High Wind in Oregon, April 15, 2018

Area Forecast Discussion
National Weather Service Medford OR
1056 AM PDT Sun Apr 15 2018

.UPDATE...Strong gusty south winds are developing in the southern
Shasta Valley and for many areas east of the Cascades, including
Klamath Falls. Gusts of 45 mph have been observed at Weed, CA and
Klamath Falls, OR. With the jet moving in place and daytime mixing
expect these gusty winds to continue.  So have added wind
advisories the Shasta Valley and expanded the wind advisory on the
east side to include much of Klamath, Lake and Modoc counties as
well as northeast Siskiyou County. The upper level 700 mb jet of
50 kt will move over Siskiyou and Klamath counties late this
morning through this afternoon then shift east. So expect winds to
diminish in the late afternoon and early evening for these areas.
However south winds are expected to remain strong and gusty in
Lake and Modoc counties into the evening as this jet gradually
shifts east. Please see the NPWMFR for details on the wind
advisories.

&&

.PREV DISCUSSION... /Issued 847 AM PDT Sun Apr 15 2018/

SHORT TERM...A surface low and front are along the Southern
Oregon coast this morning. This front will gradually push inland
to the Cascades this morning into early this afternoon then east
of the Cascades late this afternoon and early this evening. This
front will bring rain and mountain snow as well as strong winds
east of the Cascades.

Models remain on track with the timing and strength of this
front. Moderate precipitation will spread over western areas today
with light to moderate precipitation east of the Cascades.
Moderate precipitation has developed along the coast and will
spread across western areas and to the Cascades this morning into
early this afternoon. East side areas will see precipitation peak
in the mid afternoon through early evening period. Through this
afternoon, snow levels are expected to remain between 5000 and
5500 feet from the Cascades west and between 5500 to 6500 feet
east of the Cascades. Light to moderate snow of around 4 to 9
inches is possible in the Cascades as well as over mountains in
western and southern Siskiyou county, mainly above 5500 feet.
However, with fairly warm daytime road temperatures, expect
impacts on roadways to be limited.

Snow levels will lower behind the front this evening and tonight
as a cold and showery air mass moves into the region. This will
bring light snow in showers to higher terrain. By late this
evening expect snow levels down to 3000 feet and then down to 2000
to 3000 feet Monday. As an upper low moves over the region and a
couple shortwaves move inland tonight and Monday, expect
widespread showers across the area. With lowered snow levels,
light snow accumulations are expected over higher terrain tonight
and Monday.

Strong gusty winds will also be an impact for eastern areas today.
Models continue to show good agreement with a 45 to 55 kt 700 mb
jet moving over the region. These winds are expected to mix down
and bring strong gusty wind to Lake and eastern Modoc county with
gusts to 50 mph. Other areas east of the Cascades will also see
gusty winds with gusts of around 30 to 40 mph. West of the
Cascades, gusty winds are also expected to develop in the Shasta
Valley with gusts up to around 40 mph today. A wind advisory is
in place for eastern areas, including Lake and eastern Modoc
counties, where the strongest winds are expected. Please see the
NPWMFR for details. Winds are expected to diminish in the evening.

Models also show weak instability over inland portions of the area
today ahead of the frontal passage, mainly from the Cascades east.
Currently given this weak signal, do not expect much chance for
thunderstorms though. As the upper low moves into place tonight and
Monday, it will bring cold air aloft, weak instability and CAPE to
the area. This is expected to bring a slight chance for
thunderstorms tonight along the coast and coastal waters with the
slight chance of thunderstorms spreading inland over the area on
Monday. Additionally small graupel or hail may accompany stronger
showers on Monday.

AVIATION...A cold front will move
through the area from this morning at the coast to this afternoon in
the Klamath basin. Cigs will lower to MVFR, first along the coast
then slowly spread inland overnight and bringing terrain
obscuration. Areas IFR cigs are possible with the front early this
morning at the coast. Winds will generally shift from southerly to
westerly or northwesterly Sunday afternoon as the cold front moves
through. Freezing levels will lower sharply behind a cold front, by
about 2000 feet. Additionally, winds will become gusty this
afternoon in Northern California and in areas east of the Cascades.
-FB

MARINE...Updated 200 AM PDT Sunday 15 April 2018...A cold
front will move through the waters this morning and then move inland
this afternoon. Satellite imagery shows some strengthening of this
low and associated front as it moves toward the coast. Advisory
level winds are expected to linger until this morning, but steep
seas will continue through tonight. Showers continue into Monday
with a slight chance of thunderstorms. Swell dominated seas increase
again Monday evening and continue through the week. The next front
will approach the waters Wednesday morning. -FB

PREV DISCUSSION (edited)... /Issued 308 AM PDT Sun Apr 15 2018/

Behind the front a cold and showery airmass will move into the
area as an upper low moves over the region and a couple shortwave
disturbances moves inland around the low. Snow levels will be
between 2000 and 3000 feet, so widespread rain and snow showers
are expected on and off on Monday. A few thunderstorms will be
possible as well. That being said, these showers will provide
breaks in between so it will not be wet all day long. The stronger
of the two shortwaves is likely to move through Monday evening
when another burst of light to moderate precipitation is expected.
Areas of light showers will linger Monday night into Tuesday,
with decreasing coverage Tuesday afternoon. A ridge will build
inland late Tuesday, bringing a very brief period of dry weather.

The next system will move into the area on Wednesday bringing some
light precipitation throughout southern Oregon and northern
California. Snow levels will have risen a little bit due to the
ridge on Tuesday, but will generally remain around 4000 feet.
Impacts from this system are not expected to be significant at
this time, but it is always important to pay attention in case
things change.

Then, models are indicating a decrease in precipitation chances
by Thursday night and Friday in response to a building ridge of
high pressure. On Saturday, another weak system is poised to pass
to our north around the aforementioned ridge, with a slight
chance for precip north of the Umpqua Divide next weekend.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory until 8 PM PDT this evening for ORZ030-031.
     Wind Advisory until 5 PM PDT this afternoon for ORZ029.

CA...Wind Advisory until 8 PM PDT this evening for CAZ085.
     Wind Advisory until 5 PM PDT this afternoon for CAZ084.
     Wind Advisory until 5 PM PDT this afternoon for CAZ081.

Pacific Coastal Waters...Small Craft Advisory for hazardous seas until 11 PM PDT this
     evening for PZZ350-356-370-376.

CC