122
FXUS66 KEKA 032205
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
305 PM PDT Wed Jul 3 2024

.SYNOPSIS...Extreme, record breaking heat will begin to peak across
the southern half of the area today with heat continuing to spread
northward at the same time. Heat will bring continued Major Heat
Risk alongside enhanced fire weather concerns.


&&

.DISCUSSION...A strong dome of high pressure has properly built over
the area over the last 24 hours. Across the southern half of the
area, highs in many valleys are already in excess of 100 degrees
with even a few locations such as Ukiah expected to break 110. Heat
will continue to intensify and move north today as gentle offshore
flow tonight helps to push heat closer to the coast. Today will most
likely be the day of greatest HeatRisk for the southern half of the
area with most likely highs of 108 to 116. Areas of extreme risk are
expected especially in midslope location which have seen virtually
no overnight relief with lows struggling to drop below 80.

While most models still show a weak surface low forming off the
coast of Central California over the next couple days, few models
show it having much impact on the heat. Though it may slighlty
weaken heat for the southern half of the area, it will mostly just
shift the focus of heat further north into Trinity and Humboldt by
Thursday. Regardless, near record breaking heat will continue for
the entire interior through the week. Though conditions will be
dangerously hot along the Trinity River already today, NBM suggest
the peak heat further north around Friday. By this point, NBM shows
a 70 to 90% chance of highs above 110 all along the Trinity River
Valley. Per usual, Big Bar is expected to be the hottest station
with highs around 120. HeatRisk is only slightly diminished in the
north thanks to lower nighttime temperatures closer to 60 through
the week.

Heat will even begin to move towards the coast as the week wears on
and onshore flow continues to weaken. High pressure settling through
the week will help create an increasingly shallow marine inversion
which may, at times, be totally pushed offshore by easterly
nighttime winds. While a sea breeze will cool off coastal areas each
afternoon, increasingly clear and hot mornings may allow high to
approach 80 by late in the week. By Thursday and Friday, NBM shows a
50 to 70% chance of brief highs over 80 as close to shore as Arcata
and downtown Crescent City.

The vast majority of cluster ensemble members show the ridge
persisting and only very slowly beginning to weaken by early next
week. Essentially no models show the ridge fully breaking down
within the next 10 days. With that in mind, dry and much above
average temperatures are here to stay for the foreseeable future.
/JHW


&&

.AVIATION...VFR conditions prevail at all terminals with gusty
northerly winds >25 knots continuing at CEC. The coastal pressure
gradient will begin to slacken and move offshore this evening as the
orientation of the high pressure ridge shifts. Winds expected to
rapidly diminish and turn offshore overnight, allowing a southerly
reversal to round Pt. Arena and develop north of Cape Mendocino just
before sunrise. HREF is indicating haze and broken low level
ceilings gradually filling in around Humboldt Bay and propagating
MVFR ceilings northward. Southerly flow may not be quite strong
enough to reach CEC within an already weak marine layer. A more
potent stratus deck stemming from the SF Bay area has the potential
to fill in along the entire north coast Thursday evening into early
Friday morning, substantially enhancing the marine layer and
producing widespread IFR ceilings.


&&

.MARINE...Near-shore wave heights are still elevated but slowly
diminishing as the coastal pressure gradients slackens and moves
offshore. Steep and hazardous seas as well as gales force gusts
expected to continue in the northern waters and southern outer
waters through tonight, diminishing from south to north. Winds and
seas will subside considerably by tomorrow 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 Thursday into Friday, potentially
producing widespread marine fog. Northerly winds expected to
redevelop late this weekend.


&&

.FIRE WEATHER...The building heatwave will continue to bring
enhanced fire danger through the week, but especially through
Thursday. 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 30 to 40%. Even with only gentle terrain
winds, such dry conditions will promote critical fire weather
conditions each afternoon.

There are several areas where enhanced winds will generate more
widespread and long lasting critical conditions. As the high cross
shore, a building pressure gradient has remained aligned with the
Sacramento Valley promoting gusty northeast winds along the
Sacramento foothills. These have weakened through this morning,
although many sites are still reporting gusts of 12 to 18 mph. With
RH values in the single digits, critical fire weather conditions
continue in southeast Lake County today.

Elsewhere, periods of critical fire weather are expected during the
afternoon 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. The power of thermal belts have already been
observed with some midslope areas not even dropping below 80 this
morning. Fire Weather conditions will only slightly begin to ease by
this weekend. /JHW


&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     Heat Advisory from 11 AM Thursday to 8 PM PDT Saturday for
     CAZ102.

     Heat Advisory until 8 PM PDT this evening for CAZ104-106-
     112.

     Excessive Heat Warning until 8 PM PDT Saturday for CAZ105-
     107-108-110-111-113>115.

     Red Flag Warning until 8 PM PDT this evening for CAZ264.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Hazardous Seas Warning until 3 AM PDT Thursday for PZZ450.

     Gale Warning until 2 AM PDT Thursday for PZZ470.

     Gale Warning until 9 PM PDT this evening for PZZ475.

&&

$$

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