490
FXUS66 KMFR 272118
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
218 PM PDT Sat Apr 27 2024

.SHORT TERM...Tonight through Sunday night 4/28...RADAR imagery
is showing a band of showers moving across southern Oregon and
northern California along a frontal boundary. This frontal
boundary has pushed a bit farther south than what was originally
thought, and could put down some light rain largely along and west
of the Cascades with a few areas east of the Cascades also
picking up on the rain. These showers will largely dissipate
overnight, but the cloudy weather will continue. This will help to
moderate the overnight lows somewhat and keep them from reaching
freezing west of the Cascades and in the upper 20s to low 30s east
of the Cascades.

Generally unsettled, cloudy weather with a few lingering showers
along the coast and in Douglas County will be possible on
Saturday. Then, the next front will approach the Pacific
Northwest Sunday night into Monday. The bottom line is that we are
not expecting any hazardous impacts at this time. More information
about this system is in the long term portion of the discussion
below. -Schaaf

.LONG TERM...Monday through Saturday, April 29 - May 4, 2024...
WNW flow aloft will continue to bring systems from the Gulf of
Alaska into the PacNW early next week. This combined with low-level
onshore flow will keep things on the cool, unsettled side with
highest precipitation probabilities in NW sections of our CWA, while
SE sections (south and east of the Cascades) remain on the dry side.

An upper trough will swing through Monday morning and this will
bring a shot of showers (60-90% chance) to the coast eastward to the
Cascades. We can`t rule out a shower or two around the Rogue
Valley/Medford area Monday, but most of the time will be rain free.
Snow levels will drop to as low as 3000 feet by Monday morning, 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 Monday morning, be aware of the potential for some slick spots
in those areas. South of the OR/CA border, we don`t think much
precipitation will make it over the mountains and it will just be
partly cloudy. As such, it`ll be cold first thing Monday morning for
some frost in the lower Klamath, Scott and Shasta valleys.

This system exits to the east Monday 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. Once again, we`ll be on the southern fringes
of this system, so PoPs (for showers) remain 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. Overall, temperatures
will remain near to below normal. Frost/freezing conditions west of
the Cascades are becoming more likely given the main area of precip
potential is north of the Umpqua Divide. Frost (lows 33-36F) chances
(50-80% chance) are highest for a few hours in the typically colder
locations (Illinois/Applegate Valley/Grants Pass areas) both Tue/Wed
mornings. Freezing conditions (<=32F) are possible (20-30% chance)
in the Illinois Valley as well.

As the upper trough shifts to the east, things dry out on Wednesday
with some sunshine and a slightly milder afternoon (high temps back
closer to seasonal normals). Models maintain some degree of
uncertainty after Wednesday with NBM still showing some PoPs (20-
30%) across NW portions of the CWA. This stems from a smaller
percentage of model members (GEFS/Canadian and to an even lesser
extent ECENS) showing a flat upper ridge and a weak trough, you
guessed it, skimming over the top Wednesday night into Thursday.
More plausible scenarios feature a bit stronger ridge and no precip
along with a more significant warm up. We`ll see how it shakes out,
but it does appear that temperatures should rebound to above normal
levels Thu/Fri. Models are showing a potentially more substantial
trough moving in next weekend, but confidence in the details is low
at this point. -Spilde


&&

.AVIATION...27/18Z TAFs...A front will bring some light rain
and/or showers to the coast and over to the Cascades this
afternoon and evening. VFR will be the predominant condition,
though ceilings/visibilities could lower to MVFR (perhaps even
local IFR) at times. Higher terrain will also be occasionally
obscured.

For Medford and areas to the south and east, expected mostly VFR
today. The front may cause isolated showers and brief lower
ceilings. Winds will be occasionally gusty (20-25 kt) this
afternoon/evening east of the Cascades, including at Klamath Falls,
but strong winds are not expected.

Tonight into Sunday morning, mostly VFR will prevail, though areas
of MVFR can be expected along the coast. -Spilde


&&

.MARINE...Updated 200 PM Saturday, April 27, 2024...Gusty south
winds, isolated showers and steep seas will continue into late this
afternoon, resulting in conditions hazardous to small craft through
all marine areas. The front will continue eastwards and winds will
shift to west and weaken this evening, but seas will remain steep
through late tonight/very early Sunday.

Overnight, winds will ease and seas will transition to longer period
swell. Seas do remain elevated, but they won`t be as steep.
Relatively calmer conditions will likely continue through Sunday,
then another front will move into the waters Monday and bring
stronger winds. The pattern will continue to remain active next
week, but we`re not anticipating any hazardous conditions into at
least the middle of next week. -CSP


&&

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

PACIFIC COASTAL WATERS...Small Craft Advisory until 11 PM PDT this
     evening for PZZ350-356-370-376.

&&

$$