textproduct: Eureka

KEY MESSAGES

* Unseasonably hot temperatures will peak Saturday with close to record breaking daytime highs. Such temperatures will generate Moderate HeatRisk across the interior through mid next week.

* Shallow, diurnal marine layer persisting along the coast through the weekend.

* Nearly 0% chance of wetting rain for the next 10 days.

SYNOPSIS

High pressure peaking this weekend will create unseasonably hot and dry conditions for the interior. Morning fog will be most likely along the North Coast with potential clearing for the afternoon. Winds will generally be light.

DISCUSSION

An unseasonably high upper level ridge continues to build over NW California. This upper level ridge will force a very stable atmosphere with afternoon compressional heating down at the surface. Heating has a chance (~50-60%) of breaking the record at KUKI in Ukiah with many other inland valleys reaching temperatures in the upper 90s to triple digits. It seems the hottest valleys will be those that are orientated North to South. These temperatures are extreme and it is recommended to take extra precautions to prevent heat borne illnesses such as increased shade and hydration, especially for sensitive demographics. Moderate HeatRisk is expected and a Heat Advisory has been issued for valleys in Lake and interior Mendocino counties.

Over the next few nights, colder air will flow down slopes before settling into valleys. This will cool down temperatures at valley level while leaving the midslope and upper ridges warm overnight. Relative humidity's will remain low at the higher elevations as a result as well. Coastal areas, especially in Del Norte and N. Humboldt can expect continued overcast skies and areas of light drizzle.

Looking further ahead, high pressure will slowly weaken through next week, though above average interior temperatures are likely to linger through Wednesday. Both the GEFS and EPS global ensemble models show a very weak cutoff low impacting the area around Monday. At most, this low will lift the marine layer and promote some drizzle. There is mixed confidence, but about 50% of models show another peak of highs near 100 on Tuesday behind the low. Other than weakening high pressure, there is no impactful weather on the horizon. There remains a near zero chance of wetting precipitation for at least the next 10 days. Long Range forecast suggest this dry pattern is most likely to persist through at least the second week of October. /JHW & DS

AVIATION

Coastal stratus has returned to the North Coast with LIFR conditions expected through the early afternoon (~21Z). Daytime conditions show possible clearing for the coast with a 40% chance of the fog bank remaining over terminal spaces. North winds are expected for the entire coastline tomorrow. Mendocino coastal terminals have a higher chance (>=80%)of remaining VFR tomorrow. Either way, LIFR is expected to return Saturday evening (around 02Z) as a shallow marine layer remains in place. Inland terminals are expected to have VFR with afternoon, terrain-driven, upslope/upvalley winds. Gusts could be strong near elevated terrain in the afternoon due to intense surface heating this weekend as well. DS

MARINE

Moderate to strong winds wind have persisted in the outer waters with much calmer winds closer to shore. Steep short period seas over 10 feet will remain in the outer waters with some steeper seas around 7 feet at 9 seconds bleeding into the inner waters. Beyond short period seas, a very minor southwest swell is augmenting the sea state. Winds will weaken through the weekend as high pressure pushes east of the area. Outer water gusts will most likely drop below 21 kts by Saturday afternoon with seas also dropping below 5 feet. These more subdued conditions will likely persist into early next week. /JHW

FIRE WEATHER

A building upper level ridge continue to build over the West. This will lead to compressional heating and a stable environment. The resulting weather is expected to be hotter and drier through the weekend, increasing fire danger. Near record high temperatures for October will aid in ERC values cresting back near the 90th percentile early next week. That said, very weak terrain winds and increasingly long nights will prevent Burning Index values from reaching above the 70th percentile. These values imply fire may be unusually easy to ignite but spread potential is only moderate. It should be know that ridgetops could experience enhanced winds with gusts up to 15mph during the peak of the afternoon. There is little chance of weather induced ignitions. Enhanced conditions will persist through next week. /JHW

EKA WATCHES/WARNINGS/ADVISORIES

CA... Heat Advisory from 11 AM to 11 PM PDT Saturday for CAZ112- 113-118>120.

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 9 AM PDT Saturday for PZZ470-475.