Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Eureka California
332 PM PDT Monday Oct 20 2014
Synopsis...a cold front will continue moving eastward away from
the area this evening. However a low pressure trough will move
across the area this evening and overnight. The low pressure
trough will produce showers and a slight chance for an isolated
thunderstorm which may contain small hail across north west
California this evening. Then showers will occur after midnight.
Another frontal system will approach the area by Wednesday with
rain chances continuing the middle to late this week.
Short term (today through thu)...a cold front was moved across the
region today producing widespread rain. Rainfall a little over an
inch occurred at Cooskie Mountain RAWS in the King Range. The
front has moved east of the are this afternoon. However a low
pressure trough will move across the region this evening and
overnight. Showers will continue moving across the area this
afternoon through tonight with a cold pool associated with the
Post frontal trough. Instability associated with the cold pool
this afternoon and evening will result in a slight chance for an
isolated thunderstorm moving across the region primarily before
midnight. Lightning has been detected offshore this afternoon. As
a result of the cool temperatures aloft...some of the strongest
showers and thunderstorms may produce some small hail across some
areas. Showers will diminish overnight into Tuesday. Rainfall
totals will generally range from near 2 inches in the mountains of
del Norte County and the King Range to around 0.25 inches in
southern Mendocino County and the eastern valleys of Trinity
County with this system. As the cold pool moves overhead...snow
levels will drop to near 6k feet this evening with some snow
showers possible. Not expecting any accumulation as the airmass
will be modifying quickly.
Temperatures across the area tonight into early Tuesday will be
pretty chilly with interior locations forecast to see temperatures
in the middle to upper 30s. However there will be too much low level
moisture and clouds for a frost threat.
Shortwave ridging will build over northwest California Tuesday
resulting in drier conditions. A cold front will approach the
area Wednesday slowly moving southeastward into Thursday. High
levels of moisture are associated with this system. Higher values
of moisture will occur across del norte and northern Humboldt
Long term (thu night through mon)...both the GFS and European model (ecmwf) are in fairly
good agreement in the upper level features with trough moving inland
Saturday night, a ridge building on Sunday and another trough
approaching Monday. Surface features differ though with European model (ecmwf)
lifting a warm front north into coastal Humboldt and del norte counties
by noon Friday while GFS shifts it south into Mendocino County and
then pulls it north about 6 hours later. This makes a difference in
where the rain is focused with the ec having the rain mainly in the
coastal areas north of the cape while GFS has it south of the cape
in the morning before shifting it back north in the afternoon. Kept
the higher rainfall probabilities north of the cape per European model (ecmwf). Both
models then swing cold front through Friday night into Saturday
morning. Showers behind the front then taper off Saturday night.
A few lingering showers are possible Sunday but they will be
mainly up in del Norte County. Another front approaches Monday but
mainly dry. /Dean
Aviation...a cold front that moved into the region caused
conditions overnight and through morning to vary considerably
across the region. LIFR to MVFR prevailed from the coastal areas
to the coastal Mountain Valley interior. Cec & acv received
respectable rainfall with areas over the points receiving well
over an inch. There were pockets of scattered skies today. However
most areas maintained mostly cloudy skies. The aviation weather
threat: diurnal and dynamic influences continue to help develop
showers and even isolated thunderstorms through at least early
Marine...winds associated with the cold front are subsiding a
little slower than expected but will continue the decreasing trend
tonight. They will increase again Wednesday ahead of the next cold
front with speeds 20-30 knots in the outer waters north of the cape and
have extended the small craft in those waters.
The large westerly swell will peak at 14 to 16 feet with periods of
14 to 16 seconds this evening. Small craft advisories remain in
effect for the entire marine area. There is a stationary low in the
Gulf of Alaska and another longer period westerly swell train will
enter the waters Wednesday with heights 12 feet at 14 seconds.
Another front is expected about Friday and though the details differ
increasing southerly winds are again expected. /Dean
Northwest California coastal waters...
Small Craft Advisory until 11 PM PDT Tuesday for pzz450-455.
Small Craft Advisory until 7 PM PDT Saturday for pzz470.
Small Craft Advisory until 11 PM PDT Tuesday for pzz475.
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