Wildfire in Oregon, November 1 to 20, 2020

Area Forecast Discussion
National Weather Service Medford OR
1052 PM PDT Sat Oct 31 2020

.Updated Aviation Discussion.

.UPDATE...
Updates have been made to the sky cover and sensible weather
portions of the forecast to better account for low clouds in
parts of the Umpqua Basin and the expected progression of those
clouds overnight into Sunday morning.

Additionally, some adjustments were made to the sky cover and fog
forecast along and near the coast for tonight through Sunday
evening as a weak marine stratus surge develops over the next 24
hours.

&&

.DISCUSSION...
A weak trough of low pressure exists at the surface across
northwestern California and along and near the Coast Range of SW
Oregon this evening. This is resulting in a light wind flow from
the southeast across the exposed ridges this evening, with light
winds elsewhere.

Overnight into the morning some low clouds are expected in the
Umpqua Basin and a weak marine stratus surge is expected along
and near the coast. Guidance suggests the low clouds and fog will
generally be from the beaches westward until late Sunday afternoon
or evening, though Brookings and Gold Beach and nearby areas
could be affected earlier.

Potential record highs the next couple of days are likely to be
the last for the foreseeable future as cooler weather with an
increasing possibility of rainfall moves in this week. It's likely
to take until Friday into the weekend for most inland areas east
of Douglas and Josephine counties to be affected by measurable
rainfall, however. ~BTL

&&

.AVIATION...For the 01/06Z TAFS...VFR conditions are expected
through the TAF period. The one exception could be in Roseburg where
there's a chance for patchy shallow fog to develop towards daybreak
Sunday. The one thing that could prevent patchy low clouds and fog
from developing will be the offshore flow. If it's sufficient, then
it will remain VFR, but decided to lean on the side of caution.
Later shifts will need to monitor this. -Petrucelli

&&

.MARINE...Updated 900 PM PDT Saturday 31 Oct 2020...A couple of
changes were made to the forecast this evening. First was to reduce
winds given the buoys have shown diminishing winds in the last few
hours as the thermal trough has weakened and shifted inland. Second
the coverage of small craft conditions haver been reduced to be
mainly confined to areas south of Bandon and beyond 8 nm from shore
between Port Orford and Pistol River. Despite the decrease in winds,
a northwest swell between 8 and 10 feet at 10 seconds combined with
wind driven seas will still result in small craft conditions lasting
into tonight.

Calmer conditions are expected Sunday through Monday afternoon.
South winds will increase Monday night into Tuesday ahead of an
approaching front and could approach small craft for a brief time
Tuesday afternoon in the northern waters.

Late next week, a storm system is poised to bring significant west
to northwest swell of 15 to 18 feet at 15 seconds. This could create
issues with higher surf and large breakers, especially at the coast.
Confidence in the details (namely the height and period of this
incoming swell) are low, but wanted to highlight the drastic change
in pattern that is coming. -Schaaf/petrucelli

&&

.BEACH HAZARD...Updated 200 AM PDT Saturday 31 OCT 2020...A long
period swell group will arrive Sunday afternoon and likely persist
into early Monday morning. This arriving swell will have the
potential to create beach hazards due to waves running further
onshore than normal, or sneaker waves. A beach hazards statement for
these sneaker waves will continue. Remember, sneaker waves can knock
unsuspecting beachgoers down and sweep them out to sea where shock
and hypothermia will occur quickly. Logs and other debris can be
lifted and carried by these waves, crushing or entrapping
unsuspecting victims underneath. Never turn your back on the ocean,
and avoid swimming in the ocean on Sunday afternoon through Monday.

&&

.FIRE WEATHER...Updated 200 PM PDT Saturday Oct 31 2020...
The latter portion of next week, Thursday night or Friday, is likely
to see the beginning of a long-awaited, long-lived transition to
much cooler, and wetter conditions. There is a high level of
uncertainty regarding the coverage and amounts of precipitation.
But, the probability will be highest in southwest Oregon. There is
also a possibility that the higher terrain will receive snow.

