Wildfire in California, June 25 to 30, 2021

Area Forecast Discussion
National Weather Service Medford OR
401 AM PDT Fri Jun 25 2021

.DISCUSSION...

Record breaking heat is the main story through the weekend.
Temperatures will gradually warm up today breaking the triple
digits in some of our warmer valleys with slightly cooler
temperatures east of the Cascades and a cool upper 70's along the
Oregon coast. That warming trend continues into Saturday and
eventually reaches a crescendo on Sunday. During this time, we're
looking at high heat risk for many of valleys west of the
Cascades through the weekend into early next week. Heat risk
helps communicate an area's susceptibility to heat related
illness based on it's daily climatology. High heat risk suggests
vulnerable groups are at risk through the weekend if cooling
resources are not available. Because of this, an extreme heat
warning remains in effect for the entire forecast area, with
special emphasis on the valleys.

As for temperature records, all our inland climate sites(ie not
North Bend) are expected to break their high temperature records
on Sunday. The only one which may fall short is Alturas with a
record high of 99 set back in 2015, we're expecting 100 this
Sunday. In addition, Roseburg's highest June temperature record of
104 set on June 30th 1942 is expected to fall to our forecast
high of 110. Also, Medford's all time June high of 111 set back
on June 22nd 1992 is also expected to fall to our forecast high of
113. The national blend of models(NBM) high temperatures do have
a wide distribution for Roseburg and Medford, but it still shows a
60% to 70% chance of breaking those June records.

After Sunday, temperatures trend lower as the high shifts to the
east over Idaho. 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 seven
consecutive days above 100 degrees for Medford. This would rank
as the 6th longest streak of days above 100 degrees in Medford if
the forecast holds. The record is 10 set back in August of 1967.
Just for laughs or depressive thoughts, the NBM is indeed
forecasting 10 days at or above 100 degrees in Medford at this
time....

-Smith

.AVIATION...For the 25/06Z TAF Cycle...The marine layer has
compressed over the past several hours as high pressure builds over
the area. IFR cigs/visibilities are expected to continue along the
coast and into coastal valleys, with some clearing back to the
immediate coastline by late Friday morning or early afternoon. Low
clouds and visibility will move back onshore again late Friday
afternoon and evening. Over the remainder of the area, VFR
conditions will prevail through Friday under a drying and warming
atmosphere. Keene

&&

.MARINE...Updated 230 AM PDT Friday 25 June 2021...North winds
will gradually decrease this morning. There may be another round of
gusty winds and steep seas Saturday night into Sunday. Winds will
become southerly Sunday night into Monday as low pressure moves in
from the southwest. Northwest swell will build Tuesday, and a
thermal trough with increasing north winds may develop late Tuesday.
Keene/Sven

&&

..FIRE WEATHER...Updated 250 PM PDT Thu, 24 Jun 2021...
Convective activity, thus far, this afternoon, has only yielded a
handful of CG strikes, all in SE Modoc County. There have been some
healthy cells with plenty of in cloud rumbles across Lake and
Klamath counties in the Bly to Lakeview area, but no down strikes
have yet to be detected.

Model guidance suggests that the forecast remains on track for
lightning to increase over NorCal this afternoon and evening, and
for isolated thunderstorms in Klamath and Lake counties. The
majority of the model guidance suggests we'll see an uptick in
activity through about 5 PM PDT, and then a fairly rapid downward
trend in lightning coverage by about 7 PM PDT. There is a
possibility that the RFW might need to be extended out a little if
the later spectrum of the model solutions were to verify, but
lightning coverage will likely max out around 5PM PDT. Of note,
models suggest a shortwave moving through the area late this
afternoon that is likely to move storms along a bit faster and
spread them from the Medicine Lake area, across the Shasta Highlands
and probably into western Siskiyou County. This shortwave is
important because current shear is lacking for getting multi-
cellular thunderstorms, so what we've mostly seen, thus far, is
short lived cells, which are less likely to yield abundant lightning
than more organized multi-cells. Significant wetting rain will occur
with some cells, but strikes outside of storm cores will also occur.

Very hot, dry, and potentially unstable conditions are still
expected Friday into early next week, with record high temperatures
almost certain for many locations Saturday through Monday. Monthly
June high temperature records are likely to be broken, and there is
about a 30% probability that even all-time record high temperatures
could be threatened on or about Sunday/Monday.

It should be noted that a recent look at local Fire Weather Guidance
(FWG) and analogs suggest some pretty low afternoon RHs Friday
through Monday, as well as some moderate to poor ridgetop RH
recoveries, especially across the higher terrain centered over NW
California. The strong thermal trough Sunday afternoon-evening
through Tuesday also suggests gusty afternoon and evening winds
across the area. This all bears watching for some wind/RH
RFW's along with the building heat and drying fuels. ~BTL

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Excessive Heat Warning from 11 AM Saturday to 11 PM PDT Tuesday
     for ORZ023>031.

CA...Excessive Heat Warning from 11 AM Saturday to 11 PM PDT Tuesday
     for CAZ080>085.

Pacific Coastal Waters...Small Craft Advisory until 11 AM PDT this morning for PZZ376.