020
FXUS66 KMFR 052337
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
437 PM PDT Tue Aug 5 2025

...Updated AVIATION Discussion for 00Z TAFs...

.DISCUSSION (Today through Monday)...

Overview:

There will be a small chances for light rain showers and drizzle
along/near the coast and Umpqua Basin tonight into Wednesday. After
this, we are heading into a stretch of dry weather well into next
week. Temperatures through Thursday will be below normal. By Friday,
the heat will return with triple digits possible through the weekend
and into early next week. This will lead to a "Moderate" to "Major"
Heat Risk Friday through Monday. In fact, there could be isolated
areas of "Extreme" Heat Risk on Monday. This heat will also
strengthen a thermal trough that may lead to a Chetco Effect this
weekend with areas in/around Brookings seeing well above normal
temperatures.

Further Details:

Zonal flow will be evident over the PacNW through about Thursday.
Then a trough strengthens and passes through the Northern Great
Basin and will modify the pattern. Until then, within the zonal
flow, models are indicating a weak perturbation passing over the
forecast area. This will spread weak PVA across the forecast area
tonight through Wednesday evening. This could be enough energy to
support weak rain showers and/or drizzle mainly along/near the
coast and the Umpqua Basin. PWATs are well over an inch across
these locations, so cannot rule out at least a small chance
(15%-35%) for light showers over the land given the energy aloft.
Not expecting much QPF through this stretch, and wouldn`t be
surprised if very few locations actually accumulated much
precipitation. Nevertheless, its a non-zero chance and will be
included in the forecast.

The trough passing on Thursday will bring northwesterly flow and
maintain the cooler airmass for one more day. By Friday, we will
start to see heights rising aloft and a much warmer airmass
settling over the PacNW. Triple digits will be possible starting
Friday and will continue through the weekend and into early next
week for many lower elevation/valley areas. During this stretch,
we will see "Moderate" to "Major" Heat Risk. Heat related hazards
could become an issue this weekend and into early next week as we
enter our next heat wave. Monday in particular looks to be the
warmest day through this stretch and could produce isolated areas
(e.g. Medford) of "Extreme" Heat Risk. The record for Medford is
109 set back in 1971. We are currently forecasting a high of 107.

The heat will help increase the pressure gradient across the
forecast area, and this will lead to increased wind speeds
Thursday night through Saturday night (periods through the
overnight and afternoon hours). While thunderstorms may not be an
issue, we could start to see an overlap of critical wind speeds
and RH through this heat wave which could lead to at least
elevated fire weather concerns. Once HiRes data comes in, we can
add more details to the wind speeds. This will likely be the
deciding factor for Red Flag Warnings because critical RH is
likely through this upcoming heat wave. The pressure gradient and
wind direction could lead to a Chetco Effect as well, and
temperatures could end up being close to 90 for Brookings over the
weekend.

&&

.AVIATION...06/00Z TAFs...VFR levels are present across northern
California and southern Oregon this afternoon, with patches of highs
clouds moving to the east as well as popcorn cumulus over east side
terrain. Early Wednesday morning, a weak upper trough will bring
MVFR to IFR ceilings along the Oregon coast. MVFR ceilings are
possible over the Umpqua Valley later in the morning or early in the
afternoon. Drizzle or light showers are possible, which may locally
lower visibility. Levels could return to VFR across the area near
the end of this TAF period or early in the next one. -TAD

&&

.MARINE...Updated 200 PM PDT Tuesday, August 5, 2025...Sub-
advisory conditions are expected through early Thursday. A
northwest swell will build into the waters later today ahead of a
weak front, but seas will remain at or below 7 ft through early
Thursday. There could be some light showers with this front,
mainly north of Cape Blanco.

Conditions deteriorate Thursday afternoon as a thermal trough
builds along the coast. This will bring strong gusty north winds
across the waters, along with steep to very steep seas that will
continue into the weekend. Advisory level winds/seas are likely
south of Cape Blanco by Thursday afternoon, with conditions
worsening north of Cape Blanco from Friday onward. Through this
stretch, we are expecting moderate to strong winds, possibly
reaching gales, and steep to very steep wind-driven seas.
Conditions should start to improve late Sunday into Monday as the
thermal trough weakens. /BR-y


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...None.

CA...None.

PACIFIC COASTAL WATERS...None.

&&

$$