377
FXUS66 KMFR 192350
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
450 PM PDT Tue Aug 19 2025

.UPDATE...Aviation Discussion Updated.


&&

.AVIATION...20/00Z TAFs...Along the coast, areas of IFR to LIFR
will develop tonight and persist into Wednesday morning, with
clearing in the mid to late morning. Inland, expect VFR through the
TAF period.



&&

.PREV DISCUSSION... /Issued 116 PM PDT Tue Aug 19 2025/

DISCUSSION (Today through Monday)...

Overview:

Noteworthy items for this forecast are as follows:

* Heat: A heat wave is expected to start Thursday and will likely go
  through the weekend and potentially into early next week with
  triple digits possible through this stretch.

* Fire Weather: Not seeing an overlap of critical winds and critical
  RH values, but the heat wave will bring an increased drying trend
  and critically low RH values. This will result in elevated fire
  weather concerns, but wind speeds should keep us from any Red Flag
  Warnings at this time. Please see the Fire Weather discussion
  below for more information.

* Rain/Thunderstorms: No reasonable widespread chances for
  rain/thunderstorms anytime soon. However, by this weekend far
  eastern parts of the forecast area could see increased chances for
  isolated rain and perhaps a thunderstorm or two Sat-Mon.

Further Details:

In the upper levels, we have a broad area of high pressure consuming
much of the southern CONUS while hurricane Erin is currently east of
this area. Hurricane Erin will push north and disrupt the high
pressure to the west and northwest which will result in height rises
over our forecast area through later parts of this week as Erin gets
absorbed into the main flow. This will result in a warmer airmass
and triple digit temperatures through the end of the week and
potentially into next week. This timeframe may become accompanied by
heat related hazards such as a Heat Advisory or Extreme Heat
Warnings starting as early as Thursday but certainly by this weekend
as some areas could be around 105-110 for highs. At this time, the
warmest days look to be Fri-Sun with the peak of the heat
potentially Saturday.

The placement of the high pressure will allow for monsoonal moisture
to get pulled northward. At the same time, we will have weak
perturbations riding the northern periphery of this high pressure.
The combination of upper level energy and moisture could result in
precipitation across mainly eastern parts of the forecast area
Saturday through Monday. Any shift in the high pressure could result
in the energy aloft and moisture getting diverted in either a
positive or negative manner as far as precipitation goes. Will
continue to monitor but at this time widespread severe weather does
not appear likely, but if a thunderstorm forms it could become
strong with lightning and strong outflow gusts as the main threats.
These storms would be tied very closely to daytime heating, so these
would likely be pop-up storms through peak heating (2pm-8pm).


-TAD

MARINE...Updated 100 PM PDT Tuesday, August 19, 2025...Conditions
are expected to remain relatively calm through tomorrow morning.
Wednesday afternoon into Thursday, the thermal trough will return
and then persist into the weekend, with moderate to occasionally
strong north winds and steep seas, especially south of Cape
Blanco.

FIRE WEATHER...Updated 200 PM PDT Tuesday, August 19, 2025...
Southwest flow aloft is bringing seasonal temperatures, drier
conditions, and normal diurnal winds to start the week. A
shortwave disturbance looks to move over the area on Wednesday,
which will bring cumulus development over area terrain but other
impacts are not expected.

High pressure in the Four Corners is expected to build a strong
upper level ridge that will affect area conditions on Thursday
then continue through the weekend. This will bring temperatures 5
to 10 degrees above normal across the area on Thursday, possibly
into next week. Most west side valleys have multiple days of 100
degree temperatures in the forecast. The Umpqua Valley and warmer
east side areas (Modoc and southern Lake counties) are starting to
see some high 90s. Nighttime recoveries are currently forecast to
remain moderate, but periods of easterly flow overnight may bring
locally low recoveries to area peaks and ridges. This possibility
looks higher over western Siskiyou County terrain. While some
terrain may approach critical dryness conditions, right now winds
look to stay light enough to avoid hazardous conditions.

On Saturday, monsoonal moisture is forecast to start increasing
over the area. With ample surface heating expected, signs of
convective thunderstorms are starting to appear on Saturday and
Sunday afternoon and evening. Without significant instability to
contribute to development, coverage is likely to be isolated and
generally east of the Cascades. These possibilities will come into
more focus as the weekend approaches.

The forecast beyond Sunday shows some variability. Temperatures
look to stay above seasonal norms but may cool a few degrees. If
monsoonal moisture continues to move into the area, afternoon and
evening thunderstorms remain a possibility. With current forecast
values, wet thunderstorms seem like a meaningful possibility when
activity does develop.

-TAD

&&

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

PACIFIC COASTAL WATERS...Small Craft Advisory from 11 AM Wednesday to
     midnight PDT Friday night for PZZ356-376.

Small Craft Advisory from 8 PM Wednesday to midnight PDT Friday
     night for PZZ350-370.

&&

$$