740
FXUS66 KMFR 191540
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
840 AM PDT Thu Jun 19 2025

.DISCUSSION...The forecast looks largely on track. We will await
the ability to analayze the new suite of 12Z data before making
any adjustments for the regular afternoon forecast issuance.
Things we will be paying particular attention to include the
possibility of extending the slight chance risk of thunderstorms
during Friday afternoon and evening farther east...from the
coastal waters north of Cape Blanco across Coos and Douglas
counties, but possibly also into far northern Klamath and far
northwest Lake counties. Also, removing any mention of
thunderstorms in the Saturday forecast.

Thirdly, rainfall amounts during Friday and Saturday still look
to be focused in southwest Oregon, especially north of the Umpqua
Divide...with a quarter to three quarters of an inch forecast for
Coos and Douglas counties into far western Klamath County. But,
rainfall amounts may need to be trended slightly lower. Around a
quarter of an inch is forecast for Curry County. Total Rogue
Valley rainfall in the 06Z data looked to be more of less than a
tenth of an inch rather than in a range of a tenth to a quarter of
an inch. Most of northern California and south central Oregon
still are expected to receive measureable rain, but the main
story there will be cooler temperatures and cloudy skies.

A warming and drying trend begins Sunday. Also of note, is the
potential for weak instability that may warrant mentioning a
modest risk of late day thunderstorms, limited in scope, varying
in location from day-to-day from Sunday through Wednesday. Stay
tuned for our next update this afternoon.

&&

.AVIATION...19/18Z TAFs...Some of the smoke from the Applegate Fire
settled in underneath a low-level inversion, which is now breaking.
So, locally reduced visibility can be expected to improve in the
vicinity of the fire. But, breezy northwest winds will develop
there, and for all TAF sites, again this afternoon into this evening.
Peak gusts again will be in the 20-25 kt range.

Also, marine stratus along the Umpqus Divide and southern portions
of the Umpqua Basin will continue to erode during the remainder of
the morning.

Afternoon/evening cumulus buildups are expected to occur in Lake
County, out near the Warner Mtns, with a slight chance of
thunderstorms in far southeast Lake County.

MVFR ceilings may develop at the coast, especially north of Cape
Blanco this evening with rain developing around 09Z, late tonight.
-DW

&&

.MARINE...Updated 800 AM Thursday, June 19, 2025...Breezy north
winds continue north of Cape Blanco, with stronger winds and steep,
hazardous seas from Cape Blanco southward. An unseasonably cool and
wet system arrives Friday and Saturday with showers and breezy west
to northwest winds. Isolated thunderstorms are possible Friday
afternoon and evening, mainly north of Cape Blanco. A thermal
trough, along with north winds and steep seas, returns early next
week. North winds are likely to reach advisory strength south of
Cape Blanco by Sunday evening, with steep seas into mid-week. -DW

&&

.PREV DISCUSSION... /Issued 442 AM PDT Thu Jun 19 2025/

DISCUSSION...Satellite imege shows scattered mid and high level
clouds moving from southwest to northeast. At the same time,
marine stratus is forming along the Umpqua Divide, portions of the
Umpqua, and Coquille Basin. The marine stratus in these areas are
expected to expand in coverage between now and mid morning. The
marine stratus will burn off late this morning. Most locations
will be dry today. An upper trough will be moving towards the area
from the northwest this afternoon. The net result will be cooler
afternoon temperatures for the interior and gusty afternoon and
early evening breezes east of the Cascades and interior westside
valleys. Instability is marginal in southeast Lake and Modoc
county later this afternoon, this will result in cumulus build
ups, and could not rule out an isolated thunderstorm or two.

The upper trough will settle over the area Friday and Saturday.
The upper trough is pretty strong for this time of the year and is
likely to result in much cooler temperatures (15-20 degrees below
normal) for the interior with showers likely west of the Cascades
Friday afternoon, then over most locations Friday night through
Saturday. There is sufficient evidence to suggest isolated
thunderstorms are possible along and west of the Cascades,
centered along and north of the Umpqua Divide, and the coastal
counties Friday afternoon into early Friday evening. The main
driving factor for the slight chance for storms is marginal
instability from daytime heating and a cold air mass aloft.
Isolated storms will linger into Friday evening, then as we lose
daytime heating so do the isolated thunderstorms.

Instability parameters suggest instability is marginal at best
and there was not enough evidence to support a mention of
Saturday. The main reason for this is were expecting extensive
cloud cover which will be sufficent enough to limit the amount of
daytime heating, thus keeeping the afternoon temperatures below
their convective values.

The cool and unsettled weather will be short lived with dry and
warmer weather returning by the start of next weeek, but there is
some evidence suggesting another upper trough could settle back
into the Pac NW the latter part of next week. -Petrucelli

&&

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

CA...None.

PACIFIC COASTAL WATERS...Small Craft Advisory until 11 PM PDT this
     evening for PZZ356-376.

&&

$$