NWS Medford, OR wrote its last area forecast discussion before the first event at Sep 5, 10:14 AM PST, 2 hours 18 minutes earlier.
Area forecast discussion, Sep 5, 10:14 AM PST, 2 hours 18 minutes before
Area Forecast Discussion
National Weather Service Medford OR
1114 AM PDT Thu Sep 5 2024
...Updated the aviation section...
.AVIATION...09/05/24...18Z TAFS...VFR prevails this morning, except
for patchy lingering LIFR at the coast south of Cape Blanco. This
marine stratus will gradually erode through the afternoon. This
evening, LIFR/IFR will return to the coast and persist into Friday
morning. Improvement will be slower than today, but is still
expected during Friday afternoon. Inland, aside from patchy smoke
and haze from wildfires, it will remain VFR through Friday morning.
Instability will develop Friday afternoon with isolated
thunderstorms possible for eastern Douglas and northeast Jackson
counties, north of Lake of the Woods, and eastward across northern
Klamath and Lake counties. -DW
&&
.PREV DISCUSSION... /Issued 933 AM PDT Thu Sep 5 2024/
DISCUSSION...This morning's satellite shows marine stratus towards
Brookings and clearer skies elsewhere. The marine stratus could
slowly work northward through the day, but overall there will be
some passing high clouds and smoke/haze from wildfires today. The
ridge is situated over the Pacific Northwest, and this will give
us the warmest day in the forecast period. Triple digits are
forecast for west side valleys, so the Heat Advisory will continue
this afternoon. The only updates that were needed was to add the
widespread smoke to southern Oregon and northern California today.
The chance for thunderstorms returns tomorrow for the Cascades
and areas east, but it also includes western Siskiyou and
Josephine County. The thunderstorms chances and temperature
changes will be reviewed today. -Hermansen
MARINE...Updated 830 AM Thursday, September 5, 2024...There
will be mostly light north winds today with a moderate west-
northwest swell. North winds increase a bit tomorrow, with steep
seas expected to develop tomorrow afternoon and then continue
through Saturday. A small craft advisory has been added over the
outer waters (beyond 10 NM from shore). Steep seas could also reach
the inner waters tomorrow night, but confidence in this occurring is
a bit lower, so will allow future shifts to assess this potential.
North winds persist the remainder of the weekend, but should be
lighter with lower seas.
-Spilde/Hermansen
PREV DISCUSSION... /Issued 301 AM PDT Thu Sep 5 2024/
DISCUSSION (Today through Wednesday)...
Overview:
Forecast highlights continue to be in the realm of heat and
thunderstorm chances. The latter of which will play a role on fire
weather concerns due to the threat of lightning, but the hot and
dry conditions will be a concern for fire weather as well. Heat
Advisories are in place over portions of the westside today
through tomorrow night. We will likely need some sort of fire
weather product out for Friday, but neighboring offices agreed to
let the dayshift coordinate those watches and warnings. That
said, we will be near critical fire weather conditions this
morning (poor overnight recoveries) and today for hot and dry
conditions.
Further Details:
High pressure aloft continues to dominate the weather over the
PacNW with triple digits possible for numerous locations today.
Current water vapor imagery from GOES-18 indicates very dry air in
the mid levels, and we will see mostly clear skies across the
region today. This will lead to a very hot and dry airmass as
critical RH values come to fruition with afternoon minimums in the
teens and single digits. The one saving grace today is that wind
speeds are not too breezy this afternoon, and this was ultimately
the limiting factor towards NOT issuing any fire weather
warnings/watches for today. With the heat today, it would not be
out of the question to see some record(s) potentially tied or
broken today. For example, the record for Medford is 103 and we
are forecasting a high of 105 at KMFR.
High pressure will start to break down Friday morning as a
shortwave trough starts to influence the weather over the PacNW
with southerly flow developing aloft. PVA will spread over the
area along with upper level divergence which could help trigger
thunderstorms along with convective temperatures being reached.
However, we are going to be lacking moisture, especially in the
low to mid levels as forecast soundings indicate deep inverted-v
sounding profiles Friday afternoon. With DCAPE progged to be
around 500-1200 J/kg, any thunderstorm that develops will have the
potential for strong gusty erratic wind speeds around 50 mph.
Based on forecast hodographs, storm motion has the potential to be
around 20 knots, and this would likely make the 50mph outflow
more likely. Of course, we would need a thunderstorm to actually
develop and then collapse to create these evaporative cooling
processes, so there are some uncertainties for tomorrow. That
said, the main threats would be lightning and strong outflow wind
gusts tomorrow afternoon and evening. PWATs could be around 0.50"
to 0.85", so storms won't necessarily be "dry" but lightning
induced fires will be a concern. See the fire weather section
below for further details.
After the shortwave passes through the region this weekend, zonal
to a southwest flow will develop in the upper levels as another
trough starts influence our weather. The GFS and EC went from
good agreement yesterday to out of phase with this next pattern
change, so the result is a decrease in confidence for some of the
details on Friday. The GFS has the trough much farther south
which would impact our forecast area more. While uncertainty
remains, we are looking at the potential for several rounds of
rainfall through next week. Hopefully we can get some better
consistency going forward. One thing for sure is that we are
looking at much cooler temperatures next week. In fact, Wednesday
could be 20-25+ degrees cooler for many locations when compared to
this afternoon. Lastly, widespread rainfall is a possibility next
week with the probability for 0.10" or more of rainfall around
10-40 percent across the entire forecast area. The chances get
higher the farther west one goes.
-Guerrero
FIRE WEATHER...
Hot, dry, and unstable conditions will continue into this weekend. A
thermal trough along the coast will push inland today. Breezy
easterly winds and moderate to poor overnight recoveries are
expected over the ridges tonight. A headline is in place for these
conditions and we will continue to monitor this pattern. This
afternoon/evening winds are expected to be below critical levels. An
exception may be in the southern Shasta Valley and southern Scott
Valley, where a brief period of gusty southerly wind and critically
dry humidities are possible this afternoon/evening.
On Friday, an upper level disturbance will approach northwest
California and send limited moisture into the region. This will
bring a chance (15-30%) for thunderstorms across most inland areas
Friday afternoon and evening. Breezy to gusty south winds are also
possible on Friday for areas east of the Cascades. However, with the
additional clouds on Friday, expect temperatures to trend slightly
less hot and humidities less dry. Lightning and gusty outflow winds
(50mph) from thunderstorms remains the main concern during this
period. This disturbance will gradually move inland Saturday, with
additional chances for thunderstorms, mainly from the Cascades
eastward.
Sunday and Monday, temperature are expected to trend less warm as an
upper trough approaches. This trough and associated front will then
move into the region Tuesday, resulting in chances for rain, cooler
temperatures, and a potential for breezy to gusty winds through the
rest of the week.
-Guerrero
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Heat Advisory until 10 PM PDT Friday for ORZ021-023-024-026.
CA...Heat Advisory until 10 PM PDT Friday for CAZ080.
PACIFIC COASTAL WATERS...Small Craft Advisory from 11 AM Friday to 11
AM PDT Saturday for PZZ370-376.
&&