Excessive Heat Watch 4, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
855 AM PDT Tue Jul 6 2021

.UPDATE...

We made a few changes to the forecast this afternoon. First and
foremost the probability of thunderstorms is very low in northern
Lake and Klamath Counties today. Instability is very low around
200 j/kg of convective available potential energy in a relatively
high shear environment. If storms do somehow form, the lightning
will be on the drier side given the dry layers below the storm
base. Some gusty winds are also possible if storms do eventually
form.

Also, fire activity looks muted in northern California this
morning. However, the Jack fire in Douglas County does look
active given the smoke around the fire. We adjusted the smoke in
the forecast accordingly for the rest of the day.

-Smith

&&

.DISCUSSION.../Issued 636 AM PDT Tue Jul 6 2021/

Low pressure moving northward west of the coast today along with a
northward surge of the monsoonal trough from the Great Basin will
bring an increase in afternoon and evening winds and some
instability to the forecast area today. High temperatures are
likely to be very similar to what was observed yesterday- about 10
degrees above the 1991-2020 normal period normals. There is a
slight possibility of dry thunderstorms over northern Klamath and
Lake counties late this afternoon and evening as an upper level
trough moves through with elevated moisture and instability.
Additionally,the latest 12Z NAM12 guidance suggests a storm is
possible in the Warners later today. The main concern for most of
the area will be afternoon and evening winds, strongest east of
the Cascades, where gusts of 25 to as high as 40 mph are possible.
For areas from the Cascades westward gusts of 20 to 30 mph are
generally expected. With the ongoing dry conditions, these winds
are likely to dry vegetation further and continue to yield
potential fire spread concerns.

Overnight into the morning, the Jack Fire- just east of last
year's Archie Creek fire burn scar- has been indicating a
substantial amount of heat. The Juanita Fire in Modoc County has
also been showing up on the Nighttime Microphysics channel
indicating active fire there.

All in all, after today's breezy to windy conditions fade
tonight, we're likely to see an inland surge of the marine layer
into the Umpqua Basin and better RH recoveries for most areas.
Wednesday and Thursday are expected to feature less wind,
slightly cooler temperatures, but also lower afternoon RH in some
areas.

Temperatures surge back upward Friday into the weekend, coming
down only slightly as we head into the following week. ~BTL

&&

.AVIATION...For the 06/12Z TAF Cycle...LIFR conditions from the
marine layer blankets the marine waters and locations along the
coast, including the coastal valleys and the Coquille Basin. Stratus
should burn back to the beaches later this morning, however, it's
possible that coastal sites remain under LIFR conditions through the
TAF period, especially south of Cape Blanco. Any clearing this
afternoon will likely be brief, with LIFR conditions expected to
return early this evening.

Over the remainder of the area...expect mainly VFR conditions with
areas of MVFR vsbys in smoke and haze across portions of southeast
Siskiyou County, southern Klamath, southern Lake and Modoc Counties
as well as in eastern Douglas County due to area wildfires.
Additionally, expect gusty winds across the region this afternoon
and evening.

The marine layer will deepen Tuesday evening, so we expect a push of
stratus farther inland Tuesday night that may affect more of the
Umpqua Basin, perhaps even at Roseburg. -Spilde/BR-y

&&

.MARINE...Updated 130 AM PDT Tuesday 6 July 2021...The thermal
trough will weaken today, allowing the gusty north winds to ease and
seas to subside by this afternoon. These improved conditions will
continue into Wednesday, but will be brief as the thermal trough
rebounds Wednesday afternoon. Gusty north winds increase again
Wednesday afternoon and evening and persist into the weekend. This
will bring the return of steep to very steep seas, especially south
of Cape Blanco. /BR-y

&&

.FIRE WEATHER...Updated 630 AM PDT Tuesday, 6 July 2021... Today
will be a critical fire weather day for areas east of the Cascades
and a day of elevated concern for much of the rest of the
interior. Gusty winds and low RH are expected along with a dry and
unstable air mass above the surface indicated by Haines 5-6
conditions from the Rogue Valley and northern California eastward.
A Red Flag Warning is in effect from 2-8 PM PDT for much of FWZs
284 and 625, all of FWZ 285, and most of FWZ 624. There is also a
slight possibility of dry thunderstorms across northern Klamath
and Lake counties as an upper level trough with limited moisture
swings in.

Conditions cool some Wednesday and Thursday in the wake of the
low, but afternoon RHs are likely to lower. Easterly winds later
this week mean lesser recoveries at night as heat builds yet
again. ~BTL

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning from 2 PM this afternoon to 8 PM PDT this
     evening for ORZ624-625.
     Heat Advisory until 11 PM PDT this evening for ORZ026.
     Red Flag Warning from 2 PM this afternoon to 8 PM PDT this
     evening for ORZ622.

CA...Red Flag Warning from 2 PM this afternoon to 8 PM PDT this
     evening for CAZ284-285.
     Heat Advisory until 11 PM PDT this evening for CAZ080-081.

Pacific Coastal Waters...Small Craft Advisory until 11 AM PDT this morning for
     PZZ350-356-370-376.