Area Forecast Discussion
Issued by NWS Eureka, CA

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000
FXUS66 KEKA 191137
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
437 AM PDT Thu Jul 19 2018

.SYNOPSIS...Hot temperatures are likely across interior valleys
today, followed by slightly cooler conditions during the weekend.
Otherwise, isolated thunderstorms will be possible Friday
afternoon through Sunday across portions of Mendocino and Trinity
Counties.

&&

.DISCUSSION...Hot afternoon temperatures from 100 to 110 are
forecast to occur across Trinity and interior Mendocino Counties
this afternoon...followed by a slight cool down going into the
weekend. Reference the latest Heat Advisory statement for
additional information on elevated heat risk conditions over the
interior.

Otherwise, an upper-level anticyclone was positioned over the
southern Great Basin/Four Corners Region early Thursday morning,
with sub-tropical moisture, characterized by PW values from
1.5-2.0 inches, spreading west-northwest across southern
California. The upper high is forecast to become re-centered over
the southern High Plains by Friday night, which will yield
midlevel southerlies over CA, and subsequently allow PW values
from 1.0-1.5 inches to spread north toward Mendocino County. This
moisture combined with steep mid/upper-level lapse rates will
result in a marginally unstable airmass, with MUCAPE values
ranging from 200 to locally 1000 J/kg (based on NAM output)
emanating from a lifted parcel near 700 mb. This thermodynamic
environment combined with modest midlevel convergence and
isentropic upglide may be sufficient for a few elevated
thunderstorms (mainly over Mendocino County) Friday night.

Subtropical moisture is forecast to spread north across the
remainder of NWRN CA during the weekend. Strong heating and a
steep lapse rate environment will develop across the interior
mountains Saturday and Sunday afternoons, which will support
additional isolated thunderstorm development from northeastern
Mendocino County north across Trinity County.

Following the weekend, an upper high is forecast to become
centered over the Colorado Plateau and southern Great Basin by
midweek. Intense afternoon heating will become probable once again
across the interior, with high temperatures at or above 100 F
developing across the valleys of Mendocino and Trinity Counties
Tuesday, Wednesday, and Thursday.

&&

.AVIATION...Low clouds and some light fog have developed once
again along portions of the Redwood Coast. However, clouds are not
as expansive over the adjacent coastal waters as the past few
days. In addition, the marine layer is a bit shallower and
forecast to become more so over the next 24 hours. Additionally, N
winds have increased over the coastal waters, with decreases in
cloudiness downstream from Cape Blanco and an offshore component
to the low-level wind flow forecast for coastal Del Norte County.
All this points to less coastal cloudiness and faster improvement
in ceilings at KCEC and KACV this morning. High resolution models
show some lingering cloudiness near and just N of Cape Mendocino,
and this may occasionally affect the immediate coast from Humboldt
Bay S to the cape. Winds over land will be generally light, with
gusts near 20 knots during the afternoon at KCEC. VFR conditions
are expected to continue at KUKI. /SEC

&&

.MARINE...Northerly winds will continue to increase today. A Gale
Warning remains in effect for the N outer waters for frequent
wind gusts over 35 knots. The Gale Warning for the S outer waters
goes into effect around midday today, with conditions more
marginal in that area. The strongest winds will be over the N
portion of the zone as well as within the expansion fan downwind
of Cape Mendocino. Seas will build to 12 to 15 feet in the outer
waters today. Conditions will slowly improve late in the weekend
as the inland thermal trough pivots to a more NE to SW
orientation. However, a Hazardous Seas Warning may be required for
a portion of the marine waters after the gales begin to subside.
/SEC

&&

.FIRE WEATHER...Weak low pressure is forecast to develop offshore
from San Francisco during the next 24-36 hours. As that occurs,
ridgetop winds will take on an easterly component, and locally
become gusty over the mountains of Del Norte County. This will
result in areas of elevated fire weather conditions...but a Red
Flag Warning does not appear warranted at this time due to
marginal RH values occurring during the period of strongest winds.

Otherwise, model guidance shows monsoon moisture spreading north
to at least Mendocino County by Friday night. Modest MUCAPE,
locally near 1000 J/kg, is forecast to be rooted near 700 mb.
The potentially unstable atmosphere combined with midlevel
convergence and isentropic upglide may be sufficient for isolated
elevated thunderstorm development Friday night. Thereafter,
surface based thunderstorm development becomes more probable
Saturday afternoon, and again Sunday afternoon, over Trinity and
northeastern Mendocino Counties.

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory until 9 PM PDT this evening for CAZ107-108-110-111-
     113.

NORTHWEST CALIFORNIA COASTAL WATERS...Gale Warning until 4 AM PDT
     Saturday for PZZ470.

     Small Craft Advisory until 4 AM PDT Friday for PZZ455.

     Small Craft Advisory until 4 AM PDT Saturday for PZZ450.

     Small Craft Advisory until 11 AM PDT this morning for PZZ475.

     Gale Warning from 11 AM this morning to 4 AM PDT Friday for
     PZZ475.

&&

$$

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