Heat Advisory 3, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
810 PM PDT Sat Jul 29 2017

.DISCUSSION...Our main concerns for the next week are heat and,
related to that, weather that will impacts fires and fire crews
around the area. Today will be the "coolest" day for most of the
forecast area through Friday at least. Temperatures today peaked
at about 5 degrees above normal for this time of year, and by
Wednesday afternoon temperatures will peak at about 20 degrees
above normal. An Excessive Heat Watch at NPWMFR continues to
highlight the scorching temperatures expected next week.

A few thunderstorms formed over extreme SE Lake County earlier, and
just east of Modoc County, but those have diminished and we don't
expect any more thunderstorms tonight. Smoke from many fires across
the area will impact various locales tonight, and we've focused on
Western Siskiyou, Modoc, Southern Lake, and NE Jackson Counties as
likely areas to see some tonight.

Tomorrow will feature, as already mentioned, hotter and drier
conditions with gusty afternoon winds along and west of the
Cascades. Generally lighter winds are expected east of the Cascades,
especially compared to normal summertime afternoon winds.

&&

.AVIATION...30/00Z TAF CYCLE... Along the coast...late tonight the
marine layer will return. Though it won't be as strong as this
morning, expect IFR to LIFR cigs and vis. There is some uncertainty
with timing, since lower conditions will depend partially on when
the offshore wind component diminishes.

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 western
Siskiyou County, Modoc County, and over the Cascades. -MSC/Sven

&&

.MARINE...Updated 238 PM PDT Saturday 29 July 2017...A thermal
trough in northern California will remain in place into next week
with north winds and steep to very steep seas. The thermal trough
will strengthen through early next week with gales beyond about 5 NM
from shore and south of Gold Beach. Meanwhile small craft conditions
will affect areas from Bandon south through Sunday evening. The
models suggest gales and small craft conditions could expand in
coverage Sunday night through Monday evening which will expand the
coverage area of gales and small craft conditions. Please see MWWMFR
for more details. -Sven/Petrucelli

&&

.FIRE WEATHER...Updated 330 PM Saturday 29 July, 2017...There is
a slight chance of thunderstorms this evening and Sunday evening
over the Warner Mountain region with strong outflow wind gust
potential. Also, very dry and unstable conditions are expected in
portions of fire zone 285 this evening including the July Complex
which could result in rapid fire spread.

Gusty northeast winds will be strongest at the southern portion of
the Oregon coastal range and in western Siskiyou County and will be
stronger than last night with gusts to 30 MPH. This will contribute
to moderate near and at ridge top humidity recoveries tonight.
Conditions will be similar on Sunday night. While not quite as
strong, northeast winds will remain gusty and recoveries will trend
worse Monday night and Tuesday night with locally poor humidity
recovery. While it isn't likely, there is a chance that conditions
in far southwest Oregon reach red flag warning criteria on Monday
night and Tuesday night. Offshore winds will be noticeably weaker
Wednesday night but recoveries will be nearly as poor as the
previous couple of nights.

Hot weather will escalate to record breaking heat Monday through
Friday with the hottest temperatures likely at mid-week. There is a
slight chance of thunderstorms over a wider area on Monday with weak
instability and moderate amounts of moisture aloft indicated to be
most substantial over Siskiyou and Modoc Counties into the southern
portions of Klamath and Lake Counties. The risk of thunderstorms
will decrease Tuesday as a ridge strengthens with warming aloft
limiting the convective potential. The risk of thunderstorms will
then increase late in the week with the development of a southerly
flow aloft. Activity on Thursday and Friday (especially Thursday) is
more likely over the Sierra Nevada, but cannot be completely ruled
out to extend into our area. By Saturday/day 7, an increase in
moisture aloft and at least slight cooling is likely as a trough
moves to the northern California coast. -DW

&&

PREV DISCUSSION... /Issued 257 PM PDT Sat Jul 29 2017/

DISCUSSION...Current satellite shows mostly clear skies over the
forecast area. Low clouds from this morning have burned off and
now cumulus is bubbling up over the higher terrain along and east
of the Cascades. Not expecting much more than these buildups as
the best moisture and instability are just to the east of the
area. However, there is marginal moisture and instability
lingering in the eastern portions of Lake and Modoc counties. It's
possible for some of the cumulus there to throw out a bolt or two,
so have left a slight chance of thunderstorms for those areas.

The big story for the week will the very hot temperatures and how
long they are supposed to last. A strong ridge will build over the
area bringing temperatures to 10 to 20 degrees above normal through
at least Thursday, possibly into next weekend. Valleys west of the
Cascades and in northern California are expected to be in the triple
digits. Overnight temperatures will be very warm as well and little
relief will be felt overnight with low temperatures dropping only
into the upper 60s to lower 70s. An excessive heat watch remains in
effect for this. East side valleys will get their share of hot
temperatures as well. Most locations will be in the upper 90s,
hovering around the century mark. Overnight temperatures will remain
warm there as well and have expanded the excessive heat watch to
account for places like Klamath Falls that usually cool down at
night.

This prolonged period of hot temperatures will bring the potential
for heat related illnesses. Unless you have to be outdoors this
week, remain in a cool place and be sure to check on those without
A/C. These hot temperatures will also stress outdoor animals and
livestock, so be sure they have shade and water available. Also, if
you plan to cool off in area rivers and lakes, remember the water is
still cold, especially compared to outside temperatures.

Another concern during this heat is the thunderstorm potential. Much
like today, another small threat exists for eastern portions of
Modoc and Lake counties. Again, parameters are marginal, but it's
still worth mentioning a slight chance. On Monday, as the ridge
begins to nudge west, the area of instability does as well, mainly
for most of Modoc and Lake counties and then portions of Siskiyou
and Klamath counties Again it's only a slight chance as moisture
isn't too abundant. Then as the ridge builds in further over the
area, instability decreases for Tuesday through Thursday.

Currently it looks like the heat will break on Friday and, as is
typical with the heat breaking, the thunderstorm threat returns and
covers a much broader area. It's too early in the forecast period to
pin down exact details, but it's worth noting that models are
showing active weather on Friday and Saturday, mainly east and south
of the Cascades and Siskiyous. /BR-y

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Excessive Heat Watch from Monday morning through Thursday
     evening for ORZ021-023>030.

CA...Excessive Heat Watch from Monday morning through Thursday
     evening for CAZ080>085.

Pacific Coastal Waters...Small Craft Advisory until 5 AM PDT Wednesday for PZZ356-376.
     Gale Warning until 5 AM PDT Wednesday for PZZ356-376.
     Small Craft Advisory from 11 AM Sunday to 5 AM PDT Wednesday for
     PZZ350-370.

NSK/MNF/SBN