005
FXUS66 KMFR 160602
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
1102 PM PDT Mon Jul 15 2024

Updated AVIATION Section

.DISCUSSION...Radar imagery is showing a few lingering showers
across southern Oregon and northern California, although any
precipitation actually reaching the ground would be exceptionally
light. Dry air at the surface (as indicated by an inverted V
sounding) brought about an unusual recipe for storms where
downdrafts reached the surface and traveled far distances away
from the storm. This lead to many reports of tree branches
breaking and downing power lines, tree limbs falling onto homes,
and the firefighters camp at the Salt Creek Fire being heavily
disrupted across the Rogue Valley this afternoon and early
evening. Winds were not exceptionally strong, but with drought
stressed trees with leaves; it is easy to see storms like these
produce winds to fell limbs and otherwise diseased trees. That
being said, we did report a 59 mph wind gust at the Montague
airport this afternoon and a 48 mph gust at the Medford airport.

In general, we expect the thunderstorm threat to be mainly over
for tonight. Am making no changes to the forecast at this point,
but will need to evaluate whether the fire weather watch for the
northern portion of our area along and east of the Cascades should
become a Red Flag Warning. In other news, temperatures will be
hot again tomorrow, and will continue the heat advisory for West
Side Valleys in Oregon. Please see the previous discussion below
for more details on the forecast in full. -Schaaf

&&

.AVIATION...16/06Z TAFS...Thunderstorms have ended across the area
late this evening. It should be quiet for most of the remainder of
the night. However, another surge of mid-level moisture and elevated
instability will move in Tuesday morning and overspread the area
Tuesday afternoon. This will bring another round of isolated to
widely scattered thunderstorms. Once again, these cells will have
high bases and very dry sub-cloud layer, so this will create the
risk for strong outflow winds that can propagate a very far distance
from the storms themselves. Wind gusts could be 35-45 kt in the
stronger cells. And, with any thunderstorm, there is a risk of cloud
to ground lightning. These could pop up just about anywhere, but are
most likely in an arc from northern Douglas County down to the
Warner Mtns in Modoc County. Gusty winds are likely Tuesday
afternoon/evening without thunderstorms in the Shasta/southern Rogue
valleys (25-30 kt).

Marine stratus is impacting the coast and will bring IFR/LIFR to
North Bend overnight into Tuesday. With a bit more onshore flow,
expect stratus to be a bit more stubborn to break in some areas,
especially along the south coast. Don`t think convection inland will
materialize at the coast, but there is a low chance (10%) that a
cell drifts back toward the coast (northern Coos) Tuesday afternoon.

Main visibility reductions with the Shelly fire will be in the
immediate vicinity of the fire. Otherwise, VFR will prevail in most
areas for the next 24 hours. -Spilde

&&

.PREV DISCUSSION... /Issued 516 PM PDT Mon Jul 15 2024/

DISCUSSION...Well-heated atmosphere combined with the low off the
northern California coast has resulted in isolated thunderstorms
from western Siskiyou county extending east and northeast to Modoc
and Lake county. Gusty outflow of 50-60 mph can be expected with
any storms (Recent Montague METAR ob and Juniper Creek Raws ob)
and expect any activity to remain south and east of Medford this
afternoon and evening. Hi-res models continuing to show the
atmosphere too dry on the west side to support storms over here
even if cells migrate into the area or get initiated by an
advancing outflow boundary. Activity area-wide should die off
after 9pm.

The upper low off the coast will lift northward on Tuesday with a
short wave wrapping from SW to N-NE across the CWA. we expect to
see a 20-30 percent coverage of showers and thunderstorms develop
in advance of the wave from an area north of Medford to eastern
Douglas county and across the east side. Much of the activity
across the Cascades and west should progress north of the CWA by 5
or 6 pm while the east side activity should linger into Tuesday
evening. Not much rain expected with the activity in general -
mainly a tenth of an inch or less, but local amounts of a quarter
are possible with some training cells.

Winds are a concern for Tuesday afternoon as the low moves north
up the coast. Deep, very warm and dry layer of the atmosphere will
be unstable and model indications are that lower atmospheric
winds will be significant from the south and southwest. Should
see some afternoon gustiness from the south then from the west
over the west side here. Mainly southwesterly over the east side.
15 mph gusting to 25-30 mph looks reasonable for most areas.
Convection again should be monitored for potentially strong and
gusty, possibly severe, wind gusts.

