384
FXUS66 KMFR 081837
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
1137 AM PDT Sat Jun 8 2024

.DISCUSSION.../Issued 504 AM PDT Sat Jun 8 2024/

The upper level pattern will begin to transition today. The ridge
axis will shift east of the Cascades and a weak trough will
approach the region. Ahead of this trough, a shortwave is passing
through the area early this morning, bringing a swath of mid and
high level clouds. There are some light returns showing up on
radar, but we don`t expect these returns to amount to anything.
Elevated instability just isn`t there for any thunderstorm
development this morning, and while a few areas may see some
sprinkles out of these showers, it will be very isolated and
limited to areas west of the I-5 corridor and over the marine
waters. Ahead of this shortwave, areas of stratus have returned to
portions of the coast, with quiet conditions overall expected for
the morning hours.

With the shift in the upper level pattern, high temperatures today
will be around 5 to 10 degrees cooler for locations west of the
Cascades compared to Friday`s readings. A few records were broken
yesterday: Mt Shasta City recorded 95 degrees, breaking the old
record of 92 set in 2015 and Alturas recorded 93 which ties the
record set in 1996. Klamath Falls came close, reaching 90 degrees
which is just shy of 91 set in 1996. While we expect several degrees
of cooling west of the Cascades, temperatures east of the Cascades
will only be cooler by a few degrees, reaching into the mid to upper
80s. We don`t anticipate any record challenging temperatures today
as high temperatures will be several degrees out of reach of current
records.

The forecast is on track for a likely broader area with more
thunderstorm activity this afternoon and evening. The focus for
activity is expected to be in similar areas as the previous two
days: in the vicinity of the border of Klamath and Lake counties,
extending primarily into the northern portions of those counties,
including Chemult and Summer Lake, where coverage of storms
(isolated to scattered) will be greater today. A secondary, isolated
risk for storms will cover much of Siskiyou and Modoc counties, the
remainder of south central Oregon, and the southern Oregon Cascades
and Siskiyou Mountains. SPC has delineated a Marginal Risk (10-20%)
for isolated severe thunderstorms east of the Cascades, indicating a
5% chance of severe winds (gusts to at least 58 mph) or hail (at
least 1 inch diameter). Overall, the atmosphere is fairly similar to
the previous two afternoons with similar CAPE and LI values, but
there is a modest increase in bulk shear, up to 35 to 40 kts today
vs 25 to 35 kts the previous afternoons. We`ve witnessed a few
strong to severe storms the previous afternoons as well, and with
the increase in bulk shear, storms could persist longer today and
increase the chance for severe winds and/or hail. Regardless if
thunderstorms reach severe criteria or not, expect strong gusty
winds with and near thunderstorms as well as the potential for hail.

The previously mentioned weak trough passes through the region late
tonight into Sunday, and guidance indicates the potential for
showers and isolated thunderstorms to continue across northern
Klamath/Lake Counties during this time. The cooling trend continues
on Sunday as the weak trough passes through, with the most notable
cooling expected east of the Cascades where high temperatures are
expected to be about 7 to 10 degrees cooler. West Side will cool
further as well, but only by a few degrees. We`ll see yet another
day of thunderstorm potential Sunday afternoon, but the focus will
shift eastward into Lake and Modoc counties as the trough pushes the
moist unstable air farther east as the day progresses.

Late Sunday into Monday, energy from this week trough gets cut off
from main flow and forms a cut off low off the coast of southern
California. The flow will become more zonal over the PacNW through
about mid-week, resulting in a stabilizing atmosphere and the loss
of daily thunderstorm potential. With zonal flow, we don`t
anticipate a big warm up, but temperatures will remain about 10
degrees above normal for the first half of the week. /BR-y

&&

.AVIATION...08/18Z TAFs...An isolated thunderstorm has already
popped up this morning ahead of an upper level wave and some modest
mid level moisture. Thunderstorm activity will pick up into the late
afternoon and early evening as the atmosphere destabilizes. The
bulk of the activity will develop east of the Cascades and in
northern California.

The thunderstorm threat will persist overnight east of the Cascades
and in the central Cascades as the upper level wave approaches the
Oregon coast. Some models also show a bulk of moisture around 7000
to 9000 feet above sea level, which could aid in initiating
convection overnight. Right now the threat of overnight
thunderstorms remains low, although these events are sometimes
underdone in the models.

Overall, be on the lookout for thunderstorms across the forecast
area, especially farther to the east through the TAF period. Lower
ceilings around 1000 feet are anticipated near the coast overnight
as high pressure begins to build. IFR ceilings are most likely,
although periods of LIFR ceilings also remain possible.


&&

.MARINE...Updated 800 AM Saturday, June 8, 2024...North winds
will be just strong enough to produce an area of steep seas
hazardous to small craft south of Ophir today and tonight, generally
beyond 2 NM from shore. Then, a moderate west swell moves in tonight
through Sunday. During this time, the thermal trough will
restrengthen, bringing increasing north winds and steep to very
steep seas Sunday into early next week, especially south of Cape
Blanco. Conditions will at least remain hazardous to small craft
south of Cape Blanco through midweek. -Spilde


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...None.

CA...None.

PACIFIC COASTAL WATERS...Small Craft Advisory until 11 AM PDT Monday
     for PZZ356-376.

     Hazardous Seas Warning from 5 AM Sunday to 11 AM PDT Monday for
     PZZ356-376.

&&

$$