269
FXUS66 KMFR 161207
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
507 AM PDT Fri Aug 16 2024

.DISCUSSION...Satellite imagery this morning shows the marine
layer blanketing the Coast and waters north of Cape Blanco and
has filled the Umpqua Basin. This should be extent of the inland
intrusion of the marine layer tonight as it doesn`t look deep
enough to "spill over" the Rogue-Umpqua Divide. Skies are clear
for much of the remainder of the region, though there is some
fog/low clouds in portions of northern Klamath County north of
Chiloquin. Rather quiet conditions are expected today ahead of a
more eventful Saturday. There will be moisture and weak
instability present today, but with a lack of a defined trigger
coming through the region, thunderstorm chances are at a minimum
today. It`s likely there will be some cumulus buildups east of the
Cascades and over the higher terrain and there`s a small chance
(5-10%) a few of those buildups could result in a brief shower.
Otherwise, dry conditions are expected today along with continued
below normal temperatures (afternoon highs in the mid to upper 80s
for West Side Valleys and upper 70s to low 80s for areas east of
the Cascades). Despite the reprieve from the summer heat, smoke
will be a continued nuisance through the forecast period, and
probably longer. An Air Quality Alert (issued by partnering
agencies) is in effect for Klamath and Lake counties, and we have
relayed those via AQAMFR.

The cooler than normal pattern will continue as a deep, large scale
trough develops off the PacNW Coast late tonight into Saturday and
lingers there well into next week. The center of the low will be at
it`s southern most location on Saturday before it drifts northward
Sunday into early next week. As such, Saturday will be the day with
the highest precipitation potential through at least mid-week.
Confidence is fairly high that much of the area along and west of
the Cascades will see measurable precipitation (80-90% chance of at
least 0.01"), with wetting rains possible (25-50% chance of >=0.25")
over portions of western Siskiyou, Jackson and eastern Douglas
Counties. Models indicate ample instability to go with this moisture
so there is high confidence in thunderstorms occurring west of the
Cascades with this precipitation on Saturday. Strong storms are
possible on Saturday and the Storm Prediction Center (SPC) has a
portion of our region in a Marginal Risk (5-14% chance) of an
isolated severe thunderstorm over Jackson and eastern Douglas
Counties on Saturday. The main threat would be large hail and
damaging winds. If you have outdoor plans on Saturday, be prepared
for wet and windy conditions with widespread showers and scattered
thunderstorms. There is a good chance (50-70%) that the wildfires
burning in eastern Douglas County receive some beneficial
precipitation from this event, though there is some uncertainty
regarding amounts. Regardless, this event should help to reduce fire
activity and (hopefully) reduce smoke output, providing some relief
from the persistent smoky conditions.

Meanwhile, areas east of the Cascades are likely to remain dry and
deal with strong gusty winds. There will be a sharp gradient between
where precipitation chances drop off and the concern for strong
winds combines with low humidities and results in critical fire
weather conditions (see fire weather discussion for more details).
Current guidance suggests this gradient will be along and near the
Warners, extending northward to Winter Ridge/Summer Lake area. West
of that area, the chance for 0.01" of precipitation is about 50%,
while the chance for 0.10" drops to 10%. Farther east towards
Lakeview and Alturas, the chance for 0.01" of precipitation is only
10% with no solutions indicating a chance for higher amounts. The
bigger concern east of the Cascades will be strong winds where south
to southwest winds 20 to 25 mph with gusts 30 to 35 mph will be
common and gusts of 40 to 45 mph are not out of the question across
the higher terrain. The East Side won`t be the only place with
strong winds. The remainder of the region will see gusty winds too,
especially in the Shasta Valley, but winds will be strongest east of
the Cascades.

From Sunday onward, low pressure will drift northward and
precipitation chances will come to an end. We`ll remain under a
cooler than normal pattern with gusty afternoon breezes. Shortwaves
will rotate around this low pressure and into the region through the
forecast period, though the timing of these are difficult to
pinpoint at this time range. Stay tuned and monitor for updates as
these shortwaves could result in either enhanced afternoon winds
(possible fire weather concerns) or additional thunderstorm chances
at some point during the week. /BR-y

&&

.AVIATION...16/12Z TAFS...MVFR marine stratus is present over
the near shore waters from Cape Blanco northward, and inland into
the Coquille, Camas, and Umpqua valleys. This includes North Bend
(KOTH). This marine stratus will burn off during the morning with
ceilings gradually transitioning to clear skies late this morning
into early afternoon. A southerly surge of coastal IFR is expected
to reach Curry County, including Brookings and Gold Beach, after 03Z
this evening, with a mix of IFR and MVFR returning north of Cape
Blanco after 06Z. This will include the Coquille and lower Umpqua
valleys, and North Bend (KOTH). By early Saturday morning, showers
will become likely over the near shore waters and coastal area with
a slight chance of thunderstorms.

