Wedderburn, Oregon Weather Forecast Discussion

827
FXUS66 KMFR 182124
AFDMFR
Area Forecast Discussion
National Weather Service Medford OR
224 PM PDT Thu Sep 18 2025
.DISCUSSION...Satellite image shows a weak upper trough lurking
offshore and at the same time moisture is moving in the southern
part of the forecast area in advance of a weak upper low in
combination with some tropical moisture from the remnants of
Tropical Storm Mario. High and mid level clouds are already moving
up from the south.
Instability is expected to increase this afternoon. However
depending on the amount of cloud cover, this could put a cap on the
amount of thunderstorms this afternoon. The general consensus
suggest any storms that pops up will be mainly centered around
western Siskiyou County, including the Trinity Horn. Meanwhile, less
cloud cover is expected in the northern Cascades and this could
result in more instability late in the afternoon. The net result
will be building cumulus. However, we`ll have to keep a close watch
on any signs of isolated storm development late this afternoon into
early this evening.
Any isolated storms will end early this evening with dry weather
overnight tonight. Some of the high res guidance hints at some
potential overnight showers and perhaps an isolated thunderstorm or
two west of the Cascades from Josephine County north to northeast to
eastern Douglas County, but the evidence is not sufficient enough to
have anything in there at the moment.
Cloud cover will increase overnight tonight through the day Friday.
mainly at the high and mid levels. Models and high res guidance
shows marginal instability and trigger Friday afternoon and early
Friday evening. However, with the expected increase in cloud cover,
temperatures will have a harder time reaching their convective
potential. The exception will be in areas where cloud cover is less.
This will tend to be west of the Cascades and western Siskiyous. In
summary, were not expecting anything more than showers and isolated
thunderstorms for portions of northern California, Siskiyous,
southeast Klamath and Lake county. There`s some evidence supporting a
slight chance of storms in the Cascades from Crater Lake north which
could be a function of less expected cloud cover, marginal
instability and trigger.
Any isolated thunderstorms will end early Friday evening with dry
weather overnight Friday. Some of the guidance shows convective
feedback Saturday morning in portions of Northern California and
east of the Cascades, thus isolated showers are possible in these
areas.
Saturday afternoon the models are a but more robust with the QPF
fields Saturday afternoon. However were expecting more cloud cover
which will put a cap on thunderstorm development. Therefore we`ll
have showers increasing in the afternoon and lasting into early
Saturday evening mainly in northern California and Cascades east.
It`s not out of the question that there could be embedded storms
Saturday afternoon and evening.
Showers and isolated storms will end Saturday evening with dry
weather Saturday night. A weak upper trough and surface front will
bring intermittent light rain mainly from Cape Blanco north along
the coast and northwest Douglas county Sunday morning. The front
will dissipate as it moves onshore, with showers ending towards
midday with dry weather in the afternoon. Expect breezy winds east
of the Cascades and the typical valley winds for the interior
westside valleys Sunday afternoon into early Sunday evening.
In the wake of the upper trough, upper ridging will build in for
Monday and Tuesday bringing dry and much warmer afternoon
temperatures for the interior. However on the flip side with clear
skies expected along with longer nights, this will open up the door
for temperatures to drop off pretty quickly after dark for east of
the Cascades, especially in the valleys with temperatures getting
close to or just below freezing both Sunday night into Monday
morning and again overnight Monday into Tuesday morning.
Beyond Tuesday, the operational models from last night were in
pretty good agreement with the overall pattern. Now the latest GFS
shows the upper low centered near the southern California/Mexico
border, while the ECMWF has the low positioned in the Bay area. The
individual ECMWF ensemble means are showing almost a 50/50 split
solution between continued dry and warm or slight cooling with more
cloud cover and showers. The clusters also show varying solutions.
