NWS Medford, OR wrote its last area forecast discussion before the first event at Feb 28, 3:39 PM PST, 21 minutes earlier.
Area forecast discussion, Feb 28, 3:39 PM PST, 21 minutes before
Area Forecast Discussion
National Weather Service Medford OR
339 PM PST Wed Feb 28 2024
.SHORT TERM...Today through late Thursday...Currently we have a
broad, deepening upper level low sitting in the Gulf of Alaska,
with a trough stretching down the northwest US offshore. Ahead of
the trough, a warm front is moving northeast through north OR and
WA and a cold front moving towards the area, though still well
offshore at this point. Precipitation is currently spread across
the coast into Douglas and Josephine county and is moving
northeast through the region. Winds are starting to gradually pick
up along the coast and over the higher terrain as the cold front
approaches.
Impacts will increase tonight with the arrival of the cold front,
with strong winds in our windier areas (coast and coastal headlands,
mountainous areas such as the Cascade and Siskiyou mtns, the Shasta
Valley, and pretty much all areas east of the Cascades) and heavy
coastal rain and mountain snow. Starting with winds, models are
still showing strong pressure gradients and model 700mb winds of 70
to 80 kt. These will be working their way to the surface in the form
of strong, gusty winds, with sustained wind speeds of 30 to 45 mph
and gusts up to 60 to 65 mph in the aforementioned windier areas.
Strong gusty winds will increase from the west to the east late
today into Thursday, starting at the coast and along the headlands
this evening and moving inland overnight and Thursday morning. A
High Wind Warning remains in effect for these areas (see the
detailed hazards map or the NPWMFR), and strong winds will blow any
loose objects around and make travel difficult, especially for high-
profile vehicles. At lower elevations, conditions will be breezy,
with gusts to about 25 mph.
Stronger precipitation moves in late this evening and tonight, with
heavier precipitation along the coast and over the mountains. Snow
levels will generally start around 4,500 to 5,000 feet tonight,
before swiftly lowering to 2,000-2,500 feet overnight into Thursday
morning. High resolution models are indicating a rather strong line
of precipitation along the cold front moving southeast into the
region early Thursday morning, with associated heavy precipitation
rates. This strong precipitation can drag snow levels down with it,
and we could see snow levels of 1,500 feet in areas as this passes
through. Our particular areas of concern are the Illinois Valley
(especially the south valley and Hayes Hill) and the I-5 passes
between Grants Pass and Canyonville, and possibly Jacksonville Hill
and Ashland (mostly the higher elevations), though certainty is
lower for the latter two areas. Roads are still quite warm from our
spring-like weather earlier, so there's still some uncertainty in
how much snow will accumulate on roadways, but if precipitation
rates are high enough then you could see snow starting to accumulate
on the roads in these areas. Snow levels will rise again slightly
Thursday afternoon, so the main concern for these areas is Thursday
morning.
Speaking of heavy precipitation, snow over the mountains will be
heavy starting at about 4 AM and lasting through the afternoon.
There is a very good chance (90-100%) for 1 inch per hour snowfall
rates over all area mountains, including all Cascade passes, and a
60-70% chance for 2 inch an hour rates over higher portions of the
Cascades (especially towards 10 AM). Heavy snow and gusty winds will
combine to create very low visibility conditions, even periods of
whiteout conditions, and travel over the mountains will be very
hazardous. Snow will also start to spread east of the Cascades, in
the Mt. Shasta City area, and over Siskiyou Summit on I-5 Thursday,
and while snow amounts will be less than those over the mountains,
gusty winds and snow will still result in poor visibility
conditions that will make travel difficult.
The front will move east through Thursday, exiting the region late
in the day. As it passes, precipitation will turn more
showery/intermittent and snow levels will drop again Thursday
evening into overnight as cold air settles in. Winds will see a
slight decrease but generally remain gusty as active weather
continues into the late week. -CSP
.LONG TERM...(Friday through Monday)...The pattern will
remain cold and active during this time period with an upper trough
pretty much parked over the area with a series of shortwaves moving
through resulting in periods of enhanced showers. This cold air mass
is more typical of early January. Precipitation will be of the
convective variety, meaning there will be times when not much is
happening, and times where showers (some moderate to heavy) will be
present.
Friday morning will be a time period of concern with scattered to
numerous snow showers over the passes on I-5 between Grants Pass and
Canyonville, Hays Hill Summit, Jacksonville Hill, and Camas
Mountain. These areas are likely to experience road snow
accumulations during the morning hours. Additionally snow could
accumulate in Ashland, especially the hills surrounding Ashland
above 2000 feet.
As we get further into the daylight hours Friday, the combination of
a higher sun angle will allow road temperatures to warm up
sufficiently where snow showers for the most part will melt. The
exception will be in areas that get under a heavier shower. In this
case, snow will briefly stick on the roads.
Because we'll be in a convective pattern. We could be dealing with
moderate to strong winds east of the Cascades, and possibly the
Shasta Valley, although not as likely due to a southwesterly
component to the winds. Even though the current high wind warning is
set to end at 4 am pst Friday, we could end up extending this in the
future or have a combination of high wind warnings and wind
advisories.
