489
FXUS66 KMFR 271801
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
1101 AM PDT Sun Apr 27 2025

.DISCUSSION...Updated Aviation and Marine Sections...

&&

.AVIATION...27/18Z TAFs...Cloud cover remaining in the wake of a low
pressure system is keeping levels generally at VFR or MVFR this
morning with areas of higher terrain obscured. Some light showers
continue in parts of Lake and Modoc counties. Breezy north to
northwest winds develop east of the Cascades this afternoon/evening.

Onshore flow will keep some amount of cloud cover along the Oregon
coast north of Cape Blanco as well as into the Umpqua Valley tonight
into Monday morning. Deep moist boundary layer should allow some
ceilings to spill into the Rogue Basin as well. Other areas look to
remain at VFR. -Spilde/Hermansen

&&

.MARINE...Updated 830 AM Sunday, April 27, 2025...Steep seas will
continue in all area waters today. Strongest northerly winds and
steepest seas are expected south of Cape Blanco. A weak thermal
trough looks to develop next week, sustaining gusty northerly winds
and steep seas in waters south of Cape Blanco.

Stable upper level conditions will allow for more improvement in the
middle of the week. A strong thermal trough is not forecast, so
periods of below advisory seas will be possible. An approaching
front may bring steep swell and marine showers near the end of the
week. -TAD/Hermansen

&&

.PREV DISCUSSION... /Issued 438 AM PDT Sun Apr 27 2025/

SHORT TERM...A closed upper level low is centered smack-dab in
the middle of Nevada early this morning. This low, which moved
across southern California yesterday, has been responsible for the
wetting precipitation across much of the area the last couple of
days. Most areas picked up between 0.25-0.75 of an inch of
rainfall since Friday (some more - East Side/Modoc, some less -
Coast/Umpqua). Looking at observations of lightning, it was quite
active across the East Side yesterday afternoon/evening,
especially over Modoc/Lake counties. Almost 250 CG flashes were
observed. The good news is those storms came with plenty of
rainfall. In fact, Alturas, which measured 0.83" yesterday, almost
doubled the record for the date, which was 0.42" set in 2012.
Here in Medford, two-day precipitation was 0.31", and in Klamath
Falls was 0.44", officially.

Current radar is still showing a corridor of light rain showers
stretching from Harney/SE Lake counties in Oregon southwestward
across Modoc and into Lassen/Shasta counties in California. These
continue to rotate from NE to SW around the NW periphery of the
low. Precipitation chances persist in those areas this morning.
After a brief break, it does remain unstable over in those areas
this afternoon, so we still can`t rule out isolated/scattered
showers. Lightning probabilities though are 10% or less. The
remainder of the area will dry out today. Low cloud cover this
morning will give way to at least partial sunshine this afternoon.
It should be noted that the low cloud cover is resulting in some
thick fog up around Siskiyou Summit on I-5 and other higher passes
this morning, so slow down and use caution if traveling through
there this morning. It`ll remain on the cool side in most
locations, with high temps for the west side valleys mostly in the
60-65F range, except 65-70F in the lower Klamath Valley of
western Siskiyou County. Breezy north to northwest winds will pick
up this afternoon. Generally expect wind gusts of 20-25 mph west
of the Cascades, but 25-35 mph will be common east of the Cascades
(can`t rule out a gust to 40 mph over the far east side deserts
out toward Hart Mtn).

High pressure builds in tonight and that`ll mean patchy fog for
some valleys. It`ll be short-lived though due to the shorter
nights. Frost could form in some of the colder west side valleys
too (Scott/Shasta/Illinois), but only for a couple of hours close
to sunrise. Overall, expect dry, milder weather Monday ahead of
the next (weak) short wave trough that will swing through on
Tuesday. We are lacking any noteworthy instability, so we`re not
expecting any thunderstorms, but there will be a chance (20-40%)
for light showers (QPF < 0.10") across northern and eastern parts
of the forecast area. -Spilde

LONG TERM...Then a dry pattern will develop until Friday. It`ll
get warm again Wed/Thu with the peak in the warmth on Thu. We`re
forecasting 84F for a high here in Medford. A deeper negatively
tilted trough is anticipated to develop offshore Friday with the
trough axis extending down from British Columbia. The base of the
trough and vorticity maximum will pass over the forecast area.
This coupled with with widespread ample CAPE (upwards of 600 J/kg)
will likely lead to showers and thunderstorms. Bulk shear values
around 40-50 knots would allow for updrafts maintaining, so we
could have a couple strong storms, but its too early to say with
much confidence the coverage of these thunderstorms. DCAPE values
are on the lower end, and this is evident with forecast soundings
indicating moist low levels. In fact, extended range forecast
soundings show a "tropical" like soundings with a very moist
column. This would inhibit strong downburst potential, so the main
threat could end up being lightning with small hail. Will
continue to monitor this because Friday could be impactful from a
rain and lightning point of view. PWATs are around an inch in some
areas, so we will need to also keep an eye on heavy rainfall
chances. Early indication suggest the system is progressive, and
the mean flow could result in fast moving cells which would limit
rainfall amounts over one area. Stay tuned as we refine the
details over the coming days. -Guerrero/Spilde

&&

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

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

&&

$$