FXUS66 KMFR 191103
Area Forecast Discussion
National Weather Service Medford OR
403 AM PDT Sun Aug 19 2018
.DISCUSSION...Hot weather with somewhat heightened thunderstorm
chances is on tap for the next several days, then weather will
transition to cooler, and at times clearer, during the second half
of the week.
A long wave ridge with its axis between 130W and 140W will amplify
over the next few days. A short wave will ride down the backside of
the upstream trough later today, which could serve as a trigger for
thunderstorms, but instability and moisture are not impressive and
and concentrated mainly in the northern and central Cascades. So
kept schc thunderstorms to a limited area north of Crater Lake this
afternoon. Moisture transport from the south will strengthen this
evening, which will bring schc thunderstorms to a more widespread
swath of northern Klamath and Lake Counties. However, recent runs of
the NAM/GFS project moisture may go a bit too far east of the
forecast area to have an impact on thunderstorm chances.
Temperatures today will be a bit cooler than yesterday, then looking
forward there won't be much change in highs today through Tuesday.
The exception will be the coast and Umpqua Basin, where the return
of low level easterly flow will lower coverage of marine stratus,
allowing conditions to warm. Highs through Tuesday will be near
normal along the coast, and generally 5-10 degrees above normal over
the inland areas. The highs will be several degrees lower in areas
covered by thick smoke.
Models have come into better agreement that a low will cut off
from the general flow late Monday into Tuesday, which could bring
a chance of thunderstorms to a large swatch of our CWA as
moisture wraps around the low late Monday through Tuesday evening.
So, it's looking likely that there will be thunderstorms in the
Medford CWA, but determining where they'll develop is a challenge.
Wednesday into Thursday, the low should fill and shift out of the
area, and we'll transition to onshore flow, and temperatures will
start a slight downward trend day to day. Thursday into Friday, a
dry cold front will push into the area. So, the slight cooldown
should continue into the weekend, and more importantly, this front
should temporarily clear smoke out of the area. -McAuley
.AVIATION...For the 19/12Z TAFs...IFR to LIFR stratus and fog will
impact the Coos/Douglas coasts overnight into Sunday. Lower
conditions will push inland to the western edge of the coastal
hills, and then last until at least 18-20z Sunday. Some stratus may
persist along the immediate coast Sunday afternoon. Expect IFR to
LIFR to push back onshore Sunday evening.
Inland, VFR will prevail in Roseburg and the Umpqua Basin. But,
basically from the Umpqua Divide southward and the Cascades
eastward, expect wildfire smoke to at least occasionally reduce
visibility to MVFR. IFR and local LIFR visibility should be expected
immediately down wind of the active wildfires, primarily in the
the Illinois Valley, across northern California, and much of
the east side from Klamath Falls south and east. -Spilde/Schaaf
.MARINE...Updated 100 AM PDT Sunday 19 August 2018...A thermal
trough will continue to produce both small craft north winds and
wind driven seas. The gustiest winds and steepest seas will occur
south of Cape Blanco through this evening with advisory fresh swell
continuing through Monday night. A quick break is expected mid week
before the next thermal trough builds in again. -Schaaf
.FIRE WEATHER...Updated 330 AM Sunday August 19th...A thermal
trough currently situated along the coast will move inland today
as an upper trough approaches the area. Breezy conditions are
expected this afternoon and evening ahead of the trough. Relative
humidity values will continue to be low during this time and with
the expected increase in winds, critical fire weather conditions
will be met in southern Modoc. Thus, a Red Flag Warning is in
effect for that area, including the Stone Fire. It's probably
worth mentioning that confidence is high that RH will reach
critical levels... though confidence is more moderate that winds
will reach criteria. It will be close, and though winds may meet
strict criteria for 3 hours straight, we still feel this warrants
a warning given that fuels are near record dry.
The upper trough will cut off on Monday and linger over the area
into at least Wednesday, bringing a slight chance or chance of
thunderstorms to a large swatch of our CWA as moisture wraps
around the low late Monday through Tuesday evening. So, it's
looking likely that there will be thunderstorms in the Medford
CWA, but determining where they'll develop is a challenge. We
look forward to future runs of convection allowing models that
will project out to Monday and then Tuesday.
The trough will exit off to the east by Wednesday afternoon and
conditions will stabilize for Thursday. The next item of concern
after then, will be a dry cold front pushing through Thursday into
Friday, likely bringing periods of breezy winds. /BR-y/M&M
OR...Air Quality Advisory.
CA...Red Flag Warning from 4 PM this afternoon to 8 PM PDT this
evening for CAZ285.
Pacific Coastal Waters...Small Craft Advisory until 5 AM PDT Tuesday for
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