Low pressure moving across the eastern Pacific brought a cold front with moderate amounts of snow to the Cascades at elevations above 4000 feet.
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The episode as NWS MFR wrote it up.
Low pressure moving across the eastern Pacific brought a cold front with moderate amounts of snow to the Cascades at elevations above 4000 feet.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Medford, OR wrote its last area forecast discussion before the first event at Nov 18, 2:44 PM PST, 4 hours 16 minutes earlier.
Area Forecast Discussion
National Weather Service Medford OR
244 PM PST Sat Nov 18 2023
.SHORT TERM...The first front of the forecast is already bringing
precipitation to most of the region at this time. Some of the
showers are showing pretty decent returns on the radar with some
light graupel being reported, but so far no lightning. This may
change later this afternoon as a colder air mass moves in aloft. A
strong intensifying northwesterly jet on the back of the upper
trough will bring cooler air, dropping 500 MB temperatures from
around -20C to near -25C later this evening, bringing both lower
snow levels and instability ahead of the cold front. Precipitation
will intensify as the left exit region of the strong jet brings
stronger dynamics as the region becomes more unstable. The best
chances of instability according to the SPC HREF is in northern
California over Shasta county where a 50% chance of thunderstorms
is indicated. However, even though there is lesser chances north
of there, there should be weak instability of much of the region,
and a slight chance is possible over much of the west side into
early evening. As is typical, the bulk of the precipitation will
be ahead of the cooler air with snow levels above ~6500-7000 feet.
As the colder air mass continues to move in snow levels drop to
~3000 feet Sunday morning, but the bulk of the precipitation will
be through by then. The winter weather advisory for the Cascades
above 4000 feet remains in effect from 7 PM this evening through
10 AM Sunday.
Showers taper off through the day Sunday as an upper ridge builds
in quickly behind the exiting front with the ridge level winds
switch to the north, cutting off the moisture flow into the
region. A very weak front moves in Tuesday on the back of the
flattening upper ridge bringing light precipitation from the
Cascades westward. -Sven
.LONG TERM...Wednesday through Saturday, November 22-25, 2023...
On Wednesday, an upper level trough will move through the upper
ridge and this will lead to an increase in cloud cover and a higher
chance of rain (30-50% chance), mainly from the Cascades westward.
Initially, snow levels will remain high, up around 7000 feet, as
this trough moves in. The upper trough will swing through Wednesday
night with precip chances increasing south and east of the Cascades.
Some guidance is showing the upper trough amplifying a bit during
this period, which could bring a little precip enhancement to NE
California and Lake County. Even so, 43% of GEFS ensemble members
and 26% of ECMWF ensemble members show no precipitation at all for
Alturas/Lakeview, which is still a fairly high probability of not
having any precipitation at all with this system. Either way,
precipitation should mostly be light. Snow levels drop to 4000-4500
feet behind the surface cold front and, overall, it'll be a bit
cooler for everyone on Thanksgiving Day. Other than slight chance to
chance PoPs (15-35%), precipitation should be diminishing/ending
across the area or exiting to the east. Friday into next weekend,
models are showing the upper ridge re-amplifying near or just beyond
130W, which would keep much of the area in a drier northerly flow
aloft. Ensemble means and clusters are showing this pattern to
persist at least until Monday, Nov 27th. -Spilde
&&
.AVIATION...18/18Z TAFs...Pretty complicated weather pattern across
the area today. A cold front offshore is leading to southerly flow
aloft in advance of it. There are still some lingering low
clouds/fog (MVFR/IFR) in the valleys west of the Cascades this
morning, but these should break up by around noon as the front gets
closer to the coast and winds begin to mix up the atmosphere.
Satellite is already showing some wave action over the interior
mountains, so flights in and out of the terminals should prepare for
at least some bumpiness/turbulence.
The strong front will arrive at the coast this evening, with gusty
west winds developing across the coastal waters and at the coast
with SSE winds shifting rather abruptly to westerly across the
remainder of the area. In addition to the turbulence, pre-frontal
low level wind shear is possible at most terminals. Expect a
period of moderate to heavy rain with this front, with significant
impacts to visibility and widespread terrain obscuration
developing this evening and continuing through tonight and into
Sunday morning. Freezing levels of around 7000 to 8000 feet will
lower quickly to around 4000 feet with the passage of the front.
-BPN/Spilde
&&
.MARINE...Updated 200 PM Saturday November 18, 2023...Winds will
increase further and shift from southerly to westerly as the cold
front moves through the waters and onshore by this evening. Gales
are likely for much of the area beyond 10 nm from shore, with large,
very steep warning level seas across the entire region tonight
through Sunday morning. The wind-driven seas will be followed by
fresh west swell.
Winds will diminish Sunday, but seas will remain steep as the
ongoing swell gradually diminishes into Monday morning. Another
weaker front is expected Tuesday into Wednesday, followed by gusty
north winds and steep seas through the remainder of the week.
-Smith
&&
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory from 7 PM this evening to 10 AM PST
Sunday above 4000 feet for ORZ027-028.
CA...None.
PACIFIC COASTAL WATERS...Small Craft Advisory until 4 PM PST this
afternoon for PZZ350-356-370-376.
Hazardous Seas Warning until 10 AM PST Sunday for PZZ350-356-
376.
Gale Warning until 10 AM PST Sunday for PZZ370-376.
&&
SBN/SBN/SBNThe national radar mosaic for the moment the first event began.
1 heavy snow. Local standard time, as filed.
NOHRSC analysis indicated storm totals of 4 to 12 inches of snow from the Lake of the Woods area northward.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Oregon in 2023Every state in 2023This day in weather historyWarnings in Oregon, November 2023
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 1147670.