Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 221312

National Weather Service Eureka CA
612 AM PDT Fri Oct 22 2021

.SYNOPSIS...A series of storms will bring rain and periods of
gusty winds through the weekend. The heaviest rain periods will
occur tonight and Sunday. Wet and unsettled weather will continue
on Monday and Tuesday of next week.


.DISCUSSION...The shield of moderate to heavy precipitation
continues to shift E as individual cells move NE. Isolated to
scattered showers trail this area of precip. One lone thunderstorm
has fired up over the N outer coastal waters closer to the
approaching upper trough and vorticity maximum in the base of the
trough. A few more storms may develop and move toward the coast.
Rain and high elevation snow is winding down over the River
Complex burn scar, so may be able to end the Flash Flood Watch a
bit early.

Another front will move into the area on Saturday, keeping periods
of precipitation in the forecast. However, a much more
significant storm system will approach the Pacific NW Saturday
night and Sunday. The surface low will rapidly deepen to 942 mb W
of WA by midday Sunday. Another atmospheric river will push into
the area Saturday night. This ribbon of deep atmospheric moisture
will slow as it progresses S, with the heaviest rainfall amounts
expected to focus over Mendocino, Lake, and S Humboldt counties.
These are the areas that been the driest thus far this fall, but
antecedent rainfall from the most recent system still totaled 1
to 3 inches in many areas. As a result, the threat of minor
flooding will be fairly uniform across the area (lower rain
amounts coupled with higher antecedent rainfall across the N).
However, the main threats will continue to be run-off over burn
scars. Thus, locations with the highest rainfall rates will be the
most problematic.

Southerly winds will increase once again with the Sunday system,
maxing out Sunday morning. The S winds will bring some downslope
flow along portions of the coastal plain. This will warm and dry
the lower layer of the atmosphere, possibly delaying the onset of
rain and reducing rainfall amounts a bit along the coast. Wind
gusts over 40 mph are possible near the coast with some higher
gusts across coastal terrain. Instability is forecast to increase
late Sunday into Monday, with isolated thunderstorms possible over
the coastal waters and along the coast, perhaps spreading farther
inland. Unsettled weather will continue into the first half of
the coming week. /SEC


.AVIATION...The upper level trough retreats north but leaves
shortwaves in its wake. LIFR at KCEC overnight has improved this
morning to IFR as showers have eased and visibility has slightly
improved. MVFR conditions for the rest of the TAF period at KCEC
with vicinity showers returning. KACV is expected to improve to VFR
with ceilings below 5000 feet and showers returning tonight as
precipitous weather continues. Rain showers continue at KUKI with
winds becoming more variable. /EYS


.MARINE...A break from the and gusty winds as bands from the
pacific storms ease for a few hours. Moderate winds return
Saturday morning with a break in the afternoon but return again
Sunday morning at near Gale force. A persistent upper mid level
swell continues from the west with a substantial set arriving
Sunday evening. There may be need for a High Surf Warning as
breaking waves on shore could reach 25-28 feet and last well into
Monday. Small Craft Advisories may need to be upgraded to
hazardous seas to accommodate for the sea state. /EYS


.HYDROLOGY...Heavy rain rates will increase the potential for
localized flooding, particularly on Sunday. Debris flows on burn
scars, mainly the River Complex and Monument burn scars in Trinity
County, will be possible if hourly rain rates reach or exceed 0.8
inch per hour. Area rivers will rise in response to the rains, but
levels are forecast to remain well below flood stage. /SEC


.BEACH HAZARDS...W to NW swells are expected to continue through
the weekend. Another, more significant swell train is forecast to
arrive late Sunday and Monday, with surf heights building to over
25 feet. A High Surf Advisory/Warning may be needed. /SEC


CA...Flash Flood Watch until 8 AM this morning for CAZ107.

     Small Craft Advisory until 3 PM Saturday for PZZ450-455-470-475.


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