textproduct: Eureka

KEY MESSAGES

* Colder temperatures with chances for interior frost this week.

* Chances for isolated light showers and rain this week, particularly in southern and eastern Mendocino, Trinity, and Lake counties.

SYNOPSIS

Below normal temperatures are expected for the next week as a cold front ushers in cooler air to the region. A few showers will be possibly on Monday. Occasional showers are expected in southern and eastern Mendocino, Trinity, and Lake counties later Tuesday into Thursday.

DISCUSSION

Low coastal clouds and foggy conditions will erode behind a frontal passage. As an area of low pressure approaches the area, high and mid level clouds will gradually increase resulting in mostly cloudy conditions for the entire forecast area.

There is high confidence that this area of low pressure will never fully make it to the Northwest California coast and instead cut-off from the flow and drift south over the far eastern Pacific toward central and southern California. A few showers might form over eastern and southern portions of the forecast area Monday and Monday night, but generally dry conditions are expected as this low sinks south. Wrap around moisture on the north side of this low cloud bring some light rain to southern areas of the forecast area and in the higher terrain on Tuesday and Wednesday with a 10-30% chance of rain during that timeframe. Farther north and west dry conditions are currently forecast to continue during that time frame with potentially some light offshore flow aloft reducing coastal stratus Tuesday into Wednesday. As this low ejects northeast over central and southern California, there is some indication that a deformation axis could form on the northwest side of the low resulting in light rain in the southeastern potion of the forecast area on Thursday. Confidence in this remains low but is certainly a reasonable possibility with 30-40% chances of rain included in the forecast from Trinity County south through eastern Mendocino and Lake counties. Temperatures throughout Monday through Thursday are forecast to be 5-15 degrees below normal across the interior and around 5 degrees below normal at the coast.

Dry conditions are likely to return on Friday as a ridge noses into Northwest California. Temperatures won't change much but the overall weather conditions for the region should improve. The next question is whether a more active weather pattern could develop starting next weekend. Looking at cluster guidance, around 70% of the ensemble is showing a trough somewhere near the Northwest California coast and around 50% indicate the potential for notable rainfall. At this time the probabilities included in the forecast are around 30-40% Saturday and Sunday next weekend. It wouldn't be a shock to see probabilities decrease considering the model tendency to be too strong with systems in the extended periods during the transition season. Stay tuned to see how this trends over the next few days.

AVIATION

A passing front and area of low pressure is deepening the marine layer. This is allowing of the low level inversion to weaken and improve CIGs and VIS. VFR to MVFR conditions will develop through Monday morning. The front will continue to bring some light drizzle into the afternoon. The deepened marine layer has a growing chance at making it over the terrain into UKI, potentially lowering ceilings below 1700 ft AGL. There is a 30% chance for ceilings less than 1000ft and 50 to 60% chance for under 3000 ft at UKI through 15Z Monday.

MARINE

Northerly winds will decrease tonight as an area of low pressure approaches the waters. Southerly winds ahead of this system will increase on Monday but never get particularly strong as the low fails to make it fully toward the coast. Thus, small crafts are not going to be needed for the wind itself. However, this low will also bring in a mid-period westerly swell that will likely peak over 10 feet Monday night into Tuesday, which would be large enough for small craft advisories for all waters. Northerlies will redevelop on Tuesday and gradually strengthen and expand through the end of the week. Additional small craft advisories may be needed late in the week.

FIRE WEATHER

An area of low pressure will slide south off the Northwest California coast through Monday night. What was originally looking like a decent shot for wetting rain across the area, is now looking much less likely through Tuesday. However, the system will bring cooler temperatures and higher humidity by Monday along with a bit of gusty northwesterly winds during the afternoon hours. Some wrap around moisture Tuesday through Thursday could bring rain to eastern and southern areas of the forecast area, but probabilities of wetting rains still remain less than 30%, highest in southern Mendocino and Lake counties. The low will deliver some instability to the region Wednesday, increasing mixing heights and bringing a low (8 to 10%) chance for thunderstorms for eastern Trinity County and southward.

EKA WATCHES/WARNINGS/ADVISORIES

CA... Frost Advisory until 9 AM PDT this morning for CAZ108-110- 111-114.

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory from midnight tonight to 8 PM PDT Tuesday for PZZ450-455.

Small Craft Advisory from 11 PM this evening to 8 PM PDT Tuesday for PZZ470-475.