Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 261200

National Weather Service Eureka CA
500 AM PDT Thu Apr 26 2018

.SYNOPSIS...Marine layer clouds will persist along most of the
coast today, while isolated thunderstorms will be possible over
the interior mountains this afternoon into this evening. An
upper-level low will bring cooler weather with scattered showers
Friday through Sunday.


Persistent marine layer cloudiness is covering all coastal areas
early this morning, extending inland to the coastal ranges as
well, and will only deepen today as an offshore upper-level low
approaches. Do not expect this cloudiness to retreat even as much
as yesterday, and locations near the coast will remain overcast
and cool into Friday morning. High temperatures over interior
areas will be 4 to 8 degrees cooler than yesterday as the
aforementioned upper-low begins to approach, but will still be
above normal. As colder air aloft and some mid-level moisture
begins to work in, there will be a risk of isolated thunderstorms
over the mountainous terrain of interior northwest California
later this afternoon and this evening. Guidance is generally
pointing towards the best chance in an axis from the northeast
corner of Mendocino county, across western Trinity county and into
extreme eastern Humboldt County. MUCAPE values of up to 1000 j/kg
and even bulk shear 35-50 knots may allow any storm that does form
to have some staying power, but with moisture lacking, expect any
storms to be isolated and below severe limits. Would not totally
rule out some elevated showers reaching the northern Humboldt
coast this evening, though do not have these in the forecast at
this point.

The upper-low will shift eastward across our area on Friday, then
begin to lift out on Saturday. Temperatures will be much cooler
across inland areas Friday through Sunday, in the 55 to 65 range
for highs. These days will also present a better chance for more
widespread but still scattered shower activity, especially north
of Mendocino county. With the coldest air aloft shifting overhead
on Friday, will need to keep an eye out for some small hail in the
heaviest showers, but do not see a significant or widespread
threat of that hazard. Model guidance is in better agreement now
with another reinforcing trough dropping in from the north-
northwest on Sunday, which may result in an increased risk of
scattered showers along the north coast and especially the
mountainous terrain of Del Norte county. Rainfall amounts each day
will be fairly light, with some areas dodging showers, especially
farther south into Mendocino County.

Medium-range model guidance continues to be in good agreement with
a building ridge of high pressure next week, with dry weather
likely Monday through Thursday accompanied by plenty of sunshine
and warming temperatures. Coastal areas may be quite breezy Monday
and Tuesday with offshore northerly gales. /AAD


.MARINE...No marine hazards in effect into the start of the weekend.
Fairly light south and west winds and low seas in the NW California
waters. The seas are mostly from light to moderate westerly swells
moving into our waters.

By the second half of the weekend, winds will shift north and
increase. With the stronger north winds, we will have resultant
steep wind waves. Do expect hazardous marine conditions in store
from Sunday into early next week. North winds will get to gale force
level, thus producing very steep wind waves. Looks like the
strongest winds will be from Sunday night into Tuesday. /RCL


.AVIATION...Widespread marine stratus covering the West Coast from
southern California all the way up to Washington coast. Both KACV
and KCEC was stuck in mostly IFR conditions overnight, with ceiling
heights around 600 feet. Meanwhile, KUKI remained VFR all night. The
marine stratus was trying to expand into Ukiah from the south, but
it was not successful in doing so.

Do expect IFR conditions to persist through the next 24 hours for
KCEC and KACV, as the marine stratus is still having a tight grip
over the area. For KUKI, do expect VFR conditions to prevail for the
next 24 hours. /RCL




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