Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Eureka California
531 am PST Wednesday Dec 4 2013
high pressure will drop southward across the Pacific northwest with
very cold air filtering in. Low temperatures will be especially
cold, with freezing conditions at the coast. Skies will be mostly
sunny through Thursday but there will be a chilly northerly breeze.
The next storm system will affect our area on Friday with rain at
the coast and snow inland.
Short-term (today through thursday)...
with high pressure pressing southward from eastern Washington and
Oregon, clear skies and mainly light easterly winds overnight have
allowed temperatures to drop into the low 30s and upper 20s along
much of the coast, with teens across the deeper interior valleys.
Will tie or break the record of 30 degrees at Eureka for this
morning, and near record lows at Crescent City and Ukiah as well.
This was right on track with the forecast, and a good indication of
what kind of temperatures we can expect for tonight.
Expect another mostly sunny day today but high temperatures will be
3 to 5 degrees colder than yesterday. Winds will still be gusty this
afternoon, but not quite as strong as yesterday. As the thermal
trough shifts offshore, drier air will filter toward the coast from
the interior with a weaker gradient and lighter winds over land
heading into tonight. Clear skies once again will allow temperatures
to drop, even quicker than yesterday evening with winds dropping off
sooner and drier air in place. This will allow for lows generally 2
to 5 degrees colder tonight. MOS guidance is actually indicating
near 19 at the Arcata Airport, and middle 20s at kcec. Think this is a
bit overdone, but middle-20s are looking like a good bet for much of
the coastal plain north of Cape Mendocino, hence a hard freeze
warning has been issued. The last time we dropped into the middle-20s
across a large portion of the north coast was December of 2009.
Comparing the synoptic pattern and degree of cold air aloft of these
events, the upcoming cold snap looks very similar. Meanwhile the
Mendocino coast will easily see freezing conditions at the coast
north of Point Arena, and potentially middle-20s across inland valleys
like the Anderson Valley. Aad
Middle to long term (thu through wed)...
models continue to lock in on a strong upper shortwave and weak area
of low pressure approaching from the northwest. Timing is more
certain now, and confidence is growing in snow-levels and potential
snowfall amounts. An impressive area of isentropic lift around the
290k level will wrap eastward across northwest California Friday, ahead of
the area of low pressure. Weak surface advection and a lack of warm air
entrainment into the system will mean that snow levels will stay low
inland, despite the track of the low to our north and the S/southeast flow
ahead of the system. Snow may even occur around 1000 feet elevation
near the coast Friday morning, especially if skies remain clear for
awhile Thursday night. Snow levels will rise to 2000 feet as the
heavier precipitation arrives, except further inland across Trinity County.
Generally thinking 3 to 6 inches for much of Trinity County, with
some higher amounts in orographically-favored areas. Thus will
probably need a Winter Weather Advisory in the next 24 hours or so. The
quick-movement and lack of deeper moisture will limit heavier
The rest of the weekend will dry out, with the concern shifting back
to low temperatures Saturday and especially Sunday morning. Another
hard freeze will be possible at the coast with single-digits in
interior valleys of Trinity County. Most guidance hints at a weak
system passing through on Monday, which would be just some scattered
light showers at best...with potentially more significant wet
weather by the middle of next week. Aad
Aviation...brisk and dry northerly flow will maintain widespread
VFR conditions across the region. Coastside air terminals will
continue to see gusty afternoon and evening northerly winds.
Marine...the current pressure gradient is maintaining northerly
gale conditions across the outer waters and a fresh to strong breeze
with steep short period seas to the inner waters. Wind gusts will be
marginal for the inner waters, but with gales across the outer
waters large seas should propagate into the inner waters. These
conditions will continue through this tonight and then improve on
Thursday as the gradient weakens. Winds and seas should increase
again Friday into the weekend as a storm moves through the region.
California...hard freeze warning from 1 am to 9 am PST Thursday caz001.
Freeze warning until 9 am PST this morning caz002.
Freeze warning from 1 am to 9 am PST Thursday caz002.
Northwest California coastal waters...
Small Craft Advisory until 9 PM PST this evening pzz450-455.
Gale Warning until 9 PM PST this evening pzz470.
Gale Warning until 3 am PST Thursday pzz475.
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