531
FXUS66 KMFR 300243
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
743 PM PDT Sun Jun 29 2025

...Updated the Aviation section...

.AVIATION...30/00Z TAFs...Conditions early this evening are VFR,
with a patch of stratus near Cape Arago, and scattered low topped
cumulus buildups over the higher terrain. Later this evening, expect
marine stratus to develop and expand along the coast north of Cape
Blanco, and into the Coquille Basin, resulting in IFR conditions
that will persist through much of Monday morning. Clearing to VFR is
expected for the afternoon, before a similar return to IFR north of
Cape Blanco during Monday evening.

Also, instability will develop inland Monday afternoon with a slight
chance to chance of thunderstorms from the Coastal Range eastward
during the afternoon and evening. Storms will be most numerous
between 22Z and 03Z, from Siskiyou County into Klamath and northern
Lake counties. This includes the Cascade Crest, Yreka, and Klamath
Falls. /DW

&&

.MARINE...Updated 200 PM PDT Sunday, June 29, 2025...Moderate to
strong north winds and very steep wind-driven seas will persist
through at least Tuesday evening. Strong winds, and very steep wind-
driven seas are likely south of Port Orford, where gales are likely.
Meanwhile, Small Craft conditions are expected over the rest of the
waters. North winds and seas will diminish some Tuesday night into
Wednesday, but the southern waters could still experience at least
Small Craft conditions with Hazardous Seas Warning conditions south
of Port Orford. -Petrucelli

&&

.PREV DISCUSSION... /Issued 303 PM PDT Sun Jun 29 2025/

DISCUSSION...Two main features remain the focus of the forecast
today through at least Wednesday: Heat and thunderstorms. The
upper level pattern has transitioned and high pressure over the
Desert Southwest will exert more influence in the weather over
southern Oregon and northern California today into Monday, with a
thermal trough at the surface. This is bringing clear skies across
the entire forecast area, aside from a thin layer of marine
stratus along the immediate coast. We`ll see another round of
gusty afternoon breezes today more typical for this time of year,
including along the coast where gusts up to 30 mph are expected
this afternoon, especially north of Cape Blanco.

High temperatures will trend warmer by about 5 to 10 degrees today
as the heat cranks up. Today will be the warmest day of the forecast
period for areas west of the Cascades. Temperatures will be quite
similar on Monday for West Side, but then East Side temperatures
will peak on Monday (although cloudiness from thunderstorms and
monsoonal moisture inflow could limit high temperatures Monday, more
on that below). Highs today across the West Side will be in the
upper 90s to low 100s, while the highs on Monday for the East Side
will peak out around 90 to 95. Temperatures will then cool slightly
heading further into the week, but will remain above normal. We
don`t have any heat related headlines with this event, there will be
a moderate risk of heat related illnesses today into Monday for much
of the area away from the immediate coast. This level of heat will
affect most people sensitive to these temperatures, but especially
for those without adequate hydration and/or effective cooling. Take
the proper precautions to prevent heat illness, and if seeking
relief by swimming in area waterways, be advised that river water
temperatures are still cold, as the more persistent snowpack
continues to provide fresh, cold, meltwater.

Meanwhile, weak low pressure is developing off the coast of
California today, where it will linger offshore through Monday, then
meander inland into central California Tuesday into Wednesday. This
is a classic thunderstorm pattern for the region. Southerly flow
will begin to pumping moist and unstable monsoonal moisture into the
region today. This combined with warm surface temperatures will lead
to ample instability and with lobes of energy rotating around the
low pressure as it moves eastward, will all this coming together to
result in scattered thunderstorms across the region both Monday and
Tuesday. Things could get started as early as this afternoon across
far southern Siskiyou and Modoc Counties as moisture first enters
the region. At the very least, expect plenty of cumulus buildups
along the Siskiyous and southward. An isolated shower or
thunderstorm is not out of the question in the typical hot spot near
the Trinity Alps and the Warners of Modoc County, and this has been
added to the forecast. Confidence is low on this since the mid-
levels of the atmosphere are really just beginning to moisten up
today.

