787
FXUS66 KMFR 112344
AFDMFR

Area Forecast Discussion National Weather Service Medford OR 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


&&

.FIRE WEATHER...Updated 200 PM PDT Thursday, July 11, 2024...


...Red Flag Warning in effect for Gusty Winds and Low RH from 2 pm
until 8 pm pdt Friday for portions of Fire Zones 624 and 625 in
Oregon and Fire Weather Zones 284 and 285 in California...

...Fire Weather Watch in effect Saturday afternoon into Sunday
evening for abundant lightning on dry fuels for Fire Weather Zones
624 and 625 in Oregon and Fire Weather Zones 284 and 285 in
California...

The immediate short term concern will by gusty winds and low
relative humidity for portions of the eastside Friday afternoon and
early Friday evening. Models guidance is consistent in showing
stronger winds at the surface during this time with relative
humidities actually a couple of ticks lower than whats expected
today. This in combination with slightly stronger winds aloft and
increasing instability will allow the stonger winds aloft to
transfer near or at the surface. It was a close call for critical
conditions to be met in Fire zones 280 and 282. However, the extent
of the smoke from the Shelly Fire in Fire Zone 280 should be enough
to put a cap on the magnitude of the winds Friday afternoon. For
Fire Zone 282, winds just aren`t there, but we will have the evening
shift take another look at this, and it`s possible they could be
added to the existing warning. Stayed tuned.

The next item of concern is thunderstorms for this weekend. A weak
upper low currently off the southern California coast will slowly
move north over the next few days. As it does, it will tap into some
monsoonal moisture that will get transported up towards our area.
The main question for Saturday will be amount of mid level moisture.
However, given we will have had hot temperatures for the past 10
days has allowed fuels to become very dry. Therefore, even isolated
lightning will be very efficient in causing new fire starts.

Out of the two days (Saturday and Sunday), Sunday could be the more
favorable day for storm activity because mid level moisture will be
higher as the upper low moves closer to our area which will tap into
even more monsoonal moisture in addition to a stronger trigger and
generally higher CAPE values. Not only will the storm activity be
higher, but the coverage area of storms could expand west to include
portions of Fire Zones 280, 281, 621, and possibly the south end of
Fire zone 623. For now we`ll hold off on issuing a Fire Weather
Watch for these areas given were still a few days out, but it`s
possible a watch will expand these areas by this time tomorrow.

The reason for the Fire Weather Watch for Fire Zones 624, 625, 284
and 285 for both Saturday and Sunday is because confidence is higher
for storms to affect these areas both days. Even though the watch
goes from Saturday afternoon into Sunday evening, the best chance
for storms will be during the afternoon and early evening hours with
nothing expected later in the evening Saturday through Sunday
morning.

It also should be noted that for both Saturday and Sunday, but
especially Saturday, any storms are likely to be high based and
result in little if any rainfall reaching the ground. -Petrucelli


&&

.AVIATION...12/00Z TAFS...Gusty northerly winds persist along the
Oregon coast north of Cape Blanco this afternoon and are likely to
continue through the TAF period. Gusts up to 35 kts have been
observed at North Bend, with gusts up to 44 kts measured between
North Bend and Bandon. Marine stratus should return tonight, with
areas of IFR and LIFR levels continuing into late Friday morning.

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 230 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


&&

.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.

&&

$$