS/ADVISORIES

CA... Coastal Flood Advisory from 11 PM this evening to 2 AM PDT Wednesday for CAZ103.

Red Flag Warning from 1 PM this afternoon to 2 AM PDT Wednesday for CAZ403-409>412.

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 3 AM PDT Saturday for PZZ455-475.