High Wind in California, March 5, 2021

Area Forecast Discussion
National Weather Service Medford OR
800 PM PST Thu Mar 4 2021

.DISCUSSION...05/00Z NAM in. 05/00Z GFS in through 78hr.

Strong winds have developed across the Medford forecast area, with
the strongest winds along the coast, and in the Rogue and Shasta
valleys. Winds will pick up later east of the Cascades. Very
little in the way of precipitation so far, at least over the land
areas.

A long wave upper level trough is now lined up near 130W, and the
associated cold front is poised off the Pacific Northwest coast.
The front has become parallel to the upper level flow, and weak
short waves are moving north along the frontal boundary. This will
slow the eastward progress of the front quite a bit, and it may
actually retrograde a bit before it moves onshore late Friday
morning. So, this will be an extended wind episode. The front
will move through the Medford forecast area through the rest of
the day Friday, finally clearing to the east of the area Friday
night. The front will weaken as it moves through the east side, so
winds will begin to weaken even before the front moves through.
High Wind Warnings and Wind Advisories are in effect until late
Friday morning along the coast, and until Friday evening east of
the Cascades. See NPWMFR for details.

As far as precipitation goes, moisture from an atmospheric river
will be pulled into the area as the front moves onshore, but the
duration of the event will only be around 12 to 18 hours. Usually
snow levels don't drop until the front has moved through, and by
that time precipitation is diminishing. However, the models are
indicating cold air wrapping around bringing snow levels down
before the tail end of the front is through. This would bring low
end warning snow amounts to western Siskiyou county with snow
levels dropping to around 3000 feet. Confidence is not high at
this time with any aspect of this event.

The upper level trough will move onshore Saturday morning in a
weakened state and will clear to the east of the area by Saturday
afternoon. Showers will decrease Friday night through Saturday
with snow levels dropping to near the valley floors west of the
Cascades early Saturday morning. However, current road
temperatures are in the 80s along the I-5 corridor, and any snow
that falls on anything that isn't insulated from the ground will
melt very quickly.

The post frontal break will be short, as the next front will move
onshore Sunday.

Extended Discussion from the Thursday afternoon AFD...Sunday 07
Mar through Thu 11 Mar 2021. Not much has changed in the overall
scheme of things. Confidence is high a fairly active pattern will
continue during the forecast period. However it may not be all
that bad overall. It won't be completely dry, but there could be
larger periods of dry time. By next week, storms originating from
the Gulf of Alaska will drop down into the Pacific northwest.
Typically these result in cooler and unsettled weather.

A cold front will weaken as it moves onshore Sunday which is being
supported by operational ECMWF and GFS, thus limiting the amount of
precipitation, especially inland away from the coast and coastal
mountains. This is also being supported by the ensembles and
individual ensemble members.

Monday through Tuesday, the general consensus is for the upper low
to drop in from the northwest, but remain offshore Monday night into
Tuesday which should keep precipitation at a relative min during the
morning, then increasing in the afternoon and early evening hours.
Even then precipitation is not expected to be significant enough
where it's going to cause major issues for the higher passes. Some
snow will accumulate over the higher passes, but not enough where
it's going to be a concern.

While the exact timing this far out could vary over time, we are
confident it will remain cool and unsettled Wednesday and Thursday.
Not only the operational ECMWF and GFS show this, but so do the
individual ensemble members of the ECMWF and GEFS. Precipitation
amounts during this time are not expected to be significant at any
one time during this period which will help to limit road snow
concerns, especially during the daylight hours. Some snow will
accumulate at night for the higher passes and possibly the lower
passes on I-5 between Grants Pass and Canyonville. However, since
its early to mid March, the longer daylight hours and higher sun
angle should result in little or no road snow for the lower passes,
at least during the daytime. -Petrucelli

&&

.AVIATION...For the 05/06Z TAF Cycle...The main concern during the
TAF period will be low level wind shear for the coast, including
North Bend and inland westside, including Roseburg and Medford.
Right now, the strong winds have surfaced at most of these airports,
which is precluding the need for the wind shear. However, once the
winds at the surface die off, the wind shear will likely re-
establish in these locations (as well as for other west side Valley
airports).

Additionally, strong southeast to south winds will also impact south
to north oriented valleys such as the Shasta Valley, and across the
higher terrain, and some low level turbulence should be generally
expected. Low level wind shear is not expected east of the Cascades
due to moderate to strong winds aloft mixing down to the surface.

VFR ceilings and visibilities are generally expected through the TAF
period, but there's a chance that they become MVFR as the front
slowly moves ashore. So areas along the coast may see it this
evening into tonight, West of the Cascades tomorrow morning and East
of the Cascades Friday afternoon. Areas of terrain obscuration are
expected anywhere it is raining. -Schaaf

&&

.MARINE...Updated 800 PM PST Thursday 04 Mar 2021...Strong gales
and periods of storm force winds are expected this evening into
Friday morning along with very steep wind driven combined seas
peaking in the 17 to 27 foot range. While storm conditions should
remain beyond 10 nm from shore, storm force gusts are possible
elsewhere, especially in the vicinity of headlands and capes. The
highest combined sea heights are most likely to occur about 20NM
west of Bandon and the lowest along and near protected portions of
the coast.

Wave models have returned to indicating the possibility of a west-
northwest swell peaking in the 13 to 19 foot by 16 second range
Sunday into Monday. Thereafter, seas are expected to fall to below
10 feet on or about Tuesday. -Schaaf

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning until 7 PM PST Friday for ORZ030-031.
     Wind Advisory until 7 PM PST Friday for ORZ029>031.
     High Wind Warning until 10 AM PST Friday for ORZ021-022.
     High Surf Advisory until noon PST Friday for ORZ021-022.
     Wind Advisory until 1 PM PST Friday for ORZ026.

CA...Wind Advisory until 7 PM PST Friday for CAZ084-085.
     Winter Storm Watch from Friday afternoon through late Friday
        night above 3000 feet in the for CAZ080.
     Winter Weather Advisory from 4 PM Friday to 4 AM PST Saturday
        above 4500 feet in the for CAZ082.
     High Wind Warning until 7 PM PST Friday for CAZ081.

Pacific Coastal Waters...Gale Warning until 10 AM PST Friday for
        PZZ350-356-370-376.
     Hazardous Seas Warning from 10 AM to 7 PM PST Friday for
        PZZ350-356-370-376.
     Storm Warning until 10 AM PST Friday for PZZ370-376.

15/15/13