099
FXUS66 KMFR 032328
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
428 PM PDT Thu Jul 3 2025

.UPDATE...Aviation discussion updated.

&&

.PREV DISCUSSION... /Issued 237 PM PDT Thu Jul 3 2025/

DISCUSSION...Today through Saturday night...Another shortwave
trough is approaching the region this afternoon. This will pass
through the region overnight tonight into Friday while merging
with an upstream shortwave, resulting in a broad low pressure over
the Pacific Northwest for the Fourth of July holiday. Overall,
this will bring near to slightly below normal temperatures today
through Saturday. On the other hand, isolated to scattered
thunderstorms will persist over the region through Friday evening.
Much like recent days, the focus for thunderstorm activity today
will mostly be across eastern Klamath, Lake and Modoc counties,
though isolated thunderstorms are possible farther westward into
western Siskiyou County and the Cascade Foothills of
Jackson/Douglas Counties.

Heading into the overnight hours, the incoming trough takes on a
negative tilt as it moves overhead, and this combined with
sufficient moisture and instability will lead to showers and
thunderstorms continuing tonight into early Friday morning. The
focus for activity looks to be along the Cascades north of Lake of
the Woods and areas eastward into Klamath County generally north
Klamath Falls towards Chemult/Fort Rock area. While moisture and
instability are more limited for areas west of the Cascades, there
are some members of the high resolution suite of models that show
some activity firing up across portions of eastern Jackson/Douglas
Counties before quickly shunting off to the north and east. As such,
we`ve included a slight chance (10-20%) mention of thunderstorms for
areas generally east of Grants Pass/Shady Cove/Steamboat.
Shower/thunderstorm activity continues into the early morning hours
of Friday across northern portions of Klamath and Lake Counties
before activity wanes around 9-10am or so. Though activity will
wane, the break will be short-lived with another round of
showers/thunderstorms developing Friday afternoon across northern
portions of Klamath and Lake Counties.

Aside from the thunderstorm threat on Friday, the Fourth of July
holiday should be a rather pleasant one across the region with
temperatures being the coolest of the forecast period. In fact,
afternoon highs on this July 4th will hover around 5 to 10 degrees
below normal, with up to 15 degrees below normal in some places.
There will be some lingering cloud cover around west of the
Cascades, but overall, mostly to partly sunny skies are expected.
We`ll finally get a break in this persistent thunderstorm pattern on
Saturday as a brief period of ridging develops and afternoon highs
trend warmer by about 5 to 10 degrees.

This break will be short-lived, however, as another low pressure
develops off the coast of California and lingers there into next
week before finally moving off to the northeast around mid-week. The
position of this trough looks farther north than the one from
earlier this week, and this will have implications on where the best
moisture/instability line up. Current guidance maintains a dry
forecast through this time period, but pattern recognitions would
say that there will be at least slight chance of thunderstorms at
some point between Sunday-Wednesday. An isolated thunderstorm or two
could develop as early as Sunday across western Siskiyou, but
moisture looks too marginal for any significant activity, and
cumulus buildups are the more likely scenario. Heading into early
next week, however, moisture increases and storms look more
plausible for Monday afternoon. By Tuesday, the best
moisture/instability/dynamics look to be farther north of the area.
As the trough passes overhead on Wednesday, this would be another
opportunity for increased thunderstorm activity in the area. Stay
tuned as details on location and timing of this trough become more
clear over the coming days. In the meantime, guidance shows the
return of hot temperatures as strong high pressure over the Desert
Southwest retrogrades westward and exerts more influence over the
region. /BR-y

&&

AVIATION...04/00Z TAFs...VFR is expected in all areas through
this evening, except where thunderstorms may produce periods of
IFR/MVFR ceilings and visibilities. MVFR?IFR conditions will also
return to the coast and coastal valleys this evening and tonight,
and potentially will spill into the Umpqua Basin by morning. These
areas should clear to VFR by tomorrow afternoon.

Isolated to scattered thunderstorms are expected in the area through
this evening and tonight. Aside from reduced flight conditions in
heavy rain, gusty winds and hail are also possible. -BPN

&&

MARINE...Updated 230 PM PDT Thursday, July 3, 2025...Gusty
north winds and steep seas will continue for waters south of Cape
Blanco late tonight. Conditions will improve with relatively light
winds and seas expected Friday into early Saturday. The thermal
trough pattern returns late Saturday, bringing the return of gusty
north winds and steep seas. This will likely result in conditions
hazardous to small craft returning by Saturday afternoon and
persisting into early next week. /BR-y

&&

FIRE WEATHER...Updated 200 PM PDT Thursday, July 3, 2025...
Thunderstorms continue to be the main concern. There will be another
round of thunderstorms this afternoon and evening, focusing on FWZ
625 into eastern FWZ 624. This is where the Red Flag Warning is in
effect through 11 PM tonight. These storms will be moving north
through the evening. Some storms could be dry.

Keep in mind, lightning strikes outside of the precipitation cores
are possible. Due to the prolonged period of dry and warm to hot
weather, lightning efficiency will be high to very high for fire
starts. We also have to be mindful of gusty and erratic outflow
winds near and away from the core of thunderstorms.

Many models are still supporting convection continuing tonight into
Friday morning. Any overnight storms are much more likely to be high-
based, and would then have much more likelihood of being dry. While
most guidance, and the typical pattern, shows showers and
thunderstorms during this time still concentrating on Klamath and
Lake counties (and a bit into Modoc), one or two models have a band
of convection running up the Cascades from Mount Shasta to Bend late
this evening into tonight. This is the outlying solution, thus
unlikely, but something to consider. A Red Flag Warning will be in
effect from 11 PM tonight through 7 AM tomorrow for the risk of
abundant lightning on dry fuels. This area includes northeastern 623
north of Highway 140, 624 north of Highway 140, and far northern 625
north of Summer Lake.

An area of low pressure will bring another chance of thunderstorms
Friday afternoon with the main concerns in Klamath and Lake
counties. However, a Red Flag Warning will be in effect tomorrow
afternoon for the northern half of FWZ 625 as this is the area that
the thunderstorms will focus on which will bring a risk for abundant
lightning on the dry fuels.

Fortunately, it does appear that the trough will exit by Saturday,
and it appears that this will be the first day with no thunderstorm
chances anywhere within the forecast area. This break in the action
may be short-lived, however, as another upper level trough arrives
late in the weekend, and convective chances may once again return
Sunday into Monday. The deep southerly moisture flow should have
ended by that time, so with the lack in moisture, convection may not
be as widespread or as active, if it occurs at all.

Otherwise, the forecast will be for continued near to slightly above
normal temperatures, seasonal humidities, and the typical diurnal
wind patterns, although general east flow late this weekend into
early next week could lead to drying, especially across the
ridgelines, where poor to moderate recoveries are possible. -
BPN/Hermansen

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning from 11 PM this evening to 8 AM PDT Friday for
     ORZ623>625.

CA...None.

PACIFIC COASTAL WATERS...Small Craft Advisory until 2 AM PDT Friday
     for PZZ356-376.

&&

$$