Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 271551
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
851 AM PDT TUE SEP 27 2016

.SHORT TERM...Expect two additional days of very warm weather as
a ridge remains in place followed by a drop into fall like
temperatures Thursday and Friday then much cooler and wet weather
by Sunday as an upper trough moves into place.

This morning, areas of low clouds are present north of Cape
Blanco and into the Coquille and Northwest Umpqua Valley as well
as near Brookings. Low clouds are expected to clear in the late
morning and early afternoon then will return to the coast this
evening. The area remains under the influence of a high pressure
ridge today and expect another very warm day which high
temperatures in the 80s to low 90s. Also expect strong gusty north
winds along the coast and over the coastal waters this afternoon
and evening. On Wednesday the ridge axis will shift east and a
shortwave trough will move inland but remain north of the area.
This will bring a few degrees of cooling for areas west of the
Cascades. Overall, conditions will remain warm and dry on
Wednesday.

Beginning Thursday, expect a change to cooler fall like pattern as
a front moves inland and an upper level trough drops southward
along the Pacific Northwest coast. Winds will increase on Thursday
across areas east of the Cascades with west to southwest winds
gusting to 20 to 30 mph. Gusty south winds are also likely in the
Shasta Valley on Thursday. As the trough begins to move inland
Friday, expect additional cooling with high temperatures returning
to seasonal norms and expect some rain to develop, mainly along
the coast and possibly inland for some areas west of the
Cascades. Windy conditions are likely east of the Cascades and
into the Shasta Valley with the latest models supporting gusts of
30 to 45 mph in these areas on Friday. Models are in agreement
that this pattern of cool weather with a chance of rain from the
Cascades west will continue on Saturday with the trough staying
near the coast.

The trough is forecast to move inland Saturday night and Sunday.
Models are showing widespread light to moderate precipitation
developing across the area Sunday. Also snow levels will lower
down to 5500  to 6000 feet in the Cascades and Siskiyous. This
may result in some brief snow accumulations over the higher
passes. Temperature will be lowering significantly Friday through
Sunday. By Sunday expect high temperatures to be around 15 degrees
below normal for inland areas with highs in the lower 60s for
inland western valleys and in the 50s for valleys east of the
Cascades.



&&

.AVIATION...27/12Z TAF CYCLE...Low clouds blanket the coastal
waters, Coos County and the lower Umpqua River Valley overnight.
Conditions are most likely IFR cigs. Short term model brings MVFR
cigs to KRBG around sunrise. Confidence on this MVFR condition is
not very high as the low clouds are still trying to cross the
coastal range as of 0500 PDT. Conditions should return to VFR by
noon. Elsewhere VFR conditions are expected. /FB


&&

.MARINE...Updated 200 AM PDT Tuesday 27 September 2016...North winds
will continue to increase overnight through Wednesday evening as the
thermal trough redevelops. Winds and seas will reach small craft
advisory levels late this morning, with gales in the expansion fan
south of Cape Blanco late this afternoon through this evening. The
thermal 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. /FB



&&

.PREV DISCUSSION... /Issued 513 AM PDT TUE SEP 27 2016/

DISCUSSION...Model agreement is very good into Friday then in the
long term portion of the forecast there are still important
differences but the ECMWF and GFS solutions have trended toward
each other. The short and medium term trend has been that the
first couple of fronts in a series of systems on Thursday and
Friday look drier/weaker. These fronts will bring substantial
cooling and breezy to windy conditions over the higher terrain and
across the east side with a slight chance to chance of mainly
coastal rain. The arrival of a stronger front with the potential
for widespread rainfall may hold off until Saturday night at the
coast and Sunday inland.

First, a marine push has brought low clouds and patchy fog to the
coast...Coquille Valley and western Umpqua Valley. The low clouds
will dissipate through the morning. A cooling trend will begin
today with inland high temperatures still around 15 degrees above
normal. A shortwave trough will move northeast across the Pacific
Northwest on Wednesday and bring a few degrees of additional
cooling of high temperatures as well as just a few high clouds
after another early morning of coastal low clouds.

There is high confidence in a deep trough moving southeast out of
the Gulf of Alaska to the Oregon offshore waters by Friday. The
trend of cooler temperatures and stronger winds will continue
Thursday into Friday. East side wind gusts of 15 to 25 MPH are
expected on Thursday and 20 to 30 MPH on Friday. A shortwave will
create weak instability Thursday afternoon/evening with a slight
chance of a shower or thunderstorm in northern Klamath County and
marginally greater instability northeastward into north central
and northeast Oregon.

The approach of the upper low will bring an increase of clouds and
a very noticeable shift to below normal temperatures on Friday.
There also could be a few light showers with the highest
probability for the coast and Umpqua Valley.

Thereafter, model solutions diverge regarding the track of the
upper low and timing of embedded waves. Depending upon whether the
low stays farther offshore per the ECMWF or tracks closer to the
coast will likely determine whether Saturday`s weather closely
resembles Friday or if instead the probability of precipitation
will be higher. A stronger front will likely accompany the upper
low when it finally tracks inland around Sunday and could bring
an honest to goodness rainy day. There is also the potential for a
second wet system to follow in the cold northwest flow early next
week.

FIRE WEATHER...Updated 200 AM PDT Tuesday 27 September 2016...
Today and Wednesday will feature gradually cooling conditions as the
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. The accompanying surface front will bring
stronger winds Wednesday and more so on Thursday, with 30 MPH gusts
expected. In spite of cooler temperature, inland humidities south
of the Umpqua Divide may not be increasing as much as previously
thought on Wednesday or Thursday due to a much drier air mass
behind the front. We will still be monitoring for the potential
for critical fire weather conditions on both of these days,
especially Thursday.

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
week. /FB

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...None.

CA...None.

Pacific Coastal Waters...Small Craft Advisory until 2 AM PDT Wednesday for
     PZZ350-356-370-376.
     Small Craft Advisory for hazardous seas until 11 AM PDT Thursday
     for PZZ350-356-370-376.
     Gale Warning from 5 PM this afternoon to 2 AM PDT Wednesday for
     PZZ376.

$$

CC/CC/CC


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