A reinforcing shot of colder air will push into the area Friday
night as the upper trough pushes into the area. Scattered to
numerous showers are likely and this is the time period where we
could see snow down to the valley floors and possibly in the lower
valleys in Douglas County, including Roseburg. The question is will
snow accumulate in the valley floors. Much will depend on the
placement and intensity of showers. At this time, confidence is
medium to high for snow to accumulate in the Illinois Valley, and
Ashland Friday night into Saturday morning and the Winter Weather
Advisory has been extended until late Saturday morning.
Saturday afternoon will be similar to Friday in terms of road snow
impacts for the valley floors, even though snow levels will be lower
than Friday and hovering between 1500 and 2000 feet in the
afternoon. However, keep in mind, snow levels could briefly drop
just below 1500 feet in heavier showers resulting in brief and
temporary road snow accumulation before melting off once the heavier
showers pass through with peaks of sun.
As mentioned in the beginning, the pattern won't change much
Saturday night through Monday of next week. However, the only
difference is showers are expected to be lighter pretty much across
the board, this resulting in less additional snowfall accumulation,
after late Saturday morning. However we could still deal with slick
spots on roads all the way down to the valley floors again Saturday
night into Sunday morning.
Signs are pointing towards a relative break in the weather Tuesday,
followed by more active weather next Wednesday, but the air mass is
not expected to be as cold by that time, thus less of a concern for
low elevation snow. -Petrucelli
&&
.AVIATION...29/00Z TAFs...VFR/MVFR conditions continue across
northern California and southern Oregon this afternoon. Steady rain
will spreading farther inland and will continue overnight. Snow
levels will remain around 4500 to 5000 feet overnight. Then, a
strong frontal boundary will move in with additional precipitation
across the area. The freezing level will quickly drop to around 2000
feet MSL behind the front. Snow will create visibility reductions
with total terrain obscuration becoming more likely.
Additionally, gusty southerly winds will to affect wide areas
through Wednesday and Thursday, especially over elevated terrain and
along the Oregon Coast. Guidance also suggests that low level wind
shear will develop over most areas by this afternoon, particularly
affecting the coast and the Rogue Valley including the North Bend
and Medford Airports. With the highest wind speeds over the Cascades
and the Mount Shasta area. The combination of strong winds and
widespread precipitation will result in hazardous conditions, and
extra caution is encouraged. Additionally, strong winds east of the
Cascades will impact the Klamath Falls airport and an Airport
Weather Warning for the winds remains in effect for tonight.
-TAD/Schaaf
&&
.MARINE...Updated 200 PM Wednesday February 28, 2024...Gusty
southwest winds that are expected to reach gale forces will move
over all waters this afternoon and evening. These winds will build
and sustain very steep and hazardous seas. A Gale Warning will cover
all waters from this morning at 10 AM through Thursday morning at 4
AM. In this time period, wind gusts of up to 45 knots will be
possible, especially from Wednesday evening into early Thursday
morning. Peak seas will be 16 to 18 feet at 10 to 11 seconds.
Very steep and hazardous swell-built seas will continue through the
day Thursday. Elevated southwest winds will remain, but will calm
slightly to 20 to 25 kts and gusts up to 30 kts. A Hazardous Seas
Warning will cover all waters from Thursday at 4 AM through 4 PM to
communicate this continuing hazard.
Chaotic conditions will continue from Thursday evening through
Saturday as another strong front will bring another round of
elevated winds and fresh swell. While current forecasts put the
winds just below gale force, future guidance could indicate that
isolated gale force gusts could be possible with this system. Model
guidance is in agreement with this second system second system
bringing further impacts, and will continue our hazardous seas
warning which was extended through Friday night. Very steep and
hazardous conditions could continue into Saturday, and conditions
should gradually improve, but remain steep into early next week.
-TAD/Schaaf
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Storm Warning until 10 AM PST Saturday for ORZ027-028.
High Wind Warning from 1 AM Thursday to 4 AM PST Friday for
ORZ029>031.
High Wind Warning from 7 PM this evening to 7 AM PST Thursday
for ORZ021-022.
High Surf Advisory from 4 PM Thursday to 10 PM PST Friday for
ORZ021-022.
Winter Storm Warning until 10 AM PST Saturday above 2500 feet
for ORZ023>026.
Winter Weather Advisory from 4 AM Thursday to 10 AM PST Saturday
above 1500 feet for ORZ023>025.
Winter Storm Warning until 10 AM PST Saturday for ORZ029-030.
CA...Winter Storm Warning until 10 AM PST Saturday above 3000 feet
for CAZ080.
Winter Weather Advisory from 4 PM Thursday to 10 AM PST Saturday
for CAZ080-082.
Winter Storm Warning until 10 AM PST Saturday above 3500 feet
for CAZ081-082.
High Wind Warning from 10 PM this evening to 1 PM PST Thursday
for CAZ081.
Winter Storm Warning until 10 AM PST Saturday for CAZ083.
High Wind Warning from 1 AM Thursday to 4 AM PST Friday for
CAZ084-085.
PACIFIC COASTAL WATERS...High Surf Advisory from 4 PM Thursday to 10
PM PST Friday for PZZ350-356.
Gale Warning until 1 AM PST Thursday for PZZ350-356-370-376.
Hazardous Seas Warning from 1 AM Thursday to 10 PM PST Friday
for PZZ350-356-370-376.
&&