738
FXUS66 KEKA 022218
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
318 PM PDT Tue Jul 2 2024

.SYNOPSIS...A very strong heatwave will build in today bringing
Major to Extreme HeatRisk and near record breaking temperatures
across the interior Wednesday through the weekend. Heat and very dry
humidity will also enhance fire weather concerns, especially today
and Wednesday.

&&

.DISCUSSION...Temperatures will continue increasing today with
interior temperatures reaching above 100 throughout the interior,
but especially in Lake and Mendocino Counties. Rapid warming and
drying will continue through Wednesday. The southern half of the
area will see temperatures peak on Wednesday. Major to isolated
Extreme HeatRisk is expected throughout interior valleys, but
especially around Clear Lake and within the Russian River Valley. In
both areas, NBM shows a 60 to 80% chance of highs in excess of 110
Wednesday. Such temperatures are either record breaking or very
nearly for all across the southern half of the area. HeatRisk is
bolstered by the fact that overnight conditions will bring very
little relief. On valley bottoms, most likely lows are around 70
with strong thermal belts creating midslope lows closer to 80 by
Wednesday morning.

Model ensembles have come to better agreement on the development of
the ridge through the week. While most models still show a weak
surface low forming off the coast of Central California, few models
show it having much impact on the heat. Though it may slightly
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 through the week. Conditions will be
dangerously hot along the Trinity River by Wednesday and into this
weekend, NBM shows a 70 to 90% chance of highs above 110 all along
the Trinity River Valley. 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 break down late this
weekend. By Sunday, only 10% of members show the ridge pushing east.
Even by next Tuesday, 50% of ensemble members still have the ridge
sticking around, albeit slightly weakened. All that is to say, all
indicators point to strongly above average temperatures being here
to stay for the foreseeable future. /JHW

&&

.AVIATION...VFR conditions are expected to prevail across all of Northwest
California for the next 24-36 hours as dry air moves in along the
coast and the interior heats up. There could be some clouds forming
along the north edge of the King Range tonight into the area of
Fortuna but any development should be limited and unlikely to reach
ACV. Gusty coastal winds will exist this afternoon/evening as strong
gales over the coastal waters influence coastal areas. Winds will
decrease overnight only to increase again tomorrow afternoon. /RPA

&&

.MARINE...A tight pressure gradient over the coastal waters with the thermal
trough strengthening over the interior is resulting in strong gales
in the outer waters. Steep seas will propagate toward the coast
bringing hazardous seas to waters north of Cape Mendocino through
Wednesday. Winds will decrease sharply beginning Wednesday night
into Thursday as the tightest pressure gradient moves west outside
of the waters. Light to moderate southerly flow is likely to return
near the coast with the potential for a coastal stratus surge
Thursday into Friday. Northerlies return over the weekend as high
pressure strengthens off the coast. /RPA

&&

.FIRE WEATHER...The building heatwave will bring enhanced fire
danger through the week, but especially today and Wednesday. As
highs climb well above 100, RH will crater with most interior
valleys very likely (80% chance) to see minimum RH between 5 and
10%. 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. First, as the high
first builds across the area, a building pressure gradient aligned
with the Sacramento Valley will promote gusty northeast winds along
the Sacramento foothills with sustained winds of 12 to 18 mph. Such
winds have already been observed this morning with very poor RH
recoveries barely above 20 percent. Though restricted to ridgetops
at night, such winds will mix down more broadly early each
afternoon. For the forecast area, afternoon mixing will promote
widespread critical conditions in southeast Lake County today and
Wednesday, prompting a Red Flag Warning in the area.

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, with moderate, dry northeast
winds building each night on high ridges, especially in the Klamath
Mountains. 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 from 11 AM to 8 PM PDT Wednesday for CAZ104-
     106.

     Excessive Heat Warning from 11 AM Wednesday to 8 PM PDT
     Saturday for CAZ105-107-108-110-111.

     Heat Advisory until 11 AM PDT Wednesday for CAZ107-108-110-
     111.

     Heat Advisory until 8 PM PDT Wednesday for CAZ112.

     Excessive Heat Warning until 8 PM PDT Saturday for
     CAZ113>115.

     Red Flag Warning until 8 PM PDT Wednesday for CAZ264.

NORTHWEST CALIFORNIA COASTAL WATERS...
     Small Craft Advisory until 5 PM PDT this afternoon for
     PZZ450.

     Hazardous Seas Warning until 3 AM PDT Thursday for PZZ450.

     Small Craft Advisory until 9 AM PDT Wednesday for PZZ455.

     Gale Warning until 2 AM PDT Thursday for PZZ470.

     Gale Warning until 9 PM PDT Wednesday for PZZ475.

&&

$$

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