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Area forecast discussion 
National Weather Service Eureka California
320 PM PST Thursday Nov 27 2014

Synopsis...a front and associated rainfall will slowly move toward
the northern California coast tonight...eventually bringing light to
moderate rain to the area on Friday. Periods of rain will persist
through the weekend.

&&

Discussion...radar has been showing rain skirting along the far northwest
corner of the area this afternoon. All the rain reaching the ground
has been occurring in SW Oregon...with little or nothing in del Norte
County as of 3pm. Latest satellite imagery showed the narrow band of
moisture that has been streaming into SW Oregon slowly lifting
northward as a wave develops along the front west of 130w. This does
not Bode well for significant amounts of rainfall in del Norte
County this evening. Granted a few light spotty showers may develop
in the warm air advection ahead of the front...however amounts wont
be very much...perhaps a few hundredths at best. All the models
continue to show the frontal band edging closer to the norcal coast
late tonight as a positively tilted middle-level trough extending
southwestward from British Columbia slowly moves eastward. Most of
the area will stay dry tonight...with better chances of rain along
the north coast and over del Norte County late tonight.

All the models drive the narrow and slow moving frontal band
through the forecast area on Friday. The models were in pretty
decent agreement on the rain amounts which are not all that much
on friday; around a tenth in southern mendo to about 3/4 of an
inch in del norte. Not sure if there will be any significant
impacts from this first bout of rain other than it will make the
roads wet. Once again followed a blend of the cnrfc/wpc quantitative precipitation forecast
guidance here. The models take this band of rain southward Friday
night as colder air mass settles down from the north over the Pacific
northwest by Saturday. The models were not in very good agreement during
this time frame on where most of the precipitation will occur as cooling
aloft and an onshore flow develops. The GFS takes the brunt of the
rain southward into the sfo Bay area by 18z Sat while the European model (ecmwf)
has a secondary maximum occurring north of cape mendo as a new band of
rain develops. The nam12 shows both of these features...though was
not quite as widespread with the precipitation. It does look like
Saturday will continue to be wet with periodic bouts of rain or
showers due to the weak instability and cooling aloft. Snow
levels may gradually fall during this time frame...Sat into Sat
night...with levels at or above 5kft. Quantitative precipitation forecast appears to fall off Sat
night per the European model (ecmwf) and nam12...while the GFS shows precipitation ramping
up again by 18z Sunday as a short-wave rapidly approaches the
coast south of the cape. Even the New Run of the European model (ecmwf) shows this
ramp up in rain on Sunday...but has the bulk of it over the sfo
Bay area and east over the SAC valley. So the north coast and
perhaps portions of the north coast interior may not see any more
rain on Sunday. However the GFS has a band moving up the coast
during the day which would make for another soggy day. Even the
nam12 shows a new band of rain developing across mendo County on
Sunday...moving it northwestward out toward southern Humboldt by
Sunday evening. Confidence in the forecast for Sunday is not high.

The forecast does not get any clearer or well defined Sun night into
Monday or for the rest of the week for that matter. All the models show
a closed upper low moving toward the coast early to middle next week
but vary on how fast. The GFS has consistently been the fastest and
wettest. The European model (ecmwf) has been slower and less bold with the rain. The
CMC was in between the two extremes. It does look like wet and
unsettled weather conditions will continue early to middle next week.
The timing and duration of rain is still very questionable. Trying
to Pin Point the best day(s) and location(s) has proven to be very
difficult. Best approach at this point...considering all the
incongruent data...is to broad brush the forecast with equal
chances of rain or no rain. //End

&&

Aviation...conditions will gradually deteriorate tonight as a storm
system approaches northwest California. MVFR resulting from bands of
rain is expected to develop along the Redwood coast this evening,
then spread south and east during the overnight hours. Southerly
winds will be gusty ahead of the rain bands, with the strongest
winds expected along the Redwood coast and over the higher
terrain.

&&

Marine...the afternoon buoy observations show a fresh southerly
breeze north of Cape Mendocino and a gentle southerly breeze south
of Cape Mendocino. Wave heights are near 7-9 feet north of Cape
Mendocino and around 5 feet south of Cape Mendocino. Seas are mixed
with a longer period swell from the west and building wind waves
from the south. The 1718z ascat pass clipped part of our waters. It
showed winds of 20-25 knots north of Cape Mendocino and 10-20 knots south
of Cape Mendocino. The observed winds were about 5 knots stronger than
expected north of Cape Mendocino, so increased the forecasted winds
there for the short term to reflect this. Left the SC.Y's unchanged.
The models remain in good agreement showing a large storm system
impacting the coastal waters for the next few days. Southerly winds
will remain elevated through Friday. Seas will be mixed with a west
swell, which will gradually subside into the weekend, and short
period wind waves building tonight and continuing through Friday.
Saturday winds should ease and become northerly as a disturbance
tries to push through. However, models continue to show differences
in the timing of the wind shift and the strength of the winds. The
forecast continues to reflect the consensus of the models. As we go
into Sunday the models show winds becoming southerly. But again the
strength and the exact timing of the wind change differs based on
the models. Once again went with the consensus of the models. Waves
should remain elevated early next week. But how high, direction,
steepness, et cetera. Remains highly uncertain at this point given the
variability in the models.

&&

Eka watches/warnings/advisories...
California...none.
Northwest California coastal waters...
Small Craft Advisory until 9 PM PST Friday for pzz450-455.

Small Craft Advisory until 9 PM PST Friday for pzz470-475.

&&

$$

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