The forecast remains consistent with Monday and Tuesday being the
most active days, and with Monday being the best chance for storms
to develop west of the Cascades. These will be the days where
moisture and instability will be most widepsread and lobes of energy
rotating from southeast to northwest through the forecast area will
provide sufficient trigger for thunderstorm initiation. There are
some indications for overnight convection as well tonight into
Monday and again Monday night into Tuesday. Of the two nights,
Monday night has the better chance. There is some elevated
instability present late Sunday night/early Monday morning, but
moisture is marginal and there isn`t a clear trigger. If enough
ingredients did come together tonight, the best chances (10-15)% for
this to happen would be over western Siskiyou County and into the
Kalmiopsis Wilderness. Confidence in this low, as is typical with
overnight convection and the most likely scenario has convective
initiation beginning Monday afternoon, albeit maybe earlier than
typical (maybe around 2 pm vs 4 pm). Based on pattern recognition,
thunderstorms are possible just about anywhere east of the coastal
ranges on Monday, but the highest chances are focused along the
Klamath, Siskiyou and Cascade mountains and east of the Cascades.
Steering flow is generally out of the south to southeast, but then
varies in direction as the afternoon progresses. PWATs get close to
an inch by the afternoon Monday, so these storms should be rain
producers, and when combined with the weak steering flow, there
could be some moderate to heavy downpours under the core of the
storms. The Storm Prediction Center has places a large portion of
the forecast area under a Marginal Risk for severe thunderstorms on
Monday. This means there is a 10-15% chance of an individual storm
being severe, with about a 5% chance of damaging winds (60+ mph)
and/or large hail (1+ inch diameter). Regardless if damaging winds
occur or not, there will be some pretty gusty outflows with these
storms, so now is the time to prepare your property to prevent
things from getting blown about or away. If you have outdoor plans
during this time frame, stay weather aware and have a plan for
shelter should a thunderstorm develop nearby.

As previously mentioned, there are some indications that convection
carries into the overnight hours late Monday into Tuesday. Coverage
of storms will diminish late Monday evening, but very well could
continue overnight along and east of the Cascades as well as across
western Siskiyou County and northwestward into Josephine County.
Moisture will be sufficient, models indicate elevated instability,
and with the region under diffluence aloft, this could provide
enough lift to maintain shower and thunderstorm activity. While
confidence is low in the details, there is moderate confidence that
Monday night into Tuesday will be the better chance for nocturnal
thunderstorms. We have added/maintained a slight chance of
showers/thunderstorms to portions of the East Side and western
Siskiyou County. A similar set up is expected on Tuesday and we
expect thunderstorms to reform Tuesday afternoon, although with the
eastward progression of the trough, the best dynamics and support
shift slightly eastward with the focus of shower/thunderstorm
activity focused over northern California and along and east of the
Cascades, possibly as far west as the Cascade Foothills on the West
Side. Other than location, storm behavior and character should be
very similar to Monday. One fly in the ointment to consider will be
the amount of cloud cover around on Tuesday, especially if
convection continues through the previous overnight hours. With this
much moisture entering the area, and with the widespread convection
expected Monday, there may be extensive cloud cover over the area
Tuesday limiting incoming solar energy, keeping temperatures lower,
and limiting instability. If this is the case, thunderstorm coverage
would be significantly less than what is currently expected. At this
point in time, the high resolution models are indicating that shower
activity will continue into Tuesday morning, but clearing behind
this activity should allow for thunderstorm development across the
East Side and northern California.

