NWS Medford, OR wrote its last area forecast discussion before the first event at Feb 4, 9:25 PM PST, 3 hours 49 minutes earlier.
Area forecast discussion, Feb 4, 9:25 PM PST, 3 hours 49 minutes before
Area Forecast Discussion
National Weather Service Medford OR
925 PM PST Sat Feb 4 2017
.DISCUSSION...Evening update. Radar is showing low topped
precipitation on the area, as evidenced by decent precip amounts
outside of the radar indicted area, that is below the lowest
elevation beam. This is well in line with the current forecast and
will not update this evening.
PREVIOUS DISCUSSION...A moist west to southwest flow aloft with
embedded shortwaves will continue into tonight. Therefore we can
expect showers to persist with most of them concentrated along the
south coast, Coast Range and Cascades.
Gusty winds are still in the cards, especially east of the Cascades
where wind advisories remain in effect. In fact the models suggest
it will remain windy into early this evening, therefore have
extended the end time until 7 pm pst.
The models suggest a brief break is possible early Sunday morning,
but confidence is low on how long or if we get any break. The reason
is a frontal boundary is expected to remain nearly stationary over
our area tonight into Sunday morning. This front should lift north
some during the day Sunday as low pressure develops along the front
near 30 N and 135W and tracks through our northern coastal waters
Sunday afternoon. The low will then move onshore Sunday evening. As
a result, the focus for heavy precipitation should be just to our
north, but if the surface low ends up tracking further south, then
heavy rain could impact areas mainly from Cape Blanco North.
Meanwhile inland away from the coast and east of the Cascades,
precipitation will decrease and could end altogether from around mid
morning Sunday into Sunday afternoon and there's a chance we could
see some brief clearing. This could allow south to southeast winds
to surface and much like last Thursday allowing temperatures to jump
up. The forecast high of 61 for Medford is not unreasonable if the
above mentioned scenario pans out. Also snow levels should remain
high (between 5000-5500 feet), therefore any road snow impacts
should be limited to Diamond Lake and Crater Lake.
Of bigger concern will be moderate to strong winds at the coast,
Shasta Valley and east of the Cascades. Confidence is high we'll
reach high wind criteria for these areas and have upgraded the high
wind watches to a warning for these areas. In addition we also
issued a wind advisory for portions of the Shasta Valley, eastside
and south end of the Rogue Valley. Confidence is not as high in
terms of the coverage area in the Rogue Valley, especially in White
City and Eagle Point, but it is higher from around Talent south to
Ashland. Please see NPWMFR for details.
The upper trough will push southeast towards the Oregon coast Sunday
night and this will send a strong cold front in the northwest part
of the forecast area early Monday morning, then moving onshore
during the day with snow levels falling quickly. Just about everyone
across the CWA will have a period of rainfall with the front Sunday
night into Monday morning. Since the front will be moving through
fairly quickly, we're not expecting more than some minor rises on
area creeks, streams and rivers. In the higher passes like Lake of
the Woods, Siksyou Summit could experience snow covered roads by the
early morning commute early Monday morning with snow levels expected
to be around 3500-4000. Meanwhile snow levels will fall to around
2000-2500 feet west of the Cascades Monday morning. However due to
the quick nature of the front, snow amounts for the above
mentioned passes should be minor.
We'll catch a relative break in the weather Monday night into early
Tuesday morning, then warm frontal precipitation is expected to move
up from the southwest Tuesday morning into Tuesday afternoon. The
models are in disagreement with the details. it's possible snow
levels could start out around 2500 feet Tuesday morning, then
jumping up to 5000 feet Tuesday afternoon, but it's all going to
come down to timing. If the warmer air is slower to move in, then we
could be dealing with significant snow for the mountains in Siksyou
County, Mount Shasta region and cascades. As we move closer to this
time period, we'll be monitoring the potential for this.
-Petrucelli
Long term...Wednesday morning through Saturday night...Overall, the
models are in fairly good agreement throughout the extended, with
the exception of Thursday. By Wednesday morning, a warm front is
expected to have passed through the area in advance of a short lived
upper level ridge. This will maintain high snow levels as the upper
ridge temporarily builds over the area through Wednesday.
Precipitation will be scattered and light during the morning, before
picking up in intensity as an atmospheric river event moves into the
coast by Wednesday afternoon. Snow levels will be high during this
event, to the tune of 8500 feet, so moderate to heavy rain on snow
will be a concern. However, the AR event is expected to be short
lived as cold air is expected to move in Thursday afternoon, and
this should minimize flooding concerns.
