Wildfire in California, May 21 to 30, 2024

Area Forecast Discussion...UPDATED
National Weather Service Medford OR
440 AM PDT Tue May 21 2024

...New Aviation Section...

.AVIATION (12Z TAFs)...

We will start off with VFR conditions across the terminals, but an
approaching system will bring lower ceilings to the coast/inland
areas and light precipitation. IFR/LIFR conditions will be
possible tonight at North Bend, but only expecting MVFR at both
Roseburg and Medford. Confidence is fairly high for deteriorating
conditions tonight as the disturbance comes into the region.

-Guerrero

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.PREV DISCUSSION... /Issued 233 AM PDT Tue May 21 2024/

DISCUSSION...Progressive NW flow aloft will bring another
disturbance into the area tonight into Wednesday. The air mass
preceding it is pretty dry, so many areas will eke out a pleasant
spring day today. Most areas start out sunny, then we expect
increasing amounts of mostly high/mid clouds this afternoon.
Afternoon temperatures will be mostly in the 70s for the valleys
of the west side and in the 60s east of the Cascades. Clouds will
lower in NW sections by late this afternoon and there is a 20-30%
chance of showers. But, even there, odds favor it remaining dry
through 5 pm.

As the upper trough/cold front moves onshore into the PacNW,
precip chances increase tonight along the coast, near the Rogue-
Umpqua Divide, over to the Cascades and even across Oregon
sections of the East Side. Those chances are highest (generally
60-90%) in Coos/Douglas counties and near the Cascades, but drop
off to almost nil in portions of NorCal. Rain amounts of 0.10 of
an inch or less will be most common, but some reports of 0.25-0.50
of an inch may occur in the Cascades Mtns/Foothills. Models do
show some light showers also moving across the Rogue Valley, but
these will be isolated in nature. Best chance of a rain shower
here is between 3 and 9 am. Snow levels should be high enough to
preclude wintry impacts, though some wet snowflakes may mix in
with the rain showers near the higher Cascades Wednesday morning.

The front and upper trough will shift to the east of the area
Wednesday afternoon and precip chances will dwindle to almost
nothing again, except for a 20% chance of showers lingering across
the far north near Willamette Pass. Strong, gusty NW winds are
expected in many areas since we expect very good vertical mixing
and decent winds aloft (mid-level winds generally in the 35-45 kt
range). Wind gusts of 35-44 mph will be common over the mountains
and east of the Cascades (35-44 mph), but these winds should
mostly be sub-advisory level (>=45 mph).

A short wave upper ridge/subsidence will move in Wednesday night
into Thursday bringing clearing and colder conditions. Some fog
will develop in the west side valleys, especially the Coquille and
Umpqua Valleys. With the clear skies, patchy frost is possible in
the typically colder valley spots (Illinois/Applegate/Scott and
Shasta) and even some outlying areas of Medford/Ashland/Grants
Pass. It'll be cold Thursday morning over the Cascades/East Side
where lows will be in the 20s. Despite the cold start in many
areas, it will turn out sunny and milder Thursday afternoon.

Friday will be much like today. Another upper level trough will
move into the PacNW on NW flow. Most areas start out sunny, then
we expect increasing amounts of mostly high/mid clouds during the
afternoon. Clouds thicken in NW sections during the pm/eve, where
there is about a 20-40% chance of showers. Shower chances remain
mostly north of Highway 140 and Lake of the Woods in the Cascades
with precip chances south and east of there generally 10% or less.
It'll be breezy to windy and cooler again on Saturday as the
upper trough swings into eastern Washington/NE Oregon. High
pressure builds in for Sunday and Monday, Memorial Day. With
higher heights and a shift in the flow aloft to WSW, we should see
a warm up back to above normal levels early next week. -Spilde

AVIATION...21/06Z TAFs...VFR conditions will continue through
Tuesday afternoon. Guidance shows some low clouds moving along and
just off the coast, north of Cape Blanco later tonight, but it's not
expected to have an impact on flight conditions. Breezy winds are
expected at the terminals Tuesday afternoon and early evening, but
winds speeds should be less than they were earlier this afternoon.
MVFR and IFR ceilings and areas of MVFR visibilities are expected to
develop along the coast north of Cape Blanco early Tuesday evening.
These conditions are expected to become widespread along the
southern Oregon coast and into the Umpqua basin by late Tuesday
evening.  -CC

MARINE...Updated 230 AM Tuesday, May 21, 2024...Seas are
anticipated to stay fairly consistent with current conditions
through much of today with only small deviations. If anything, wind
speeds are expected to diminish across the northern waters today
bringing seas lower as well. However, areas south of Cape Blanco
will likely experience small craft advisory conditions through at
least parts of today. The current advisory goes until early this
afternoon, but we may need an expansion and extension as the next
front moves into the region. By Thursday, we may see a break in
hazardous conditions over the waters through the weekend.

-Guerrero

&&

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

PACIFIC COASTAL WATERS...Small Craft Advisory until 11 AM PDT this
     morning for PZZ356-376.

&&