764
FXUS66 KMFR 080531
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
1031 PM PDT Tue May 7 2024

Updated AVIATION Section

.DISCUSSION...A couple of low-topped (read: weak) showers are
currently ongoing in Douglas County with satellite showing some
cloud cover along the Cascades, Douglas County, the Rogue-Umpqua
Divide, and Lake County. These showers and clouds will continue to
dissipate overnight as a ridge of high presure begins to build
overhead. Freezing temperatures are expected for some West Side
Valleys, and a Freeze Warning remains in effect. Please see the
NPWMFR for more details.

Otherwise, for more information on the forecast, please see the
previous discussion below. -Schaaf

&&


.AVIATION...08/06Z TAFs...Expect VFR to prevail tonight through
Wednesday, though areas of MVFR are possible in portions of the
Umpqua Basin and Coquille Basin overnight into Wednesday morning.
These shouldn`t last much longer than 16 or 17Z Wednesday morning.
Expect gusty north to northeast winds again Wednesday afternoon,
peaking at 20 to 25 kt in Roseburg/Klamath Falls and around 30 kt at
North Bend, easing during the mid-late evening. -Spilde


&&

.MARINE...Updated 845 PM Tuesday, May 7, 2024...A thermal trough
will allow strong north winds and steep to very steep seas to expand
northward tonight into Wednesday. Worst conditions are expected
south of Cape Blanco with gales and very steep, wind-driven seas
Wednesday afternoon through early Thursday morning. Gusty north
winds and very steep seas are expected north of Cape Blanco. Current
models show a high chance (50 to 100%) for north gales from Cape
Blanco southward, highest (70 to 100%) beyond 5 nm from shore south
of Gold Beach. The thermal trough will weaken Thursday, but
lingering steep to very steep seas are possible. Lighter winds and
seas expected Friday into the weekend. -CC/Spilde


&&

.PREV DISCUSSION... /Issued 441 PM PDT Tue May 7 2024/

SHORT TERM...through Wednesday (5/8) night...Ongoing shower
activity north of the Umpqua Divide will gradually wind down this
evening. Afternoon temperatures are quite similar to recent days,
running about 10 to 15 degrees below normal for early May. Upper
level ridging will build into the region tonight and a thermal
trough will develop at the surface. Cloud cover will linger
against the terrain tonight, but where skies clear, temperatures
will drop. There are freeze concerns for those areas that clear,
and a Freeze Warning has been issued for the valleys of
Siskiyou/Josephine/Jackson counties. Lingering cloud cover could
limit the extent of freeze concerns tonight, but there is about a
40- 70% chance of low temperatures reaching 32 degrees for the
Illinois and Applegate Valleys. Confidence is higher for the
Shasta and Scott Valleys in Siskiyou County where skies are
already clear and we don`t anticipate additional cloud cover.
Chances of freezing temperatures in those locations jump to around
70-90%.

After a chilly start Wednesday morning, afternoon temperatures will
trend warmer by about 10 degrees across the area. Any lingering
cloud cover will give way to sunny skies for all areas for Wednesday
afternoon. The thermal trough will strengthen along the coast and
induce the Chetco Effect, bringing warm temperatures to the southern
Coast. Expect highs in the upper 60s/low 70s for areas west of the
Cascades and upper 50s/low 60s for areas east of the Cascades. High
pressure will continue to strengthen over the region for the latter
half of the week, and this trend in warmer temperatures will
continue into the extended period. /BR-y

LONG TERM...Thursday (5/09) through Tuesday(5/14)...

High pressure will be the rule for the majority of the extended
term, with dry and very warm conditions expected for all of southern
Oregon and far northern California, with a few possible exceptions.

Upper level ridging will extend north and east into the Pacific
Northwest Thursday, with a thermal trough north from California and
along the southern Oregon coast, 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, creating east winds aloft that will enhance and
align with the east winds at the surface. All of this will result in
very warm temperatures through the end of the week and into the
first part of the weekend. As a result, a strong Chetco effect is
forecast for the southern coast near Brookings. This pattern begins
to break down late in the weekend, which may allow a weak trough to
enter the area early next week, introducing a slight chance of
afternoon thunderstorms.

This will, in effect, produce the warmest stretch of days so far
this season. The Chetco Effect will 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 and
Saturday afternoon. For these areas, high temperatures will be more
in line with early July than early May, with highs 10 to 20 degrees
above normal for this time of year. We also expect strong inversions
and warm ridgelines overnight, which this pattern is known
to typically produce.

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 as a weak trough enters the region
from the northwest, followed by a weak trough nudging in from the
southwest. These features could be enough to tap into afternoon
instability, resulting form the warm temperatures and a slight
uptick in atmospheric moisture, resulting in a thunderstorm or two
across Siskiyou and Modoc counties, and perhaps even into some of
far southern Oregon. This is a pattern known to produce convection,
and roughly 33 percent of all the model solutions are depicting this
solution, including the bulk of the deterministics, so confidence
this far out is moderate. The NBM is not impressed, but typically
lags the GFS and ECMWF by a day, so suspect it will come more in
line with this thinking by next cycle. -BPN

AVIATION...08/00Z TAFs...NNW breezes this evening will subside
around sunset. Expect VFR to prevail through Wednesday, though areas
of MVFR are possible in portions of the Umpqua Basin toward sunrise
Wednesday. These shouldn`t last more than a few hours Wednesday
morning. Expect gusty north to northeast winds again Wednesday
afternoon, peaking 20 to 25 kt at Roseburg/Klamath Falls and around
30 kt at North Bend. -Spilde

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Freeze Warning from 2 AM to 10 AM PDT Wednesday for ORZ024-026.

CA...Freeze Warning from 2 AM to 10 AM PDT Wednesday for CAZ080-081.

PACIFIC COASTAL WATERS...Small Craft Advisory until 2 PM PDT
     Wednesday for PZZ350-370.

     Hazardous Seas Warning from 2 PM Wednesday to 5 AM PDT Thursday
     for PZZ350-370.

     Small Craft Advisory until 2 PM PDT Wednesday for PZZ356-376.

     Gale Warning until 5 AM PDT Thursday for PZZ356-376.

&&

$$