Area Forecast Discussion
Issued by NWS Medford, OR

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237
FXUS66 KMFR 221137 AAA
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
436 AM PDT Mon Jul 22 2024

Updated Aviation discussion.

.DISCUSSION...Two main features will be the weather influencers
through the work week: strong high pressure centered over the
Great Basin region and a deep low pressure over the Gulf of
Alaska. For the first half of this week, high pressure will be the
dominate weather player with low pressure taking control for the
latter half of the week and possibly into next weekend.

Not much change in the overall weather is expected today into
Tuesday as high pressure to the southwest remains in control.
Satellite imagery this morning shows a rather extensive (for this
time of year) stratus layer covering much of Douglas County, and
this stratus is even "spilling over" the Umpqua Divide and into
portions of the Illinois/Applegate Valleys this morning. Along the
coast, a lower marine stratus layer has filled in the Coquille Basin
as well as Brookings area and southward. Once this cloud cover
clears later this morning, sunny skies with conditions quite similar
to yesterday are expected for the remainder of the day. The one
difference will be the amount of thunderstorms this afternoon will
be considerably less than Sunday. Isolated thunderstorms will be
confined to southeastern areas today where moisture and instability
linger, mainly in the southeast corners of Modoc and Lake Counties.
Rinse and repeat is in store for Tuesday, with the exception of high
temperatures. Strong high pressure to the south will nudge
northwestward on Tuesday, and this will nudge Tuesday`s high
temperatures up by a few degrees. This will be most noticeable west
of the Cascades where temperatures will trend warmer by around 5 to
10 degrees.

For the latter half of the week, the pattern will slowly progress to
the east, with the Gulf of Alaska trough gradually moving inland
into Canada and Washington around mid-week. As the pattern
progresses, the ridge will be pushed farther east and, as a result,
temperatures will "cool" slightly for the latter half of the week,
returning to near normal values for this time of year. This even
includes areas east of the Cascades and across northern California.
High temperatures may even end up a few degrees below normal for the
first time since the beginning of the month! We`ll need to monitor
the potential for gusty winds as this trough pushes inland,
otherwise, relatively dry west to southwest stable flow should
continue through the week.

Smoke will be a continued nuisance through the forecast period, and
probably longer. An Air Quality Alert (issued by partnering
agencies) remains in effect for Jackson/Klamath/Lake Counties
through at least this afternoon. Latest smoke model runs do show
some general improvement late this afternoon/evening as the typical
afternoon winds increase and help disperse some of the smoke, but
confidence in this occurring is low considering it didn`t come to
fruition on Sunday. With little change in the overall weather
pattern through at least Tuesday, expect much of the same regarding
smoke/air quality through then. There is a chance for some general
improvement with the pattern change anticipated over the latter half
of the week, but confidence on extent and duration of improvement is
low at this time. Air quality is likely to be at least reduced
(severity of degradation will depend on fire activity) for the
foreseeable future until activity on area wildfires is significantly
reduced. /BR-y

&&

.AVIATION...22/12Z TAFS... Marine stratus, mainly MVFR/IFR with
patches of LIFR, is present along and near the coast from Port
Orford northward, including the Coquille Valley and areas near and
south of Brookings. Compared to Sunday, the stratus will make better
progress at eroding during late morning, with VFR expected for by
early afternoon. Areas of IFR are expected to redevelop along the
coast north of Cape Blanco this evening.

Elsewhere, including along the south coast, VFR conditions will
prevail through Monday evening with an exception. The exception will
be in the vicinity of the cluster of fires in eastern Douglas
County, and across northern portions of Klamath and Lake counties,
where visibility could occasionally lower to 3-5 miles in
smoke/haze. Hazy skies with the potential for MVFR visibilities are
also likely to persist for Jackson County, including Medford, and
the remainder of Klamath County, including near Klamath Falls. There
is also a slight chance for thunderstorms(15%)  Monday afternoon and
evening, with isolated storms expected for southeast Modoc and far
eastern Lake counties. -CC

&&

.MARINE...Updated 200 AM Monday, July 22, 2024...A thermal
trough will strengthen late today into Tuesday. Gales and very
steep, hazardous seas are expected from Nesika Beach southward
today, then for areas from Cape Blanco southward late tonight and
Tuesday. Elsewhere, Small Craft Advisory conditions with steep seas
and gusty winds are expected. The thermal trough is expected to
weaken slightly on Wednesday with lingering gusty northerly winds
and steep to very steep, short-period seas. Highest winds and seas
are expected south of Cape Blanco on Wednesday. These conditions may
persist through Friday. Current models support a medium to high
chance (50-90%) for gusty north winds reaching small craft advisory
levels for the waters south of Cape Blanco. -CC

&&

.FIRE WEATHER...Issued 400 AM Monday July 22, 2024...Along the
coast and into the Umpqua Valley, increased onshore flow this
morning has brought some cloud cover and higher humidities.
Stratus is even "spilling over" the Rogue-Umpqua Divide into the
Illinois/Applegate Valleys. Recoveries are generally better across
the whole area this morning (50-70%), with the largest 24 hour
change over Fire Weather Zone 625.

Most areas will remain dry in west-southwest flow aloft through mid-
week, but lingering mid-level moisture and instability near the
Sierra will extend northward to around SE Modoc and SE Lake counties
where an isolated thunderstorm or two could pop up each
afternoon/evening. Heights rise slightly, so it will turn hot again
Tue-Wed with widespread temperatures in the 90-100F range, except in
the higher mountains and along the immediate coast, where it will be
cooler. Fairly typical diurnal breezes are expected as well through
mid-week.

Then, a deep upper trough and low pressure over the Gulf of Alaska
will move eastward into western Canada around Wed-Thu. This will
bring increasing mid-level flow across the area with some gustier
afternoon/evening winds expected. While some west side valleys like
the Rogue and Shasta Valley will also have a slight uptick in winds,
the strongest winds will occur over the east side (generally 20-25
mph with peak gusts of 30-35 mph). Afternoon minRH values are
forecast to be down around 15% during this time, so both Wed/Thu
afternoon could see some areas near critical wind/RH thresholds.
Right now, however, these areas do not look widespread enough for a
Fire Weather Watch. We`ll maintain a headline in the Fire Weather
Planning Forecast.

Late in the week into next weekend, models are showing a closed low
off the California coast, which gets absorbed into the WSW flow
aloft and eventually cruises across NorCal Fri/Sat. Normally, we`d
be concerned about more thunderstorms, but by this time, best mid-
level moisture will move off to the east and thunder risk is low at
this time. What this should do is lower temperatures to levels that
are more typical for this time of year (highs in the low to mid 90s
for west side valleys and in the upper 80s east of the Cascades).
-Spilde/BR-y

&&

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

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.

&&

$$

MNF/CC/DW