A short wave aloft brought a band of precipitation into a cold air mass that was already in place over northern California overnight. This caused a low level snow event over the area.
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The episode as NWS MFR wrote it up.
A short wave aloft brought a band of precipitation into a cold air mass that was already in place over northern California overnight. This caused a low level snow event over the area.
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 Feb 25, 8:18 PM PST, 1 hour 42 minutes earlier.
Area Forecast Discussion
National Weather Service Medford OR
818 PM PST Sun Feb 25 2018
.DISCUSSION...No updates are planned for this evening as the
forecast is generally on track.
A cold front is moving through our area this evening and currently
stretches from far western Siskiyou County to around Medford and
off to the northeast. As expected, snowfall in the Cascades has
been impressive. We've received a report from ODOT of over a foot
of snow near Diamond Lake, and SnoTel observations in the
Cascades hint that this is probably a common occurrence through
the range.
It will continue to snow in the Cascades through the night, but
the focus of the heaviest snow now shifts farther south into the
Siskiyous and east across much of the east side as the front
traverses these areas. Expect a period of moderate to heavy snow
as the front passes, and this includes I-5 at Siskiyou Summit.
Winter storm warnings remain in effect and cover this well.
On the west side, we've received numerous reports of rain changing
to snow at the back edge of the front down as low as 1500 feet.
This is exactly as expected, and radar echoes are starting to fill
in behind the front, and satellite shows a distinct band of
precipitation with colder cloud tops redeveloping over our
northern areas. High resolution model guidance captures this, and
shows the band moving south across the west side this evening and
into the Siskiyous later tonight. This band will produce some
snow accumulations down to 1500 feet or so, and even as low as
1000 feet in the heavier bursts of precipitation. We still think
impacts from this snow will be confined mainly to areas above 1500
to 2000 feet including the I-5 passes north of Grants pass, Hayes
Hill in Josephine County, and Jacksonville Hill. However, we may
see slushy accumulations at times down to the valleys including
Grants Pass and Medford, especially overnight as it cools to near
freezing. A winter weather advisory remains in effect above 2000
feet on the west side tonight. -Wright
&&
.PREV DISCUSSION... /Issued 227 PM PST Sun Feb 25 2018/
DISCUSSION...
Short Term...Tonight through Wednesday Night...With large scale
ridging to our west and deep troughing over the central US, we
remain locked under north to northwest flow aloft. This keeps us
right in the middle of the fast lane as far as storm systems go,
and several of them will blow through over the next week. The
first of these is arriving this afternoon and evening, and RADAR
imagery this afternoon already shows precipitation coverage
increasing with each scan. Snow levels have risen to above 2000
feet, but will drop down to below 1000 feet on the back side of
the cold front this evening and tonight. Much of the
precipitation will be through by the time the snow levels make it
to the valley floors, but some light snow is still possible in
Medford, Grants Pass, and Roseburg before sunrise. Snow will
continue through the evening and overnight in the Cascades, across
the East Side, and in Northern California, while moderate to
heavy rain falls along the coast and the lower coastal valleys.
For more details on the expected snow amounts and timing, see the
winter weather message at WSWMFR.
Showers will continue across the region into Monday afternoon
with lower snow levels, but amounts will be light and limited to
a trace to a few tenths of an inch. Weak high pressure will build
in Monday evening through Monday night, clearing out showers but
not providing much of a break until the next system arrives
Tuesday afternoon. Models have not been consistent with the exact
timing or track of this next storm, particularly concerning the
surface low to the north and the passage of the front through our
area, but there is good agreement on the pattern and there has
been some consistency with the general nature and strength of the
system.
Th warm front arrives Wednesday, producing some light
precipitation with snow levels rising to roughly 3500 to 4000
feet. The cold front will follow quickly behind Wednesday evening
and night, and this will produce the bulk of the rain and snow as
it pushes through. Snow levels are expected to drop on the back
side of the front, but only down to about 2000 feet or so, and
only after the main bands of precipitation have moved through. We
expect another good dumping of snow in the mountains, with a good
dousing of rain below the snow line. The front is also likely to
produce gusty winds along the coast, in the Shasta valley, and
across the East Side, which could be a concern if the models tend
stronger. Again the details are not set in stone, and there are
likely to be changes, so stay tuned over the next day or so as
confidence improves. -BPN
Long Term...Thursday through Sunday...Model solutions show good
agreement with an upper trough dropping down from the north on
Thursday, and the trough axis becoming centered along or just west
of the coast. This will bring a cold and showery pattern to the
area Thursday and Thursday night. The trough will remain in place
over the region Friday and another disturbance may move around the
trough and into the area. The main energy with this trough will
shift eastward on Saturday. However, a shortwave trough may
continue to bring showers into the area through Sunday. Zonal flow
aloft develops Saturday night and another disturbance moving into
the area with in west flow aloft may bring continue chances for
showers.
