Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 232149

National Weather Service Eureka CA
249 PM PDT Fri Oct 23 2020

.SYNOPSIS...A few light showers are possible for the north coast
late tonight. Conditions will then dry out later this weekend,
with gusty northeast winds expected for Sunday through Monday.


.DISCUSSION...Gusty north winds having been subsiding and shifting
to the northwest today. A few stations were still flirting with
red flag criteria this afternoon, but even these sites with low
RH`s should have higher recoveries tonight. A weak disturbance in
NW flow aloft will induce a push of low level moisture and clouds
across the area tonight. Some light showers and drizzle may move
onshore over Del Norte and the northern Humboldt coast with
onshore flow late tonight...however measurable precip is expected
to be around a few hundredths to zero. Low-level moisture should
linger through Saturday with another night of good RH recoveries
overnight Saturday night.

Another stronger upper shortwave is forecast to dig south across
the Great Basin during Sunday. An exceptionally dry airmass associated
with a modified polar airmass will spread across the region Sunday
afternoon through Tuesday behind the upper wave. In addition,
strong high pressure building over the Great Basin will promote
another round of east-northeast winds gusting from 30 to 50 mph,
particularly across exposed ridges. These may flirt with wind
advisory criteria, thus have decided to hoist a high wind watch
for Lake county where high resolution model guidance has winds
hitting 35-40 mph over the ridges. ENS and NAEFS mean 850mb winds
are over the 97th climatological percentile by Sunday night
across Trinity, NE Mendocino and Lake counties. Also, the ECMWF
extreme forecast index is over the 80th percentile across the Lake
county by Sunday evening. The high wind watch may need to expanded
into portions of Mendocino county as higher resolution model data
becomes available. The wind should start to die down Monday afternoon,
however RH`s are expected to remain extremely low. Thus, it will
not take much to warrant an extension and continuation of the red
flag warning into Monday night and Tuesday morning.

Guidance indicates upper ridge building over the forecast area
through mid week as the upper trough slowly edges eastward across
the Desert SW. The warming aloft will likely promote above normal
daytime temperatures, however the dry air and clear skies will
also allow temperatures to plummet each night. Frost and freezing
temperatures will be possible each night in some of the valleys.

There is a great deal variability and spread in the guidance late
in the week, around Friday. WPC clusters indicate a slight potential
for some rain, with 27% of members out of 100 wetter than mean.
Another cluster made up of 33% of GEFS members has a slightly less
wet scenario. Some rain will be possible, though there is still a
great deal of uncertainty and about half of the members all dry.


.AVIATION...Early afternoon satellite imagery shows widespread
stratus blanketing much of the coast south of Cape Mendocino and the
Red Salmon Complex producing a decent amount of smoke. Mostly VFR
conditions are expected through this afternoon across Northwest
California, the lone exceptions will be in the vicinity of the Red
Salmon Complex and at KCEC. Haze and/or smoke will cause mostly MVFR
conditions in these areas. Stratus is expected to return to both
coastal terminals this evening and bring conditions down to IFR to
MVFR at least in the vicinity of the airfields.


.MARINE...Winds will continue a weakening trend through tonight over
most of the coastal waters, except for the southern outer waters,
where winds will remain elevated. Northerlies will ramp up again
over both outer zones starting Saturday morning and another round of
Gales are expected for both zones by around mid-afternoon on
Saturday. The Gale Watches have been upgraded to Gale Warnings
starting at 22Z Saturday through 22Z Sunday. Winds begin to ease
thereafter, but will remain somewhat elevated over portions of the
outer waters through Tuesday, particularly over the northern outer
waters. Winds will really begin to ease as we head into Wednesday,
where we are currently forecasting mostly less than 10 knots across
all coastal zones for the back half of the upcoming work week. Steep
seas will linger in the outer waters and portions of the northern
inner waters through the rest of today. Otherwise, a longer-period
west to northwest swell is forecast to begin to move through the
waters the latter half of Sunday.


.FIRE WEATHER...Tonight and Saturday, RH`s will generally be
higher with light to moderate winds. A few light showers will be
possible late Friday night and early Saturday, mainly over Del
Norte and Humboldt Counties. An exceptionally dry airmass is
forecast to spread across the region Sunday through Tuesday. That
airmass combined with very dry vegetation and east-northeast
ridgetop winds gusting from 30 to 50 mph will yield critical to
locally extremely critical fire weather conditions from Sunday
afternoon through Tuesday morning.


CA...Red Flag Warning from 11 AM Sunday to 5 PM PDT Monday for CAZ201-

     Frost Advisory from 4 AM to 8 AM PDT Saturday for CAZ107.

     High Wind Watch from Sunday afternoon through Monday morning for

 Small Craft Advisory until 9 PM PDT this evening for PZZ450.

     Small Craft Advisory until 3 PM PDT Saturday for PZZ470-475.

     Gale Warning from 3 PM Saturday to 3 PM PDT Sunday for PZZ470-



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