Wildfire in Oregon, July 31, 2017

Area Forecast Discussion
National Weather Service Medford OR
954 AM PDT Mon Jul 31 2017

.DISCUSSION...An update to the forecast is not necessary. The
focus for the afternoon forecast issuance will be the particulars
of what will be an unusually lengthy and unusually extreme level
of heat this week. This includes the possibility of reaching all-
time high temperatures, and extending the heat advisory and
excessive heat warning products beyond Thursday afternoon...through
Friday afternoon. Wednesday still is expected to be the hottest
day, but it will be nearly as hot on both Tuesday and Thursday.
Inland readings on all 3 days, Tuesday through Thursday, will
likely be higher than on any day since 1992. At these levels, and
considering temperatures will decrease much less than normal
overnight, precautions should be taken to stay cool, and hydrated.

Also of significant focus will be adjustments to the wind and
convective forecasts. As the thermal trough moves inland on
Wednesday, cooler air will move to the coast and afternoon winds
will increase in west side valleys...near the newly arrived
trough. The probability of afternoon and evening thunderstorms
today through Wednesday will be low but greater than zero.
Conditions yesterday were emblematic of the general expectation
with ridge top cumulus cloud development that was capped. The
slight chance probability will be highest today over the Cascades
and from the Modoc County ridges into southern Lake County. A
similar story on Tuesday and Wednesday with a slightly higher risk
for western Siskiyou County. The probability of thunderstorms
still is expected to increase Friday into Saturday.

&&

.AVIATION...31/12Z TAF CYCLE...At the coast and just offshore...The
latest fog image is absent of any marine stratus and this will
remain the case for the next 24 hours. The TAF at North Bend shows
VFR for the next 24 hours. Cannot not rule out very brief and
shallow cloud/fog layer between 12-14z, but confidence was not high
enough to put into the TAF. The main concern will be gusty north
winds late this morning through this evening.

Inland...VFR will continue throughout the TAF period, with the
exception of in the vcty of wildfires, where smoke could restrict
vis to under a mile. This will be most prevalent in northern Jackson
County, western Siskiyou County, Modoc County, Southern Lake County,
and over the Cascades. Additionally, there is a slight chance of
thunderstorms over the Cascades, Northern California, and points
eastward late this afternoon and evening. -Petrucelli

&&

.MARINE...Updated 830 AM PDT Monday 31 July 2017...A thermal
trough along the northern California coast will persist through
Tuesday night with steep to very steep seas driven by north winds.
Gales will affect areas south of Port Orford through Tuesday night
with small craft conditions are expected elsewhere, except beyond 3
nm from shore north of Reedsport. The thermal trough will weaken
Wednesday and winds will become lighter. In fact we could see a wind
reversal starting Wednesday night and lasting through Thursday night
with continued light winds and lower seas. Seas are likely to trend
lower into Saturday. -Petrucelli/DW

&&

.PREV DISCUSSION... /Issued 544 AM PDT Mon Jul 31 2017/

SHORT TERM...Extremely hot temperatures will develop this week
over inland areas as a high pressure ridge builds over the region.
Hottest temperatures are expected Tuesday through Thursday for
inland areas. Little relief is expected from the hot temperatures
as overnight lows only briefly lower into the 70s or 60s before
heating up again each day.

Today, inland hot temperatures will rise into the upper 90s to
mid 100s across inland valleys today, with localized temperatures
up to 110 in the lower Klamath River Valley. Temperatures will
soar higher Tuesday through Thursday with highs in the 100 to 115
range for inland valleys. With overnight lows also staying above
normal, this prolonged period of very hot temperatures will bring
dangerous conditions to the area. These hot temperatures are
notable and may represent the hottest conditions seen in the last
25 years. This will bring a dangerous situation to inland areas.
An Excessive Heat Warning and Heat Advisories at NPWMFR continue
to highlight the impacts expected from these scorching
temperatures this week.

Take a minute here to read some safety tips for this extreme heat:

* Beat the heat, check the backseat. Never leave people or pets in
  vehicles.

* Rivers are dangerously cold and have strong currents. Wear a life
  jacket if swimming.

* Monitor older adults, young children and those who are sick.

* Stay in an air-conditioned room, and stay out of the sun.

* Drink plenty of water.

Along the coast, the upper level ridge combined with a strong
surface thermal trough will also bring warm temperatures through
Wednesday. Additionally, localized hot temperatures in the 90s
are expected for the Brookings areas today and Tuesday. This is due
to offshore easterly flow bringing a Chetco effect to the south
Curry coast. The Chetco effect is likely to peak on Tuesday.
Conditions in the Brookings area may remain warm into Wednesday
morning then onshore flow is expected along the south Curry coast
Wednesday afternoon with a return to normal conditions. Along the
Coos and Douglas county coast, expect highs in the lower to mid
70s today with temperatures rising into the upper 70s on
Wednesday. The thermal trough moves inland late Wednesday and on
Thursday, all coastal areas will see a return to normal
temperatures. Also light south winds that develop Wednesday night
and Thursday may bring areas of low clouds to the coast.

