Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 241137

National Weather Service Eureka CA
337 AM PST Fri Feb 24 2017

.SYNOPSIS...A cold upper disturbance will move south across
northern California today and Saturday. Showers will develop with
the passing trough, with accumulating snowfall expected to occur
for elevations above 1500 feet.


.DISCUSSION...Morning satellite imagery shows an upper-level
disturbance moving south along coastal OR/WA. Cooling cloud tops
associated with this feature will expand southward across NWRN CA
during the late morning into the afternoon, with initial shower
development along the coast subsequently spreading east/inland.
As this takes place, cooling temperatures aloft (H5 tempertures
falling to -30 to -36 C) will aid in snow levels around 1500 feet.
Thus, showers are expected to produce accumulating snowfall over
the higher terrain, with 4-7 inches possible Friday afternoon
through Saturday afternoon for portions of Del Norte, Humboldt,
northern Mendocino, and far western Trinity Counties. Though lapse
rates will be very steep due to the cold airmass aloft...model
guidance has backed off on QPF amounts compared to past runs.
Given this trend, went with a winter weather advisory instead of a
winter storm warning.

The previously mentioned upper disturbance is forecast to exit the
region Saturday night. However, a similar trough will enter NRN CA
late Sunday afternoon, and then exit eastward by late Sunday
night. Snow levels will remain low as this wave moves across the
area, which will favor additional high elevation snow
accumulations. Winter weather headlines may be needed once again
with this second round of snow.

After Sunday, upper heights are forecast to gradually build over
the NERN PAC and west coast. This will shunt the most energetic
portion of the westerlies north of the region, which would favor
an extended period of drier weather.


.AVIATION...VFR conditions and light winds to calm conditions
will continue at KCEC, KACV and KUKI today. Showers will move
across KCEC and KACV at times this afternoon and evening
increasing cloud coverage and reducing ceilings with VFR
conditions prevailing. Cloud coverage will increase this afternoon
at KUKI with VFR conditions prevailing.


.MARINE...The winds and seas have diminished as a weak pressure
gradient prevails across the waters. An offshore low pressure
system will drift southward tonight and Saturday. The low will
weaken as it drifts southward remaining offshore. Therefore the
winds and seas will only increase slightly tonight and Saturday.
Winds and seas will diminish Saturday night. The winds and seas
will increase Sunday and Monday as a cold front moves across the
region. The winds and seas will decrease on Tuesday as a high
pressure ridge build across the waters.


CA...Winter Weather Advisory from 1 PM this afternoon to 4 PM PST
     Saturday for CAZ102-105-106-108-110.



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