Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 171033

National Weather Service Eureka CA
333 AM PDT Tue Oct 17 2017

.SYNOPSIS...High pressure will remain in control of the forecast
through Wednesday. Low pressure and an associated cold front will
bring widespread rainfall and cooling temperatures to the area
Thursday into Friday.


.DISCUSSION...Satellite imagery this morning shows a mix of clouds
over the CWA with high clouds passing over the land and stratus
building over the water. The question for today is whether or not
the stratus will make it to the coast and, if it does, will it
dissipate by the afternoon. Current thinking is that the Humboldt
coast may succumb to the stratus and then gradually clear out
while Del Norte and Mendocino remain clear. Temperatures for NW
California will be a couple of degrees cooler than yesterday.
Stratus is forecast to return to all coastal areas along NW
California tonight and into Wednesday morning as high pressure
starts to give way to deepening trough.

Widespread rainfall and cooling temperatures are anticipated
Thursday into Friday as a frontal system passes over the region.
Del Norte and northern Humboldt counties are forecast to receive
anywhere from 0.75 to 2.00 inches of rainfall with most of Del
Norte County receiving at least an inch of rain. South of HWY 299
and into Trinity County total rainfall amounts are expected to
range from 0.25 to 1.00 inches of rain. Mendocino County will
likely see rain amounts of 0.20 inches to 0.75 inches. In addition
to the rain, snow levels are forecast to drop to nearly 5000 feet
on the back side of the front. The Trinity Alps and perhaps even
the Yolla Bolly may see accumulating snow.

Moving into the weekend 500mb heights are forecast to rise which
will support gradually warming temperatures. Saturday looks to be
cool but temperatures should return to near normal for most areas
by Sunday. Models are also suggesting additional chances for light
rain for areas north of HWY 299 in Del Norte and Humboldt counties
during this time frame, similar to how a warm front may pan out.
Confidence is not terribly high for this part of the forecast, but
if rain were to occur, Del Norte would have the best chance to see
accumulating rain.


.AVIATION...Stratus north of Cape Blanco has been sliding southward
offshore over the waters through the night. High resolution models
as well as BUFKIT x-sections indicate increasing boundary layer
humidities moving onto the north coast today as northerly flow
increases offshore. Low clouds will probably impact coastal
terminals today as NW breezes develop later this morning.
The duration of IFR conditions is not certain. The potential for IFR
conditions will continue into the evening hours. Otherwise high
level cirrus clouds will stream across the region from the SW today.
Smoke may produce reduced vsbys at KUKI again this morning.


.MARINE...Light to moderate northerlies today and tonight will
diminish on Wed. Southerly winds in advance of a cold front will
produce steep wind waves offshore on Thu. Large (18-20ft) long
period west-northwest swell will build behind the front Thu night.
Large swell will persist into Friday. A warm front will probably
bring another bout of brisk southerly winds and steep southerly
waves Fri night into Sat for the northern waters. Seas will most
likely remain elevated through the weekend.


.BEACH HAZARDS AND SURF...ENP and NWPS remained consistent with
large west-northwest swell building Thu Night and Fri. Swell around
18 to 20 feet with periods near 17 seconds will start to build Thu
Night and peak early Friday morning. Swell of this magnitude will
result in large breakers in the surf zone as well as hazardous waves
in the harbor entrances. We will call attention to this threat in
the hazardous weather outlook and a weather story graphic.




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