Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 232304

National Weather Service Eureka CA
304 PM PST Thu Jan 23 2020

.SYNOPSIS...A trough will move over the area tonight providing
another round of light to moderate rain. Mostly dry conditions are
expected to redevelop on Friday in advance of another front that
promises to bring widespread rain, possibly heavy, this weekend.


.DISCUSSION...Tonight an upper level trough will move across the
area bringing rain to mainly Humboldt and Del Norte counties.
Currently there is some lightning offshore with this, but the
models are showing the instability diminishing as it gets closer.
So currently am not expecting this lightning to make it onshore.
Rainfall amounts are expected to be over an inch in the Del Norte
mountains, near an inch in southern Humboldt. Less than a half
inch is expected around Humboldt Bay and in the Trinity county
valleys. Mendocino county will see lighter amounts. These showers
will taper off quickly Friday morning and a generally warm and
dry day is expected.

Friday night through Saturday night is expected to be very wet
period, especially for areas north of Cape Mendocino. Initially a
warm front moves through Friday night and then the cold front
moves through Saturday night. There are some model differences
in the timing and location of the warm front moving onshore. It
appears the 12Z operational GFS is an outlier from the other
operational models and ensembles in showing very little precip
with the warm front. The precip is generally shown to be light
with the warm front in the models. Due to how much moisture is in
the atmospheric, it may be stronger than expected on the southwest
slopes of the mountains.

Most areas are expected to see a break in the rain on Saturday
between the warm front and the cold front, the exception will
likely be northern Humboldt and Del Norte county. Heavy rain is
expected across the area Saturday night with the heaviest rain in
Del Norte county. Rainfall amounts are expected to be over 3.5
inches in the mountains of Del Norte county the King Range. Along
the coast rainfall amounts expected around 1 inch in Eureka and
around 2 inches in Crescent City. Farther south and east rainfall
amounts will be lower with less than an inch in the valleys. For
impacts see hydrology section. Snow levels are still expected to
remain over 7,000 feet with most of the rain in this system.

Sunday the front moves through and snow levels fall to 4,000 to
4,500 feet, but most of the precip is expected to be over by that
time. There may be some snow on Scott Mountain, but it is not
expected to be much.

Long wave pattern changes very little early to mid next week.
Transient fronts will move toward the west coast from time to
time. The operational 12Z GFS has now come in line withe ECMWF and
both models are showing a strong system Sunday night into Monday,
however the GFS and NAEFS ensembles are not showing much support
for this solution. So this will need to be monitored as it gets
closer. The critical thing to watch for will be how long the
break in between the heavy rain will be. MKK


.AVIATION...Winds remained light to calm at ACV and UKI today with
a lowering CIG and occasional light showers with an approaching
front. A weaker boundary will arrive ahead of the main front, and
will mark the initial wind increase near 0Z. Expect a veering wind
profile SSE to S becoming gusty at the coastal terminals with
moderate rain and periods of IFR conditions, with the worst
conditions peaking close to 6Z.


.MARINE...Southerly winds increase across the waters today and peak
tonight, strongest in the northern outer waters. Winds weaken Friday
morning, but should remain relatively southerly and fluctuate around
low- end SCY levels for the foreseeable future as a series of weak
upper- level shortwave troughs pass overhead, with a persistent
local wind speed maximum in the northern outer waters with each
passing pulse.

Short period seas are expected to increase across the northern
waters today then rapidly diminish early tomorrow morning. Short
period southerly seas then rebuild in the northern outers in
response to more southerlies tomorrow evening, and keep a
persistent, pulsing local maximum in this zone as each of a series
of systems approaches the coast for the next week or so. A long
period west swell is expected to fill in tonight, bringing seas
above 10 ft across all zones through at least tomorrow night.


.HYDROLOGY...A very warm and moist system is expected to bring
rain to the area Friday night through Saturday night. The rain is
expected to start off slow friday night and Saturday morning. The
break in the rain on Saturday for much of the area is expected to
allow small streams to diminish. Del Norte and northern Humboldt
may not see a break in the rain. Saturday late afternoon and
overnight the heaviest rain is expected. This could bring some
small stream and urban area flooding to Del Norte county and
Humboldt county north of Trinidad in the higher terrain. Flooding
is less likely farther south and east due to the break in the

The break in the rain on Sunday should allow the mainstem rivers
to diminish, however the current RFC forecast shows the Smith
river remaining elevated and there is the potential for this to
bring some river flooding. Currently river flooding is not
expected, but it should be monitored in case this system comes in
wetter. MKK


     9 PM this evening to 9 PM PST Friday for PZZ450.

     Small Craft Advisory until 3 AM PST Saturday for PZZ470.

     Small Craft Advisory from 3 AM Friday to 3 AM PST Saturday for

     Small Craft Advisory from 9 PM this evening to 3 AM PST Saturday
     for PZZ475.



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