Scientific Forecaster Discussion
fxus66 keka 202128
Area forecast discussion
National Weather Service Eureka California
228 PM PDT Fri Sep 20 2019
Synopsis...warm and dry weather will continue across the region
through Saturday. Light showers will be possible over del norte
and northern Humboldt County on Sunday, followed by another period
of warm and dry conditions through most of next week. A storm
system late in the week may bring a return of cooler and wetter
Discussion...after early morning low cloudiness and fog in some
of the interior valleys, skies have become mostly sunny across the
area with some patches of high clouds speeding S over the
interior. Temperatures are near normal across most of the area. Northwest
to north winds have been increasing along the Redwood coast with some
gusts to 25 mph at Crescent City.
Under mostly clear skies, expect another night of good radiational
cooling tonight. Have leaned toward the low end of MOS guidance
with temperatures, but still not expecting any frost. Temperatures
will warm across the interior on Saturday, with readings maxing
out above 90 in some of the S valleys.
Clouds will be on the increase Saturday night ahead of a weak
frontal system dropping in from the north. The bulk of the rainfall
with this system will remain north of the area, and the rains will
become more scattered as they shift S. There may be some weak
instability over the north interior late on Sunday afternoon into
Sunday evening, but don't feel there is much chance of thunder.
Due to the progressive nature of this system, what rains do occur
will rapidly come to an end Sunday evening.
An upper ridge will build over the area early next week, with
warm to hot temperatures returning to the interior. There are
indications that periods of offshore flow will occur early next
week, and this could bring fairly warm temperatures to some
Redwood coast areas as well.
Long range models are still in good agreement that a large scale
trough will dig over the west portion of the US late next week. This
will bring cooler temperature and the possibility of more
Aviation...VFR conditions will prevail through the forecast period
as an offshore ridge transitions eastward over the Pacific northwest. This
will promote air mass drying and an offshore flow through Saturday.
Patches of low clouds will still be possible, primarily over the
interior valleys and around Humboldt Bay, during the late night and
early morning hours.
Marine...high pressure offshore coupled with a trough near the
California coast will maintain fresh to strong northerly breezes as
well as steep waves tonight. The axis of strongest winds should
shift outside 10nm on Saturday, however high resolution models
indicate north winds ramping up again around Pt St George and Cape
Mendocino in the afternoon and evening. Also, steep seas will be
borderline for an advisory inside 10nm on Saturday. For now will
let the advisory for the inner waters expire late tonight.
Northerly winds will ease up Saturday night into Sunday morning,
primarily north of Cape Mendocino, as a trough approaches from the
northwest. This lull will be short-lived. Guidance continues to indicate
north winds ramping up again Sunday night in the wake of this
trough. How quickly winds increase is still not certain. Right now,
it appears to be a gradual increase Sunday night.
The potential for gale force conditions will increase on Monday and
then persist through mid next week. The highest probability for
gales appears to be in the outer waters, based on the coarse
resolution of the GFS, European model (ecmwf) and nbm. Gale conditions will be
possible inside 10nm as well, primarily around Pt St George and Cape
Mendocino. The main threat for the inner waters appears to be large
steep seas generated from the strong northerlies outside 10nm. Steep
seas may hit 18 to 20 feet outside 10nm and 12 to 15 ft inside 10nm
around mid next week if gales last for 3 consecutive days. For now
will call attention to this threat in a weather story graphic.
Northwest California coastal waters...
Small Craft Advisory until 3 am Saturday for pzz450-455.
Small Craft Advisory until 9 PM Saturday for pzz470.
Small Craft Advisory until 3 am Monday for pzz475.
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