204
FXUS66 KMFR 292153
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
253 PM PDT Mon Apr 29 2024

.SHORT TERM...Tonight 4/29 through Monday night 4/30...Satellite
imagery shows some cloud cover associated with an unstable
atmosphere with RADAR showing show showers across portions of
southern Oregon and western Siskiyou County in northern
California. Most of northern California is experiencing mostly
clear skies. The showers and clouds are part of a frontal boundary
that is swung through the area earlier today. Web cameras showed
some reduced visibility due to snowfall near Willamette Pass, but
snow was not accumulating on the roads. The showers will continue
to dissipate over the next several hours.

Tonight, expect mostly cloudy skies across much of the area.
However, high resolution ensemble members are showing some
clearing in Josephine County around midnight to 3 AM. This could
let temperatures fall to freezing. With the National Blend of
models signifying an 80% chance of reaching freezing in the
Illinois Valley, have decided to upgrade the freeze watch to a
freeze warning. Higher elevations of Douglas and Jackson Counties
may reach freezing as well, but the valleys should remain
relatively warm.

On Tuesday, another weak trough pushes largely north of southern
Oregon. This will bring a few showers to the coast, Douglas County
and the Cascades from Crater Lake northward. Precipitation will be
light, and snowfall accumulations will be around 1-3 inches in the
Cascades. GEFS and EC ensembles suggest a trace of rain in Medford
proper, but not measuring. Have gone with the NBM on this.

Tuesday night could see temperatures approach freezing again for
the Illinois Valley, but want to see how tonight plays out before
issuing a freeze watch for tomorrow as some of the same issues
will exist with cloud cover associated with this front. Elsewhere,
temperatures will be cooler than normal. -Schaaf


.LONG TERM...Wednesday through Monday, May 1-6, 2024...
The first week of May will feature fairly typical spring weather.
The pattern will remain progressive, at least initially, as WNW flow
persists. One trough will exit to the east on Wednesday, so heights
will rise with surface high pressure building in strongly by
Wednesday morning. This will result in another cold morning east of
the Cascades and in most of NorCal with areas of frost and even
possibly freezing temperatures for the valleys west of the Cascades.
Highest probabilities for temperatures <=32F are in the typically
colder spots like the Illinois and Applegate valleys (50-80%
chance), while locations like the Rogue Valley and Umpqua Basin are
more likely to have temperatures bottom out in the mid to upper 30s.
This could still bring frost, so those that have done some early
gardening should consider covering sensitive vegetation or moving it
temporarily indoors. The short wave upper ridge will be over the
area resulting in at least a partly sunny, milder afternoon with
temperatures getting back closer to (but not quite) seasonal
normals. Expect highs in the mid 60s west of the Cascades with mid-
upper 50s in NE Cal and over the East Side.

The fast flow pattern across the Gulf of Alaska has been causing
some havoc in the timing/strength of another disturbance and short
wave trough expected to scoot by to our north and east Wednesday
night into Thursday. But, this system could bring another shot of
light precipitation to parts of the area. Recent 12z deterministic
GFS/EC/Canadian models are showing this system digging farther
south than the last several model runs. And, a larger percentage
of members from the 12z ensembles are also showing a stronger
system. That said, still about half of all members show a dry
scenario (for Medford) and are closer to the weaker 12z NAM. Given
the uncertainty, going to stick with the NBM, which has increased
PoPs modestly (to 30-50%) along the coast, north of the Rogue/Umpqua
Divide and over to the Cascades, but has kept things dry across
NorCal. Best chance of showers (20%) here in Medford is Thursday
morning. We`ll see if any further adjustments are necessary.
Overall, temperatures have trended downward a little for Thursday,
especially across NW sections due to the potential for increased
cloud cover and at least light precip.

The upper trough shifts into eastern Oregon and western Idaho by
Thursday evening, so it should dry out again, with another short
wave ridge building into SW Oregon/NorCal by Friday. Only modest
warming is expected with a warming air mass aloft, primarily since
yet another stronger system is forecast to dive southeastward from
the Gulf of Alaska. This could bring cloud cover back in over the
area late Friday afternoon and there`s a good chance (40-60%) of
rain along the coast by Friday evening. This system will bring a
change to cooler, wetter weather for all areas Friday night/Saturday
with a fairly high probability of rain/showers (40-80% chance).

The upper trough is likely to remain over the area next weekend with
a showery pattern persisting Saturday night into Sunday. The
cooler, wetter pattern could last into early next week as model
ensembles/clusters/NBM are showing another wetter system arriving
around next Monday. The Climate Prediction Center`s 6-10 day
outlook is also showing the bullseye of higher odds for cooler,
wetter weather (60-70% chance) squarely over NorCal and Oregon.
-Spilde


&&

.AVIATION...29/18Z TAFs...A frontal system is moving through at this
time with a mix of VFR/MVFR and showers. Partial terrain
obscurations can occur in heavier, more persistent showers.
Showers are most numerous near and west of the Cascades, but we
can`t rule out an isolated shower here or there over the East Side
and also near the Siskiyous in NW Siskiyou County. The remainder of
the area will be dry. Expect some gusty breezes this
afternoon/evening, especially east of the Cascades. Gusts up to 30kt
are possible at Klamath Falls. Conditions become mostly VFR this
evening, then another front brings a renewed risk of lower ceilings
(MVFR) and showers to the coast and Umpqua Tuesday morning. -Spilde


&&

.MARINE...Updated 230 PM Monday, April 29, 2024...Seas will be
elevated and hazardous to small craft today through Tuesday morning
due to a combination of wind seas and increasing west northwest
swell. Low pressure will move north of the waters Tuesday with seas
transitioning to high and steep WNW swells near 10 feet Tuesday
afternoon and evening. Weak high pressure will move in Wednesday
with moderate north winds, highest south of Cape Blanco. Then,
another front will move through the waters Wednesday night and
onshore Thursday. Calmer conditions are expected Friday.

-Spilde/Smith


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Freeze Warning from 3 AM to 10 AM PDT Tuesday for ORZ024.

CA...None.

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

     Small Craft Advisory until 11 PM PDT Tuesday for PZZ350-370.

&&

$$