Scientific Forecaster Discussion
fxus66 keka 201207
Area forecast discussion
National Weather Service Eureka California
407 am PST Wed Nov 20 2019
Synopsis...northeast winds will remain gusty through the day
today over the higher terrain and mountains. Mostly clear skies
are expected today through Friday, with freezing overnight low
temperatures in many of the interior valleys and patchy early
morning frost at the coast.
Discussion...a cooler and drier airmass will continue to filter
into northwest California today as high pressure builds in behind an
exiting trough. Winds along the coast will ease today, while
northeast winds across interior ridges continue to increase this
morning. Sustained winds from 15 to 25 mph are expected along the
exposed ridges, with gusts up to 45 mph are possible through
today. A red flag warning is in place for these gusty winds and
drying conditions across portions of Trinity, Mendocino, and
Humboldt counties above 1,500 feet. The cooler and drier air will
also allow for some chilly overnight temperatures each night
across interior valleys, many of which will likely fall below
freezing. Cooler temperatures will also be possible along the
coast tonight with some areas dipping into the mid to upper 30s.
As a result, some areas of patchy frost will be possible tonight
in the coastal zones.
Dry conditions are expected to continue through the weekend. The
next chance for rain will be early next week as a weak system
approaches the area from the northwest. Any rain from this system is
expected to be light. Deterministic models are coming into good
agreement about a fairly cold and wet system around late Tuesday and
into Wednesday. Confidence is slowly growing for a more widespread
rain event, but will continue to be somewhat cautious given the
wide ensemble spread.
Aviation...VFR conditions exist at acv, cec, and uki...and this
will continue through Thursday morning. Breezy northerly surface
winds will also continue at most terminals, but will begin to turn
slightly toward to the northeast later in the day. This may lead to
some low level wind shear at times, particularly during the evening
when surface winds begin to weaken and decouple from the winds
aloft. This will diminish overnight and Thursday morning as winds
aloft weaken as well. /Brc
Marine...gale to near gale force winds persist throughout the
waters this morning, and this will continue through the day and much
of the overnight hours. Seas have built to a steep 12 to 16 feet at
area buoys, with larger seas likely farther offshore. Winds will
begin to turn slightly offshore and weaken quickly overnight and
Thursday morning, allowing seas to settle to between 6 and 8 feet by
Thursday afternoon. Light to locally moderate north winds will
continue through Sunday, ensuring that seas will remain dominated by
The first in a series of northwesterly long period swells will build
into the waters quickly on Friday, reaching a height of around 11 to
13 feet with a period of 18 to 19 seconds. In addition to
maintaining elevated seas, this swell may also increase the threat
of sneaker wave activity along area beaches. This swell, including a
reinforcing surge on Sunday, will continue to dominate the waters
until increasing northerly winds bring the return of steeper seas
Fire weather...winds will continue to ramp up across interior
ridges this morning as a cut off low continues to develop to the
south and high pressure builds into the area. Overnight
observations show the dry airmass beginning to move into the area
and this trend should continue through the day today. The overlap
of strengthening northeast winds and the drying trend will lead
to elevated fire weather conditions. A red flag warning is in
place across portions of Trinity, Northern Lake, Mendocino, and
eastern Humboldt counties for elevations above 1,500 feet.
Northeast winds from 15 to 25 mph with gusts up to 45 mph are
expected through early on Thursday at the higher elevations along
area ridges above 1,500 feet. Rh's are expected to range from 15
to 30 percent this afternoon, with only poor to moderate
recoveries anticipated tonight at the higher elevations.
There is some concern about whether the northeast winds will
sufficiently dry out portions of zones 212 and 283, but the drying
trend will continue through today and at least of portions of the
zones will see elevated fire weather concerns. The situation will
continue to be monitored and if conditions are slower to dry out
than forecast, portions of these zones may need to be removed from
the red flag.
California...red flag warning until 7 am PST Thursday for caz212-276-277-283.
Northwest California coastal waters...Gale Warning until 9 PM PST
this evening for pzz470-475.
Gale Warning until 8 PM PST this evening for pzz450-455.
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