303
FXUS66 KMFR 200218
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
718 PM PDT Fri Jul 19 2024

.UPDATE...Updated the aviation section.

&&

.AVIATION...20/00Z TAFS...Along the coast, conditions are VFR
early this evening. Marine stratus will form again this evening and
move into the coastal valleys overnight, resulting in IFR
conditions. The IFR is expected to linger longer in the morning than
it did on Friday, and return earlier...(around 00Z at North Bend)
mainly by the start of Saturday evening.

Inland, VFR conditions will prevail through Saturday afternoon, with
an exception. The exception will be in the vicinity of the Trail
fire and various other fires in the vicinity of the Trail Fire. In
eastern Douglas County and across northern portions of Klamath and
Lake counties, visibility could end up between 3-5 miles. Visibility
could also be reduced southeast of the fires into northeast Jackson
County and the remainder of Klamath County, including possibly down
into Klamath Falls late tonight resulting in MVFR visibility.

A slight chance to chance of thunderstorms will develop across the
area Saturday evening and continue Saturday night. -DW

&&

.MARINE...Updated 800 PM Friday, July 19, 2024...A thermal trough
will return tonight into Saturday, then strengthening Sunday into
Tuesday. Moderate north winds and steep seas are expected south of
Port Orford beginning tonight and lasting through Saturday. Expect
conditions hazardous to small craft to expand across a larger area
on Sunday, then stronger, gale force winds are possible Monday
afternoon through Tuesday. -Spilde/DW

&&

.PREV DISCUSSION... /Issued 242 PM PDT Fri Jul 19 2024/

DISCUSSION...A high amplitude ridge remains in control of the
western third of the country, and with the trough to the northwest
over the Gulf of Alaska, this places southern Oregon and far
northern California under relatively dry and stable southwest
flow aloft. Meanwhile, a thermal trough has developed over
central California.

A shortwave impulse now lies along the southern periphery of the
trough to our southwest, and this feature will approach the area
through the day Saturday. The southerly flow ahead of the wave
will push this hot air into our area Saturday, resulting in very
warm temperatures across much of the inland areas. Most inland
valleys both east and west of the Cascades will easily reach upper
90s to low 100s for the daily high. This will be just enough
above normal to trigger Heat Risk for northern California and the
East Side, so Heat Advisories have been issued for those areas
for Saturday.

The shortwave will also provide instability and additional
moisture, while also acting is a sufficient lift mechanism to
produce a widespread slight chance to chance (generally 10-30%)
for thunderstorms Saturday into Sunday, including during the
overnight hours as the wave tracks through overhead. This event
looks very similar to the one from earlier this week, both in
overall pattern and in the dry lower layers of the atmosphere, so
we are concerned about lighting and gusty outflow winds once again,
especially given that any storms that develop will produce very
little, if any, precipitation. The focus of convection concerns
will shift to the East Side on Sunday as the wave exits the
region.

For the remainder of the week, the pattern will very slowly
progress to the east, with the Gulf of Alaska trough gradually
moving inland into Canada and Washington. As a result, we are
expecting temperatures to "cool" slightly, returning to near
normal values for this time of year, with relatively dry west to
southwest flow continuing through the week. -BPN

&&

.FIRE WEATHER...Issued 200 PM Friday July 19, 2024...

A dry and stable southwest flow continues into this evening with no
concerns for thunderstorms. However, afternoon relative humidities
will trend lower for most interior locations with values in the
single digits for portions of the East Side along with the typical
gusty afternoon and early evening breezes. This will result in near
critical conditions for portions of Fire zones 624, 625 and 285, but
were not expecting the combination of wind and RH to result in Red
Flag conditions.

