Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus66 keka 091305 

Area forecast discussion
National Weather Service Eureka California
505 am PST Mon Dec 9 2019

Synopsis...morning low clouds and areas of fog will give way to
sunshine today. A weak front will bring light rain to northwest
California Tuesday, followed by a brief period of high pressure on
Wednesday, before an extended bout of wet weather begins on
Wednesday night.


Discussion...fairly extensive low clouds and fog have enveloped
almost all valleys in northwest California, and some marine layer
cloudiness is covering portions of the coast this morning as well.
Meanwhile, some weak offshore flow is helping to keep much of the
del norte and Mendocino coast clearer. Expect most of these clouds
and fog to lift and scatter by midday. However, with such a
strong inversion under a highly amplified ridge of high pressure,
the clouds may linger into the afternoon in some of the valleys
and along the beaches as well. Either way, high pressure will
provide stable and dry weather for at least today, with likely the
sunniest day of the week for most locations, before the
inevitable return to wet weather begins on Tuesday.

For Tuesday, a weakening surface cold front and 'split' upper
level trough will approach from the west. Model guidance has
consistently depicted a period of light rain through between the
midday and evening hours. Rainfall amounts will likely range from
a tenth of an inch to locally up to a half inch with this system.
A southerly breeze will develop over the mountain ridges, but
otherwise expect light winds today to continue during the passage
of this system, and right through Wednesday. In the wake of the
weak front, high pressure will likely rebuild across California
on Wednesday both at the surface and aloft. This should allow for
a mainly dry and mild day.

More wet weather will head our way for much of the period from
Wednesday night through Saturday, with a series of fronts passing
by. Between an intense upper- level low in the Gulf of Alaska and
a strong ridge of high pressure off the coast of Southern
California, deep and moist westerly flow will support this wet
period. That said, none of the individual systems passing through
look particularly strong for northwest California. Rainfall may
end up totaling more than a few inches over the mountains of
northern Humboldt and del norte, with lesser amounts to the South.
Strong winds are not expected, and snow levels will remain high
until colder air starts to settle in from the north around Friday
night. Even then, it appears doubtful that much precipitation is
left around by the time the snow levels drop to our mountain
passes later in the weekend. /Aad


Aviation..intermittent IFR ceilings have plagued northwestern
California overnight, although light offshores have cleared the
del norte coastline early this morning. Farther south, IFR
ceilings currently still in place are expected to dissolve around
mid- morning as daytime heating mixes the lower atmosphere. Low
clouds will likely return this evening, but may be short lived as
high clouds from an approaching front move overhead late tonight
and inhibit further development. /Tdj


Marine...light northerlies offshore this morning continue to
diminish today and shift southerly tonight as a front approaches
from the west. These look to increase to marginal scy levels Tuesday
afternoon, generating short period southerly seas around 6 ft at 6
seconds. Meanwhile, a west swell is expected to fill in on Tuesday, for
combined seas of 9 to 11 ft by early Tuesday afternoon across the
outer waters. Thus have lifted a Small Craft Advisory for the outer
waters in response for Tuesday.

Southerly winds drop below advisory levels for Wednesday but remain
moderate before possibly accelerating to advisory levels again with
another frontal passage on Thursday. A significant west-northwest swell still
looks on track to steamroll the north coast late this week, with
models consistently showing the peak Thursday night of around 16 ft
at 18 seconds, before slowly decaying through the weekend. /Tdj


Eka watches/warnings/advisories...
Northwest California coastal waters...Small Craft Advisory from
9 am to 9 PM PST Tuesday for pzz470-475.



Visit US at https://www.Weather.Gov/Eureka

Follow US on facebook and twitter at:

National Weather Service Glossary of Abbreviations