NWS Medford, OR wrote its last area forecast discussion before the first event at Jul 29, 8:18 AM PST, 1 hour 42 minutes earlier.
Area forecast discussion, Jul 29, 8:18 AM PST, 1 hour 42 minutes before
Area Forecast Discussion
National Weather Service Medford OR
918 AM PDT Thu Jul 29 2021
.DISCUSSION...No updates are needed this morning. Fairly typical
summer conditions are occurring this morning with hazy skies
across the region due to wildfire smoke, mainly from the Dixie
Fire in California. In addition, there are some high level clouds
streaming over the region this morning and marine stratus is
hugging the coast. The main concern over the next few days will be
hot temperatures and thunderstorms. The focus for this afternoon's
package will be on refining the thunderstorm potential through
the weekend. For more details on the heat, as well as current
thoughts on the thunderstorm forecast, see the previous
discussion below. /BR-y
&&
.AVIATION...For the 29/12Z TAF Cycle... LIFR ceilings have moved
into locations along the coast tonight and those ceilings will
likely persist into the early morning hours. Eventually, these
ceilings will burn off shortly after sunrise.
Smoke from wildfires is not too much of an issue per monitoring
sensors and satellite, except for the Jack Fire east of KRBG and
west of Diamond Lake. However, the smoke from the Jack fire is
confined to a small area right around the fire.
We'll see scattered thunderstorms develop along and near the
Cascades, Siskiyous, and Marble Mountains later this afternoon and
evening. Expect little in the way of rain, yet look for gusty winds
near any thunderstorms that do form. -Smith
&&
.MARINE...Updated 915 AM PDT Thursday, 29 July 2021...High
pressure centered to the west and lower pressure inland will
continue to bring general northerly winds to the coastal waters
through at least early next week. The ingredient that will roughen
up the seas a bit is the northerly winds over the south of Cape
Blanco due to a weak to moderate thermal trough developing
Thursday morning and continuing into early next week. Models begin
to differ around Tuesday, with some expecting northerlies to
increase and others showing them decreasing. ~BTL/Smith
&&
.PREV DISCUSSION... /Issued 300 AM PDT Thu Jul 29 2021/
DISCUSSION...29/00Z NAM/GFS/EC in.
There was a major earthquake near the Alaska Peninsula Wednesday
evening, but the generated tsunami was small and there is no
threat to the southern Oregon coast at this time.
The Medford forecast area remains under south to southwest flow
aloft between a long wave trough in the Gulf of Alaska and a
strong high over the central U.S. This pattern is not going to
change much initially.
It will be very hot over the inland areas Thursday and Friday, and
heat risk is a concern west of the Cascades. High temperatures
will be in the lower to mid 100s in the valleys of Douglas,
Josephine, Jackson and western/central Siskiyou Counties. Overnight
lows will remain quite warm, in the mid 60s to lower 70s,
offering little relief from the heat. An excessive heat warming
(NPWMFR) remains in effect for these areas Thursday afternoon
through Friday evening.
Monsoonal moisture will continue to stream over the area. This,
combined with strong surface heating, will support isolated to
scattered thunderstorms and showers over areas inland of the Coast
Range. The highest surface based lifted indices, ranging from -1.5
to -4.0, are over western Siskiyou county, extending north and
east over Josephine and Jackson counties, then up the Cascades
into northern Klamath county. 850 mb based lifted indices
highlight roughly the same area.
On Friday, the best lifted indices are less widespread, with the
favored areas being area area arcing from the Mount Shasta area
northwest into the Kalmiopsis and the northern Cascades. However,
a stronger short wave will move through during maximum surface
heating, so convection may actually be more widespread Friday,
especially east the the Cascades.
The ridge will retrograde and amplify this weekend while the
offshore trough moves northeast. However, increased cloud cover
will make for a significantly cooler, but still hot, day Saturday.
Sunday and Monday won't be much different in that regard.
Afternoon and evening thunderstorms will continue, but due to
reduced surface heating, the location and coverage will depend
more on the trajectory of short waves embedded in the upper level
flow. That is an uncertain forecast at this time.