Farther inland, smoke will be thickest in the vicinity of wildfires
in central and eastern Douglas and southern Lane counties, where
MVFR visibility between 3-5 miles will be the predominate condition.
Smoke from these fires are likely to move into northern and central
Klamath County early this morning, and  could drift south towards
Klamath Falls. Otherwise, conditions will remain VFR. A chance of
showers will develop west of Interstate 5 early Saturday morning,
increasing to a showers likely with a slight chance to chance of
thunderstorms during Saturday, focused from the Coast Range to the
Cascades, but extending into Klamath and eastern Siskiyou counties.

-DW

&&

.MARINE...Updated 200 AM Friday, August 16, 2024...Relatively
calm conditions are expected for the next several days with light to
moderate winds and seas remaining 5 feet or less. A rather strong
upper low for this time of the year will move into the waters
Saturday and will likely bring showers with a slight chance of
thunderstorms into early Sunday morning. -DW

&&

.FIRE WEATHER...Issued 400 AM Friday August 16, 2024...Rather
quiet conditions are expected today ahead of a more eventful
Saturday. There will be moisture and weak instability present
today, but with a lack of a defined trigger coming through the
region, thunderstorm chances are at a minimum today. It`s likely
there will be some cumulus buildups east of the Cascades and over
the higher terrain and there`s a small chance (5-10%) a few of
those buildups could result in a brief shower. Otherwise, dry
conditions are expected today along with continued below normal
temperatures and moderated humidities.

There are two main fire weather concerns in the short term with the
development of an unseasonably strong low pressure off the Pacific
Northwest late tonight into Saturday: scattered thunderstorms with
potential of wetting rains along and west of the Cascades and gusty
winds combined with low RHs east of the Cascades.

Thunderstorms...there is fairly high confidence that much of the
area along and west of the Cascades will see measurable
precipitation (80-90% chance of at least 0.01"), with wetting rains
possible (25-50% chance of >=0.25") over portions of western
Siskiyou, Jackson and eastern Douglas Counties. Models indicate
ample instability to go with this moisture so there is high
confidence in thunderstorms occurring west of the Cascades with this
precipitation on Saturday. The uncertainty lies in how much
lightning there will be...will it be a convective event with
abundant lightning or will it be a broad area of showers with
embedded thunderstorms. High resolution models indicate a bit of
both with widespread showers and scattered thunderstorms. Scattered
coverage looks most favorable over Fire Weather Zones
280/621/622/617/623, but a subtle shift westward in the low position
could also include zones 620 and 616. Would like to let the dayshift
today coordinate with area IMETs regarding any fire weather watches
for abundant lightning west of the Cascades.

There will be a sharp gradient between where precipitation chances
drop off and the concern for strong winds combines with low
humidities and results in critical fire weather conditions. Current
guidance suggests this gradient will be along and near the Warners,
extending northward to Winter Rim/Summer Lake area. West of this
area, there is about a 50% chance for measurable precipitation (at
least 0.01"). Chances really drop off for amounts greater than that,
so mainly dry conditions are expected east of the Cascades in
general. Father eastward, a Fire Weather Watch has been expanded for
the combination of strong gusty winds and low RHs. The watch now
includes much of FWZ 625, the eastern half of the Modoc (FWZ 285)
and the far southeastern corner of FWZ 624. Gusty south to southwest
winds of 20 to 30 mph with gusts of 35 to 40 mph will be common
where we have the watch in place and daytime humidities are expected
to reach into the low teens in this area. Gusty winds are also
expected in the Shasta Valley and across the Klamath Basin, but RHs
should remain high enough to preclude critical conditions there.

Beyond Saturday, the upper level low will drift northward but
continue to influence the region`s weather. Precipitation chances
drop out of the forecast for Sunday onward but gusty afternoon winds
will continue through the week. Temperatures will remain cooler than
normal through the forecast period. Shortwaves will rotate around
this low pressure and into the region through the forecast period,
though the timing of these are difficult to pinpoint at this time
range. Stay tuned and monitor for updates as these shortwaves could
result in either enhanced afternoon winds or additional thunderstorm
chances at some point during the week. /BR-y

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Fire Weather Watch from Saturday afternoon through Saturday
     evening for ORZ624-625.

CA...Fire Weather Watch from Saturday afternoon through Saturday
     evening for CAZ285.

PACIFIC COASTAL WATERS...None.

&&

$$

MNF/DW