Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 280924

Area Forecast Discussion
National Weather Service Medford OR
224 AM PDT Sun May 28 2017

.DISCUSSION...A ridge of high pressure remains over the PacNW
today and will produce another mostly sunny, hot, dry day similar
to yesterday. One exception is along the coast where extensive
and stubborn stratus will keep rather cloudy, cool weather in
place. Another possible exception will be over the mountains (the
Cascades and Siskiyous, in particular) where there is at least
some chance of an afternoon thunderstorm. It will certainly be
unstable enough, but a general lack of moisture and forcing will
probably limit any convection to cumulus buildups. However, a
thunderstorm could poke through in the mountains, so the slight
chance was left in.

Conditions for thunderstorm development improve tomorrow. It will
remain hot and unstable, but moisture will increase, and
shortwaves ahead of an approaching trough will provide some
forcing to get things going. Guidance all continues to point at
the Cascades and Siskiyous as the most likely places to see
storms, but steering flow that is from the S-SE at 20-30 knots
could push a storm out over the west side valleys late in the day.
This was already well covered in the going forecast, so few
changes were made.

Changes were made to Tuesday, however, as the upper trough comes
ashore. There is a little better agreement among the guidance
that Tuesday will be noticeably cooler and more stable west of the
Cascades, so thunderstorms were pulled in favor of regular old
showers. The mountains and east side still stand a good chance for
showers and thunderstorms Tuesday, and pops were increased,
especially in the mountains. The GFS does remain a wet outlier,
but it is not quite as bullish as it was, and other models have
trended toward it as well.

From Wednesday on into next weekend, the models are in decent
agreement in showing general zonal flow with little chance for
precipitation and no obvious hot or cool spells. -Wright


.AVIATION...28/06Z TAF CYCLE...Along the coast and over the
coastal waters...MVFR cigs with areas of IFR cigs/vsbys will
prevail over the next 24 hours. Patchy drizzle is possible as
well. Over the Umpqua Basin...MVFR/IFR cigs/vsbys in marine
stratus and fog is spreading into the Basin and will progress as
far as the KRBG area, where there will be MVFR ceilings between
11z and 18z. The lower conditions will burn back to the coast
after 18z Sunday. Over the remainder of the area...VFR will
prevail through Sunday evening... but some cumulus will develop
over the Cascades and Siskiyous with isolated afternoon and
evening thunderstorms possible.


.MARINE...Updated 200 AM Sunday 28 May 2017. The marine layer
will remain quite deep over the coastal waters today, resulting in
widespread stratus and fog that could reduce visibility to less
than a half of a mile at times. Drizzle is also possible. Winds
and seas, however, will remain light.

North winds will increase with the redevelopment of a thermal
trough late tonight. They will peak (likely below small craft
advisory levels) on Monday, before weakening as a disturbance
moves onshore Tuesday. Additional weak disturbances will keep
generally light, variable winds and low seas over the area
Wednesday/Thursday and perhaps even into Friday. At this point it
looks like the thermal trough will eventually return late in the
week or next weekend. -BPN




Pacific Coastal Waters...None.

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