Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Eureka California
331 PM PST sun Dec 28 2014
Synopsis...a reinforcing cold front will bring another chance
of light showers north of the cape on Monday...followed by mostly
dry and cold conditions for much of the coming week. Easterly
winds may be quite gusty Tuesday through Wednesday as a low
pressure system deepens over central California.
Short term...(through Thursday night) a cold front has moved south
of northwest California leaving northerly flow over the region and
clearing skies. Low temperatures tonight will be several degrees
lower than last night with temperatures falling back into the 30s
for most areas and 20s in the interior.
Another much stronger cold front will dive down the West Coast on
Monday as a deep western US trough develops over the inter-mountain
west in response to a building ridge off the West Coast. A few
showers will be possible in del norte and coastal Humboldt with and
just behind the front. Snow levels will rapidly fall to near 2000
feet which could allow some near coast ridges to see some
flakes...but very little if any accumulation is expected.
The cold air mass behind this front will be significantly colder
resulting in lows falling into the 20s and teens across the interior
and near or possibly below freezing at the coast by Wednesday
morning and then again Thursday morning. The primarily mitigating
factor to cold temperatures will be a strong offshore pressure
gradient late Monday night through Wednesday behind the front as an
upper low attempts to cut off over central California. This will
likely allow mixing holding temperatures up a few degrees above
model guidance...particularly Tuesday morning.
This strong pressure gradient will also result in strong easterly
winds across the region. The ensembles indicate this will be a
highly anomalous event with 700 mb east-northeast winds between 40
and 60 knots moving over the region Tuesday night and early Wednesday.
With a very cold air mass in place and excellent mixing there is
potential for these winds to mix down to the ridge tops. Thus winds
have been ramped up with this forecast in the mountains across the
entire region. The tightest pressure gradient will likely be over
Mendocino County and Wind Advisory/watch products may be required
for Tuesday through Wednesday. Winds will not be as strong on the
valley floors but some gusty conditions are expected. Rpa
Long term...(friday through sunday)...models begin to diverge a
little late in the week regarding the eastward movement and
intensity of the ridge off the West Coast and the strength of an
upper level trough that moves into the Pacific northwest. The GFS
continues to indicate a weak front may approach the northern
reaches of northwest California bringing a chance for rain to del
Norte County by late in the weekend or early next week while the
European model (ecmwf) has dropped this feature and now indicates ridging just off
the West Coast. For now have continued a slight chance of
precipitation for the northern portion of the area with very low
confidence in the resulting weather for Sunday. Trn/rpa
Aviation...afternoon scattered VFR cumulus clouds are the only clouds
left from a front dissipating off of the Cape Mendocino coast.
Expect these clouds to decrease through the night and development of
patchy valley fog will result in MVFR to IFR conditions across
interior valleys after midnight. Valley fog will dissipate by noon.
Another weak front moving down from Oregon will bring MVFR ceilings and
light rain Monday afternoon north of cape mendo. Dean
Marine...northerly winds will slowly increase through Thursday as a
thermal trough over California and building high pressure offshore
strengthen the pressure gradient. Fresh winds and steepening seas
will begin to develop south of Cape Mendocino tonight and spread
northward by Monday afternoon. Winds in the outer waters stay just
below Small Craft Advisory until Monday night. The hrrr did show
gusts above criteria sooner for zone 475 but it was the outlier.
Winds stay below advisory criteria in the inner waters. Winds and
seas will ease again late in the week as a deep, cold upper level
trough dives over California and helps break down the pressure
gradient by weakening the thermal trough. Kml\trn
Northwest California coastal waters...none.
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