522
FXUS66 KEKA 042312
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
412 PM PDT Thu Jul 4 2024

.SYNOPSIS...The long-duration extreme, record breaking heat wave
will continue. The strong dome of high pressure will begin to center
over N CA, with even further increasing temperatures through the
weekend. Hot temperatures will remain next week. The heat risk
will also be accompanied with fire weather concerns.


&&

.DISCUSSION...Afternoon observations reveal widespread inland
temperatures over 100. Weak surface low pressure is attempting to
guide stratus up from the south and closer to the Mendocino coast.
This is expected to be achieved tonight, with coverage eventually up
the Humboldt coast. This may impact coastal temperatures if coverage
makes it over land, but models have been overestimating the cloud
cover thus far. Weakness in the northerlies with additional
southerly return flow will bring additional chances for coastal
stratus at times through the weekend. Visible satellite is not
currently showing smoke making it into the area from the Shelly
fire in Siskiyou County, but some smoke and haze may push back
west overnight.

The strong dome of high pressure (597 dam) is currently
centered just off of the CA coast. The high will continue moving
closer to N CA, and will be centered over us on Saturday, which will
be the hottest day. The center of the high will only slighlty
weaken and nudge SE, where it will remain parked thereafter. The
Excessive Heat Warning has been expanded into Southern Humboldt,
and most of the heat products have been extended through Monday
for this reason. Temperatures will only slowly tick down early
next week, but Moderate to Major HeatRisk will continue for the
interior valleys, likely much of next week.

Fire weather conditions will be a growing concern as the high
moves in and the diurnal westerly to north westerly winds become
further invigorated alongside weak coastal surface low pressure
areas. A stronger coastal trough looks to form early next week and
may be able to grab some mid level moisture around it from the
south. At this time thunderstorm formation does not seem likely,
but the pattern will be watched closely given the current drying
underway.



&&

.AVIATION...SKC prevail across all TAF sites and over the region today.
Visibilities were mostly VFR except along the coast where periods of
MVFR occurred due to haze and possibly pockets of wildfire smoke in
the morning. Winds were mostly light today as the pressure gradient
was weaken by shifting surface pressure...and a southerly reversal
of winds.  Some model data is very pessimistic about low Vis and
some stratus at the coast on Friday morning. /TAA


&&

.MARINE...Winds and seas will continue to subside considerably this
afternoon, rapidly reaching sub-advisory levels across all zones. Hi-
res models are anticipating a surge of coastal stratus riding up the
coast along a southerly wind reversal late tonight into Friday,
potentially producing widespread marine fog. Otherwise, weak NW
wind waves and a long period southerly swell will moderate wave
heights to 5-6 feet at 8 seconds through Sunday. Northerly winds
are expected to redevelop into early next week beginning in the
southern waters.


&&

.FIRE WEATHER...The building heatwave will continue to bring
enhanced fire danger through the weekend. As highs climb closer
to 110, RH has cratered, with many interior valleys reporting RH
values between 5 and 10% this afternoon. Overnight conditions will
bring little relief with very poor RH recoveries of 25 to 40%.

As the strong area of high pressure moves eastward, the local
pressure gradient will become more favorable for enhanced diurnal
winds as RH values continue to crash to the low teens and single
digits. Reg Flag conditions are expected to be met, especially in
the afternoons and evenings in NE Trinity County Saturday through
Sunday and Southern Lake County Friday through Saturday..

Elsewhere, periods of critical fire weather are expected during the
afternoons where terrain winds are enhanced, such as along the
Trinity River Valley. Strong thermal belts will help promote
critical conditions even at night, especially with moderate, dry
northeast winds building each night on high ridges, primarily in the
Klamath Mountains. JHW/JJW


&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Heat Advisory until 8 PM PDT Monday for CAZ102-112.

     Heat Advisory until 9 AM PDT Friday for CAZ104-106.

     Excessive Heat Warning until 7 PM PDT Monday for CAZ105-107-
     108.

     Excessive Heat Warning from 10 AM Friday to 8 PM PDT
     Saturday for CAZ106.

     Fire Weather Watch from Saturday afternoon through Sunday
     evening for CAZ283.

     Excessive Heat Warning until 8 PM PDT Monday for CAZ110-111-
     113>115.

     Red Flag Warning from 3 PM Friday to 11 PM PDT Saturday for
     CAZ264.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until 9 PM PDT this evening for PZZ470-
     475.

&&

$$

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