NWS Medford, OR wrote its last area forecast discussion before the first event at Aug 1, 2:02 PM PST, 2 hours 28 minutes earlier.
Area forecast discussion, Aug 1, 2:02 PM PST, 2 hours 28 minutes before
Area Forecast Discussion
National Weather Service Medford OR
302 PM PDT Mon Aug 1 2022
.SYNOPSIS...An upper low just off the coast of far northern
California will remain nearly stationary and result in continued
chances of thunderstorms and showers over the area through at
least Wednesday (and possibly Thursday). Additionally, with
southerly to southwesterly winds aloft, smoke from wildfires in
Siskiyou County, California will continue to move northward into
Southern Oregon creating air quality concerns.
KEY POINTS:
*Smoke from area wildfires may create periods of degraded air
quality. Please see the AQAMFR or the Oregon DEQ website for
more details.
*Thunderstorms may produce occasional to abundant deadly cloud to
ground lightning, gusty and erratic winds, and small hail.
*Periods of moderate to heavy rain will be possible in
thunderstorms today and Tuesday.
*Lightning may ignite new wildfires. More information is available
in the fire weather section below.
&&
.DISCUSSION...Satellite imagery is showing some cumulus build ups
across portions of southern Oregon and northern California.
These clouds are part of a larger shortwave moving northward from
Central/North California. Shower and thunderstorm activity should
increase through the evening and possibly continue overnight. A
brief break is expected Tuesday morning before the next round of
showers and thunderstorms are expected Tuesday. Models and
ensembles thus far have struggled to pinpoint which day will be
the main event, suggesting that Sunday, Monday, and now Tuesday
will be our heavy thunderstorm day. It is at least worth noting
that thunderstorms have been occurring in portions of southern
Oregon and northern California, especially in areas without
extensive smoke from the McKinney fire.
Speaking of smoke, air quality as shown on fire.airnow.gov and the
Oregon DEQ website suggest less smoke is over the Rogue Valley
this evening. However, the current thought is that smoke should
generally increase in southern portions of the valleys in Jackson
and Klamath Counties. Overall, the lack of smoke makes things a
bit more interesting as far as thunderstorms this evening and
overnight is concerned. Earlier discussions mentioned the morning
sounding Precipitable Water Column that was a daily record at 1.62
inches. This is combined with an impressive 65 degree F dewpoint
temperature, which is more typical of Midwestern summers which
draw in moisture from the Gulf of Mexico. It will be interesting
to see how the precipitable water stacks up in the sounding this
afternoon. What this means is that the showers and thunderstorms
will be wet in nature, producing periods of moderate to heavy
rain. While we don't anticipate any issues with area burn scars in
western Siskiyou County (the River Complex), we will have to keep
an eye on things. Additionally thunderstorms will have the
potential to become strong once again today with wind gusts to 40
to 50 mph and some small hail.
This pattern will continue over the next couple of days as the low
wobbles in place. The other pattern this low is intermixed with is
a ridge of high pressure over the 4 corners region of the US. This
will nudge a bit westward which may help lessen thunderstorm
chances after Wednesday. Thus, while we are still carrying a
slight chance, confidence is very low at this point. Still, the
low will remain stationary for the next several days bringing deep
southwest flow. The westward nudge of the ridge could nudge the
low a bit westward as well, allowing tropical moisture from
tropical storm Frank to move into our area over the weekend into
next week. Although not currently in the forecast, this could
create additional precipitation chances for the area. Keep an eye
to the forecast for updates.
&&
.AVIATION...IFR/LIFR conditions in marine stratus
will continue to impact many areas over the coastal waters and along
the coast through the TAF period. Current model guidance is even
keeping the low clouds over North Bend through the entire 24 hour
TAF period and looking at satellite imagery would support this
guidance. Although elevated instability exists along the coast and
just offshore today, satellite imagery shows this elevated
convection is very weak so will not include any chance for
thunderstorms at coastal sites.
Inland. Overall, expect VFR, though any storms may bring local MVFR
this afternoon and early tonight. Areas of IFR/MVFR vis in
haze/smoke in the vicinity of the McKinney fire will persist in
northern Siskiyou County and into the south end of the Rogue Valley,
up towards Medford. Isolated to scattered convection is expected
again this afternoon/evening, though smoke from the McKinney fire
will likely once again be a limiting factor. Most likely area for
scattered storms will be from the Cascades/Foothills eastward.
