296
FXUS66 KMFR 120938
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
238 AM PDT Sun May 12 2024

.DISCUSSION...Our weather pattern for the next week will continue
to be more typical for mid-June than mid-May.

The focus for the new forecast issuance was upon
adjusting the probability of showers and thunderstorms this
afternoon and evening, and the sky cover forecast today into
Tuesday morning...both to account for long-lingering coastal low
clouds and the cumulus buildups late today.

There is very good model agreement in limiting late day
instability to northern California and south central Oregon, then
returning to a stable air mass for Monday. A slight chance of
showers and thunderstorms will extend from central Siskiyou County
northeastward into northwest Modoc, southeast Klamath, and Lake
counties...continuing eastward into Harney County. This
instability (as well as the aforementioned influx of coastal low
clouds) is in response to a Pacific trough that will kick the dry,
stable ridge axis east of our area. As such, even with the
afternoon cloud development, east side cities are likely to have
their high temperatures nudge up one to a few degrees above the
values from Saturday. Meantime, the inland west side is expected
to see highs nudge a similar one to a few degrees below the values
from Saturday. All-in-all the coastal stratus, temporarily
thinning late in the day, and inland highs at 10 to 15 degrees
above normal will be representative of summer- like weather.

There is very good model agreement on the forecast into Friday,
and a more general agreement on the character of the pattern into
next weekend. For Monday through at least Thursday, a dry and
stable air mass is expected inland, with continued above normal
temperatures. With onshore winds behind the trough, temperatures
will trend less hot for Monday, a several degree drop will be
noticeable on the west side, with a just a couple to a few degrees
on the east side. Westerly breezes will develop late today, at or
barely above normal strength of 8 to 15 mph, strongest on the
east side. Breezy winds will then increase by a notch to 10 to 20
mph for Monday.

The next ridge tracking across the eastern Pacific is expected to
build into our area at mid-week. The forecast for coastal low
clouds will be a bit challenging, with northerly low level flow
expected to shift to northeast for Tuesday at least into Thursday,
producing another Chetco Effect with pronounced downslope warming
and drying for southern Curry County, near Brookings with highs
in the mid 70s to mid 80s possible. Farther north, more of a due
northerly flow will continue night and morning stratus for the
beaches from Cape Blanco northward. The ridge will also bring a
warming trend inland Tuesday into Thursday, with readings
potentially approaching those of the past couple days.

The pattern for Friday is expected to bear some resemblance to
that of today, with flow returning to onshore. A trough in the
northern branch of the jet stream, moving into the Pacific
Northwest, is likely to be sharper and seasonably strong...which
is not that strong but stronger than today`s approaching trough.
This should introduce some mentionable probability of showers and
thunderstorms for portions of our area as early as Friday,
continuing into the weekend, and send high temperatures back
closer to normal for next weekend.

&&

.AVIATION...12/06Z TAFs...Along the coast and just offshore, marine
stratus is currently being observed along the coast to around 15 nm
from shore north of Cape Blanco and has pushed farther south and is
filling along the south coast tonight, resulting in IFR ceilings.
Breezes are expected once again in the afternoon.

Inland, VFR ceilings will continue through the TAF period. The
marine stratus could work its way into the Coquille Basin late
tonight, but it should be shallow and burn off towards 18z Sunday.
-Petrucelli/Hermansen

&&

.MARINE...Updated 200 AM Sunday, May 11, 2024...A thermal trough is
going to be the guiding feature for marine conditions through the
week. This trough started to develop early this morning and will
strengthen through the day. During the day, steep seas will develop
in waters between Cape Blanco and Brookings and within 30 nm from
the shore. By this evening, steep seas are expected to cover all
waters as the trough strengthens and expands. A Small Craft Advisory
is in place for all waters from Sunday at 5 PM through Monday at 5
PM to communicate these conditions.

The thermal trough will continue to strengthen Monday evening, with
model guidance suggesting gale strength gusts in waters south of
Coos Bay and beyond 5 nm from shore. Currently, a Gale Watch is in
place for areas where these winds are forecast while a Small Craft
Advisory will continue in all other waters. This combination of
hazard products will be in place from Monday at 5 PM through Tuesday
at 5 PM.

Chaotic seas will continue and gale winds look to remain in waters
south of Cape Blanco through the week. Probabilistic guidance
suggests very high chances (50-90%) of gale gusts in southern waters
through next weekend. Long term atmospheric guidance shows upper
level instability may help to break the thermal trough up early next
week, although any conditions that far out are difficult to describe
with high confidence. -TAD

&&

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

PACIFIC COASTAL WATERS...Small Craft Advisory from 5 PM this
     afternoon to 5 PM PDT Tuesday for PZZ350-356-370-376.

Gale Watch from Monday afternoon through Tuesday afternoon for
     PZZ356-370-376.

&&

$$