Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 241612

Area Forecast Discussion
National Weather Service Medford OR
912 AM PDT MON OCT 24 2016

.UPDATE...The front is moving onshore this morning, and while
winds have reached their peak for the day along the immediate
coast, peak winds are just beginning for the West Side and will
arrive later today for the East Side. Radar imagery shows a narrow
band of moderate to heavy precipitation now moving over the
coastal ranges, and this will push east through the rest of the
day. As everything appears to be on track, no major changes were
needed to the forecast this morning. For more information, see the
previous discussion below. -BPN


.AVIATION...24/12Z TAF CYCLE... Conditions will be VFR over much of
the area tonight, but low level wind shear is expected at TAF sites
west of the Cascades tonight through 18Z Monday. At the coast, areas
of MVFR Cigs and vis are expected Monday morning in the KOTH area,
while the Curry County Coast is likely to experience IFR in heavy
rain Monday morning. Gusty winds are expected through the forecast
area on Monday. Rain and deteriorating conditions will spread inland
Monday with the front, though MVFR and IFR are likely to be confined
to areas near and west of the Coast Range and from the Siskiyous
southward. Terrain obscurations will be near total for the Coast
Mountains, Siskiyous southward and across northern California and
partial elsewhere. BTL

Note: The ceilometer at FAA site KOTH is out of service, so there
will be no ceiling observations available generally between the
hours of 04Z and 14Z.


.MARINE...Updated 330 AM PDT Monday, October 24, 2016...
South winds will reach strong gales with storm force gusts early
this morning ahead of an approaching cold front. Periods of heavy
rain, reduced visibility and thunderstorms are also expected with
this front this morning. Showers and a slight chance for
thunderstorms will continue late this morning through tonight. Behind
the front later today into tonight, a strong low will approach the
area but stay west to northwest of the waters. This strong low will
bring additional south gales to the waters late this morning through
Tuesday morning. Very high, very steep and chaotic seas will
develop late this afternoon and tonight as a high and very steep
west swell combines with very steep south winds seas. These
conditions will continue through Tuesday morning. Winds will
gradually lower Tuesday to small craft advisory levels. Very steep
hazardous seas may continue into Tuesday afternoon then gradually

Another strong storm may bring additional gales and very steep
hazardous seas to the waters on Wednesday. -CC


.PREV DISCUSSION... /Issued 350 AM PDT MON OCT 24 2016/

SHORT TERM...A pair of low pressure systems over the Pacific
waters will affect the forecast area through Wednesday, bringing
periods of gusty winds and chances for rain.

Today`s wrapped up low, currently around 45N 131W, deepened rapidly
last night. It will likely bring the most significant weather
impacts to the forecast area through the week, with a broad area of
inland Wind Advisories and High Wind Watches currently in effect.
South to north pressure gradients are increasing now, already to 6mb
between Medford and Redding. Additionally, Squaw Peak in the
Siskiyous has already gusted to 69mph this morning. Although not the
strongest of south flow wind events, data suggests solid south winds
in the places that are vulnerable to this flow, including the Shasta
Valley, southern Rogue Valley, and most areas east of the Cascades,
including Klamath Falls, Alturas, and Lakeview. Coastal winds will
peak this morning too, though not quite strong enough to warrant a
High Wind Warning there.

Another aspect to this low is thunderstorm potential over the
coastal waters and immediate coastline. A lot of lightning was
observed with this storm earlier this morning, but activity has
diminished some. Still, there is a chance for thunderstorms through
tonight over the coast and coastal waters as instability and
dynamics act in concert there.

Winds will generally peak later this morning and early afternoon
then diminish this evening. On the heels of the strongest winds, a
frontal boundary will move from west to east across the area today,
brining moderate to heavy precipitation to the coast, the Mount
Shasta area, and Western Siskiyou County, then mostly light to
moderate precipitation elsewhere. A brief period of a rain/snow mix
is possible this morning around Snowman`s Summit on Highway 89
before warmer air changes it to all rain.

The front will weaken and stall over Modoc and Lake Counties Tuesday
with mostly dry conditions and lighter winds left in its wake.  Late
Tuesday the boundary will wave back northward as a warm front,
bringing a renewed chance of rain to most areas, though
probabilities will mostly be below 50 percent, and the most recent
NAM has trended much lower on precipitation with this feature, so
we`ll see if the EC follows suit.

Another developing surface low Tuesday night into Wednesday,
again around 130W, will deliver another round of enhanced winds to
the coastal waters and most inland areas too. Winds associated
with this storm look overall less than the current storm and most
of the rain will be focused over the coast.

The long-term discussion from the previous AFD follows.

LONG TERM...Thursday through Sunday...Energy associated with a mean
long wave trough over the northeast Pacific will split on Thursday
with one part heading into the Pacific Northwest and the other
becoming a closed low off central California. The models all then
bring the low off California up into our area Friday and Friday
night. The main difference between the models is in the timing of
the arrival of this system. The ECMWF is roughly 18-24 hours faster
than either the GFS or Canadian, which is similar to what they
showed yesterday. It is notoriously difficult to deal with closed
lows, so we`ve kept the forecast similar to what we had yesterday.
That means a good chance or precipitation area-wide, but the best
chances are along the Curry coast and into Northern California. It
should be noted that some period will be much wetter than what we
currently show as that low moves through, but confidence on the
timing is not high.

Next weekend things get a little murkier. The models all maintain a
long wave trough over the Northeast Pacific, and all have a variety
of shortwaves and closed lows rotating through the main trough.
However, trying to nail down any one of these that far out will
probably be futile. Thus, we`ve simply maintained chance to likely
pops on the west side and lower pops east of the Cascades. -Wright


OR...High Wind Warning until 11 PM PDT this evening for ORZ030-031.
     Wind Advisory until 11 PM PDT this evening for ORZ029>031.
     Wind Advisory until 5 PM PDT this afternoon for ORZ026.

CA...High Wind Warning until 11 PM PDT this evening for CAZ085.
     Wind Advisory until 11 PM PDT this evening for CAZ085.
     High Wind Warning until 5 PM PDT this afternoon for CAZ081.
     Wind Advisory until 5 PM PDT this afternoon for CAZ081.

Pacific Coastal Waters...Gale Warning until 11 AM PDT Tuesday for PZZ350-356-370-376.
     Hazardous Seas Warning until 11 AM PDT Tuesday for PZZ350-376.
     Small Craft Advisory from 2 PM this afternoon to 11 AM PDT
     Tuesday for PZZ356.
     Hazardous Seas Warning until 11 AM PDT Tuesday for PZZ356.


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