370
FXUS66 KMFR 240522
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
903 PM PDT Thu May 23 2024

.UPDATE...Updated aviation and marine discussions.

&&

.DISCUSSION...Skies are mostly clear out there this evening as
the sun sets. Current satellite imagery is showing a little bit of
wispy cirrus over southwest OR/northwest CA this evening, and the
cumulus that developed over higher terrain this afternoon is
starting to dissipate. Our next weak frontal system is still well
offshore at the moment, and the marine layer stratus is also
hanging out over the east Pacific about 60-70 miles offshore. A
few minor edits were made to the forecast to reflect the fact that
increased cloudiness from the incoming front and associated marine
push inland are now expected later tonight. Otherwise, the
forecast is progressing as expected. For more details, see the
previous discussions below. -CSP

&&

.AVIATION...24/06Z TAFs...VFR conditions are expected to continue
through the TAF period for inland areas, with breezier afternoon and
evening winds at all terminals.

An approaching weak frontal system looks to push the marine layer
and its accompanying lower stratus, currently well offshore, inland
ahead of it tonight. A brief period of MVFR conditions along the
northern Curry and Coos county coasts is likely later tonight.
Northwesterly breezes will pick up ahead of the front in the early
afternoon and continue into the evening as the front approaches, but
winds won`t be as significant as the system that passed through
earlier this week.

Showery, spotty precipitation will move onshore and inland Friday
afternoon and evening. Best chances will be in northern portions of
the region (northern Douglas, Coos, Klamath, and Lake counties) as
well as along the south OR Cascade crest. Additionally, there is
about a 10-15% chance for isolated thunderstorms developing later in
the afternoon into the evening in southern and eastern Lake and
Modoc counties. -CSP

&&

.MARINE...Updated 845 PM Thursday, May 23, 2024...North winds will
gradually diminish in the expansion fan where Small Craft Conditions
are being observed. The current Small Craft is due to end at 11 pm
pdt with a brief break in the action until Friday afternoon. A weak
front will move through the waters with moderate northwest winds
with gusts up to 25 kts possible from Friday evening through
Saturday morning. Steep seas are expected in all waters, with
another Small Craft Advisory covering for all of the waters Friday
at 5 PM until Saturday at 5 PM pdt.

Past Saturday evening, upper level stability will guide conditions
into the middle of next week. Currently calm seas are forecast from
Saturday evening through at least next Tuesday. -TAD/Petrucelli

&&

.PREV DISCUSSION... /Issued 443 PM PDT Thu May 23 2024/

DISCUSSION...Temperatures will cool off the next few days as
another trough of low pressure sweeps through the region on
Friday. Both the forcing and the moisture associated with the
trough will be weak, so rain shower activity will be light, and
mainly west of the Cascades in mountainous areas; relying on
orographic ascent to help fuel them. There are only isolated
pockets on the eastern Douglas County and Northern Klamath county
where more than 0.1" of liquid precipitation is expected from
these showers; and in these areas, we expect rain and snow to mix
as the snow level will be around 4000 to 4500 feet. East of the
Cascades there is a widespread 10-20% chance for an isolated
thunderstorm. Given the lack of moisture, we would expect any
thunderstorm activity to be on the drier side, with rain only
under its core. Better chances for thunderstorm activity will be
to the east and northeast of Lake County.

Winds with this Friday system will cause the general flow to be from
the west, but elevated winds are only expected east of the Cascades
and won`t amount to much more than an enhancement of the typical
afternoon gusts. Instead, the widest ranging impact will be the
increase in humidity Friday afternoon and night.

After this trough exits the region Friday night, high pressure will
build in and we will enter a warming and drying period from Saturday
through about Tuesday. Temperatures will climb into the 80s and even
90s for much of the region, while east flow at night brings drier
air in. The windiest day of this pattern is expected to be Saturday,
while the driest should be Monday. Overall, there isn`t much model
spread in this system and this should be a quiet period overall
weather wise. The biggest unknown at this time is which nights
fog forms and where, if at all.

Some disruption to the high pressure is expected at this time
midweek, and the most likely outcome is that the disruption is weak
and short lived.
-Miles

AVIATION...24/00Z TAFs...VFR conditions will continue across
northern California and southern Oregon, with winds decreasing
overnight. An approaching upper trough will bring MVFR ceilings to
the Oregon coast Friday morning, with those ceilings moving east
through the TAF period. Gusty westerly winds will develop across
areas east of the Cascades on Friday afternoon. Precipitation
chances (30-60%) will be mostly limited to the coastal ranges and
the Cascades. Slight thunderstorm chances (5-10%) will develop over
Lake and Modoc counties near the end of this TAF period and will
increase later Friday evening. -TAD

MARINE...Updated 230 PM Thursday, May 23, 2024...Gusty northerly
winds are developing over waters south of Cape Blanco and within 50
nm from shore, with sustained speeds of 15 to 25 kts and gusts up to
35 kts near Brookings. Wind-driven steep seas are expected to build
this evening, and a Small Craft Advisory will be in place from 5 PM
until 11 PM this evening to communicate these hazardous conditions.

Calm seas will briefly return Friday morning ahead of an upper level
trough arrives in the afternoon. Showers will be possible near the
Oregon coast and north of Cape Blanco. The trough will bring
elevated northwest winds over all waters, with gusts up to 20 kts
possible from Friday evening through Saturday morning. Steep seas
are expected in all waters, with another Small Craft Advisory
covering from Friday at 5 PM to Saturday at 5 PM covering the likely
duration of steep seas.

Past Saturday evening, upper level stability will guide conditions
into the middle of next week. Currently calm seas are forecast from
Saturday evening through at least next Tuesday. -TAD

&&

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

PACIFIC COASTAL WATERS...Small Craft Advisory until 5 AM PDT Friday
     for PZZ350-356-370-376.

&&

$$