Area Forecast Discussion
Issued by NWS Eureka, CA
Issued by NWS Eureka, CA
311
FXUS66 KEKA 011130
AFDEKA
AREA FORECAST DISCUSSION
National Weather Service Eureka CA
430 AM PDT Mon Jul 1 2024
.SYNOPSIS...A very strong heatwave remain on track to bring Major to
Extreme HeatRisk and near record break temperatures across the
interior Wednesday through the end of the week. Heat very dry
humidity will also enhance fire weather concerns, especially
Tuesday and Wednesday.
&&
.DISCUSSION...Satellite imagery clearly shows an upper level trough
ejecting east this morning with a very strong ridge of high pressure
beginning to eek over the area. Very dry air from the ridge has
already wiped away any sign of upper and midlevel clouds leaving
behind marine stratus as the only visible feature.
Temperatures will begin increasing today with interior temperatures
reaching into the 90s throughout the interior, but 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 so 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 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.
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 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. 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
triumphant sea breeze will certainly 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
ridge sticking around, albeit slightly weakened. All that is to say,
all indicator point to strongly above average temperatures being
here to stay for the foreseeable future. /JHW
&&
.AVIATION...Prevailing LIFR conditions with OVC layer at FL002-FL004
and visibility in mist/fog continues impacting ACV and CEC this
morning, while VFR conditions prevail at UKI. Stratus are expected
to lift and mix out by late morning and afternoon as a high pressure
begin to builds in and promote increasing NNW winds. Expect
generally VFR conditions later in the afternoon at all terminals,
with some hazy conditions possible at CEC due to the sea spray.
Patches of low clouds will be persistent in the vicinity of Humboldt
Bay this afternoon and evening, but the hi-res model guidance
suggests the bulk of the stratus activity will stay clear at KACV.
Offshore flow component is expected to develop this evening and
increase tonight over the exposed ridges, especially in Del Norte
County where gusts from 25 to 35 mph are likely. This will yield
clear skies along much the coast late tonight and Tuesday. Surface
winds light and variable this morning, becoming NNW 10-20 kt in the
afternoon, accompanied by occasional gusty winds from 20-30
kt...with strongest gusts at CEC late afternoon/early evening.
&&
.MARINE...Northerly winds will accelerate rapidly late morning and
afternoon, with strongest winds leeward of Cape Mendocino as a high
pressure begin to builds in and a thermal trough develop int he
interior. These will favor moderate to strong pressure gradient.
Winds will steadily increase through Tuesday, with widespread
sustained strong to gale force winds and very steep through
Wednesday. Gusty northerly winds up to around 45 kt and seas around
12-18 feet @ 9-10 seconds are expected for the outer waters. A Gale
Warning is in effect for the outer waters this afternoon. This gales
will propagate in a burst of very steep seas into the northern inner
waters Tuesday evening through late Wednesday afternoon. Have to
hoisted 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 and relax the pressure gradient
on Thursday. Seas will gradually subside Wednesday evening and
Thursday, but 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 from 3 PM this afternoon to 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 from 9 AM this morning to 5 PM PDT
this afternoon for PZZ470.
Gale Warning from 5 PM this afternoon to 2 AM PDT Thursday
for PZZ470.
Small Craft Advisory until 2 PM PDT this afternoon for
PZZ475.
Gale Warning from 2 PM this afternoon to 3 PM PDT Wednesday
for PZZ475.
&&
$$
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