233
FXUS66 KMFR 131136
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
436 AM PDT Tue Aug 13 2024

...Updated AVIATION discussion...

.DISCUSSION...An upper short wave trough is swinging through
eastern Oregon early this morning. This system was able to trigger
some convection over portions of our forecast area last evening,
but all of the shower/t-storm activity has shifted to the north
and east. We are moving into a stable pattern this morning and
today should be quiet weather-wise. Morning satellite imagery is
showing most of the area devoid of cloud-cover, though some
stratus is over the marine waters and portions of Coos/northern
Douglas counties. These should erode later this morning and this
afternoon with mostly sunny skies just about everywhere. High
temperatures will largely range from 75-85F, slightly cooler at
the beaches and in the mountains, and slightly higher in the lower
Klamath River Valley of western Siskiyou County. Not bad for mid-
August. Just about the only thing keeping this from being a
banner mid-late summer day will be the smoke/haze from area
wildfires. This will be most prevalent from eastern Douglas,
northern Jackson into northern Klamath and Lake counties, but also
portions of Siskiyou County (due to the Boise fire). Oregon DEQ
has some air quality advisories out and we have relayed those via
AQAMFR.

We`ll remain under the influence of an upper trough for the
foreseeable future. As such, we are very confident that the
pattern of cooler (than normal) temperatures will continue.
Another short wave disturbance will move in on WSW flow aloft on
Wednesday. Models are showing modest instability and best moisture
from the Cascades over to the east side, but also extending down
into portions of NorCal, where we expect a chance of showers
(25-40%) and isolated thunderstorms (<25% chance). This system
will slow down as it moves through Oregon Wednesday night into
Thursday, so this will keep the risk of showers and thunderstorms
going. SPC SREF guidance is showing a higher likelihood of
thunderstorms Thursday afternoon as the low pivots east of the
Cascades by evening. Highest probabilities (25-35%) are in
northern Klamath/northern Lake counties centered on the Christmas
Valley. West side areas mostly miss out on shower/thunder
potential, but there is a slight chance (~15%) especially for
areas east/south of Medford. Expect nightly marine intrusions
on the coast through Thursday night.

On Friday, NBM is still showing some shower potential (20-30%)
from the Cascades eastward and mainly in Oregon, but we should be
on the back side of the Thursday trough and also still awaiting
the next trough/low taking shape offshore. With a lack of
forcing, I wouldn`t be surprised to see those chances drop out of
the forecast over the next few shifts.

An upper low is forecast to develop off the PacNW coast and
remain nearly stationary (wobbling around 130W) this weekend into
early next week. This should keep upper ridging locked in over
the Four Corners/Texas, while also keeping our area in a cooler
than normal pattern. Subtle changes in position/strength of this
upper low can and will play a role in if, when and where
additional showers/thunderstorms set up, so be on the lookout for
daily forecast changes. But, it doesn`t look overly wet or hot
any time soon. -Spilde


&&

.AVIATION...13/12Z TAFS...Marine stratus remains offshore tonight,
with only brief moments of higher clouds observed over North Bend.
Guidance suggests that periods of MVFR are possible but unlikely
through the rest of the morning. There`s also some agreement that a
marine layer is more likely towards the end of the TAF period.

Inland areas will mostly be VFR through the TAF period. Smoke from
the eastern Douglas county area may blow moderate to heavy smoke
west over northern Lake and Klamath counties, and light to moderate
smoke will drift to the south. Some of this smoke may reach Klamath
Falls early Wednesday morning and could impact airport visibilities,
but smoke models suggest only light amounts of smoke will reach that
far south. -TAD

&&

.MARINE...Updated 200 AM Tuesday, August 13, 2024...Light winds and
gentle north-northwest swell will keep seas below advisory levels
through the week. Swell may increase by 1 to 2 feet near the end of
the week, with long-term guidance showing a 20-30% chance of seas
exceeding 6 feet on Saturday. Those chances disappear on Sunday,
reinforcing that the sea state will be uneventful through the
beginning of next week. -TAD


&&

.FIRE WEATHER...We`re in a period of low fire weather risk due to
the influence of upper troughing near and just offshore of the
PacNW. That isn`t to say there won`t be any fire weather concerns
the next several days, but since it will be cooler with higher
humidities (at least compared to normal), there is less risk than
there typically would be for this time of year. Today we don`t
have any significant fire weather concerns, except for fairly
typical afternoon/evening diurnal breezes that will allow
existing fires to awaken after laying down during the night and
early morning. A short wave trough is expected to push onshore
Wednesday evening through Thursday evening and this will bring a
decent chance of showers and thunderstorms, mainly from the
Cascades eastward. Models are pegging Thursday as the most active
day, especially in northern Klamath/Lake counties, where
instability is greatest as the upper trough pivots east of the
Cascades. Aside from gusty outflow winds near thunderstorms, we
aren`t anticipating any unusually strong winds through the end of
the week. Friday there should be a break as another low develops
offshore and the Wed-Thu trough exits to the east.

With the high likelihood of the low remaining near and just off
the PacNW coast through the weekend, we should remain near to
below normal temperature-wise with above normal humidity, though
there is some potential for the low to be just far enough offshore
for temps to moderate a bit Sat. Since there is still some
uncertainty with just where the low will set up, some details are
likely to change, so stay tuned. -Spilde

&&

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

CA...None.

PACIFIC COASTAL WATERS...None.

&&

$$

MAS/TAD