Gale Watch 29, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
219 PM PDT Sun Sep 17 2017

.DISCUSSION...The current forecast is pretty well on track with
latest models so only a few edits today. A weak short wave is
coming onshore this afternoon. A few light showers have formed
over coastal areas and the Umpqua Basin. The associated front to
the wave is weak and narrow but is likely to bring measurable rain
to much of southwest Oregon and western Siskiyou County. So the
chance of rain in those areas has been increased a bit. For areas
east of the Cascades and northeast California, the front won't
have as much impact there so the chance of rain remains mainly at
slight chance.

A long wave trough settles over the Pacific Northwest on Monday
and remains through Wednesday. A series of short waves are
rotating around the long wave bringing periods of precipitation
and cool temperatures. A second short wave with showers will come
through Monday afternoon then the most significant wave passes
Tuesday night and into Wednesday. Rainfall totals for this period
reach around 2 inches in western Josephine County around the
Chetco Bar Fire burn scar. The Cascades from Mt. McLoughlin north
will have many areas of 1.5 inches or more. This rain amounts
could cause mudslides around burn scars. We will check with area
fire agencies and likely lead to flash flood watches for the burn
scar.

Also, the cool air pool will carry instability so isolated
thunderstorms were added to the off shore waters for Wednesday
afternoon and evening.

Smoke will be on the decrease across the area. Each short wave
will bring additional mixing of the atmosphere that will decrease
the concentration of surface smoke. Also, the rainfall will impact
area fires and reduce the production of smoke.

One more small wave follows Thursday morning then a ridge of high
pressure builds across the northeast Pacific for warmer and drier
weather for the rest of the forecast period. JBL

&&

.AVIATION...17/18Z TAF CYCLE...A cold front is approaching the
forecast area today. A mix of VFR and MVFR (due to smoke) conditions
exist ahead of the front, and the smoky conditions will likely
continue until rain spreads inland affects mainly West Side areas
tonight. Ceilings will lower to MVFR this afternoon at the coast and
into the Umpqua Basin around KRBG, and then lower further to IFR
along the front tonight near the coast. Mountain obscuration will
increase in coverage tonight and tomorrow along and behind the
front. Additionally, Gusty winds along and east of the Cascades will
create enhanced chances for turbulence today and again tomorrow.
SK

&&

.MARINE...Updated 200 PM PDT Sunday 17 September 2017...South winds
will increase this evening ahead of the first of several fronts.
Seas will become more choppy due to steeper wind waves, especially
from Cape Blanco north. Higher northwest swells will arrive in the
coastal waters as early as Monday afternoon with steep seas likely
quite close to shore from Cape Blanco north. The following fronts
will be stronger with south winds approaching Gale. Confidence is
high on the strong winds as models have been consistent on this
feature for 2 days and we have issued a Gale Watch for Tuesday
night, again from Cape Blanco north. Periods of rain with gusty
winds and steep northwest swell are likely through Thursday. High
pressure is expected to develop offshore late in the week along with
a thermal trough at the coast. This would result in a return of
strong north winds...especially south of Cape Blanco. /FB

&&

.FIRE WEATHER...Updated 115 PM PDT Sunday, 17 September
2017...Tonight through Thursday can be characterized and cool and
wet for the majority of the forecast area. Tonight's initial front
will focus rain on southwest Oregon tonight and Monday morning.
Amounts should be on the low end of wetting rain thresholds for this
first system. More wetting rains are expected late Monday into
Tuesday mainly for the Cascades, Umpqua Basin and the coast...with
snow levels dipping to around 6000 feet. East of the Cascades, winds
will trend stronger Monday compared to today and will gust to near
40 mph Monday afternoon. However, afternoon humidity will only dip
into the 25 to 40 percent range.

A stronger set of cold disturbances is likely Tuesday evening
through Wednesday evening with a wetting rain likely for most of the
area, a snow level falling to around 6000 feet and strong winds at
higher and exposed locations. West to southwest winds over the upper
slopes and ridges should peak on Tuesday night with 50kt winds
expected at 10000 ft, some of which should make it down to the
exposed ridge tops of the Cascades. Snowfall in combination with
strong winds in the high terrain will likely result in treefall. The
exception to a wetting rain may be the far east side to include
portions of Lake and Modoc Counties.

Additional weaker disturbances will follow Thursday through Friday
with additional showers mainly in southwest Oregon and continued
cool and moist conditions across the area. It will then trend drier
and warmer through the weekend into next week with easterly winds
developing. Temperatures are forecast to return to near normal on
the weekend then likely becoming above normal next week. -SK/DW

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...None.

CA...None.

Pacific Coastal Waters...Gale Watch from Tuesday evening through late Tuesday night for
     PZZ350-356-370-376.