A cold front brought unseasonably cold weather to the area, and show showers behind the front brought heavy snow to the Mount Shasta area of northern California.
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The episode as NWS MFR wrote it up.
A cold front brought unseasonably cold weather to the area, and show showers behind the front brought heavy snow to the Mount Shasta area of northern California.
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 Mar 14, 12:20 PM PST, 40 minutes earlier.
Area Forecast Discussion
National Weather Service Medford OR
120 PM PDT Sun Mar 14 2021
The Aviation section has been updated...
.AVIATION...For the 14/18Z TAF Cycle...Updated at Noon PDT...
As of 20Z, winds had shifted to northwesterly along and near the
coast while moderate to locally strong southerly winds continued
across inland locations. The strongest winds, thus far, have been in
the Shasta Valley, where gusts 40 to 50KT have been observed. We'll
need to keep an eye on KLMT through the afternoon because, while the
majority of the model guidance suggests gusts will stay below 30KT,
RDD-MFR pressure gradient is running a bit above model guidance and
high resolution models suggest peak gusts in the 30 to 35 KT range.
At this point, we have moderate confidence that winds at KLMT will
stay below the Airport Weather Warning criteria of 35KT there.
Also related to winds, SE winds have failed to make into Medford,
thus far, so the NW surface wind at KMFR is combining with SE winds
aloft to result in low level wind shear. This has been reported by a
couple of aircraft. This is likely to continue through 21Z, and
possibly until 23Z if SE winds do not mix to the SFC at that
location.
The slow moving cold front pushing in today is expected to primarily
result in MVFR conditions along the coast and across the west side
this afternoon. This evening, as the low level cold front pushes
further east onto the east side, the upper level trough is expected
to slow. This will result in rain changing to snow overnight into
Monday morning. This will lead to a period of IFR and total terrain
obscurations for elevations above about 1kft west of the Cascades,
to include KMFR south and eastward into NorCal. Showers are expected
to taper off across most of the area between 12Z and 18Z Monday
morning. ~BTL
&&
.UPDATE...
The near term forecast remains on track with the front moving
onshore around noon. Radar is picking up on precipitation off the
coast as of 9 am, but the rain is very light according to one of our
spotters. We did add some thunderstorms to the forecast over the
waters this evening into tonight. With some very cold air aloft and
the trough axis right over southern Oregon, a few rumbles of thunder
are not out of the question near the coast. Otherwise, the low level
snow and wind forecasts remain on track tonight into Sunday.
For more information about the wind and snow hazards, read the
discussion below. -Smith
&&
.DISCUSSION.../Issued 425 AM PDT Sun Mar 14 2021/
An abrupt change in the weather pattern is expected today with
rain, snow and gusty winds today, followed by low elevation snow
developing tonight and early Monday. Satellite imagery shows a
well-defined cold front just off the coast. Behind the front there
is plenty of cold cumulus. South winds have begun to increase
along the coast and over the coastal mountains. Winds will
increase further this morning along the coast and rain will begin
to push into the coast and coastal range. South winds will also
increase for inland areas this morning and afternoon, mainly over
the mountains, in the Shasta Valley and for areas east of the
Cascades in the Summer Lake area. A Wind Advisory is in effect for
gusty to strong winds that are expected in the Shasta Valley and
Summer Lake areas today into early this evening.
Late this morning into the afternoon, expect precipitation to
begin to spread inland over western portions of the area. Then rain
and snow will increase and spread across the CWA late this
afternoon and this evening. Significant snow impacts are expected
as this system moves inland. Initially, snow impacts may begin in
the higher terrain this afternoon with snow levels starting out
at about 4000 to 5000 ft, though lower (down to 3000 feet) in
upslope- favored Mount Shasta City area. However, the March sun
angle will make it difficult for snow impacts to affect roadways
at the onset of snowfall. Snow impacts will increase this evening
and tonight as temperatures cool, snow levels fall and precipitation
increases. Heavy snow impacts are expected in the Mount Shasta
City area with moderate snow impacts expected to develop across
much of Siskiyou and Modoc Counties and over the Siskiyous and
Southern Oregon Cascades. West of the Cascades, light to moderate
snow is expected. Models continue to indicate very cold air aloft
(-4 to -8 deg C at 850 mb) will move into areas west of the
Cascades this evening and tonight as the front moves eastward and
the upper low dives south-southeast, moving into Northern
California. As a result, expect snow levels to lower to 1500 to
2000 ft with the frontal passage, resulting in snow impacts on
higher passes and in some western valleys.
