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fxus66 kmfr 171639 

Area forecast discussion
National Weather Service Medford or
939 am PDT Tue Sep 17 2019

Update...bands of showers with the front are moving inland and
crossing over the Cascades at this time. A cooler air mass moves
in behind the front, bringing snow levels down the higher
elevations, including Crater Lake. There still looks to be
marginal instability in the coastal waters and near the coast, so
will leave the isolated thunderstorms in that area late this
afternoon into the overnight hours. Sven


Previous discussion... /issued 348 am PDT Tue Sep 17 2019/

Discussion...a front departed the area yesterday but not before bringing
additional significant rainfall. Klamath Falls broke a daily record
for rainfall yesterday with 0.68 inches of rainfall. Temperatures
were observed Monday with afternoon readings about 20 degrees below
normal. After taking a look at climate data, medford's high
temperature of 64 degrees Monday ranks 6th in terms of the lowest
high temperature for Sep 16.

Temperatures warm some today, by a few degrees, as another wet front
approaches from the west. Rain will reach the coast this morning,
and this will be accompanied by some gusty south winds. Wind gusts
at the coast will approach 40 mph at the CAPES and at most places
along the coast from Cape Blanco southward. The south-southwest wind
direction favors places like Azalea and the Illinois Valley for some
gusty winds late this morning and afternoon. The Shasta Valley and
areas east of the Cascades will become gusty too, but Wind Advisory
criteria (45mph) will likely not be reached. By this evening the
band of rain along the front will stretch from Siskiyou County
northeast through Northern Lake County. The front will push farther
east overnight, and as cold air aloft follows the front,
thunderstorms are possible along the coast and just inland. This
instability will affect most areas during the day Wednesday, and
there's a slight chance of thunder for the entire forecast area. As
was the case with storms over the past 24 hours, 0-6km bulk shear is
weak and instability is marginal, so we don't expect any organized,
severe storms over land. Some stronger storms are again possible
over the waters or coastline.

Drier, deep northerly flow is expected on Thursday, so precipitation
chances diminish sharply, with the best chances in lake and Modoc
County. With a cool air mass in place and some overnight clearing
skies possible, frost is possible in most areas east of the
Cascades. After a few dry days on Friday and Saturday when
temperatures creep back up to near normal readings for this time of
year, conditions return to cooler with a chance of rain Sunday. An
upper trough will likely move overhead Sunday and bring with it a
chance for rain. Ensembles suggest less rain (amounts and coverage)
than the current system, but temperatures will definitely lower by
at least 5 degrees from Saturday. Warming and drying conditions will
likely follow this upper trough. Strong offshore northeasterly winds
could follow this upper trough on Monday (plenty of gefs ensemble
members suggest this), especially since this is the season for that
sort of thing, but confidence is low 7 days out.

Aviation...for the 17/12z tafs...from the Cascades west...VFR
conditions will prevail initially, but an incoming front will bring
areas of MVFR cigs/vsbys to the coast by morning with local IFR
cigs/vsbys and obscured higher terrain. The lower conditions will
spread to the Cascades by mid-afternoon. The front will move east of
the Cascades this evening, but it will leave behind the lower
conditions with rain showers that will persist through tonight.
There will also be isolated thunderstorms over the coastal waters

East of the Cascades...VFR conditions will prevail initially, but an
incoming front will bring gusty winds this afternoon along with
increasing clouds. Rain will develop this evening with some
obscuration of higher terrain. The rain will change to showers
tonight and winds will diminish, but there will still be some
obscuration of higher terrain.

Marine...updated 230 am PDT Tuesday 17 September 2019...a front
will move through the waters today. A barrier jet will develop near
the coast, and this will bring gale force winds and very steep wind-
driven hazardous seas. Conditions will improve this evening into
Wednesday, but seas will likely remain hazardous to small craft
through Wednesday evening. Offshore high pressure and a thermal
trough near the coast will build Thursday into Friday, then weaken
Saturday. This will bring stronger northerly winds, especially south
of Cape Blanco.

Fire weather...updated 200 am PDT Tuesday 17 September weather concerns are minimal for the next several
days. The Sunday front brought sufficient wetting rainfall to
nearly all areas, resulting in a rapid reduction in fire danger.

A second strong front will move into the area today into
Wednesday, bringing another significant wetting rain event.
Precipitation will likely begin along the coast and into the lower
Umpqua valley this morning, spread inland to the Cascades by
this evening, then south and east of the Cascades overnight into
Wednesday morning. This front will be moving in on a slightly
different trajectory than the last one, but precipitation amounts
will be similar. Southeast areas (modoc) probably won't see quite as
much. It should be noted that there'll likely be another period of
gusty southwest winds today in advance of the front, especially
over the east side and in NE California but also near the coast.
Local fire weather guidance is suggesting wind gusts at the more
exposed RAWS sites in the 25-35 mph range. Even so, fuels will
remain moist and humidity high.

Thunderstorms will first affect the coast this evening. The cold
pool associated with that front will move inland Wednesday, so
isolated thunderstorms are a possibility again just about

Some showers could linger into Thursday, but most areas will
dry out late this week into the weekend with temperatures
returning to normal. Jrs/Keene


Mfr watches/warnings/advisories...


Pacific coastal waters...Small Craft Advisory until 11 PM PDT Wednesday for pzz356-376.
Gale Warning until 5 PM PDT this afternoon for
Small Craft Advisory from 5 PM this afternoon to 11 PM PDT

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