Heat in Oregon, June 11 to 12, 2019

Area Forecast Discussion
National Weather Service Medford OR
1030 AM PDT Tue Jun 11 2019

.Updated Aviation Discussion.

.UPDATE...It will be hot today, much higher than normal for this
time of year. Heat headlines remain in effect for much of the West
Side, and there have been no changes in the temperature forecast
since yesterday. Be sure to stay hydrated and cool out there today
and tomorrow.

No major changes are needed for this morning, other than to add
some areas of smoke to the valleys east and north of Crater Lake,
where smoke from controlled burns in the area have gathered due to
the overnight and early morning drainage winds.

Otherwise, the forecast area has clear skies and this will likely
continue until some cirrus begins to work north into the region
ahead of a weak upper level impulse tonight. This wave may be
enough to spark some showers late this evening and perhaps even
overnight along the Cascades, but with little evidence within the
convection models, there is a great deal of uncertainty on this.
Elevated instability is expected in the area, and the shortwave
may provide enough support to develop a few showers, but getting
things to come together just right will be difficult. Also, the
chances for isolated lightning are very low, but not zero. As a
result, have added isolated showers to the Cascades along and
north of Crater Lake for this evening and tonight, but kept
mention of thunder out.

For more details on this and the rest of the forecast, see the
previous discussion below. -BPN

&&

.AVIATION...For the 11/18Z TAFS...VFR conditions will prevail
through the TAF period. The exception will be along the coast and
just offshore where marine stratus is expected to develop with IFR
ceilings later tonight into Wednesday morning. The timing indicated
in the North Bend TAF shows lower conditions developing at 8z which
is in line with some of the guidance, but confidence on the timing
is low.

Also, please note that observations are not transmitting externally
from KOTH but the FAA has been notified and is working on this
problem. Since we are not receiving continual observations from
KOTH, we are not amending the KOTH TAF after initial issuance, and
we are continuing the AMD NOT SKED wording. -Petrucelli

&&

.MARINE...Updated 830 AM PDT Tuesday 11 June 2019...A thermal
trough along the coast will move inland today with winds and seas
lowering below advisory criteria through the afternoon. The thermal
trough will strengthen again Thursday with strong north winds and
steep wind-driven seas returning, persisting through the weekend.
Conditions will be near gale force south of Gold Beach and beyond 10
nm from shore.

&&

.FIRE WEATHER...Updated 200 AM PDT Tuesday 11 June 2019...Moisture
and instability move northward this afternoon with some cumulus
buildups over the higher terrain in Northern California, Cascades
and portions of the eastside. It will be hot once again, especially
for interior west side valley locations with triple digit readings
likely.

There are some indications for thunderstorm potential tonight and
Wednesday morning mainly west of the Cascades. An impulse moving
north into the area will bring energy and instability aloft, and
occasionally this means nighttime or morning thunderstorms. However,
our most useful suite of models show no signal for storms, and
really only one model is suggesting storms at this time (GFS). So,
we'll continue to monitor and see what changes in the upcoming suite
of data this morning.

The greater threat for showers and thunderstorms is on Wednesday
afternoon into Wednesday evening when we're anticipating a moderate
to heavy lightning event from the Cascades and Siskiyous south and
eastward. This lightning will come on the heels of a small, but
significant heat wave. In addition, gusty erratic winds are also
possible near thunderstorms.

The focus for thunderstorms Thursday afternoon and evening will be
in portions of Fire zones 624, 625 and portions of northern
California. Thunderstorm threats end after Thursday with some
cooling Friday into next weekend, but temperatures will still be
above normal. -Petrucelli/Keene

&&

.PREV DISCUSSION... /Issued 638 AM PDT Tue Jun 11 2019/

DISCUSSION...This week will easily be the hottest so far this year,
and we're expecting daily record high temperatures to be met or
exceeded today for several locations. A big upper ridge of high
pressure is centered just offshore this morning. A thermal trough,
a surface reflection of the very warm air mass will move
northerly and easterly, signaling the hottest day for inland
valleys and the north part of our coast, to include North Bend.
850mb temperatures (5000 ft temperatures--a good reading of how
warm the air mass is) will peak near 25C and this will be a daily
max for the Medford location. So, it's not surprising this will
translate to hot surface temperatures and records. We have daily
record high temperatures forecast for Medford, North Bend, Mount
Shasta City, and the Yreka area of 103, 80, 94, and 100 degrees
respectively.

As is often the case with these hottest days, there will be less-
than-normal wind in the typically-breezy valley locations, so relief
from the heat in the form of cooling breezes will be hard to come
by. We continue an Excessive Heat Warning and Heat Advisory for most
inland areas west of the Cascades. We recommend the following to
mitigate some of the potential impacts from this hot weather:

* 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.

* Take plenty of rest breaks in shade or air conditioning.

* Drink water before, during and after activities.

Tonight into Wednesday morning, a shortwave that's currently over
Central California will move north into the forecast area. Models
agree that the focus of energy will be west of the Cascades. Anytime
we have energy moving into the area at night, with some upper level
instability (which exists per forecast soundings and 700mb-300mb
Convective Available Potential Energy (CAPE)), we consider the chance
for nighttime thunderstorms. However, there's only one model that
points towards some thunderstorms, and that's the typically-overdone
precipitation field from the GFS, so we're leaving 10 percent
chances of precipitation tonight into Wednesday morning mainly from
Josephine, Curry, and Coos Counties. If any Convection-allowing
models (CAMs) start to depict thunderstorms, we'll likely introduce
the chance for thunderstorms.

Confidence increases for thunderstorms from the Cascades eastward
and Siskiyous south Wednesday afternoon. Additional energy aloft and
moisture will combine with moderate instability to bring
thunderstorms to those areas. Temperatures will cool some Wednesday
due to the big upper ridge axis shifting east of the area. Heat
warnings and advisories will continue through Wednesday because
afternoon readings will still be 15 to 20 degrees above normal for
this time of year. Afternoon breezes will be more noticeable so that
should at least provide a little relief Wednesday afternoon and
evening.

On Thursday deep westerly flow increases across the forecast area,
temperatures cool further, and thunderstorm chances are pushed
eastward to mainly Lake and Modoc Counties.

The general cooling trend with relatively stable conditions (no
thunderstorms) will likely continue through the end of the week.
Temperature trends will flatten over the weekend, but stable
westerly to northwesterly flow should continue through the weekend,
so no additional thunderstorm chances are expected.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Excessive Heat Warning from noon today to 9 PM PDT Wednesday for
     ORZ023>026.
     Heat Advisory from noon today to 9 PM PDT Wednesday for
     ORZ023>026.

CA...Heat Advisory from noon today to 9 PM PDT Wednesday for
     CAZ080-081.

Pacific Coastal Waters...Small Craft Advisory until 5 PM PDT this afternoon for
     PZZ350-356-370-376.