072
FXUS66 KEKA 021207
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
507 AM PDT Thu May 2 2024

.SYNOPSIS...A frontal will bring light rain to Del Norte
and northern Humboldt Counties today. Otherwise, dry weather
with gusty northwest winds are expected for Mendocino, Lake and
eastern Trinity Counties. A colder storm with greater amounts of
moisture will generate moderate to heavy rain Friday night through
Saturday morning. Drastically colder temperatures and light snow
are expected for the mountains above 3500 feet on Saturday.

&&

.DISCUSSION...Weakening frontal system dropping down from the NW
will generate light rain for Del Norte and northern Humboldt
Counties today. HREF continues to indicate probabilities from
80-100% for >0.20 in 6 hours north of hwy 299, primarily this
morning. We will post a graphic of estimated rain totals on
our webpage and facebook. NW influx of moisture (PWATs 150-200%
of normal) and onshore/upslope westerly flow will make for wet
and soggy conditions for Humboldt Bay area with light rain or
drizzle through the day. The light drizzle will wind down
overnight as low level westerlies shift to southerly. Wet
ground will likely yield patches of fog tonight. Light rain
with a warm front may redevelop (20% chance) early Friday morning
for coast Del Norte.

Otherwise, dry weather conditions with gusty west-northwest
breezes are forecast to continue for Mendocino, Lake and eastern
Trinity Counties today. Overnight temperatures in the interior
valleys were warmer (+5 to +15F) compared to last night due to
increased cloud cover and relentless west-northwest breezes.

A much colder upper trough and associated surface frontal system
will bring another bout of wet and unsettled weather to the
entire forecast area Friday night through Saturday. Heaviest rain
rates will most likely (80% certain) occur 11 PM Friday to 11 AM
Saturday, give or take a few hours due to errors in the forecast
and models. NBM 75th and 90th QPF percentiles are around 1 inch
over 6 hours and the official WPC guidance is very similar. We
have not seen heavy rain rates (1in/hr) since winter and expect
there will be some minor flooding of poor drainages and water
ponding on roads. The front will move SE by early Saturday and
even southern Mendocino and southern Lake will get a good soaking
of rain, 0.50-0.75in over 6 hours, mostly Saturday morning. Threat
of widespread heavy rain will be brief (6 hours or less) as the
airmass drastically cools down Saturday afternoon. Some snow
showers with light amounts are expected for elevations above
3500-4000 feet on Saturday. There may even be a dusting by early
Sunday morning down to 2000 feet, however frost is much more
probable.

Much colder temperatures (both highs and low) are expected this
weekend. High temps for the warmest valleys will struggle to reach
60F. Subfreezing temperatures are certain (100%) for the mountains.
Valleys may freeze again too, mostly in Trinity County where current
NBM data set indicates the highest probabilities (>60%) for the
coldest valleys.

Cold core trough aloft will progress into the Great Basin on Sunday.
How fast this occurs remains uncertain and a few showers may linger
into Sunday. Freezing temperatures are probable in the valleys of
Trinity, though after 0.50-1.00in of rain, fog and low clouds
will probably form and hinder the longwave cooling. The airmass
will be cold and temperatures in the mid 30`s are nearly certain
(>80% chance) for most all interior valleys.

Additional shortwave troughs in NW flow aloft may generate more
showers early-mid next week (highest chance Del Norte). It does
not look too wet with persistent rain each or all day. Broad flat
ridging and above normal 500mb heights may also build over the
area early to mid next week with precip probabilities eventually
approaching zero. Considerable uncertainty remains on how fast it
will warm next week. Cluster means lean toward slower warming with
upper trough lingering over the area. Probabilities for above normal
interior temps (> 80F) increase from 0% to 40-60% late next week. DB

&&

.AVIATION...Conditions at the coastal terminals have gradually
deteriorated overnight. Largely MVFR to IFR conditions will prevail
for much of the day as a system moves in, bringing low ceilings with
some light rain or drizzle. High-res models suggest rain could
become more showery in the late afternoon and evening hours, which
could improve conditions to MVFR or VFR in between showers. However,
there is fair uncertainty on just how much conditions would improve.

UKI will have a similar setup to today with the low level wind shear
threat diminishing by the morning hours, giving way to gusty NW
winds in the afternoon. The LLWS threat returns by the evening. Low
ceilings and MVFR to IFR conditions look likely to continue at the
coastal terminals into early Friday. JB

&&

.MARINE...As a system approaches the region winds have begun to
shift from gusty northerlies to relatively weaker westerlies. Winds
will generally continue to diminish as they turn westerly through
the day, though NW breezes south of Cape Mendocino and Point Arena
will continue through the nighttime hours. The sea state will calm
as winds diminish, with some steeper waves south of Cape Mendocino
accompanying the gusty NW winds. Winds and seas Friday will start
calmer, but southerlies will increase to 15-20 knots ahead of a cold
front arriving in the evening hours. The front will move through
quickly and northwesterlies will pick up further behind the front
Saturday. JB

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
None.
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