High Wind in Oregon, March 18, 2021

Area Forecast Discussion
National Weather Service Medford OR
905 AM PDT Thu Mar 18 2021

.DISCUSSION...An update was sent earlier to adjust wind speeds
along the high terrain across the area. The forecast was
significantly overdone in those areas, and values were adjusted
closer to what is expected for today. Upper level low pressure
offshore is resulting in gusty winds across the area this morning
with wind gusts of 40 to 50 mph occurring in the Shasta Valley
and 25 to 40 mph in the Rogue Valley. West of the Cascades, winds
will peak this morning and gradually diminish this afternoon. East
of the Cascades, current gusts of 20 to 30 mph will increase
later today, peaking this afternoon and diminishing this
afternoon. Wind advisories are in effect for these gusty winds,
and details can be found at NPWMFR. Precipitation is occurring
west of the Cascades, however, for the areas experiencing
downslope winds (like the Rogue Valley), any measureable
precipitation will likely hold off until this afternoon. For more
details on this front and the weather to follow, see the previous
discussion below. /BR-y

&&

.AVIATION...For the 18/12Z TAF Cycle...Breezy to gusty winds are
expected for much of the day over the coast and marine waters, over
the mountains, in the Shasta Valley, in the southern Rogue Valley,
and east of the Cascades, with periods of low level wind shear
likely over area valleys. Widespread mountain wave turbulence is
also likely, especially along and east of the Cascades. Light rain
along the coast this morning will spread to most of the region by
this afternoon. Conditions could improve slightly this evening once
the front passes, but another system will quickly follow tonight.
-BPN

&&

.MARINE...Updated 850 AM PST Thursday 18 Mar 2021...A front moved
onshore earlier today with strong gales and very steep wind-
driven seas. Recent 15z buoy observations were showing wave
heights in the 14-17 foot range with periods of only around 10
seconds. Since winds are easing this morning, expect slight
improvement into early this afternoon. However, this will be
short- lived as a second strong front approaches the region this
evening. South gales are expected again this evening and tonight,
along with very steep seas resulting from a mix of wind-driven
seas and building long period west swell. On Friday, hazardous
seas will continue, with the long period swell resulting in large
breaking waves around 22 to 25 feet. Area bar conditions are
likely to become hazardous during this time.

Additional fronts keep winds moderately strong through Friday into
Saturday morning. Then, high pressure will bring a break in the
activity Saturday into Sunday. Another front is expected to move
onshore Sunday night into Monday. -BPN/Spilde

&&

.PREV DISCUSSION... /Issued 453 AM PDT Thu Mar 18 2021/

DISCUSSION...Except for precipitation moving in slightly faster
than previous models had indicated showing on the radar, forecast
is proceeding on track, but looking at observations none of the
showers are reaching the ground inland north of Siskiyou county.
Winds in the Shasta valley and the Rogue Valley in Jackson county
are increasing with a current max gust of 50 mph at Weed and 35
mph at the Medford airport at this time. The RAWS MOS guidance is
now indicating a max gust of 53 KT ahead of the front at Weed, and
wind advisories look on track and winds east of the Cascades
should be increasing shortly. Showers feeding into the Mt Shasta
area are moving in and stalling as predicted, and with the
temperature at the Mt Shasta ASOS showing 38 F, and 32 F at
Snowman Summit is 32 F. Increasing precipitation rates expected to
lower the temperatures in that area the current forecast of 4000
ft for the level of heavy snow still looks on track. The Redding
to Medford gradient looks to loosen late afternoon but strong 700
mb winds aligning with the Shasta valley remains into the evening.
The current timing of the wind advisories still look on track.

A colder air mass aloft moves in behind the front this evening,
with 500 MB temperatures dropping to -30C over the waters by late
evening. Although LI's are marginal, temperatures below -30C
combined with ocean temperatures of ~52 F will bring a slight
chance of thunderstorms to the waters, and with southwest steering
flow of ~30 KT, inland from the coast a bit until they weaken.
-Sven

There will be a progressive pattern this weekend into next week
with systems coming in primarily northwest flow aloft. None of
these systems is particularly strong, but each will carry with it
locally breezy conditions along with showers -- very apt for the
arrival of spring, which will occur at 237 AM PDT on Saturday,
March 20.

An upper trough over the area Saturday will shift to the east. Even
so, moist onshore flow will persist keeping showers likely along and
west of the Cascades. It won't be an all-day rain, but showery
nonetheless. Shower chances decrease south and east of the
mountains. Snow levels of 2000-2500 feet in the morning will
increase to 3500 feet or so in the afternoon. Overall, expect max
temps about 5-10 degrees below normal, which would put highs in the
low to mid 50s for most areas along and west of the Cascades with
mid 40s over the east side and in NE California.

The next fast-moving shortwave trough will likely arrive and move
onshore Sunday night into Monday, bringing a good chance of
showers to the area with breezy conditions. The upper air
disturbance will dig into the Great Basin/Four Corners region on
Tuesday. Surface high pressure building into the area with a period
of N through E winds (offshore flow) should allow us to dry out.

Models, ensembles and clusters continue to show upper ridging
building near or just offshore of the West Coast mid-late next week.
We'll likely be on the NE periphery of the ridge, so we won't be
completely in the clear as models show a disturbance coming over the
top and flattening the ridge briefly late Wednesday into Thursday.
Even so, this appears to be more of a glancing blow with NBM
probabilities of precipitation only in the 20-30% range from
about the Umpqua Divide northward. NorCal should remain dry. A
dry pattern is likely during much of Week 2 with the Climate
Prediction Center forecasting a >60% chance of below normal
precipitation and temperatures slightly favoring above normal.
-Spilde/Sven

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory until 11 PM PDT this evening for ORZ030-031.
     High Surf Advisory from 5 PM this afternoon to 5 PM PDT Friday
     for ORZ021-022.
     Wind Advisory until 5 PM PDT this afternoon for ORZ026.

CA...Wind Advisory until 11 PM PDT this evening for CAZ085.
     Winter Weather Advisory until 11 PM PDT this evening above 3500
     feet for CAZ082-083.
     Winter Storm Warning until 11 PM PDT this evening above 4000 feet
     for CAZ082-083.
     Winter Weather Advisory until 11 PM PDT this evening above
     4500 feet for CAZ080.
     Wind Advisory until 8 PM PDT this evening for CAZ081.

Pacific Coastal Waters...Gale Warning until 5 AM PDT Friday for PZZ350-356-370-376.
     Hazardous Seas Warning from 5 AM to 5 PM PDT Friday for
     PZZ350-356-370-376.

MNF/SBN/BPN