Area Forecast Discussion
Issued by NWS Eureka, CA
FXUS66 KEKA 261236
AREA FORECAST DISCUSSION
National Weather Service Eureka CA
431 AM PDT Sun Mar 26 2017
.SYNOPSIS...A front will move across Northwest California today
producing light to moderate rain by afternoon. A trough in the
cooler air will generate additional showers tonight through Monday
morning. High pressure will build Monday afternoon and maintain
dry weather through Tuesday.
.DISCUSSION...Dry conditions have been holding through the night.
Radar has been detecting a broad area of 20 to 30 dBZ`s offshore
associated with a weak warm front offshore. We will probably
receive light rain around daybreak or shortly thereafter as the
warm front slowly progresses eastward toward the north coast.
The surface cold front will probably take til mid afternoon to
early evening to move across the forecast area. That is when steady
rain is expected. Winds with the incoming front do not look
exceptionally strong. The front will most likely occlude later today
and winds will pick up and become gusty. The ARW as well as the
coarser models indicate the potential for gusts around 40-50mph
primarily over the exposed higher terrain and coastal headlands by
early afternoon. Winds will be borderline for an advisory. As of
4AM, winds were fairly light, with gusts around 20-25MPH. It is
interesting to note that the NAM12 and other high resolution models
indicate a rain hole or dry slot developing over the greater Eureka
area later this morning as winds aloft increase. This will need to
be watched for the possibility of strong southeasterly downsloping
wind gusts which will eat away at the rain. For now we added gusts
to around 40 mph which is just under an advisory for wind.
Overall the rain with the incoming front is not looking all that
spectacular. Hydrological concerns are very minimal or non-existent.
After frontal passage by mid evening, a post frontal ridge will
build and provide a break in the showers. The air column will
start to cool down significantly behind the front and dry out too.
A secondary trough line and mid level vort max will follow later
tonight into Monday morning and spark up additional shower
activity. Mid level lapse rates will steepen in response to strong
500mb cooling, however temperatures through the entire column
will cool as well and snow levels are expected to fall to around
3kft by daybreak Monday. Freezing levels will be low enough to
consider small hail. Instability parameters (lifted indices and
CAPE) as well as mid level lapse rates are very unfavorable for
hail production. Shallow convection may still generate a mix of
rain and hail as a mid level trough line swings across the area
early Monday morning. The best location looks to be across Del
Norte and far northern Humboldt counties. Confidence is by no
means high due to the lack of instability and available buoyant
energy to sustain updrafts.
After this short-wave impulse moves across the area Monday
morning, upper level ridging will build over the area and squash
any showers that try to sprout up with daytime heating.
An offshore wind flow pattern will develop Monday night resulting
in dry and stable weather conditions through Tue. The latest GFS
and ECMWF remain consistent with bringing another front toward the
coast Tue night. There were still some variations between the two
models on how fast the rain will arrive and how long it will
last. The models differed also on the southern extent of the rain.
It is not going to be a major dumping, however, Del Norte and
Humboldt counties will probably receive some light rain. Upper level
ridging will return by Fri and provide for another day or so of dry
weather. The ECMWF and GFS hint at a weak front riding over the
ridge toward the latter portion of next weekend that may generate
some light rain, primarily along the coast and over Del Norte
county. A spring like weather pattern is starting to take shape with
surface northerlies dominating offshore.
.AVIATION...VFR conditions and light winds to calm conditions will
continue at KCEC, KACV and KUKI through the early morning. Ceilings
and/or visibilities will decrease today as a weak cold front moves
through the region. Showers will move across the region at times
today associated with the weak cold front. VFR to MVFR conditions
will prevail at KCEC, KACV and KUKI later this morning and this
afternoon as the front and showers move across the region. A high
pressure ridge will build across the region in the wake of the
weak cold front on Monday.
.MARINE...Winds will increase today as a weak cold front approaches
and moves across the waters. The front will move across the waters
this afternoon. Showers will move across the waters at times
today associated with the cold front. The winds will increase
along the cold front. The winds and seas will be higher across the
outer waters and in or near any showers. The winds will diminish
tonight. Seas will increase Monday and remain elevated through
Wednesday as a westerly swell propagates across the waters. Small
craft advisories are in effect across the near shore waters and
southern outer waters through this afternoon due to increasing
winds as the cold front moves across the waters. A gale warning is
in effect across the northern outer waters through this afternoon
primarily due to wind gusts as the front passes across the
waters. Small craft advisories are likely across all the waters
Monday through Wednesday due to elevated seas associated with the
NORTHWEST CALIFORNIA COASTAL WATERS...
Small Craft Advisory until 3 PM PDT this afternoon for PZZ450-
455-475. Small Craft Advisory until 9 AM PDT this morning for
PZZ470. Gale Warning from 9 AM this morning to 3 PM PDT this
afternoon for PZZ470.
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