Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Eureka California
402 am PDT Sat Oct 25 2014
Synopsis...rain will give way to showers after sunrise this morning
while winds ease for a short time. An approaching Post frontal
trough will cause increasing winds again by middle morning. This trough
has the potential to bring strong shower activity with possible
small hail...gusty winds...and occasional lightning. Showers will
taper in the late afternoon and evening as high pressure begins to
build over the area.
Short term (today through tuesday)...a cold front moving across the
area early this morning is bringing gusty winds and areas of heavy
rain. This front should pass most of the region by sunrise allowing
for a brief respite from the rain and wind. However, a vigorous Post
frontal trough will begin to make its way into the region within a
few hours after sunrise. Winds will again increase as this trough
approaches. The High Wind Warning and wind advisories will remain in
place as the timing looks to be on track as models are showing up to
80 knots of wind at 850mb along the del norte coast later this morning.
Infrared satellite analysis this morning shows a well occluded low with a
defined cold front and Post frontal trough as stated above. However,
it looks like there is a strong secondary trough wrapping around the
base of the low. This will be the severe weather threat for today.
Models continue to show plenty of wind shear, both directional and
speed around this secondary trough, as well with the 0-6km shear in
the 40 knots range. Mu convective available potential energy remain solid as well, peaking midday at
over 1000j/kg. Negative lifted indice's will also accompany this period. All
that to say, this secondary Post frontal trough will be rather
vigorous with plenty of convective ability. The convection should
have plenty of updraft potential, accompanied by cooling air aloft,
which will help to generate some small hail and lightning. As such,
have updated the forecast to indicated isolated thunderstorms across
the area with this trough. Teetered on whether or not to go
scattered, but held off for now as the overall coverage remain
uncertain. The other threats with this updraft will be potential for
some rotation which has the outside chance of producing a tornadic
cell or two. This should mainly be over the waters, but cannot be
ruled out across the interior as well. With the greatest threat over
the coastal waters, have included a slight chance of a waterspout in
the forecast. Convection will also allow winds to mix down to the
surface from aloft, which can create strong gusty winds around
thunderstorms. As such, have continued to highlight small hail and
gusty winds with these thunderstorms through the day on Saturday.
The main threats for today will be strong winds in the early morning
hours followed by convection developing during the middle to late
morning hours. Convection will bring occasional lighting, possible
small hail, locally gusty winds, and an outside chance of a brief
tornado or two.
Showers will diminish in intensity in the afternoon hours as the
Post frontal trough slides off the east. A lingering shower cannot
be ruled out into early Sunday. As the upper trough passes off to
the east, a cool air tap will bring lowering temperatures to northwest cal with
daytime highs struggling to get out of the 50s on Sunday. Overnight
lows across the interior could drop to below freezing Monday night
into Tuesday. A building ridge on Sunday could help this with
clearing skies and calm winds. In the late fall and winter, cold air
tends to get trapped in the valleys and cause cooler temperatures than
models would pick up on. With that, we are below model guidance for
temperatures during this time.
The next front will arrive overnight Monday into Tuesday with rain
expected to remain north of Mendocino County. This front will be
very weak in comparison to todays system. Bfg
Long term (tue night through fri)...moist zonal flow and another
frontal system on Tuesday will probably generate more rain in the
northern zones with less of a chance in the southern zones. Little
or no changes were made to the forecast here. GFS and European model (ecmwf) start
to diverge on Wednesday and Thursday as the flow amplifies and another upper
trough slowly approaches the coast. Models were not in real good
sync...but it does look like mild and perhaps wet weather
conditions will persist next week. Boosted precipitation chances some but
still not confident enough at this point to go more than 50% even
in del Norte County.
Aviation...strong gusty southerly winds along the coast will
persist through the day. Wind shear will be an issue as winds just
off the surface, especially near cec, will be as high as 70 knots.
Uki winds will be less but still gusty. Visibility will remain down with
widespread rain across the region. Behind the front visibility will
improve, but strong showers will bring it down locally. These
showers will have the possibility of bringing small hail,
lightning, and gusty erratic winds. Tafs will be a challenge today
as conditions will be bouncing behind the front in the showers.
Will aim to get the broad pattern in the forecast and hit any sig
changes in the weather. Bfg
Marine...vigorous low pressure system will spin up offshore
today. Winds will ramp up this afternoon and evening...however
the strongest winds will most likely arrive late tonight into
Saturday morning with the cold front. Gusts up to 50 knots will be
possible either late tonight or early Saturday...mainly near
cape mendo. A Post frontal trough may also kick up the winds
Sat afternoon as instability increases in the cooler air behind
the front. Nwps has short period seas hitting 15 to 20 feet late
tonight into Sat morning. See no reason to go against the model
at this point. Gale warnings have been posted for all
marine zones...starting this afternoon in the outer waters
and then expanding into the inner waters late tonight.
High Wind Warning until 5 PM PDT this afternoon for caz003.
Wind Advisory until 11 am PDT this morning for caz004.
High Wind Warning until 5 PM PDT this afternoon for caz001.
Wind Advisory until 2 PM PDT this afternoon for caz002-076.
Northwest California coastal waters...
Storm Warning until 2 PM PDT this afternoon for pzz470.
Storm Warning until 11 am PDT this morning for pzz475.
Gale Warning until 9 PM PDT this evening for pzz450-455.
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