-- Discussion containing changed information from previous version are highlighted. --
276
FXUS66 KMFR 102258
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
358 PM PDT Fri May 10 2024

...New Aviation Section...


.AVIATION (00z TAFs)...

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VFR conditions are expected at the terminals throughout the valid
TAF period with one caveat for North Bend (KOTH). There may be
enough low level moisture and a marine push to potentially drop
ceilings under 1000 feet at KOTH, but confidence is higher we do
not see any categorical changes from VFR. However, we could see a
FEW to SCT deck overnight into Saturday morning around 500 feet,
and the thinking here is we should stay in VFR given the amount
of dry air in the lower levels.

-Guerrero
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&&

.PREV DISCUSSION... 
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/Issued 357 PM PDT Fri May 10 2024/

DISCUSSION...Satellite imagery shows clear skies over most of the
forecast area, with scattered fair weather cumulus clouds in
portions of Lake, Klamath and Modoc Counties. The latest surface
analysis shows the thermal trough just off the Oregon coast and has
expanded north compared to this time yesterday. Similar to
yesterday, gusty east to northeast winds are bring observed at the
mid slopes and ridges. The east winds will also be favorable for a
Chetco effect to set up with Brookings expected to warm up late this
afternoon. Currently it`s 83 degrees which is 4 degrees warmer
than at this time yesterday, this afternoon highs into the upper
80s is likely. The offshore flow and favorable southeast flow at
925 mb is also resulting warmer temperatures near North Bend where
it`s currently 71 degrees which is 2 degrees warmer then
yesterday at this time, thus afternoon highs in the lower to mid 70s
there is likely.

Were still looking at a rather quiet pattern through most of next
week days with afternoon temperatures warming up a tad on Saturday,
followed by a slight cool down Sunday into next week.

The thermal trough will shift inland over the interior westside
valleys later this afternoon with generally light winds expected.
Afternoon temperatures could push 90 degrees in portions of the
Rogue and Illinois Valley, and Umpqua Basin which will be the
first time this season many of these areas could get to 90 or just
a hair above that. Meanwhile winds east of the Cascades will be
lighter than yesterday as winds aloft are lighter, therefore any
mixing of winds aloft near the surface later this afternoon will
not be strong.

Tonight will be dry and the thermal trough will weaken. This will
allow the marine stratus to form over the waters and along the coast
late tonight and lasting into Saturday morning. Models, particularly
the NAM actually show light QPF over the marine waters, which
typically equates to marine stratus development. The one element
working against this is that the boundary layer is not quite as
moist compared to the surface.

Saturday will be dry and warm again for the interior. The thermal
trough will remain inland on Saturday and this will open up the door
for weak onshore flow near and at the coast resulting in much
cooler afternoon temperatures for Brookings and North Bend. The
marine stratus will linger along the coast and offshore in the
morning, then peel back just off the coast Saturday afternoon.

Saturday night will be dry with weak onshore flow bring solid layer
or marine stratus back along the coast and could make it`s way a bit
inland into portions of the Coquille Basin.

Most areas will be dry Sunday with slight cooling Sunday afternoon
for the interior. Some of the data suggest there could be enough
instability and trigger for a isolated storms to pop up late in the
afternoon and early evening in portions of northern California and
the Warners in Lake County. The operational GFS continues to be the
most bullish with the extent of the instability, while others not so
much. The thermal trough will shift east Sunday resulting in breezy
afternoon winds for the interior westside valleys and east of the
Cascades.

A weak upper trough will move through Monday, with the net result
being slight cooling, with gusty afternoon and early evening breezes
east of the Cascades, and the interior westside valleys.

The operational ECMWF and GFS show the upper ridge remaining west of
the forecast area Tuesday and Wednesday with a dry, stable west to
northwest flow over our area and temperatures above normal for most
interior locations.

Thursday through Friday is where the operational models differ with
the ECMWF showing an upper trough moving into the Pac NW while the
GFS builds an upper ridge over the Pac NW. Meanwhile 70% percent of
the clusters favor the upper ridging and the ECMWF ensemble mean
shows the upper trough swinging through Washington and northern
Oregon. This track typically does not result in precipitation for
our area, so the most likely scenario will be continues dry weather
with afternoon temperatures above seasonal norms. -Petrucelli

AVIATION...10/18Z TAFs...VFR conditions are expected at the
terminals throughout the valid TAF period. The only noteworthy item
involves North Bend tonight when we could see just enough low level
saturation to produce some thin clouds overnight, but these should
burn off by mid morning if they develop. Thinking here is a FEW to
SCT deck under 1000 feet AGL will be possible overnight/early
Saturday morning. Otherwise, should be great flying conditions with
plenty of sunshine and generally light wind speeds.

-Guerrero

MARINE...Updated 200 PM Friday, May 10, 2024...Steep seas will
return tomorrow (Saturday) as northerly wind speeds increase to
around 15-20 knots with gusts potentially around 30 knots. During
which time a thermal trough starts to develop south of Cape Blanco.
Starting Saturday afternoon, these conditions will build steep seas
in our waters south of Cape Blanco, and in waters north of Cape
Blanco beyond 10 nm from shore. As a result, a Small Craft Advisory
will be in place from Saturday at 5 PM through Monday at 5 AM.

Hazardous conditions will likely exist into next week as the thermal
trough strengthens. Current model guidance shows fluctuating periods
of both hazardous seas and gale force winds south of Gold Beach
starting Monday and going through Wednesday morning. There is some
uncertainty with regards to areal coverage and timing of these
hazards, so confidence is a little low at this time on issuing
further hazards. That said, there is a high likelihood for hazardous
conditions over the waters through middle of next week, with Tuesday
being the potentially worse day on the waters. The probability for
wind gusts of 41 knots or greater on Tuesday is around 70% (areas
around Cape Blanco), and going south to upwards near 95% chance for
our southern waters. In fact, the southern waters has a 50-75%
chance at seeing gusts of 48 knots or greater on Tuesday. We will
refine the details, but look for the current small craft advisory to
transition to a hazardous seas and/or gale warning for early parts
of next week.

-Guerrero
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&&

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

PACIFIC COASTAL WATERS...Small Craft Advisory from 5 PM Saturday to 5
     AM PDT Monday for PZZ356-370-376.

&&

$$