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

Clouds remain entrenched along the coast today as the marine layer moistens ahead of an approaching area of low pressure. Coastal clouds will expand inland into coastal valleys and the marine layer should deepen overnight. As the 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 by Monday into Tuesday.

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...18Z TAF

Cloud cover has been very persistent along the coast today with IFR conditions at all coastal terminals. Satellite indicates that the stratus is already beginning to push back inland, thus it is unlikely to see any clearing today. Statistical guidance indicates the stratus should descend back toward the surface overnight reducing visibilities into LIFR, but an approaching area of low pressure would support the opposite of this to occur with ceilings remaining in IFR instead of LIFR but areas of drizzle developing. Either way, conditions are not expected to improve much through Monday morning. Farther inland VFR is expected to prevail away from the near coastal ridges and valleys. Increasing higher level clouds will develop ahead of this approaching area of low pressure overnight.

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.

EKA WATCHES/WARNINGS/ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 5 PM PDT this afternoon for PZZ470.

Small Craft Advisory until 9 PM PDT this evening for PZZ475.