Area Forecast Discussion
Issued by NWS Medford, OR
FXUS66 KMFR 310810
Area Forecast Discussion
National Weather Service Medford OR
110 AM PDT SUN JUL 31 2016
.DISCUSSION...31/00Z NAM/GFS/EC IN.
There were four cloud to cloud lightning strikes over southeast
Lake County Saturday afternoon...but no cloud to ground strikes. A
thunderstorm got going just southeast of the Medford CWA this
evening...but no strikes within the CWA. That storm has now moved
off to the east. Skies are clear over the Medford CWA except for
some marine stratus offshore.
The main item of concern Sunday through Tuesday will be wind and
very dry conditions.
The winds will be generated by two troughs moving onshore to the
north of the area. The first one is moving through to the north
now and is relatively weak. This will bring some gusty winds to
the east side Sunday. This combined with very low relative
humidities will likely create Red Flag Warning conditions over
Modoc county. Sunday highs inland will be cooler than the
Saturday highs...around 5 degrees above normal over Oregon and 5
to 10 degrees above normal over northern California.
The second trough will move onshore Tuesday morning and this one
will be much stronger. The models are trending slower with this
feature. At this time it looks like it will push a dry front
onshore Monday night into Tuesday...and winds will be strong and
gusty east of the Cascades Monday afternoon and evening.
This...combined with the very dry air already in place may once
again make for Red Flag Warning conditions over the area. Monday
highs will be similar to the Sunday highs. If the trough slows
much more...it may be windy on the east side Tuesday as well.
Tuesday will be the coolest day of the week. Inland highs will be
near normal over most of the area...and a bit below normal over
the Oregon west side.
Long term forecast discussion from the Saturday afternoon AFD with
some edits and updates. Wednesday to Saturday...As usual with
summertime fronts...the cold air is fairly shallow and daytime
temperatures are expected to warm back up Wednesday and Thursday.
Nighttime temperatures will be near or slightly below seasonal
norms. Inland highs will be near normal values...and the Wednesday
highs will be a degree or two warmer over most of the area. Southwest
Oregon and western Siskiyou County will have to contend with the
return of thermal trough and offshore flow which will keep
conditions warm and dry (in term of nighttime humidity).
For Friday and Saturday...both the GFS and ECMWF are in fairly
good agreement that an upper level low pressure will drop into
southern BC or possible NW Washington with a broad trough down as
far south as northern California per EC and just to southern
Oregon per GFS. If the trough is strong enough...it may turn winds
aloft southerly enough to advect some monsoonal moisture into the
area. That...combined with the cooling aloft provided by the
trough may allow thunderstorms to develop Friday afternoon and
evening and possible Saturday afternoon and evening as well. Won`t
add it to the forecast just yet but if the models consistently
support this scenario thunderstorms may have to be added to the
forecast down the road. This may send another cold front into our
forecast area...cooling off temperatures toward the end of the
week. Gusty winds will be a concern again toward the end of next
.AVIATION...31/06Z TAF cycle...North to northeast winds above the
surface in the 925mb layer along the Coos County coast are
forecast to be in the 20 to 30 knot range through the morning with
an additional 3 degrees Celsius of cooling at that layer. This is
expected to be enough to keep ceilings out of KOTH, but MOS
guidance indicates it coming in in the 400-800 foot range. Thus,
confidence in the forecast there is only low to moderate.
Elsewhere, VFR will prevail through the TAF period as clear skies
continue with gusty afternoon and evening winds. BTL
.MARINE...Updated 1045 PM PDT Saturday 30 Jul 2016...A thermal
trough along the coast and high pressure offshore will continue to
produce moderate to strong north winds and steep to very steep
wind driven seas through late Sunday. Hazardous seas are expected
over most the waters through tonight with gales south of Cape
Blanco. On Sunday expect gales and hazardous seas south of Cape
Blanco and small craft advisory conditions to the north. The most
hazardous winds and seas are expected beyond 5 nm from shore.
Winds will decrease slightly on Monday but still expect a mix of
steep to very steep seas over the waters as well as gusty winds
south of Cape Blanco. Isolated gales are also possible Monday
afternoon and evening from 15 to 25 nm from shore south of
Brookings. Winds are expected to rise to gales again by Tuesday
evening and may continue through late next week. BTL/CC
.FIRE WEATHER...Updated 855 PM PDT Saturday 30 July 2016...
Please see above section regarding the Bybee Creek Fire. We had
1-2 hours of critical fire weather conditions at 3 locations in
the Modoc today, just short of the 3 hour duration needed to
constitute Red Flag conditions. There is concern for gusty winds
and low relative humidities for the next few afternoons/early
evening hours starting Sunday. The Red Flag Warning for a good
portion of FWZ 285 remains in effect for Sunday afternoon and
early evening. The fire weather watch for Sunday for southeast FWZ
624 for Sunday afternoon and evening has been cancelled because
winds are not expected to be high enough for critical fire weather
conditions there based on the zone specific criteria.
The models show Monday and possibly Tuesday being windier. An
upper low is expected to drop southeast towards northwest
Washington Monday afternoon with an increasing southwest flow
ahead of the low. For now we have the Fire Weather Watches out
for FWZ 285 and southeast portions of FWZ 624 and it is possible
this watch may need to be expanded. BTL/Petrucelli
OR...Fire Weather Watch from Monday afternoon through Monday evening
CA...Fire Weather Watch from Monday afternoon through Monday evening
Red Flag Warning from noon to 9 PM PDT Sunday for CAZ285.
Pacific Coastal Waters...Small Craft Advisory until 2 AM PDT Tuesday
Gale Warning until 5 AM PDT Sunday for PZZ356.
Hazardous Seas Warning until 5 AM PDT Monday for PZZ356.
Hazardous Seas Warning until 5 AM PDT Sunday for PZZ350-370.
Small Craft Advisory from 5 AM Sunday to 2 AM PDT Tuesday for
Gale Warning until 5 AM PDT Monday for PZZ376.
Hazardous Seas Warning until 2 AM PDT Tuesday for PZZ376.