National Weather Service Raw Text Product

600 
FXUS66 KMFR 272109
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
209 PM PDT Fri Jun 27 2025

.DISCUSSION...The broad weak overhead trough has once again 
provided support for a strong marine push along the coast this 
morning, where stratus and fog pushed into all the coastal valleys
and into the Umpqua Basin all the way to Roseburg. With the trough
weakening and ridging beginning to nudge into the area, the marine
layer will be suppressed, and is expected to only push into the
coastal valleys, and maybe only just spilling into western
portions of the Umpqua Basin just before sunrise. 

The ridge will also bring an end to the near normal temperatures
of the last several days. Along with the redevelopment of the 
thermal trough over California and the southern Oregon coast, the
ridge will support a rise in temperatures of about 5 to 10 
degrees Saturday, and another 5 to 10 degrees on Sunday. Sunday 
will be the warmest day of this warm spell for areas west of the 
Cascades, then Monday could be the warmest for the East Side 
(although cloudiness from thunderstorms and monsoonal moisture 
inflow could limit high temperatures Monday, more on that below). 
The West Side valleys on Sunday will see highs in the upper 90s to
low 100s, while the highs on Monday for the East Side will peak 
out around 90 to 95. Temperatures will then cool slightly heading
further into next week, but will remain above normal. The heat on
Sunday/Monday will not reach HeatRisk thresholds, but could still
pose a risk to susceptible populations and those working or
playing outdoors. Take the proper precautions to prevent heat
illness, and if seeking relief by swimming in area waterways, be
advised that river water temperatures are till cold, as the more
persistent snowpack continues to provide fresh, cold, meltwater. 

As is typical with periods of heat in the region, it will come to
an end with the threat of thunderstorms. With the ridge passing 
just to our east and strengthening as it moves over the Rockies, a
trough develops off the coast of California, which then attempts 
to move onshore around Monday or Tuesday, taking on a negative 
tilt as it does so. This is a classic pattern for convection here,
with the trough tapping into monsoonal moisture from the south, 
and taking advantage of the warm surface temperatures and cooler 
temperatures aloft to produce instability across the inland 
portions of the forecast area. 

Not much has changed in regards to the thunderstorm forecast. 
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 very low, and
wording has been left out of the forecast, but a non-zero chance 
is there. Most likely, Sunday will be the "priming-of-the- pump" 
day, with little to no 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 (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 (although some models show showers and 
stray thunder right along the southern coast 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, although a few models are showing the
arrival of another trough late in the week, keeping showers and
thunderstorms in mind as we head into next weekend. -BPN

&&

.AVIATION...27/18Z TAFs...VFR will prevail across the area 
through this afternoon, aside from a few small pockets of MVFR along 
the immediate coast. MVFR/IFR conditions are likely to return with 
the marine layer to the coast and the coastal valleys this evening 
and tonight, but coverage should be less than this morning. 
Elsewhere, VFR will continue for inland areas, with afternoon 
breezes of up to 20 kt possible this afternoon, strongest east of 
the Cascades. -BPN 

&&

.MARINE...Updated 200 PM PDT Friday, June 27, 2025...The thermal 
trough is starting to develop along the south Oregon coast and this 
has resulted in increasing north winds. Winds will continue to 
increase the rest of the afternoon with Small Craft conditions 
likely for most of the southern waters late this afternoon into 
Saturday afternoon. Winds will be strongest south of Gold Beach. 

Moderate to strong winds are likely Saturday, strongest south of 
Port Orford where Gales and very steep wind driven seas are likely 
by late Saturday afternoon. Meanwhile, Small Craft conditions will 
expand over the rest of the waters. These conditions are likely to 
last into the start of next week, possibly longer. -Petrucelli

&&

.FIRE WEATHER...Updated 300 PM 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. The exception 
will be the south coast where afternoon temperatures could get into 
the low 80s due to an offshore flow and Chetco effect due to 
offshore flow with the thermal trough positioned just off the south 
Oregon coast. The thermal trough will also bring enhanced E-NE winds 
at the mid slope/ridge level tonight and again Saturday night. 
However, overnight recoveries tonight morning 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.

Sunday 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 form off the California coast 
Sunday. At the same time, the upper ridge shifts to the Four Corners 
region. This will usher in a south to southeast flow aloft from 
California into southern Oregon, and 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. However, the most likely scenario is convective 
showers for Monday morning. Monday afternoon and evening will be the 
time period of concern with the shear number and areas affected by 
thunderstorms. Steering winds Monday are expected to be light, 
therefore storms that develop will be slow movers and could produce 
locally heavy rain, but this is still a few days out, so the details 
could change. 

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 until 11 AM PDT Sunday 
     for PZZ350-356-370-376. 

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

&&

$$