Red Flag Warning 23, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
1047 AM PDT Tue Aug 26 2025

.DISCUSSION.../Issued 536 AM PDT Tue Aug 26 2025/
Warm temperatures continue across a broad ridge, while a weak low
pressure system looks to remain off the California coast.
Southerly flow aloft looks to continue supplying atmospheric
moisture to fuel afternoon and evening rain showers and convective
thunderstorms. Current guidance shows good agreement for activity
across northern California and areas east of the Cascades, with
lesser chances over Jackson, Josephine, and eastern Douglas
counties. Activity looks to decrease quickly in the late evening
and nighttime hours.

Above average temperatures as well as rain shower and
thunderstorm chances look to remain in the forecast for Wednesday,
but with less activity expected over a smaller area. With the low
weakening and shifting northward, chances for showers and
thunderstorms west of the Cascades decrease with the best chances
in northern California counties.

The broad upper ridge looks to stay in place through the end of
the week. Deterministic imagery from both the ECMWF and GFS show
a low pressure system pushes into the ridge and may bring some
cooling through the weekend. There's some slight variations in how
the low behaves. These variations may account for wide ranges of
possible temperatures in the NBM's long-term guidance. Using
Medford as an example, a 10-degree range in the interquartile
range for next week does communicate some uncertainty. The
movement of the low pressure system is somewhat erratic as it
pushes into the larger ridge, making any concrete impacts
difficult to forecast. Given the current resiliency of the upper
ridge and expected warm temperatures through next week, there's
little surprise in ECMWF and GFS meteograms showing little
organized signals for rainfall through early September. -TAD

&&

.AVIATION...26/18Z TAFs...Marine stratus is keeping IFR and LIFR
conditions in place along the coast. We should see these ceilings
being to lift a bit this afternoon into MVFR levels at some
locations. We'll also see thunderstorms pop up again mainly east of
the Cascades and in northern California. These storms can locally
lower ceilings and visibilities and cause gusty and erratic winds.
This lightning activity is expected to decrease quickly in the
late evening and nighttime hours.

-Smith/TAD

&&

.MARINE...Updated 800 AM PDT Tuesday, August 26, 2025...A thermal
trough will maintain gusty north winds and steep seas across all
area waters through this evening. The thermal trough will weaken and
conditions will improve from tonight onward, with relatively calm
conditions continuing into the weekend. The thermal trough could
return with north winds and steep seas early next week.

&&

.FIRE WEATHER...Updated 200 PM PDT Monday, August 25, 2025...Some
slight cooling is expected over the next few days, but highs are
expected to remain above normal through much of the week. Excessive
heat warnings remain in effect. Please see NPWMFR for more details.
Humidities will slowly improve over the next few days, especially
eats of  the Cascades, as monsoonal moisture flows into the region
from the south, but this also means that there will be a threat of
thunderstorms through Wednesday.

The "Four Corners" high has retreated back to the southeast, with a
weak but broad trough now overhead. The broad circulation with this
trough can be seen on radar and satellite imagery spinning over the
Cascades just northeast of Bend. This has allowed temperatures to
cool slightly, along with help from increased cloud cover, but heat
remains a concern for areas west of the Cascades and inland from the
coast. At the same time, this circulation is pulling more moisture
up from the south into areas along and east of the Cascades, while
pulling in some drier air from the north into areas to the west,
accounting for the clearer skies there. A special sounding was taken
this morning at Medford, and found that precipitable water was at
just under 1.2 inches, nearly but not quite a daily record for this
calendar day. This makes sense given some of the heavy rainfall
amounts recorded in portions of the area yesterday.

Today, conditions will be very similar to yesterday. Therefore, the
thunderstorm threat returns for many of the same areas, including a
bit farther to the west across the western slopes of the Cascades
and into the Rogue Valley and surrounding mountains. Due to the more
widespread lightning threat today, a Red Flag Warning remains in
effect for these most likely affected areas. Details can be found at
PDXRFWMFR. Given the high moisture content ofthe atmosphere, these
storms will be wet, and could produce heavy rain within the cores,
but could still produce gusty outflow winds of up to 50 mph
and abundant lightning outside those cores.

Showers and a few isolated thunderstorms could continue east of the
Cascades tonight and into early morning. Confidence is low, but
given the moisture inflow and expected elevated instability, the
chances are enough to warrant some concern. Any storms overnight are
more likely to be dry, but again, with so much moisture, we do not
expect fully dry storms.

Afternoon and early evening thunderstorms remain a concern for
Tuesday and Wednesday, as instability persists and moisture
continues to flow into the region. With so much moisture coming into
the mid levels, clouds may inhibit daytime heating and therefore
inhibit convective development, so this puts some uncertainty in to
the forecast. However, given conditions will be similar again on
Tuesday, another Red Flag Warning will be issued for the same areas.
Wednesday could see another round of lightning and Red Flags, but
that should be the last day for substantial convective development.

Models are showing more seasonable conditions and low to no chance
for convection by the end of the week. -BPN

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning until 9 PM PDT this evening for ORZ617-620>625.

CA...Red Flag Warning until 9 PM PDT this evening for CAZ280>282-284-
     285.

PACIFIC COASTAL WATERS...Small Craft Advisory until 11 PM PDT this
     evening for PZZ350-356-370-376.

&&