Wildfire in California, August 1 to 31, 2017

Area Forecast Discussion
National Weather Service Medford OR
1035 PM PDT Mon Jul 31 2017

.Updated aviation discussion.

.DISCUSSION...Current satellite and radar imagery show buildups
over northern California and areas east of the Cascades, all
mingled amidst lots of smoke from numerous wildfires. No lightning
strikes have been observed, but we maintain a slight chance of
storms mainly from the Cascades eastward. Our main concerns for
this week continue to be extreme heat and, related to that,
weather that will impacts fires and fire crews around the area.
Today's temperatures peaked at about 15 degrees above normal for
most areas. Afternoon high temperatures will rise further by about
10 degrees by Wednesday afternoon. An Excessive Heat Warning and
Heat Advisories at NPWMFR continue to highlight the scorching
temperatures expected this week.

Since the forecast for extreme heat is pretty much guaranteed, here
again are some actionable safety tips for this extreme heat:

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

* 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.

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

* Drink plenty of water.

Please see the previous discussion below for more details on the
heat, critical fire weather conditions, and thunderstorm potential
over the next several days.

&&

.AVIATION...01/06Z TAF CYCLE...At the coast and just offshore...The
latest satellite imagery is mostly absent of any marine stratus
(except for areas along the shore south of Cape Blanco) 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 morning through the day.

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 and Northern California late Tuesday
afternoon and evening. -Sven/SK

&&

.MARINE...Updated 200 PM PDT Monday 31 July 2017...A thermal
trough along the northern California coast will persist through
Tuesday morning with steep to very steep seas driven by north winds.
Seas are likely to trend lower Tuesday into Saturday with seas south
of Cape Blanco remaining steep into Wednesday. -DW

&&

.FIRE WEATHER...Updated 700 PM 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 are in
effect for today and Tuesday for this. Also Fire Weather Watches
have been issued for Wednesday through Thursday for gusty winds and
low humidity for much of the West Side. The combination of very low
humidity (day and night) and breezy conditions warrants a heads up
for this. 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 into this evening. On
Tuesday the models show increasing instability and moisture in
portions of Northern California and the Cascades with weak
shortwaves moving in these areas late Tuesday afternoon and evening
which could be enough to trigger a storm or two.

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.

Practically 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/SK

&&

.PREV DISCUSSION... /Issued 447 PM PDT Mon Jul 31 2017/

DISCUSSION...An unusually strong ridge aloft will build over the
west coast through Wednesday and persist through Thursday. At the
surface, the coastal thermal trough will move inland during the
daytime hours and move back toward the coast at night before
making a farther inland intrusion on Wednesday and Thursday. The
temperature forecast for this week has undergone slight adjustment
to reflect a consensus of the latest model data. A weak onshore
wind was enough to keep it cooler at Brookings today, but a Chetco
effect with downslope warming is expected to return tonight
through Tuesday into early Wednesday morning. With higher
confidence, the excessive heat warning and heat advisory products
/PDXNPWMFR/ that are now in effect have been extended beyond
Thursday evening and now end on Friday evening. Readings on Friday
will be similar to those of Today with the most extreme heat
forecast for Tuesday through Thursday, including highs in the 100
to 115 degree range for inland valleys and overnight lows also
staying well above normal. Daily records will be broken and all-
time high temperature records are possible. Wednesday is likely to
be the hottest day for most of our area, but it may be Thursday
east of the Cascades.

This heat wave will bring a dangerous situation to inland areas.
Take heed to be safe this week:

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

* 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. Avoid heat stress or heat stroke due to
  over-exertion.

* The best bet to find cooler temperatures is to head to the
  coast. Be careful of the opposite extreme if going to lakes or
  rivers. They are likely to be dangerously cold and Rivers may
  have strong currents. Wear a life jacket if swimming.

Another concern is the possibility of thunderstorms starting new
fires. The current visible satellite picture shows cloud cover
basically as forecast with more widespread coverage than in
the previous few days of generally low topped cumulus over the
higher terrain. There is little possibility of a thunderstorm
this evening...a few to several strikes are not entirely out of
the question. But, given extreme dryness at the lower levels, there
is even a smaller probability of any thunderstorms generating
measureable rainfall. There will be mainly just cumulus buildups
again on Tuesday and Wednesday with additional warming aloft
limiting the convective potential. But, there is a slight chance
accompanying the highest amounts of available moisture aloft in
Siskiyou County.

Model agreement begins to diminish on Thursday, but this is also
when the upper level pattern begins to shift. The GFS has more of
a southeasterly flow then the easterly NAM, and thus shows a
higher probability of increased mid-level moisture extending
northward from the Sierra Nevada into our area. Thus, the slight
chance of thunderstorms remains in effect solely for Siskiyou and
Modoc Counties with adjustment possible as Thursday draws nearer.

The probability of thunderstorms will increase late in the week
into early next week as an eastward shift of the ridge allows a
southerly flow to develop and gradually takes an edge off the
extreme heat...retreating to merely very hot with highs likely to
still be above 100 degrees for most west side valleys and the
lower 90s on the east side. While these thunderstorms would be
much more likely to produce at least moderate rainfall amounts
than any thunderstorms from now into Thursday, the much greater
frequency of lightning has a significant risk of starting new
fires.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Heat Advisory from noon Tuesday to 8 PM PDT Friday for
     ORZ021-027>030.
     Excessive Heat Warning from noon Tuesday to 8 PM PDT Friday for
     ORZ021-023-029.
     Excessive Heat Warning until 11 PM PDT Wednesday for ORZ022.
     Excessive Heat Warning until 8 PM PDT Friday for ORZ024>028.
     Red Flag Warning until 9 PM PDT this evening for ORZ619-622-623.
     Red Flag Warning from noon to 9 PM PDT Tuesday for ORZ619-623.
     Red Flag Warning from noon to 9 PM PDT Tuesday for
     ORZ616-620-622.
     Fire Weather Watch from Wednesday afternoon through Thursday
     evening for ORZ616-617-622-623.
     Heat Advisory from noon Tuesday to 8 PM PDT Friday for ORZ023.

CA...Heat Advisory from noon Tuesday to 8 PM PDT Friday for
     CAZ082>085.
     Excessive Heat Warning from noon Tuesday to 8 PM PDT Friday for
     CAZ083>085.
     Excessive Heat Warning until 8 PM PDT Friday for CAZ080>082.

Pacific Coastal Waters...Small Craft Advisory until 11 AM PDT
Wednesday for      PZZ350-356-370-376.      Gale Warning until 2 AM
PDT Tuesday for PZZ356-376.      Hazardous Seas Warning until 11 AM
PDT Wednesday for      PZZ356-370-376.

NSK/DW/SBN