Area Forecast Discussion

SYNOPSIS

Showers and possibly a thunderstorm are expected through this evening. Later tonight and early Wednesday showers will diminish, although there may be a few around still. Thursday and Friday are expected to be dry with chilly overnight temperatures. A few showers and below normal temperatures are expected for the weekend and into early next week.

DISCUSSION

The upper level low is approaching the coast and starting to move onshore. This is expected to bring a few thunderstorms to the area this afternoon. There is still some uncertainty on how much clearing there will be and this could impact how much instability there. Snow levels look to have risen above 5500 or 6000 feet, so have allowed the winter weather advisory to expire. Some of these showers or thunderstorms may be stronger and could produce some small hail or gusty winds. Tonight the showers are expected to weak, but may continue through the night. Wednesday a few showers are expected to remain in the area, but these are expected to be fairly weak and it is unlikely there will be thunderstorms. There may be a slight uptick in the shower coverage in the afternoon.

Wednesday night into Thursday high pressure starts to build in and showers are expected to come to an end. There may be enough clearing for some of the colder spots in to see freezing or near freezing temperatures. This will need to be monitored through day on Wednesday to see how many clouds are lingering in the area. Thursday is expected to see mostly clear skies and Thursday night may be the coldest night this week. Currently the forecast is showing lows in the cold spots of 35 to 40 degrees, but if there is good clear skies and dry air some spots may still see freezing temperatures.

For the weekend and into early next week there is a chance for rain showers. The ensemble clusters are showing an upper low develop well to the west of southern CA. There is also an upper level low low over the Canadian Plains. Over the weekend and into early next week these start to get closer and some lowered heights are in between them. This will eventually allow some showers to develop over the interior mountains each afternoon. There is also a slight chance of chance of rain near the coast, but this may end up as some light drizzle. Overall it looks like temperatures will remain near or below normal over the weekend and into early next week with highs in the interior valleys only in the 60s. MKK

AVIATION

A surface low pressure center off the NW CA coastline is keeping cloud decks elevated. VFR is forecasted for most terminals through the TAF period with brief MVFR possible (20-30%) if rainshowers line up directly over terminal spaces, yet these should be very short-lived if they form at all. Inland conditions will have a slight threat of thunderstorms, especially in Trinity, Lake, and interior Mendocino counties. A PROB30 group has been added for KUKI, yet this 30% chance should be applied to all interior terminals for those interested. Overnight conditions calm over the forecast area with a chance of light rainshowers for the North Coast before a dry end to the week.

MARINE

Seas continue to trend lower through the morning. South to southeast winds will continue through the day as a weak surface low pressure center meanders outside the northern outer waters around 280nm west of Cape Mendocino. This afternoon, a few gusts around 20- 25 kt are possible (20-30% chance) north of Cape Mendocino up to Trinidad Head or so. Otherwise, wind speeds are forecast to remain below advisory level today. The surface pressure gradient remains relatively flat over the coastal waters leading winds speeds to be calm through Wednesday as the weak low moves out of the area. Greater atmospheric instability associated with cold air aloft may result in isolated thunderstorms capable of gusty winds through the afternoon. High pressure builds in offshore on Thursday as the low pressure center travels to the southeast. This pressure gradient will force northerly winds and steep short period waves Thursday through Friday. Mid-range forecast models show some areas south of Cape Mendocino having near gale to gale force gusts through this time period. Advisories will likely be necessary for small vessels.

EKA WATCHES / WARNINGS / ADVISORIES

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