-Petrucelli/Sargeant
&&
.MARINE...Updated 200 PM PDT Monday, 1 August, 2022...A weak upper
low will remain centered west of the waters through tonight. There
is much less instability over the coastal waters today compared to
yesterday. There is still the wee little chance of an isolated
thunderstorm over the coastal waters this evening but at this time
we are just expecting scattered alto cumulus clouds over the very
extensive low marine layer clouds.
In terms of the synoptic pattern, light north to northwest winds are
expected through Wednesday as the offshore low drifts westward.
North winds are then likely to increase, possibly reaching advisory
levels Thursday afternoon as a thermal trough develops and
strengthens. This is expected to build steep seas to advisory levels
Thursday evening into Friday.
Additionally, smoke from inland wildfires and marine layer fog will
reduce visibilities across the coastal waters, and could become very
dense at times. -Sargeant
&&
.FIRE WEATHER...230 PM PDT Monday, 1 August, 2022...
Red Flag Warning headlines for today and the watch that was out for
tomorrow have been combined into one warning, valid through 11PM PDT
Tuesday, primarily due to a shortwave trough moving into the forecast
area this evening through early Tuesday morning. This shortwave
trough is likely to enhance showers and thunderstorm activity during
the overnight time period and, likely, draw it back westward to
areas west of the Cascades. There's then likely to be a bit of a
break in the action late Tuesday morning into early Tuesday
afternoon before we see another round of what's likely to be
significant thunderstorm activity in the afternoon and evening.
More specifically, cloud cover and light showers continue this
afternoon from the Marble Mountains to the Siskiyous, and northward
along and near Cascades. This cloud cover and shower activity will
limit the potential for thunderstorm development in that area for
much of the afternoon, but there will be an increasing probability
of some embedded lightning strikes in that shower and cloud shield
as we head into the afternoon and evening. Areas west of that cloud
shield, from west of the Klamath River in Siskiyou County to
Josephine and Douglas counties bear some watching for surface based
thunderstorm development as surface heating into the mid 90s and
dewpoints well into the 60s combine. However, there's also a hazy
smoke shield from about Grants Pass northward that will hinder
thunderstorm development some there. East of the cloud cover, across
Modoc and Lake counties heat is building, but moisture values are
not as high. Thunderstorms are expected to develop in that area mid-
late afternoon and then tap into extensive moisture west of there to
expand westward this evening. All in all, through the afternoon,
we're watching the more cloud free areas for potential rapid
development of thunderstorm activity with lesser activity likely
elsewhere.
This evening through early Tuesday morning an upper level impulse
moving northward from the San Francisco Bay area is expected to
increase shower and thunderstorm coverage across the forecast area,
to include some areas west of the Cascades. The HRRR model, which
parameterizes smoke in its forecast, has been consistent in bringing
a low pressure vortex of showers and thunderstorms through Siskiyou
and Jackson counties overnight. There has been some question as to
whether or not Josephine and Douglas counties get in on the action,
how much ride through the Mount Shasta FWZ 282, and how much is rain
versus thunderstorms. Overall signals indicate it is a significant
concern for down strikes as it moves in, but will likely morph into
an area of rain as it encounters extensive smoke from the McKinney
Fire and heads onto the east side. There, it's likely to slow and
rain itself out.
After a brief lull late Tuesday morning into early Tuesday
afternoon, a new round of scattered showers and thunderstorms is
expected to develop from western Siskiyou County, Josephine County,
and eastern Douglas County eastward. Abundant lightning, gusty
outflow winds, and locally heavy rainfall are all possible with the
thunderstorms. Localized severe thunderstorm warning level wind
gusts around 60mb will be possible, as well as small hail, and
locally heavy rain that could result in urban and small stream
flooding in some areas.
Please note that we have significant fire start concerns due to the
ongoing dryness of the vegetation due to our long term drought and
recent record breaking heat wave. At the same time, record high
precipitable water values today mean that storms the next couple of
days will be energetic and capable of locally heavy rainfall that
will slow or prevent fire growth. This could result in hold over
fires once we dry out again. Finally, gusty outflow winds of 40 to
60 mph will be possible with the stronger thunderstorms. After
Tuesday, it looks like lingering shower and thunderstorm activity is
more likely to be south and east of us and/or isolated if it's in
our area (most likely Friday). ~BTL
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning until 11 PM PDT Tuesday for ORZ617-620>625.
CA...Red Flag Warning until 11 PM PDT Tuesday for CAZ280>282-284-285.
Pacific Coastal Waters...
None.