782
FXUS66 KMFR 120521
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
1021 PM PDT Thu Jul 11 2024

...Updated AVIATION discussion...

.DISCUSSION...The forecast is on track for tonight. Officially,
the streak of triple digit temperatures did end today as
Medford`s observed high only reached 99 degrees. While high
temperatures remained about the same across northern California
and southern Oregon, nighttime lows will generally be cooler than
last night`s. Effective nighttime cooling does help to alleviate
heat illness potential somewhat, but current temperatures are
still warm enough to be hazardous to vulnerable or unprepared
individuals.

Warm temperatures continue across the area on Friday. A
combination of gusty winds and low daytime humidity will pose
fire weather risks for areas east of the Cascades on Friday
afternoon and evening. Please see NPWMFR and the fire weather
discussion below for more details. -TAD

&&

.AVIATION...12/06Z TAFS...Gusty northerly winds persist along the
Oregon coast north of Cape Blanco this evening and are likely to
continue through the TAF period. Gusts approaching 40 kts have been
observed at North Bend. Marine stratus has brought IFR levels to the
Oregon coast north of Cape Blanco, with periods of LIFR possible
early Friday morning. Levels could rise to MVFR or VFR late Friday
morning, with lower ceilings returning Friday evening.

Inland areas are generally expected to remain at VFR. Smoke from
fires in western Siskiyou and central Jackson counties may locally
lower visibilities. -TAD

&&

.MARINE...Updated 800 PM Thursday, July 11, 2024...A thermal
trough will continue to bring moderate to strong north winds to all
waters through this weekend. Gale force winds are expected at times
south of Cape Blanco along with very steep, hazardous seas through
Friday night. Peak winds and seas are expected this evening and
again Friday evening. Elevated winds and seas continue Saturday and
gradually ease on Sunday, but some amount of disturbed seas will
persist into next week. -Spilde/Smith

&&

.FIRE WEATHER...Issued 300 PM Wednesday July 10, 2024...

...Near critical fire weather conditions possible through at least
this weekend...

Hot, breezy, low humidities, and occasional unstable afternoon
conditions will persist through this weekend, and this will lead to
near critical fire weather conditions. Additionally, we have a
chance for thunderstorms this weekend, mainly across the eastside.

Wind speeds are not too impressive this week, but they certainly
will be on the breezy side around 10-20 mph, with speeds becoming
more of a concern for Red Flag conditions by Friday over the
eastside and parts of Siskiyou County. Single digit RH values are
also forecast this week during the afternoon hours across the
eastside and some isolated westside valleys like Northern
California. These factors, on top of this prolonged drying stretch
will result in elevated to critical fire weather conditions nearly
every day this week. This afternoon and tomorrow afternoon may fall
just short of actually reaching those critical thresholds due to the
wind. While no official warnings are out now, it will be very
borderline today and tomorrow afternoon for fire weather conditions,
so the threat is there even if we aren`t hitting "criteria".
Conditions worsen as the week progresses, and we will likely see Red
Flag Warnings coming to fruition as early as Friday.

For the thunderstorm potential, it should be noted that the trend
stay the same from yesterday for both Saturday and Sunday. We were
seeing slight increases early in the week, but those trends have
flatlined. A lot will depend on how a ridge of high pressure sets up
over the Four Corners region as this will direct monsoonal moisture
northward. There is about a 10-20 percent chance for isolated
thunderstorms both Saturday and Sunday.

-Guerrero

&&

.PREV DISCUSSION... /Issued 444 PM PDT Thu Jul 11 2024/

..Updated AVIATION discussion...

