textproduct: Eureka

SYNOPSIS

Dry weather with seasonable temperatures today. Wet weather and possible thunderstorms Monday. Chance for rain and possible interior thunderstorms Tuesday through Thursday.

DISCUSSION

Shortwave trough that triggered a few thunderstorms in Trinity County yesterday afternoon and evening has scooted off to the northeast. A deeper and wetter trough outside 130W will slowly advance toward the North Coast this afternoon through Monday morning. Bulk of rain and convective activity with this next trough will arrive on Monday. Generally light to locally moderate rainfall is forecast on Monday, however there is a 20% chance of isolated thunderstorms and a 10% chance for heavier rain rates (>0.25in/hr) due to steep lapse rates associated with cold air aloft for mainly the coastal ranges. We will post a graphic of estimated rain amounts for Monday.

Tuesday and Tuesday night, the upper level trough settles over the region. The potential for moderate to heavy rain is forecast to diminish. Confidences for thunderstorms remain low for Tuesday afternoon and evening.

Another shortwave trough will dive southward along the West Coast on Wednesday. The GFS and ECMWF indicate an increase in precipitation across the interior Wednesday afternoon and evening. The GFS sounding shows increasing instability and steep mid level lapse rates during this time period. Thus, there is a slight chance (15%) of thunderstorms for the interior on Wednesday, especially for Trinity County. On Thursday, wrap around precipitation will be possible for Trinity, eastern Mendocino and northern Lake. Once again deterministic model soundings indicate potential for storms. Otherwise, drier and warmer conditions are anticipated Thursday into Friday as ridge builds offshore. Another trough approaches the coast by next weekend and appears to split or develop into a cut-off. Forecast confidence this trough or cut- off low will generate more precip or storms remains very low at the moment.

AVIATION

(06Z TAFs)...A deep marine layer continues to develop over the coast into Sunday morning. Mostly MVFR conditions are expected for ACV and CEC, but borderline IFR ceilings could develop early Sunday morning. There could be drizzle into Sunday morning associated with the approaching trough. Winds will remain relatively light with mostly onshore flow after sunrise. With the deep marine layer, there is a non-zero chance for MVFR conditions to develop for UKI around sunrise. Confidence is low, but there is still the possibility of this occurring.

MARINE

The marine forecast remains on track with recent buoy observations confirming expected trends. Winds continue to be southerly while speeds will gradually increase into Sunday ahead of the approaching frontal system, though winds are expected to remain below 15 knots.

A couple of swells are worthy of mention. A mid-period west to northwest swell and a long-period southerly swell. Combined seas will be relatively calm, generally 3 to 4 feet. Conditions are expected to remain well below Small Craft Advisory criteria through the weekend. However, two primary hazards exist: patchy dense fog may develop into Sunday morning, reducing visibility for mariners. Secondly, the frontal passage on Monday will bring a chance (15-25%) of thunderstorms, especially for the waters north of Cape Mendocino. Mariners should be aware of the potential for erratic, gusty winds and dangerous lightning with any storms that develop.

FIRE WEATHER

Dry weather and near normal temperatures are expected today. Generally, onshore westerly breezes are expected again this afternoon. Cooler temperatures, higher relative humidity, and a chance for wetting rain is expected Monday. Below normal temperatures and a chance of rain and interior thunderstorms will continue Tuesday through Thursday as an upper level low slowly moves across the area. A warming and drying trend will be possible on Friday, however another trough may bring cooling and more showers next weekend.

EKA WATCHES/WARNINGS/ADVISORIES

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