020
FXUS66 KMFR 122127
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
227 PM PDT Sun May 12 2024

.SHORT TERM (Today through tomorrow night)...

Overview:

The main item of importance in the short term is the thunderstorm
potential (~20-25%) this afternoon across eastern portions of the
forecast area. Otherwise, breezy afternoon wind speeds (15-20mph)
are possible, and overall mostly sunny skies across the region
outside of our thunderstorm potential areas. The main threat today
is lightning as we are not expecting severe weather. That said,
lightning kills too many people each year, and having a plan for
when thunderstorms develop is always the best approach towards
outdoor activities.

Further Details:

A closed low over the Pacific Ocean is creating a split flow type of
pattern over the western CONUS. The northern stream does have a
shortwave within the northwest flow, and this will help produce
thunderstorms this afternoon in conjunction with areas reaching
convective temperatures. The dynamics and kinematics are not
really impressive today, so this will likely be ordinary type
thunderstorm day with difficulty maintaining an updraft.
Deterministic models are mostly suggesting around 200-500 J/kg of
MUCAPE. This has increased slightly from yesterday. The problem
today is the timing of variables phasing together. By the time the
shortwave trough axis starts to come inland and swing through the
forecast area producing lift, we will be losing some of the
instability noted in the atmosphere today. Currently, the day
cloud phase distinction product from satellite is indicating a
struggle for vertical growth within a cu-field over eastern
portions of the forecast area. This is likely due to lack in
forcing as well as lack of moisture, especially the low levels. In
fact, forecast soundings resemble an inverted-v on the eastside,
so there is a chance for gusty outflow wind speeds if a
thunderstorm collapses. These speeds could be as high as 40-50
mph. That problem of course is we need a thunderstorm to actually
develop to have this possibility, which may be a struggle this
afternoon and evening. Outside of the risk for very isolated
strong outflows, lightning is really the main threat today. We are
not expecting the chance for thunderstorms to go beyond 9-10pm
tonight.

-Guerrero

.LONG TERM (Tuesday through Sunday)...

The longer term forecast begins with upper level, long-wave
ridging starting to move into the western U.S. from the Pacific.
The axis of the ridge will remain offshore, leading to northerly
flow aloft. Another thermal trough, an area of low pressure
induced by warm air, will continue to strengthen along the
southern OR/northern CA coast Tuesday into Wednesday. This is a
very similar pattern to the one we saw earlier in this week, one
which brings higher than average temperatures to the area (more
typical of June than May), dry weather, and sunny skies.

At lower levels, northerly flow will start to shift NE to
easterly Tuesday through Wednesday. This will set off the Chetco
Effect, where air is funneled down the Chetco River Valley and
warms as its forced down towards sea level, which will result in
warm temperatures for Brookings and the surrounding southern Curry
County coast. Highs look to be in the high 70s to mid 80s through
Thursday, peaking Wednesday. Farther north, more of a due
northerly flow will continue night and morning stratus for the
beaches from Cape Blanco northward. Inland, we`ll continue to see
warm temperatures each day, especially in valleys. Highs in the
80s up to 90 degrees are expected in western, inland valleys,
peaking Wednesday, while east side locations will see high 70s to
low 80s, likely peaking Thursday. Finally, mountainous areas will
see highs in the 60s, warming slightly each day through Thursday.

Model differences increase Friday into the weekend, but generally
agree that the ridge will flatten and move east as a shortwave
trough approaches from the northwest Friday into Saturday. Not a
lot of ensemble members are enthusiastic about any precipitation,
but showers and thunderstorms are possible with this pattern. The
trough will help moderate temperatures Friday into the weekend,
though they`ll remain warmer than average in most areas. A more
progressive pattern with more troughs and transient ridges looks
likely heading into next week.

-CSP

&&

.AVIATION (18Z TAFs)...

Marine stratus remains over the Oregon coast, bringing IFR and
LIFR ceilings. Model guidance suggests that this marine layer may
thin for a couple hours late in the afternoon. Marine clouds will
return this evening and remain through the end of the TAF period.

Other areas of northern California and southern Oregon will
generally remain under VFR conditions through the TAF period. 15-25%
chances of thunderstorms will develop over northern California and
areas east of the Cascades this afternoon. Extra caution may be
necessary around developing cells this afternoon. Thunderstorm
chances will dissipate quickly this evening.

-TAD/BPN

&&

.MARINE...Updated 200 PM Sunday, May 12, 2024...The strengthening
thermal trough will produce gusty north winds and steep wind-
driven seas this evening through Monday morning, with gales and
very steep seas expected by Monday afternoon. The strongest winds
and most hazardous seas will occur in the afternoon, especially
south of Cape Blanco. The thermal trough is forecast to remain in
place throughout the next week, with little day-to-day change.
Small Craft Advisories and Gale Warnings are in effect through
Wednesday, and are likely to be extended, with similar conditions
forecast all the way through next weekend.

-BPN

&&

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

PACIFIC COASTAL WATERS...Small Craft Advisory until 2 PM PDT Monday
     for PZZ350-356-370-376.

Gale Warning from 2 PM Monday to 11 AM PDT Wednesday for PZZ350-
     356-370-376.

&&

$$