NWS Medford, OR wrote its last area forecast discussion before the first event at Sep 7, 2:30 PM PST, 3 hours 28 minutes earlier.
Area forecast discussion, Sep 7, 2:30 PM PST, 3 hours 28 minutes before
Area Forecast Discussion
National Weather Service Medford OR
330 PM PDT Mon Sep 7 2020
.UPDATE...Satellite imagery and surface observations over
northeast Oregon are showing blowing dust and reduced visibilities
heading towards northern Klamath and Lake Counties. This haboob is
likely to intensify around and downwind of area dry lake beds
such as Summer Lake, Christmas Lake, and Alkali Lake, amongst
others, reducing visibilities significantly along area roadways
such as Highways 31 and 395. Due to these concerns, we have issued
a Blowing Dust Advisory for the entirety of the East side through
this evening. -BPN
&&
.PREV DISCUSSION... /Issued 257 PM PDT Mon Sep 7 2020/
DISCUSSION...On satellite a haboob with a mass of smoke can be
observed at the leading edge of the dry front of the approaching
dry front. Have added blowing dust to the forecast east of the
Cascades, mainly below 5k ft, above which it should be dispersed
by the higher wind speeds. The first instances of blowing dust
will arrive in NE Lake County in approximately two and a half
hours. Have visibility reduced to 2 1/2 SM in the forecast but,
observations from within the dust cloud reveal visibilities much
lower in the most concentrated pockets down to 1/2 SM.
Added a freeze warning for some valleys late Tuesday night east
of the Cascade crest north of Chiloquin in Klamath County,
surrounding the Fort Rock area in Lake County, and around Alturas
in Modoc County. Some MOS guidance shows temperatures higher than
what is currently forecast, but this seems the more reasonable
MinTs at the moment. This is also assuming that an inversion sets
up in these locations, which at the moment, model soundings are
showing. It is possible though for frost surrounding the above
mentioned areas on Tuesday night from Sprague River north in
Klamath County, and for a larger area surrounding Fort Rock. Did
not issue a frost advisory for similar areas tonight due to the
high wind speeds expected all night.
Wanted to message a caution associated with the high wind speeds
that hasn't been yet, and that is for the possibility of downed
power lines and/or power poles. Similarly, downed tree limbs,
especially along ridge tops where winds will be strongest, pose a
threat to hikers, campers, and those driving mountain roads.
Not much change to the temperature forecast for the area,
especially in the short term where heat risk remains for areas
west of the Cascades. Areas from the Cascades east will see a
significant cool down Tuesday, while the coast will observe some
of it's warmest temperatures all year. Brookings has the chance to
observe a particularly strong chetco effect, but have held off
going with the hottest temperatures in the guidance due to
uncertainty in the wind direction forecast.
Wednesday and Thursday hot temperatures move back inland and MaxTs
will reach into the upper 90s. However, overnight lows should be
better and this prolonged heat risk will finally subside. On
Thursday winds, mostly over the water, become southerly and cause
a surge of marine stratus to move north. This is expected to be
dense enough to cause trace and minimal measurable amounts of
precipitation along the coast. Also, it will create very foggy
conditions along the coast and over the marine waters at least
through friday and possibly into the weekend. -Miles
AVIATION...For the 07/18Z TAFs...The main aviation impact during
this TAF period will be increasing north winds this afternoon,
followed by strong, gusty northeast through east winds overnight
into Tuesday morning leading to low-level wind speed shear (LLWS)
for most terminals.
First, marine stratus hugging the coast north of Cape Blanco this
afternoon will push well offshore overnight into Tuesday. Wildfire
smoke from all the fires to the south is already getting pushed
southward away from our area, but we still could get some smoke from
the fires to the north as winds continue to shift.
Winds will begin in earnest later this afternoon, mostly felt along
the coast and at elevation, but also across much of the east side.
Winds gusts to 35kt are possible at KLMT, where an airport weather
warning may be necessary.
A dry front will push through this evening with north winds
becoming northeast, then easterly overnight. 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. -Spilde
MARINE...Updated 230 PM PDT Monday 7 September 2020....A thermal
trough near the coast will continue gusty north winds and steep to
very steep seas into early this evening. The steepest seas will be
beyond 30 nm from shore averaging 8 to 10 feet. Closer in, within
about 10 nm from shore, seas will be around 5 to 7 feet.
The thermal trough will move offshore overnight into Tuesday bringing
gusty northeast winds north of Cape Blanco with the highest seas in
the outer waters and fresh swell dominating south of Cape Blanco.
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
east 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
Friday. -Spilde
FIRE WEATHER...Updated 200 PM PDT Monday 7 September 2020...A
critical fire weather pattern will remain in place into Wednesday.
Over the east side, it will be a porpoising event with critical
condition this afternoon and evening and again Tuesday afternoon
and evening 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 RH recoveries at night. Red Flag Warnings are in effect for the
entire Medford forecast area. Winds will diminish Wednesday, but
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.
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Blowing Dust Advisory until 1 AM PDT Tuesday for ORZ029>031.
Freeze Watch from late Tuesday night through Wednesday morning
for ORZ029>031.
Red Flag Warning from 11 AM Tuesday to midnight PDT Tuesday
night for ORZ616>625.
Wind Advisory from 9 PM this evening to 11 AM PDT Tuesday for
ORZ030-031.
Heat Advisory from 11 PM this evening to 11 PM PDT Tuesday for
ORZ021-023-024.
Red Flag Warning until 11 PM PDT this evening for ORZ624-625.
Excessive Heat Warning until 11 PM PDT this evening for
ORZ024-026.
Heat Advisory until 11 PM PDT Tuesday for ORZ022.
Red Flag Warning from 11 AM Tuesday to 11 AM PDT Wednesday for
ORZ615.
CA...Blowing Dust Advisory until 1 AM PDT Tuesday for CAZ084-085.
Freeze Watch from late Tuesday night through Wednesday morning
for CAZ085.
Red Flag Warning from 11 AM Tuesday to midnight PDT Tuesday
night for CAZ280-284-285.
Wind Advisory from 9 PM this evening to 11 AM PDT Tuesday for
CAZ085.
Red Flag Warning until 11 PM PDT this evening for CAZ284-285.
Red Flag Warning from 11 AM Tuesday to 11 AM PDT Wednesday for
CAZ281.
Excessive Heat Warning until 11 PM PDT this evening for
CAZ080-081.
Red Flag Warning until 5 PM PDT Wednesday for CAZ282.
Pacific Coastal Waters...Small Craft Advisory until 11 PM PDT Tuesday for PZZ350-356.
Heat Advisory from 11 PM this evening to 11 PM PDT Tuesday for
PZZ356.
Small Craft Advisory until 5 AM PDT Wednesday for PZZ370-376.
Hazardous Seas Warning until 5 PM PDT this afternoon for PZZ376.