Cooler weather by 5-10 degrees will prevail Wednesday through
Friday in the wake of the low. So the Heat advisory headlines will
abate. However, the longer range solution supports the high
strengthening over the area again with the NWS Heat Risk forecasts
indicating more heat highlights possible starting again Saturday
or Sunday. Stavish

MARINE...Updated 245 PM Monday, July 15, 2024...Breezy north
winds will continue over most of the waters through tonight with
steep, choppy seas. These will gradually diminish as the thermal
trough weakens tomorrow with continued light winds and seas through
Thursday. The thermal trough will restrengthen Friday into the
weekend with possible advisory strength northerly winds and steep
seas. -Spilde/Hermansen

AVIATION...16/00Z TAFS...Thunderstorm outflows and cloud to
ground lightning are the main risks for inland areas early this
evening, but mostly just Medford. Here at the airport in the last
hour or so, SE outflow winds peaked near 35kt (or 40 mph). And,
earlier there was a peak gust 50+ kt (~60 mph) at Montague airport
in central Siskiyou County. We issued an airport weather warning for
the Medford airport for wind gusts of 35 kt through 530 pm. The
majority of the activity is in western Siskiyou County extending
northward to SW Jackson and into SE Josephine County. Expect
activity to wane around sunset. Activity should stay
south of Roseburg.

Stratus and fog are hugging the coast near Cape Blanco and
southward, while it has cleared at most areas to the north,
including North Bend. The clearing will be short-lived, however, as
stratus/fog are expected to return this evening and persist into
Tuesday morning. Gusty north winds along the coast this evening
will ease, then we are not expecting winds to be as gusty on
Tuesday.

Thunderstorms have caused smoke from the Shelly fire to mix down
to the surface and we have even had some whiffs of smoke from it
here in Medford as the cells moved through. But, the main visibility
reductions with that fire will be in the immediate vicinity
of the fire. -Spilde

FIRE WEATHER...Issued 300 PM Sunday July 14, 2024...Thunderstorm
potential remains the focus of the forecast efforts through
Tuesday. Strong high pressure will linger over the Great Basin
region into next week and a weak low pressure will move northward
just offshore of the California coast, finally moving out of the
region Tuesday night into Wednesday.

Isolated to scattered thunderstorms have already kicked off this
afternoon, with scattered activity expected to be focused over
western Siskiyou County and the Siskiyou Mountains today. Storm
coverage will be isolated east of the Cascades, and gusty outflows
of 35-45 mph remain a concern with any thunderstorms. Storm motion
today over the Siskiyous is from south to north, so it`s possible
for storms over the Siskiyous to get pushed northward into
Jackson/Josephine Counties this afternoon or evening. We`re
maintaining a Red Flag Warning through 9 PM today for lightning on
dry fuels, and more details can be found at RFWMFR. High resolution
models are showing some returns moving over the region tonight, but
the chance for thunder remains fairly low overnight tonight.

For Tuesday, moisture is shifting northward and thunderstorm
activity will shift northward as well. The best chances for Tuesday
look to be along an arc from southern Lake County northwestward
across Klamath County/Crater Lake into fire weather zone 617 and
eastern Douglas County east of the I-5 corridor. We`ll be in a bit
of transition pattern as drier air moves up from the south. The
trough will be taking on a negatively tilted orientation which is a
common wind maker pattern for us well. Strong gusty south winds are
expected across northern California, especially in the Shasta Valley
as well as in the Rogue Valley. These strong winds will combine with
low daytime RHs to result in near critical to critical fire weather
conditions for Tuesday afternoon.

Tuesday night into Wednesday, low pressure finally swings through
and out of our region. Given the negative tilt of the trough, it
could kick off some nocturnal storms, but it looks more like a
situation where storms develop along the Douglas/Lane County border
and then moves north out of our area. Moisture looks to be well
north and east of the region on Wednesday, so thunderstorm chances
drop out of the forecast after Wednesday afternoon and typical
summer weather conditions return. /BR-y

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Fire Weather Watch from Tuesday afternoon through Tuesday
     evening for ORZ616-617-623>625.

     Heat Advisory until 8 PM PDT Tuesday for ORZ024-026.

     Red Flag Warning from 2 PM to 8 PM PDT Tuesday for ORZ622.

CA...Red Flag Warning from 2 PM to 8 PM PDT Tuesday for CAZ281.

PACIFIC COASTAL WATERS...Small Craft Advisory until 2 AM PDT Tuesday
     for PZZ350-356-370-376.

&&

$$