668
FXUS66 KMFR 142153
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
253 PM PDT Wed Aug 14 2024

.DISCUSSION...Cumulus clouds are starting to build generally in
southern Jackson county...south central Siskiyou county...and much
of Klamath and Lake counties...where thunderstorms are forecast.
There is quite a bit of uncertainty with the westward extension of
thunderstorms...especially for the rogue valley...where smoke may
keep us from getting to the convective temperature. Either
way...the short term models have been very consistent in
thunderstorms initiating generally along a line from Yreka into
Klamath Falls between 3 and 5 pm. Showers and thunderstorms will
move northeast...impacting the northern half of Klamath and Lake
counties around 10 pm. The activity will move out of the area
around 5 am Thursday before a very short break in the action.

The second round of thunderstorms is expected develop in Klamath
and Lake counties early Thursday afternoon. The best chance for
thunderstorms (25% to 35% chance) will be mid Thursday afternoon
into the early evening hours over northern Lake county. Please see
below for more information regarding fire weather concerns.

Otherwise...our focus shifts to this weekend as an upper low drops
south along the PacNW coast Friday into Saturday. There is a lot
of uncertainty with the position of the low and how it impacts the
precipitation forecast over the weekend. For instance, about a
third of the clusters indicate precipitation across much of the
area Saturday with the upper low a bit more to the east...compared
to two thirds to the clusters indicating the low position more to
the west...leading to a lesser chance of precipitation. About a
third of ensemble members show absolutely no precipitation for
Medford...where some show upwards of a half inch of rain.
Additionally...depending on the position of the low...there will
be the possibility of thunderstorms. Again...still a lot of
uncertainty with the weekend storm...but we will continue to
monitor closely and hone in on details over the next few days.

-Riley

&&

.FIRE WEATHER...Issued 245 PM Wednesday August 14, 2024...Upper
level troughing will remain the dominant weather pattern through the
forecast period. This will continue the trend of cooler than normal
temperatures, moderated humidities and breezy afternoon winds. The
two main fire weather concerns on the horizon are thunderstorm
potential today through Thursday and the development of a deep upper
low offshore over the weekend which could bring some strong winds to
the area.

First the thunderstorm potential...a shortwave trough will be moving
into the region today and linger over the area through Thursday.
With ample moisture and modest instability, isolated to scattered
thunderstorms are expected. Initially, isolated thunderstorms are
expected over portions of northern California, then spreading north-
northeastward into Oregon after sunset and into the overnight hours.
Isolated thunderstorm coverage is the most likely scenario today
mainly along and east of the Cascades (possibly as far west as the
Rogue Valley/Medford), but scattered coverage is possible as storms
move into Oregon across Fire Weather Zones (FWZ) 624/625. There will
be a break in thunderstorm activity early Thursday morning. The
trough will linger over the region Thursday afternoon, however, and
this will provide a better opportunity for scattered thunderstorms
over FWZ 624/625 due to daytime heating effects. Due to these
factors, a Red Flag Warning for abundant lightning on dry fuels will
be in effect starting this evening, and details can be found at
RFWMFR. Storms are expected to have some precipitation with them,
but lightning strikes outside of precipitation cores are possible
and cause for concern. Additionally, expect gusty and erratic winds
near thunderstorms with strong outflows that can travel a good
distance from the originating storm.

There has been a concern for the smoke moving to areas east of the
Cascades in the coming days with westerly flow. The HRRR smoke model
is matching well with the current satellite picture. With this in
mind, the westerly winds are on track to move the smoke to areas
east of the Cascades with the highest concentrations in Klamath
County. The smoke may be heavy enough to hinder thunderstorm
development, but convective temperatures are in a reasonable range
to reach, even if smoke does stay in the area of the Red Flag
Warning. The atmosphere will stabilize some on Friday. There will be
lingering moisture and instability, but without a sufficient
trigger/forcing mechanism, it`s likely there will be some cumulus
buildups east of the Cascades and over the higher terrain.

The next concern turns to a deep, large scale trough that develops
off the PacNW Coast late Friday into Saturday and lingers there well
into next week. This will bring some precipitation chances to the
region, though confidence is low on the details regarding where and
amounts. Ensembles suggest the best chances are along and west of
the Cascades, but there could be thunderstorms to accompany these
precipitation chances. The other element of concern with this low
pressure (and where the higher confidence lies) is the potential for
strong south to southwest winds. Guidance suggests gusts of 30-40
mph for areas east of the Cascades and in the Shasta Valley on
Saturday and Sunday afternoons. These strong winds could combine
with low humidities (which ultimately depends on where precipitation
chances occur) and result in critical fire weather conditions. Stay
tuned for updates as subtle shifts in the position of this low could
have big changes on the forecast. /BR-y/Hermansen

&&

.AVIATION...14/18Z TAFS...Generally VFR through the TAF period. An
upper trough remains in place over the Pacific northwest, bringing
more westerly winds that help to limit smoke accumulation west of
the Cascades. However, that does also mean that smoke may impact
visibilities east of active fires. For this area, that includes
possible periods of moderate to heavy smoke over Klamath, Lake,
eastern Douglas, and western Siskiyou counties.

Upper level instability could bring some thunderstorm chances later
today. 15-30% thunderstorm chances are present over Lake, Klamath,
and eastern Siskiyou and Jackson counties this afternoon and
evening. These chances will decrease early Thursday morning, with 15-
20% thunderstorm chances lingering over Klamath and Lake counties
through the end of the TAF period. Lightning, locally heavy rain
showers, and gusty erratic winds are possible hazards around any
storms that do develop. -TAD

&&

.MARINE...Updated 230 PM Wednesday, August 14, 2024...Relatively
calm conditions are expected for the next several days with light to
moderate winds and seas remaining 6 foot or less. There will be a
slight uptick in winds Thursday into Friday south west of Gold
Beach, but they will remain below advisory levels. A rather strong
upper low for this time of the year will move into the waters
Saturday and will likely bring showers over the waters.
-Petrucelli

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning from 8 PM this evening to 11 PM PDT Thursday
     for ORZ624-625.

CA...None.

PACIFIC COASTAL WATERS...None.

&&

$$