As the upper low continues moves further inland, becoming
centered over northern California, additional cold air advection
will bring snow levels down to 500 to 1000 feet late tonight and
Monday morning. A notable feature with this system is that the
GFS and NAM operational models (and GEFS and European ensemble
mean) indicate 850 mb temperatures dipping to around -7 to -8C.
This will be the coldest temperature at that level (850mb) since
2018 and the coldest March temperatures at that level since 2012.
How much precipitation is left when those very cold readings
arrive is in question, but it's safe to say that some valleys west
of the Cascades will see some snowfall late tonight and Monday
morning. We can't even rule out some snowflakes all the way to the
coast with how cold the air mass is. Showers will be focused
mainly over the mountains and foothills during this time period.
However snow showers may bring light snowfall of a trace to
generally less than an inch to valleys west of the Cascades.
For the latest details on the Winter Storm Warnings in south-
central and southeast Siskiyou County and the Winter Weather
Advisories for other areas, please see the WSWMFR for details.
Light showers, a result of ongoing upslope flow, could continue
Monday afternoon and evening, but no substantial precipitation
is expected. High temperatures will be much cooler with
temperatures of 15 to 20 degrees cooler compared to Saturday's
high temperatures. Additionally, cold temperatures are expected
Monday night with most western valleys in the 20s to lower 30s
and temperatures dropping into the lower to mid 30s along the
coast. East of the Cascades, low temperatures are expected to be
in the mid to upper teens Tuesday morning.
PREV LONG TERM DISCUSSION... /Issued 232 PM PST Sat Mar 13
2021/...Tue, March 16th through Sat, March 20th and Beyond... By
Tuesday morning we'll be under weak high pressure ridging behind
the Sunday-Monday upper level trough and associated cold front.
There will be a split jet stream along the west coast, with the
northern branch moving over southeastern Alaska and British
Columbia and the southern branch moving across California.
Meanwhile, there will be an upper level trough centered over the
Gulf of Alaska. Temperatures across the area on Tuesday will
remain cool, with valley highs in the 40s and 50s. While this puts
high temperatures about 5 to 7 degrees below the 1981-2010
calendar day averages, it should be a brilliant afternoon with
partly cloudy to mostly sunny skies Tuesday.
Clouds are expected to increase Wednesday as the southern branch
of the jet stream moves northward over our area and broadens.
While guidance suggests low probabilities of showers Wednesday
afternoon and evening under diffluent southwest flow, it's not
hard to imagine some spits and sprinkles over the hills and some
snow flurries over the mountains above about 5kft as skies will
be partly to mostly cloudy. It will also be milder, with valley
highs mostly in the 50s and lower 60s.
Thursday the upper level trough in the Gulf of Alaska will move
closer to the coast and then it will move inland over the weekend,
exiting to our east early next week. This will send a couple of
cold frontal boundaries onto the coast and through the forecast
area Thursday into Friday with showers likely over the weekend and
into Monday to possibly even Tuesday.
