102
FXUS66 KMFR 290947
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
247 AM PDT Mon Apr 29 2024

.DISCUSSION...Satellite imagery this morning looks a lot like it
has for the past few mornings...widespread cloud cover along and
west of the Cascades with mostly clear skies east of the Cascades
and south of the Siskiyous. Radar imagery and surface observations
indicate light shower activity along the coast and into the
Umpqua Basin. Rinse and repeat is in store through at least
midweek as WNW flow aloft maintains onshore flow with multiple
disturbances passing through the Pacific Northwest. We`ll remain
on the southern fringes of these shortwave troughs, so
precipitation chances will continue to be highest (60-90% chance)
along the coast and north of the Rogue- Umpqua Divide and into the
Cascades north of Lake of the Woods. It`ll be dry for areas south
and east of those locations (though an isolated shower or two
can`t be ruled out) with gusty breezes (25-35 mph) developing in
the afternoons through Tuesday. Snow levels will hover around
3500-4000 ft today as the next disturbance passes through, but any
snow accumulations will be confined to the mountains generally
above 4500 feet. Highest amounts will be from about Crater Lake
northward, where 2-5" could accumulate. Up to an inch of snow is
possible over Highway 140 near Lake of the Woods with a skiff also
possible on parts of Highway 97 north of Chiloquin. So, if
traveling early this morning, be aware of the potential for some
slick spots in those areas.

This system exits to the east this evening, so shower chances
diminish, but it will be followed by another upper disturbance that
will swing through northern Oregon Tuesday and into Idaho Tuesday
night into Wednesday. Similar to the disturbance expected today,
PoPs (for showers) will be highest across the north, lowest across
the south. Snow levels bottom out near 2500 feet Tuesday morning,
but again most, if not all, snow accumulation will be in the
mountains north of Crater Lake with even less accumulations expected
than today`s system. The upper trough will exit to the east Tuesday
night into Wednesday, so precip chances drop to almost nil.

A few cold mornings are in store for West Side Valleys both Tuesday
and Wednesday mornings, and there will be some potential for
frost/freeze conditions. On Tuesday morning, the concern looks to be
limited to the Illinois Valley and the typically colder locations.
Confidence in freeze potential for Tuesday morning is limited by
potential lingering cloud cover. However, there could be a few hours
of clearing just after midnight tonight before cloud cover increases
again with the next disturbance moving in on Tuesday. A Freeze Watch
remains in effect for this potential, and details can be found at
NPWMFR. For Wednesday morning, the frost/freeze potential looks more
widespread for West Side Valleys (increasing to 25%-50% chance) due
to more widespread clearing of skies. Additional freeze products are
likely to follow in the next few shifts.

Heights rise on Wednesday as the upper trough continues to shift to
the east, resulting in at least partial sunshine with a dry and
slightly milder afternoon (high temps back closer to seasonal
normals). However, yet another upper trough coming out of the Gulf
of Alaska Wednesday night will skim by to our north on Thursday. As
has been the case for recent systems, models are showing most of the
precip staying well to our north, but a 20-30% chance of showers
persists for areas along the coast and across northern Douglas
County. Modest warming will continue with highs in the upper 60s to
low 70s west of the Cascades and generally in the mid 60s over the
East Side.

Confidence is increasing in the overall pattern expected for late
week and into the weekend, though confidence in details remains low
at this point. Friday should be a dry day for most as a shortwave
ridge passes through the region and temperatures trend warmer by a
few degrees compared to Thursday. Details become fuzzy Friday night
into the weekend.

Cluster analysis indicates that about 90% of the solutions bring
some semblance of a trough affecting the region this weekend, but
the question is how deep/strong is the trough? Of that 90% of
solutions, about a third of them (dominated by the EC) lean toward a
weak trough while the remaining 60% show a deeper/stronger trough,
but are split on the location of the trough. These differences make
it challenging to be confident in details at this point, but
overall, it looks like a general trend of lower temperatures with
increasing and more widespread precipitation chances can be expected
for the weekend. -Spilde/BR-y

&&

.AVIATION...29/06Z TAFs...VFR levels continue across most of
northern California and southern Oregon this morning, with isolated
MVFR ceilings possible along the Oregon coast or over elevated
terrain.

An approaching front will bring rainfall across areas west of the
Cascades on Monday morning, with occasional showers possible over
northern Klamath and Lake counties. The combination of 3500 to 4000
foot snow levels and westerly flow aloft is expected to limit snow
showers to over the Cascades. These rain or snow showers can locally
lower visibilities and ceilings as well as obscure elevated terrain.
Activity will decrease through Monday afternoon and evening. -TAD

&&

.MARINE...Updated 200 AM MOnday, April 29, 2024...A front will move
through the waters this morning with moderate west winds and low end
small craft advisory conditions into Tuesday morning. Low pressure
will move north of the waters Tuesday and bring in high and steep
swells into the waters Tuesday afternoon and evening. Weak high
pressure will move over the waters Wednesday, then another front
will mover into the waters Wednesday night, and move onshore
Thursday. Calmer conditions are expected Friday. -Petrucelli

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Freeze Watch from late tonight through Tuesday morning for
     ORZ024.

CA...None.

PACIFIC COASTAL WATERS...Small Craft Advisory from 5 PM this
     afternoon to 11 PM PDT Tuesday for PZZ356-376.

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

&&

$$

MNF/MAP/MAS/TAD