DISCUSSION...High pressure responsible for the recent day`s
oppressive heat has weakened some and shifted to the southeast, now
centered over the Great Basin region. This will result in slightly
cooler temperatures for the area, most noticeable west of the
Cascades where zonal flow will keep temperatures 5 to 10 degrees
above normal. East of the Cascades and across northern California,
high pressure will have more of an influence and maintain high
temperatures 10 to 15 degrees above normal. Additionally, overnight
temperatures will remain 5 to 15 degrees above normal, which will
limit relief from the daytime heat. A Heat Advisory remains in
effect for much of the area away from the coast and south of the
Rogue-Umpqua Divide, with an Excessive Heat Warning continuing for
western and central Siskiyou County. These headlines are in effect
through Saturday evening, and details can be found at NPWMFR.

Air quality remains largely in the good category across the region,
except in the vicinity of the Shelly and Salt Creek Fires where air
quality is worse. This is expected to remain the case as we don`t
expect a significant shift in the weather pattern that would bring
smoke in a different direction. Though we don`t expect a significant
shift in the pattern, there will be subtle changes through this
weekend that will bring some enhanced fire weather concerns. More
details can be found in the Fire Weather Discussion below, but the
two main concerns are gusty winds and low daytime humidities on
Friday and the chance for thunderstorms on Saturday and Sunday, and
possibly into early next week.

As previously mentioned, zonal flow will set up over the Pacific
Northwest through the weekend and our area will be on the southern
periphery of the zonal flow as well as on the northwest periphery of
strong high pressure over the Great Basin region. Meanwhile, weak
low pressure off the coast of California will become more organized
today into the weekend. This will induce southerly flow over the
area, and allow for some unstable and moist air to filter into the
region this weekend. A mid level jet associated with this low will
move over the region on Friday, and this will bring strong gusty
winds to the area, especially east of the Cascades where gusts of 25
to 35 mph will be common. This combined with low daytime humidities
will lead to conditions conducive to the rapid spread of any new or
ongoing fires. Please see the RFWMFR for more details.

With high pressure centered over the Great Basin and low pressure
off the coast of California, this is a classic thunderstorm pattern
for our region. The mid-levels remain too dry for thunderstorm
development on Friday, but as southerly flow continues into Saturday
and Sunday, the mid-levels will moisten up and thunderstorm chances
enter the forecast on Saturday. For Saturday, current guidance keeps
isolated thunderstorms to areas east of the Cascades. Instability is
pretty weak in this area and moisture is marginal, but shortwaves
passing through in the zonal flow could be enough of a trigger to
kick a few storms off on Saturday. As we head into Sunday, moisture
increases and instability also increases. Guidance also shows a
subtle westward shift of the ridge/low pressure pattern, which could
lead to some storms developing over western Siskiyou County and
maybe even over the Siskiyous. Confidence in the westward extent of
thunderstorm potential is low at this time, and will be interested
to see how high resolution models resolve this pattern once we enter
that timeframe.

Early next week, guidance shows thunderstorm potential possibly
continuing through the first half of the week, with the threat
shifting east of the Cascades after Sunday. The low pressure off the
California coast will open up and get swept into the westerlies
early next week, and bring an end to thunderstorm potential around
mid-week as drier, more stable southwest flow returns to the region.
/BR-y

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Heat Advisory until 9 PM PDT Saturday for ORZ024-026-029>031.

     Red Flag Warning from 2 PM to 8 PM PDT Friday for ORZ624-625.

     Fire Weather Watch from Saturday afternoon through Sunday
     evening for ORZ624-625.

CA...Excessive Heat Warning until 9 PM PDT Saturday for CAZ080>082.

     Heat Advisory until 9 PM PDT Saturday for CAZ083>085.

     Red Flag Warning from 2 PM to 8 PM PDT Friday for CAZ284-285.

     Fire Weather Watch from Saturday afternoon through Sunday
     evening for CAZ284-285.

PACIFIC COASTAL WATERS...Small Craft Advisory until 5 PM PDT Sunday
     for PZZ350-356-370.

     Gale Warning until 8 AM PDT Saturday for PZZ356-376.

     Small Craft Advisory from 8 AM Saturday to 5 PM PDT Sunday for
     PZZ376.

&&

$$