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Area forecast discussion 
National Weather Service Medford or
237 PM PST Thursday Nov 26 2015

Discussion...evening update. With the dewpoints about three degrees
colder than last night am expecting the fog that develops to be more
closely confined to near the rivers and other bodies of
water...except for the coast were strong offshore flow should keep
fog offshore. Sven

Short term...tonight through Sunday Omega block is over
the West Coast today. That is when a ridge of high pressure is
held in place by anchoring lows just upstream and downstream. Over
the next few days, the Omega block morphs into a Rex block as the
deep low over the Great Basin retrogrades under the ridge. This
keeps a steady weather pattern over the forecast area through the
weekend. The hard freeze warning was scaled back to areas below
3000 feet mean sea level and significantly below freezing. The frost advisory
on the coast was expanded to include portions of the Coos County

A kicker trough begins to move into the western edge of the upper
ridge Sunday. This starts to dislodge the Great Basin trough and
move it out to the east. Both the Euro and GFS models are in good
agreement on this. Heading into Monday morning, some differences
begin to show up in the models. As the kicker approaches the coast,
the GFS is a bit stronger and further north. Previous GFS runs have
moved this low around quite a bit but it has been consistently on a
track that would take it into this area. The ec has been trending
steadily towards the GFS solution but not as strong. Jbl

Long term...Monday through Thursday night...the forecast for
early next week focuses on the breakdown of the Rex block pattern
over the western states with the development of a split flow aloft
and transition to a wet and relatively warm onshore flow.
Confidence is higher in the character of the weather next week
rather than the specifics of the strength and position of
individual disturbances. The change to southwesterly onshore flow
leads to the possibility of additional snowfall at the highest
peaks but also rain falling on snow at lower peaks and much of the
east side.

The probability of precipitation was removed from the Monday
forecast as confidence is higher that high pressure will linger over
the West Coast with a closed low centered beyond 130w. The evolution
of that low...both its track and strength are still very much in
question. The 12z European model (ecmwf) is consistent in focusing more energy in the
southern branch of the split flow and tracking the low toward
Southern California Monday night into Tuesday...though it has
trended more progressive with more of a southeast rather than south
track. Meantime...the 12z GFS has trended closer to yesterday's GFS
ensemble solution with a slower and weaker solution that does remain
focused in the northern branch of the jet. As in the 00z suite of
data...the European model (ecmwf) solution would keep our area dry through Tuesday
night while the GFS would send a warm front northeastward that may
reach the southwestern portion of our area...Curry and western
Siskiyou counties...before the end of Monday night. The GFS is about
18 to 24 hours faster and slightly stronger than the European model (ecmwf) with a
weak to moderate cold front that would follow around
Tuesday/Wednesday. Both models indicate a stronger warm system may
follow around Thursday. /Dw


Aviation...for the 26/18z taf cycle...conditions on Friday will
resemble those of today. IFR will redevelop in the Umpqua basin this
evening and persist through much of Friday morning. Otherwise... VFR
will continue through this evening then overnight into early Friday
morning...patchy fog with areas of MVFR visibilities is expected in
the other west side valleys.


Marine...updated 200 PM PST, Thursday 26 Nov 2015...lighter
easterly winds and seas are expected tonight into Saturday. Seas may
become high on Sunday into Sunday night with building swell ahead of
a low pressure system that may affect the waters throughout early
next week. The seas forecast for Monday into Tuesday are still
moderate to high but were lowered slightly to reflect an increase in
confidence that the low will be slower to arrive. There is still low
confidence in the exact track and strength of the low but increased
confidence that the pattern will turn active next week with a series
of disturbances to affect the eastern Pacific. /Dw/fb


Mfr watches/warnings/advisories...
or...frost advisory from 10 PM this evening to 9 am PST Friday for
Hard freeze warning from 10 PM this evening to 9 am PST Friday
for orz026.


Pacific coastal waters...none.


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