Scientific Forecaster Discussion
Area forecast discussion...corrected
National Weather Service Eureka California
729 am PDT sun Mar 9 2014
moderate to heavy rain will expand southward across northwest
California and continue today and tonight as a front slowly passes
through. After some lingering showers early Monday, much of the
week looks dry and mild as strong high pressure returns.
band of heavy rain associated with weakening cold front is
continuing to push southeastward across Humboldt County as of 4 am.
However kbhx radar clearly shows band is becoming stationary near
and south of Cape Mendocino, so expect the rest of the band to slow
to a crawl. All guidance indicates the best forcing will continue
to gradually shift southward so expect a slow expansion of the
steady rain southward into Mendocino County through the day today.
High pressure ridge nudging in ahead of the next sharp shortwave
trough is to blame for slowing of the cold front. Rainfall rates
of a tenth to a quarter-inch per hour are common within the plume
of heavy rain, with locally double that in orographically-favored
areas. Winds gusted to 30 miles per hour or so along the del norte coast and
exposed higher terrain overnight, but will quickly ease this
Integrated water vapor transport will lessen this morning so
rainfall rates may not be quite as high as the band shifts south
into Mendocino. Ivt then remains steady-state through this evening as
shortwave approaches. Weaker forcing north of Cape Mendocino may
ease rainfall rates later this morning into the afternoon, but
eventually will increase again later today into this evening as positive vorticity advection
and upper-divergence with right-rear quadrant of jet-streak pass through.
NAM seems to be the outlier pushing the moisture plume southward
and drying out much of the area faster this evening, despite
similar timing of upper trough compared to other guidance. Thus
forecast rainfall amounts remain on-track, with 1 to 4 inches
across northwest California. Lowest amounts will be eastern Trinity and
southern Mendocino, while a total of 4-6 inches falls across the King
Range, South Fork mtn, and the Siskiyous. Main hazards will be
localized Urban and Small Stream flooding during times of heavier
rain, along with Rockslides in the steeper terrain.
Rain will taper to showers overnight as colder air aloft finally
moves in. Instability will increase enough to warrant keeping the
slight chance thunder in for del Norte County early Monday morning. Am
not too impressed with the relatively progressive nature of the
trough, but low-level lapse rates will be quite steep for a short-
time, allowing for some low-topped convective showers. As trough
passes by, drier air will move in and stability will increase,
with shower activity coming to an end for all but the Siskiyous or
Trinity Alps by Monday PM. Skies will clear across much of the area
as well, especially along the coast and over Mendocino County.
Tuesday morning there will likely be some fog in the interior
valleys. Where this is limited, temperatures may be quite frosty,
and the first frost advisory of the Spring may be necessary for northern
Mendocino County. The rest of the forecast continues to look high
and dry with high pressure both at the surface and aloft dominating most
of the week. Removed any mention of rain through next weekend.
Unfortunately for those hoping for more beneficial rains, the next
week to 10 days does not look good, with guidance in good agreement
with an anomalously strong upper ridge building over California next
weekend. Expect sunshine and increasingly warm temperatures inland
through the week, possibly reaching into the low 80s in the interior
valleys next weekend. Aad
Aviation...moderate and gusty winds will prevail at kcec and kacv
this morning as a cold front moves through the region. Rain will
occur at kcec and kacv becoming moderate to heavy at times today.
Therefore MVFR and IFR conditions will occur with LIFR conditions at
times during heavier rain showers as ceilings and visibilities
decrease. VFR conditions and light to moderate winds will continue
at kuki this morning. However rain showers moving through the area
will reduce ceilings and/or visibilities to MVFR and IFR conditions
at times today at kuki.
Marine...a cold front moving through the region has increased the
southerly winds and the seas across the waters. The seas will
increase this morning and remain elevated through tonight. The winds
will shift to the north tonight then increase across the southern
outer waters Monday night and Tuesday.
Northwest California coastal waters...
Small Craft Advisory until 3 PM PDT this afternoon pzz450.
Small Craft Advisory until 9 PM PDT this evening pzz455-470.
Small Craft Advisory until 5 am PDT Wednesday pzz475.
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