Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 192203
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
303 PM PDT Tue Sep 19 2017

.DISCUSSION...Cool and unsettled weather will continue through at
least Thursday. The weather will begin to dry out Friday, then we
could be looking at dry and warmer weather this weekend through at
least the middle of next week.

Were at a relative break in shower activity. The latest visible image
shows the leading edge of a warm front approaching the Oregon coast.
Steady precipitation is expected to arrive in southwest Oregon early
this evening and move inland tonight. This are could get some
significant rainfall and the concern is still there for possible
flooding. Therefore a flash flood watch remains in effect. Details on
this can be found at FFAMFR.

At the same time a strong upper trough for this time of the year
will push south tonight through Wednesday. There will be plenty of
energy, so expect moderate to heavy precipitation along the coast,
coastal mountains and Cascades. These areas could pick up between
1.50 and 2.00 inches of precipitation from this evening through
Wednesday evening. Even some westside valley locations could pick up
0.25 to 0.50 of an inch or more rainfall during the same time
period. Snow levels will be higher compared to last night, so were
not expecting any accumulations in places they did last night/early
this morning.

The above mentioned upper trough will bring in a colder air mass
aloft and snow levels could lower enough for wet snow to accumulate
near Diamond Lake, Crater Lake Park Entrance up to the Rim and Mount
Ashland Ski area, especially in the presence of heavier showers
Wednesday afternoon, but there`s a better chance for snow to stick
there after dark Wednesday as road temperatures begin to lose
surface heating. Right now, snow levels are expected to be around
6,000 feet Wednesday, but could briefly lower to around 5500 feet in
heavier showers. So while it may be snowing at these levels,
accumulating snow should be higher up in elevation due to the warm
ground and roads. Snow levels could lower to near 5000 feet
Wednesday night with 1-2 inches of wet slushy snow is possible near
Diamond lake and 2-4 near Crater Lake and Mount Ashland Ski area, so
anyone planing on traveling in these areas should be prepared for
winter like conditions.

In addition 500mb temperatures between -25 and -26 C will move
overhead Wednesday afternoon over the marine waters and portions of
Douglas County during the time of max heating, therefore could not
rule out a slight chance of thunderstorms Wednesday afternoon into
early Wednesday evening.

There is less confidence in the weather for Thursday. In general,
the models show different solutions with the locations of
precipitation. For example, a couple of solutions show another
disturbance moving south along the Oregon coast which if correct
would bring little in the way of precipitation. However one model
solution brings the disturbance further inland resulting in a
greater chance for showers over a good portion of the area. This was
pretty much the case yesterday, so we`ll continue to lean towards
the drier GFS and ECMWF solution, but further adjustments may be
necessary.

Precipitation will not be the only impact. Moderate to strong winds
are also possible along and east of the Cascades into early this
evening and again Wednesday afternoon and early evening. Right now,
were not expecting winds to reach any criteria, but it`s something
we`ll have monitor.

Friday will be a transition day as the upper trough shifts east
with a dry northerly flow. Still could not rule out a few showers
along the northern Cascades and eastside, but they should be the
exception. Dry and warmer weather returns next weekend as an upper
ridge builds over the eastern Pacific. At the surface, a thermal
trough will develop with increasing offshore flow in southeast
Oregon and Western Siksyou County. There is increasing confidence we
could remain in a prolonged period dry and warmer weather for most
of next week and beyond, but this is not a slam dunk. -Petrucelli


&&

.AVIATION...19/18Z TAF CYCLE...A mix of MVFR/VFR ceilings are
expected area wide tonight into Tuesday morning with terrain
obscured. The lowest conditions will be in the most persistent
showers, along the coast and over the Cascades north of Lake of the
Woods. Freezing levels will lower to 5000-6000 ft MSL. Winds will
become stronger in many showers, particularly at the coast.
Additionally strong winds (outside of showers) are also expected
east of the cascades, including at KLMT.  -Schaaf/Spilde

&&

Updated 200 PM PDT Tuesday 19 September 2017... A cold front
is expected to push into the marine waters later tonight and south winds
will increase as a result.  However,  these winds are expected to stay
within Small Craft Advisory thresholds.  Steep north west swell will also
continue to impact the area for tonight as the low pressure system in the
Gulf of Alaska slides down into our region.  We can expect these steep
north west seas to continue into tonight and tomorrow before the swell wave
heights start to decrease late Wednesday into early Thursday.

Eventually, high pressure will develop and a thermal trough will position
it`s self along the coast and south of Cape Blanco.  We are getting into that
time of year when the temperature different between land and water is not going
to be that great,  so winds associated with this thermal trough will be small craft
advisory at best. -Smith


&&

.FIRE WEATHER...Updated 130 PM PDT Monday, 19 September
2017...The focus in the near-term is safety as the landscape becomes
quite cold, wet, and windy.

Breezy to windy conditions will affect most of the forecast area
through Wednesday, with strongest winds east of the Cascades and in
the highest terrain. Any weakened trees from wildfire will be
susceptible to falling due to the strong winds in the highest
terrain, especially where some wet snowfall weighs them down.
Snowfall will impact primarily areas above 6000 ft with several
inches accumulation possible.

Moderate to occasionally heavy rain could cause debris flows and/or
wash out rural forest roads, especially in the Coast Range on the
Chetco Bar wildfire burn scar late this afternoon into Wednesday
morning.

Warming and drying is expected beginning Friday. We are expecting
broad northeast to east flow over the weekend, and afternoon
humidity will likely lower into the 20s and 30s across the forecast
area. Model trends are suggesting a dry and warm period that lasts
through next weekend. Additionally, the Climate Prediction Center`s
8-14 day outlook is calling for enhanced chances for above normal
temperatures and below normal precipitation. In short, this wet and
cool period will likely be followed by a steady and long-duration
warming and drying trend.


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Flash Flood Watch through Wednesday morning for ORZ022-024.
     Flash Flood Watch from 11 PM PDT this evening through Wednesday
     afternoon for ORZ025.

CA...None.

Pacific Coastal Waters...Small Craft Advisory until 5 AM PDT Thursday for
     PZZ350-356-370-376.
     Small Craft Advisory for hazardous seas until 5 PM PDT this
     afternoon for PZZ350-356-370-376.

$$


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