373
FXUS66 KEKA 012159
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
259 PM PDT Mon Jul 1 2024

.SYNOPSIS...A very strong heatwave remains on track to bring Major
to Extreme HeatRisk and near record breaking temperatures across the
interior Wednesday through the end of the week. Heat and very low
humidity will also enhance fire weather concerns, especially Tuesday
and Wednesday.


&&

.DISCUSSION...Temperatures will begin increasing today, with
interior temperatures currently running 5 to 10 degrees hotter than
yesterday, especially in Lake and Mendocino Counties. Rapid warming
and drying will persist 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.
Such temperatures are either record breaking or very nearly 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.

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 impact on the heat. Though it may slighlty weaken
heat for the southern half of the area, it is more likely that it
will just shift the focus of heat further north into Trinity and
Humboldt. Regardless, near record breaking heat will continue for
the entire interior through through the week. Though conditions will
be dangerously hot along the Trinity River by Wednesday, NBM
suggests 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. For Hoopa in particular, this could easily
approach the all time high temperature record of 111. 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.
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 Crescent City.

The vast majority of cluster ensemble members show the ridge
persisting and only very slowly beginning to break down 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...LIFR at the coast has been primarily replaced with VFR
as of this time. Northwesterly winds will continue to increase with
gusty winds at the coastal terminals today. Stratus will likely
return tonight once temperatures cool and clouds off the coast push
back inland. At KUKI, VFR conditions are persisting with gusty
northwesterlies this afternoon. Mild winds should eventually return
this evening with variable speeds after sunset.


&&

.MARINE...Northerly winds will accelerate rapidly this
afternoon/evening, with strongest winds leeward of Cape Mendocino as
a high pressure begin to builds in and a thermal trough (in
correlation with the incoming execessive heat inland) develops.
These dynamics will favor moderate to strong pressure gradient. The
pressure gradient will drive counterclockwise flow around the West
with our coastal waters being where the winds blow from the north
along the coast. Winds over the waters accelerate due to minimal
friction between the land-sea interface. Winds will steadily
increase from this afternoon through Tuesday, with widespread
sustained strong to gale force winds and very steep seas through
Wednesday. That all said, A Gale Warning is in effect for the outer
waters this afternoon. These gales will propagate in a burst of very
steep seas into the northern inner waters Tuesday evening through
late Wednesday afternoon, and thus we have published a Hazardous
Seas Warning for zone 450 as result.

These winds will gradually ease from south to north throughout the
second half of the day on Wednesday. A southerly wind reversal will
move north along the Mendocino Coast (as of right now it does not
pass the Cape) and relax the pressure gradient on Thursday. Seas
will gradually subside Wednesday evening and Thursday. However,
steep seas will persist across the waters into the weekend.


&&

.FIRE WEATHER...The building heatwave will bring enhanced fire
danger through the week, but especially Tuesday 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.
Though restricted to ridgetops at night, such winds will mix down
more broadly early each afternoon. For the forecast area, afternoon
mixing will promotes widespread critical conditions in southeast
Lake County Tuesday 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 on night, especially 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 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 from 11 AM Tuesday to 11 AM PDT Wednesday for
     CAZ107-108-110-111.

     Heat Advisory from 11 AM Tuesday to 8 PM PDT Wednesday for
     CAZ112.

     Excessive Heat Warning from 11 AM Tuesday to 8 PM PDT
     Saturday for CAZ113>115.

     Red Flag Warning from 2 AM Tuesday to 8 PM PDT Wednesday
     for CAZ264.

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

     Hazardous Seas Warning from 5 PM Tuesday to 5 PM PDT
     Wednesday for PZZ450.

     Small Craft Advisory until 3 AM PDT Wednesday for PZZ455.

     Small Craft Advisory until 5 PM PDT this afternoon for
     PZZ470.

     Gale Warning until 2 AM PDT Thursday for PZZ470.

     Gale Warning until 3 PM PDT Wednesday for PZZ475.

&&

$$

Visit us at https://www.weather.gov/eureka

Follow us on Facebook and Twitter at:
https://www.facebook.com/NWSEureka
https://www.twitter.com/NWSEureka

For forecast zone information
see the forecast zone map online:
https://www.weather.gov/images/eka/zonemap.png