Thus, the forecast beyond Tuesday is a bit clouded. For now we`ll
keep a slight chance of precip in the forecast with slight cooling,
but confidence on this is low. -Petrucelli
&&
.AVIATION...18/18Z TAFs...Satellite image shows marine stratus
burning off from a few hours ago. VFR conditions are likely through
the TAF period for the inland terminals. However. high and mid level
clouds will move up from the south during the afternoon and tonight.
Isolated storms could be a concern in western Siskiyou County late
this afternoon and evening. Along the coast and just offshore, VFR
conditions are expected tonight, although some guidance suggest
marine stratus could form towards 10z at North Bend. -Petrucelli
&&
.MARINE...Updated 200 PM PDT Thursday, September 18,
2025...Strong, north winds (gales in some areas south of Cape
Blanco) and steep to very steep seas will continue this afternoon
and tonight. Wave heights will peak around 10 feet in the north and
up to 15 feet in the south. The thermal trough causing the hazardous
conditions will weaken on Friday with winds and seas gradually
subsiding to a more typical 5-7 feet by evening. Even so, conditions
could remain hazardous, especially to small craft. Improving
conditions are expected with light to moderate winds/seas this
weekend, though moderate northwest swell could build into the waters
later Sunday into Monday. Stronger north winds and steeper seas
could redevelop sometime early-mid next week, but confidence in that
is low at this time. -Spilde
&&
.FIRE WEATHER...Updated 200 PM PDT Thursday, September 18,
2025...The leading edge of a moisture plume associated with the
remnants of what was once Tropical Storm Mario are heading into
NorCal this afternoon. With some instability present, there is an
isolated lightning risk in portions of NorCal, especially western
Siskiyou County late this afternoon/evening. Instability wanes
quickly this evening, but weak forcing from any convection that does
manage to get going and some elevated CAPE will drift northward
across the west side tonight and into Lane County by Friday morning.
We don`t think any storms will materialize, but there`s a non-zero
chance (~5-10%) something develops tonight.
The main axis of moisture will then surge northward into the area on
Friday. While there is still an isolated lightning threat,
especially in NorCal, but also up the Cascades and eastward, the
broad plume of cloud cover should limit the instability, and
therefore the amount/coverage of lightning. This looks like a more
showery pattern, as opposed to thunderstorms. As such, we are
indicating a higher chance of showers (~25-40%) with just a slight
chance of thunder (~15%).
The thunder risk continues into Saturday as the axis of moisture
begins to shift to the south and east (feeling the influence of a
trough offshore. Still there is a slight chance of thunderstorms in
NorCal and from the Cascades eastward.
By Sunday, a cold front will approach the coast and move onshore.
This could bring a little light rain/drizzle to the coast/NW Douglas
County, but will mostly be a deeper marine push west of the
Cascades. It`ll be a mostly dry frontal passage across the remainder
of the area, but will increase afternoon west winds, especially over
the East Side. Some of our in-house guidance is showing peak wind
gusts at the typically windier RAWS sites in the 25-35 mph range.
Models are then showing the upper ridge building in over the area
Monday/Tuesday with a warm-up. The warm-up will be muted, however,
since the mornings will be cooler, especially over the East Side,
where temperatures could dip into the lower to mid 30s. On Tuesday,
the NBM is now showing a high temp high of 95F here in Medford, so
could be a very warm one after a cool morning. After that,
confidence is VERY low in how another surge of sub-tropical moisture
moves northward. Some scenarios bring this moisture directly
northward into our area around mid-week with showers/thunderstorms
and a cooling trend. Another scenario shows much of the moisture
pushing south and east of the area with a gradual lowering of
heights and another weakening cold front moving onshore.  Given the
varying scenarios, a blended approach was taken in the extended.
-Spilde
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...CA...None.
PACIFIC COASTAL WATERS...Gale Warning until 11 AM PDT Friday for
     PZZ356-376.
Small Craft Advisory until 11 AM PDT Friday for PZZ350-370.
Hazardous Seas Warning until 11 AM PDT Friday for PZZ370.
&&
$$

NWS mfr Office Area Forecast Discussion