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Area forecast discussion 
National Weather Service Medford or
307 PM PDT sun Aug 2 2015

Discussion...an upper level low pressure system off the
California coast continues to send moisture north-northwestward
from Nevada into northern California and southwest Oregon. There
has been a stubborn corridor of thick middle/upper level cloud
cover and scattered showers from Douglas County southeastward to
western Modoc County. The cloud cover has largely prevented
convection so far this afternoon due to a lack of surface heating
and instability in these areas. However, on the edges of the thick
clouds, where some sun was able to poke through, convection
developed over portions of northwest California and moved into
Curry County in the last hour or so. Various lightning networks
indicated about 100-150 cloud to ground lightning strikes on the
west end of the Kalmiopsis Wilderness with a few bolts at the
beaches near Gold Beach and Port Orford. The main vorticity lobe will
swing northward through the east side late this afternoon through
tonight. Current radar imagery is showing thunderstorms developing
in the vicinity of the Warner Mountains and also just northwest of
Lakeview. Expect this area to be the focus for showers and
thunderstorms through tonight. There is some destabilization also
taking place in western Siskiyou County and expect we should see
some cells develop there too, albeit perhaps closer to or after
00z (5 PM pdt). Since the flow aloft is from the south and
southeast, much of the action will propagate north- northwestward
through the evening hours. Thunder potential will continue through
the overnight hours, but should dwindle back to showers by
sunrise.

By Monday, the flow aloft will turn southwesterly. Most of the
energy from the vorticity lobe will have lifted north of the area, but
an axis of instability will remain from the Siskiyou/Marble
Mountains north-northeastward up the Cascades to northern Klamath
and lake counties. Expect an area of scattered thunderstorms to
develop near the Cascades in the afternoon, then move east-
northeastward over the Fremont-Winema National Forest areas during
the late afternoon and evening. Activity should be more isolated
back toward the southwest.

On Tuesday, models are showing another southerly surge of moisture
as another shortwave approaches the norcal coast. The nam12 is
farther north and west than the rest of the models with this
feature showing potential for activity to move back west of the
Cascades. But for now, have gone with the consensus (a bit
farther south and east) and have an area of showers and
thunderstorms possible in the same general locations as on Monday
from Siskiyou County north-northeastward up along the Cascades to
the east side.

The shortwave will finally move inland on Wednesday and most areas
will dry out, though we have maintained a slight chance of
thunderstorms in portions of eastern Modoc and lake counties. Dry
weather will continue into Thursday, then another upper low off
the California coast will move in late in the week into the
weekend. This may bring another round of showers and
thunderstorms...especially from the Cascades eastward. Spilde

&&

Aviation...for the 02/18z taf cycle...areas of smoke will persist
through tonight for all taf locations except for North Bend and
Roseburg with reduced visibilities and limited vertical visibility.
Outside the smoke, conditions will be VFR. Isolated thunderstorms
are possible over parts of the area through this evening, especially
in areas that have little or no cloud cover which includes parts of
Curry County and Lake County east of the Cascades. Storms may
produce gusty, erratic winds and brief MVFR cigs/vis. At the coast,
areas IFR stratus will return again tonight. -Petrucelli

&&

Marine...updated 200 PM PDT Sunday 2 August 2015...offshore high
pressure and weak low pressure near the coast will keep winds light
and seas small through Tuesday morning. The models are in good
agreement showing a thermal trough and high pressure offshore
strengthening Tuesday afternoon. This will bring increasing north
winds and choppy seas late Tuesday afternoon and is likely to last
into at least Thursday. -Petrucelli



&&

Fire weather...updated 250 am PDT Sunday 2 August 2015...with
clearing in northwestern California and extreme southwest Oregon
thunderstorms have quickly developed this afternoon. The storms have
been mostly over the southern coastal ranges so far...but the line
of showers that extend along the vorticity axis that stretches
from the storms in Curry County to Lassen County are showing
intensification and am expecting this to continue as the shortwave
continues to move north behind the exiting cloud shield. Elevated
instability remains past 6z tonight with another...weaker short
wave moving across the region keeping the possibility of isolated
thunderstorms overnight. By early morning the cloud deck from the
previous evening's thunderstorms should exit most of the
region...allowing better surface heating than today. The flow that
is feeding moisture into the region will become more
southwesterly...push the unstable air mass to the east with
thunderstorms developing in northern California...the Cascades and
the east side. The flow continues its westerly shift with only
isolated thunderstorms expected from the Cascades eastward and
northern California. By Wednesday the flow will be northwesterly
across the entire region with high temperatures near or below
ninety degrees across the entire area. Sven

&&

Mfr watches/warnings/advisories...
or...red flag warning until 5 am PDT Monday for orz625.
Red flag warning from 2 PM to 11 PM PDT Monday for
orz617-623>625.
Red flag warning until 5 am PDT Monday for orz624.
Red flag warning until 11 PM PDT this evening for
orz615-616-619-620-622.
Red flag warning until 5 am PDT Monday for orz617-621-623.

California...red flag warning until 11 PM PDT this evening for
caz280-281-284.
Red flag warning until 5 am PDT Monday for caz285.

Pacific coastal waters...none.

$$

Mas/sbn/map/czs

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