813
FXUS66 KMFR 201124
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
424 AM PDT Sun Apr 20 2025

...New Aviation Section...


.AVIATION (12Z TAFs)...

Marine layer is staying just off shore, and should remain outside
of the TAF terminal location for most of the day until winds turn
more north/northwesterly. At this time, expecting MVFR clouds to
impact KOTH through the remainder of the TAF period. There may be
MVFR clouds as far inland as KRBG, but at this time confidence
was higher to remain VFR for the three inland terminals. That
said, we do have a BKN deck around 4,000 feet introduced at KRBG
this evening. Otherwise, expecting afternoon breezes to pick up
today in a typical diurnal fashion.

-Guerrero

&&

.PREV DISCUSSION... /Issued 309 AM PDT Sun Apr 20 2025/

DISCUSSION (Today through Saturday)...

Overview:

The forecast remains at a low impact level with regards to weather
hazards. Another weak disturbance will glance the area today, and we
have a very small chance for showers/thunderstorms across southern
parts of both Siskiyou and Modoc counties this afternoon/early
evening. A pattern change with more active weather through next
weekend is expected to start on Thursday. Too early to say with much
confidence the threat for widespread hazards, but early indications
point towards the chance for thunderstorms as the main threat.
Otherwise, seasonable temperatures expected through this forecast
with occasional breezy afternoons.

Further Details:

Forecast soundings across Siskiyou and Modoc counties indicate
convective temperatures will be realized today. A shortwave trough
will pass through the PacNW, and the base of this trough will bring
an area of upper level vorticity across the forecast area this
afternoon and early evening. Moisture is the lacking variable here,
but given convective temperatures will be realized today with upper
level dynamics, we cannot rule out isolated thunderstorms over
northern California where a couple hundred J/kg of MUCAPE will
exist. With the limited moisture, we are going to need these other
variables to time out correctly to get these thunderstorm chances
realized. Therefore, the probability of an updraft maintaining is
low, but its not a zero chance so have maintained the slight chance
for thunderstorms across northern California.

Beyond today, we will be under a northwesterly to zonal flow pattern
for a few days with only weak embedded shortwaves until a more
robust cyclone develops on Thursday. A broad area of cyclonic flow
will develop off British Columbia on Thursday, and this will usher
in a couple rounds of rainfall as a cut-off low meanders over this
area through the weekend. At this time, MUCAPE values are limited to
around a few hundred J/kg (upwards near 400 J/kg), and this pattern
would be conducive for thunderstorms, but its too early to say with
much confidence the overall threat level. That said, bulk shear is
low, so thunderstorm updrafts would struggle in this environment.

Lastly, we will have a couple breezy afternoons most notably today
and Friday, but we fall short of any advisory or warning level wind
speeds at this time.

-Guerrero

AVIATION...20/06Z TAFs...Winds have started to die down and VFR
conditions are present and will continue through the TAF period
for all locations inland. The coast is starting to see MVFR
ceilings tonight. Near the end of the TAF period gusty northerly
winds will return, especially for the coast and east side.

-Smith/Hermansen

MARINE...Updated 200 AM Sunday, April 20th...Seas south of Gold
Beach are still seeing hazardous seas, so a warning has been
issued through Monday morning with steep seas elsewhere. Winds
increase again and come close to gales Monday, so a Gale Watch has
been issued for areas near and south of Port Orford. Hazardous
seas will be possible south of Port Orford Tuesday with steep seas
elsewhere.

-Smith/Hermansen

&&

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

PACIFIC COASTAL WATERS...Small Craft Advisory until 11 AM PDT Monday
     for PZZ356-376.

Small Craft Advisory until 2 PM PDT this afternoon for PZZ350-
     370.

     Hazardous Seas Warning until 11 AM PDT Monday for PZZ356-376.

     Gale Watch from Monday morning through Monday evening for PZZ356-
     376.

&&

$$