Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 261104

Area Forecast Discussion
National Weather Service Medford OR
404 AM PDT Wed Jul 26 2017

.DISCUSSION...As the upper low continues to move slowly inland
today, another round of thunderstorms continues in the forecast
area. Isolated thunderstorms in Klamath and Jackson counties
continue to slowly meander to the southwest on an vort axis that
is spinning around the upper low with elevated instability over
the region. A similar patter of instability over the region as
yesterday will bring a similar pattern of thunderstorms over the
area today. The steering winds are very weak today and other than
building storms in the direction of a vort axis that will slowly
move east as we approach and pass max heating today storms will
generally latch to higher terrain today. The upper low will slowly
open as it progresses east through the evening, shifting the
instability to the far east side by Thursday morning.

Heights rise into the weekend with temperatures rising above 100
Saturday in the Rogue valley and Northern California. The thermal
trough deepens on the coast with offshore flow increasing on the
southern Oregon coast Friday night into Saturday. With this have
raised low temps along the southern Oregon coast Friday night and
will likely have to raise high temperatures Saturday. Weak
moisture flow into the region returns pockets of instability and
slight chances of thunderstorms, mostly in western Siskiyou county
and the east side toward mid wee next week. Sven


.AVIATION...25/18Z TAF CYCLE...Along the coast and over the coastal
waters...Isolated MVFR/IFR cigs will increase to areas of MVFR/IFR
cigs this evening and spread into the coastal valleys and lower
Umpqua valley tonight.  The lower conditions will clear back to the
coast by late Wednesday morning. Over the remainder of the
area...VFR conditions will prevail...but there will be isolated to
scattered thunderstorm activity, peaking in the afternoon and
evening. Some higher terrain will be obscured near thunderstorms.


.MARINE...Updated 230 PM PDT Tuesday 25 July 2017...Conditions
will remain hazardous to small craft for all areas tonight with
winds diminishing north of Cape Blanco. Seas will subside below
small craft advisory levels north of Cape Blanco on Wednesday, but
the thermal trough will remain in place through the remainder of
this week and into this weekend, with small craft advisory
conditions persisting south of Cape Blanco. -Spilde


.FIRE WEATHER...Updated 200 PM Tuesday 25 July 2017...Scattered
thunderstorms are forecast over the majority of the forecast
area this afternoon and evening, focused primarily from the
Siskiyous and Cascades eastward. However, thunderstorms do have
the potential to move off the terrain and over the West Side
valleys. Some storms will produce wetting rain because of the
increasing moisture and expected slow storm motion, but abundant
lightning will still cause fire starts.

Tonight there is continued potential for thunderstorms, and it looks
like the biggest threat will be east of the Cascades. It now looks
like some areas will have scattered coverage, so the Red Flag
Warning will be extended through the night for those areas.

On Wednesday the upper low that is now along the Northern California
coastline will move eastward, so the area of potential thunderstorm
activity will also move eastward.  Therefore, the Red Flag Warning
for Wednesday will not include some west side areas that are in
today`s warning.

The thunderstorm threat will diminish Wednesday night as the upper
low moves out to the east of the area and southwest to west
flow aloft develops over the area. This will likely lead to
breezy west winds during the second half the week.


OR...Red Flag Warning from 11 AM this morning to 11 PM PDT this
     evening for ORZ624-625.
     Red Flag Warning from 11 AM this morning to 11 PM PDT this
     evening for ORZ617-621-623.

CA...Red Flag Warning from 11 AM this morning to 11 PM PDT this
     evening for CAZ280-281-284-285.

Pacific Coastal Waters...Small Craft Advisory until 11 PM PDT Friday for PZZ356-376.
     Small Craft Advisory for hazardous seas until 5 PM PDT this
     afternoon for PZZ350-356-370-376.


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