NWS Medford, OR wrote its last area forecast discussion before the first event at Sep 4, 1:00 PM PST, 30 minutes earlier.
Area forecast discussion, Sep 4, 1:00 PM PST, 30 minutes before
Area Forecast Discussion
National Weather Service Medford OR
200 PM PDT Fri Sep 4 2020
.DISCUSSION...04/12Z NAM/GFS/EC in.
A hot and dry forecast remains in place through next Friday,
though it may be a tad cooler Tuesday and again toward the end of
next week.
Strong high pressure currently centered over Nevada is bringing
south to southeast flow aloft over the area. This has brought up
a lot of wildfire smoke from the California fires. The flow aloft
will become more southwesterly with time as the high drifts east,
and this will act to slowly shunt the smoke east with time.
The high will continue to drift east into Saturday, then will
retrograde back west Sunday into Monday, as a long wave trough
digs into the Great Plains and Intermountain states. The ridge
will set up shop offshore Monday.
Inland temperatures will respond accordingly. Tomorrow will be a
bit cooler, but still quite hot. At this time, it looks like the
hottest day will be Sunday, and Monday will only 1-3 degrees
cooler.
The main concern is fire weather, and that aspect of the forecast
is detailed in the fire weather discussion below. Red Flag
Warnings are in effect at this time, see PDXRFWMFR for details.
Another concern is the heat, and a Heat Advisory remains in
effect into Sunday. While the daytime highs are very hot, the
nights are getting longer and this allows more overnight cooling,
allowing some respite from the heat. See PDXNPWMFR for more
details.
The trough digging into the intermountain states will eventually
affect the area, bringing cooler northerly flow. The east side
will see quite a bit of cooling Tuesday, and the west side will
cool off a bit as well. This pattern will also bring low level
easterly flow to the ridges, and overnight humidity recoveries,
which won't be all that great to begin with, will get worse Monday
night and Tuesday night.
The trough will move off to the east Tuesday into Wednesday, and
the offshore ridge will build back in from the west, bringing
another warming trend to the area Wednesday into Thursday.
&&
.AVIATION...For the 04/18Z TAFs... Along the coast, IFR over the
ocean and MVFR ceilings along the immediate coast will linger for
most of the afternoon. For the inland portions of the coastal
valleys, lower ceilings are expected to burn off. More low MVFR
ceilings will impact the coast again on Friday night.
VFR will prevail away from the coast through Friday. Smoke will also
linger west of the Cascades and in northern California. Look for
lower VFR visibilities near the Red Salmon fire and in some of the
valleys west of the Cascades this morning. Visibilities will improve
into the day, except near the Red Salmon Fire. Gusty winds are also
expected during the afternoon today. -Miles
&&
.MARINE...Updated 130 PM PDT Friday 4 September 2020....High
pressure will persist into Saturday morning with areas of fog,
diminishing seas, and weak southerly winds. North winds then return
Saturday and increase into Sunday evening with seas likely becoming
steep to very steep in the outer waters south of Cape Blanco.
We're expecting north winds to begin to increase Saturday evening
with small craft conditions covering the outer waters. Winds will
continue into increase into Sunday but, confidence is lower that
winds will reach gale force. However, north winds will still be
strong and will create hazardous sea conditions. Therefore have
swapped the gale watch for a hazardous seas watch on Sunday. Seas
will be highest in the outer waters at 10 - 12 feet south of Cape
Blanco Sunday night. -Miles
&&
.FIRE WEATHER...Updated 200 PM PDT Friday 4 September 2020...Dry
and hot weather will continue for interior locations for the next 7-
10 days with zero chance of thunderstorms.
Three concerns exist through early next week and they are all for
gusty winds and low relative humidity. The first concern will be
into this evening, the second is Saturday afternoon and evening. The
first two concerns will be east of the Cascades and portions of the
Rogue Valley. Third is expected to be Monday afternoon east of the
Cascades and Monday night into Wednesday from the Cascades west,
although concerns could still continue east of the Cascades. Details
on all of this follow below.
The combination of stronger winds aloft ( which could mix down near
or at the surface and tighter pressure gradient will be the main
contributing factors for gusty winds into this evening and again
Saturday afternoon and evening. Because relative humidities will be
low (with some areas east of the Cascades flirting with single digit
values), it's not going to take much wind for conditions to reach
critical levels. Thus a Red Flag Warning remains in effect into this
evening and the Fire Weather Watch has been upgraded to a Red Flag
Warning for tomorrow afternoon and evening.
Also, it still looks favorable for gusty winds and low relative
humidity west of the Cascades, specifically in the Rogue Valley into
this evening and again Saturday afternoon and evening which could
reach Red Flag Warning criteria. This is due in part to a slightly
stronger onshore flow and increasing pressure gradient, but not
strong enough for cooler afternoon temperatures.
The evidence is becoming stronger regarding a significant east wind
event next week. The operational models and many model/ensemble
members are in good agreement showing an upper level trough (inside
slider) moving south into northeast Oregon Monday with a dry cold
front moving into the area. This pattern is expected to result in
gusty north to northwest winds and low relative humidity Monday
afternoon east of the Cascades, followed by steady east winds across
the entire area Monday night into Wednesday. Temperatures would
remain quite hot west of the Cascades, but would trend cooler on the
East Side. However, humidities would suffer greatly, dropping to
minimums in the single digits to low teens across nearly the entire
area, and recoveries becoming poor for a significant portions of the
region. Because if the increasing confidence of this event playing
out, very dry fuels and a holiday weekend upon us, we decided to
issue a Fire Weather Watch for east of the Cascades starting Monday
afternoon into Monday evening, then Monday evening into Tuesday
evening along and west of the Cascades. The exception is Fire
Weather Zones 615, 618, and 619, mainly because confidence is not
high enough relative humidities will be low enough in Fire Zone 615
and winds may not be strong enough in 618 and 619. However this
could chance, so stay tuned for the latest updates on this. Details
on all the Red Flag Warning and Fire Weather Watches can be found at
RFWMFR. -Petrucelli
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning until 8 PM PDT this evening for ORZ624-625.
Red Flag Warning from 2 PM to 8 PM PDT Saturday for ORZ624-625.
Fire Weather Watch from Monday morning through Monday evening
for ORZ624-625.
Heat Advisory until 11 PM PDT Monday for ORZ024-026.
Fire Weather Watch from Monday evening through Tuesday evening
for ORZ616-617-620>623.
Red Flag Warning until 8 PM PDT this evening for ORZ622.
Red Flag Warning from 2 PM to 8 PM PDT Saturday for ORZ622.
CA...Fire Weather Watch from Monday morning through Tuesday evening
for CAZ284-285.
Heat Advisory until 11 PM PDT Monday for CAZ080-081.
Fire Weather Watch from Monday evening through Tuesday evening
for CAZ280>282.
Red Flag Warning until 8 PM PDT this evening for CAZ285.
Red Flag Warning from 2 PM to 8 PM PDT Saturday for CAZ285.
Pacific Coastal Waters...Small Craft Advisory from 11 PM Saturday
to 5 AM PDT Monday for PZZ350-356-370-376.
Hazardous Seas Watch from Sunday morning through late Sunday
night for PZZ376.
15/15/05