Wednesday through the Fourth of July holiday weekend...By Wednesday,
the upper level low responsible for all the instability shifts far
enough east to limit thunderstorm chances to far eastern Lake and
Modoc Counties. Temperatures will have trended cooler compared to
this weekend, returning to near seasonal normals. Guidance shows
another low pressure affecting the region late Thursday into Friday,
but coming through in westerly flow and positioned farther north
than the one expected early next week. One positive to this, is that
temperatures would remain near normal for the Fourth of July holiday
and thus no heat waves for the holiday. The flip side to that,
however, is that thunderstorm chances could return to the forecast
during the holiday weekend. Given that this is a different
pattern/trajectory of the low pressure, thunderstorm coverage would
likely be less, but stay tuned as we get past the upcoming event and
details on the next become more clear. /BR-y


FIRE WEATHER...Updated 200 PM PDT Sunday, June 29, 2025...The
main concern ahead will be isolated to scattered thunderstorms for
most areas away from the coast Monday afternoon into Monday evening,
then again Tuesday afternoon and evening in northern California, and
Cascades east in Oregon. Confidence has increase for thunderstorms
to be isolated at first early Monday afternoon, with storms
increasing in numbers and coverage as the afternoon progresses
Monday into Monday evening. Storms early Monday afternoon may not
produce much of any precipitation to start, then the chance for
wetting rain could increase mid to late Monday afternoon and
evening. The main reason for the increase chance in wetting rain is
steering winds will be light and high moisture content throughout
the column of the atmosphere. Thus, storms will be slow movers
providing the bigger window of opportunity for storms to produce
locally moderate to heavy precipitation. However, that does not mean
that all storms will produce wetting rain. Some could also produce
little to no rain, because model soundings show a rather dry sub
layer below.

Keep in mind, lightning strikes outside of the precipitation cores
are possible. Due to the prolonged period of dry and warm to hot
weather, lightning efficiency will be high to very high for fire
starts. Given the above mentioned and increasing confidence for both
Monday and Tuesday, the Fire Weather Watch for abundant lightning on
dry fuels Monday afternoon/early evening has been upgraded to a Red
Flag Warning, and a Fire Weather Watch has been issued for the same
reason and for the same zones Tuesday afternoon/early evening.
Please see RFWMFR for more details.

It will be hot again Monday with afternoon highs in the upper 90s
to low triple digits for the interior westside valleys and low to
mid 90s east of the Cascades. The caveat will be the amount of cloud
cover Monday. If there`s enough cloud cover, it could result in
forecast highs for the eastside ending up lower than whats in the
forecast.

We also have to be mindful of gusty and erratic outflow winds near
and away from the core of thunderstorms.

Monday night, some evidence points towards the potential for
nocturnal storms Monday night, but confidence on this is low and it
will be something that we`ll need to monitor. Stay tuned.

In the meantime, dry weather is likely through tonight, with the
typical afternoon and early evening breezes and low relative
humidity. An upper low off the California coast will begin to bring
some monsoonal moisture into Northern California late this afternoon
and tonight. Basically today is the day where the pump will be
primed for what we are expecting Monday and Tuesday. The most likely
scenario late this afternoon with the increase in monsoonal moisture
will be cumulus build ups over the mountains around the Trinity
Horn, Mount Shasta and points east to northeast of Mount Shasta. The
worst case will be a few isolated storms in these areas late Sunday
afternoon into Sunday evening.

Tuesday, the thunderstorm threat is expected to be along and east of
the Cascades and northern California. Guidance and instability
parameters are in better agreement suggesting storms could be
isolated to scattered Tuesday afternoon into early Tuesday evening
in the same Fire zones as what were expecting Monday, and a Fire
Weather Watch has been issued. Like Monday, steering winds will be
light, therefore storms Tuesday will be slow to move, and this along
with high PWATS between 1.00-1.25 inches could result in locally
heavy precipitation.

Wednesday, the focus for storms should be confined to portions of
Lake county, and portions of Northern California as the upper low to
the south gets kicked eastward as an upstream upper trough moves in
from the west. Even then, storms are expected to be isolated.

The concern for thunderstorms could carry over into Thursday as an
upper trough approaches the area from the west with the best chance
for storms along and east of the Cascades and portions of northern
Cal. -Petrucelli

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...CA...Red Flag Warning from 2 PM to 8 PM PDT Monday for CAZ280-281-
     284.

Fire Weather Watch from Tuesday afternoon through Tuesday
     evening for CAZ280-281-284.

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

     Gale Warning until 11 PM PDT Tuesday for PZZ356-376.

&&

$$