Area Forecast Discussion Issued by NWS Medford, OR
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000
FXUS66 KMFR 270352
AFDMFR
Area Forecast Discussion
National Weather Service Medford OR
852 PM PDT Tue Mar 26 2024
.DISCUSSION...-- Changed Discussion --
Some scattered showers are moving eastwards over the
coast and northern Doulas County this evening ahead of a warm
front. A quick update was made to the forecast to extend the area
where we`re expecting precipitation to better reflect radar
imagery. Otherwise, the forecast looks on track.
This warm front will continue to bring light precipitation to the
area tonight, mostly to the coast into Douglas County.
A cold front will then arrive early Wednesday morning, bringing
more widespread moderate to heavy precipitation and areas of gusty
winds, especially to the Shasta Valley in central Siksiyou County
and higher terrain east of the Cascades where wind advisories are
in place for tomorrow. Plenty of warm flow out ahead of this
front will result in rising snow levels, so snow impacts aren`t
expected in the first part of this system below 5,500 feet. For
areas 5,500 feet and above in the Cascades, a winter weather
advisory begins early Wednesday morning through the evening for
heavy snow. Travel over the mountains will be hazardous for much
of tomorrow, especially in the late morning into the afternoon,
when snowfall rates exceeded an inch an hour are possible (80+%
chance for the higher Cascades) and very low visibility conditions
are expected.
For more details about this system and the rest of the forecast,
please see the previous discussion below. -CSP-- End Changed Discussion --
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.AVIATION (27/00Z TAFs)...-- Changed Discussion --
VFR conditions prevail across the region
this afternoon and evening with increasing high level clouds ahead
of the next front expected to arrive tonight into Wednesday morning.
Low level wind shear concerns will increase tonight between 06z-10z,
mainly along the coast and into the Umpqua Basin (including North
Bend and Roseburg), wind shear concerns will linger in these places
through mid Wednesday morning. Otherwise, gusty winds are expected
to increase along the coast, east of the Cascades, across the higher
terrain and in the Shasta Valley late tonight into Wednesday
afternoon. -Schaaf/BR-y-- End Changed Discussion --
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.MARINE...-- Changed Discussion --
Updated 800 PM Tuesday, March 26, 2024..Mixed westerly
swell will build into waters today due to a 5 to 6 ft west swell at
14 seconds and 2 to 5 ft west swell at 19 to 21 seconds. Then, a
strong front approaches later this evening and moves onshore early
Wednesday morning. This will bring increasing southerly winds,
reaching gales, and very steep and chaotic seas late this evening
and overnight. In addition to the gales, expect very steep chaotic
seas that are a mix of 8 ft west swell at 15 to 16 seconds and 10 to
14 ft southerly wind seas.
Winds will ease for a brief period early Wednesday morning into the
afternoon, then increase again Wednesday evening and overnight. High
end advisory southwest winds are expected during this time, but
could approach gales Wednesday night. Seas will remain very steep
and hazardous through Thursday as high to very high west swell
builds behind this front Wednesday and Thursday.
Winds diminish late Thursday into Friday and seas will gradually
lower on Friday but remain high and steep into the afternoon. Winds
will turn northerly Friday afternoon as a thermal trough develops.
There will likely be a brief period of sub-advisory conditions on
Friday, but it will be short lived as northerly winds strengthen and
seas become steep and wind driven through the weekend. /BR-y-- End Changed Discussion --
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.PREV DISCUSSION... -- Changed Discussion --
/Issued 453 PM PDT Tue Mar 26 2024/
SHORT TERM...Through Friday morning (3/29)...Calm conditions will
continue this afternoon across northern California and southern
Oregon. Upper level clouds are approaching from the Pacific while
low level cumulus develop as lower level airflow moves over the
terrain. Partial cloudy skies and light winds will persist through
tonight.
An approaching low pressure system will bring more activity through
Wednesday and Thursday. A warm front will arrive from the west early
Wednesday morning, followed closely by a more impactful cold front.
Precipitation will move eastward across the area, with the Oregon
coast forecast to get substantial rainfall through the day
Wednesday. The heaviest period will be Wednesday morning, with
heaver rainfall continuing south of Cape Blanco into the evening.
Through Wednesday and Thursday, areas south of Cape Blanco will
total between 2 and 3 inches of rainfall while areas farther north
will stay between 1 and 1.5 inches. The Illinois Valley will get
between 1 and 2 inches of rainfall and the Umpqua Valley will get
between 0.5 and 1 inches.
Thunderstorms will also be possible with this pair of fronts,
mostly over Coos and Curry counties through the day Wednesday.
Chances along the Oregon Coast will remain between 20-20% through
Wednesday and Thursday, while slight 15-20% chances will move
inland during the day Thursday and reach as far east as Klamath
County. Overall thunderstorm chances are expected to decrease
through Friday morning.
Snow levels will start high behind the warm front, rising to 5500 to
6500 feet on Wednesday morning. The abundant moisture will bring
heavy snowfall to higher terrain, especially over Mount Shasta and
the Cascades. While the high snow levels will keep heavy snowfall
over the remote Mount Shasta peaks, well-traveled areas in parts of
the Cascades are facing potentially hazardous snowfall amounts.
