923
FXUS66 KMFR 261137 AAA
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
435 AM PDT Wed Jun 26 2024


Updated Avaition Discussion

.AVIATION (12Z TAFs)...

IFR conditions have spread along the coast. Light drizzle this
morning may result in local LIFR and there is a small chance (<20%)
for some light precipitation tonight into Thursday morning along the
coast as well. Inland of the coastal mountains, expect mainly VFR
conditions. Some areas of MVFR/IFR may develop this morning and
again this evening in the Umpqua Basin, mainly northwest of
Roseburg. Another breezy/gusty day is expected this afternoon and
evening ahead of an incoming front.

-CC

.DISCUSSION...Satellite imagery early this morning shows a plume
of mid-level moisture streaming northeastward across norCal and
into portions of southern Oregon. There is just enough elevated
instability to touch off some showers with very high cloud bases.
Precipitation falling from these clouds is mostly aloft (virga)
due to a very dry sub-cloud layer. While a few drops have managed
to reach the ground here and there, we`ve been hard-pressed to
find any reporting stations with more than a trace. Lightning has
been sparse beneath this moisture plume, but in the last hour or
so, one stronger cell developed near Newell in NW Modoc County and
was able to generate a few CG lightning flashes. This has some
implications with respect to fire weather given expected strong
winds and low RH this afternoon/evening. More on that below. The
good news is that this will be pushing out of the area with most
activity and the risk of lightning ending by 8 or 9 am.

Meanwhile, off to the west, a deeper push of marine stratus is
impacting all of the coast and has overspread much of interior
Coos County. It`ll continue to advance inland through the early
morning hours reaching portions of the Umpqua Basin (maybe
Roseburg) and the Camas Valley. This marine layer is resulting in
some mist/drizzle in places along the coast and will continue to
do so through about 8 or 9 am. The clouds should break up some
late this morning and this afternoon as a strong upper trough
offshore heads toward western Washington. This will send a mostly
dry cold front onshore that will move rapidly south and east of
the area by this evening. Overall, today will be cooler for all
but the far SE part of the CWA. Inland areas will average 5-15F
lower than yesterday, with highs only in the mid 80s here in
Medford. The main impact today will be the winds, which will be
gusty this afternoon and evening, especially east of the Cascades
and in portions of northern California. SW winds in those areas
shift to WNW during the evening, but will be generally from a NW
direction for areas west of the Cascades. Gusts of 30-35 mph will
be common, but could reach 40 mph at some of the more exposed RAWS
locations. This will result in fire weather concerns as any new
or existing fires will spread rapidly due to the strong winds. Winds
subside this evening as the pressure gradient weakens and the
core of the upper troughs pushes into northern Idaho by Thursday
morning.

We expect another strong marine push tonight into Thursday
morning west of the Cascades with some cloud-cover likely spilling
over the Rogue-Umpqua Divide and into the Rogue and Illinois
Valleys. Some light rain and/or drizzle/mist are possible along
the coast and into portions of Douglas County again during this
time frame. The clouds likely bank up against the Siskiyou
Mountains Thursday morning, then break up during the day. Thursday
likely will be the coolest day of the forecast period with highs
in the upper 70s and low 80s for the valleys west of the Cascades
and in the 70s over the east side. Most mountain locations and the
coast will have highs in the 60s.

Short wave ridging will arrive on Friday providing mainly sunny
skies and a warmer afternoon inland. Still could be some marine
stratus at the coast in the morning, but these should break up as
northerly winds turn gusty again there. Winds will be slightly
more offshore (northeasterly) though around Brookings, so we`re
looking at highs in the low 70s down there.

The next upper trough will move toward the PacNW Friday night and
onshore Saturday into Sunday. Another mostly dry frontal passage.
Wash, rinse and repeat, it seems. So, expect another period of
increased afternoon/evening breezes, highest east of the Cascades.
But, this should keep temperatures from deviating too much from
normal levels. Any precip would be associated with the deepening
marine layer and primarily focused across NW sections of the CWA.

Heading into the 1st week of July, nothing stands out as earth-
shattering weather-wise. We`ll maintain the pattern that we`ve
been in for a while now with some potential for upper ridging in
NorCal around Wed/Thu, which would allow things to warm up. Even
so, model guidance wants to continue bringing troughs into the NE
Pacific and even the PacNW at times, which will keep the real hot
stuff to the south and east (where it should be!) and a generally
unfavorable pattern for thunderstorms. -Spilde


&&

.MARINE...Updated 230 AM Wednesday, June 26, 2024...Relatively
calm conditions are expected through at least Thursday morning. A
weak front will push through the region today, bringing a deep layer
of low clouds along a chance of showers or drizzle. A return of
gusty  northerly winds is expected late Thursday into Friday night,
with steep seas likely south of Port Orford. Gusty northerly winds
and steep seas may begin late Thursday afternoon into Thursday
evening, then increase on Friday. Models indicate small craft
advisory level conditions are likely during this period.  Another
front and deep marine layer are likely to disrupt the pattern, with
improved conditions Saturday afternoon through Sunday. -CC


&&

.FIRE WEATHER...Mid-level moisture will continue to advance
northeastward early this morning, but most of this should shift to
the north and east of the area by around 8 or 9 am. While there
have been isolated showers/virga with some of this moisture, most
precip has had a tough time reaching the ground. In addition, and
mostly as expected, thunderstorms have been very sparse beneath
this moisture plume, but in the last hour or so (around 2 am) one
cell materialized over NW Modoc County near Newell. It managed a
few CG lightning flashes and there was one in extreme SE Lake
County as well. A slight chance of thunder still exists until
just after sunrise, but then that risk ends. Our biggest fire
weather concern today will be the ramp up in SW winds expected
east of the Cascades and portions of northern California this
afternoon in combination with low humidity. The strong upper
trough heading into Washington will induce a strong pressure
gradient across the area and good vertical mixing will tap into
the increased mid-level flow. SW winds over the east side and in
NorCal will be 20 to 30 mph this afternoon with gusts to 40 mph.
There is a low probability of winds exceeding 40 mph at some of
the more exposed RAWS locations. Overall, expect minRH values this
afternoon in the 10-15% range for far east side areas. A Red Flag
warning is in effect from noon until 8 pm PDT for strong
winds/low RH for FWZs 624/625 in Oregon and 285 in California.
Any new fire starts or existing fires will have the ability to
spread rapidly. Breezy winds are likely most everywhere else, but
should also be accompanied by slightly higher RH (at least
compared to yesterday). Much better humidity recoveries are
expected tonight for all areas with another deep marine push to
bank up against the Cascades/Siskiyous. We`ll get a break on
Thursday without much wind and higher humidity, though expect
fairly typical breezes to develop in the afternoon. It will warm
up again Friday with gustier winds expected again over the
weekend, especially east of the Cascades. -Spilde

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning from noon today to 8 PM PDT this evening for
     ORZ624-625.

CA...Red Flag Warning from noon today to 8 PM PDT this evening for
     CAZ285.

PACIFIC COASTAL WATERS...None.

&&

$$

MAS/CC/JWG