Wildfire in Oregon, October 1 to 23, 2017

Area Forecast Discussion
National Weather Service Medford OR
845 PM PDT Sat Sep 30 2017

.DISCUSSION...An update was just sent, primarily to raise pops
across northern and eastern Douglas County for the next 24 hours.
Deep, moist onshore flow aided by a ~150KT upper jet edging in
over the area is leading to measureable rain over portions of
Douglas County, especially west-facing slopes in the mountains.
Observations from the eastern Douglas foothills show rainfall of
up to 0.05 in the last hour, with totals around a tenth of an inch
so far in some places. The synoptic situation changes little over
the next 24 hours, so there is little reason to think this won't
continue. Pops and associated parameters have been updated through
tomorrow. Also of note: snow levels are around 7500 feet this
evening, but they will fall through the night, bottoming out
perhaps as low as 5500 feet by tomorrow morning. This should
bring a dusting of snow to the higher elevations such as Crater
Lake. The rest of the area will see much spottier precipitation or
none at all, especially in areas downsloped by a northwest wind.
This includes much of the east side, California, and the
Rogue/Illinois Valleys. We can't really rule out a shower, but
they will be few and far between. -Wright

&&

.AVIATION...01/00Z TAF CYCLE...MFR is expected to remain VFR
through the TAF period. Deep, moist onshore flow will bring
clouds to much of the forecast area. However, most locations will
remain VFR through the TAF period. The exception will be north of
the Umpqua Divide where occasional MVFR Cigs are expected at
times, especially along the coast and over the mountains and
foothills where showers are also expected. There is a possibility
of IFR Cigs/Vis in fog around KOTH tomorrow morning. -Wright

&&

.PREV DISCUSSION... /Issued 253 PM PDT Sat Sep 30 2017/

DISCUSSION...Cool northwest flow will continue tonight into tomorrow.
A 120kt jet streak will nose into the area this evening, which
could help some showers develop in the northern portion of our
area, with highest chances in the Cascades tonight into tomorrow.
Precipitation, if any, will be a few hundredths of an inch.

A slight chance of precipitation will continue through Monday for
the Umpqua Basin and coast north of Cape Blanco. A weak thermal
trough along the coast develops Monday into Tuesday, and Brookings
will have above normal afternoon temperatures these days. An
upper low over northern California will support east winds Monday
night into Tuesday. Winds will be strongest over higher terrain,
particularly in the Coastal Range and in western Siskiyou County.
Parts of the East Side could have showers Monday afternoon and
evening as moisture wraps around the low... and again Tuesday
afternoon.

The second half of the week will feature a warming and drying trend.
The 12z runs of the GFS and ECMWF show much better model agreement
than previous runs for this time frame. Wednesday into Thursday,
the upper low should exit the forecast area and drift towards the
northern Rockies. This should cut off any chance of precipitation
for the rest of the week. -MSC

MARINE...Updated 250 PM PDT Saturday, 30 September 2017...
Onshore flow continues this afternoon as an upper level trough
lingers across the Pacific Northwest. This trough will keep the
thermal trough fairly weak and shifted inland today through early
Sunday resulting in generally light winds and seas. North winds
and seas are then expected to increase to advisory levels south of
Gold Beach late Sunday afternoon or evening as a colder air moves
southward along the coast. Small craft advisory level conditions
are then likely to expand northward to include more of the area
Monday and Tuesday as the thermal trough returns and winds and
seas increase. BTL

FIRE WEATHER...Updated 200 PM PDT Saturday, 30 September 2017...
Today through Monday, an upper trough over the region and north to
northwest winds aloft will result in generally cool flow off of the
Pacific Ocean. An upper level disturbance moving through in the
northwest flow will move across north portions of the area Sunday
and bring areas of light showers to southwest Oregon, especially
along the coast, into the Umpqua and into the Southern Oregon
Cascades. Model forecasts continue to show that these showers will
bring light rainfall (of less than a tenth of an inch). On tuesday,
models are showing higher confidence on the track and timing of a
second upper level shortwave moving down into the area. This second
upper disturbance is forecast to move into the area Monday night,
then shift south into north-central California during the day
Tuesday as an upper low, before lifting east-northeast out of the
area on Wednesday. Some light showers are possible over the Cascades
and east side but confidence is low in the amount and exact location
of any shower activity.

Winds will be breezy during the late afternoons and early evenings
through Tuesday, especially for areas east of the Cascades. For
western locations, expect north to northwest winds in the afternoon.
Overnight, coastal mountains and ridges west of the Cascades will
see mainly light to moderate north to northeast winds with good to
moderate recoveries through Tuesday morning.

As the second upper disturbance develops into a low over north or
north-central California and lifts east-northeast Tuesday night into
Wednesday, expect drier conditions to develop. Models forecasts
continue to show a potential for a period of moderate to locally
poor ridgetop recoveries and breezy east-northeast winds west of the
Cascades as the upper level low moves south of the area. This
pattern with east to northeast winds overnight and moderate ridge
recoveries on western mountains may continue into Thursday and
Friday. -CC

&&

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

CA...None.

Pacific Coastal Waters...Small Craft Advisory from 5 PM Sunday to
     11 PM PDT Tuesday for PZZ356-376.