NWS Medford, OR wrote its last area forecast discussion before the first event at Sep 23, 1:47 PM PST, 1 hour 13 minutes earlier.
Area forecast discussion, Sep 23, 1:47 PM PST, 1 hour 13 minutes before
Area Forecast Discussion
National Weather Service Medford OR
247 PM PDT Sat Sep 23 2023
Updated aviation discussion.
.DISCUSSION...Southwesterly flow continues ahead of an approaching
low pressure system. Unfortunately, these winds are blowing smoke
from the Smith River Complex fires directly across Jackson County
and western Siskiyou County. Additionally, smoke from the Tyee Ridge
COmplex fire is moving across the Umpqua Valley. Accumulated smoke
may linger overnight in these areas as surface winds calm.
Temperatures look to cool on Sunday as a cold front associated with
an upper level low pressure system approaches the Oregon coast.
Winds will turn southerly Sunday morning, making smoke a concern for
Josephine and Douglas counties. These southerly winds are expected
to funnel in to the Shasta Valley starting Sunday afternoon, making
high winds a concern for the area. Chances of precipitation through
Sunday will be best along the Oregon coast (70-90%) with chances
decreasing to the east (30-60%). Rainfall amounts for Sunday are not
expected to be impactful.
Monday will be the most active day as the cold front starts to move
over the area. Widespread precipitation is expected through the day
Monday, with areas south of and including Port Orford expected to
get 2-3 inches of rain. Coastal areas north of Port Orford will get
1-2 inches of rain, and other areas east of the Cascades will get
0.5-1.5 inches. The east flank of the Cascades will get 0.25-0.5
inches, and lower amounts will fall farther to the east.
Possible rainfall totals remain a concern for some of the larger
burn scars in the coverage area, as this is the first significant
post-summer rainfall and could sweep up loose debris over
hydrophobic surfaces. A Flood Warning is in place from Sunday 11
PM through Monday 8 PM to cover the areas from these fires:
Flat Fire, Anvil Fire, Tyee Complex, Smith River Complex, Head
fire, and (2022) McKinney burn scar. Please see FFAMFR for
additional details on the Flood Warning. Localized flooding is
also possible in areas with poor drainage, or where drainage
becomes obstructed by debris. Use extra caution in areas of
accumulated or standing water.
Elevated gusty winds are also expected Monday as the cold front
moves eastward. In most areas, these winds will not be impactful,
but are worth noting given the likely wet surfaces that will be
present. Winds along the coast will be strong (15-25 mph, possible
40 mph gusts), and southwest flow may bring higher than expected
winds into the Illinois Valley. Strong winds are expected to
continue in the Shasta Valley though most of Monday as well as
across areas east of the Cascades. A Wind Advisory is in place from
Sunday 2 PM until Monday 2 PM for the Shasta Valley, and from Monday
2 AM though Monday 8 PM for eastern Klamath, southern Lake,
northeast Siskiyou, and most of Modoc counties. Please see NPWMFR
for more details about the Wind Advisory.
Post-frontal showers look to continue west of the Cascades through
Tuesday, and a weaker front will support widespread light rainfall
Wednesday. Guidance still varies on what to expect going in to
October, with both the GFS and ECMWF global models split on further
rainfall chances for next weekend. -TAD
&&
.AVIATION....24/00Z TAFs... Radar imagery shows a band of
precipitation starting to come ashore in the region in Coos County,
with a period of light rain and MVFR conditions expected from this
as it passes through North Bend. Conditions may be up and down for a
period after, but general improvements back to MVFR will be the
trend later this evening. This is a fairly weak front and won't make
much in the ways of impacts further inland as it breaks apart.
Meanwhile, smoke from the Smith/Happy Camp complexes and the Anvil
Fire has been thicker and been advected further than expected into
the Rogue Valley/Medford area and the Umpqua Basin/Roseburg
respectively. Smoke models are far too optimistic in modeled
visibility impacts from this, but am expecting a trend towards
dispersion and improving visibilities through the evening, though
confidence in how much dispersion isn't high.
