081
FXUS66 KMFR 170142
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
642 PM PDT Thu May 16 2024

.UPDATE...Updated the aviation section.

&&

.AVIATION...17/00Z TAFs...VFR conditions prevail for most of the
area. The exception is along the coast north of Cape Blanco where
areas of IFR conditions are occuring. Gusty breezes are present this
evening across the region, strongest near the coast and east of the
Cascades with gusts peaking around 25 kt.

A marine push is expected late this evening and overnight, bringing
an expansion and thickening of marine stratus, with a slight chance
of showers, to the coast and inland into the Umpqua Basin. IFR
ceilings should lift to MVFR along the coast after 09Z as the marine
layer deepens and spreads inland. Expect MVFR ceilings in the Umpqua
Basin that are likely to spill into the Rogue and Illinois Valleys
late tonight. This stratus is expected to clear during Friday
morning. /DW

&&

.MARINE...Updated 200 PM Thursday, May 16, 2024...A thermal
trough pattern, while weaker today, will maintain gusty north winds
and steep to very steep seas through the weekend. Seas will be
steepest and winds will be strongest south of Cape Blanco and during
the afternoons and evenings. With the thermal trough weaker today, a
very brief period of improved conditions is expected north of Cape
Blanco tonight into early Friday. The thermal trough strengthens
again by Friday and steep seas are expected to return north of Cape
Blanco. Given the very brief period of improved conditions, have
decided to just continue the advisory through tonight and into the
weekend. As the thermal trough strengthens Friday, a brief period of
northerly gales is possible late Friday afternoon beyond 15 nm from
shore and south of Pistol River.

The thermal trough will linger through the weekend, maintaining
gusty north winds and steep to very steep seas. Conditions improve
early next week as the upper level pattern changes and the thermal
trough gets disrupted through the first half of the week. /BR-y

&&

.PREV DISCUSSION... /Issued 217 PM PDT Thu May 16 2024/

SHORT TERM...The rest of this afternoon through Friday night...
What a difference a day makes in Brookings! The coastal eddy
(southerly onshore winds near the coast) that formed last night kept
it cloudy and much cooler there today. At this time yesterday (2 pm
PDT), it was 89F. Today, it`s sitting at 57 degrees, 32F lower than
yesterday. The thermal trough that brought the strong offshore NE
winds the last couple of days weakened some today. This resulted in
the eddy and effectively cut off the warming NE winds a.k.a. the
"Chetco Effect". The clouds have mostly dissipated there early this
afternoon, but temperatures probably won`t be able to rebound much
higher than the low to mid 60s. Clouds have cleared along the coast
north of Cape Blanco this afternoon and aside from a few fair
weather cumulus here and there, it is sunny and warm across most of
the rest of the area.

A cold front is pressing south and eastward across Washington
currently. It will reach NW Oregon early this evening, then move
across our area tonight through Friday morning. Breezy winds can be
expected in advance of this front through this evening, but nothing
too atypical -- gusts in the 20-30 mph range. We aren`t anticipating
much with this cold front, other than a marine push with a cool down
on Friday. A few light rain showers (15-30% chance) could form
overnight near the higher terrain from the Siskiyous northward, with
highest PoPs from the Rogue-Umpqua Divide northward. Any showers
that do form should end by early Friday morning. Clouds push all
the way into the Cascades/Siskiyous, including here in the Rogue
Valley by Friday morning, but won`t get past the Cascades. They
also won`t last that long -- with a quickly drying air mass, most
areas will turn out sunny again Friday afternoon. Overall, most
inland areas will have 5-15 degrees (F) of cooling compared to
today. The largest drop in temps compared to today will be over the
east side. With the flow turning offshore again behind this front,
it could actually be a little warmer than it was today along the SW
Oregon coast.

A chilly night is expected east of the Cascades Friday night with
lows in the mid 20s to mid 30s. West side valleys will be chilly
as well (at least compared to recent nights), but not quite cold
enough for frost with lows in the upper 30s to low 40s. -Spilde

LONG TERM...Saturday 5/18 through Thursday 5/23...Southern Oregon
and northern California will be mostly under the influence of a
ridge of high pressure for most of the weekend, a trough of low
pressure will dig southward over eastern Washington and Idaho.
Precipitation chances will remain to our north, and the main concern
will be breezy to gusty northwesterly winds--particularly in the
afternoons and evenings (gusting to 30 mph in some places,
especially along ridgetops). Otherwise, this pattern will keep us
near or slightly below normal temperatures for this time of year.
Still, we are not looking at freeze concerns west of the Cascades
(nor frost at the coast or Umpqua basin).

By Monday, an additional trough pushes southward, but this front
will be closer to central Oregon. This could bring additional breezy
winds, but also our first shower chances--particularly along the
higher terrain of the Cascades and coast range in Douglas and Coos
County. Rainfall will be relatively light, and thunderstorms are
generally not expected (less than a 10 percent chance).
Temperatures, however, will be several degrees cooler than over the
weekend.

Then on Tuesday into Wednesday, another low spins southward, this
time over western Oregon and could bring additional showers and
thunderstorms (chances are just less than 15 percent at this time).
Winds will continue to be relatively breezy and temperatures will
remain slightly below normal through the end of the week. Since the
weather will be based on a low pressure system that has not formed
yet, the confidence is relatively low--especially since the impacts
will be tied to the location of the low. Used the National Blend of
Models and am forecasting the most likely scenario at this point
since clusters are in general agreement over the large scale and
differ over some of the smaller features. Keep an eye to the
forecast for updates.

Ensembles show that this low shifts eastward Thursday evening and is
replaced with another weak trough digging southwest across the
Pacific Northwest with limited precipitation chances toward the end
of the work week. -Schaaf

&&

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

PACIFIC COASTAL WATERS...Small Craft Advisory until 11 AM PDT
     Saturday for PZZ350-356-370-376.

Hazardous Seas Warning until 11 AM PDT Saturday for PZZ356-376.

&&

$$