The other concern for those involved in air attack on the various
fires in our area will be visibilities lowering to 3-4sm in the
vicinity of the Trail Fire and surrounding complexes near the Trail
Fire in eastern Douglas County. The latest run of the HRRR smoke
fields show the smoke being transported east to southeast late this
afternoon and evening. However there are fires up in Lane County
that will get transported into eastern Douglas County, so we may not
see any improvement through tonight. Meanwhile, smoke from the Trail
and other fires in eastern Douglas County will push southeast into
Klamath County late this afternoon, then into Klamath Falls proper
tonight, and visibility could be reduced to 4-6sm. Tonight, as the
mixing height decreases, the smoke will settle and be confined to
around the perimeter of the fires resulting in MVFR visibility
between 3-5sm. However, a northeast drainage winds could bring smoke
towards Medford resulting in visibility lowering to 5sm northeast of
the Medford Airport late this evening and tonight.

There is now an increased concern for thunderstorm this weekend.
Saturday, an upper trough will move up from the south just off the
California coast and could tap into some monsoonal moisture with a
southeast flow aloft. At the same time, there`s good agreement, the
upper trough will become negatively tilted Saturday afternoon into
Saturday night. Based in part on pattern recognition, this could be
problematic in that we could see storms break out mid to late
Saturday afternoon in portions of northern California, east of the
Cascades, and some could slip into the southern portions of Fire
zones 619, 620 and 621 late Saturday afternoon due to a stronger
flow aloft which could allow storms to come off the mountains and
move north into the lower elevations.

Saturday night, the axis of the upper trough is still south of our
area which heightens the concern for nocturnal storms west of the
Cascades, and portions of the eastside in Oregon Saturday night.
Many times the models will not show signs of unstable conditions
with this type of pattern, then the next thing you know something
breaks out of nowhere. The pattern that is setting up is one where
the instability is elevated, and thus the convection will be
elevated as well. The most recent data points to a heighten concern
for nocturnal storms along and west of the Cascades Saturday night
into Sunday morning. This has lead to a higher confidence for a Fire
Weather Watch for the Cascades west for abundant lightning on dry
fuels and a Fire Weather Watch has been issued. Keep in mind given
how dry and hot it has been for the interior and near the coast,
that lightning efficiency is high to very high for fire starts. Also
gusty and erratic winds are a concern which could further increase
fire activity on existing fires. Some of the high res guidance are
showing some reflectivity, and PWATS are higher, therefore there we
could see some rain out of these storms that could reach the ground,
but it will not provide much help in preventing new starts given how
dry and hot it`s been. Even though the Fire Weather Watch is for the
Cascades west, that does not mean the eastside will be in the free
and clear. There is concern for nocturnal storms in portions of Fire
zone 624 Saturday night, however the confidence is not as high for
isolated to scattered storms, so they were left out of the watch for
now, but this could change should future data shows evidence to the
contrary. With all that said, this is not a slam dunk, but at the
same time it cannot be discounted.

The upper trough axis shifts north during the day Sunday. Any threat
for storms could be confined to the early morning hours over the
northwest part of our area, then shifting north late Sunday morning
through Sunday afternoon with a drier and stable southwest flow
moving into the area. The exception could be in portions of Fire
zone 623, 624, 625 and along the Warners in Fire Zone 285 where
isolated storms are possible late Sunday afternoon.

Monday, a dry and stable southwest flow will set up with any chance
for storms shifting east and northeast of our area. It will be
cooler with gusty afternoon and early evening breezes for the
interior westside valleys and east of the Cascades.

The rest of next week is pointing towards dry weather, with ridging
nudging back into the area. This will result in afternoon
temperatures trending upwards from Tuesday and beyond. Also the
concern will shift towards moderate to locally poor overnight
recoveries for the mid slopes and ridges in southwest Oregon and
western Fire zone 280, and the typical gusty afternoon and early
evening breezes for the interior westside valleys and east of the
Cascades with low afternoon RH`s. -Petrucelli

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Heat Advisory from 11 AM to 11 PM PDT Saturday for ORZ029>031.

     Fire Weather Watch from Saturday afternoon through Sunday
     morning for ORZ615>620-622-623.

CA...Heat Advisory from 11 AM to 11 PM PDT Saturday for CAZ081>085.

PACIFIC COASTAL WATERS...Small Craft Advisory from 2 AM to 11 PM PDT Saturday for PZZ356-
     376.

     Gale Watch from Monday afternoon through Tuesday evening for
     PZZ356-376.

&&

$$