212
FXUS66 KMFR 050525
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
1025 PM PDT Sat May 4 2024

...New Aviation Section...


.AVIATION (06Z TAFs)...

Precipitation has diminished across the region, but expecting
isolated showers to pick back up around sunrise and continue
through the day. The hard part is timing if the terminals will be
impacted or not, but due to isolated nature will go with vicinity
mention for now unless it becomes clearer for impacts at the
terminals. Otherwise, terminals should be mostly VFR with stints
of MVFR. Confidence was not high enough to introduce IFR at this
time, but low level saturation could lead to brief periods of IFR
and may need to be reevaluated tonight if confidence increases in
timing.

-Guerrero

&&

.PREV DISCUSSION... /Issued 839 PM PDT Sat May 4 2024/

DISCUSSION...An upper low is moving onshore into the region this
evening as our recent wet front finally exits. Precipitation has
become scattered and showery this evening. Showers will start to
decrease in coverage tonight but see a re-surgence tomorrow
(Sunday) morning as the low spins another round of moisture into
the region. Cold temperatures from the low will lead to snow
levels continuing to fall slightly to 2,500-3,000 feet early
Sunday morning before rising again Sunday afternoon. This will
also lead to chilly morning temperatures, and a Freeze Warning for
the Shasta and Scott valleys in northern CA is in place from 2 AM
to 8 AM Sunday. For more details, please see the previous
discussion below. -CSP

AVIATION...05/00Z TAFs...A strong frontal system has mostly passed
through the region this afternoon, but low pressure following the
main frontal band will lead to intermittent, showery precipitation
continuing for most of the weekend. Widespread MVFR conditions and
terrain obscurations are expected to continue, though some
improvement to VFR tonight is expected in areas, including the Rogue
Valley. This improvement may not be linear, with conditions bouncing
between MVFR and VFR. Snow levels will continue to lower this
evening and tonight, and rain showers will transition to snow east
of the Cascades. Winds will continue to be gusty along the coast and
east of the Cascades with the low pressure. Precipitation will begin
tapering off later Sunday afternoon and conditions are expected to
improve area wide. -CSP

MARINE...Updated 830 PM Saturday, May 4, 2024...Showers will
dissipate through this evening, with a very low chance for a
thunderstorm before sunset. Isolated showers are expected to
redevelop tomorrow around sunrise and go throughout the day.
Moderate west winds and steep fresh short period west swell will
continue through tonight, then southwest winds increase Sunday
ahead of another front that will move through late Sunday night
into Monday. Seas are likely to remain elevated Monday night into
Tuesday with building west-northwest swell. After that, we expect
high pressure to build in mid-late next week with a thermal trough
strengthening along the coast. This will bring a return of
stronger north winds and steep seas, highest south of Cape Blanco.

PREV DISCUSSION... /Issued 234 PM PDT Sat May 4 2024/

SHORT TERM...Through Tuesday morning...A low pressure system
continues to bring activity across northern California and southern
Oregon. Reports have indicated 2 to 3 inches of rain along the
Oregon coast in the past 24 hours, as well as 4 inches of snow in
areas around Mount Shasta. The main band of rainfall is moving
across Klamath and Lake counties while scattered showers continue
west of the Cascades. Existing daytime hazards have all expired, as
elevated winds over east side areas have slowed and the heaviest
snowfall over western Siskiyou County and the Cascades has passed.

Other hazards will continue through the night. Instability from the
low pressure system brings the possibility of thunderstorms through
the night tonight. Current chances are at 20-25% across areas west
of the Cascades, with lower 10-20% chances to the east. These
chances will remain into the last hours of Saturday before
decreasing through Sunday morning.

Additionally, a Freeze Watch has been elevated into a Freeze Warning
for the Shasta and Scott Valleys in Siskiyou County. Temperatures in
these valleys are forecast to be in the high 20s to low 30s tonight
into early Sunday morning. The Freeze Warning will be in place from
2 AM until 8 AM on Sunday morning. Other areas, including the
Illinois Valley and the southern Rogue Valley, may see temperatures
at or near freezing. But the possibility of substantial periods of
freezing temperatures are low (10-20%), so warnings were not issued
for these areas. Near-freezing temperatures in the mid-30s are
forecast, so extra care for sensitive plants and animals may still
be beneficial.

The low pressure system will follow the Oregon-California border
through Sunday, keeping cooler temperatures and precipitation in the
Forecast for Sunday. Snow levels are expected to rise to about 4000
feet, limiting snowfall to the Cascades and the highest terrain to
the east. Thunderstorm chances are not in the forecast.

A warm front will follow behind the low pressure system on Monday,
bringing another round of precipitation across the area. This front
looks to be non-impactful, with some limited thunderstorm chances
over Klamath and Lake counties on Monday evening. Precipitation
will be highest over the Cascades, with 3 to 6 inches of snow
forecast over the Cascades and unremarkable rainfall amounts over
lower elevations.
-TAD

Long Term...Tuesday (05/07) through Saturday (05/11)...The
extended period starts as "third winter" comes to an end, and a
familiar pattern of high pressure builds in. During this period of
high pressure strong, gusty north winds will be present along the
coast and east winds will develop inland. The warm bubble around
Brookings due to the Chetco effect is expected to be on display at
the end of the work week.

This diurnal pattern of wind flow will bring in drier air to the
region, but the magnitude of the warmth will be limited. The current
forecast calls for the heat to peak either Friday or Saturday in the
low to mid 80s and overnight lows barely scraping into the upper 40s
or low 50s. The reason for this low peak in high temperatures
appears to be a retrograding low pressure center, which is expected
to undercut the ridge as it moves in from around Utah.

-Miles

AVIATION...05/00Z TAFs...A strong frontal system has mostly passed
through the region this afternoon, but low pressure following the
main frontal band will lead to intermittent, showery precipitation
continuing for most of the weekend. Widespread MVFR conditions and
terrain obscurations are expected to continue, though some
improvement to VFR tonight is expected in areas, including the Rogue
Valley. This improvement may not be linear, with conditions bouncing
between MVFR and VFR. Snow levels will continue to lower this
evening and tonight, and rain showers will transition to snow east
of the Cascades. Winds will continue to be gusty along the coast and
east of the Cascades with the low pressure. Precipitation will begin
tapering off later Sunday afternoon and conditions are expected to
improve area wide. -CSP

MARINE...Updated 200 PM Saturday, May 4, 2024...Showers will
dissipate through this evening, with a very low chance for a
thunderstorm before sunset. Moderate west winds and steep fresh
short period west swell will continue through tonight, then
southwest winds increase Sunday ahead of another front that will
move through late Sunday night into Monday. Seas are likely to
remain elevated Monday night into Tuesday with building west-
northwest swell. After that, we expect high pressure to build in mid-
late next week with a thermal trough strengthening along the coast.
This will bring a return of stronger north winds and steep seas,
highest south of Cape Blanco. -BPN

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...CA...Freeze Warning from 2 AM to 8 AM PDT Sunday for CAZ080-081.

PACIFIC COASTAL WATERS...Small Craft Advisory until 8 PM PDT Monday
     for PZZ350-356-370-376.

&&

$$