Excessive Heat in Oregon, June 26 to 30, 2021

Area Forecast Discussion
National Weather Service Medford OR
829 AM PDT Sat Jun 26 2021

.UPDATE...The heat is on, but it is not the only game in town. The
thermal trough, which extends along the coast all the way north
to Washington, will slowly begin its trek to the east today, and
this will bring us record breaking heat for the next few days.
That is our major concern for this forecast period, but we are
also keeping an eye on the potential for thunderstorms next week
as monsoonal moisture creeps up from the south. This would be a
typical scenario following a heat wave such as this one, and
models continue to trend towards the idea of increased
thunderstorm chances, especially east of the Cascades, beginning
as early as Tuesday evening, but more likely a bit later in the
week. More information on the heat and the thunderstorm potential
can be found in the previous discussion below.

Otherwise, only a few changes were needed to update the forecast
this morning, mainly to bring things in line with the current
satellite observations which depict the marine stratus along the
coast pushing offshore and dissipating ab it earlier than
expected. -BPN

&&

.AVIATION...For the 26/12Z TAF Cycle...LIFR to IFR low clouds and
fog extend across the coastal waters and along shore, and farther
onshore into the Coquille and lower Umpqua valleys. Coastal
conditions will slowly begin to improve after sunrise. LIFR will
persist over much of the waters and immediate coast, but mainly VFR
is expected in coastal valleys from late morning through the
afternoon. Another surge of stratus into the coastal valleys is
expected during Saturday evening. Elsewhere, VFR conditions will
prevail for inland areas through Saturday evening. -DW/Sven

&&

.MARINE...Updated 800 AM PDT Saturday 26 June 2021...Offshore high
pressure will persist through Saturday night, but stratus and fog
eddies will produce southerly winds at times along the southern
Curry County coast. North winds will increase Saturday night into
Sunday as the thermal trough expands north. South winds will likely
develop Sunday as an offshore low moves north. The thermal trough
will strengthen along the coast Wednesday, and this will bring
strong north winds and steep to very steep seas to the area,
especially south of Cape Blanco.

&&

.PREV DISCUSSION... /Issued 402 AM PDT Sat Jun 26 2021/

DISCUSSION...

The two warmest and most impactful days of this heatwave are upon
us this weekend as temperatures push well into the 100's within
the inland valleys. For today, we're looking at Medford tying a
record of 107 set back in 2015 with all our other climate sites
coming within 1 to 2 degrees of their respective records. With
such warm daytime high temperatures, overnight low temperatures
will be in the lower 70's west of the Cascades and lower 60's east
of the Cascades. These two factors will begin to create heat
stress in groups without access to cooling facilities.

The situation won't improve on Sunday, which will likely be the
warmest day over southern Oregon and our area of northern
California. Latest model guidance is predicting a high temperature
of 114 in Medford, 113 in Roseburg, 101 in Klamath falls and
Alturas, 102 in Mount Shasta City and finally 109 in Montague, all
breaking their respective high temperatures records for the 27th.
As for all time high records, Roseburg is expected to break their
all time high temperature record(109) with Montague tying(109)
and Medford coming within 1 degree(115). Those forecasts should
show how anomalous this event is, especially with it occuring in a
statistically cooler time of summer compared to late August, the
statistically warmest time of the year. It's a broken record
again as lows in the mid 70's Sunday night offer very little
relief to those without cooling facilities.

After Sunday, temperatures trend lower as the high shifts to the
east over Idaho and the thermal trough weakens and shifts inland.
However, temperatures are still expected to remain above 100
through the forecast period. To put an emphasis on the longevity
of this heat, we are currently forecasting 8 consecutive days
above 100 degrees for Medford, with one already occuring
yesterday. With 9 days above 100, this would rank as the 3rd
longest streak of days above 100 degrees in Medford if the
forecast holds. The record is 10 set back in August of 1967. This
record could be met or broken by the end of next weekend, with the
bulk of model guidance continuing the heat through their full 10
day forecast term. High clouds from thunderstorms might be the one
thing that throws a wrench in this temperature streak.

It should be noted that several ensemble members, and a few of
the deterministic model runs, are trying to push monsoonal
moisture into the region by Wednesday next week. The national
blend of models probability of thunder is around 15 percent on
Wednesday afternoon east of the Cascades. This low probability of
thunder appears to continue Thursday and Friday east of the
Cascades as this monsoon moisture moves north.

-BPN/Smith

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Excessive Heat Warning until 11 PM PDT Thursday for ORZ023>031.

CA...Excessive Heat Warning until 11 PM PDT Thursday for CAZ080>085.

Pacific Coastal Waters...Small Craft Advisory from 11 PM this evening to 8 PM PDT Sunday
     for PZZ356-376.