Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 290937

Area Forecast Discussion
National Weather Service Medford OR
237 AM PDT Mon May 29 2017

.DISCUSSION...A strong upper ridge of high pressure continues to
dominate our weather this morning, but things will begin changing
today as a trough approaches from the west. The ridge axis has
already shifted just east of us, and this will allow for an
increase in moisture and instability which will lead to some
thunderstorms today. The focus remains over the mountains where
instability is strongest, capping the weakest, and where the
terrain can provide its own trigger. Modest height falls and some
PVA this afternoon will also provide additional trigger to boost
the thunderstorm potential today. As mentioned, the bulk of storms
should remain in the mountains, but steering flow is slightly
east of due south, which may allow a storm to drift out over the
valleys late today. There is a lot of convective inhibition in the
valleys, but if a storm is able to get off the mountains, there
is a lot of low level instability to work with.

Tomorrow will be noticeably cooler and showery as the upper trough
moves onshore. The GFS has backed off on the hefty precipitation
it had been showing, and now the models generally agree that we`ll
see some showers Tuesday, but not a big deal. We could still see
a thunderstorm from Crater Lake east on Tuesday, but this also
shouldn`t be a big deal.

The remainder of the week should be relatively quiet with zonal
flow aloft, temperatures around normal, and some passing showers
from time to time. We may start to warm up a little next weekend
as ridging develops offshore. This will also lead to a thermal
trough and stronger north winds over the waters. -Wright


.AVIATION...29/06Z TAF CYCLE...A mix of MVFR/IFR ceilings will
persist over the coastal waters and along the coast tonight
into Monday with patchy fog and drizzle. Marine stratus will
spread into the Umpqua Basin, including Roseburg around 09z
with MVFR prevailing there through about 19z. The low cigs will
erode back to near the coast Monday afternoon. The rest of the area
will be VFR. However, isolated afternoon and evening showers and
thunderstorms are possible from western Siskiyou County up the
Cascades Monday afternoon and evening...which may be accompanied by
locally gusty winds and small hail.


.MARINE...Updated 200 AM Monday 29 May 2017...Winds are currently
light over the area...but there is widespread stratus and fog that
could produce some drizzle and occasionally reduce visibilities to
less than a half of a mile.

North winds have already started to increase this morning as a
thermal trough redevelops. Winds and seas will peak this afternoon
(likely below small craft advisory levels), then will weaken as a
disturbance moves onshore Tuesday. Additional weak disturbances will
keep generally light, variable winds and low seas over the area
Wednesday/Thursday and even into Friday. The thermal trough is now
expected to return late Friday into next weekend with strengthening
north winds and steepening seas over most of the area, especially
south of Cape Blanco. -Spilde/BPN




Pacific Coastal Waters...None.

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