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000
FXUS66 KMFR 231154
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
454 AM PDT Sat Sep 23 2023

Updated AVIATION Section

.DISCUSSION...An upper level trough will begin to move into the
Pacific Northwest today with a strong cold front reaching the
coast late Sunday afternoon and Sunday night, then moving inland
Monday morning and afternoon. Behind the front, a large upper
trough will push inland over the region Monday night and Tuesday.
With the front, strong, gusty winds and moderate to heavy
rainfall impacts are expected late Sunday through Monday. The
highest wind impacts will be along the coast and into the Shasta
Valley. Heaviest rainfall will be along the coast, over the
coastal mountains and into southwest Josephine and western
Siskiyou County.

Today, the main impacts will be mainly with air quality as
southwest flow ahead of the trough allows wildfire smoke from
fires in northern California and southwest Oregon to spread
across the area. Otherwise, expect near seasonable temperature and
breezy afternoon winds across inland areas and a chance for light
rain showers along and near the coast.

The pattern will change beginning Sunday as a strong front
approaches. Late Sunday into Monday, the front will gradually move
inland with widespread rain spreading across the area. Heaviest
rain (1 to 3 inches) is expected along the coast and into the
coastal mountains, southwest Josephine  and western Siskiyou Co
with moderate rain (0.5 to 1.25 inches) across the Umpqua Valley,
Jackson County, central Siskiyou County and the Cascades. Lighter
rain is expected east of the Cascades. While this rainfall will
be mostly beneficial as we are coming out of the dry season, there
is a risk that moderate to heavy rainfall could produce debris
flows on this season`s burn scars. A flood watch continues in
portions of Curry, Coos, southwest Douglas County and western
Siskiyou County (please see the FFAMFR for details). The watch
covers areas where debris flow or flash flooding are a concern,
including around the Tyee Ridge, Anvil, and Head fires.
Additionally, localized water accumulation or road ponding may be
an issue anywhere with poor drainage, or drainage clogged with
debris. Rainfall may also result in slick roadways. Use extra care
traveling around areas of accumulated or standing water.

With this front and upper trough there is also a chance (15-25%)
for thunderstorms Sunday evening/night over the coastal waters and
Monday morning through Monday evening for the coast, coastal
mountains and inland into western Douglas, western Josephine and
extreme western Siskiyou Counties.

Finally, ahead of and with the frontal passage, strong gusty
winds are expected to develop across much of the area. Models show
a 45 to 60 kt 700 mb jet (southwest winds) moving inland over the
area Sunday evening and Monday, and a 50-65 kt low level jet
(southerly winds) moving into the coast Sunday afternoon and
night. High resolution models and model guidance support a
potential for high winds (gusts 50-65 mph) along the coast and
into the Shasta Valley late Sunday into Monday. A high wind watch
remains in effect for the coast and southern Shasta Valley
(NPWMFR). For other inland areas expect gusty south to southwest
winds, strongest over the mountains and east of the Cascades. The
National Blend of Models shows a high chance for gusts of 34 mph
or greater (60-90% chance) for most all areas east of the
Cascades late Sunday through Monday with a 30-60% chance of seeing
gusts of 41 mph or greater. Locally, model guidance supports
gusts of around 50 mph, including over the higher mountains in
eastern Klamath, Lake and Modoc Counties and in the Summer Lake
area. Where rain is more limited on Sunday (across Lake County),
gusty winds may result in blowing dust, especially for areas
across northern and east- central Lake County.

Behind this front, the upper trough will move into the area
bringing a showery and cool pattern Monday night and Tuesday. Then
another frontal system may move inland late Tuesday night and
Wednesday.


