Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 250234

National Weather Service Eureka CA
734 PM PDT Mon Jun 24 2024

.SYNOPSIS...Interior warm and dry conditions continue through
Tuesday while marine stratus dampens coastal temperatures. An upper
level disturbance mid-week will allow for relatively cooler
temperatures through Thursday. Warming temperatures will develop at
the end of the week.


.UPDATE...This afternoon thunderstorms developed in the San
Joaquin valley and made is as far north as Stockton. The Satellite
shows convective clouds as far north as Napa county. IR Satellite
also shows widespread convective off the central CA coast. The
CAMS are showing some light returns in the modeled reflectivity
over Mendocino and Lake counties. The low levels look to be dry so
there may be some gusty winds associated with the showers. So
have added thunderstorms to the forecast for Tuesday in southern
Mendocino and Lake counties. These areas look like they have the
highest probabilities of seeing a few lightning strikes, but it is
possible these storms could make it farther north. This will need
to be monitored as it gets closer. MKK


.PREV DISCUSSION... /issued 256 PM PDT Mon Jun 24 2024/

DISCUSSION...The afternoon visible satellite reveals mostly blue
skies and stubborn stratus along the very immediate Humboldt and Del
Norte coast. Mid to high level clouds are also observed streaming
into S and CENT CA this afternoon from a sub-tropical moisture plume
being guided in ahead of an approaching NE Pacific trough. Occasional
lightning strikes are being observed along the CENT CA coast and
over the ocean well offshore.

Mid-level moisture will arrive in Lake and Southern Mendocino
counties after midnight. Regarding potential impacts, model
guidance is struggling to resolve instability with the mid to
upper moisture. Soundings show very dry low-levels, so if a
thunderstorm were to form, it would be mostly dry at the surface.
The NAM model suite continues to bring in a fair amount of MU
CAPE, but the model may be underestimating cloudcover. The
question will be if the anomalous moisture, with PWAT values up to
1 to perhaps 1.16 inches will be sufficient for isolated high-
based thunderstorm development during peak heating with forcing
from terrain influence and a subtle shortwave/PVA band. Confidence
is low on this solution, and the zones to continue to watch will
be in the far southern Mendocino and Lake County. Any convective
showers that do form will create gusty, erratic winds.

The jet stream continues to remain unusually active for the season,
with the oscillating progressive ridge to trough pattern to
continue. The next trough is due Wednesday, and it will knock inland
temperatures back to near or below seasonal norms. The trough will
enhance westerly winds on Wednesday and to a lesser extent Thursday,
particularly in Lake County where gusts to 30 mph will be possible
through and over the favored terrain. /JJW

AVIATION...Coastal stratus from overnight and this morning will
continue to erode away to the immediate coast. Coastal terminals are
forecast to stay at VFR into mid to late this evening. Westerly to
north-westerly winds to 10 knots are expected throughout the region
through the day. Mid to late this evening a reversal in winds along
the Del Norte Coast will bring up to 10 knot southerly winds
ushering in more coastal stratus. Coastal stratus is expected to
envelop the usual areas along the coast with MVFR to IFR ceilings
most likely overnight. Winds will die down at Ukiah late this
evening with the terminal remaining in VFR throughout the current
TAF period.

MARINE...In general, northerly winds will weaken throughout the
marine zones despite a slight uptick in winds in the lee of Cape
Mendocino. Throughout tonight and into early tomorrow morning, the
outer waters and southern inner waters are forecasted to support
marginal steep, short period seas that meet small craft criteria. By
mid morning tomorrow, seas are forecast to drop below small craft
advisory conditions in the waters. Meanwhile a minor northwest swell
of 5 feet at 11 seconds will persist through the day today and then
decay through tomorrow. Northerlies are forecast to remain below 15
kt for most zones tomorrow through Thursday morning, aside from the
persistent 15-20 kt northerlies expected directly downwind of Cape
Mendocino. Winds may strengthen again Thursday afternoon and into
this weekend.

FIRE WEATHER...A plume of subtropical moisture will begin to arrive
after midnight tonight. Though lacking instability, the moisture
may trigger some gusty showers or an isolated dry thunderstorm
through terrain enhancement in South Mendocino and Lake County.
Though chances are very low (less than 10%), if strikes do occur,
any grass fire starts would be capable of rapid spreading on
Wednesday when an upper trough passage enhances westerly winds.
Winds gusting to 30 mph and low RH values to the upper teens can
be expected Wednesday. The onshore flow will be gusty on Thursday
to a lesser extent, and RH values will tick up to the low 20s.


     Small Craft Advisory until 3 AM PDT Tuesday for PZZ455.

     Small Craft Advisory until 9 AM PDT Tuesday for PZZ470-475.



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