Area Forecast Discussion
Issued by NWS Medford, OR
FXUS66 KMFR 270300
Area Forecast Discussion
National Weather Service Medford OR
800 PM PDT MON SEP 26 2016
.DISCUSSION...27/00Z NAM IN.
A rex block is now in place over the western U.S with the low over
Baja California and the ridge over the intermountain states. Low
level flow turned onshore Monday afternoon as the thermal trough
moved inland...and flow aloft has become southwesterly. Skies
remain clear over most of the Medford CWA...but there is marine
stratus over the coastal waters and along the coast...mostly north
of Cape Blanco.
Monday was the hottest and driest day of the string...except along
the coast which was cooler due to the return of onshore flow.
Marine stratus will surge into the coastal valleys and Umpqua
Basin Monday night...and a weak front will move onshore Tuesday
morning. It will be dry except for possible drizzle along the
coast. The associated marine push will cool temperatures 5 to 10
degrees on the west side and just a few degrees on the east side.
Inland highs will be 5 to 15 degrees above normal on the west side
and 15 to 20 degrees above normal over the east side and northern
The cooling trend will continue into Wednesday as the ridge moves
slowly east and a trough to the west moves closer to the coast.
The east side and northern California will cool more slowly than
the west side. High temperatures will be 5 to 10 degrees above
normal on the west side and 10 to 15 degrees above normal over the
east side and northern California. Wednesday will be dry.
Extended discussion from the Monday afternoon AFD...Thursday
through Monday. On Thursday, an upper level trough will move
closer to the area. Southwest flow aloft will increase with some
gusty winds expected to develop east of the Cascades in the
afternoon. Isolated showers could develop over the Cascades,
especially north of about Lake of the Woods, but instability
parameters still look marginal, so have not included thunder.
Friday, the first significant short wave associated with the
trough approaches and moves into the area. This will likely bring
some showers to the coast with precipitation chances waning to
slight chance or nil east of the Cascades. Models are showing some
CAPE and negative LI moving into the coast north of Cape Blanco
and also the lower Umpqua Valley, so have added a slight chance of
thunder there during the afternoon/early evening. Shower chances
persist Friday night at the coast due to onshore flow, but it will
likely get quite chilly east of the Cascades where skies are
expected to clear for a while.
By this weekend, models diverge in the timing of the upper trough
as it drops southward along the coast...quite likely due to the
development of a strong jet (130-140kt) upstream over the North
Pacific. Despite the variations in the models, still expect much
cooler conditions with temperatures 5-15 degrees below average and
multiple chances at wetting rainfall. Right now, it appears the
best chance will occur with a disturbance riding along the jet
Sunday night into Monday. Details are likely to change though, so
stay tuned! -Spilde
.AVIATION...27/00Z TAF CYCLE...The latest visible image shows
marine stratus in the vicinity of North Bend and MVFR and occasional
IFR cigs could move in the area around 1z. Current TAF reflects
this, but confidence is low to medium on the timing and it could
move in earlier. So watch for updates on the TAF. The models suggest
the marine stratus could push far enough inland to include the
Umpqua Basin and the latest LAMP guidance and high resolution
moisture fields supports this idea towards 14z. Therefore we`ll
introduce MVFR CIGS into the TAF at Roseburg. There`s a chance these
conditions could come in sooner, so later shifts will need to
reevaluate. Elsewhere, VFR conditions will continue through the TAF
.MARINE...Updated 800 PM PDT Monday 26 September 2016...North winds
will continue to increase tonight through Wednesday evening as the
thermal trough redevelops. Winds and seas will reach small craft
advisory levels tonight into Tuesday. Winds will rise to gales in
the expansion fan south of Cape Blanco Tuesday evening with small
craft conditions elsewhere. The trough will weaken and move inland
Wednesday and Thursday and winds and seas will diminish at that
time. A cold front will move onshore Friday...followed by another
one Saturday night.
.FIRE WEATHER...Updated 800 PM PDT Monday 26 September 2016...
Tuesday and Wednesday will feature gradually cooling conditions
as the upper ridge moves east and loses its influence over the
region. As an upper trough to the west moves closer, temperatures
will drop more noticeably on Thursday. This upper trough will
bring increasing winds Wednesday and more so on Thursday, with
30mph gusts expected. Humidities will increase some Wednesday into
Thursday, but we will still be monitoring for the potential for
critical fire weather conditions on both of these days, especially
The cooling will continue into the weekend as an upper low sends a
series of systems into the area. A system may bring a wetting rain
to the coast and Umpqua Valley Friday then to much of the area over
the weekend or early next week. It is too early to know exactly how
much rain falls or where it falls, but confidence is fairly high
that the pattern will shift to be much cooler and wetter late this
Pacific Coastal Waters...Small Craft Advisory from 11 AM Tuesday to
2 AM PDT Wednesday for PZZ350-356-370-376.
Small Craft Advisory for hazardous seas from 8 PM this evening
to 11 AM PDT Thursday for PZZ350-356-370-376.
Gale Warning from 5 PM Tuesday to 2 AM PDT Wednesday for PZZ376.