The ridge will weaken Monday through Thursday while the trough
remains in place. Flow aloft will turn more westerly with time ,
and this will cut off the flow of monsoonal moisture. Therefore,
the Tuesday forecast moves the area of showers and thunderstorms
off to Lake County Tuesday, and Wednesday and Thursday look to be
dry. Temperatures won't change much, as the cooling of the air
mass will be roughly balanced by heating due to less cloud cover.
AVIATION...For the 29/06Z TAF Cycle... LIFR ceilings have moved
into locations along the coast tonight and those ceilings will
likely persist into the early morning hours. Eventually, these
ceilings will burn off shortly after sunrise.
Smoke from wildfires is not too much of an issue per monitoring
sensors and satellite, except for the Jack Fire east of KRBG and
west of Diamond Lake. However, the smoke from the Jack fire is
confined to a small area right around the fire.
We'll see scattered thunderstorms develop along and near the
Cascades, Siskiyous, and Marble Mountains later this afternoon and
evening. Expect little in the way of rain, yet look for gusty winds
near any thunderstorms that do form.
-Smith
MARINE...Updated 225 AM PDT Thursday 29 July 2021...There was a
earthquake of magnitude of 8.2 detected near the Alaska Peninsula
Wednesday evening. The tsunami warning center has determined
there is no tsunami threat for the Oregon or California coastline.
Otherwise, high pressure centered to the west and lower pressure
inland will continue to bring general northerly winds to the coastal
waters through at least early next week. The ingredient that will
roughen up the seas a bit is the northerly winds over the south of
Cape Blanco due to a weak to moderate thermal trough developing
Thursday morning and continuing into early next week. Models begin
to differ around Tuesday, with some expecting northerlies to
increase and others showing them decreasing. ~BTL/Smith
FIRE WEATHER...Updated 300 AM Thursday 29 July 2021...Deep
southerly flow will continue to bring monsoonal moisture into the
area through Monday. It will be quite hot through Friday over the
inland areas, especially the west side, with the hottest day on
Friday.
High resolution model guidance is showing some terrain-based
thunderstorm initiation on Thursday over portions of Siskiyou county
in California as well as over the Cascades and the Umpqua Divide in
Oregon. Additionally, a weak short wave will move in from the south
which could initiate some additional convection during peak heating
in northern Klamath County. A Red Flag Warning remains in effect for
portions of Fire Zone 280 in California and for portions of Fire
Zones 621, 622, 623, 617, and 624 in southern Oregon. Elsewhere, the
triggers remain relatively weak and isolated storms will be possible
east of the Cascades.
A similar set up will occur on Friday, but with additional moisture
moving in at the mid levels and a stronger trigger moving up from
the south, the chances for scattered thunderstorms will spread over
a larger area of southern Oregon and northern California, including
areas east of the Cascades. A Fire Weather Watch remains in effect
Friday afternoon and evening for most of the areas covered by the
Thursday Red Flag Warning, with the addition of portions of Klamath,
Lake, and Modoc Counties. See RFWMFR for more details.
It is worth noting that some of our west side valleys could
experience thunderstorms should our high resolution guidance be on
track, but these storms will likely flow over the valleys from the
surrounding mountains, and be more isolated in nature, this is
especially true for Fire zones 620 and 622 both Thursday and Friday.
The moisture will continue moving into our area throughout the
weekend, bringing additional cloud cover, some cooler temperatures
this weekend, and hopefully some widespread showers. Instability
remains relatively high; so a few showers may produce some
lightning, but storms should remain isolated despite the scattered
nature of showers over the weekend.
Thunderstorm chances will be limited to Lake County Tuesday, and
Wednesday and Thursday look to be dry.
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR... Fire Weather Watch from Friday afternoon through Friday evening
for ORZ617-621>625.
Excessive Heat Warning until 11 PM PDT Friday for
ORZ023-024-026.
Red Flag Warning from 2 PM this afternoon to 11 PM PDT this
evening for ORZ617-621>624.
CA...Fire Weather Watch from Friday afternoon through Friday evening
for CAZ280-281-284-285.
Red Flag Warning from 2 PM this afternoon to 11 PM PDT this
evening for CAZ280.
Excessive Heat Warning until 11 PM PDT Friday for CAZ080>082.
Pacific Coastal Waters...Small Craft Advisory until 11 PM PDT Saturday for PZZ356-376.
MNF/JRS/CZS