A second concern with this weather pattern is the potential for
thunderstorms. Models continue to support a slight chance for
thunderstorms over portions of Northern California and for areas
in the Cascades and eastward today and Tuesday. The potential for
thunderstorms is due to some mid level moisture moving up from the
south and southeast and combining with daytime instability.
Forcing is weak though. So mainly expect cumulus build-ups to
develop in these areas during the afternoon and into the evening
today and Tuesday. However cannot rule out an isolated
thunderstorm or two, especially over the mountains in Sikiyou
county and in the Cascades. Areas east of the Cascades also have
a slight risk for thunderstorms. Of note, any storms that form
would likely have a high base and may have little rainfall with
them.

Late in the week, as a broad shortwave trough approaches the coast
from the southwest then remains near the coast on the weekend and
into next Monday. This trough will bring additional moisture and
instability and will bring an increased risk for thunderstorms. Best
chances for storms to develop, continue to be over Siskiyou and
Modoc counties in Northern California and from the Cascades eastward
in Southern Oregon. However, depending on the track of the trough,
storms may be possible west of the Cascades at times. Confidence is
low on the details for thunderstorm develop due to variability in
the strength and track of the shortwave.

FIRE WEATHER...Updated 320 AM Sunday 30 July, 2017...Very hot and
dry conditions will continue away from the coast for most of the
week with near record breaking heat Tuesday and Wednesday and maybe
Thursday. The magnitude of the heat on each of these days is
expected to be the hottest in the last 25 years. This will be of
high concern for crews involved in firefighting efforts and it is
highly recommended they stay hydrated and take steps to avoid heat
exhaustion or even heat stroke. Even crews in the higher elevations
will not be immune to the heat with afternoon temperatures expected
to be in the 90s with little relief at night.

The thermal trough is expected to hover west of the Cascades the
next few days resulting in at least a Haines 5 conditions with
Haines 6 more than likely over the fires. Red Flag warnings and fire
weather weather watches remain in effect for today and Tuesday. Also
a Fire Weather Watch remains in effect for gusty winds and low
relative humidity across northwest sections of the the area Tuesday
afternoon and evening. Please see RWFMFR for more details on all of
the warnings and watches.

Thunderstorms...The models show marginal instability along and east
of the Cascades and northern California this afternoon and evening.
However, the air mass remains dry below 500mb with little or no
trigger. The most likely outcome will be building cumulus over the
Cascades and mountains in northern California and east side. However
could not rule out a stray thunderstorm or two, therefore the slight
chance of thunderstorms have been retained late this afternoon and
evening. On Tuesday the models show increasing instability and
moisture in portions of Northern California and Cascades with weak
shortwaves moving in these areas late Tuesday afternoon and evening
which could be enough to trigger a storm or two. Therefore have
decided to add a slight chance of thunderstorms in these areas.

Meanwhile, the thermal trough will remain along the coast resulting
in breezy east to northeast winds near and at the ridges in portions
of Fire zones 618, 619 and 280 tonight into Tuesday morning with
moderate recoveries. While not quite as strong, northeast winds will
remain gusty and recoveries will trend worse tonight Tuesday night
with locally poor humidity recovery. Offshore winds will become
noticeably weaker Wednesday night but recoveries will be nearly as
poor as the previous couple of nights.

No thunderstorms are expected Wednesday. Both the ECMWF and GFS show
a weak upper trough approaching the California coast Thursday night
through Friday which could tap into some monsoonal moisture. This in
combination with multiple shortwaves moving into our area could
bring an increased chance of thunderstorms and its not out of the
question we could be dealing with nocturnal storms Thursday night
with more thunderstorms possible Friday and Friday night. Keep in
mind it's still a ways out and the details on where the best chance
for thunderstorms will be are likely to change in upcoming days, but
given the high fire danger, this is something that we'll need to
keep a close watch on. -Petrucelli

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Heat Advisory from noon Tuesday to 8 PM PDT Thursday for
     ORZ021-027>030.
     Excessive Heat Warning from noon Tuesday to 8 PM PDT Thursday
     for ORZ021>029.
     Red Flag Warning from noon today to 9 PM PDT this evening for
     ORZ619-622-623.
     Fire Weather Watch from Tuesday afternoon through Tuesday
     evening for ORZ619-622-623.
     Fire Weather Watch from Tuesday afternoon through Tuesday
     evening for ORZ616.
     Heat Advisory from noon Tuesday to 8 PM PDT Thursday for ORZ023.

CA...Heat Advisory from noon Tuesday to 8 PM PDT Thursday for
     CAZ082>085.
     Excessive Heat Warning from noon Tuesday to 8 PM PDT Thursday
     for CAZ080>085.

Pacific Coastal Waters...Small Craft Advisory until 5 AM PDT Wednesday for
     PZZ350-356-370-376.
     Gale Warning until 5 AM PDT Wednesday for PZZ356-376.

DW/MAP/BTL