Clearing skies combined with longer nights and a cool air mass allowed temperatures to drop below freezing at some locations in southwest and south central Oregon.
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The episode as NWS MFR wrote it up.
Clearing skies combined with longer nights and a cool air mass allowed temperatures to drop below freezing at some locations in southwest and south central Oregon.
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 Sep 28, 7:05 PM PST, 5 hours 55 minutes earlier.
Area Forecast Discussion
National Weather Service Medford OR
805 PM PDT Tue Sep 28 2021
.DISCUSSION...29/00Z NAM in.
Showers, mostly over the Umpqua Basin and adjacent Cascades, are
diminishing over the area this evening as an upper level ridge
builds into the area. This will be a flat dirty ridge, so while
it will be dry tonight, there will be high clouds streaming over
the area.
It will be a cold night across the area. Freezing temperatures
are expected over all of the east side and portions of northern
California. Areas of frost are also expected in some of the colder
spots of the west side (Prospect, Applegate, Williams), but
probably not Medford. Freeze Warnings and Frost Advisories are in
effect. See NPWMFR for details.
A weak short wave will move through Wednesday morning. This may
bring some light precipitation to the coast north of Cape Blanco,
Wednesday into Wednesday night, but that's about it.
The ridge will build in more strongly behind the short wave, and
this will clear the high clouds out for a short period of time.
The ridge will break to the east of the area Wednesday night and
the flow aloft will become southwesterly. A series of systems
supported by upper level short waves will move onshore Wednesday
night into Thursday night, but the bulk of the energy will be
directed to the north of the Medford forecast area. Once again,
precipitation will be limited to the north coast.
The strongest of the short waves will move onshore Thursday
night. The associated front will push into the area Thursday night
and clear to the east by Friday. Precipitation will be light with
this front and limited to a slight chance of rain or drizzle
along the coast, the Umpqua Basin, and the adjacent Cascades.
Enough moisture may also bank up against the Siskiyous for a
slight chance of drizzle Friday morning.
North to northeast winds will increase over the upper slopes/ridges
of southwest Oregon and western Siskiyou County late Thursday
night into Friday night, with gusts in the 20-30 mph range. It
will be windy along the coast and offshore waters as well during
this time frame. Breezy north to northeast winds will also
develop in the Umpqua Valley and the Illinois Valley. High
temperatures will cool a few degrees across the northern and
western portions of the Medford forecast area, but there won't be
much change elsewhere.
Once that front moves out, there will be a long break in the
frontal action as a ridge builds in from the southwest. This will
force the storm track well north of the area and Saturday through
Monday look to be dry and quite warm over the inland areas with
above normal high temperatures.
The next upper trough will approach the coast Tuesday with a
slight chance of rain there toward evening. Models are suggesting
a trend toward cooler and possibly wetter weather for the middle
of next week.
&&
.AVIATION...29/00Z TAFs...Along the coast...Expect mainly VFR
conditions overnight with mid and upper level clouds continuing to
move into the area before reducing tomorrow afternoon.
Inland...Mountain obscurations will persist, although VFR conditions
at terminals is expected overnight. Given the recent rainfall, there
is potential for valley fog tonight into Wednesday morning, but we
think mid level clouds moving in from the west will prevent
widespread fog, so we've left it out of the TAFs for this issuance.
Keene/Miles
&&
.MARINE...Updated 800 PM PDT Tuesday 28 September 2021...Conditions
hazardous to small craft are expected to persist for all areas
through early Wednesday morning as steep west-northwest swell
continues. Seas subside below Small Craft Advisory conditions
criteria later Wednesday morning. Generally light winds increase
some from the south on Wednesday afternoon as a front approaches.
Another west-northwest swell will arrive Thursday night and may
bring back Small Craft Advisory conditions to the forecast area.
After this swell subsides over the weekend, there is increasing
confidence in several days with conditions below Small Craft
Advisory criteria. Keene/Miles
&&
.FIRE WEATHER...Updated 800 PM PDT Tuesday 28 September 2021...
Wetting rain fell across nearly all of the Medford forecast area
Monday, and some locations near the coast and in the Umpqua Basin
got anywhere from 1 to 3 inches. The biggest short term concern at
this time is travel on muddy forest roads. The region will see a
warming and drying trend into Thursday. A weak and mostly dry cold
front will bring a slight chance of rain Thursday to the west side
north of the Umpqua divide. Unseasonably dry conditions with above
normal temperatures are expected then from Saturday into next week.
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Freeze Warning from 2 AM to 10 AM PDT Wednesday for ORZ029>031.
Frost Advisory from 2 AM to 10 AM PDT Wednesday for ORZ024-026.
CA...Freeze Warning from 2 AM to 10 AM PDT Wednesday for CAZ084-085.
Frost Advisory from 2 AM to 10 AM PDT Wednesday for CAZ080>082.
Freeze Warning from 2 AM to 10 AM PDT Wednesday for CAZ080-082.
Pacific Coastal Waters...
Small Craft Advisory until 5 AM PDT Wednesday for
PZZ350-356-370-376.
15/15/05The national radar mosaic for the moment the first event began.
2 frost/freeze. Local standard time, as filed.
Reported low temperatures in this zone ranged from 22 to 29 degrees.
Reported low temperatures in this zone ranged from 22 to 30 degrees.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Oregon in 2021Every state in 2021This day in weather historyWarnings in Oregon, September 2021
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: 977069, 977070.