The main concern late in the week will be with lowering snow levels
and the potential for significant snow accumulations. As the upper
trough moves into place on Thursday, expect widespread showers with
lowering snow levels. Models continue to show snow level lowering
from around 2500-3000 feet Thursday morning down to 1000-1500 feet
Thursday night and locally down to 500 feet elevation. This combined
with widespread showers will bring a chance of snow down to western
valley floors. There remains variability in the model solutions
though on how much precipitation will occur with showers though. So
confidence is low on snow amounts.
Friday into Saturday, expect additional shower activity and
continued lower snow levels. However model solutions vary on the
placement of the trough and track of any additional shortwave
disturbances moving into the area. This will be key in how
widespread showers are Friday into Saturday.
Expect the pattern to transition to a zonal flow pattern with a
shortwave trough to the north by Sunday. Additional shortwave moving
down from the north and an approaching low pressure system offshore
may bring some continued precipitation into the area, especially
from the Cascades west. -CC
AVIATION...26/00Z TAF CYCLE...A cold front will move southeast
across the area this evening and tonight with widespread mountain
obscuration and mainly MVFR with occasional IFR and VFR.
Precipitation will spread across the region ahead of this front with
snow expected for LMT between 00-10z. Periods of IFR and moderate
snow may occur at LMT this evening. Snow levels will drop everywhere
behind the front beginning this evening. RBG and MFR could see snow
showers late tonight between 10Z and 14Z as precipitation tapers
off. Conditions will gradually improve during the morning Monday
with a mix of VFR/MVFR cigs then becoming VFR areawide Monday
afternoon. -CC
MARINE...Updated 200 PM PST Sunday 25 Feb 2018...A cold front
will bring increasing southwest to west winds into this evening.
Behind the front, steep seas due to a dominant northwest swell will
build to a peak on Monday. Seas will subside Tuesday into Wednesday.
Then, another round of steep heavy swell will come in late Wednesday
into Thursday, with gales likely.
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 4 AM PST Monday for ORZ029>031.
Winter Storm Warning until 4 AM PST Monday for ORZ030.
Winter Weather Advisory until 4 AM PST Monday above 2000 feet in
the for ORZ023-024-026.
Winter Storm Warning until 4 AM PST Monday above 2500 feet in
the for ORZ025.
Winter Storm Warning until 4 AM PST Monday for ORZ027.
Winter Storm Warning until 4 AM PST Monday for ORZ029.
Winter Storm Warning until 4 AM PST Monday for ORZ028.
Winter Weather Advisory until 4 AM PST Monday below 2500 feet in
the for ORZ025.
CA...Winter Weather Advisory until 4 AM PST Monday for CAZ081>085.
Winter Storm Warning until 4 AM PST Monday above 2000 feet in
the for CAZ080.
Pacific Coastal Waters...Small Craft Advisory until 4 PM PST Tuesday for
PZZ350-356-370-376.PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MEDFORD OR
525 PM PST SUN FEB 25 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0523 PM HEAVY SNOW 3 S DIAMOND LAKE 43.13N 122.14W
02/25/2018 E12.0 INCH DOUGLAS OR DEPT OF HIGHWAYS
DOT ESTIMATES "MORE THAN A FOOT OF SNOW" AT
THE HIGHWAY 230 & 138 INTERCHANGE NEAR
DIAMOND LAKE.
&&
WRIGHTPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MEDFORD OR
939 PM PST SUN FEB 25 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0936 PM HEAVY SNOW 2 SW SISKIYOU SUMMIT 42.04N 122.60W
02/25/2018 E4.0 INCH JACKSON OR DEPT OF HIGHWAYS
ODOT REPORTS 3-4 INCHES OF SNOW FELL ON I-5
AT SISKIYOU SUMMIT DURING THE COLD FRONTAL
PASSAGE.
&&
WRIGHTThe national radar mosaic for the moment the first event began.
2 heavy snow. Local standard time, as filed.
A spotter 2SSW Weed reported 7.0 inches of snow in 8 hours ending at 26/0900 PST.
A spotter at Tennant reported 6.0 inches of snow in 6 hours ending at 26/0400 PST.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2018Every state in 2018This day in weather historyWarnings in California, February 2018
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: 732138, 732141.