&&

.AVIATION...23/12Z TAFs...IFR/LIFR is widespread along the
coast, especially from Cape Blanco southward this morning. Areas of
MVFR stratus exist north of Cape Blanco, including at North Bend and
portions of interior Coos Couny. These lower conditions will become
VFR later this morning/early this afternoon as a weak front
dissipates near the coast. This front could bring some light
showers/light rain to North Bend through this evening, but nothing
more than a brief/vicinity shower near Roseburg. Lower ceilings will
likely return to the coast tonight. Farther inland, VFR will prevail
with just some high and mid level cloudiness at time in Medford and
at Klamath Falls. However, areas of smoke and/or haze could limit
visibility to MVFR at times, especially at Medford this morning.
-Spilde


&&

.MARINE...Updated 230 AM September 23, 2023...Relatively calm
conditions are expected to continue today, with light to moderate
southerly winds and low seas as a cold front weakens over the area.

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). Model 925 mb winds approach 75kt in the northern outer zone
Sunday night (beyond 10 NM from shore north of Cape Blanco), which
could result in occasional storm force wind gusts there (greater
than 55 kt). We`ll be monitoring this to see if an upgrade is
necessary.

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. This typically results in at least small craft conditions
and possibly gales. Ensemble members show about a 30-40% chance of
gale force wind gusts across the northern waters (north of Cape
Blanco) during this time period, but this appears like a fairly
quick-moving system, so it shouldn`t last too long. We`ll continue
to evaluate and focus more on specifics as we get closer. -Spilde


.FIRE WEATHER...Updated 200 PM PDT Friday, September 22,
2023...Warm and dry weather will continue today with breezy
afternoon winds. Minimum humidities will remain low, especially
east of the Cascades and for valleys in Jackson and Siskiyou
counties, but not critically low. So we aren`t anticipating any
critical fire weather conditions through the forecast period.

A moist front will arrive Sunday into Monday followed by a large
scale trough. This will influence the weather through at least
the middle of next week. Strong gusty winds are expected ahead of
and with the arrival of the front Sunday afternoon and night with
gusty winds continuing into Monday but humidities will be
increasing at the same time. High wind watches are in place for
exposed and elevated areas along the coast and for areas in the
southern Shasta Valley due to the potential for winds to gust up
to 65 mph (Please see the NPWMFR for details). Strong, gusty winds
are also expected across higher peaks in western Siskiyou County,
the Siskiyous and from the Cascades east late Sunday through
Monday afternoon (gusts 30-45 mph likely and locally higher 50-60
mph).


Widespread wetting rainfall is expected late Sunday through
Monday, which will be moderate to heavy at times west of the
Cascades.

Storm total rainfall (late Sunday afternoon through Monday night)
of 1 to 3 inches is expected along the coast and over coastal
mountains with 1 to 2 inches across southwest Josephine and
western Siskiyou Counties. Further inland across the Umpqua,
Jackson county and central Siskiyou County, storm total rainfall
of around 0.5 to 1.25 inches is expected. The heaviest rainfall
rates are expected late Sunday evening through Monday afternoon
for these areas along the coast, into Josephine and western
Siskiyou Co. The National Blend of Models shows a high probability
(80-90%) of greater than an inch of rain in 24 hours (Sunday
evening through Monday afternoon) along the coast, into the
coastal mountains and over the mountains in western Siskiyou Co.
The National Blend of Models also indicates a 40-60% probability
of over 2 inches of rainfall in 24 hours across Curry County and
extreme southwest Josephine and extreme western Siskiyou
counties. 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. Rainfall is also expected east of the Cascades as
well, but amounts will be significantly less...generally
0.15"-0.50" for fire weather zones 624 and eastern 284, and a
tenth of an inch of less across the Modoc and fire weather zone
625.

Deep upper troughing remains over the area Tuesday with cool and
showery weather continuing through much of next week. -CC


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Flood Watch from Sunday afternoon through Monday evening for
     ORZ021>024.

     High Wind Watch from Sunday afternoon through late Sunday night
     for ORZ021-022.

CA...Flood Watch from Sunday afternoon through Monday evening for
     CAZ080-081.

     High Wind Watch from Sunday afternoon through Monday afternoon
     for CAZ081.

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.

&&

$$

CC