Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Medford or
253 PM PDT Wednesday Jul 27 2016

Discussion...a broad upper ridge will remain over the region for the next few
days, driving a thermal trough along the coast and hot, dry
conditions. Temperatures will be over 10 degrees above normal in
most places through Friday. Thursday and Friday will be the warmest
days, with triple digit temperatures expected for most west side
valleys Thursday and Friday, including the rogue, Illinois, and
Applegate valleys, and the valleys in Siskiyou County. On the east
side... 100 degrees is possible in areas of Modoc County including
Alturas, Adin, and day. Mid to upper 90s is expected in the valleys
of Klamath and Lake County.

Friday afternoon, models indicate some moisture advection into the
sierras and Siskiyous. Weak instability is forecast in those areas,
and will allow for cumulus buildups and possible thunderstorms. Kept
thunderstorm potential in the forecast at slight chance, as
conditions are marginal. The main moisture source is monsoonal,
which may not be depicted well in the models, and there is no strong
trigger. Steering flow will be weak, around 5 knots, so any storms
that form will stay anchored over high terrain over the Trinity
Alps, Marble Mountains, southern Cascades, and Medicine Lake area.

Conditions will cool somewhat Friday into Saturday, as the pattern
transitions to broad troughing and stronger onshore flow, with a
cold front moving inland late Saturday. Temperatures will still be
above normal Saturday, but generally closer to 5 degrees above
normal. Winds will increase, especially over the east side. There is
a slight chance of thunderstorms over portions of southern Klamath
and lake counties and northeastern Siskiyou and northwestern Modoc
Saturday afternoon, as the front may provide a trigger. Again,
conditions are marginal as projected moisture is very low.

The ridge will continue to shift eastward early next week, giving
way to onshore flow at lower levels and temperatures should cool to
near normal. -MSC


Aviation...27/18z taf cycle...VFR conditions will continue for the
next 24 hours. The exception will be along, at and just off the
coast. Marine stratus is expected to move back just offshore around
5 nm from shore around 0z, then along the coast (north of cape
blanco) between 1-3z. The marine stratus will push back into the
Coquille Valley overnight tonight into at least mid morning
Thursday. Moderate to strong and gusty winds are expected for most
areas along the coast and offshore for most of the period, but will
decrease some during the overnight hours. -Petrucelli


Marine...updated 212 am PDT Wednesday, 27 July 2016...
the forecast remains on track for strong gales in most of the
coastal waters area south of Cape Blanco through Sunday. Recent
model guidance also indicates a similar wind regime may very well
continue into next week, and through next week as well. Through
Thursday winds just above the surface increase to as much as 50 kt.
As a result, the area of gales is expected to expand and there may
be occasional storm force gusts over a small area west of Brookings
between approximately 10 and 40 nm from shore this afternoon through
Thursday evening. Sven


Fire weather...updated 200 PM PDT Wednesday, 27 July 2016...
dry and hot conditions will continue through Thursday. A thermal
trough along and near the coast will remain there will continue to
bring light to moderate northeast winds in the coastal mountains
along with moderate humidity recoveries tonight into early Thursday
morning. Winds will be generally light away from the coast, though a
bit breezy and gusty in the evenings, following typical Mountain-
Valley cycles.

The main challenge Friday and Saturday will be the potential for
thunderstorms or a lack thereof. The models are in general agreement
showing weak low pressure west of California on Friday. Some of the
models suggest the low will open up with weak positive vorticity advection moving northeast
towards northern cal. In contrast the ec has the low positioned
further to the southwest with little or no positive vorticity advection (trigger for storm
development). In addition, there is some disagreement with the
amount of mid level moisture present and degree of instability in
northern cal Friday afternoon and evening. For example the GFS shows
increasing mid level moisture around 500mb, but it's lacking around
700mb. The NAM shows more moisture around 700mb, but not much around
500mb. The one thing I would like to see is a stronger trigger and
at the present time, it's just not there. Gut feeling is we probably
won't get anything, but not i'm not confident enough to remove them.
Given the high fire danger in the areas that could be affected,
we'll keep the a slight chance for thunderstorms in the Trinity Alps
late Friday afternoon and evening, possibly drifting northeastward.
Keep in mind the details on this could change, so watch for updates
on this in the coming days.

On Saturday current guidance shows the focus for thunderstorms
shifting northeast into portions of lake, Klamath County. Even then
were still looking only at a slight chance. Like Friday, the models
are showing different solutions with the amount of mid level
moisture and areas of greatest instability.

Another concern will be the potential for a dry cold front and gusty
winds to occur both ahead of a cold front on Saturday and behind it
on Sunday. Humidities will remain low over the weekend, so the
combination of low humidity and gusty winds will lead to at least
elevated fire danger, especially for east side locations. It will
also bring a 5 to 10 degree cool down this weekend into next week
which will eventually bring humidities up a few percent, at least
west of the Cascades. -Petrucelli


Climate...updated 650 am PDT Wednesday, 27 July 2016...
July 2016 is currently on track to finish 0.2f below the 1981-2010
normal for the month of July for the Medford Airport. This is true
even with the hot temperatures currently in the forecast. The last
time this location experienced a below normal temperature month was
November 2015. Before that the last below normal temperature month
was January of 2014. Btl

Mfr watches/warnings/advisories...


Pacific coastal waters...Small Craft Advisory until 2 PM PDT Sunday for
Gale Warning until 2 PM PDT Sunday for pzz356-376.



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