Scientific Forecaster Discussion
Area forecast discussion...corrected
National Weather Service Eureka California
350 am PDT Tuesday Jun 2 2015
Synopsis...today and Wednesday will see mainly dry conditions
with seasonable temperatures. Scattered showers and thunderstorms
will return to the interior from Thursday into the weekend as an
upper level low sinks south of the area.
Discussion...the upper level trough continues to lift out of
the area this morning. This has shut off most of the showers this
morning...although there are a few lingering showers in del norte
and northern Trinity counties this morning. The Humboldt coast may
see some drizzle as well. At the coast fog has developed and is
dense in some locations. Interior areas will likely see some
clearing this afternoon...however the coast is expected to remain
Tonight a weak shortwave is moving through. The main impact from
this wave is expected to bring some fairly heavy drizzle at the
coast and clouds over the interior. The wave arrives after peak
heating and moisture is limited so thunderstorms over the
interior look unlikely.
Wednesday morning a brief ridge builds over the area before
another shortwave moves into the area in the afternoon. This may
bring a few showers or thunderstorms over over the Trinity Alps
and yolla bollys. Onshore flow will persist so expect the coast
will remain mostly cloudy through much of the day.
Wednesday night into Thursday this shortwave continues to sink
south and starts to become a cutoff low. Confidence is growing
that this low will bring thunderstorms to the interior areas on
Thursday. With the core of the low just to the south of the area
shear is modest...only about 25 knots of bulk shear. This may be
enough to produce some small hail...but expect the storms will
mainly be pulse thunderstorms. Instability is decent with the GFS
showing bullseye of around 700 j/kg over southern Trinity County.
Friday into early next week the forecast is highly dependent on
the exact track of the low. There is the potential for pop-up
thunderstorms each afternoon with the upper level in the vicinity.
Friday left the thunderstorms out of the forecast...this GOES
along with the GFS forecast but the European model (ecmwf) would indicate the potential
for thunderstorms. For the weekend into early next week left the
thunderstorms in the forecast over the interior...but a slight
shift in the upper level could change this. Left the thunderstorms
at only a slight chance...but as this gets closer this may need to
At the coast there may be some more clearing than we have seen
lately. Friday as the upper level low sinks south it produces
offshore flow in our area. This forecast will also be highly
dependent on the track of the low...but Friday looks fairly clear
at the coast. For the weekend into Monday there may be some
clearing...but offshore is weaker and confidence is low on this.
Aviation...morning fog satellite shows stratus/fog along the coast
and in some of the interior valleys. Likewise, the taf sites range
from IFR/LIFR along the coast (due to ceilings/visibilities) to VFR
across the interior (where skies are clear). Along the
coast...expect conditions to improve to VFR by this afternoon as
winds gradually increase along the coast due to a strengthening
pressure gradient offshore. But the timing of this is uncertain.
Inland...IFR in some of the valleys will burn off this morning.
Otherwise, VFR will prevail.
Marine...the buoys this morning are reporting a light to gentle
breeze and mixed seas ranging from 2-3 feet. The 0450z ascat pass
clipped our waters, but showed winds ranging from calm to 10 knots.
This was as much as 5 knots lower than our forecast, so adjusted the
morning wind forecast down slightly to account for this. These
light winds and low seas will end over the next 24 hours. The
Pacific high will move towards the coast and strengthen today
through Thursday. At the same time a thermal trough will develop
across interior California. The interaction between these two will
increase the pressure gradient across our waters today into
Thursday. This will lead to increasing northerly winds and
building short period seas. Issued the first headlines for this
across the southern waters where winds will increase this
afternoon. See the mww and the mws for more details. There is
still some minor differences in the models over how strong the
winds will get (generally within about 5 kt), so went with a
blend, which keeps this forecast fairly close to the previous
forecast. Northerly near gales are expected to develop across zone
475 Wednesday morning, then spread northward into zone 470
Wednesday night. Gale conditions are expected in these zones on
Thursday and Friday. Northerly winds aren't expected to be this
high across the inner waters, but their still should be fairly
strong wind gusts. Additionally, steep fresh swell generated
across the outer waters will likely propagate into the inner
waters during this time frame. Conditions look like they will
start improving on Friday night as the strongest winds shift to
Northwest California coastal waters...
Small Craft Advisory from 3 PM this afternoon to 5 am PDT
Thursday for pzz475.
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