031
FXUS66 KMFR 162327
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
427 PM PDT Fri May 16 2025

.UPDATE...Aviation Discussion.


&&

.AVIATION...17/00Z TAFs...A front will move into the area tonight
bringing light rain, mountain obscurations and increasing MVFR
and local IFR conditions. Along the coast, VFR will transition to
a mix of MVFR and IFR early this evening around 01-03z, then a mix
of MVFR/IFR will persist tonight through Saturday morning.
Inland, VFR conditions will persist through early this evening,
then MVFR will spread inland around 05-11z and persist through
Saturday morning. MVFR conditions will be widespread across much
of southern Oregon along with local IFR and widespread mountain
obscurations. Across northern California, expect a mix of VFR and
MVFR conditions tonight through Saturday morning.

Also, there is a slight chance (15-20%) of thunderstorms late
tonight through Saturday afternoon for Lake County and eastern Modoc
County, including Lakeview. This risk will reach a peak during
Saturday afternoon over the Warner Mountains.

Ceilings will gradually lift Saturday afternoon, transitioning to
mainly VFR expect with continued showers, expect areas of MVFR to
linger through the day.

&&

.PREV DISCUSSION... /Issued 253 PM PDT Fri May 16 2025/

DISCUSSION...Cloud cover is rebuilding this afternoon ahead of
an approaching upper trough. The first impacts from this
approaching system will be thunderstorm chances developing east of
the Cascades late tonight into early Saturday morning. The best
chances (10-15%) will be across Modoc and southern Lake counties,
with lesser chances (5-10%) covering eastern Klamath and northern
Lake counties. Any thunderstorms that develop are likely to be
isolated and remain below severe thresholds. Thunderstorm chances
increase to 15-20% across Lake and Modoc counties on Saturday
afternoon before decreasing through Saturday evening and night.
Other areas are expected to see at least light showers at some
point between Saturday morning and Sunday afternoon. Overall
amounts will be unimpactful. Coos County, the Cascades, areas
around and east of Lakeside, and the Warner Mountains are expected
to see between 0.25 and 0.50 inches of rainfall. Occasional snow
showers are possible over the Cascades early Sunday morning, but
accumulation is not expected. The Umpqua Valley may see 0.10
inches of rainfall, and other areas will have rainfall measured in
the hundreths. Temperatures will cool through the weekend as the
trough moves over the area.

Seasonal temperatures under zonal flow aloft look to continue
through the week. A couple of weak disturbances may briefly affect
conditions for certain locations. On Monday, a weak front could
bring some clouds to Coos and eastern Douglas counties. Brief
showers are possible over these areas on Monday morning and
afternoon, but amounts will be one or two hundreths at most. On
Wednesday or Thursday, a weak disturbance could bring gusty winds
and isolated showers to the northernmost border of the CWA.
Deterministic guidance for both the ECMWF and the GFS show some
upper instability passing over the area, with some variation in
timing and structure. Individual ensemble members for both the GFS
and ECMWF are split on showing the disturbance or not, and those
that show it do so with some variation in timing and location.

Zonal flow continues on Friday, with some uncertainty for the
weekend. While both models show some amount of upper level ridging,
the strength and position of the ridge vary. The general expectation
seems to be additional warming on Saturday and Sunday, but little
overall consensus on how warm next weekend will be. NBM
probabilistic guidance echos this uncertainty, with daytime highs
forecast to be from seasonal temperatures to 10 degrees above on
next Sunday. -TAD

MARINE....Updated 200 PM Friday, May 16, 2025...A trough will
produce light showers with moderate winds and moderate swell
dominated seas tonight through Sunday morning. Northwest winds will
be strongest Saturday evening south of Brookings. Another seasonable
system will follow on Monday with winds veering from south to
northwest. Northerly winds will increase on Tuesday from the brief
development of a thermal trough near shore. Meantime, building seas
on Tuesday may possibly becoming high and steep with the combination
of the higher wind waves and a building west-northwest swell at 13
seconds. Conditions are likely to improve slightly on Wednesday.
-DW

&&

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

CA...None.

PACIFIC COASTAL WATERS...None.

&&

$$