856
FXUS66 KMFR 271122
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
422 AM PDT Fri Jun 27 2025

.DISCUSSION...Updated Aviation Discussion...

&&

.AVIATION...27/12Z TAFs...Satellite imagery is showing MVFR/IFR
ceilings along the coast near and north of Cape Blanco as well as
down around Brookings. This will continue through the morning,
pressing inland into portions of the lower Umpqua Basin toward
sunrise. These may impact Roseburg for a few hours before VFR
returns mid-late Friday morning. VFR prevails elsewhere tonight
through Friday evening. Gusty breezes in the 20-25kt range will
develop again Friday afternoon, strongest east of the Cascades. -
Spilde/Hermansen

&&

.PREV DISCUSSION... /Issued 342 AM PDT Fri Jun 27 2025/

DISCUSSION...A marine push will continue to bring lower ceilings
to the coast and is expected to push inland into the Umpqua Basin
near Roseburg. This will start to clear later this morning and
sunnier skies will be found this afternoon. Temperatures this
morning will begin near normal in the 40s and 50s with 30s in
northern Lake and Klamath counties.

Temperatures this afternoon will also be similar to yesterday, near
normal. The weekend will have a warm up as a ridge builds into the
area along with a thermal trough along the coast. Temperatures
Saturday afternoon will warm 5-10 degrees above normal, and another
jump in temperatures will come Sunday with more 90s in the forecast.
Sunday is looking to be the warmest of the week for areas west of
the Cascades with a slight increase Monday east of the Cascades.
Thunderstorm threats follow with rise in heat early next week,
please see the long term discussion for more details.

Long term...Convection may begin as early as Sunday afternoon over far
southern portions of Siskiyou and Modoc counties, depending on
how far north the moisture will get by the peak heating hours of
the afternoon. Confidence on thunder Sunday afternoon is low, and
wording has been left out of the forecast, but the chance is
there. Most likely, Sunday will be the "priming-of-the-pump" day,
with little convection but definite signs of increasing moisture.
As moisture continues to push north into our area, and with some
support from weak energy aloft, more widespread convection could
then begin as soon as early Monday morning (very low probability),
although the most likely scenario has convective initiation
beginning Monday afternoon. I suspect that the area will be
greeted by altocumulus clouds and a feeling of "high" humidity
Monday morning, showing the arrival of the moisture and potential
instability of that afternoon.

Given the pattern, thunderstorms could form up anywhere east of
the coastal ranges Monday, with the marine layer limiting
development along the coast and perhaps into the Umpqua Basin as
well. Most convection should be concentrated along the Klamath,
Siskiyou, and Cascade mountains, as well as the East Side, with
cells then drifting off the terrain and into the valleys.
Steering flow appears weak, so storms may be slow moving, leading
to more hit-or-miss "popcorn" style convection.

Some models then continue shower and perhaps thunderstorm
activity overnight, although confidence on that is low. There is
much more confidence on thunderstorms reforming Tuesday afternoon,
although with the eastward progression of the trough, the best
dynamics and support would then be over northern California and
along and east of the Cascades. Other than location, storm
behavior and character should be very similar to Monday. Storms
could then continue on the East Side into Tuesday night, with
some models even keeping some form of convective showers over Lake
County into Wednesday afternoon.

In short, it is nearly a certain thing that there will be
lighting across the majority of the forecast area both Monday and
Tuesday afternoons. Based on current guidance, we do not expect
very strong or severe thunderstorms, but small hail and gusty
winds are possible. Also, given the high moisture content in the
atmosphere that the models are depicting, these storms will be
wet, and could produce periods of moderate to heavy rainfall. As
always with thunderstorms, lightning will be a threat, not only in
regards to new wildfire starts, but also to anyone attempting to
enjoy outdoor recreation in the area.

One caveat to this scenario will be cloud cover. With this much
moisture entering the area, and with the widespread convection
expected Monday, there may be extensive cloud cover over the area
Tuesday limiting incoming solar energy, keeping temperatures
lower, and limiting instability. This has occured with events
like this in the past, and has significantly reduced thunderstorm
development and blown the forecast on the second or third day,
and this may be another example. Keep up to date with the latest
forecasts as the details regarding this thunderstorm threat become
more clear over the next few days.

Broad cyclonic flow and lower heights then continue over the
area for the remainder of the forecast term (midweek next week).
This should keep temperatures at or just above normal, with
mostly dry conditions. -BPN

MARINE...Updated 200 AM PDT Friday, June 27, 2025...The thermal
trough south of Gold Beach strengthens today and even more so over
the weekend. Conditions hazardous to small craft will develop this
afternoon from Cape Blanco south as north winds increase and seas
steepen. Winds will be strongest south of Gold Beach.

Winds will increase further Saturday as advisory level winds and
seas likely spread north of Cape Blanco, with gales and very steep
seas possible south of Cape Blanco. The outlook for next week is for
the thermal trough to remain strong and maintain hazardous
conditions, especially south of Cape Blanco. -Petrucelli/Hermansen

FIRE....FIRE WEATHER...Updated 330 AM PDT Friday, June 27,
2025...Mostly low impact fire weather conditions are expected the
rest of this week with fairly typical diurnal (afternoon/evening)
breezes, seasonable humidity and near to above normal warmth.

A strengthening upper ridge will bring hotter weather to all but the
immediate coast this weekend with continued drying. Even the south
coast could have highs in the 70s to near 80F Saturday. A brief
period of enhanced E-NE winds at the mid slope/ridge level is
expected tonight and again Saturday night. However overnight
recoveries today not don`t look all that bad. Saturday overnight
recoveries will be moderate, but probably not enough to be
concerned about any watches/warnings. Temperatures increase across
the interior Saturday with widespread highs in the 90s on Sunday.
Monday will be the hottest day, with afternoon temperatures near
or at triple digit values for the interior westside valleys.

At the same time, an upper low will consolidate off the California
coast Sunday. The upper ridge shifts to the Four Corners region and
this pattern sets up south to southeast flow aloft from California
into southern Oregon. This will begin to tap into some monsoonal
moisture that will slide up into northern California Sunday
afternoon and evening. The most likely scenario Sunday afternoon
into Sunday night will be building cumulus over the mountains in
northern California, because there is little or no trigger, mid
level moisture is lacking and instability is marginal at best. Worst
case scenario will be a couple of isolated storms near the Trinity
Horn and points northeastward towards the Shasta Valley late in the
afternoon and early evening hours Sunday. In summary, Sunday will be
the day in which the pump is primed for whats expected for Monday.

Monsoonal moisture will increase late Sunday night through Monday
and at the same time mid level moisture and trigger will increase.
This will set the table for resulting in thunderstorms over most of
the area inland away from the coast, with storms developing as early
as Monday morning. Right now, the expectation is for thunderstorms
to be isolated Monday morning, then the shear number and areas
affected increasing Monday afternoon into Monday evening.

It`s worth noting the risk for nocturnal storms are next to, but not
zero Sunday night, with an elevated risk for lightning Monday and
Tuesday night. The main storm threat shifts to the Cascades and
points south and east Tuesday into Wednesday. As fuels continue to
dry out and the calendar shifts from June to July, fire danger will
increase. So, be on the lookout for potential Fire Weather
Watches/Red Flag Warnings as we head into next week. -Petrucelli

&&

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

PACIFIC COASTAL WATERS...Small Craft Advisory from 2 PM this
     afternoon to 11 AM PDT Sunday for PZZ350-356-370-376.

Gale Watch from Saturday afternoon through Sunday morning for
     PZZ356-376.

&&

$$