985
FXUS66 KMFR 300421
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
921 PM PDT Sat Jun 29 2024

.DISCUSSION...

The only change made to the forecast was adding in fog along the
coast and over the coastal waters tonight. METAR observations are
already report visibilities down to 2 miles along the coast near
Crescent City and Florence. The fog and lower ceilings should
spread to other locations later tonight. A marine push should make
it into the Umpqua Basin with some lower ceilings making it till
sunrise. Otherwise, no changes other than the fog and sky cover.

Read the previous discussion for more information beyond tonight.

-Smith

&&

.AVIATION...30/00Z TAFS...Low clouds and fog will spread along the
coast late this evening and tonight, clearing to VFR in the late
morning. Areas of IFR/MVFR are expected to spread into the Umpqua
Basin to Roseburg early Sunday morning. These clouds will clear in
the late morning to VFR. Elsewhere, expect VFR across the area.
Smoke from a few wildfires could produce some locally low visibility
near those fires, otherwise the smoke will not be an issue near
terminals.
-CC

&&

.MARINE...Updated 800 PM Saturday, June 29, 2024...Winds and seas
will be lower through Sunday. However, areas from Brookings south
within about 15 NM of shore could observe brief and isolated
advisory level seas as winds peak in the afternoon, generating a
steep wind wave. If in this area, watch Buoy 27 to monitor
conditions in this area to be safe before heading out.

Later a very strong thermal trough is expected to develop next week
beginning Monday afternoon and lingering towards the end of the
week. The peak should be either Tuesday or Wednesday evening, and
the guidance is trending towards Tuesday; although very little drop
off in intensity is expected Wednesday. As for the wind speeds
expected during the peak of the thermal trough, the chance for gale
force wind gusts south of Cape Blanco is 80% or greater (90% plus
south of Pistol River) and this will drive very steep waves. There
is also a moderate (20-50%) chance that gale force winds develop
over the waters north of Cape Blanco and south of Cape Arago.
Confidence is low if these gusts will be frequent enough to warrant
any sort of Warning north of Cape Blanco, however. Comparing this
event to the past, this is getting into the top end of events, and
to summarize, this occurrence of the thermal trough northerlies will
not be one to mess with.
-CC/Hermansen

&&

.PREV DISCUSSION... /Issued 601 PM PDT Sat Jun 29 2024/

DISCUSSION...An approaching upper trough is bringing streaks of mid-
level clouds across the area. Cumulus clouds are also developing
over terrain east of the Cascades this afternoon. Slight (5-10%)
chances for thunderstorms still remain in the forecast for the
northern Klamath/Lake County border area this evening. The cumulus
field indicates that moisture is available, but the forcing
components aren`t very exciting. Some isolated thunderstorms are
probably the worst case scenario.

As the trough continues eastward on Sunday, similar seasonal
temperatures will continue across the area. While less moisture will
be available in the atmosphere, more energy will be present. Surface
CAPE amounts in the 200-400 J/Kg ranges will be present in Lake and
Modoc counties while some upper level vorticity will be present as
well. However, how these factors will line up has some uncertainty.
This results in some 10-15% thunderstorm and precipitation chances
for Lake and Modoc counties on Sunday evening into the night.

An upper ridge will develop in the wake of the upper trough,
bringing hot, dry, and windy conditions across the area through the
upcoming week. Chances for triple digit temperatures in the Rogue
Valley are up to 60-70% across Wednesday, Thursday, and Friday.
Other west side valleys will see similar temperatures. Other areas
will still see unseasonable warmth, with the mid 70s expected along
the Oregon coast and the mid 90s forecast east of the Cascades
through the middle and end of the week. Higher temperatures without
additional moisture will result in lower relative humidity amounts
(10-20% for inland areas), which will dry out any fuels that aren`t
already there. And afternoon winds will continue to develop in this
stable pattern.

These conditions do bring both personal health and fire safety
concerns. Gusty winds can easily transport sparks and embers to new
areas. And with additional daytime heating resulting in higher
nighttime temperatures, guidance suggests areas of Level 3 (High
Risk) or 4 (Very High Risk) of HeatRisk in the Rogue, Shasta, Scott,
and western Siskiyou Counties by the end of the week. While official
warning products haven`t been created yet, these outcomes have been
a constant feature and some amount of hazardous heat products looks
inevitable. These considerations are especially important given the
approach of the 4th of July, a day where people want to be outside
and to play with flammable objects.

There`s some uncertainty in a low pressure system moving over Canada
helping to flatten the ridge this weekend and possibly lowering
temperatures a few degrees. NBM probabilistic guidance does show
some uncertainty for temperatures to end the next weekend, with
"only" a 30% chance of 100 degree temperatures in Medford on July
8th. However, the Climate Prediction Center has the area under
areas of above average temperatures and below average
precipitation in the 8-14 Day and Weeks 3-4 outlooks. So while
there may be some details in the forecast yet to be determined,
hot and dry conditions look to continue for an unfortunate amount
of time. -TAD

FIRE WEATHER...Updated 200 PM Saturday, June 29, 2024...

..Very Hot and Dry Wednesday through Saturday...

There is a very small chance (around 10%) for thunderstorms east of
the Cascades this evening, particularly for the northern portions of
Klamath and Lake counties. We are unlikely to receive more than a
handful of lightning strikes, with weak lift, and a capping
inversion aloft.

As the next disturbance rotates around the base of a trough over the
Pacific Northwest, there will be less moisture available compared to
today, but a more favorable vertical temperature profile with
another day of seasonable surface temperatures, but cooler
temperatures at 500 mb. As such, there is a slightly higher
probability of thunderstorms Sunday afternoon and evening, over a
broader area...much of the east side with a focus for Lake and Modoc
counties.

Elsewhere, conditions will remain seasonable through Monday with
breezy afternoon winds. A strong warming and drying trend will begin
Monday night as high pressure builds in. This will bring moderate to
locally poor humidity recovery to ridges. The poorest recoveries and
hottest temperatures are expected from Wednesday morning into the
weekend, with critical weather conditions possible. There is concern
for both critically poor night-time ridge top humidity recovery
(mainly in zones 619 and 620, the higher terrain of Curry and
western Josephine counties), and also gusty afternoon winds
accompanying a very dry air mass. The limiting factor is likely to
be wind speeds, while the hot and dry aspect looks like a slam dunk
to occur.  -DW

&&

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

CA...None.

PACIFIC COASTAL WATERS...None.

&&

$$