Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 261209

National Weather Service Eureka CA
510 AM PDT Wed Jul 26 2017

An upper-level low situated near Covelo this morning, will continue
to bring a chance for showers and isolated thunderstorms to portions
of the region through this evening. High pressure will build across
the region for the remainder of the week, bringing drier and warmer
conditions to the area. Coastal clouds and patchy fog will develop
each night and persist through the morning for the next few days.


(Today and tonight)

The much talked-about upper low is currently spinning near Covelo
this morning. One lone shower has popped just east of there, with
the latest GOES-16 low-level infrared water vapor loop showing
additional cumulus trying to develop across much of Mendocino
County. With the pocket of the cooler air residing over this region,
this makes sense and it would be surprising to see another shower or
two, and perhaps a thunderstorm, to develop as the latest SPC
mesoanalysis and GOES-16 data indicating some weak instability

The next area of concern is across southern Oregon. Here, the latest
imagery data described above and Doppler radar loop shows an area of
showers and a couple thunderstorms developing as they move
southwest. The latest high resolution HRRR model seems to
initialized this activity the best this morning, and it brings the
convection into southeastern Del Norte, northeastern Humboldt, and
northwestern Trinity counties around sunrise. The NAM also supports
this general scenario, albeit a little further northwest.
Instability is a little higher in this region, with the latest
analysis showing about 300-800 J/kg of MUCAPE. This will be
sufficient to maintain the activity, should it make it this far
southwest.  Dangerous cloud to ground lightning, mall hail, and
gusty winds would be the main storm concerns.

Heading into the afternoon and evening, the latest soundings
continue to show sufficient instability developing, MUCAPEs of 400-
1200 J/kg and mid-level lapse rates around 7.5 deg. C/km. Given the
boost from diurnal heating, we should see decent cumulus development
across the interior, with a few storms developing. Similar to the
morning, lightning, gusty winds, and small hail will be a concern.

For the overnight hours, coastal low clouds and patchy fog will
develop, with just a few clouds elsewhere. Temperatures will bottom
out near seasonal values tomorrow morning.

(Thursday through Tuesday)

Warming temperatures for the interior will be the main thing to
watch for the remainder of the week, as a ridge of high pressure
aloft builds across the state. Aside from potential low clouds/patchy
fog development along the coast at night, the weather pattern looks
pretty benign. As the ridge builds across the region, increasing
heights aloft will allow the interior valleys to warm, with
afternoon highs climbing into the 100 to 105F range in the typical
warmer locations. /PD


An upper low will shift EWD across the region today,
with associated thunderstorm potential becoming most probable over
Trinity County and points north and east. Otherwise, marine stratus
(yielding IFR ceilings) occurring along the coast is forecast to
partially clear this afternoon and then redevelop overnight.
Elsewhere, model guidance continues to hint at low cloud potential
at UKI, which is plausible given the presence of stratus one county
to the south and persistent low-level southerly winds...will
continue to monitor.


High pressure over the NERN Pacific and a thermal trough
of low pressure over interior CA will favor continued small craft
northerlies over the outer waters during the next 7 days. Inland
temperatures are forecast to warm further during Friday, Saturday,
and Sunday. This will aid in tightening the surface pressure
gradient, such that occasional gale force gusts will become slightly
more probable during late week. Otherwise, model guidance indicates
that tropical cyclone activity occurring southwest of Baja
California will yield a large period southerly swell that will enter
the coastal waters during early to middle portions of next week.


The main concern lies with our thunderstorm potential today. Similar
to the past few days, dangerous cloud to ground lightning, gusty and
erratic thunderstorm winds, and small hail will be the main storm
concerns. This was the case yesterday portions of Del Norte county
and into northeastern Humboldt County, where some smoke plumes were
observed and are being investigated. Luckily, the storms yesterday
were fairly wet across this region based on reports.

Farther south across Mendocino County, a few storms developed here
as well, and surprisingly made it all the way to the coast as they
moved westward. Lightning activity was also good in this region, and
we don`t know if any fires were started. The main concern about this
region and Trinity county is the fuels are much drier compared to
farther north, posing more of a fire concern. A few thunderstorms
may yet develop this afternoon, with some showers trying to build
further already. Heading into the afternoon, the best chance for
convection will be from Covelo east. /PD


PM PDT Saturday for PZZ470-475.



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