772
FXUS66 KMFR 182137
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
237 PM PDT Sat May 18 2024

.SHORT TERM...Temperatures this afternoon will continue warming
to the 60s and low 70s east of the Cascades with 70s in the west
side valleys. The coast and the Cascades will be the cooler spots
with 50s and low 60s. A trough will be passing through central
and eastern Oregon, and isobars are condensed in this area,
indicating an increase in winds. Winds near the Cascades and east
will be evidence of this, especially on ridges, with 15-20 mph
winds and gusts near 20-30 mph this afternoon.

An upper level low will be in southwestern Canada this weekend and
this will dip into the PNW. A 5%-20% chance for rain is
highlighted for Sunday morning and afternoon in the marine waters,
northern Douglas County and the Cascades north of Crater Lake.
Although these chances have been added, overall looking at a few
hundreths to fall at best.

While this trough lowers, a cooldown will come for the day Sunday.
For comparison, temperatures this afternoon are expected to be
slightly above normal near Medford and east with slightly below
normal temperatures west. By Sunday all locations will be 5 to 15
degrees below normal. The spots that will see the largest cooldown
will be east of the Cascades as they`ll go from highs in the low
70s to the upper 50s and low 60s.

By Tuesday an upper low will come from western Canada and this path
will come closer to the western United States coast, so more impacts
will be possible and this will be discussed in the long term.
-Hermansen

.LONG TERM...Tuesday morning through Saturday night.

The extended forecast starts out with an upper level wave pushing
into the Pacific Northwest from the north.  The precipitation
chances increase slightly over northern sections of our forecast
area with northern California remaining dry on Tuesday.  The
probability precipitation currently maxes out around 50 percent over
the high Cascades with lower probabilities east and west of the
Cascades. A cold front will likely accompany this wave and given the
time of year, the chance of thunderstorms should be in the cards.
Right now, the probability of thunder is only about 10 percent for
most of our Oregon areas, although that could increase as more
model data comes in. It seems like the timing is good with the
cold front pushing in the evening, which is during the time of max
heating.

Temperatures trend roughly 5 degrees lower on Wednesday as some of
the cooler air filters in behind the cold front. The upper level low
appears to sit right over us. With very little shear, less potential
instability and cold air aloft, the weather pattern suggests pop up
showers are most likely. The NBM keeps a low 10 to 20 percent chance
of precipitation across sections of the forecast area on Wednesday
with the best chances east of the Cascades and around Douglas
County.

Thursday has a high probability of being a break in the action with
an upper level low departing the area.  The NBM still is holding on
to some low probability of precipitation chances across Oregon.
Perhaps there are a few ensemble members that are keeping the upper
level low around, or perhaps the next low is arriving a little
earlier.

In any case, the most likely solution is another upper level
approaching from the north on Friday with precipitation chances
increasing. The whole forecast area has a 10 to 15 percent chance of
precipitation on Friday afternoon and evening. Some ensemble members
are taking a bit longer to bring the low into southern Oregon and
northern California, whereas a smaller majority has it here on
Friday.

Overall, an active weather pattern with minimal weather impacts is
anticipated in the extended forecast. We`ll have to watch out for
some stronger thunderstorms, although it`s hard to see a lot of
instability building under this cooler north to northwest flow.

-Smith

&&

.AVIATION...18/18Z TAFs...Clear skies and VFR conditions will
continue through this evening for the vast majority of the forecast
area. The main impact to aviation inland from the coast will be
gusty north-northwest winds this afternoon and early evening.

Along the coast, mainly north of Cape Blanco: A slight offshore
component to the wind will likely keep the marine layer at bay
through sunset with gusty north winds being the main impact. After
sunset, stratus with MVFR ceilings will likely surge onshore.

Tonight stratus will surge from the coast into the Umpqua Basin, but
it is unlikely to reach areas farther south. -Wright

&&

.MARINE...Updated 225 PM Saturday, May 18, 2024...A strong
thermal trough along the coast will produce north gales and very
steep wind driven seas south of Cape Blanco through Monday evening.
Conditions will be less severe but still hazardous to small craft
north of Cape Blanco.

Model guidance came in with stronger winds today, and those winds
are starting to materialize in observations this afternoon. As a
result, the hazardous seas warning was replaced with a gale warning
for much of the southern waters. These conditions will be most
severe during the afternoon and evening hours each day through
Monday with both winds and seas easing late at night into the early
morning.

Low pressure approaching from the north will disrupt the thermal
trough by Tuesday with winds diminishing and seas becoming dominated
by longer period swells. -Wright

&&

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

PACIFIC COASTAL WATERS...Small Craft Advisory until 11 PM PDT Monday
     for PZZ350-356-370-376.

Gale Warning until 11 PM PDT Monday for PZZ356-376.

&&

$$