Flood Watch 5, NWS Eureka, CA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
434 AM PST Tue Mar 7 2023

.SYNOPSIS...Another winter storm will bring a period of heavy snow
for elevations above 1500 feet this afternoon through tonight.
Cold and showery weather will persist into Wednesday before drier
condition develop Wednesday night. An atmospheric river storm will
bring heavy rain, higher snow levels and strong winds Thursday
into Friday. Periods of heavy rain and gusty winds with high snow
levels are forecast for the weekend and early next week.

&&

.DISCUSSION...Widespread shower activity continued to impact
Northwest California overnight as southwesterly flow continued in
advance of a cold upper low anchored to our NW. Highest rain
rates have been out toward the coast and coastal mountains with
snow generally above 1500-2000 feet. High resolution ensemble
guidance and convective allowing models continue to indicate
precipitation rates increasing this afternoon through tonight as
this cold core trough aloft moves across the area. So far precip
rates have been mostly light. Snowfall is not expected to be
significant this morning except for the mountains of Del Norte
County.

There will likely be enough instability to support thunderstorms
with small hail at the coast and a brief period of heavy snowfall
rates across the coastal mountains and interior this afternoon
through tonight. Total snowfall of 4 to 12 inches is expected
this afternoon through tonight at elevations over 1500 feet in Del
Norte, Humboldt, and Trinity counties with some lighter
accumulation down to as low as 1000 feet. Farther south in
Mendocino and Lake counties snowfall will be lighter with
generally 3-6 inches as far south as northern Lake County and 1-3
inches near Cobb. Winter storm warnings are up for portions of Del
Norte, Humboldt, and Trinity counties while winter weather
advisories have been issued for Mendocino and Lake counties. A
winter weather advisory has also been hoisted for small hail
accumulations this evening for coastal Del Norte and coastal
Humboldt counties.

This system will be the last in the series of cold storm systems
bringing low elevation snow for the foreseeable future. It is
highly probable that the weather pattern will shift substantially
beginning on Thursday as an atmospheric river storm takes aim on
California. Strong southerly winds with a barrier jet will develop
on Thu. A high wind watch or wind advisory will need to be considered
over the next couple of shifts. Multiple deterministic models as
well as ensemble guidance indicates wind gusts over 50 mph for the
coastal ridges and headlands. Heavy rain is also expected Thu
night and Fri morning. Main stem rivers will see rapid responses
by Fri. Snow levels will rise substantially, over 4000 feet by
Friday and only the highest mountain peaks will have snow.
Additional storms with high precipitable water (PWAT) or
integrated water vapor transport (IVT) will likely bring more
moderate to heavy rain rates over the weekend into early next
week. Flooding of small streams, creeks and low-lying areas with
poor drainage will be possible. This is quite a dramatic pattern
shift to cold weather with feet of snow to strong south winds,
heavy rain and possible flooding.

&&

.AVIATION...Ceilings have lowered to MVFR levels this morning, with
IFR settling into the UKI valley. Light showers will continue moving
in off the ocean, and will present some opportunity for TEMPO IFR.
There is a 20% for thunderstorms at ACV and CEC through this
evening. Small hail will also be possible in the showers and
thunderstorms. Ceiling will slightly lower tonight, but showers will
become more isolated with breaks in the clouds eventually
developing.

&&

.MARINE...Southerly winds will increase a bit throughout the day
ahead of a front. There will be isolated gusts up to 25 kts this
afternoon through this evening while a mid period NW swell subsides.
Isolated thunderstorm chances will continue through tonight, mostly
for the northern waters. A brief burst of northerly winds gusting to
20 kts will develop behind the front early Wednesday morning. A
strong low pressure area will begin moving south along the Pacific
NW coast late on Wednesday. Southerly winds will begin ramping up in
response Wednesday evening, and will continue strengthening through
Thursday. Storm strength gusts of over 50 kts now look likely on
Thursday.

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Winter Weather Advisory from 6 PM this evening to 1 AM PST
     Wednesday for CAZ101-103.

     Winter Storm Warning until 4 AM PST Wednesday for CAZ102-
     104>106.

     Winter Storm Warning from 10 AM this morning to 4 AM PST
     Wednesday for CAZ107-108.

     Winter Weather Advisory from 10 AM this morning to 4 AM PST
     Wednesday for CAZ110-111-113>115.

NORTHWEST CALIFORNIA COASTAL WATERS...
None.
&&

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For forecast zone information
see the forecast zone map online:
https://www.weather.gov/images/eka/zonemap.png

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