Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 121553
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
853 AM PDT Wed Aug 12 2020

.UPDATE...Clouds associated with the dry cold front and trough
have pushed into the coast and the Umpqua Basin this morning, and
will gradually sweep through the area through the afternoon. This
is a sign of slightly cooler temperatures for today, but these
will be short lived as heat will quickly return for the latter
part of the week and especially this weekend. An Excessive Heat
Watch remains in effect for many of the West Side valleys and the
valleys of western Siskiyou County.

We are also keeping an eye on smoke, which has filled the lower Klamath
and Salmon River Valleys, with haze extending to the northwest
over the Shasta Valley, into TuleLake and the Klamath Basin, and
on into central Lake County. Thunderstorms are also a main focus
of efforts today, mainly for Saturday and Sunday afternoons, which
now looks like it should have some influence from the remnants of
Hurricane Elida. We will need to keep a close eye on this, as the
tropical moisture could make for an interesting situation.

Otherwise, the current forecast looks on track, and with the
exception of some changes to smoke coverage and clouds, no major
updates were needed. See the previous discussion below for more
detail on the coming week. -BPN

&&

.AVIATION...For the 12/12Z TAF Cycle...Areas if LIFR/IFR are
occurring along many areas of the coast and inland into the Coquille
Basin. These lower conditions should improve later this morning,
similar to what occurred yesterday. For the remainder of the area,
VFR conditions prevail and will do so through the TAF period. Expect
some high level cloud cover to stream through today as a weak front
moves through the area along with another round of gusty winds this
afternoon and evening.

The exception to VFR will be in the vicinity of the Red Salmon Fire
complex in far western Siskiyou County. Conditions in that area will
likely be reduced at times due to wildfire smoke. /BR-y

&&

.MARINE...Updated 830 AM PDT Wednesday 12 August 2020...A thermal
trough will rebuild near the coast late this afternoon, and strong
gusty north winds and steep wind driven seas will develop at that
time south of Cape Blanco. The trough will strengthen  further
Thursday, bringing conditions hazardous to small craft north of Cape
Blanco with gales possible south of Cape Blanco. Winds and seas will
peak Friday, then gradually diminish Saturday into Sunday as the
thermal trough weakens. Conditions will drop below advisory criteria
by Sunday morning and relatively calm conditions will then prevail
into the first half of next week.


&&

.PREV DISCUSSION... /Issued 446 AM PDT Wed Aug 12 2020/

Updated Aviation Discussion...

DISCUSSION...Today will be the coolest day of the week with
expected high temperatures about 5 degrees below normal for this
time of the year. Stronger than normal afternoon breezes are
expected again today thanks to an approaching cool front. We
maintain a Red Flag Warning for portions of Modoc County this
afternoon, where the combination of gusty winds and low
humidity...along with recent cloud to ground lightning...will
bring critical fire weather conditions.

Friday will trend warmer, and Saturday and Sunday will be downright
hot, with hot weather potentially lingering into Monday. Widespread
record-breaking heat is not expected, but conditions won`t be far
from it. Afternoon temperatures over the weekend will peak at 15
degrees above normal, and there will be a high risk for heat impacts
for much of the population in valleys west of the Cascades to
include the Rogue, Umpqua, Illinois, and Shasta Valleys. To give a
bit of historical perspective, the record high temperature for
Medford for Aug 15 is 108, and we`re forecasting a high temperature
of 105 this Saturday, Aug 15. For Roseburg, we`re forecasting 98 on
Saturday, and this would tie the record for Aug 15. For
Yreka/Montague, we`re forecasting a high of 99, and the record of
Aug 15 is 105.

With heat typically comes at least a slight chance for thunderstorms
sometime during the period of warmest temperatures. This will be no
different.  The GFS has been consistent in showing some instability
from Northern California northward into Southern Oregon. Midlevel
moisture is generally too low for many storms per the GFS, but
the pattern of deep southerly flow and hot temperatures suggests
at least a slight chance for storms, so we are maintaining that
over mostly Western Siskiyou County for Saturday afternoon and
evening. We`ll keep an eye on the data and consider expanding this
area north and eastward pending increasing evidence of sufficient
trigger and moisture.

Moving forward, after another hot day on Sunday, an upper trough to
the northwest should start to influence the weather next week and
bring breezy and cooler conditions. How cool is a big question, and
models haven`t provided a clear signal yet.


FIRE WEATHER...Updated 400 AM PDT Wednesday 12 August 2020...Gusty
winds will impact much of the area today (trending lower west of
the Cascades compared to yesterday) but will be most significant
over portions of Modoc County where we have a Red Flag Warning in
effect for this afternoon and evening. Afternoon humidity in Modoc
County will dip to near 10 percent this afternoon. Wind will blow
on recent cloud to ground lightning flashes in Lake and Modoc
Counties, so this is particularly concerning.

Generally dry conditions with seasonable breezes are expected
Thursday and Friday, and this will be followed by significantly
hotter temperatures Saturday and Sunday. Enough moisture,
instability, and trigger could reach the forecast area on
Saturday afternoon for storms to form over Western Siskiyou
County. Right now limited moisture suggests isolated storms at
most, but we`ll have to watch the data as deep southerly flow that
the models are currently suggesting typically means a broader
area of storms are possible. Keene

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Excessive Heat Watch from Saturday morning through Sunday
     evening for ORZ023-024-026.

CA...Excessive Heat Watch from Saturday morning through Sunday
     evening for CAZ080-081.
     Red Flag Warning from 2 PM this afternoon to 8 PM PDT this
     evening for CAZ285.

Pacific Coastal Waters...Gale Watch from Thursday afternoon through Saturday morning for
     PZZ356-376.
     Small Craft Advisory from 5 PM this afternoon to 5 PM PDT
     Thursday for PZZ356-376.

$$


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