textproduct: Eureka

KEY MESSAGES

* Interior Heat: Above normal temperatures continue for the interior through Tuesday. High temperatures in the 90s to around 100 likely.

* Slight chance thunderstorms. A 10 percent chance for thunderstorms early Tuesday morning. Chances increase to 20 percent in Trinity County Tuesday afternoon. Dry lightning and gusty winds will elevate fire risk.

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

SYNOPSIS

Hot temperatures return to much of the interior today. Monsoonal moisture will bring cloud cover and moisture through Tuesday. Isolated thunderstorms or showers are possible today and Tuesday in the interior.

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 possibly exceeding 100. Minor to locally moderate HeatRisk is expected. Monsoonal moisture from the south has started to stream over the area in the form of high clouds. So far, none of this moisture has resulted in showers with measurable precipitation. CAMs do show some potential shower activity today in the eastern and southern portions of the area. Instability remains low, but a stray sprinkle from a shower is possible.

Tonight and early Tuesday, additional moisture arrives to the area bringing additional shower and low-end thunderstorm chances. Convection is already being observed off the coast and this moisture arrives sometime Tuesday morning. High-resolution models are showing an increase in instability at this time (100-200 J/kg of CAPE). There is still large model variability on where this moisture plume is Tuesday. However, Trinity County is the most likely to see convection by mid morning into the afternoon. Model soundings show inverted-V profiles with very dry low level conditions. Downdraft CAPE of nearly 1000 J/kg is being observed on some model soundings and PWATs of nearly 0.9 inches support precipitation loading. All this points to a strong wind threat around any storms that develop. Should thunderstorms develop, wind gusts could reach or exceed 55 mph within stronger storms. The HRRR among other models show instability remaining into the evening and overnight hours, but chances decrease to around 10-15% with the highest 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. Next Sunday and Monday, more monsoonal moisture is expected to stream north over the area. The NBM is showing over 1 inch PWATS and some low end instability. This will need to be watched as it gets closer as the NBM already has some 10 to 20 percent chances for thunder. At this point these look like they may be on the wetter side. /JB/MKK

AVIATION

18Z TAFS..A strengthened low level inversion has held a shallow band of stratus along the North Coast. Afternoon heating allowed for some scattering from the immediate coast, but duration was limited. The stratus, while remaining shallow will fill back in Monday evening. Areas fog, potentially dense at times is expected through Tuesday morning. There should be improvement in ceilings and visibility going into 18Z Tuesday.

An unstable environment associated with an approaching disturbance may disrupt the inversion and stratus later Tuesday morning, but the instability will be aloft above the inversion. Interior thunderstorms are forecast over mainly Trinty County Tuesday and Tuesday night from the passing disturbance. The storms will be capable of strong downdraft winds or even microbursts and may expand into interior Humboldt and Del Norte Counties, especially overnight Tuesday.

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 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 Friday. 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 0.6 feet over the astronomical tide Sunday evening resulting in a high tide of 8.8 feet. This will likely put water levels around 8.9 feet at the North Spit in Humbodlt causing and cause minor flooding again this evening. This may continue Tuesday night as well before astronomical tides start to diminish Wednesday night/Thursday morning. MKK

EKA WATCHES/WARNINGS/ADVISORIES

CA... Coastal Flood Advisory from 10 PM this evening to 1 AM PDT Tuesday for CAZ103.

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

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 5 AM PDT Friday for PZZ455-475.

Small Craft Advisory until 5 PM PDT this afternoon for PZZ470.