Thursday seems to be the one day that the models disagree
significantly. By Thursday morning, the GFS spins up a surface low
inside of 130W, moving it north along the PacNW coast and into
towards Vancouver Island. The EC does not show this and instead
maintains a broad surface low centered out near 140W. The difference
in solutions leads to significant differences in winds for the area.
If the GFS is right, winds would be quite strong along the coast and
over the waters, with breezy to gusty conditions inland. The EC on
the other hand, would still have breezy and gusty winds, just not as
significant. Confidence is low in the GFS solution at this point as
it is only the second model run to show this. Also, looking at the
GFS Ensembles, there are only a few members to show this solution.
For now, went with a blend of the two models with more of a lean
towards the EC and previous forecast. Either way, it will be windy
and wet Thursday with heavy rain expected along the coast and into
western Siskiyou county.
Snow levels will come down to around 4500 feet Thursday night and
showers are expected to continue through Saturday as the upper level
trough passes to the east. Current model runs are showing a drying
trend Saturday afternoon as an upper level ridge nudges into the
area. /BR-y
&&
.AVIATION...05/00Z TAF Cycle...Offshore low pressure will move inland
on Sunday. This will result in a continued mix of IFR/MVFR/VFR
ceilings and visibilities through Sunday. VFR ceilings will be most
common but with rain and the IFR conditions with terrain obscuration
will be mainly near the coast and over the mountains. As the low
nears the coast, low level southerly winds will increase with low
level wind shear expected at the coast including KOTH and into the
Umpqua Valley/KRBG between 10Z and 18Z. The wind shear should end
late morning as the stronger winds also occur at the surface. Strong
gusty southerly winds are expected to persist into Monday, except
for winds backing to northerly at the coast beginning late Sunday
evening. Winds will be strongest at the coast, over the mountains,
in the Shasta Valley, and across the east side. /DW
&&
.MARINE...Updated 530 PM PST Saturday 4 February 2017...
High and very steep seas will slowly build into Sunday morning. On
Sunday morning, a low will move into the waters from the southwest
with rapidly increasing winds. Gale to storm force south winds are
expected through the day into Sunday evening with wind wave
dominated seas building to 15 to 20 feet. The strongest winds will
cover a wider swath of the waters south of Cape Blanco...from around
5 to 50 NM from shore but will extend across the inner waters near
Cape Blanco and northward to the vicinity of Coos Bay. Winds will
back to northerly from north to south during Sunday night with seas
remaining very steep but beginning to diminish. Conditions will
improve late Sunday night into Tuesday but the pattern will remain
active with a front likely to bring advisory strength southerly
winds with steep seas on Monday. Another very strong front is
possible Wednesday night into Thursday and may bring another round
of strong winds and very steep and high seas. /DW
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning from 10 AM Sunday to 1 PM PST Monday for
ORZ029>031.
Wind Advisory until 7 PM PST this evening for ORZ030-031.
Wind Advisory from 10 AM Sunday to 1 PM PST Monday for
ORZ029>031.
Winter Weather Advisory until 4 AM PST Sunday for ORZ027.
High Wind Warning from 4 AM to 10 PM PST Sunday for ORZ021-022.
Wind Advisory from 10 AM to 10 PM PST Sunday for ORZ026.
CA...High Wind Warning from 10 AM Sunday to 1 PM PST Monday for
CAZ085.
Wind Advisory until 7 PM PST this evening for CAZ085.
Wind Advisory from 10 AM Sunday to 1 PM PST Monday for CAZ085.
High Wind Warning from 4 AM Sunday to 1 AM PST Monday for
CAZ081.
Wind Advisory from 4 AM Sunday to 1 AM PST Monday for CAZ081.
Pacific Coastal Waters...Storm Warning from 4 AM to 7 PM PST Sunday
for PZZ350-356-370-376. Gale Warning from 4 AM to 7 PM PST
Sunday for PZZ350-356-370-376. Hazardous Seas Warning
until 4 AM PST Sunday for PZZ350-356. Hazardous Seas Warning
from 7 PM Sunday to 4 AM PST Monday for PZZ350-356. Hazardous
Seas Warning until 4 AM PST Monday for PZZ370-376.