textproduct: Eureka

SYNOPSIS

Warm temperatures persist through early next week for the interior. Overcast conditions at the coast are stubborn, keeping temperatures near normal. Interior temperatures could break 90F for interior valleys Monday and Tuesday.

DISCUSSION...SHORT TERM

A broad H5 ridge of high pressure is beginning to dominate over the Pacific Northwest through the end of the week. While this high pressure is not overly anomalous, 8-12dam above normal, it will lead to a warming trend through early next week. Most of this warming will begin this weekend for the interior. Clear skies and continuously subsiding air will cause increasing daytime temperatures, especially Saturday through Tuesday. This heating will force gusty, up-valley winds each afternoon through Tuesday. Nighttime winds will be calmer and have downslope or downvalley flow as cool air drains into lower elevations. This wind pattern will force cooler air to settle in the valleys while ridgetops remain warm leading to thermal belts development. Nighttime temperature differences between ridgetops and valleys could be as strong as a 15F difference by next week.

While clear skies dominate interior areas, coastal communities will remain under a widespread layer of overcast conditions through the end of the week. High pressure will compress the marine layer leading to stubborn marine stratus. This stratus decreases the impact from radiational daytime heating and nighttime cooling keeping temperatures mild. HREF data shows probabilities of low- cloud coverage close to ~90% overnight for coastal areas. Daytime probabilities decrease to ~40%, especially for coastal areas not around Humboldt Bay. This could lead to periodic clearing for those areas in the afternoon.

LONG TERM...Both GFS and ECMWF ensemble data shows relatively dry conditions through the middle of next week. The upper level ridge is forecasted to breakdown on Wednesday as a possible frontal system impacts the area. CPC 6-10day outlooks compared to 8-14day outlooks show slightly cooler temperatures and a higher chance of precipitation. So while it might be warm this weekend and early next week, this warm spell is not forecasted to last long.

AVIATION

Stratus is in place along the coast and 10 to 20 miles inland. This is expected to expand inland and lower some more towards morning. Generally these are expected to be IFR to MVFR, although there may be a few pockets of LIFR. Thursday early afternoon there may be a few breaks in the stratus at KACV and KCEC, but the both the REFS and the HREF show only an hour or two of possible VFR conditions. So kept MVFR conditions in place. The probability of clearing increases significantly Friday afternoon. MKK

MARINE

Gentle to moderate northerly breezes continue through the day Thursday across the waters. The waves remain a combination of an 8 and 13 second swells. These are around 3 and 5 feet respectively. These are expected to continue through Thursday, although the periods are expected to get closer. The short period wind driven waves are also expected to start to increase. So have combined the two mid period swells so the short period waves will be visible in the CWF.

Thursday night and Friday a weak frontal boundary approaching the area will diminish the winds north of Cape Mendocino. Farther south northerly winds starts to increase by Friday afternoon. The HREF is showing an 85 percent chance of a fairly large area south of Cape Mendocino exceeding 21 kt at 5pm on Friday. Saturday these stronger winds are expected to expand farther north with 15 to 20 kt across much of the area north of Cape Mendocino. This is expected to build the short period wind driven waves to around 4 to 7 feet. Stronger winds are expected on Sunday with near gale to gale force gusts possible by Sunday afternoon. Breezy northerly winds are expected to continue into early next week. MKK

PREV DISCUSSION

/issued 308 PM PDT Wed May 6 2026/

SYNOPSIS...Weak high pressure building into the area will gradually warm inland temperatures through Thursday. Closer to the coast widespread low clouds will linger keeping temperatures cooler. Friday will see slightly cooler temperatures and more clouds. For the weekend and into early next highs are expected to warm each day with many inland areas seeing the 90s by Monday.

KEY MESSAGES: Near to above normal inland temperatures Thursday with some cooling Friday.

Breezy north winds this weekend with well above normal temperatures inland.

Minor to moderate heat risk is possible on Monday in Mendocino, Lake and Trinity counties.

DISCUSSION...High pressure is building over the area in the wake of a departing low. This will bring clearing skies and warming temperatures for much of the interior. Stratus has retreated to the usual coastal areas of Humboldt, Del Norte and Mendocino counties and will return with less coverage overnight into Thursday morning than previous past few days. Though HREF does have a less vigorous low level cloud cover Thursday afternoon, stratus is expected to straddle the coastline and will linger around Humboldt Bay and the coastline up to the Oregon border.

Thursday night into Friday a weak front will bring some mid level clouds and cooler temperatures to Trinity county. This may bring some drizzle to the coast, but at this point no real rain is expected. Friday night into Saturday northerly winds are expected to increase. Offshore flow is expected overnight with breezy afternoon winds. Inland areas are expected to warm again on Saturday and with mostly clear skies areas closer to the coast will likely warm up too. The breezy northerly winds typically keep the immediate coast in the low 60s. The warming trend is expected to continue into early next week. At this point the first day expected to see moderate heat risk in the far inland areas is Monday. However, there is some potential an upper low could develop off the coast weaken the wind flow allowing clouds and marine air creep into the coastal counties limiting the heating potential. MKK/EYS

AVIATION...The marine layer remains deep and embedded along the coast and farther inland. The MVFR ceilings from this layer will once again lower with overnight cooling, with high confidence for IFR levels. With building high pressure, and additional compressional effects, LIFR levels are possible. Guidance is trending with higher probabilities for this scenario. Probabilities for LIFR are at this time 20-30%, but MOS guidance is latching on to lower ceilings.

MARINE...Northerly winds increase some today, to around 15-17 kts, mainly in the southern waters around the cape. Similar conditions will continue Thursday, with short period seas of 3 to 5 feet and some small mid period swells. Thursday night into Friday a weak front approaching the area is expected to bring lighter winds north of Cape Mendocino. Only around 5 to 10 kt and these may briefly become west or southwest. Farther south the winds are expected to increase to around 15 to 20 kt. Behind the front on the weekend winds are expected to increase to near gale or gale force as high pressure builds in again. There is expected to be a fairly small northwest swell through much of the period. Friday night and Saturday behind the weak front the swell may increase slightly with periods jumping up to around 15 seconds, but heights remain around 3 or 4 feet. MKK/JJW

EKA WATCHES/WARNINGS/ADVISORIES

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