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Area forecast discussion 
National Weather Service Medford or
528 am PDT Monday Aug 3 2015

Updated aviation section.

Aviation...for the 03/12z taf cycle...areas of stratus and fog
with IFR/LIFR ceilings/visible at the coast this morning will retreat
offshore late this morning, then return again tonight. Areas of
smoke will produce MVFR visible over southwest Oregon, including kmfr
and klmt at times. Conditions may worsen to IFR this afternoon as
the fires produce more smoke. We will also see thunderstorms
develop over the Cascades and east side this afternoon which will
produce MVFR ceilings/visible along with gusty erratic winds. -Wright


Previous discussion... /issued 324 am PDT Monday Aug 3 2015/

approximately 1000 cloud to ground lightning strikes have been
recorded by blm lightning in the last 24 hours across the forecast
area. On the bright side, temperatures were down an average of 12
degrees from the previous day and relative humidities were up,
leading to some rainfall with showers and thunderstorms. While
most areas still received less than 0.10", areas that got more
lightning such as the Warner Mountains to around Lakeview, Curry
and Josephine counties, and Modoc and Klamath counties did
generally get 0.10" or more. A cluster of thunderstorms in
southeastern Klamath and Lake County resulted in wind gusts of
30-45 miles per hour as well as rain amounts in the 0.30-0.80" range. In
other areas, such as Jackson County and areas along and near the
Cascade crest, cloud cover and smoke resulted in cooling which
prevented more than a few cloud to ground strikes.

This morning our convergent 500mb vorticity maximum that has been
in the forecast area with it's associated cloud band over the last
24 hours is still drifting slowly northeastward over the
northeastern half of the area. Water vapor imagery clearly
indicates an upper level shortwave trough along and west of Cape
Mendocino. This feature is of utmost concern today because a
return of pronounced surface heating along with this feature and
now ample surface moisture are expected to combine to bring
another round of thunderstorms to the area. Model 850mb computed
lifted indices are on the order of -2c to -5c on the gfs20 and -4c
to -8c on the nam12 for this afternoon and evening from about the
Oregon caves area northeastward across the interior west side,
southeast into the Marble Mountains, across the Siskiyous, and
in the Cascades. In fact, for the interior west side model
guidance is showing the greatest cape values depicted in the last
4 days over the area, which means there is plenty of instability,
even compared to recent days. The limiting factor this afternoon
and evening for thunderstorms in many areas appears to be
moisture, especially moisture in the 600-500mb layer. In short, we
expect that thunderstorm coverage will not be astounding today,
but isolated to scattered thunderstorms will produce significant
amounts of lightning where they do occur.

Additionally, for active wildfire areas, known and unknown, where
upstream smoke does not significantly limit sunshine, we expect
that low level instability will lead to locally gusty winds and
the potential for smoke columns to develop thundershowers over
areas of focused heat.

Red flag warnings are in effect today for the Cascades,
Siskiyous, and Marble Mountains and portions of the Oregon east
side. Locally moderate rainfall amounts are expected with some of
the storms in the mountains, but new fire starts that could spread
from outflow winds are of concern this afternoon and evening.

Tonight we should finally catch a break before another round of
showers and storms try to percolate north in northern California.
Expect storms Tuesday afternoon and evening to be slow movers and
isolated except in western Siskiyou County where scattered storms
are expected. Cloud cover and high humidities should limit the
potential of new starts, but we'll need to get a check on fuel
receptiveness to determine if another red flag warning will be
needed there. Of note, it appears there were at least 12 new fires
reported in that area in the last 2 days.

Another upper level trough, likely cooler than the current one,
is expected this weekend in to early next week. Btl

Marine...updated 900 PM PDT Sunday 2 August 2015...weak low
pressure over the waters this morning will move inland, and high
pressure will build in from the west. This will result in an
increase in north winds and the development of a light chop this
afternoon. North winds and seas will build Tuesday and remain
moderate through Wednesday. Winds will strengthen further later in
the week and possibly reach gales over the southern waters
Thursday and Friday. -Wright

Fire weather...updated 230 am PDT Monday 3 August 2015...
thunderstorms have diminished this morning as a trough axis
gradually moves north of US. We can't really rule out a few random
strikes over our northern zones this morning, but in general all
that's left are showers which will also continue to move north and
decrease. As a result, all remaining red flag warnings for this
morning have been dropped.

There remains quite a lot of cloud over the area, but satellite
shows an area of clearing south of US which is in between the
previously mentioned trough axis and another off the California
coast. This clearing will move over US through the morning and early
afternoon, which will bring some sun back to the area and start the
destabilization process all over again. The combination of surface
heating, modest cooling aloft, and moisture left over from the
showers/storms of the last 24 hours, will result in some pretty
impressive instability today, especially over the Cascades and
Siskiyous. As mentioned, there is another weak trough axis off the
California coast, which will move through here this afternoon and
provide the trigger for more showers and thunderstorms.

We already have a red flag warning out for portions of the east
side, which looks fine, but red flags will be expanded to include
the Cascades and Siskiyous today. It is possible for a storm to get
out over portions of the west side valleys this afternoon,
especially the southern portion of zone 622 (rogue valley), but
confidence isn't high enough to include any west side valley
locations in the warning at this time. -Wright


Mfr watches/warnings/advisories... flag warning from 2 PM this afternoon to 11 PM PDT this
evening for orz624-625-617-621-623. flag warning from 2 PM this afternoon to 11 PM PDT this
evening for caz280.

Pacific coastal waters...none.


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