FXUS66 KMFR 191541
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
841 AM PDT Fri Jul 19 2024

.DISCUSSION...A few adjustments were made to the forecast. The
main change was to fine tune the sky cover to better represent
the latest visible image and update the coverage of the areas to
patchy areas of smoke and haze from the various wildfires in
eastern Douglas County. Dry and hot weather continues today with a
dry stable southwest flow. Our next focus of concern will be this
weekend with the threat of thunderstorms returning. The first
threat of storms are still expected to be in northern Cal late
Saturday afternoon and evening, followed by nocturnal storm threat
west of the Cascades and portions of the eastside Saturday night.
For details on this, see the previous discussion below.


&&

.AVIATION...July 19/12Z TAFS...Along the coast and just offshore,
marine stratus is burning off with most of the coast showing clear
to mostly clear skies. VFR conditions are expected the rest of the
day, with marine stratus re-forming again this evening resulting
in IFR conditions.

Inland, VFR conditions will prevail through the TAF period. The
exception will be in the vicinity of the Trail fire and various
other fires in the vicinity of the Trail Fire in eastern Douglas
County where visibility could end up between 3-5 miles through
20z. This afternoon and tonight, visibility could be reduced
southeast of the fires in eastern Douglas County, including
northern Klamath County, then possibly down into Klamath Falls
later tonight resulting in MVFR visibility. -Petrucelli


&&

.MARINE...Updated 230 AM Friday, July 19, 2024...Weak low pressure
offshore has disrupted the thermal trough pattern. Weak winds and
low seas will persist into Friday morning. A weak thermal trough is
expected to return Friday and strengthen this weekend with the
strongest winds south of Cape Blanco. Advisory strength northerly
winds and steep seas will be present Saturday, then gales and steep
to very steep seas are possible early next week.
-Hermansen/Sargeant


&&

.PREV DISCUSSION... /Issued 343 AM PDT Fri Jul 19 2024/

DISCUSSION...High pressure resides over the SW U.S with low
pressure over the Gulf of ALaska. A weak trough is skirting north
up the PacNW coast. Fairly dry atmosphere over the area this
morning with the 00z Medford sounding revealing only .54" of
precipitable water. This is much drier versus the normal whereby
only 25 percent of days have shown .58" or less this time of year.
So, we're highly confident in the no-rain forecast.

After welcome cool morning temperatures area-wide generally in the
50s, we'll be heating up again to mid 90s to near 100 over the
western valleys and low to mid 90s east side. Not quite as hot as
a majority of days experienced thus far in July for the region,
but still 5 to 10 degrees above normal. That will change into
Saturday as highs increase to 10 to 15 degrees above normal for
the inland areas. This will be close to Heat Advisory conditions
for The Rogue and Illinois Valleys, and for areas east and south.
Leaning against the headline at this point considering the cooler
nighttime temps, the amount of heat we've experienced thus far in
July, and the short-lived duration of this episode - things will
taper off Sunday through Tuesday.

Another short wave will approach the region in the S-SW flow
aloft Friday and progress through on Saturday. This prompts slight
chances (generally 10-20%) for thunderstorms Saturday into Sunday.
We've left the forecast mostly in tact from the Thursday issuance.
No red flag expected for this episode. Confidence has generally
increased for storms Saturday and current forecast looks on track.
Things should be confined to the far east side Sunday as the wave
moves east. Drier SW flow over the region for Monday through next
week. Stavish

&&


FIRE WEATHER...No significant changes from Thursday forecast -
discussion issued 200 PM Thursday July 18, 2024...A dry and
stable southwest flow continues through Friday with no concerns
for thunderstorms. However, afternoon relative humidities will
trend lower for most interior locations with values in the single
digits for portions of the East Side through Friday along with the
typical gusty afternoon and early evening breezes. This will
result in near critical conditions for portions of Fire zones 624,
625 and 285, but were not expecting the combination of wind and
RH to result in Red Flag conditions.

The other concern for those involved in air attack on the various
fires in our area will be visibilities lowering to 3-4sm in the
vicinity of the Shelly and Trail Fires. The latest run of the HRRR
smoke fields show the smoke being transported east to southeast of
those fires late this afternoon and evening, therefore visibility
could be reduced to 4-6sm into early this evening. Tonight, as the
mixing height decreases, the smoke will settle and be confined to
around the fire perimeter of the fires resulting in MVFR visibility
between 3-5sm. Also smoke could also settle in the valleys adjacent
to the Shelly Fire.

There's still a concern for thunderstorm this weekend. Saturday, an
upper trough will move up from the south just off the California
coast and could tap into some monsoonal moisture with a southeast
flow aloft. At the same time, there's good agreement, the upper
trough will become negatively tilted Saturday afternoon into
Saturday night. Based in part on pattern recognition, this could be
problematic in that we could see storms break out mid to late
Saturday afternoon in portions of fire zones 280, 281 and 284.

Saturday night, the axis of the upper trough is still south of our
area which heightens the concern for nocturnal storms west of the
Cascades, and portions of the east side in Oregon Saturday night.
Many times the models will not show signs of unstable conditions
with this type of pattern, then the next thing you know something
breaks out of nowhere. The pattern that is setting up is one where
the instability is elevated, and thus the convection will be
elevated as well. Not saying this is a slam dunk, but at the same
time it cannot be discounted.

The upper trough axis shifts north during the day Sunday. Any threat
for storms could be confined to the early morning hours over the
northwest part of our area, then shifting north late Sunday morning
through Sunday afternoon with a drier and stable southwest flow
moving into the area. The exception could be in portions of Fire
zone 623, 624 and 625 where isolated storms are possible late Sunday
afternoon. Not convinced anything will happen in these areas, but
there are some signals suggesting it cannot be discounted either.

Monday, a dry and stable southwest flow will set up with any chance
for storms shifting east and northeast of our area. It will be
cooler with gusty afternoon and early evening breezes for the
interior westside valleys and east of the Cascades.

The rest of next week is pointing towards dry and cooler weather,
but afternoon temperatures will still be above normal for the
interior. However, the concern will shift towards moderate to locally
poor overnight recoveries for the mid slopes and ridges in southwest
Oregon and western Fire zone 280, and the typical gusty afternoon
and early evening breezes for the interior westside valleys and east
of the Cascades with low afternoon RH's. -Petrucelli

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...CA...None.

PACIFIC COASTAL WATERS...Small Craft Advisory from 2 AM to 11 PM PDT
     Saturday for PZZ356-376.

&&

$$