NWS Medford, OR wrote its last area forecast discussion before the first event at Sep 8, 8:34 AM PST, 26 minutes earlier.
Area forecast discussion, Sep 8, 8:34 AM PST, 26 minutes before
Area Forecast Discussion
National Weather Service Medford OR
934 AM PDT Tue Sep 8 2020
.DISCUSSION...Bottom-line: Extremely critical fire weather conditions
continue through this evening for all areas and through tomorrow for
areas from the Cascades westward. Widespread windy conditions are
being observed this morning thanks to strong easterly flow aloft and
a tight east to west surface pressure gradient. Not much will change
today in this setup. The winds won't be quite as strong this
afternoon as this morning but still can be considered windy through
the day. Gusts to 70 mph have been observed in the Coast Range this
morning at Onion Mountain RAWS west of Grants Pass. Gusts to 50 mph
have been observed in the Bear Creek Valley near Ashland. Drought-
stressed trees could fall in these types of winds, so be please be
aware of this threat. To account for this, we have a Wind Advisory
in effect through this morning for east of the Cascades and through
tomorrow for portions of the Rogue Valley.
Red Flag Warnings continue through the day for all areas due to
gusty winds and low humidity, and details can be found in the Fire
Weather Discussion below.
Smoke from all these fires will impact most areas from the Cascades
westward today. During the day, a narrow plume of smoke from the 242
wildfire north of Chiloquin is suggested by the models to impact
areas from Butte Falls west to Grants Pass and Galice. This will
continue through tomorrow. Its likely that more areas are impacted
by smoke tonight as it filters into the valley in a more stable
atmosphere.
Regarding temperatures today...hot conditions continue, especially
at the coast where offshore, easterly winds will result in
temperatures 10 to 20 degrees above normal. No doubt smoke will put
a wrench in some of the temperature forecasting, so consider today's
forecast a worst case scenario for hot temperatures, and its likely
that smoke will shield some areas from the hottest conditions.
Please see the previous forecast discussion below for more
details.
&&
.AVIATION...For the 09/12Z TAFs...The main aviation impact during
this TAF period will be strong, gusty northeast through east winds
this morning leading to low-level wind speed shear (LLWS) for most
terminals. This includes the strongest winds over ridges and across
much of the east side. Additionally expect areas of reduced
visibility (MVFR with local IFR) across the area due to wildfire
smoke.
Behind a front, gusty east winds have developed across the area.
With a nighttime inversion around 1500 feet AGL, winds have decouple
(eased) at the surface for most valley locations, with the strongest
winds expected over the higher terrain. But, this has also resulted
in LLWS of 25-40 kt at that level above KOTH, KRBG and KMFR. Some
valleys oriented more to these wind directions could see some
significant wind gusts this morning morning. Conditions should be
mostly VFR aside from any wildfire smoke visibility reductions.
-CC
&&
.MARINE...Updated 300 AM PDT Tuesday 8 September 2020....A
strong thermal trough near the coast will move slightly offshore
today into Tuesday night. This is resulting in gusty northeast winds
and steep, choppy seas across the waters. Strongest winds will be
north of Port Orford. However, almost all areas will be affected by
steep seas with the highest seas in the outer waters. We've
maintained a small craft advisory during this time for most areas
except the immediate coast due to a mix of fresh swell and wind seas
from northeast winds creating a chaotic sea state, but this is
especially true beyond about 20 nm from shore.
The trough will remain offshore through Thursday, weakening with
time. Winds and seas will be relatively light Wednesday into
Saturday. -CC
&&
.FIRE WEATHER...Updated 300 AM PDT Tuesday 8 September
2020...Extremely critical fire weather conditions continue through
this evening for all areas and through tomorrow from the Cascades
westward. Over the east side, it will be a porpoising event with
critical condition this afternoon and evening and again Wednesday
afternoon due to gusty winds and low RH. From the Cascades west,
it will be a constant event into Wednesday afternoon due to gusty
winds combined with low RH during the day, and gusty winds with
poor to very poor RH recoveries at night. Red Flag Warnings are in
effect for the entire Medford forecast area into this evening,
then just from the Cascades west tonight into Wednesday afternoon.
Winds will gradually diminish Wednesday east of the Cascades, but
pressure gradients remain rather tight along the Cascades, so
gusty winds are expected to continue in this area and conditions
will still be critical across the west side. From Thursday on, it
will remain hot and very dry, but there will be a very gradual
cooling and moistening trend. Winds will diminish, and this will
be the primary factor in keeping overall conditions below Red Flag
Warning criteria. Petrucelli/Keene
&&
.PREV DISCUSSION... /Issued 341 AM PDT Tue Sep 8 2020/
DISCUSSION...The latest surface analysis shows a thermal trough
along the coast that will only strengthen over time today. This has
resulted in a strong pressure gradient along the Cascades. At the
same time stronger winds aloft are occurring and the combination of
all of these will result in moderate to strong winds, especially
over the higher terrain. Downsloping will also occur in the south
end of the Rogue Valley bringing gusty winds from about Talent south
to Ashland and a wind advisory remains in effect for these areas.
Wanted to message a caution associated with the high wind speeds,
and that is for the possibility of downed power lines. Similarly,
downed tree limbs, especially along ridge tops where winds will be
strongest, pose a threat to hikers, campers, and those driving
mountain roads.
Downsloping winds are also occurring in the north coast, including
North Bend where it's currently 72 degrees F. This does not happen
on a regular basis, but when downsloping occurs in this area, it's
not all that unusual for temperatures to warm up there and in other
places. In fact several other locations in Coos County are very mild
at this time, except for the more sheltered areas. Downsloping will
continue into this afternoon with temperatures pushing near or just
a few degrees above 90 degrees F at North Bend.
