960
FXUS66 KMFR 231142
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
442 AM PDT Thu May 23 2024

...New Aviation Section...


.AVIATION (12Z TAFs)...

VFR conditions are expected through much of this TAF cycle. North
Bend (KOTH) is on the fringe on low clouds, so this site may need
amendments if those clouds advance farther than anticipated (<20%
chance). Otherwise, we are expecting KOTH to go into MVFR by
tonight as low clouds settle in the area. Skies are expected to
generally clear over the land today, but high clouds will
infiltrate over the area later tonight.

-Guerrero

&&

.PREV DISCUSSION... /Issued 305 AM PDT Thu May 23 2024/

DISCUSSION...Satellite imagery early this morning is showing a
clear sky across most of the forecast area. The exceptions are
near the coast and portions of the Umpqua Basin (fog/low
clouds), but also near the Cascades north of Crater Lake and also
in portions of northern/eastern Lake County where patchy
stratocumulus exists. Some high cirrus clouds can also be seen
streaming into NorCal from offshore. The Medford CWA is between
systems today, so after a chilly start, this afternoon will turn out
milder. Most areas will have 5-10F of warming compared to yesterday,
but it`ll be 10-20F higher in the Cascades, including at Crater Lake
National Park. It won`t be nearly as windy as it was yesterday, but
we do expect fairly typical NNW breezes (8-15 mph) this afternoon.

Tonight, some mid and high level clouds will overspread the area,
so it likely won`t be as chilly as it is this morning. Clouds will
lower along the coast as another disturbance arrives in the NW
flow aloft. PoPs are mostly negligible through the overnight CWA-
wide, though there is a 20% chance of showers north of Cape Blanco
toward morning.

The associated upper trough will swing across the area on Friday.
Since there is likely to be more cloud cover and scattered
showers, it won`t be as warm as today, except perhaps the far east
side where highs will be near or perhaps a couple of degrees
higher than today. Gusty WNW breezes are expected to kick up again
in the afternoon, especially east of the Cascades. While most of
the activity across the area will be showers (and of the hit-or-
miss variety), weak instability over the east side (~100-200 J/KG)
and 850 LI`s of -2 could be just enough to initiate a
thunderstorm or two. So, a slight chance of thunderstorms (~20%)
has been maintained in the official forecast for Friday pm/eve.
Models show the upper trough/cold front pushing east of the
Cascades late Friday night into Saturday morning, but shower
chances continue across north and west sections and also the far
east side. Saturday will be another cooler than normal spring day
with decreasing PoPs and increasing sunshine. The high temperature
trend will be near or slightly lower (2-5F) compared to Friday.

With a clearing sky and easing winds, we expect a chilly night
Saturday night. Lows in the mid to upper 30s are expected in the
colder valleys of the west side. So, while not too large a concern
for frost just yet, keep checking temperature forecasts if you
have sensitive vegetation.

High pressure will build into the area for the remainder of the
Memorial Day weekend, with temperatures jumping back to above
normal levels. Expect mainly sunny, warm afternoons with highs in
the 70s and 80s, except at the coast where highs will be in the
low to mid 60s. Models show WSW flow aloft on Tuesday with a weak
upper trough offshore poised to move onshore. This should maintain
a mostly dry forecast, though isolated showers could visit the
coast and the Cascades. We might also be considering the potential
for isolated showers/thunderstorms over far SE sections for the
pm/eve, but that is a long shot (<10% chance) at the moment.

Substantial uncertainty continues in the forecast from Wednesday
through late next week. Some guidance rebuilds a weak upper
ridge, which would bring a more significant warm up, but a higher
percentage of of the ensembles/clusters brings the offshore upper
trough into western Canada/PacNW to keep things a bit on the
cooler side (closer to normal) with scattered showers, mainly
across the north. -Spilde

AVIATION...23/06Z TAFs...Patchy fog and/or low clouds could
result in some lower MVFR/IFR conditions this morning in Douglas
and Coos counties; otherwise, fairly quiet and non-impactful
aviation conditions are expected through Thursday. -Spilde/Sandler

MARINE...Updated 230 AM Thursday, May 23, 2024...Seas are expected
to gradually ease through the rest of this morning/today and later
tonight, but northwest/northerly wind speeds nearshore south of Cape
Blanco will be around 25 knots today and tonight. Another low
pressure system approaching the region Friday will produce light
rain, and will also bring in a fresh swell Friday night into
Saturday. Seas may become hazardous to smaller vessels Friday night
through Saturday night. At this time, we are holding off issuing
headlines given only moderate confidence (low/moderate/high), but
all of the waters may end up needing a headline to account for this
threat. Then we see another ease in conditions through about mid-
week. By Wednesday, seas may become more chaotic once again as
strong northerly winds develop within a thermal trough.

-Guerrero

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Frost Advisory until 8 AM PDT this morning for ORZ024-026.

CA...None.

PACIFIC COASTAL WATERS...None.

&&

$$