FXUS66 KEKA 052150

National Weather Service Eureka CA
250 PM PDT Fri Jun 5 2020

.SYNOPSIS...A cold low pressure trough will bring substantially
cooler temperatures, blustery onshore winds, occasional showers
and isolated thunderstorms this weekend mainly north of Mendocino
County. Mainly dry weather and near normal temperatures are
expected next week.


.DISCUSSION...The approaching upper level trough has brought a
deep marine layer to Humboldt and Del Norte counties today. This
may partially break up at the coast in the evening, but many
inland areas near the coast may stay cloudy. High clouds will
continue to increase tonight as the system approaches the area.

Saturday mid and high clouds are expected across much of the area.
Around midday or early afternoon showers are expected to start to
move across mainly Humboldt and Del Norte counties. A few will
extend into Trinity and Mendocino counties. There is some
instability, even some a few hundred joules of surface cape at
the coast as these start to move onshore. There is also a
vorticity max with the trough as well. This will bring the
potential for a few thunderstorms in the afternoon and evening.
These are expected to remain north of Mendocino county. Overnight
there is some elevated instability that lingers through midnight,
but then diminishes overnight. Showers will likely continue but
the thunderstorm potential is low so have taken them out of the
forecast. There may be some small hail with these showers and
thunderstorms as the freezing levels are fairly low, however it
doens't look cold enough for there to be significant accumulation
on the roadways. Snow levels will fall to around 4,500 feet in the
afternoon and evening, although most of the accumulation is
expected to remain above 5,000 feet. Even at the highest
peaks 2 to 4 inches is the most expected. Rainfall amounts in
Humboldt and Del Norte county are still expected to be around a
quarter to half inch with local amounts up to an inch in the
mountains. These amounts may vary quite a bit due to the showery
nature of the precip expected.

Sunday morning showers will start to taper off as the upper level
trough starts to pull out of the area. Around midday and early
afternoon there may be a slight increase in showers and another
slight chance for thunderstorms over Trinity county with some
daytime heating. Temperatures are only expected to warm into the
60s, but with the cold air aloft this will bring enough
instability for a slight chance of thunderstorms. Sunday night
into Monday morning will be the coldest night. Frost is likely in
many of the Trinity county valleys and possible in NE Mendocino
county and eastern Humboldt.

Monday and warming drying trend is expected with most inland areas
seeing highs back in the 70s. Tuesday this warming trend is
expected to slow as a very weak system moves through. Some light
rain or drizzle is possible on the Del Norte or Humboldt coasts
with just a few clouds elsewhere. Late in the week another upper
level low is expected to approach the area bringing the potential
for more rain on Friday or the weekend. MKK


.AVIATION...An extensive stratus deck remains along the North Coast
and some of the coastal river valleys this afternoon as the marine
layer depth has increased above 3000 feet ahead of an approaching
trough. Conditions have improved to MVFR at KCEC and KACV as of
early afternoon after bouts of drizzle and IFR/LIFR during the
morning hours. Although some additional improvement is possible
later this afternoon, generally expect MVFR ceilings to persist
through the evening and most of the night at these sites as the
trough gets closer to the coast. Rain will begin to spread into KCEC
around 18z Saturday along with a slight chance of thunderstorms as
instability increases with the arrival of colder air aloft. Expect
these conditions to spread south towards KACV later in the day on
Saturday. Meanwhile, KUKI and other interior airfields will likely
remain VFR through the TAF period with mainly just some increasing
mid-high level cloud cover as the trough moves over NW CA. /CB


.MARINE...Northerly winds and seas have diminished rather quickly
today as the coastal pressure gradient weakens ahead of the
advancing trough. Cancelled the remaining Small Craft Advisories for
the southern zones as any stronger winds and locally steeper seas
should be confined to areas near and downwind of Cape Mendocino for
the remainder of the evening. Relatively light winds and calmer seas
should prevail through Saturday before moderate west-northwest winds
move in on the back side of the trough later this weekend. The
combination of increasing short period seas and an increasing NW
swell could push sea states back toward advisory conditions by late
Saturday night into Sunday. A northerly wind regime looks to become
re-established early next week. /CB





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