Not much change is expected today. It will be dry and hot for most,
if not all interior west side valley locations with gusty winds at
times. A heat advisory remains in effect until 11 pm pdt this
evening. Also a new fire has occurred near Highway 97 near Chiloquin
and since were in a easterly flow, the smoke from this fire has
pushed into the Rogue Valley with reduced visibility and points
west, this areas and patchy areas of smoke have been added to the
forecast.
Strong offshore flow will continue tonight with continued gusty
winds, especially along the Cascades, mid slopes. Ridges and any
other exposed areas. We could still experience gusty winds in the
south end of the Rogue Valley. Winds east of the Cascades are
expected to diminish, but gusty breezes are still possible over the
ridges.
Wednesday remains dry and hot, but overall temperatures may end up a
couple of degrees cooler than today. Also downsloping will continue
west of the Cascades in Douglas and Coos county, so we could see
another warm day near and at the coast, Including North Bend.
The thermal trough will weaken Wednesday night with east winds
diminishing along the Cascades. At the same time marine stratus could
return over the waters and possibly along the coast by Thursday
morning. Weak onshore flow is expected which should result in more
typical afternoon temperatures for most, if not the entire coast.
Thursday though Saturday will remain dry with a strong upper ridge
over the area, so we'll continue to have hot temperatures for the
interior west side valleys with values pushing close to triple
digits. The ridge axis shifts east Sunday as an upper trough
approaches from the west and the thermal trough shifts east of the
Cascades. Onshore flow will increase some with cooler afternoon
temperatures expected west of the Cascades.
Next Monday, the operational ECMWF shows a rather robust front
moving into the area Monday afternoon and night with increasing
chance of precipitation. However find this suspect given we have
strong ridging in the area. What's most likely to happen (and would
not be surprised if future models runs show this) is the trough and
associated cold front will lose it's punch and weaken significantly
as it pushes into the ridge. Therefore have did not mention any pops
during this time period, but they are not zero. In contrast, the GFS
is weaker and has the trough position further offshore as it slows
down as it runs into the ridge. Of note: the individual ensemble
members (ECMWF and GFS) also show similar solutions to the
operational. -Petrucelli
AVIATION...For the 08/06Z TAFs...The main aviation impact during
this TAF period will be strong, gusty northeast through east
winds overnight into Tuesday morning leading to low-level wind
speed shear (LLWS) for most terminals. This includes the strongest
winds over ridges and across much of the east side. Wind gusts to
35kt are possible at KLMT, where an airport weather warning is in
effect through this evening.
Wildfire smoke from all the fires to the south is already getting
pushed southward away from our area, but smoke from the fires to
the north and east will increase which will result in reduced
visibilities.
A dry front will push through overnight with north winds becoming
northeast, then easterly. Enough of an inversion will develop around
1500 feet AGL for winds to decouple (ease) at the surface for most
valley locations, with the strongest winds expected over the higher
terrain. But, this will result in LLWS of 30-40 kt at that level
above KOTH, KRBG and KMFR. Some valleys oriented more to these wind
directions could see some significant wind gusts overnight into
Tuesday morning. Conditions should be mostly VFR aside from any
wildfire smoke visibility reductions. -DW
MARINE...Updated 300 AM PDT Tuesday 8 September 2020....A
strong thermal trough near the coast will move slightly offshore
today into Tuesday night. This is resulting in gusty northeast winds
and steep, choppy seas across the waters. Strongest winds will be
north of Port Orford. However, almost all areas will be affected by
steep seas with the highest seas in the outer waters. We've
maintained a small craft advisory during this time for most areas
except the immediate coast due to a mix of fresh swell and wind seas
from northeast winds creating a chaotic sea state, but this is
especially true beyond about 20 nm from shore.
The trough will remain offshore through Thursday, weakening with
time. Winds and seas will be relatively light Wednesday into
Saturday. -CC
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Frost Advisory from 4 AM to 8 AM PDT Wednesday for ORZ030.
Red Flag Warning until midnight PDT tonight for ORZ625.
Freeze Warning from 4 AM to 8 AM PDT Wednesday for ORZ029-030.
Wind Advisory until 11 AM PDT this morning for ORZ030-031.
Frost Advisory from 4 AM to 8 AM PDT Wednesday for ORZ029-031.
Heat Advisory until 11 PM PDT this evening for ORZ021>024.
Red Flag Warning until midnight PDT tonight for ORZ624.
Red Flag Warning until 5 PM PDT Wednesday for ORZ616>623.
Red Flag Warning until 11 AM PDT Wednesday for ORZ615.
Wind Advisory until 2 PM PDT Wednesday for ORZ026.
Small Craft Advisory from 11 PM this evening to midnight PDT
tonight for ORZ023.
CA...Wind Advisory until 11 AM PDT this morning for CAZ085.
Frost Advisory from 4 AM to 8 AM PDT Wednesday for CAZ085.
Red Flag Warning until midnight PDT tonight for CAZ284-285.
Red Flag Warning until 5 PM PDT Wednesday for CAZ280.
Red Flag Warning until 11 AM PDT Wednesday for CAZ281.
Red Flag Warning until 5 PM PDT Wednesday for CAZ282.
Pacific Coastal Waters...Small Craft Advisory until 11 PM PDT this evening for
PZZ350-356.
Heat Advisory until 11 PM PDT this evening for PZZ356.
Small Craft Advisory until 5 AM PDT Wednesday for PZZ370-376.