Wildfire in Oregon, July 12 to 31, 2017

Area Forecast Discussion
National Weather Service Medford OR
919 AM PDT Wed Jul 12 2017

.DISCUSSION...The forecast was updated this morning to reflect
diminishing low clouds in the Coquille Valley. The marine layer is
expected to similarly extend into Coos County and also reach the
Douglas County coast this evening into Thursday morning. One of the
main items of interest for the afternoon package will be the
extent of hot and breezy conditions with low relative humidities
during the next week. Also, the need for any adjustments to the
probability of afternoon and evening thunderstorms from Friday
into early next week. A few low topped cumulus buildups are
expected over the higher terrain today and Thursday. We will need
to examine the full suite of data, but a slight chance of
thunderstorms may need to be introduced to Friday. The 12Z GFS has
arrived and indicates weak instability over the Siskiyou
Mountains, Cascades, and Lake County. The Saturday forecast is
also a candidate for adjustment as the GFS has shifted the pattern
slightly farther to the east. It develops another region of weak
instability on Saturday from Siskiyou County northeastward across
the east side. The probability of thunderstorms diminishes early
next week with a shift to a westerly flow aloft.

&&

.AVIATION...12/12Z TAF CYCLE...VFR will continue for the next 24
hours with one exception. IFR will linger until around 17Z in the
Coquille Valley then develop again around 02Z this evening at the
coast north of Cape Blanco extending into the Coquille Valley and
Coos Bay including North Bend. -Petrucelli/DW

&&

.MARINE...Updated 200 AM PDT Wednesday 12 July 2017...High pressure
offshore and a thermal trough near the coast will produce moderate
north winds into tonight. Winds will ease up some on Thursday into
Friday, then increasing again Saturday into early next week with
gales possible for the southern waters by Sunday. -Petrucelli

&&

.PREV DISCUSSION... /Issued 451 AM PDT Wed Jul 12 2017/

Low pressure over the NE Pacific and high pressure over the
Rockies will keep a fairly static weather pattern in place over
the region for the next several days. Dry southwest flow aloft
combines with temperatures up to 5 degrees above normal for inland
areas. This, with with occasional weak shortwaves and slightly
breezy conditions will provide for continued drying of forest
fuels allowing fire danger to ramp up a notch by the weekend and
into early next week.

With breezy dry flow over the region yesterday a couple of new
fires erupted over the east side late in the day at and Hart
Mountain and to its north. Smoke was also continuing to be
produced in western Siskiyou county by the Island incident.

As we move into the weekend a slight chance for thunderstorms
still looks appropriate for Saturday mainly from Siskiyou county
extending to their northeast across south-central Oregon. Then on
Sunday things may be trending to push this threat eastward but
have held off on any changes for now. Any storms will likely not
be big rain-makers.

The models indicate the upper low over the NE Pacific will
migrate down the BC coast and then break up and move inland over
Canada and the PacNW from mid to late next week. This should allow
for increased breeziness and a subtle cooling trend. Stavish

FIRE WEATHER...Updated 200 AM Wednesday, 12 July 2017...
Hot, dry, and breezy westerly winds are expected each afternoon and
evening through this weekend. The windiest day is very likely to be
Thursday when southwest winds will affect the Shasta Valley and
Cascades eastward. Instability and moisture are expected to increase
for Friday through Sunday as the pattern becomes more favorable for
thunderstorm activity, but confidence in timing and location of
potential thunderstorms remains generally low. The combination of
heat and possible remnant moisture from former Tropical Storm Eugene
will bring the slight thunderstorm threat Friday into this weekend
to Northern California and the East Side.

Keep in mind, the details on the thunderstorm threat Friday into
this weekend are likely to waiver on day to day, so watch for
updates on this. Altogether, we'll continue to be sandwiched between
low pressure to the northwest and the four corners high to the
southeast, making us susceptible to small variations in each of
these for our variations in sensible weather to include thunderstorm
potential.

The models show a southwest flow aloft returning Monday into the
middle of next week, bringing a drier air-mass aloft and more stable
conditions with the bulk of the mid level moisture and instability
shifting east of our area. Note, the GFS and ECMWF show a shortwave
moving into our area, but mid level moisture is lacking. The details
on this could change in the days to come, but taking this at face
value does not look favorable for thunderstorms. BTL/Petrucelli

&&

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

CA...None.

Pacific Coastal Waters...Small Craft Advisory until 11 PM PDT this
     evening for PZZ356-376.

DW/SK/MAP