758
FXUS66 KMFR 070340
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
840 PM PDT Mon May 6 2024

.DISCUSSION...The frontal system that arrived early this morning
has made it most of the way out of our region this evening, though
scattered showers linger, especially over the northwest portion.
These will continue to wind down overnight into tomorrow
(Tuesday) morning as ridging builds in aloft, lingering longest
over the Cascades and eastern Douglas County. Cloud cover will
also gradually be breaking up through this period, and many areas
will see clear skies by the end of the day. After another cool
morning, high temperatures tomorrow afternoon will be a few
degrees warmer than today`s, and a northwest afternoon breeze will
set up as the day progresses. For more information about the
forecast, see the previous discussion below.

-CSP

&&

.AVIATION (00Z TAFs)...

North Bend will have to deal MVFR ceilings for the next several
hours before conditions return to VFR. Otherwise, the other
terminals are forecast to remain in VFR through this cycle, but
please note ceilings for both Medford and Roseburg will be close
to MVFR at times. We will put both of these terminals around a 40%
chance at seeing MVFR conditions through this cycle, so given the
proximity to categorical changes, we will take a close look at
subsequent TAFS. The big question for tonight is low level
saturation and fog/BR potential. For now, confidence was not high
enough to include due to vicinity of upper level disturbance.

&&

.MARINE...Updated 800 PM Monday, May 6, 2024...A thermal trough will
strengthen Tuesday afternoon; as a result, north winds will become
gusty and steep wind-driven seas will develop--highest south of Cape
Blanco. Wind speeds will peak during Wednesday afternoon/evening,
but gusty northerly winds will persist into Thursday night. During
this stretch (Wed-Thu), gale force winds are likely (85% or greater)
across our southern waters. Given these conditions, a Gale Watch for
areas from roughly Port Orford southward is in effect. The strength
of the thermal trough has trended stronger as new data comes in.
Consequently, a hazardous seas watch is in effect for all remaining
areas north of the Gale Watch, and we are considering expanding the
gale watch north of Cape Blanco. The thermal trough will weaken
Friday into next weekend resulting in weaker north winds and lower
seas.

-Guerrero

&&


PREV DISCUSSION... /Issued 240 PM PDT Mon May 6 2024/

SHORT TERM...Through Wednesday morning...Scattered showers
continue across northern California and southern Oregon this
afternoon as an upper trough moves over the area. Currently, most of
the activity is over Jackson and eastern Douglas counties. Radar is
showing sporadic pixels of 40 dBZ reflectivity over northern Lake
County, indicating instability present in the area. Model guidance
does have a 15-25% chance for thunderstorms over most of southern
Oregon through this afternoon, with lower 5-10% chances over
Siskiyou, Modoc, and southern Klamath counties. These thunderstorm
chances will dissipate overnight.

Post-frontal showers will keep 40-60% shower chances over the
Cascades tonight, but amounts will be negligible. Cold nighttime
temperatures will continue tonight into Wednesday morning, with low
40s along the Oregon coast, mid to high 30s for west side valleys,
and mid to high 20s east of the Cascades. Near freezing temperatures
remain in the Shasta and Scott valleys tonight, but a Freeze Warning
has not been issued for tonight. That product addresses duration as
well as temperature, and the confidence in meeting duration
thresholds is not high. Additionally, temperatures may be warmer
than expected if cloud cover persists into the night. Localized
areas may still experience periods of freezing or below
temperatures, so extra caution with plants and animals is encouraged.

Tuesday is expected to be calm across the area during a transition
from active to stable weather under upper level ridging.
Temperatures west of the Cascades are expected to be in the mid 50s
to low 60s, while they will stay in the low 50s east of the
Cascades. Any lingering showers should clear out by Tuesday
afternoon. Gusty winds will develop in eastern Lake County, gusting
to 25-30 mph before calming overnight. Colder temperatures will
continue Tuesday night as well, with similar expectations of near
freezing conditions in the Shasta and Scott valleys into early
Wednesday morning. -TAD

Long Term...Wednesday (5/08) through Monday(5/13)...

