Scientific Forecaster Discussion
fxus66 keka 162256
Area forecast discussion
National Weather Service Eureka California
256 PM PST Thu Nov 16 2017
Synopsis...cold and unstable air from the North Pacific will
generate occasional showers and high elevation snow showers through
tonight. A colder and drier air mass will settle over the region on
Friday and continue through the weekend. More rain is expected next
Discussion...scattered shower activity continued to spread across
the area through the day. A few of the heavier showers produced very
small hail generally north of Cape Mendocino, some occurring inland
to around Blue Lake. Expect showers to gradually decrease in
coverage and intensity through the night. With dropping freezing
levels, the chance of small hail in heavy showers will continue over
the north, particularly along the Redwood coast and occasionally
affecting Highway 101. Temperatures will be cooler overnight, with
low temperatures reaching the mid to upper 30s in areas that have
yet to see a killing freeze. Although this is typically the
temperature range where we begin to see frost formation, this
cooling will be almost completely advection-based with clouds
lingering most or all of the night, particularly in the normally
colder valleys. As a result, little frost is expected. The evening
shift will continue to monitor for earlier clearing.
As snow levels drop through the night, continued showers will
produce more and more snow at higher elevations of the interior. As
a result, have hoisted a Winter Storm Warning and a Winter Weather
Advisory based on anticipated snow accumulations. Snow totals of 6
to 8 inches are possible in the highest elevations of southeast del Norte
County with 4 to 6 inches possible in higher elevations of extreme
NE Humboldt and north Trinity counties. Less than an inch or two of snow
are expected on most mountain passes, but Scott Mountain Summit may
see over two inches of snow.
Low temperatures on Saturday morning will drop well into the 30s,
with some pockets of upper 20s possible in areas that haven't
experienced a killing freeze. A frost advisory are likely during
this period (even at the coast), with freeze warning possible for
portions the interior.
After dry weather from Saturday into the weekend, more rains are
expected next week. The global models seem to be focusing the
heaviest rains across the area late Tuesday into early Wednesday,
but a prolonged period of rain is anticipated. This will likely be
an atmospheric river event, but the focus of the heaviest rain is
still uncertain. Stay tuned! /Sec
Aviation...SW-NW flowing showers continued across the region
into middle afternoon. MVFR ceilings & visible were more frequent in
showers that occurred before Noonday. Showers will diminish
through the evening. Nevertheless, a slight chance for a
thunderstorm is still possible into late afternoon/early evening
due to ongoing instability associated with cold air troughing
being translated over the north coast. Through the remainder of
the period, residual moisture, light winds and clearing areas
could lead to a few reports of patchy fog development along
portions of the immediate coast and local interior valleys.
Marine...a few days of calm marine weather before conditions
becoming hazardous again starting on Sunday. Seas have been
subsiding through the day, as a result of diminishing wind. By this
afternoon, seas were down to 8 to 9 feet at around 11 to 14 seconds.
The short period wind wave was no longer the dominant wave group, as
the long period swell was taking over. Winds will be around 10 to 15
kt and westerly through tonight. Winds will switch to the north as
high pressure moves into California/NV/or on Friday. Winds will shift to the
south on Saturday. With light to moderate winds, the resultant wave
height will be fairly low. Combined seas of 8 to 9 feet tonight,
then down to 6 feet on Friday, 4 to 5 feet on Saturday.
Sunday will be the day when we transition back to hazardous marine
conditions as a weather front approaches the Pacific northwest and
tighten the southerly pressure gradient over northwest California waters.
South wind will be increasing to small craft level for the northern
waters on Sunday. The resultant combined seas will also go up to 11
feet. Gale conditions will be possible on Monday. After that,
forecast confidence decreases significantly. European model (ecmwf) and GFS have
disagreement on the general pattern. GFS suggests a stronger
southerly solution, while European model (ecmwf) is hinting on intervals of north and
south winds. Hopefully the models will come into better agreement
in future runs. /Rcl
California...Winter Weather Advisory until 4 am Friday for caz105-107-108.
Winter Storm Warning until 4 am Friday for caz102-105-107.
Northwest California coastal waters...
Small Craft Advisory until 3 PM this afternoon
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