483
FXUS66 KMFR 072151
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
251 PM PDT Fri Jun 7 2024

.DISCUSSION...Satellite imagery is showing some cumulus building
across the higher terrain of southern Oregon and northern
California before being dislodged from the mountains and
continuing to grow. Some of these clouds are beginning to build up
to high enough levels for freezing to occur, especially across
northern Klamath and Lake Counties, and thunderstorms may occur
later this afternoon and evening. Thunderstorms will be possible
northeast of Mt. Shasta, and in Klamath and Lake Counties, however
a few cumulus build ups are happening in the Siskiyous and Marble
Mountains of Western Siskiyou County, so this will need to be
monitored. Forecast soundings continue to show modest CAPE values
(>500 J/kg) and have an inverted V structure which traditionally
signals the potential for strong winds and downdrafts. However, we
are missing the bulk shear for a more organized event. This means
that a couple storms may overachieve and product 50 to 60 mph
wind gusts. These types of storms will be most possible in
northern Klamath and Lake Counties this evening, and to a lesser
extend eastern Siskiyou County. Thunderstorms will be possible a
bit farther west in Siskiyou County and in Modoc County this
evening. (Areas west of the Cascades will not see any
thunderstorm potential through this weekend.) The SREF and HREF
both are in line with thunderstorm chances peaking between 5 pm
and 8 pm, and this seems to be present with what is occurring on
Satellite. In addition, conditions will be relatively unstable
for fires, and we may see continued quick growth for new wildfires
in the area (like the Sulphur Incident near Happy Camp).

This thunderstorm pattern is part of our overarching ridge of high
pressure across the Pacific Northwest and associated thermal
trough which has moved inland today. This will lead to hot
temperatures spanning 15 to 20 degrees above normal this afternoon
and early evening. Temperatures will trend cooler and humidities
will trend higher beginning Saturday as the ridge breaks down and
is replaced by a trough pushing through the Gulf of Alaska.

This ridge breakdown will also continue to mean thunderstorm
chances for the next couple of afternoons and evenings--
particularly for areas east of the Cascades and northeast of Mt.
Shasta. This is in part due to the deep southwest flow continuing
to push through the area. The SREF and HREF are showing a more
robust signal for thunderstorms tomorrow evening; so will need to
continue evaluating the possibility for severe weather. As of now,
it seems like 1 or 2 storms might overachieve to become strong or
even severe, but no organized severe weather threat is likely. For
portions of northern Klamath and Lake Counties, the thunderstorm
threat will likely continue overnight where traditionally drier
thunderstorms occur at night. Sunday will be a repeat with
afternoon thunderstorms possible and cooler weather, but the
thunder threat will largely cease after sunset.

The pattern becomes more zonal in nature Monday into the rest of
the week as additional systems attempt to push inland across the
Pacific Northwest. Right now, ensembles predict that we`ll be dry
with continued slightly above normal temperatures and breezy
afternoon winds. -Schaaf

&&

.AVIATION...07/18Z TAFs...Widespread VFR conditions prevail through
the TAF period over most locations with a few exceptions. There are
more thunderstorms in the forecast that could impact locations in
northern California and east of the Cascades. This probability of
cloud to ground lightning near Klamath Falls is about 20%.
Ceilings will be higher with soundings showing bases about 8000
feet above ground level. Gusty winds in excess of 35 knots near
terminals remains a possibility near storms this afternoon.

Data also suggests a low chance of IFR ceilings building into the
coast later tonight into tomorrow morning.

-Smith

&&

.MARINE...Updated 230 PM Friday, June 7, 2024... Winds and seas will
gradually decrease later today, but will lower even more tonight
into Saturday as the thermal trough weakens.

The break will be short-lived, however, as a moderate west swell
moves in late Saturday through Sunday. At the same time, the thermal
trough will restrengthen, bringing increasing north winds and steep
seas to all waters Sunday into early next week. -Spilde/Smith

&&

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

PACIFIC COASTAL WATERS...Small Craft Advisory until 5 AM PDT Saturday
     for PZZ350-356-370-376.

Hazardous Seas Warning until 5 PM PDT this afternoon for PZZ356-
     376.

&&

$$