textproduct: Eureka

SYNOPSIS

Rain is expected to develop early Sunday with snow levels around 5,000 feet. The heaviest rain is expected in Mendocino and Lake counties. Monday a few showers are expected as colder air moves in. Monday night and Tuesday snow is expected above 1500 to 2500 feet impacting most highways through the interior. Lighter rain and low elevation snow are expected Wednesday and Thursday

DISCUSSION

A frontal boundary is approaching the area this morning. This is expected to bring rain, snow and gusty winds to the area today. Snow levels today are expected to be over 5,000 feet. The heaviest rain is expected to be in Mendocino and Lake counties where 1 to 2 inches is expected in around 18 hours. Local amounts of up to 3 inches are possible in the mountains. This may cause some minor flooding of small streams, streets and low lying areas.

As the first system moves out of the area, Monday is expected to be fairly dry through the daylight hours. Periods of light rain are possible, but rainfall amounts are expected to be mainly less than a quarter of an inch. Snow levels are expected to start falling through the day, but only drop to around 3,000 to 4,000 feet by late afternoon.

The real cold air is expected to start moving into the are Monday evening and will likely be in place when the heavier precip starts in the late evening. The models have slowed down the time of this precip slightly, however this just allows the cold air to move in ahead of the precip. Confidence is high that Humboldt and Del Norte counties will see widespread heavy snow above 2,000 feet and possibly down lower. Confidence is lower on exactly how low snow levels will get. The current forecast is showing over a foot of snow on Hwy 299 at Berry Summit with similar amounts on Hwy 199 at the Collier Tunnel. Snow fall amounts are slightly less on Oregon Mountain and Buckhorn Summit with less precip that far inland. This much snow will likely cause significant travel impacts and may bring down trees and possibly power lines. Smaller roads such as Mattole Road and Shelter Cove road as well as numerous county roads farther inland will likely also see snow. So have added southwestern Humboldt to the winter storm warning. There is more uncertainty on the impacts to the highways in Mendocino and Lake counties. For now snow amounts at the lower elevations look lower, but will leave the winter storm watch in place to highlight this uncertainty. Elevations below the snow level, especially along the coast, may see small hail. With temperatures likely lingering around 40, this may allow small hail to accumulate on Tuesday. A winter weather advisory may be needed to highlight this as well.

Showers and low snow levels are expected to continue on Wednesday and Thursday although at this point amounts look quite a bit lighter. There will likely be some breaks in the rain and snow even though the current forecast broad brushes the pops due to uncertainty on timing. Additional rain and snow are expected on Friday, although snow levels are expected to start rising. MKK

AVIATION

As the low pressure system approaches, high level clouds are being pushed east. Plenty of mixing at ground level with instability assisting with the deepening of the marine layer. This will make for a thicker cloud deck and could effect approach and departure from the terminals. Low level wind shear is anticipated at KUKI overnight into Sunday with velocity and directional shear. Most guidance suggests rain to arrive to the Humboldt and Del Norte coasts Sunday morning, with models showing this staying offshore until mid morning Sunday. VFR conditions are likely to remain at the coastal terminals until this rain arrives. MVFR ceilings are likely once rain arrives.

MARINE

The large northwest swell continues at 10 ft or so at the buoys as of 07z. Southerly winds will continue with sustained winds at 15-20 and widespread gusts of 20 to 30 kts. The southerlies will begin to ease by the early evening on Sunday, around 01z, but could remain breezy south of the Cape with gusts of 15 to 25 kts. Between decaying swells and wind waves, combined seas of 9 to 12 ft are likely Sunday morning. The center of the low pressure will move through the waters Monday, bringing stronger northerly winds. Gale force gusts are possible in the outer waters Monday evening depending on the location of the low. Winds turn westerly Tuesday and are likely to remain breezy with gusts of 20 to 30 kts. Winds turn northerly and begin to ease by midweek as the low pressure moves out of the area. However, a northwesterly large, steep mid period swell of around 16 to 18 ft at 14 seconds will build in Tuesday and Wednesday. This will keep seas elevated into Thursday.

EKA WATCHES/WARNINGS/ADVISORIES

CA... Winter Storm Warning from 7 PM Monday to 4 PM PST Wednesday for CAZ102-104-105-106.

Winter Storm Warning from 7 AM Sunday to 4 PM PST Wednesday for CAZ107-108.

Winter Storm Watch from Monday evening through Wednesday morning for CAZ110-111-114-115.

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 3 AM PST Monday for PZZ455-470- 475.