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FXUS66 KMFR 271642
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
842 AM PST Mon Jan 27 2020

.DISCUSSION...Satellite and radar show some incoming clouds and precipitation
ahead of the next system which will arrive this morning. The next
system, however, will arrive right on its heels this evening.
This system is the next atmospheric river-style system and will
bring moderate to spotty heavy rain overnight tonight.

Ahead of this system, winds could become very gusty, especially
for the coast. Confidence is not high enough to issue a high wind
warning quite yet since the low is weakening as it moves through
the area and the gradients are not traditionally high enough, but
it is worth noting that some of the models are showing the coastal
jet setting itself up at 925 mb starting this afternoon. Have
resigned ourselves to a no-lead time high wind warning if
necessary, but have updated the forecast to increase winds at the
coast. -Schaaf

&&

.MARINE...Updated 830 AM PST Monday, 27 Jan 2020...
The active weather pattern will generally continue across the
coastal waters through next weekend resulting in seas remaining
steep to very steep into at least Friday.

A warm front will move northward through the area this morning, then
winds will increase to gale force across much of the area causing
seas to become very steep late this afternoon through early Tuesday
morning. Combined seas are likely to peak at 14 to 17 feet late
tonight into early Tuesday morning with peak swell from 280 degrees
at 14 feet with a dominant period of 14 seconds.

The next frontal system will move through Wednesday with advisory
level winds likely. Westerly swell bears some watching Wednesday
into Thursday. Some of the models previously had it reaching 17 feet
at 17 seconds Thursday, but have since backed down slightly to 15
feet at 18 seconds.

After warm frontal activity Thursday, mild temperatures and a break
in the weather are expected Friday into Saturday as the active
weather briefly shifts northward. This warm break is expected to be
short lived because a well defined frontal system is then likely to
move in from the northwest Saturday night into Monday. This will
result in a wind shift to gusty northerlies and a return to cooler,
wet weather. ~BTL


&&

.PREV DISCUSSION... /Issued 453 AM PST Mon Jan 27 2020/

DISCUSSION...Confidence remains high in the near term forecast of wet
and breezy to windy conditions today into Tuesday morning. This
will likely be the strongest system of the week. It has begun
early this morning with warm frontal rain into Curry County and
the western portion of Siskiyou County so far. Snow levels will be
around 5500 to 6000 feet today as the warm front tracks
northeastward with the bulk of precipitation extending from the
coast to western portions of the area east of the Cascades...around
the Highway 97 corridor from eastern Siskiyou County into Klamath
County.

The cold front follows to the coast late this afternoon then
across the area tonight. The frontal passage will produce a peak
of southerly winds with gusts of 20 to 35 mph expected to be
common, and gusts up to 55 mph at coastal headlands. The front
will also bring a peak of precipitation intensity tonight with
moderate to heavy amounts expected at the coast into the coast
range of mountains, and light to moderate inland. The intensity of
precipitation will produce ponding of water on roadways and rises
on small creeks and streams. But, this still looks to be mainly a
beneficial rain with snow levels still above most of the major
passes...around 5000 to 5500 feet. 2 to 4 inches of snow is
expected for Diamond Lake and Crater Lake.

The axis of the associated upper level trough will swing across
the area on Tuesday morning with snow levels falling to around
4000 to 4500 feet. The short duration of the passage of this
disturbance on Tuesday morning will limit snow amounts but
Siskiyou Summit, Chemult, and Snowmans Summit could receive an
inch or so of accumulation with around 3 inches of additional snow
likely for the Diamond Lake/Crater Lake area.

A modicum of uncertainty creeps into the forecast for Tuesday
afternoon with model variability in the extent to which a post-
frontal shortwave trough will spread a new batch of light to
possibly moderate showers into the area in a northwest flow aloft.
Snow levels are expected to dip just a bit during the day to be
around 4000 feet, but the coldest of solutions would indicate an
accumulation as low as 3500 feet as showers taper off early
Tuesday evening.

Model uncertainty increases further thereafter, although compared
to the past couple of days there is better agreement that ridging
offshore of California will be slower in building toward our area,
and thus weaker. As such, there is a higher probability that a
new warm front focused north of our area will extend far enough
southward to bring rain north of the Umpqua Divide (into Coos,
Douglas, and northern Klamath Counties) beginning either Wednesday
morning or Wednesday afternoon. For elsewhere, the probability of
precipitation would taper both southward and eastward. The faster
solution of the GFS would still see light precipitation linger
into Wednesday evening while the slower depiction shows similarly
light lingering showers overnight.

High pressure still initially centered far to the southwest will
likely show a growing influence on our weather with a warming
and drying trend Thursday into Saturday. That means that a dry day
is possible on Thursday, especially for Lake and Modoc Counties.
But, there is still a likelihood of a measureable amount at the
coast into Douglas County with the probability again (as on
Wednesday) gradually lower as one travels farther southward or
eastward. The probability of precipitation is lowest this week
during Friday into Saturday morning, which means that is also a
time with a higher possibility of night and morning valley low
clouds and fog.

Late in the weekend into early next week, a broad trough over the
northern Pacific is likely to kick the Californian ridge into the
desert southwest and usher in a colder and wetter pattern. The
length of time that this pattern lingers, timing of disturbances
in this colder northwest flow aloft, and the strength of
disturbances is highly uncertain. But, it is worth mentioning that
the GEFS ensemble mean solution brings snow levels down to around
2500 feet late Sunday night/early Monday morning with perhaps an
inch or two of snow.

AVIATION...For the 27/12Z TAF Cycle...
A warm front pushing in from the southwest will cause rain and snow
to overspread the area this morning. IFR to MVFR along the coast
with total terrain obscurations in the coastal mountains should be
expected. Wind shear will also develop along the coast this morning,
especially in the KOTH area, and this is likely to persist through
the TAF period due to strong winds just above the surface. Inland
areas are likely to experience MVFR with pockets of IFR and
increasing terrain obscurations as the warm front moves through this
morning. The cold front will then move across the coastal waters and
onto the coast this afternoon with upslope precipitation under a
southwest flow. This evening and overnight expect the front to
slowly move inland, but fragment from the terrain as it does so.
Moderate to heavy rainfall is expected along and near the coast and
wind shear is expected to push into portions of Josephine and
Douglas counties, including KRBG. ~BTL

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...None.

CA...None.

Pacific Coastal Waters...Small Craft Advisory until 10 PM PST Friday for
PZZ350-356-370-376.
Gale Warning from 4 PM this afternoon to 4 AM PST Tuesday for
PZZ350-356-370-376.

$$
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