Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Eureka California
330 PM PDT Tuesday Oct 13 2015
Synopsis...warmer than normal and dry conditions are expected
through much of the work week away from the immediate coast. A
weak front may bring light rain to the region on Saturday.
Discussion...clear skies have dominated today as offshore flow
north of an upper low has spread dry air over northwest
California. This has allowed temperatures to warm well above
normal and Ukiah may break the record high temperature for the
date. Similar conditions are expected on Wednesday except
southerly flow will increase along the immediate coast as the
upper low drifts ever so slightly farther north. This will allow
coastal cloud cover to redevelop tonight along the Mendocino coast
and then spread north around Cape Mendocino during the day on
Wednesday. The NAM is the most Adamant about this solution and
then also lingers the stratus along the coast through Friday.
Considering the upper low will allow for some light offshore flow
aloft...opted to allow for some partial clearing during the
afternoon hours each day.
The upper low will also bring increasing moisture to the region with
the NAM and GFS producing small quantitative precipitation forecast signatures over the higher
terrain Thursday and Friday afternoons. However these same models
also show limited instability and some capping which will likely not
allow many...if any...showers to develop. Precipitation chances
have been left below 15 percent Thursday afternoon but increased
into the slight chance category for Friday afternoon ahead of an
advancing deep trough.
Models remain consistent that this trough will push into northwest
California Friday night into Saturday bringing a brief period of
rain to many areas of the region as a cold front moves inland. There
is high confidence in measurable precipitation for del Norte County
and most of Humboldt County through Saturday...but lower confidence
for areas farther south and east. Increasing instability behind the
frontal system will likely allow for spotty interior showers and
maybe even a thunderstorm or two to develop Saturday
afternoon/evening which could continue through early Sunday morning.
Precipitation totals will generally be light with a few hundredths
to two tenths of an inch...though some locally heavier amounts will
be possible in the mountains of del norte and Humboldt counties.
Southern Mendocino may see very little rain at all from this
system but instead only benefit from lower temperatures.
Mostly dry conditions will return on Sunday as the upper trough
moves into the Desert Southwest. There is high uncertainty in the
forecast for early next week with the European model (ecmwf) indicating a stronger
ridge building over the West Coast behind the departing trough than
the GFS. Thus no changes were made to the extended periods of the
forecast. Temperatures have been kept slightly above normal and
chances for precipitation are near climatology. Rpa
Aviation...VFR conditions and light winds will continue at kcec and
kacv through the early evening. Ceilings and visibilities will
decrease later this evening to MVFR and IFR conditions at kcec as
stratus and patchy fog develop over some coastal areas. Light
winds to calm conditions will prevail at kcec overnight. VFR
conditions and light winds to calm conditions will prevail at kacv
tonight. VFR conditions and light winds to calm conditions will
continue at kuki through Wednesday.
Marine...an offshore high pressure system interacting with an
inland thermal low pressure trough is beginning to weaken. Winds
have diminished and seas will subside the next few days as the
offshore high pressure system weakens further. Light to moderate
winds will become southerly by Wednesday as a weak low pressure
system develops over the waters. A moderate westerly swell from a
North Pacific storm will continue to propagate through the waters
through tonight. A weak cold front will move through the region this
Northwest California coastal waters...none.
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