511
FXUS66 KMFR 290550
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
904 PM PDT Sun Apr 28 2024

...Updated AVIATION Discussion...

.DISCUSSION...The forecast is on track for this evening. Radar
indicates some light showers over Douglas County as well as over
the Cascades and around Mount Shasta. Overnight temperatures will
remain above freezing for areas west of the Cascades tonight.

A cold front will bring precipitation to west side areas starting on
Monday morning, with some showers possible over northern Klamath
and Lake counties as well. Snowfall will be limited to Cascades
peaks with amounts looking to remain below advisory thresholds.
While substantial road accumulation is not currently expected,
snow showers can still lower visibility or locally slick
conditions. Extra caution is advised for anyone traveling over
the Cascades through the day Monday.

Please see the previous discussion for more details about the
short- and long-term forecasts. -TAD


&&

.AVIATION...29/00Z 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 800 PM Sunday, April 28, 2024...Weak high
pressure southwest of the waters will result in light to moderate
west winds and moderate seas this evening. A front will move through
the waters early Monday morning with stronger west winds and low end
small craft advisory conditions into Tuesday morning. A low with
some high and steep swells will then move into the waters Tuesday
afternoon and evening. A thermal trough is anticipated to build
briefly Wednesday into Wednesday night with northerly winds
increasing south of Cape Blanco. Calm seas and weak winds are likely
Thursday into Friday.

-DW

&&

.PREV DISCUSSION... /Issued 442 PM PDT Sun Apr 28 2024/

SHORT TERM...Tonight 4/28 through Monday night 4/29...Satellite
imagery is showing some cloud cover across portions of southern
Oregon and northern California with radar showing some light
showers in northern Douglas County moving into Lane County. Expect
a relatively benign rest of the afternoon and evening.

Then, the next front swings into the Pacific Northwest late
tonight into early Monday morning and brings the next dose of
precipitation with it. Snow levels will be lower around 3500 feet
or so, but precipitation amounts will largely be light with the
heavies amounts being focused in the Cascades north of highway
140. Still, snowfall amounts are expected relatively light with
the highest amounts of 2 to 5 inches possible for Crater Lake,
Diamond Lake, and Willamette Pass. Meanwhile, Siskiyou Summit on
I-5 might see a dusting of snow with highway 97 east of the
Cascades seeing less than an inch possible.

Cloud cover will linger and will heavily influence temperatures.
This will keep afternoon high temperatures low, and could allow
for overnight lows to stay moderately warmer. Despite clearing
skies, we`re not expecting a freeze tonight for the Illinois
Valley (15 percent chance or less). However with the next cold
front coming through, the chances of a freeze Monday night into
Tuesday morning increase to 60 percent, but cloud cover may
inhibit freezing temperatures. Have issued a freeze watch for
Monday for portions of the Illinois Valley. Please see the NPWMFR
for more details. -Schaaf

LONG TERM...Tuesday through Sunday, April 30 - May 5, 2024...
A cool spring weather pattern will continue into Tuesday as WNW flow
aloft brings yet another upper air disturbance into the PacNW from
the Gulf of Alaska. Some cold/frosty spots are possible in the
morning in the valleys west of the Cascades, primarily south of the
Umpqua Divide. As the upper trough moves across northern Oregon,
gusty breezes will develop Tuesday afternoon, especially east of the
Cascades. We`ll remain on the southern fringes of this system, with
highest PoPs (for showers) across the north. There is a fairly
high probability of precipitation (50-80% chance) from the coast to
Douglas County and over to the Cascades north of Crater Lake.
Amounts appear to be on the light side again, generally 0.10-0.20
for the Coos Coast Ranges and along the Lane/Douglas county border
with maybe a couple of inches of snow above 4500 feet north of
Crater Lake. South of the Umpqua Divide, precip chances diminish
quickly to below 20% Tuesday, though an isolated shower/sprinkles
cannot be ruled out. The upper trough will exit to the east Tuesday
night into Wednesday, so precip chances drop to almost nil. Another
cold night is expected, so frost/freeze potential will again be in
play for the west side valleys. The potential for frost (lows 33-
36F) is highest (50-80% chance) for a few hours in the typically
colder locations (Illinois/Applegate Valley/Grants Pass areas) with
freezing conditions (<=32F) possible (20-30% chance) in the Illinois
Valley as well.

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 the last 3 days, models are
showing most of the precip with this system 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.

Uncertainty increases late next week into the weekend. The majority
of models/ensembles show at least brief upper ridging again on
Friday with approximately another 5 degrees of warming (compared to
Thursday). Then, guidance is showing a potentially more substantial
trough moving in Friday night into next weekend with higher PoPs and
lower temps, but confidence in the specifics of timing/strength
right now remains low. -Spilde

&&

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

CA...None.

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

     Small Craft Advisory from 5 AM Monday to 11 PM PDT Tuesday for
     PZZ350-370.

&&

$$