Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 012308

National Weather Service Eureka CA
308 PM PST Mon Mar 1 2021

.SYNOPSIS...Dry weather, along with near-normal daytime and cool
nighttime temperatures, will occur across northwest California
through Wednesday. Precipitation chances will then increase Thursday
into the weekend.


.DISCUSSION...An upper low is presently developing well WSW of the
area, with surface low development near 39N/129W. Convective
cloudiness continues to develop closer to the upper feature while
stratiform cloudiness expands over the coastal waters. The upper low
is forecast to drop S over the next 24 hours before rounding the
base of a broader E Pacific trough and moving toward S CA. The
surface low is forecast to move SW away from the area. Although low
cloudiness may initially spread farther inland along coast this
afternoon and perhaps into the evening, developing offshore flow
should act to reduce low clouds overnight and shift them offshore.

Cold overnight temperatures will once again lead to frost formation.
Have issued a frost advisory for Lake and interior Mendocino
counties. There may be frost across portions of the N coastal
Humboldt and Mendocino coastal zones, but uncertainty is higher in
these locations due to the aforementioned coastal cloudiness along
with surface winds. The oncoming shift will monitor cloud, wind, and
temperature trends for possible advisory expansion into these zones.

Frost will again be possible Wednesday morning. Otherwise, dry
weather is forecast to persist through mid-week. Thereafter, model
guidance shows a cold upper trough digging over the NERN PAC
Thursday, and then ejecting eastward across the West Coast Friday
and Saturday. A period of moderate to locally heavy frontal rain
will be possible Friday afternoon and evening. There is
uncertainty regarding timing and amount of precipitation. The GFS is
more progressive and heavier with precip, while the ECMWF holds
frontal precip offshore longer and has lower QPF. It appears
rainfall amounts of around an inch are likely for portions of the
North Coast. However, there is the potential for more rainfall,
particularly across Del Norte County. Pre-frontal advisory level
southerlies may occur across exposed ridges and coastal areas Friday
morning. Light mountain snow also appears possible during Saturday
as a cold post-frontal mid-level airmass spreads east across the
region. /SEC


.AVIATION...Stratus/fog formed along much of the North Coast
overnight. However, the stratus/fog had a greater impact at CEC where
conditions were IFR/MVFR. By 16z (8AM), nearly all the marine clouds
had receded well offshore. Late-morning-afternoon saw minor haze
obstructions at the coast. By mid-afternoon, MVFR CIGS/VIS advected
from north to south into CEC as winds shifted. Afternoon CU/SC also
formed over the near coastal hills and moved across ACV airport...
dropping CIGS into MVFR. Overnight with light offshore flow again,
VFR conditions will generally be widespread, however a few protected
valleys may see patchy fog development. Another consideration for
Tuesday morning is the fact that afternoon CU/SC did form along the
near coastal hills and may again spread over ACV along with possible
coastal stratus and fog affecting some coastal locations. /TA


.MARINE...Gusty winds from SSW are producing gusts this afternoon
near Cape Mendocino that are at advisory criteria but will not last
long enough for a headline.  Sea state is somewhat benign until
Tuesday morning when a NW swell around 11 feet at 15 seconds builds
in the northern outer waters, then spreading to all waters by
tomorrow evening. Of particular interest is the front brought on by
a cold upper trough, expected Thursday. South East winds producing
up to 35 kt sustained with gusts 30 to 42 kt, could produce
hazardous sea conditions with combined wind waves and southerly mid-
period swell.  The situation will be monitored and hazards will be
updated accordingly. SC.Y is in effect beginning Tuesday morning for
the previously mentioned NW swell. /EYS


CA...Frost Advisory from 11 PM this evening to 9 AM Tuesday
      for CAZ110>115.

     Small Craft Advisory from 6 AM Tuesday to 6 AM Wednesday
      for PZZ470.
     Small Craft Advisory from 6 PM Tuesday to 6 AM Wednesday
      for PZZ455.
     Small Craft Advisory from noon Tuesday to 6 AM Wednesday
      for PZZ450-475.


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