Storm Watch 3, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
917 AM PDT Thu Apr 5 2018

.DISCUSSION...

Forecast appears on track with a little wind in some of the
valleys and precipitation falling along the coast. Look for the
cold front to continue it's progression towards the coast today
resulting in widespread rain and snow levels rising to 7500 to
8000 feet later on this evening.

Only change made for today was lowering temperatures a degree or
two with the widespread cloud cover and the latest high resolution
guidance showing slightly cooler temperatures. Look for
temperatures in the lower 60's in the west side valleys for highs
today.

-Smith

&&

.AVIATION...05/12Z TAF CYCLE...A cold front is moving toward
Northern California and Southern Oregon this morning. This will
bring a mix of MVFR and VFR cigs, rain, gusty winds (strongest at
the coast, over the mountains, and east of the Cascades), and
widespread terrain obscuration sweeping west to east through the day
today. Rain will taper off briefly this evening, but another round
of rain will arrive late tonight. This has a better chance of
producing IFR ceilings and visibility compared to the round of lower
ceilings and rainfall today.

Nieuwenhuis/Firmin

&&

.MARINE...Updated 845 AM Thursday, 5 April 2018...The pattern
becomes active today and will continue into next week. Several
fronts will bring multiple rounds of strong southerly winds and very
steep, hazardous seas. Small Craft Advisory level conditions are
expected this morning, with low-end gales and very steep and
hazardous seas expected this afternoon in many areas.

Another even stronger front is expected late Friday into Saturday,
with gale force winds possible. Models are showing high-end gales
with this system, and we've issued a Gale Watch for this upcoming
low pressure. We'll likely be upgrading to Gale Warnings with the
afternoon or tonight's forecast package. Models have trended the low
center further away from the coast Friday night, and thus confidence
in storm force winds occurring is decreasing, but we'll monitor the
trends closely. Yet another strong front is possible early next
week. Overall, the weather over the next week will bring significant
impacts to mariners.

Keene/Firmin

&&

.PREV DISCUSSION... /Issued 607 AM PDT Thu Apr 5 2018/

SHORT TERM...An active pattern with progressively stronger fronts
is expected to impact the area through Saturday and bring wet and
windy conditions. The first of these fronts will push into the
coast this morning and will gradually shift inland this afternoon
and evening. Light to moderate precipitation and breezy winds are
expected with this front. Then an atmospheric river will set up
as a low approaches the northern California coast from the
southwest and brings warm and moist onshore flow. Initially,
heaviest rain will be aimed just south of the CWA over portions of
the northern California. However, model solutions are indicating
that widespread moderate rain will spread northward across the
area late Thursday night and Friday morning as the surface low
approaches the coast near the California-Oregon border.
Precipitation continues Friday afternoon but may decrease in
amount.

Then Friday evening and night, a strong front is forecast to
bring moderate to heavy rain along with strong winds to the area.
Models are in good agreement showing a deepening low pressure
system moving towards the PacNW and bringing a strong cold front
towards the coast. This low is expected to deepen to around 970 to
975 mb Friday night as it moves inside of 130 W and tracks
towards the Washington coast. Ahead of this front, expect
widespread moderate and locally heavy rain to spread across the
CWA Friday evening and night. Heavy rain is possible in Curry and
western Siskiyou counties Friday night with moderate rain to
locally heavy rain across other areas. Snow levels are expected to
remain high around 10000 feet Friday evening and night then
quickly lower to 5000-6000 feet during the day Saturday as cold
air aloft moves into the area.

As a result of these systems Thursday night through Friday night,
moderate to heavy rain is expected to impact much of the CWA. 24
hour rainfall amounts are expected to be around 1 inch for many
inland areas, including locations east of the Cascades. Higher 24
hour rainfall totals of 1.5 to 3 inches are expected for areas
along the coast into western and south- central Siskiyou counties
as well as into the Cascades. This heavy rain will result in
rises on area rivers and streams and may bring ponding and
localized stream flooding. Will need to monitor additional model
runs for details as this system approaches.

In addition to rain, this strong front is also forecast to bring
strong and gusty winds to the area late Friday and Saturday.
Models show a strong mid level jet and an increasing surface
pressure gradient Friday night into Saturday as the front moves
inland. This is expected to bring strong and gusty winds to most
the area with the strongest winds along the coast, in the higher
mountains and east of the Cascades. High wind watches are in
effect for these areas Friday evening through Saturday. Please see
the NPWMFR for details. The exact strength and track of the low
will be factors in how strong winds are with this front. In
addition, as a trough moves in behind the front later on Saturday
and brings a cool and slightly unstable environment, expect
increased vertical mixing and gusty winds over the area. These
strong winds may linger into Saturday evening, especially for
areas east of the Cascades, then lower.

Lastly, model solutions support a slight chance for thunderstorms
over the coastal waters as this front moves into the coast Friday
evening. As the front pushes inland and an upper trough gradually
moves into the area, cold air aloft and slightly unstable
conditions will bring a slight risk for thunderstorms on Saturday,
with best chances along the coast during the morning and east of
the Cascades in the afternoon.

PREV LONG TERM DISCUSSION... /Issued 314 PM PDT Wed Apr 4 2018/

LONG TERM...Sunday 12z onward...

Moist onshore flow will continue Sunday on the backside of the
trough. A strong ridge won't build in immediately, so showers
remain possible throughout the day. The ridge will strengthen on
Monday bringing mainly clear skies and a very spring like day for
the start of the work week.

The next system will impact the region on Tuesday with a low
undergoing cyclogenesis during Tuesday morning.  A cold front will
then push onshore and bring widespread precipitation to northern
California and southern Oregon.  Snow levels will start out around
6000 feet and then fall to  4500 feet behind the front. Some snow is
possible above 5500 feet.  Compared to the system on Saturday, this
one isn't packing as much of a punch. It strengthens, but the low
center only falls to 976 mb given what both models are currently
showing. Winds will probably be an issue over the east side and
perhaps the coast as 700 mb flow is showing winds around 60 knots
along and ahead of the front Tuesday morning.

As for timing of this system,  the GEFS forecast for the most part
has the low arriving Tuesday morning.  However,  a few ensemble runs
are holding off until later on Tuesday.  None the less, it's a high
confidence forecast for precipitation along the coast during Tuesday
morning.  Since the timing is still an uncertainty,  precipitation
inland could hold off a bit later Tuesday.

There is the potential for another front on Wednesday. However, the
GFS and ECMWF are on opposite pages with one model predicting rain
and the other one keeping things dry.  One of the reasons for this
is because one model has an extra shortwave to kick the front
through faster.  Really can't commit to one model, so what happens
on Wednesday is up in the air.  However, the trough should move on
shore next Thursday bringing some rain yet again.

-Smith

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Watch from Friday evening through Saturday afternoon
     for ORZ021-022.
     High Wind Watch from Friday evening through Saturday evening for
     ORZ030-031.

CA...High Wind Watch from Friday evening through Saturday evening for
     CAZ085.

Pacific Coastal Waters...Gale Watch from Friday evening through Saturday afternoon for
     PZZ350-356-370-376.
     Small Craft Advisory until 5 AM PDT Friday for PZZ350-356-376.
     Gale Warning until 5 PM PDT this afternoon for
     PZZ350-356-370-376.
     Hazardous Seas Warning from 5 PM this afternoon to 5 AM PDT
     Friday for PZZ350-356-370-376.
     Small Craft Advisory until 5 PM PDT this afternoon for PZZ370.

Smith/Firmin/Keene/Nieuwenhuis