From Wednesday night through Saturday current projections are for
1 to 2.5 inches of water across Curry, southwestern Josephine,
and far western Siskiyou County, a half inch an inch across Coos
County, most of the Douglas County, and the Mount Shasta area, and
a quarter to a half inch across most of Jackson County. Areas
east of the Cascades are likely to get around a quarter of an inch
around Chemult to nothing across the drier valleys of the east
side. However, Friday and Saturday the GFS model does suggest the
possibility of some showers and some isolated thunderstorms for
areas east of the Cascades which could bring at least some
measurable precipitation to those drier areas. Snow levels look as
if they will generally fluctuate between 4kft and 6kft. A few
inches of new snow is expected across most locations above 5kft,
but elevations above 6500 feet in Siskiyou County could see 7 to
15 inches of snowfall.
While an upper level ridge looks as if it will move in the early
to middle part of next week (22nd-23rd), there will also be
another upper level trough moving into the Gulf of Alaska. Thus,
we're likely to experience a drier period mid-late next week with
warmer temperatures. The ensembles indicate some precipitation
from this next upper level trough moving into the area late next
week through next weekend (roughly the 25th-28th). ~BTL
&&
.MARINE...Updated 845 AM PST Sunday, 14 Mar 2021...
NDBC buoy data remains unavailable, but information from the Umpqua
Offshore Buoy 229 is available at cdip.ucsd.edu. Polar orbiting
satellites are also still providing some wind data for areas beyond
10NM of the coast. Due to the lack of data from the NDBC buoys, we
have less data to calibrate the forecast for those areas as compared
to normal.
A strong cold front will continue to bring southerly gales this
morning with very steep, wind driven seas. The impact will be less
for locations within 5 nm from shore such as the waters near
Florence, Reedsport and Coos Bay. Mariners should also prepare for
steep wind driven seas reaching 10 to 15 feet with a dominant wave
period under 10 seconds. Combined seas are expected to peak around
noon, but building west-northwest swell combined with a smaller
southwest swell is expected to bring another round of hazardous,
high, and very steep seas Sunday night into Monday.
Seas then begin to subside, but are likely to remain high and steep,
10 feet or higher, through Monday night. Seas then begin to subside
Monday morning, but are likely to remain high and steep through
Monday night.
Seas diminish further into Tuesday evening, reaching a minimum of 5
to 6 feet. We'll see a break in the active weather Tuesday and
Wednesday before another fairly strong front moves in Thursday.
~BTL/Miles
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory until 8 PM PDT this evening for ORZ031.
Hazardous Seas Warning until 5 PM PDT Monday for ORZ021-022.
Winter Weather Advisory from 5 PM this afternoon to 10 AM PDT
Monday below 2000 feet in the for ORZ023>026.
Winter Weather Advisory from 5 PM this afternoon to 10 AM PDT
Monday for ORZ028.
CA...Winter Storm Warning from 4 PM this afternoon to 10 AM PDT
Monday above 3000 feet in the for CAZ082.
Winter Weather Advisory from 5 PM this afternoon to 10 AM PDT
Monday above 2000 feet in the for CAZ080.
Winter Weather Advisory from 8 PM this evening to 10 AM PDT
Monday for CAZ081.
Wind Advisory until 8 PM PDT this evening for CAZ081.
Winter Storm Warning from 4 PM this afternoon to 10 AM PDT
Monday for CAZ083.
Winter Weather Advisory from 8 PM this evening to 10 AM PDT
Monday for CAZ084-085.
Winter Weather Advisory from 5 PM this afternoon to 10 AM PDT
Monday for CAZ083.
Pacific Coastal Waters...Gale Warning until 2 PM PDT this afternoon for
PZZ350-356-370-376.
Hazardous Seas Warning until 5 PM PDT Monday for PZZ350-356.
Hazardous Seas Warning from 2 PM this afternoon to 5 PM PDT
Monday for PZZ370-376.The national radar mosaic for the moment the first event began.
2 heavy snow. Local standard time, as filed.
A spotter 2SSW Weed reported 12.0 inches of new snow in 21 hours ending at 15/1000 PDT.
A CocoRAHs observer 5N Weed reported 12.0 inches of new snow in 24 hours at 15/1100 PDT.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2021Every state in 2021This day in weather historyWarnings in California, March 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: 937670, 937834.