Area Forecast Discussion
Issued by NWS Eureka, CA
FXUS66 KEKA 291010
AREA FORECAST DISCUSSION
National Weather Service Eureka CA
310 AM PDT Sat Apr 29 2017
.SYNOPSIS...A weakening frontal boundary will impact far
northwestern California during Sunday morning, resulting in minor
rain chances for locations north of Eureka. Dry weather and
moderating temperatures will then prevail over much of the region
during the new work week.
.DISCUSSION...A highly amplified upper flow pattern was present
over the WRN CONUS Saturday morning, with a ridge present offshore
over the Pacific, and a deep trough located across the Rockies. A
minor upper impulse is forecast to move through the top of the
ridge Saturday night into Sunday morning, which will drive a
weakening surface front southward toward far NWRN CA. Light
showers will be possible as a result. Thereafter, model guidance
shows the upper ridge gradually shifting EWD through the middle of
the upcoming week...eventually becoming positioned over the Great
Basin by 00Z Friday. Several processes are forecast to occur as
the ridge shifts east. First, low-level temperatures will
progressively moderate, such that values at 850 mb reach 18 C on
Wednesday. This will support moderating high temperatures Tuesday,
Wednesday, and Thursday...which was depicted well in the
inherited forecast. Second, the airmass will be more prone to
destabilization as a subsident regime exits east, and NWRN CA
becomes exposed to embedded WSWLY upper disturbances. This could
yield deep moist convection over the mountainous terrain of
Trinity County. Thus, a slight chance of thunderstorms was
introduced for Thursday and Friday afternoon/evening.
.AVIATION...Other than a patch of MVFR clouds over Eureka and in
the Eel delta, VFR conditions will prevail at all terminals today.
This patch of cloud may reach KACV by daybreak, producing brief
MVFR ceilings. This patch of low cloud will dissipate with daytime
heating and mixing by mid morning. Surface and boundary layer
humidities will ramp up substantially tonight. BUFKIT profiles,
NAM/ARW as well as the GFS boundary layer fields indicate a weak
front passing to our north tonight. This front will produce a
shallow push of moist air by early Sunday. MVFR or IFR conditions
are expected at both KACV and KCEC late tonight into Sunday
morning. Confidence is not high on the specifics, however
conditions will likely deteriorate at the coastal terminals
.MARINE...Light to moderate northerlies will prevail through the
forecast period. Northerly winds will ease up today as a weak
front approaches from the NW. Seas will gradually subside as well.
Winds and seas in the southern waters will remain at or near
small craft advisory level through the weekend, however.
North winds will likely increase some late Sunday afternoon into
Sunday night and Monday as the offshore ridge strengthens.
Advisories for waters other than PZZ475 appear marginal at the
moment. Thus will let the going headlines run their course.
The northerly flow pattern is forecast to persist through next
week as high pressure remains firmly entrenched offshore. Periodic
fronts will disrupt the strength of the northerlies north of Cape
Mendocino. South of the Cape, winds will remain strong enough to
generate steep and hazardous seas through the week.
NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory until
3 AM PDT early this morning for PZZ450-455.
Small Craft Advisory until 9 AM PDT this morning for PZZ470.
Small Craft Advisory until 5 AM PDT Wednesday for PZZ475.
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