852
FXUS66 KMFR 022146
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
246 PM PDT Thu May 2 2024

.DISCUSSION...A few showers linger this afternoon along and east
of the Cascades, but these will continue to dissipate and move
east, likely exiting the area this evening. Beginning tonight,
ridging aloft will dry the area out and make for mostly clear
skies through Friday morning. With those clear skies, the passage
of the cold front will allow temperatures tonight to be cooler
than last night, but lows should still stay above freezing for all
areas west of the Cascades.

The next system arrives at the coast Friday, with precipitation
beginning at the coast in the afternoon, then spreading to the
Cascades by evening, and the rest of the area overnight. Similar
to the frontal system early this morning, this front will move in
from the west, resulting in much less downsloping for western
valleys than in other patterns. Precipitable water associated with
this front, however, will be greater with a stronger inflow of
moisture, resulting in greater precipitation amounts. Rain amounts
of a half inch or more are almost guaranteed for almost all areas
in southern Oregon and far northern California, with up to 2 or
even 3 inches of rain possible along the coast. Winds will not be
a primary concern with this system, with model fields not showing
significant mid-level wind speeds for most of the area. However,
there is some indication that gusty winds will develop over
eastern Modoc and Lake counties as the front swings through
Saturday afternoon.

Snow levels will initially be quite high at the beginning of the
event, rising to above 7,000 feet, before decreasing overnight
Friday into Saturday to 3,000 to 4,000 feet as the cold front
passes and precipitation becomes more intermittent/showery. This
will result in snow lowering down to area passes, including those
over the Cascades on Hwys 140 and 138 (where we`re expecting 3-6
inches early Saturday through early Sunday) and Siskiyou Summit on
I-5 (likely less than an inch). As road surfaces are still quite
warm, a lot of this will melt on paved surfaces, but lower
visibilities could still make travel over the mountains difficult
at times.

Showery, on-and-off again precipitation continues late Saturday
into Sunday as low pressure lingers aloft. Shower coverage will
shrink and taper off through the day Sunday as the low moves SE
and another transient ridge moves into the area. Another front
moves in Monday, this one much weaker with the majority of light
to moderate precip falling over northwest portions of the region.
Snow levels will generally be 4,000 to 5,000 feet. Onshore flow
and lingering moisture will lead to light, scattered showers
continuing into Tuesday.

Mid to late next week, large scale ridging returns to the area,
and we will transition to a more warm-season type pattern with
temperatures warming to above normal for early May, and very
little, if any, chance for precipitation. Also, this pattern
would suggest a thermal trough developing along the coast, with a
Chetco Effect keeping the area around Brookings warm. The general
east flow across the entire area would also support strong
overnight inversions, but given how late we are in the season,
valley fog is not likely to develop. -BPN/CSP

&&


.AVIATION...02/18Z TAFs...Along the coast, areas of MVFR conditions
and rain showers will continue through early afternoon, then are
expected to improve to VFR late this afternoon and this evening.
Some lingering MVFR ceilings are possible near and around North
Bend/Coos Bay into early this evening though. Inland, scattered
showers are continuing from the Southern Oregon Cascades eastward
and across Northern California. More isolated shower activity is
occuring west of the Cascades. Mountain obscurations, MVFR
conditions and local IFR ceilings are expected with showers through
this morning and into this afternoon. Conditions are expected to
improve to VFR late this afternoon for most all inland areas.
Tonight, expect mainly VFR inland except for local MVFR ceilings.
Along the coast, another front will bring rain and a mix of MVFR/IFR
conditions late tonight into Friday morning. -CC

&&

.MARINE...Updated 200 PM Thursday, May 2, 2024...Fresh northwest
swell will persist through tonight. Then a front moves across the
waters Friday with moderate to heavy rain, gusty south winds and
steep seas. South winds will increase Friday morning and peak in the
afternoon. Steep seas dominated by fresh west swell are expected
Friday night into Saturday morning. A slight chance of thunderstorms
(20%) is expected on Saturday. West seas trend less steep Saturday
afternoon through Sunday and there will be continued periods of rain
showers (60%-80% chance). Another front arrives on Monday with a
potential for gusty south to southwest winds followed by building
west-northwest seas Monday night into Tuesday.

-CC

&&

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

PACIFIC COASTAL WATERS...Small Craft Advisory from 8 AM Friday to 11
     AM PDT Saturday for PZZ350-356-370-376.

&&

$$