Upper level ridging and a thermal trough along the coast will
produce a drying trend with very warm, near record afternoon
temperatures this afternoon into Tuesday, with moderate ridge top
recoveries.

The ridge will gradually give way to low pressure troughing over the
Pacific Northwest. From Tuesday afternoon through Thursday
afternoon, the weak southern end of a series of disturbances will
brush Coos and northern Douglas counties with occasional chances of
light showers. Meantime, the remainder of the area will continue to
experience much warmer than normal afternoons, but with a trend of
improvement in minimum RH. The extreme of warmth and dryness away
from the coast and Umpqua region is expected on Monday, and will
resemble the conditions from yesterday (Friday).

The big change looks to occur Friday. It is likely to be well into
2021 before our area next has a day with such warm high temperatures
and low minimum RH approximating the early to mid-week conditions.
-DW/BPN

&&

.PREV DISCUSSION... /Issued 349 PM PDT Sat Oct 31, 2020/

DISCUSSION...Dry weather will continue through at least Monday
with cold to chilly starts to the mornings followed by mild
afternoons. The latest visible image shows clear skies over most
of the forecast area. The exception is in portions of the Umpqua
Basin where leftover marine stratus remains and most of this
should burn off in the next couple of hours. However there is a
chance it may not clear out at all south and southwest of
Roseburg including Camas Valley.

Inland ares are experiencing very mild temperatures for this time
of the year. Last check Medford was 81 degrees which is going to
break the old record of 75 set back in 2015 and 1949! This will
likely be the last 80 degree day we experience this year in
Medford (although were forecasting a high of 77 degrees tomorrow).

A thermal trough will remain along the coast with weak to
moderate offshore flow which should prevent marine stratus from
developing along the coast. However we can expect marine stratus
to develop once again in portions of the Coquille and Umpqua
Basin late tonight and lasting into Sunday morning. Elsewhere it
will remain clear.

Sunday will be similar to today with a chilly start to the morning
followed by a mild afternoon. high temperatures in the Coquille
and Umpqua Basin will be tricky and much will depend on how soon
the marine stratus burns off. The thermal trough is expected to
weaken and move onshore and this will result in weak onshore flow
at the coast with marine stratus returning to the coast overnight
Sunday night.

Monday will remain dry with a mild afternoon temperatures for most
inland locations. Temperatures Monday are expected to be a few
degrees lower than Sunday, but still above normal for this time of
the year.

Tuesday, the ridge axis shifts east and a weak upper trough will
approach from the west. At the same time a weak front will bring
some rain to the coast, coastal mountains, Cascades and mainly
north of the Umpqua Divide. Even then were only expecting light
rainfall amounts.

Tuesday will mark what will be a change in the pattern from dry
and warmer to a cooler and wetter. This will be a gradual chance
with the aforementioned weak front on Tuesday, followed by
another one Wednesday afternoon or evening and a third on
Thursday. The Wednesday and Thursday front are not expected to
bring much in the way of precipitation. Despite the cooling
Wednesday and Thursday, afternoon temperatures will still be above
normal for this time of the year.

The main event in terms of cooler and wet weather will come by the
end of next week. A stronger front will arrive Friday morning
bringing a good chance of measurable precipitation west of the
Cascades. At the same time, the coolest air mass so far this
season is expected to move into the area Friday night which could
bring snow levels down to around 3000 feet by Saturday morning.
However the main question will be how much moisture will be left
by the time this happens. Even then the Cascades and Siskiyous
could pick up a good shot of snow Friday night as the front moves
through and snow levels lower. Keep in mind this is still a long
ways out and the details will likely change in terms of the
timing, but the evidence is stronger that we'll end up cooler and
wetter next weekend. -Petrucelli

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Beach Hazards Statement from Sunday afternoon through Monday
     morning for ORZ021-022.

CA...None.

Pacific Coastal Waters...
- Beach Hazards Statement from Sunday afternoon through Monday morning
  for PZZ350-356.
- Small Craft Advisory until 4 AM PST Sunday for
  PZZ350-356-370-376.

BTL/MAP/CC