Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 101239

National Weather Service Eureka CA
439 AM PST Tue Dec 10 2019

.SYNOPSIS...A weak front will bring light rain to Northwest
California this afternoon and this evening, followed by another
brief period of drier weather for part of Wednesday. An extended
period of wet weather will follow, with on and off light to
moderate rain from Wednesday night through Friday or Saturday.


.DISCUSSION...It has been a dry and mild but mostly cloudy night for
northwest California. Low clouds have been fairly extensive along
the coast and through most valley areas. However, these clouds are
temporarily scattering and may allow for some partial dim
sunshine before more clouds increase by the late morning hours.
Expect a dry morning for most of our area, before our brief
respite from this wet December comes to an end.

A weak front and associated upper trough is approaching from the
west, and we are already seeing some specks of low reflectivity
showing up offshore on KBHX radar. Models have been surprisingly
consistent with this system, sending a brief shot of mainly light
rain across northwest California mainly between this afternoon and
this evening. Some light rain may reach parts of the coast as
early as midday. Rainfall amounts will generally range from a
tenth to to a few tenths of an inch, but a few orographically-
favored locations like the King Range and the mountains of eastern
Del Norte may reach up to a half inch. Snow levels will be at or
above 5500 feet.

In the wake of this front, some scattered showers will linger
through the overnight hours, and even into early Wednesday morning
in select spots. Most of the area though should expect a dry
morning on Wednesday before the next system makes it`s presence
felt in northwest California. Would not totally discount the idea
of some brief dim sunshine early in the day, but similar to
Tuesday, it should be limited and short-lived before clouds
increase and thicken once again. Models have been trending a
little faster with the next shot of rain, and would expect at
least some spotty light rain to move into Humboldt and Del Norte
counties by the afternoon hours on Wednesday.

Light to moderate rain will then expand across our region
Wednesday night into Thursday as a fairly strong westerly Pacific
jet takes aim, between a strong upper-low over the Gulf of Alaska
and a flattening upper ridge off the southern California coast.
IVT values will not be particularly impressive, but will be
maximized as vectors orient perpendicularly to the coast. A number
of impulses will pass through the zonal flow, enhancing the
coverage and intensity of the rain at times. The precipitation
will gradually become more showery heading into Friday as
somewhat cooler, drier, and more unstable air begins to filter in
from the north. Total rainfall amounts from Wednesday night
through Friday night look to range from a half inch to two inches
north of Mendocino county. Lighter amounts will be found to the
south, with locally a few inches possible in the mountains of
interior Del Norte County. Aside from increased southerly breezes
mainly across the ridges, winds will be a non- issue with this
period of wet weather.

Snow levels will begin to fall below 5000 feet late Friday, and
may approach 3000 feet across northern portions of our area over
the weekend. One last weak system projected to pass by over the
weekend may result in some snow across the higher mountain passes,
but amounts at this point look fairly minor. The consensus of
ensemble and deterministic models point toward a progressive ridge
giving us a period of dry weather from Sunday into early next
week, but the pattern continues to look modestly wet after that.


.AVIATION...IFR ceilings have scattered across Northwestern
California overnight as a front approaches the coast early this
morning. MVFR ceilings should develop and lower through the first
half of today, with rain and IFR ceilings along the coast as early
as this afternoon as the front moves onshore. Associated rain
showers should pass by late tonight, however ceilings will likely
remain after the frontal passage, as another front is looking to
move across the region tomorrow and Thursday.


.MARINE...Southerlies strengthen today as a front approaches from
the west. These look to increase to marginal SCY levels in the
outers this afternoon, generating short period southerly seas around
6 ft at 6 seconds. Meanwhile, a W swell is expected to fill in late
today , for combined seas of 9 to 11 ft by early this afternoon
across the outer waters.

Southerly winds drop below advisory levels Wednesday morning but
remain moderate before possibly accelerating back to advisory levels
again with another frontal passage Wednesday night and Thursday. A
significant WNW 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.


 9 AM this morning to 9 PM PST Wednesday for PZZ470-475.



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