107
FXUS66 KMFR 152356
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
456 PM PDT Thu Aug 15 2024

.Updated Aviation Discussion.

.DISCUSSION...Cumulus continues to build and develop over north
central Klamath county this afternoon...with thunderstorm
development to begin within the next few hours. The short term
models are struggling with the initiation of thunderstorms in
Klamath and Lake counties this afternoon...as some indicate the
activity should have started by now...and some indicate that it
should start in the next few hours. Either way...confidence has
diminished a bit for this event.

Once any chance of thunderstorms ends this evening...we are
expecting a break in the activity on Friday ahead of an
unseasonably strong low impacting the region on Saturday.

An upper low will move south from the British Columbia coastline
toward the Pacific northwest coastline Friday morning into
Saturday. The upper low is forecast to be right off the southern
OR coastline Saturday afternoon into early Sunday morning...before
lifting north...but still keeping us in a trough pattern. The main
concern with this storm will be thunderstorms generally along and
west of the Cascades with strong gusty downdraft winds Saturday
afternoon and evening. In fact...the Storm Prediction Center has
this same area in a Marginal Risk for severe weather (with the
severe wind threat) on Saturday afternoon and evening.
Additionally...areas along and west of the Cascades are expected
to receive between a quarter and a half inch of rain. The east
side is not expected to receive much if any rain or
thunderstorms...however there will be gusty southwest winds...with
wind gusts upwards of 35 kts. Please see the fire weather
discussion below for more information on thunderstorm/wind threats
and our fire weather concerns.

Precipitation will move out of the area on Sunday morning...with
dry conditions through the rest of the forecast period. The
meteograms are in good agreement that we will remain dry after
this weekend...with the exception of a few members showing very
light precipitation possible mid week...however confidence is low.
There is quite a bit of uncertainty in the upper level pattern
mid next week as 20% of the clusters show the upper low off the
coast shifting north...keeping us dry with warmer
temperatures...where a little over 50% of the clusters showing
broad troughing over the Pacific Northwest with cooler temps and
the possibility of precipitation. Either way...continue to monitor
the forecast for the latest information.

-Riley

&&

.AVIATION...16/00Z TAFS...Along the coast and just offshore, marine
stratus is working down towards the coast and should result in
lowering ceilings at North Bend towards 3z, although there`s a
medium change the lower ceilings could arrive an hour sooner than
whats indicated in the TAF. Ceilings should remain VFR south of Cape
Blanco for most of the night with marine stratus forming between 10-
12z. Marine stratus will burn off with ceilings gradually increasing
late Friday morning into Friday afternoon.

Inland, VFR conditions will continue through the TAF period. The
exception will be in the vicinity of wildfires in central and
eastern Douglas and southern Lane county, where MVFR visibility
between 3-5 miles will be the predominate condition for most of the
TAF period. Smoke from these fires are likely to move into central
and northern Klamath County this evening and  could drift south
towards Klamath Falls late tonight. For now we kept VFR visibilities
at Klamath Falls, but it will be a close call between 10-14z as the
smoke drifts towards the airport.

The threat for thunderstorms is expected to stay northeast of the
forecast area. However an isolated storm or two are possible until 2-
3z this evening in northern Lake and Klamath County. -Petrucelli

&&

.MARINE...Updated 130 PM Thursday, August 15, 2024...Relatively
calm conditions are expected for the next several days with light to
moderate winds and seas remaining 6 foot or less. There will be a
slight uptick in winds Thursday into Friday south of Cape Blanco,
but they will remain below advisory levels. A rather strong upper
low for this time of the year will move into the waters Saturday and
will likely bring showers over the waters through early Sunday
morning. -Petrucelli/TAD


&&


.FIRE WEATHER...Issued 215 PM Thursday August 15, 2024...Upper
level troughing will remain the dominant weather pattern through
the forecast period. This will continue the trend of cooler than
normal temperatures and breezy afternoon winds. The two main fire
weather concerns on the horizon are thunderstorm potential today
and the development of a deep upper low offshore over the weekend
which could bring some strong winds and storms to the area.

First the thunderstorm potential...a shortwave trough is lingering
over the area today. With ample moisture and modest instability,
isolated to scattered thunderstorms are expected. The trough will
linger over the region this afternoon, however, and this will
provide a better opportunity for scattered thunderstorms over FWZ
624/625 due to daytime heating effects. Thunderstorms will once
again move north-northeastward into Oregon this afternoon and
evening. Although there has been a concern for smoke to be a
limiting factor on thunderstorm development, temperatures are
warming to near the convective temperature needed, so a Red Flag
Warning for abundant lightning on dry fuels remains in effect
through this evening. The only change to the Red Flag Warning is
that it was trimmed to end a few hours earlier because guidance has
showed the main concern of thunderstorms being north and east of our
area by then. Details can be found at RFWMFR. Storms are expected to
have some precipitation with them, but lightning strikes outside of
precipitation cores are possible and cause for concern.
Additionally, expect gusty and erratic winds near thunderstorms with
strong outflows that can travel a good distance from the originating
storm.

The atmosphere will stabilize some on Friday. There will be
lingering moisture and instability, but without a sufficient
trigger/forcing mechanism, it`s likely there will be some cumulus
buildups east of the Cascades and over the higher terrain.

A closed low moves near the southern Oregon coast late Friday into
Saturday, and the next thunderstorm concern will be on Saturday. New
guidance brings more confidence on measurable rainfall for west side
valleys. Between 5 PM Friday to 5 PM Saturday, there is now a 70%
probability to see 0.10" in Medford compared to last night`s
forecast of 50%. Roseburg increased slightly from 65% to 70% in the
same time period. Klamath Falls almost saw their probability for
0.10" more than double, going from 15% to 37%. Forecast soundings
support fast moving storms with 0-6 bulk shear in the 25-50 knot
range. The factor of these storms being fast movers suggests the
flash flooding threat is moderate if storms don`t over run the same
location quickly.

Winds and RH... The other element of concern with this low pressure
is the potential for strong south to southwest winds. Guidance
suggests gusts of 30-40 mph for areas east of the Cascades and in
the Shasta Valley on Saturday and Sunday afternoons. These strong
winds could combine with low humidities (which ultimately depends on
where precipitation chances occur) and result in critical fire
weather conditions. There is confidence that portions of 625
(including the Warner Peak Fire) will meet critical thresholds for a
Red Flag Warning, so have gone for a Fire Weather Watch in this area
from 21Z Saturday - 03Z Sunday, and more details can be found in
RFWMFR. Stay tuned for updates as subtle shifts in the position of
this low could have big changes on the forecast. /BR-y/Hermansen

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning until 8 PM PDT this evening for ORZ624-625.

     Fire Weather Watch from Saturday afternoon through Saturday
     evening for ORZ625.

CA...None.

PACIFIC COASTAL WATERS...None.

&&

$$