492
FXUS66 KMFR 081204
AFDMFR

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

.DISCUSSION...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...08/12Z TAFs...Marine stratus has developed in the lower
Umpqua Valley of western Douglas County as well as much of Coos
County, including North Bend, this morning. At North Bend, the
ceiling is MVFR at around 1000-1400ft, but farther north up the
coast, ceilings are IFR (even LIFR) up near Florence/Newport with
observations running in the 300-400 ft range. Another "fickle
finger" of stratus extends north along the California coast up to
around Brookings where ceilings are a mix of IFR/LIFR in the 400-
700ft range. These ceilings should all gradually peel back offshore
by late morning or early afternoon before returning late tonight
(near or after 08z).

Meanwhile, an upper level short wave is bringing some mid and high
clouds into NorCal and SW Oregon early this morning, thickest of
which, however, are scooting northward west of the Cascades and over
the coastal waters. This upper level disturbance and enhanced mid-
level moisture will be enough to trigger some convection this
afternoon and early this evening as the atmosphere destabilizes.
Most of the convection will occur near and to the east/south of the
Cascades/Siskiyou mountains. Focus areas will be in northern
Klamath/Lake counties (40-60% chance), but activity will also extend
southwestward into NorCal down to around the Trinity Alps. We have
indicated VCTS in the Klamath Falls TAF for late this afternoon,
with the probability of thunder in the 15-25% chance range. With any
thunderstorms this afternoon/evening, there could be strong, gusty
outflow winds and hail. Activity in NE sections (northern
Klamath/Lake counties) could continue into the night, since an upper
level trough will be moving onshore, maintaining upper level
forcing. -Spilde

&&

.MARINE...Updated 200 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.

&&

$$

MNF/MAS