Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 252314

National Weather Service Eureka CA
414 PM PDT Mon Sep 25 2017

.SYNOPSIS...Warm, sunny and dry conditions can be expected over
the next few days, even in coastal locations. A weak cold front
will bring slightly cooler temperatures and perhaps a brief period
of very light rain Friday.


.DISCUSSION...As high pressure aloft steadily builds eastward onto
the west coast, temperatures have continued to climb throughout
the region. Afternoon high temperatures will likely reach the low
to mid 80s across much of the interior by the time all is said and
done this afternoon, with mid to upper 60s along the immediate
coast. Lows tonight will also be warmer than the previous night,
with no trace of frost expected across interior valleys. This
upward trend in temperatures will continue tomorrow and Wednesday
as two things occur: 1. The inland thermal trough of low pressure
will slide offshore. 2. Downsloping northeasterly and easterly
winds will persist tonight through Wednesday night. Both of these
factors will lead to building temperatures throughout the region,
including along the coast as the marine layer is eroded away. The
warmest day is expected to be Wednesday, with inland valley
temperatures in the mid 90s and coastal temperatures well into the

While Thursday will also be warm, temperatures will begin a
gradual cooling trend as the upper level ridge of high pressure
begins to weaken. This will continue into Friday as a weak cold
front passes through the region, bringing temperatures down to
very near normal values for this time of year. Latest model trends
suggest a slightly stronger cold frontal passage than in past
forecasts, and it now appears plausible that Humboldt and Del
Norte counties could see some light precipitation Friday as the
front passes. If this does occur, rain totals will be very light
and may be mostly restricted to the higher coastal ridges due to
persistent dry air in the lower levels.

Beyond Friday, it appears that the region will remain locked in a
northwest flow pattern, which is a fairly significant departure
from past forecasts. Instead of maintaining above normal
temperatures for the foreseeable future, it appears that
temperatures will remain near to perhaps even slightly below
normal over the weekend. /BRC


.AVIATION...Upper level ridging will continue to bring mostly
cloud free skies to the region for the next day or two. A rather
dry marine later will also keep coastal stratus development to a
minimum tonight. The only other concern will be some easterly
winds aloft which could result in minor wind shear concerns near
Ukiah tonight into Tuesday morning followed by at all the
terminals Tuesday night into early Wednesday morning. /RPA


.MARINE...Northerly winds persist across the coastal waters with
the pressure gradient likely at its tightest point today. As an
upper level ridge moves over the west coast, the thermal trough
will push west and over the coastal waters. This will allow winds
to become much lighter by Tuesday night into Wednesday. Winds may
become calm or light southerly by Wednesday and into Thursday.
Seas will subside in response falling to near 3 feet by Thursday.
As weak front may bring a few showers to the waters on Friday
followed by a return to northerly winds over the weekend. /RPA


.FIRE WEATHER...A westward-shifting thermal trough and increasing
offshore winds will result in elevated to critical fire weather
conditions across parts of the region late tonight through
Wednesday morning. Offshore winds will gradually begin to
increase overnight tonight at high elevations, peak mid to late
Tuesday morning, and decrease slightly Tuesday afternoon. While
peak winds are expected Tuesday morning, they will likely remain
gusty and offshore along ridgelines and upper slopes through
Wednesday morning. These winds are expected to decrease relatively
quickly during the day Wednesday.

Meanwhile, the inland thermal trough will gradually shift offshore
Tuesday and Wednesday, resulting in warming conditions both inland
and along the immediate coast. Humidity will also drop as a
result, with low afternoon minimums and only moderate overnight
recoveries. Some of the windier high elevation ridges will likely
have quite poor recoveries, especially Wednesday night.

Overall, the most critical fire weather conditions are expected to
occur across the higher terrain of interior Mendocino and Lake
counties, where the warmest temperatures and lowest humidity will
combine with relatively strong offshore flow. Meanwhile, fuels in
these areas are much drier than areas to the north that have
received substantial September rains. As a result, a Red Flag
Warning has been issued for early Tuesday morning through early
Wednesday morning for these areas...specifically fire weather
zones 276 and 277. Periods of critical fire weather will also be
possible across eastern Trinity county, the King Range, and
perhaps even coastal Mendocino county. /BRC


CA...Red Flag Warning from 3 AM Tuesday to 8 AM PDT Wednesday for

NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory until 9 AM PDT Wednesday for PZZ470-475.

     Small Craft Advisory until 4 AM PDT Tuesday for PZZ450-455.



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