323
FXUS66 KMFR 270544
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
1043 PM PDT Fri Apr 26 2024

...Updated AVIATION discussion...

.DISCUSSION...

Radar is starting to clear up this evening as we lose solar
heating. In fact, KMAX just switched into VCP 35(clear air mode)
a few minutes ago. Models show 500 mb heights building later
tonight and that should help clear things out a bit tonight.
Pockets of frost are also possible, although valley temperatures
appear to stay in the upper 30`s west of the Cascades instead of
lower 30`s. Dewpoints are also pretty warm and in the lower 40`s, so
it`s hard seeing temperatures really crashing if we clear out. In
fact, there should be potential for pockets of fog, especially in
the Umpqua Basin later tonight.

-Smith

&&

.AVIATION...27/06Z TAFs...The night is starting with generally VFR
levels across northern California and southern Oregon. Some ceilings
along the Oregon coast are occasionally down to MVFR levels, and may
fluctuate overnight. There`s a 5-10% chance of visibilities dropping
to MVFR levels in the Umpqua Valley early Saturday morning if some
patchy fog develops, but the confidence in that is not high enough
to enter into the TAFs.

A weak front will bring more showers to the area late Saturday
morning, with the Oregon coast and the Cascades having the best
chances for rain through the TAF period. Inland areas west of the
Cascades should see periodic showers, while little activity beyond
some gusty winds is expected east of the Cascades. -TAD

&&

.MARINE...Updated 800 PM Friday, April 26, 2024...West swell is
continuing to build steep seas in all waters. A Small Craft
Advisory is in place until 2 AM on Saturday morning to communicate
these continuing conditions.

Seas look to remain generally calm through the weekend and into next
week. An approaching front may bring wind-built steep seas to waters
north of Gold Beach through Saturday afternoon and evening with calm
seas returning before Sunday. Current forecast wave heights are just
barely at Small Craft levels, and confidence in the affected area is
low. Additional guidance will help to determine if another brief
period of steep seas is expected.

Active weather continues next week, although marine impacts look
minimal. Approaching systems will bring precipitation chances (40-
60%) on Monday and across the latter half of the week. Probabilistic
guidance suggests a very small (10-20%) chance of waves exceeding 12
feet on Tuesday morning, but chances for larger waves are otherwise
nonexistent next week. This indicates that conditions beyond steep
seas are exceptionally unlikely through next Friday. -TAD

&&

.PREV DISCUSSION... /Issued 446 PM PDT Fri Apr 26 2024/

SHORT TERM...Tonight 4/26 through Saturday night 4/27...Radar
imagery is showing numerous showers across southern Oregon and
northern California. These showers will continue this afternoon
and taper off over the evening. These showers are being caused by
a frontal boundary that moved through the area earlier this
morning. A couple of thunderstorms may be possible this afternoon,
mainly along and east of the Cascades. The HREF didn`t show much
that impressed me regarding showers, but a lightning strike was
already recorded in Lassen County, California. Some of these
showers may produce some moderate to heavy precipitation.

As showers taper off tonight, some clearing may occur; but skies
will remain mostly cloudy which will keep temperatures moderated
and will preclude any frost or freeze concerns.

Another front will swing by southern Oregon and northern
California tomorrow. This system may bring additional light
precipitation to areas mainly along and west of the Cascades.
Snow levels will be around 5000 feet, and 1-2 inches of snow will
be possible in the Cascades. Impactful weather, however, is
generally not expected

LONG TERM...Sunday through Friday, April 28 - May 3,
2024...Zonal flow (west to east) across the Pacific Sunday into
Tuesday will maintain a storm track mostly to our north. At times,
disturbances will swing through, resulting in an increase in
shower chances, but mainly across NW sections of the CWA. On
Sunday, onshore flow will contribute to a 30-60% chance of showers
north and west of the Umpqua Divide with PoPs diminishing quickly
south and east of there. It looks like a mainly dry, at least
partly sunny day elsewhere (including here in the Rogue Valley)
with gusty breezes (25-35 mph) developing in the afternoon. The
next upper air disturbance will move through Sunday night into
Monday. Once again, the main forcing for precipitation will be to
our north, but there`s a high probability of showers (50-70%)
along the coast and over to the Cascades. Again, precip chances
drop off quickly to the south and east of the mountains. We can`t
rule out a shower or two around the Rogue Valley/Medford area
during that time period, but most of the time will be rain free.
Snow levels Sunday night could dip to around 3500 feet or so, but
any light snow accumulations (1-3") should be confined to the
Cascade mountains from around Crater Lake northward. This system
exits to the east Monday evening, followed by another upper
disturbance that will swing through northern Oregon on Tuesday.
For a third time, we`ll be on the southern fringes of this system,
so PoPs remain highest across the north and west, lowest across
the south and east. Overall, temperatures during this period will
be near to below normal. Widespread frost/freezing conditions west
of the Cascades appear unlikely at the moment, but a colder night
or two is possible, especially if skies clear and remain clear
all night. Best chance right now for frost is Monday night/Tue
morning with the usual suspects (Illinois/Applegate Valley/Grants
Pass areas) having the highest probability (30-60%).

There remains quite a bit of uncertainty regarding mid-late next
week. Recent 12z deterministic guidance wants to dry things out
across the area Tuesday night into Wednesday with a return of higher
heights by Thu/Fri. Some multi-model members have also gone in this
direction, which would potentially bring a substantial warm up. This
is being reflected in recent blended guidance as well with some
lowering of PoPs in the Wed-Fri time frame. However, there are still
several members that fall into a cluster of similar solutions (~20%)
that bring another upper trough into the area maintaining a cooler,
wetter regime. At this point, confidence in any of these solutions
is low, so we prefer to keep the official forecast closer to the
NBM, which results in modest PoPs (generally 20-40%) area wide
during the period. Temperatures should trend higher as well, but
we haven`t gone quite as high as the 12z models would show just yet.
-Spilde

&&

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

PACIFIC COASTAL WATERS...Small Craft Advisory until 2 AM PDT Saturday
     for PZZ350-356-370-376.

&&

$$