High pressure will be the rule throughout the entire extended term,
with dry and very warm conditions expected for all of southern
Oregon and far northern California.

Upper level ridging will build into the region from the eastern
Pacific on Wednesday, with a thermal trough developing over
California and far southwestern Oregon. The thermal trough will then
strengthen and extend northward along the coast through Thursday
night, creating generally east winds through the remainder of the
week. Meanwhile, the upper level trough that passed over the area
earlier in the week will retrograde, moving back to the west and
setting up over the Great Basin, just south of the ridge, which by
this time will extend across the Pacific Northwest and into the
northern Rockies, creating east winds aloft that will correlate and
enhance the east winds at the surface. All of this will result in
very warm temperatures through at least the first part of the
weekend, with a strong Chetco effect likely along the southern coast
near Brookings. This pattern begins to break down over next weekend,
which may allow a weak trough to enter the area early next week.

With all of this in mind, many changes were made to the forecast to
adjust temperatures and winds to fit the expected pattern. The
Chetco Effect will begin Wednesday ,then peak on Thursday, with
highs in Brookings expected to reach the 80s (and a few models even
suggest 90 degrees is possible) Thursday afternoon and perhaps
Friday as well. When the thermal moves inland, the south coast will
begin to cool as the marine layer regains control, while
temperatures for most inland areas will reach their warmest Friday
afternoon or Saturday afternoon. For these areas, high temperatures
will be more in line with early July than early May. Forecast
temperatures were adjusted to fit this thinking, while also
considering the strong inversions and warm ridgelines that this
pattern typically produces during the overnight and early morning
hours.

Once the thermal trough moves inland, the prevailing flow will take
on a more westerly onshore component, and temperatures will begin to
gradually cool Sunday and Monday. Some models suites suggest the
possibility of a weak front arriving around this time, but given the
warm and dry conditions ahead of it, any frontal passage will most
likely remain dry. -BPN

AVIATION...06/18Z TAFs...MVFR ceilings are affecting the coastal
terminals early this morning and these conditions will remain
through about 21z before more consistent VFR conditions set in. This
front will cause showers over inland areas eastward to the Cascades
through late this afternoon/early this evening. Many higher terrain
areas will be obscured. Scattered showers over NorCal are also being
observed on radar from Mt. Shasta west and will continue through
this TAF period. VFR will prevail, though may briefly lower to MVFR
in showers. Gusty WSW winds are expected east of the Cascades,
including at Klamath Falls this afternoon, where peak gusts of
around 30 kt are expected.
-Spilde/Miles

MARINE...Updated 150 PM Monday, May 6, 2024...lingering fresh
swell and incoming northwest swell dominate the sea state at the
moment. Winds will remain out of the northwest through this evening,
becoming more northerly overnight. A thermal trough will strengthen
Tuesday afternoon with north winds becoming very gusty and steep
wind-driven seas develop, highest south of Cape Blanco. Wind speeds
will peak during Wednesday afternoon/evening, but gusty northerly
winds will persist into Thursday night. During this stretch (Wed pm-
Thu), gale force, especially across the southern waters are very
likely (90% or more). As such, we have issued a gale watch for areas
from roughly Port Orford southward. As new data comes in, the
strength of the thermal trough has been growing. We have added a
hazardous seas watch to all remaining areas and are considering
expanding the gale watch north of Cape Blanco. The thermal trough
will weaken Friday into next weekend resulting in weaker north winds
and lower seas. -Spilde/Miles

&&

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

PACIFIC COASTAL WATERS...Small Craft Advisory from 2 PM Tuesday to 11
     AM PDT Wednesday for PZZ356-376.

Gale Watch from Wednesday morning through late Wednesday night
     for PZZ356-376.

     Hazardous Seas Watch from Wednesday morning through late
     Wednesday night for PZZ350-370-376.

&&

$$