textproduct: Eureka

SYNOPSIS

A few light showers are expected Monday. Monday evening the cold air moves in with rain and snow starting right behind it. Monday night and Tuesday a strong winter storm is expected to bring heavy snow, especially in Humboldt and Del Norte counties. Snow levels are expected to be around 1500 to 2000 feet, but local areas may be lower. Additional rounds of rain and low elevation snow are expected through the week.

Discussion

KEY MESSAGES:

* Monday night through Tuesday night heavy wet snow will generate dangerous travel conditions, downed trees and possible power outages. This is expected to impact mountain passes highways 199, 299, 36, and 3. This may also impact highway 101.

* Small hail accumulation expected for low elevations along NW California Coast with heavy showers, especially on Tuesday.

* Additional periods of light rain and low elevation snow are expected Wednesday and Thursday.

WEATHER PATTERN OVERVIEW AND FORECAST CONFIDENCE:

The upper level low and associated frontal boundary that brought rain to the area on Sunday is moving out of the area and only a few rounds of light rain are expected through the day on Monday. Snow levels in the morning are expected to be around 4,000 feet.

Water Vapor satellite shows the cold weather system diving south off the coast of Washington this morning. Temperatures (and snow levels are expected to fall rapidly in the evening. The models are showing the precip picking up later in the evening after the cold air has moved in. By 10pm Monday when the precip starts to pick up snow levels are expected to be around 1500 to 25000 feet, lowest in the north. These snow levels are expected to continue to fall into Tuesday morning. The models show these snow levels dropping around 1200 to 2500 feet Tuesday morning. This is expected to bring heavy snow, especially late Monday night into Tuesday morning. 6 to 18 inches is expected in many areas above 2,000 to 3,000 feet. Higher amounts are expected at higher elevations, especially in Del Norte and Humboldt counties.

This cold air is also expected to bring some instability. Some of the stronger showers may help drive snow levels lower and these may reach sea level. No accumulation is expected, but it is possible Eureka or Arcata could see a few flakes of snow mixing in with the rain. While snow is unlikely at the coast, small hail showers are likely. These may cover the roads with small hail and with temperatures near 40 this will not be quick to melt and the roads will be slippery.

Tuesday night and Wednesday the rain and snowfall amounts will be lighter, especially in Trinity county, but the air will be colder. Early Wednesday snow levels are expected to be around 1,000 to 1,500 feet. However most areas only expected to see 1 to 3 inches of snow. This precip will be showery and there could be locally higher amounts. Again this could drive snow levels down and some light snow is possible at the coast, but not likely.

Wednesday night into Thursday morning another round of rain and snow is expected. Snow levels look to be around 1500 to 2500 feet once again, however there is a lot of uncertainty on where this system will track. The ECMWF EFI is around 0.5 to 0.6 highlighting the potential for heavier snow. So this will definitely be a system that needs to be watched and a winter weather advisory may be needed. Friday and possibly Saturday as well there may be a break in the heavier rain and snow. Then the models are highlighting another strong system on Sunday. The ensembles are starting to highlight increased IVT and potentially heavy rain on Sunday. MKK

AVIATION...(06Z TAFs).

Post frontal conditions are continuing light rain at the coastal terminals which is likely to wane into the morning, bringing light to calm winds and obscurations in the way of mist at flight deck level. Stratus, mid level, and high clouds lose density Monday morning but are still likely to maintain scattered and broken at their respective altitudes. The next approaching system will bring northerly gusts to KCEC and KACV by the late morning and afternoon respectively. Instability persists in front of the next front with weaker troughing due to an elongated and shallow gradient. With the next front we see an embedded shortwave and tighter gradient. Geostrophic flow from the NW will source stronger wind gusts Monday evening, veering westerly by Tuesday morning. /EYS

MARINE

The persistent 8-10ft wave heights from the residual swell have finally trended down. Wind waves are more active with the southerly fetch over area waters becoming the dominant factor in wave generation. With the next approaching system we see geostrophic meridional flow from the NW, which will bare down on the area waters by Monday afternoon. Models are more in agreement and confidence is high in the occurrence of 35-38kt gusts in the southern waters from Monday afternoon through Tuesday morning and so a Gale warning has been hoisted to cover the hazard. Small craft advisories will cover the conditions up until that point for the southern inner and outer waters, meanwhile covering the northern waters for the entirety of the duration of the conditions through Tuesday late afternoon. Combined seas just under 10ft as the wind wave fills in. An additional swell is expected on Tuesday afternoon and evening. Currently have gone with the wave model for wave heights, but they could come in higher like the last system. MKK/EYS

EKA WATCHES/WARNINGS/ADVISORIES

CA... Winter Weather Advisory from 10 PM Monday to 7 AM PST Wednesday for CAZ101-103.

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

Winter Storm Warning from 10 PM Monday to 4 PM PST Wednesday for CAZ104.

Winter Storm Warning until 4 PM PST Wednesday for CAZ107- 108.

Winter Weather Advisory from 10 PM Monday to 4 PM PST Wednesday for CAZ110-111-114-115.

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory from 10 AM Monday to 3 PM PST Tuesday for PZZ450.

Small Craft Advisory until 1 PM PST Monday for PZZ455.

Gale Warning from 1 PM Monday to 10 AM PST Tuesday for PZZ455.

Small Craft Advisory until 3 PM PST Tuesday for PZZ470.

Small Craft Advisory until 10 AM PST Monday for PZZ475.

Gale Warning from 10 AM Monday to 10 AM PST Tuesday for PZZ475.