Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 250542

Area Forecast Discussion
National Weather Service Medford OR
1042 PM PDT MON OCT 24 2016

.AVIATION...25/06Z TAF CYCLE...Instability will keep thunderstorms
possible offshore and along the coast (including KOTH) through
around 25/09Z. Inland, conditions are highly variable. Most of the
area will be MVFR or better with occasional lowering to IFR in
showers. An area of clearing has moved over KMFR and fog is
forming and may bring IFR/LIFR conditions to the terminal until
at least 25/09Z. An area of higher cloud will arrive soon and may
reverse the fog trend at KMFR, but confidence in this is low.
Pilots should be prepared for the possibility of LIFR conditions
throughout the night at KMFR. Similar problems may develop at KLMT
later if clearing develops there. -Wright

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.


.PREV DISCUSSION... /Issued 804 PM PDT MON OCT 24 2016/

DISCUSSION...Updates were already issued this evening to adjust
pops/weather and lower the wind headlines on the east side. No
further updates are planned.

The cold front has moved east of the area, and winds are
diminishing as gradients relax. Gusty winds are still certainly
occurring, especially over the mountains and open areas on the
east side, but all obs are well below criteria and guidance
suggests this trend continues tonight, so the high wind warnings
and advisories were lowered.

Evening radar shows thunderstorms edging into the coastal waters
off Gold Beach associated with a vigorous shortwave moving through
the area. The global models are too far west with the instability,
but hi-res models such as the HRRR are picking up on this nicely
and show this instability moving right up to the coast and then
gradually shifting north tonight. The area of isolated
thunderstorms was expanded to cover all the waters and just inland
from the coast. Most of these areas will not see lightning tonight,
but it certainly can`t be ruled out.

Widespread showers are occurring from west-central Siskiyou County
into the Oregon Cascades and sliding slowly east. Further west,
showers have become more isolated except in the southwest-facing
upslope areas where showers will likely continue all night. There
will be a general downward trend in shower activity tonight over
most valleys as most of the energy moves north and we find
ourselves in between systems. Pops were adjusted as such. -Wright

PREV DISCUSSION... /Issued 258 PM PDT MON OCT 24 2016/


Short Term...Tonight through Thursday Night...Satellite and radar
imagery show the front has passed through most of the West Side, and
now is lies right along the spine of the Cascades. To the West,
winds have diminished and precipitation continues as showers, with
the heaviest precipitation along the southern slopes. To the East,
steadier rain and gusty winds continue. Due to this, the wind
headlines for the Rogue and Shasta valleys have been cancelled, but
the ones for the East Side will continue into this evening, as the
front slowly slides through. For more details on the updated wind
headlines, see the hazardous weather message at PDXNPWMFR.

The upper level low responsible for the wind and rain today will
remain offshore, drifting slowly north tonight through Tuesday. A
second trough will then swing under this one from the south, and
slide north along the coast Tuesday night and Wednesday. This will
bring another round of wind and rain to the area Wednesday morning.
Although pressure gradients with this system are forecast to be
lower and the surface low is not expected to deepen as it slides
through, winds may still reach advisory levels in the Shasta Valley
and over the East Side. Confidence is low, but further model runs
this evening and tonight should tilt the scales in one way or the

Precipitation is another matter. With models showing 6 to 12 hour
differences in the timing of the front, and also depicting the
chance that the front could stall along the coast for a brief time,
there is a wide range of precipitation amounts that could result.
have opted towards the slower solutions, due to the weaker dynamics
and flows associated with the system, and brought the main band of
precipitation onshore along the southern Oregon coast Wednesday
afternoon, then gradually sliding it east through the evening and
into Wednesday night. Rainfall amounts will be heaviest wherever
this band stalls, with heaviest amounts along souther slopes and
east to west trending ridgelines. West Side valleys will most likely
be sheltered, and should only receive light amounts, while the bulk
of the moisture inflow never really makes it east of the Cascades.

Showers are then forecast to continue through Thursday as onshore
flow continues, conditions should dry out a bit Thursday night as
weak upper level ridging nudges into the region, but this break will
be brief as another system approaches from the south, continuing the
unsettled and wet pattern into the long term. -BPN

LONG TERM...Friday through Monday...Models start this time frame in
fairly good agreement with a closed 500 mb low at 39 N and 136 W at
the same indicated 544 height. This first system of the extended
period brings rain ahead of a warm front Saturday. The models remain
in good agreement as the upper low moves down to about 100 nm
offshore of Northern CA. This brings the triple point of this system
directly over our forecast area Sunday. From there, models are in
broad agreement with a deep upper level trough over the coastal
waters off of the Pac NW, and the timing of systems will be
impossible this far out and have broad-brushed chance pops through
the remainder of the extended. -Sven

MARINE...Updated 200 PM PDT Monday, October 24, 2016...Showers
and isolated thunderstorms will continue through tonight. Behind
the front later tonight, a strong low will approach the area but
stay west to northwest of the waters. This strong low will help to
maintain south Gales to the waters 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, but very steep hazardous seas may continue into
Tuesday afternoon then gradually lower.

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




Pacific Coastal Waters...Small Craft Advisory until 11 AM PDT Tuesday
     for PZZ356.
     Gale Warning until 11 AM PDT Tuesday for PZZ350-356-370-376.
     Hazardous Seas Warning until 11 AM PDT Tuesday for

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