545
FXUS66 KMFR 020002
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
502 PM PDT Wed May 1 2024

.Updated Aviation Discussion.

.AVIATION...02/00Z TAFs...Conditions will remain VFR through early
this evening, with gusty, breezy west to northwest winds east of the
Cascades, including at Klamath Falls. An approaching front will
result in ceilings lowering to MVFR, then IFR at the coast later
this evening into tomorrow morning. Even though the TAF at North
Bend shows a prolong period of IFR ceilings, it`s possible there
could be brief periods of MVFR ceilings after 13z.

Inland west of the Cascades, VFR ceilings will lower to MVFR tonight
north of the Umpqua Divide, confidence on the timing of lowering
ceilings indicated in the Roseburg TAF could be delayed by an hour
or two. Medford is expected to remain VFR through the TAF period,
however the higher terrain will be at least partly obscured towards
11z.

East of the Cascades, VFR ceilings will continue into tonight, then
MVFR will follow at Klamath Falls as precipitation moves in. Areas
of mountain obscuration are expected after 12z until the end of the
TAF period. -Petrucelli

&&


.DISCUSSION...

.Short Term...Tonight through Saturday...Warmer temperatures and
dry conditions have been the rule today under ridging aloft.
Mostly clear skies today will start to give way to increasing
clouds late this afternoon and evening as the next trough
approaches from the northwest.

This next system, smaller in scale and weaker than most, will
arrive tonight, then pass overhead through Thursday. Due to the
angle of the system, there will be considerable westerly onshore
flow on the front side, along with relatively little in the way of
strong winds out of the south. This type of pattern typically
produces a good shot of wetting rain across the region, especially
along and west of the Cascades, with little in the way of
downslope drying. As a result, most areas in Oregon should see
measurable rain, although northern California may not be as lucky,
as those areas will remain well south of the main moisture flow
and dynamics. Temperatures will trend towards normal for this time
of year, which means snow levels with this event will remain at
or above 5000 feet, so winter impacts will remain confined to the
backcountry and the highest passes, and even then, those impacts
will be minimal.

Most precipitation will dissipate or move out of the area by
Thursday night as the next ridge briefly builds in overhead, but
some light showers are likely to continue into Friday morning
west of the Interstate 5 corridor as a weak warm front skirts by
just offshore. Then, the next system arrives late Friday into
Saturday.

This system, much like the last, will see more of a westerly
onshore flow and little in the way of southerly winds, so once
again, downsloping will be minimal (except east of the Cascades)
and most areas will see a good shot of rain or snow. There will be
cooler air arriving with this front, and snow levels are expected
to drop to between 3000 and 4000 feet, lowest Saturday morning
just after the passage of the cold front. Some minor winter
impacts are expected across many of the area passes, including the
Cascade passes and Siskiyou Summit, but due to warm ground
temperatures, accumulations on roadways may be as significant as
they otherwise would be. This system also appears to have a
stronger moisture inflow than the last one, so rainfall amounts
Friday into Saturday will be fairly potent. 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. Meanwhile, snowfall
amounts of between 6 and 12 inches will be common in the
mountains. The cooler, wetter weather pattern with post-frontal
showers will continue Saturday afternoon, and although there is
only a slight chance (around 15%), we cannot rule out a
thunderstorm or two behind the front Saturday afternoon.

.LONG TERM DISCUSSION...Saturday night though Wednesday...The
cooler and showery pattern will continue Saturday night into
Sunday as an upper level low remains over the area. Showers will
continue on Sunday but will decrease in coverage as the low shifts
eastward. High temperatures on Sunday are expected in the mid 50s
in the west side valleys and along the coast, with highs in the
mid to upper 40s for valleys east of the Cascades.

Models continue to show an active pattern into early next week. A
front moving into the area on Monday will bring high chances (50 to
85 percent) for precipitation for areas from the Southern Oregon
Cascades west as well as into western Siskiyou and northern Klamath
counties. Expect chances (20 to 50 percent) for precipitation
elsewhere east of the Cascades and across Northern California.
Precipitation amounts with this front on Monday will be mainly
light. Snow levels will range from 4000 to 5500 feet. Then onshore
flow will allow for lingering showers on Tuesday, especially across
southwest Oregon zones with lesser chances across Northern
California.

We may get a reprieve from the active weather as the Climate
Prediction Center 8-14 day outlook continues to favor a return
toward more "normal" conditions (temps/precip) for the second week
of May (May 9-May 15). -CC

&&


.MARINE...Updated 200 PM Wednesday, May 1, 2024...A weak front
will move through the waters tonight into Thursday with a modest
increase in short period west-northwest swell. A break Thursday
night will bring calmer conditions, then the active pattern resumes
with rain and hazardous conditions for small craft possible Friday
into Saturday morning. Weak winds and a slight increase in short
period west-northwest swell dominated seas are expected during the
weekend. The next in a series of fronts is likely to arrive on
Monday. -DW


&&

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

CA...None.

PACIFIC COASTAL WATERS...None.

&&

$$