A second, much stronger front approaches the coast tomorrow, which
will lead to gusty southerly winds at the coast and east of the
Cascades as the pressure gradient tightens ahead of it.
Additionally, ceilings lowering and pre-frontal precipitation will
lead to periods of MVFR at the coast. -CSP
&&
.MARINE...Updated 200 PM September 23, 2023...Relatively calm
conditions are expected to continue into tonight, with light to
moderate southerly winds and low seas. A weak cold front will move
through the waters late this afternoon.
A strong storm for this time of the year will begin to take shape
tonight with a surface low deepening near 140W and 45N, moving
northeast Sunday, then more northerly Sunday night. Meanwhile, a
strong occluded front (for this time of the year) will approach the
waters Sunday with south winds increasing to advisory levels quickly
during the morning. Strong gales and a period of very steep,
hazardous seas are then expected across all waters by Sunday
afternoon, lasting through at least Sunday night (Gale Warning is in
effect). Models have backed off slightly on the 925 mb winds with
the high res guidance showing winds close to 70 kts early Sunday
evening in the northern outer zone (beyond 10 NM from shore north of
Cape Blanco). The net result would be a lesser chance for storm
force winds. However, we'll continue to monitor this.
The front will move inland Monday morning and winds will gradually
diminish below gales. However, a fresh swell will quickly follow the
passage of the front late Monday morning, with west swells peaking
in the 14-18 foot range at 14 seconds Tuesday. So, while winds will
ease, the very steep, hazardous sea state will persist through
Tuesday afternoon.
By mid week, models show another low headed toward Vancouver Island
with a front approaching the waters Tuesday night into Wednesday
morning. However, this low unlike the the first one is weaker and
the expected incoming front is weaker. The general consensus among
the models shows at least Small Craft conditions, with gales not
expected at this time. This will be a quick moving system, this
Small Craft Conditions probably lasting not much longer than 6
hours. -Petrucelli
&&
.FIRE WEATHER...Updated 200 PM PDT Saturday, September 23, 2023...No
fire weather concerns are anticipated through the forecast period,
at least not in the traditional sense. A weak front is passing
through the region this afternoon and this will bring some enhanced
breezes across the area with below normal afternoon temperatures.
Light rain is possible this afternoon and evening, with the best
chances expected along the coast and inland to roughly the
Roseburg/Grants Pass I-5 corridor.
The attention turns to a large scale trough expected to arrive
Sunday and influence the weather through much of next week. Strong
gusty winds are expected ahead of and with the arrival of this
trough, but humidities will be increasing at the same time.
Widespread wetting rainfall is expected late Sunday into Monday,
which will be moderate to heavy at times west of the Cascades.
Rainfall is expected east of the Cascades as well, but amounts will
be significantly less...generally 0.25"-0.40" for fire weather zones
624 and eastern 284, and a tenth of an inch of less across the Modoc
and fire weather zone 625. Given the relatively hefty precipitation
amounts (1" to 3") expected over the ongoing fires, debris flows
and/or landslides are a concern and a Flood Watch is in effect most
of these burn scars. This includes the Flat fire, Anvil fire, Tyee
Complex, Smith River Complex, the Head fire and the McKinney burn
scar from 2022.
Deep upper troughing remains over the area Tuesday with cool and
showery weather continuing through much of next week. /BR-y
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Flood Watch from Sunday evening through Monday evening for
ORZ021>024.
Wind Advisory from 2 AM to 8 PM PDT Monday for ORZ029>031.
CA...Flood Watch from Sunday evening through Monday evening for
CAZ080-081.
Wind Advisory from 2 PM Sunday to 2 PM PDT Monday for CAZ081.
Wind Advisory from 2 AM to 8 PM PDT Monday for CAZ084-085.
PACIFIC COASTAL WATERS...Small Craft Advisory from 8 AM to 2 PM PDT
Sunday for PZZ350-356-370-376.
Gale Warning from 2 PM Sunday to 11 AM PDT Monday for PZZ350-356-
370-376.
&&
TAD/MNF/MAP