Area Forecast Discussion
Issued by NWS Eureka, CA
FXUS66 KEKA 080004
AREA FORECAST DISCUSSION
National Weather Service Eureka CA
404 PM PST Wed Dec 7 2016
Light rain and mountain snows will continue through tomorrow
morning, before precipitation becomes more showery in nature. The
wet pattern will continue for several days ahead, as waves of energy
in the atmosphere bring several bouts of rain to the region
(Today and Tonight)
The forecast has been somewhat tricky today. Persistent dry
easterly flow helped delay the onset of precipitation earlier,
while also keeping afternoon temperatures in check. As a result,
afternoon highs were lowered about 3 to 5 degrees across the
board. Earlier radar returns also had a bright-banding signature.
Taking a closer look at the freezing levels and radar signatures,
it looks like the numerical models were running about 500 to 1000
feet too high with the forecast snow levels, especially along the
leading edge of the precipitation shield, where spotter reports,
social media, and webcam loops showed snow levels down to about
1200 feet near Crescent City, Kneeland, and as far south as
Willits. Some rates have been observed in the 0.5 to 1 inch/hr
range. As a result, the Winter Weather Advisory for northern
Trinity County was extended to 10 am tomorrow, as we expect a
slower erosion of the colder air, with the advisory also expanded
into eastern Del Norte County for the same time period, and
farther southwest into eastern Humboldt County through 4 am. The
soundings also show a potential for the freezing drizzle (-FZDZ)
for all of these areas, especially the eastern half of Trinity
County, where drier air aloft may cut off saturation above the
-10c Isotherm, while low level saturation maintains sufficient
moisture for -FZDZ to develop. While the changeover to all rain
will occur faster in eastern Humboldt compared to locations
farther north and east (possibly as early as late this evening),
given the model/observational trends, we ran the advisory through
4 am to account for any wet bulb effects.
(Thursday through next Wednesday)
Not a whole lot of change is seen in the latest numerical runs for
the extended period. Precipitation will decrease in coverage and
intensity tomorrow, before another wave brings a renewed increase
in precip for Friday, as another vort make in the west northwesterly
flow aloft traverses the area. A general showery pattern looks to
persist through the weekend, before additional short wave troughs
and surface fronts start to affect the region early next week,
bringing widespread rainfall, some of which will be moderate to
locally heavy. Several inches of rainfall may occur, as a potential
atmospheric river setup develops. Plenty of time to watch this in
later runs though, so we`ll wait and see. /PD
Increasing clouds and lowering ceilings ahead of an
approaching warm front. The easterly to southeasterly winds will
increase late tonight as the front approaches the coast. The light
rain is expected to start in Mendocino County and spread northward
this evening. MVFR possible during frontal passage early Thursday
morning. Otherwise VFR conditions expected to prevail overnight.
Light turbulence can be expected during climb and descent will be on
the increase through the evening and overnight hours. Low level wind
shear is possible through early Thursday morning as the front
approaches the coast.
The warm front did slow down during the day today. The
strong southeast winds that are in the southern waters will spread
north of the Cape tonight as a warm front approaches from the SW.
The boundary will steadily move closer to the coast overnight and is
expected to move inland early Thursday morning. A Gale Warning
remains in effect for the northern and southern outer waters and
southern inner waters. In the northern outer waters, the Gale
Warning was extended from late Thursday morning to late Thursday
afternoon afternoon. Confidence is not high that the northern inner
waters will receive gales force winds so a small craft advisory
continues through late Thursday afternoon. The strongest winds are
expected near Pt St George and the areas 8 to 10 NM offshore.
The offshore storm will generate a very large and steep southerly
wave system tonight, up to 14 to 5 feet. This southerly wave system
should decay quickly after winds subside late Thursday afternoon. A
westerly wave system will start to arrive on Friday with wave
heights that should be sufficient to warrant an advisory. Seas
should slowly lay down by Sunday.
CA...Winter Weather Advisory until 4 AM PST Thursday for CAZ105-106-
Winter Weather Advisory until 10 AM PST Thursday for CAZ102-107.
NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory until 8 PM PST this evening for PZZ470.
Gale Warning from 8 PM this evening to 4 PM PST Thursday for
Small Craft Advisory until 6 PM PST this evening for PZZ455.
Gale Warning until 4 AM PST Thursday for PZZ455.
Small Craft Advisory from 8 PM this evening to 4 PM PST Thursday
Gale Warning until 4 AM PST Thursday for PZZ475.
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