Area Forecast Discussion
Issued by NWS Eureka, CA

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000
FXUS66 KEKA 121127
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
427 AM PDT Wed Aug 12 2020

.SYNOPSIS...Warm, dry conditions will continue through Friday
across interior areas. Overnight clouds and fog will dissipate
during the late morning along the coast, leaving sunny skies and
mild temperatures during the afternoon. A warming trend is
expected Friday and into the weekend. There is a slight chance of
thunderstorms on Saturday in the interior.

&&

.DISCUSSION...An upper level trough moving over the area has
brought some subtle changes to the weather in the area. Inland
areas will see temperatures a few degrees cooler today than
yesterday. This has also weakened the marine inversion which has
limited the stratus coverage. The marine layer has deepened
slightly, but is mainly limited to the immediate coast. Winds
will generally be out of the west to northwest aloft and at the
surface through much of the day. This will generally push smoke
from the Red-Salmon complex into northern Trinity and siskiyou
counties.

Tonight offshore is expected to develop, although initially it
will be fairly weak. This will help to diminish the stratus at
the coast and clearing is expected in most areas by mid to late
morning. However this may push some smoke into northern Humboldt
county Thursday morning. Temperatures inland are expected to
remain fairly similar to Wednesday in the mid to upper 90s.

Thursday night into Friday offshore flow is expected to
strengthen. This will bring a better chance of seeing smoke in
northern Humboldt and southern Del Norte counties. This may be
strong enough to keep most of the coastal clouds off the coast.
Temperatures at the coast are expected to be above normal with
highs near 70 possible. Inland temperatures are expected to many
areas in the lower elevations warming to around 100.

Saturday an upper level low approaching from southwest will bring
some moisture up from the south and the potential for
thunderstorms Saturday afternoon and evening. It still looks like
the best chances will be east of South Fork Mountain in Trinity
county. The GFS is showing nearly 400 to 600 j/kg of cape in
Northern Trinity county with good lapse rates aloft. This is in
decent agreement with the NBM that is showing around 300 j/kg of
cape. The shear looks like it will be around 20 kt and storm
motion will generally be from the south. These storms may be
fairly dry, the bases will be quite high. There is also a
shortwave rotating around the low.

Saturday is also expected to the hottest day across the interior
and possibly at the coast. Inland valleys are expected to be 100
to 105 and the coast may see temperatures around 70. It is
possible that a thin marine layer could persist and keep
temperatures in the low 60s at the immediate coast, but for now
most model guidance is showing temperatures around 70.

Sunday the low continues to approach, but is weakening and
filling. Lapse rates aloft start to weaken and the flow becomes
more southwest making the potential for thunderstorms much lower.
This may cool interior temperatures a few degrees. At the coast
the marine layer will likely deepen and bring more normal
temperatures to the coastal areas.

Early next week the upper level trough generally remains off the
coast with southwest flow over the area. There are some small
chances of some thunderstorms, but for now the potential looks too
low to be included in the official forecast. Temperatures in the
interior are expected to moderate slightly and the coast will
likely see night and morning marine clouds. MKK

&&

.AVIATION...By 3AM, GOES-17 Night Fog product revealed low clouds
remaining more expansive over the coastal waters S of Cape
Mendocino, with northerly winds around the cape suppressing any
northerly advection. However, stratus continues to expand from
Humboldt Bay into KACV yielding LIFR Cigs. Localized southerly flow
quickly streamed the cloud layer into KCEC. Stratus was also
observed edging closer to KUKI up the Russian River Valley. Local
southerly winds are light in area, but may be enough to usher in
brief periods of IFR in the dawn hours. The ACV profiler indicates
the marine layer has deepened ever more slightly overnight, albeit
with a weakened inversion. Improvement and periods of VFR are
expected to return to coastal terminals tomorrow in a typical
diurnal summer pattern. Broad troughing will hold this pattern
through Thursday as high pressure begins to build in from the west.

&&

.MARINE...Northerly winds and steep seas will be on the increase
overnight. First felt in the southern waters as an upper low
approaches from the SW, the winds will then expand in all outer
waters as high pressure then builds in from the west and invigorates
the pressure gradient. Winds and seas will increase enough over the
N outer waters Thursday to warrant a Gale Watch, where winds will
gust upwards of 40 kt and seas will build to around 12 feet through
Friday before slowly backing down.

&&

.Fire Weather...Slightly cooler temperatures are expected today,
although RH will remain low. Recoveries on the ridges have been
low this morning, but most valleys are seeing moderate recoveries.
Tonight and Thursday are expected to see these conditions persist.

Friday high pressure and offshore flow brings increasing
temperatures and light offshore flow. RH in the low teens is
expected in the afternoon with temperatures around 100. Friday
night into Saturday morning will see poor recoveries once again
with weak offshore flow. Saturday afternoon and evening there is
the potential for thunderstorms over the interior. For now the
best chance looks to be over Trinity county, but they could make
it into NE Humboldt and interior Del Norte county. Currently only
expecting isolated coverage at most, but this could change as it
gets closer. Some of these thunderstorms could contain gusty
winds. MKK

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...None.
NORTHWEST CALIFORNIA COASTAL WATERS...
Gale Watch from Thursday afternoon through Friday morning for
     PZZ470.

     Small Craft Advisory until 2 PM PDT Thursday for PZZ470.

     Small Craft Advisory until 11 PM PDT Friday for PZZ475.

&&

$$

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