NWS Medford, OR wrote its last area forecast discussion before the first event at Aug 25, 9:32 AM PST, 1 hour 51 minutes earlier.
Area forecast discussion, Aug 25, 9:32 AM PST, 1 hour 51 minutes before
FXUS66 KMFR 251640 AFDMFR
Area Forecast Discussion
National Weather Service Medford OR
1032 AM PDT Fri Aug 25 2023
...Updated Aviation Discussion...
.DISCUSSION...The thunderstorms yesterday brought 323 strikes to
the forecast area, the majority of which occured in western
Siskiyou county and north into Oregon west of the I-5 corridor.
The main concern today is smoke, and the latest models line up
pretty well with what is in the current forecast and will not
update this morning. -Sven
&&
.AVIATION...25/18Z TAFs...MVFR/IFR will continue for much of the
western half of Douglas and Siskiyou Counties as well as Curry,
Coos, Josephine, Jackson County including TAF sites (KOTH, KRBG,
KMFR) because of mist or smoke. The smoke will continue through the
TAF period with some fluctuation between categories.
IFR coastal stratus are expected to lift this afternoon, while the
smoke will remain. However, the smoke make not reduce visibilities
too much at KOTH. Otherwise, the coastal stratus and fog will return
to the area, including at KOTH again tonight. -Schaaf/BPN
&&
.PREV DISCUSSION... /Issued 328 AM PDT Fri Aug 25 2023/
DISCUSSION...Shower and thunderstorm activity is gradually
winding down this morning, with current activity (~2 am) focused
over Coos/Douglas Counties as well as Lake County. This activity
is courtesy of a negatively tilted trough moving through the
region this morning. This latest round of shower/thunderstorm
activity has around 300 lightning strikes with rainfall amounts
that have generally been less that a tenth of an inch. There was a
heftier cell earlier tonight where the core of the storm moved
over the Mt Yoncalla RAWS (near Drain, OR) and 0.41" was measured
out of that cell.
Moisture and instability will continue moving northward this morning
and West Side showers/thunderstorms will move north of the forecast
area by sunrise. Showers and isolated thunderstorms will continue
moving north through Lake County this morning and gradually diminish
after sunrise. Once this activity ends, dry conditions are expected
for the remainder of the day as the trough and associated
moisture/instability move well north and east of the area.
Temperatures will be a few degrees cooler compared to yesterday's
values, and with thick smoke across the region, afternoon highs may
even end up a few degrees cooler than what is in the forecast. Mid
90s (mid 80s) for valleys west (east) of the Cascades are expected
through the weekend, and though these values are only around 2 to 5
degrees above normal for this time of year, poor air quality due to
wildfire smoke may limit cooling options for those without adequate
air conditioning as opening windows may not be an option for some.
Speaking of smoke, air quality is quite poor across the region this
morning, and unfortunately, not much change is expected through the
weekend as the upper level pattern will remain relatively
stationary.
Low pressure will stall off the Oregon coast, and this will maintain
south to southwesterly flow over the region, which will continue to
push smoke from the Smith River Complex north and eastward. The
position of this low will be farther north and west than the
previous low pressures earlier this month and this is not optimal
for bringing the moisture rich, unstable monsoon air into the
region. This will likely lead to dry conditions for much of the area
through the weekend, though some isolated showers/thunderstorms
could be possible over the far eastern portion of the forecast area
(Lake County and eastward) on Saturday. This low will gradually push
eastward late weekend into early next week. As this happens, high
pressure over the intermountain west will amplify and slow the
inland progression of this low pressure. Eventually the low pressure
pushes into the ridge and moves over the Pacific Northwest Tuesday
into Wednesday. Given the very dry air it'll move into, very little,
if any, precipitation is expected with this system. That said, the
best chances for any precipitation will be along the coast and into
the Umpqua Basin. For the remainder of the area, however, the most
notable change will be cooler temperatures (about 5 to 10 degrees
below normal) and likely some enhanced afternoon breezes. There is
the potential for some air quality improvement as this system passes
through next week due to the large scale, though temporary, pattern
change. Predicting smoke impacts at this time range, however, is
very challenging and confidence in the extent of, if any,
improvement is low at this time. /BR-y
MARINE...Updated 200 AM PDT...Weak low pressure will set up
over the waters today with light winds that will shift to south this
morning. Relatively calmer conditions are then likely to persist
this weekend into early next week. -DW/BPN
FIRE WEATHER...Updated 200 AM PDT Friday, August 25,
2023...Shower/thunderstorm activity will continue to wind down
this morning, which is occurring faster than was anticipated. The
Red Flag Warning (RFW) was cancelled early for Fire Weather Zones
(FWZ) 280/618/619/620/621 and the RFW for FWZ 618/616 will now
expire at 5 am PDT instead of 11 am. Around 300 lightning strikes
have been recorded with this recent round of activity and most
rainfall observations were under 0.10". One storm core did move
over the Mt Yoncalla RAWS (near Drain, OR) and 0.41" was recorded
under that cell. West Side activity is expected to move out of the
area by sunrise, and isolated showers/thunderstorms over Lake
County should come to an end just after sunrise. Moisture and
instability will move north and east of the forecast area later
this morning, and dry conditions should persist for the remainder
of the day and through the weekend. Another round of breezy south
to southwest winds are expected this afternoon, mainly east of the
Cascades and in the Shasta Valley. Humidities will remain above
critical values, however, so we aren't expecting any critical fire
weather conditions today.
The forecast through the weekend will largely be a rinse and repeat
as low pressure remains stalled off the Oregon Coast. We'll remain
under southerly flow with this pattern, but the low won't be far
enough south to bring in monsoon air so dry weather will likely be
the rule for the weekend. There are some slight chances, however,
for showers/thunderstorms across eastern portions of FWZ 625 on
Saturday, but coverage looks isolated at this time.
Low pressure will move inland late weekend into early next week, and
temperatures will trend cooler. There are some indications of some
light precipitation possible with this system, but chances (10-20%)
are best for areas along the coast north of Cape Blanco and maybe
into the Umpqua Basin. East of the Cascades, however, there could be
some heightened fire weather concerns on Tuesday as this trough
swings through and winds increase in response. Depending on how low
humidities get, critical fire weather conditions could be possible
Tuesday afternoon. /BR-y
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...None.
CA...None.
PACIFIC COASTAL WATERS...None.
&&
SBN/SBN/SBN