Snowfall will start fast on Wednesday morning, with moderate to high
chances (50-90%) of accumulation rates reaching an inch per hour
along Cascades peaks. Slight chances (20-40%) of rates reaching 2
inches per hour are briefly possible Wednesday evening. Given this
extended period of possible heavy snowfall rates, a Winter Weather
Advisory is in place for areas of the Cascades above 5500 feet and
north of Highway 140. The Advisory will start at Wednesday at 5 AM
and continue through 11 PM.
The cold front trailing behind the warm front will bring snow levels
down to 3000 to 4000 feet by Thursday morning. This will allow for
snowfall over higher terrain west of the Cascades as well as across
wide areas east of the Cascades. However, with the bulk of the
moisture past the area, amounts over low-lying areas will be
fractions of an inch. Higher elevation areas may see 1 to 3 inches
and remote parts of westernmost Siskiyou County may see up to 6
inches.
Hazardous winds are also expected during the day Wednesday. Gusty
southerly winds are expected to funnel into the Shasta Valley and
reach speeds of up to 50 mph. A Wind Advisory is in place from
Wednesday from 8 AM until 2 PM to cover the period of strongest
winds. Advisory winds don`t quite reach Grenada and Montague, but
gusts of 30 to 40 mph could reach those cities. An additional Wind
Advisory is in place from Wednesday at 11 AM through 11 PM for areas
across Lake County and over the Warner Mountains in Modoc County,
where gusts of 50 mph are also possible. Elevated winds are also
expected across the area Thursday afternoon and evening, but
currently those winds are not expected to reach hazardous speeds.
-TAD
Extended Discussion...(Friday through Tuesday)...The upper low will
move southeast towards northwest Cal Friday, taking most of the
energy with it into that area. A cool air mass along with weak
dynamics will still result in convective showers and cool weather
over portions of the area. Precip amounts Friday will be light.
The upper low will dig south to southeast towards the Bay Area
Friday night and south of there Saturday. However there`s some
evidence we`ll get some return flow into northern Cal and southern
Oregon during this time. Northern Cal has the best chance of getting
measurable precipitation while southern Oregon should be far enough
north where precip amounts will be light. Showers will be far and
few in between Saturday morning, then we could see an uptick in
shower coverage Saturday afternoon due to daytime heating and
increasing instability. However, were still expecting light
precipitation amounts.
Showers will diminish Saturday night into Sunday as a northerly flow
begins to set up. Still could not rule out some showers in northern
Cal and portions of the East Side due to the proximity of the upper
low still within ear shot during this time.
The general consensus is for the upper trough to move southeast of
our area Monday with a continued dry north to northeast flow as an
upper level ridge builds in which typically results in dry weather.
The upper ridge remains a fixture Tuesday with continued dry and
milder weather. It`s worth noting the ensemble clusters are pretty
much lock in step with the operational models for the start of next
week, thus the higher confidence of dry and mild weather.
-Petrucelli
AVIATION (27/00Z TAFs)...VFR conditions prevail across
the region this afternoon and evening with increasing high level
clouds ahead of the next front expected to arrive tonight into
Wednesday morning. Low level wind shear concerns will increase
tonight between 06z-10z, mainly along the coast and into the Umpqua
Basin (including North Bend and Roseburg), wind shear concerns will
linger in these places through mid Wednesday morning. Otherwise,
gusty winds are expected to increase along the coast, east of the
Cascades, across the higher terrain and in the Shasta Valley late
tonight into Wednesday afternoon. -Schaaf/BR-y
MARINE...Updated 200 PM Tuesday, March 26, 2024..Mixed westerly
swell will build into waters today due to a 5 to 6 ft west swell at
14 seconds and 2 to 5 ft west swell at 19 to 21 seconds. Then, a
strong front approaches later this evening and moves onshore early
Wednesday morning. This will bring increasing southerly winds,
reaching gales, and very steep and chaotic seas late this evening
and overnight. In addition to the gales, expect very steep chaotic
seas that are a mix of 8 ft west swell at 15 to 16 seconds and 10 to
14 ft southerly wind seas.
Winds will ease for a brief period early Wednesday morning into the
afternoon, then increase again Wednesday evening and overnight. High
end advisory southwest winds are expected during this time, but
could approach gales Wednesday night. Seas will remain very steep
and hazardous through Thursday as high to very high west swell
builds behind this front Wednesday and Thursday.
Winds diminish late Thursday into Friday and seas will gradually
lower on Friday but remain high and steep into the afternoon. Winds
will turn northerly Friday afternoon as a thermal trough develops.
There will likely be a brief period of sub-advisory conditions on
Friday, but it will be short lived as northerly winds strengthen and
seas become steep and wind driven through the weekend. /BR-y-- End Changed Discussion --
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.MFR WATCHES/WARNINGS/ADVISORIES...
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OR...Wind Advisory from 8 AM to 2 PM PDT Wednesday for ORZ031.
Winter Weather Advisory from 5 AM to 11 PM PDT Wednesday above
5500 feet for ORZ027-028.
CA...Wind Advisory from 8 AM to 2 PM PDT Wednesday for CAZ081-085.
PACIFIC COASTAL WATERS...Gale Warning until 11 AM PDT Wednesday for
PZZ350-356-370-376.
Hazardous Seas Warning from 11 AM Wednesday to 11 PM PDT
Thursday for PZZ350-356-370-376.-- End Changed Discussion --
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