Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 111652

Area Forecast Discussion
National Weather Service Medford OR
852 AM PST Mon Dec 11 2017

.DISCUSSION...No updates are needed for this morning. The latest
visible image and surface observations show low stratus with areas
of freezing fog in portions of the Umpqua Basin, Illinois Valley
and north end of the Rogue Valley including Grants Pass and
Medford. This mornings sounding is almost identical to the past
couple of mornings with a strong inversion. The freezing fog and
dense fog advisories remain in effect. Please see NPWMFR for more

Conditions will not change much, if at all the next few days. It
won`t be until the end of the week where we`ll have our first
chance of precipitation in almost 2 weeks. -Petrucelli


.AVIATION...11/12Z TAF CYCLE...IFR/LIFR conditions will continue
this morning for RBG and MFR TAF sites.  This is essentially a
persistent forecast as the inversion has strengthened even more
tonight. IFR/LIFR conditions will continue until the early afternoon
hours on Monday for the Umpqua Valley and should lift around the
noon hour in the Rogue Valley.

VFR conditions will prevail elsewhere, including the coast and
coastal waters.


.MARINE...Updated 830 AM PST Monday, Dec 11th, 2017...High
pressure will continue to produce relatively calm conditions through
much of the week. A dissipating cold front will brush the outer
portions of the coastal waters area late today, resulting in a
slight increase in west swell through Tuesday afternoon. North winds
will increase Wednesday as high pressure rebuilds. A more active
weather pattern is expected this weekend with increased swell and
periods of increased southerly winds. /BR-y


.PREV DISCUSSION... /Issued 356 AM PST Mon Dec 11 2017/

DISCUSSION...A strong ridge over the Intermountain West will
continue to be the main feature dominating our weather much of
this week. Taking a look at the latest pass from the polar
orbiting satellite, Suomi NPP, the NASA SPoRT nighttime
microphysics imagery via the VIIRS instrument is showing areas of
low clouds/fog in the Umpqua Basin from about Scottsburg to Elkton
and Drain south along Interstate 5 to around 227 Canyonville. We
currently have a dense fog advisory in effect for those areas.
More fog/stratus can be seen in the Rogue/Illinois Valleys, and
indeed, fog has developed here at the airport in the last hour. A
freezing fog advisory is in effect in these locations. Specific
advisory details can be viewed at NPWMFR. Patchy fog is also
showing up in the lower Klamath River Valley as well as the Scott
Valley and in the Christmas Valley over northern Lake County. 24
hours ago, the imagery was virtually the same, and with little
change in the atmospheric profile, a persistence forecast will
once again be favored over any single piece of guidance with
respect to sky/temperatures today.

An offshore front will make its way toward the coastal waters
late today and tonight, but will dissipate Tuesday as it runs
into the strong ridge. The ridge will re-establish along the West
Coast Tuesday through Thursday resulting in more of the status
quo - morning fog/stratus in the valleys west of the Cascades that
will have difficulty breaking in some areas during the
afternoons. Overall, it will remain cool/chilly in the valleys
with milder conditions along the coast and at elevations just
above the valley floors. -Spilde

LONG TERM...Thursday night until next Tuesday...No changes. A
short wave trough will break through the ridge Friday. This trough
will bring a little bit of rain and perhaps some freezing rain
east of the Cascades Friday morning. The freezing rain should be
very light looking at the model QPF output and the soundings east
of the Cascades.

After this quick hitting system moves through Friday, a deep
trough will setup in the Gulf of Alaska. In general, models are in
pretty good agreement with what will happen as an atmospheric
river type event will impact the region. This should result in
wetting precipitation for the majority of next weekend. The only
reason for a little lack of confidence is how models are still
changing run to run with exact timing and location. Right now the
forecast calls for snow levels around 4000-6500 feet on Saturday
before the snow levels rise on Sunday. The bulk of the
precipitation will arrive when snow levels are higher, so not
willing to commit to say that the mountains will see enough snow
to make a difference in the snow pack.

After Sunday night, it appears some more precipitation will be on
the way during the Tuesday and Wednesday time frame. It`s still
unclear how strong that upcoming system might be or if it will
miss the Oregon area entirely. -Smith


OR...Air Stagnation Advisory until 2 PM PST Thursday for
     Dense Fog Advisory until 10 AM PST this morning for ORZ023.
     Freezing Fog Advisory until 10 AM PST this morning for


Pacific Coastal Waters...None.

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