textproduct: Eureka

KEY MESSAGES

* Hot temperatures return late week and into the weekend, with hotter temperatures and widespread Moderate to locally Major HeatRisk early to mid next week

* Elevated fire danger returns late in the week and into next week with periods of breezy winds and increasingly hot, dry conditions.

* Westerly to northeasterly winds through the weekend and into Monday will bring the greatest fire weather risk.

SYNOPSIS

Temperatures begin trending hotter. Breezy afternoon winds elevate fire danger in eastern Trinity, eastern Mendocino, and Lake counties. Hot interior temperatures in combination with periods of breezy winds through the weekend and into Monday, further increase the fire weather risk.

DISCUSSION

An upper level trough over the Gulf of Alaska will continue to affect weather patterns over Northwest California today and tomorrow. Stratus is then expected to deepen and expand over the coast and down coastal river valleys again overnight tonight. Cooler than average temperatures will continue today and tomorrow for the interior as the upper low affects the area. The rest of this week and into the weekend, northerlies will continue to strengthen over the ocean restarting upwelling and leading to the usual cooler near shore ocean temperatures. This will cause cool air advection into coastal areas which will help trend coastal temperatures back towards normal. A pronounced shortwave perturbation will advance over N CA Thursday. Moisture and instability will be very limited, so only mid to high level clouds should result. This feature may act to disrupt the inversion and clear out the low clouds Thursday afternoon.

A Four Corners/Desert Southwest dome of high pressure will then begin to strengthen Thursday. The 500mb ridge will continue to strengthen, reaching 597 to up to 600dm by Friday, and this will translate to hot interior temperatures. Temperatures will likely reach or exceed 100 in some of the warmer valleys Friday and through the weekend as a result. Probabilities for interior temperatures over 100 further increase going into next week, with high chances (60 to 80%) for temperatures over 100 by Monday, and moderate chances (40%) for temperatures over 104 Tuesday of next week. Currently, this heat setup looks to bring widespread Moderate to locally Major HeatRisk. There is a 30-50% chance for isolated areas of Major HeatRisk Monday and especially Tuesday, though the timing of peak heating may change.

Fire weather concerns will become elevated again with the duration of the building heat along will periods of breezy conditions. See the Fire Weather section below. /JJW /JLW

AVIATION

06Z TAFs.The influence of NE Pacific troughing maintains a relatively deep marine layer for the season. A shallow layer to LIFR levels may form overnight Wednesday, with bouts of light drizzle and perhaps TEMPO fog.

A compact shortwave trough will push through Thursday afternoon, and there are indications it could disrupt the inversion and aid in full late afternoon, perhaps as early as the late morning hours. If this occurs, it is uncertain how fast the stratus will return. /JJW

MARINE

Northerly winds north of Cape Mendocino look to generally remain below 20 kts through Friday. The focus of stronger northerlies will remain around and south of Cape Mendocino. Northerlies of 20-25 kts in these southern zones, locally with gale conditions up to 30 kts around the cape, can continue to be expected through Friday. Short period northerly seas will increase over the waters while a small long period southerly swell slowly fades.

A ridge of high pressure will then strengthen through the weekend, bringing increased chances for gale strength northerlies over much of the waters. There is growing confidence for strong northerlies with sustained gale strength winds of 34kts and gusts approaching or exceeding 40 kts as troughing to the north squeezes against the strong ridge to the SE. Subsequent steep seas over 15 ft will develop over the weekend and into early next week. Gale conditions could start as early as late Friday in portions of the southern zones. /JJW

FIRE WEATHER

Afternoon westerly breezes will likely bring isolated areas of enhanced fire weather danger and perhaps brief critical conditions locally. Overnight recoveries will begin to decline Thursday and Friday with building heat and drying conditions from a strong Four Corners/Desert Southwest ridge of high pressure. Triple digit high temperatures can be expected in the interior Friday and through the weekend. Chances for temperatures over 100 increase Monday and especially Tuesday of next week. Min RH will drop back into the mid to low teens Thursday and Friday.

A trough of low pressure will move eastward over the Pacific Northwest over the weekend, squeezing a strong pressure gradient against the existing ridge to the SE. Stronger afternoon westerly winds will develop as a result, with chances for gusts over 25 mph increasing to 50 to 70% for a good portion of the interior Saturday afternoon. A robust burst of dry NE winds will likely follow to departing trough later Sunday through Monday over the interior ridges of Trinity, Humboldt and Del Norte counties.

Minimum RH is expected to come up slightly with the westerly flow Saturday. RH will trend much lower, to the low teens and likely some single digits through Monday, and then remaining dry into mid next week /JJW

EKA WATCHES/WARNINGS/ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 5 AM PDT Saturday for PZZ455-475.