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Area forecast discussion 
National Weather Service Medford or
810 PM PDT Friday Jul 31 2015

Discussion...01/00z NAM in.

A fairly typical thunderstorm pattern is in place over the Medford
County Warning Area with southerly flow aloft advecting monsoonal moisture into
the area. Thunderstorms developed Friday afternoon...mostly over
the higher terrain of northern California and in Oregon from the
Cascades east. These storms are likely dry or mostly the
reported precipitation amounts are very light and spotty. In
addition...two fires in Douglas County became plume- driven due to
the hot and unstable conditions.

The other story is the heat...Medford peaked at a toasty 109f
today...which broke the record for today.

The next concern is a short wave embedded in the southerly flow
now over Siskiyou and Modoc counties. This short wave is
supporting a line of convection which may continue through the
night as it moves into Oregon. The wave will weaken as it comes
through though...and will move into northern Oregon Saturday
morning. Once again...the main concern is dry lightning.

The hot temperatures and afternoon/evening thunderstorms will
continue through the weekend. Friday was likely the hottest day
over the area and a cooling trend will commence Saturday...but it
will still be quite hot with the forecast highs for Medford 104f
for Saturday and 97f for Sunday.

Convection on Saturday will be due to surface heating as there
will not be any short waves or deformation zones around to support
upper level instability or difluence. Expect scattered thunderstorms
to develop over the higher terrain of Siskiyou County and the

Sunday will be a different story short waves will move
over the east side during maximum surface heating. Expect
scattered thunderstorms over that area at that time.

Extended discussion from the Friday afternoon afd...Monday through
Thursday. The upper ridge over the area begins to break down and
shift east Monday. As it breaks down...the thunderstorm threat
decreases in SW Oregon but remains for northern California and
east of the Cascades into Tuesday. Later in the week...the upper
flow turns southwest and takes the atmospheric moisture to the
east of the area. The solutions from the GFS and ec models have
some differences from midweek on. The GFS puts the area under a
very weak flow between a cutoff low west of 130w and a shortwave
in British Columbia. The ec has a more substantial low along the
pacnw coast. The end result is pretty similar...cooler dry


Aviation...for the 01/00z taf cycle...two main concerns exist.
First, are isolated thunderstorms over the Cascades....northern
California and portions east of the Cascades with possible gusty
outflow winds until 4-5z. Second, is reduced visibility from two
wildfires in Douglas County, which could bring MVFR visibilities in
haze and smoke east of Interstate 5 in Douglas County and Rogue
Valley including Medford through tonight. Otherwise VFR conditions
will continue for the next 24 hours. The exception will be along the
coast where marine stratus will re develop resulting in IFR ceilings
between 5-7z. -Petrucelli


Marine...updated 245 PM PDT Friday 31 July 2015...a thermal trough
near the coast will continue to bring moderate to strong north winds
and choppy wind-driven seas reaching advisory criteria through this
evening. The models continue to show borderline small craft for
winds tonight into Saturday for the outer waters, but suspect it may
be overdone. For now we'll go with the idea of winds and seas
lowering tonight into Saturday given the thermal trough is expected
to weaken and move inland. Winds and seas are expected to gradually
lower this weekend...but will remain moderate through next
week...with a possible return to advisory conditions in the southern
outer waters as early as Wednesday. -Petrucelli


Fire weather...updated 800 PM PDT Friday 31 July flag
warnings have been issued for Haines 6 on existing fires for both
the Cable Crossing fire (fire weather zones 616) and the Stouts fire
(straddling the border of 616/617). Isolated to scattered
thunderstorms also prompted a red flag warning for the eastern
portion of zone 617.

Isolated to scattered storms are possible over a much wider area
Saturday, owing to increasing moisture, instability, and the
possibility of a good trigger arriving through the southerly flow
aloft. Storms will likely start off dry and then tend to get
wetter through the evening, especially over California. Red flag
warnings have been issued over much of our forecast area to
highlight this potential. It is noteworthy that some guidance
shows these storms continuing through Saturday night across the
west side Oregon zones...and fire weather watches are also in
effect for Sunday.


Mfr watches/warnings/advisories... flag warning until 11 PM PDT this evening for
Red flag warning from 2 PM to 11 PM PDT Saturday for orz624.
Fire Weather Watch from Sunday afternoon through late Sunday
night for orz621>625.
Red flag warning from 2 PM to 11 PM PDT Saturday for
Red flag warning until 9 PM PDT this evening for orz616.
Heat advisory until 11 PM PDT Saturday for orz023.
Red flag warning until 11 PM PDT this evening above 500 feet for
for orz617.
Red flag warning from 11 am to 11 PM PDT Saturday for
Heat advisory until 11 PM PDT Saturday for orz024-026. flag warning until 11 PM PDT this evening for
Fire Weather Watch from Sunday afternoon through late Sunday
night for caz280-281-284-285.
Red flag warning from 2 PM to 11 PM PDT Saturday for
Heat advisory until 11 PM PDT Saturday for caz080-081.

Pacific coastal waters...Small Craft Advisory for winds until 11 PM PDT
this evening for pzz356-370-376.
Small Craft Advisory for hazardous seas until 11 PM PDT this
evening for pzz350-356-370-376.



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