Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Eureka California
304 PM PDT Friday Sep 19 2014
Synopsis...high pressure will bring dry conditions and warm
temperatures to much of northwest California through the weekend.
Coastal clouds will return this weekend as a southerly surge of
stratus moves up the northwest California coast.
Discussion...there is an upper level low dropping south off the
central California coast with a high pressure ridge nosing in from the west.
There were significant temperature rises inland with highs 10-20
degrees warmer inland than Thursday. With a light offshore easterly
flow, drier air was making its way into the area and rh's were as
much as 20-40 percent lower inland than Thursday. Relative humidity recoveries at the
higher elevations will only reach about 50 percent tonight and there
will be some easterly winds but will only highlight this in the fire
weather forecast. Moisture will still be trapped in the inland
valleys with low clouds and fog again developing late tonight. Smoke
from Happy Camp fire will spread into northern Humboldt and del
norte counties for hazy skies into Saturday morning before the winds
become southerly in the afternoon. The thermal trough is expected
to get pushed off the coast with southerly winds developing. A
southerly surge will push clouds up along the mendo coast Sat and
then all the way to the or border by Sun morning.
The closed low will drift NE this weekend as a deep low approaches
from the west. There will be enough moisture and instability for
some afternoon cumulus over the inland mountains but left out mention of
convection. Main message is deep low moving inland for the middle of
the week. GFS and ec continue consistent pattern of dissipating a
front off the coast on Monday with the main trough approaching Wednesday.
Next much stronger front is expected to move inland late Wednesday morning
and afternoon. Latest integrated water vapor transport shows values
2-4 South Dakota above normal which happens about every 10 years. Confident in
rain developing though timing is still unclear. Forcasting most of
the rain to be Wednesday afternoon and night though it could a little
earlier and start late Tuesday night. Main negative tilted trough doesn't
swing inland until Thursday so could get a brief break in the rain
behind front and then showers developing again Thursday. Lapse rates
don't look unstable enough for tstsm but that will have to be
watched. After Thursday morning, ec and GFS diverge with GFS trying to
bring in ridge while ec has another trough. Left scattered
showers in the forecast as an average of both models. By Friday
afternoon, wpc forecasting rainfall amounts of 2.5 inches near cec
and at least half an inch everywhere else. Dean
Aviation...due to the increased low-level moisture due to recent
rains...low clouds and fog covered most of the Redwood coast...the S
Mendocino coast...and many interior valleys this morning. Cloudiness
over the valleys dissipated fairly quickly from middle to late morning
with daytime heating...but coastal cloudiness has been slower to
erode. Cloudiness and fog are expected to redevelop this evening and
overnight in similar areas. Areal extent may be a bit less...
particularly well inland where less rainfall occurred. Models are
indicating inland thermal trough shifting west overnight tonight with S
flow likely advecting coastal fog northward along the coast. This
fog may even make its way around the cape before daybreak.
Additionally...S flow may once again advect cloudiness up the
Russian River valley toward kuki before dawn. /Sec
Marine...winds will increase over the north offshore waters later
this afternoon and tonight in response to the tightening pressure
gradient between high pressure offshore and the west drifting thermal
trough. Have continued Small Craft Advisory for this area and
extended in time a few more hours into Sat. Conditions may briefly
reach small craft criteria in the northwest portion of zone 475...but
feel areal extent and duration will preclude headline. 2 main
swell trains will affect the area over the next several days. One
with a period 10 to 12 seconds will persist through the weekend and
early next week out of the northwest to west. Another larger west train is
expected arrive by the middle of next week with an initial period
of 15 to 16 seconds. /Sec.
Northwest California coastal waters...
Small Craft Advisory until 3 PM PDT Saturday for pzz470.
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