Area Forecast Discussion
Issued by NWS Medford, OR
FXUS66 KMFR 260300
Area Forecast Discussion
National Weather Service Medford OR
800 PM PDT SUN SEP 25 2016
.DISCUSSION...26/00Z NAM IN.
A strong long wave ridge has built into the west coast and the
ridge axis is now breaking to the east of the area. Low level
easterly flow has weakened. Skies remain clear over the entire
Medford CWA...except for some thin cirrus.
Temperatures warmed up quite a bit today...but the thermal trough
will swing inland over southwest Oregon Monday...so that day will
be the driest and hottest day of the coming week over inland areas.
The return of onshore flow will bring cooler temperatures to the
coast along with marine stratus in the afternoon or evening. Clear
skies will persist over the remainder of the area. Temperatures
along the coast will cool to near normal values...although it will
be warmer than normal in the morning along the south coast. Inland
highs will be 15 to 20 degrees above normal.
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 around 10
degrees on the west side Tuesday. The east side and northern
California will also be cooler...but only by a few degrees.
The cooling trend will continue into Wednesday...but 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. Dry conditions will persist.
Extended discussion from the Sunday afternoon AFD...Thursday
through Sunday. The weather pattern will begin to transition toward
cooler and wetter late this week as an upper level trough digs
southeastward from the Gulf of Alaska. Southwest flow aloft will
increase Thursday afternoon and expect some gusty winds to develop
east of the Cascades. Even though we`ll begin to cool down and
humidity should still be a notch above critical levels, we`ll have
to monitor this for potential fire weather concerns. 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.
The upper trough will likely set up somewhere near or just off
Vancouver Island Friday into the weekend. This will allow multiple
disturbances to rotate onshore, each bringing a chance of
precipitation along with a significant cool-down. We`ll see
temperatures nose-dive during this time frame, with daytime highs
probably 5-15 degrees below normal. Precipitation chances will be
highest along the coast and into the Umpqua Valley over to the
Cascades with many areas along and west of the Cascades likely
receiving wetting rainfall. Snow levels will drop to about 5500
feet, which means the mountains could see some accumulating
snowfall, most likely during the nights. -Spilde
.AVIATION...26/00Z TAF CYCLE...VFR conditions are expected through
the next 24 hours for inland locations. At the coast, there is a
chance IFR CIGS and VIS could develop in the vicinity or at North
Bend late around 10z, but confidence is low to medium. Fog now went
with reduced visibility with scattered low clouds at North Bend, but
this will need to be reevaluated for the 6z TAF issuance.
.MARINE...Updated 800 PM PDT Sunday 25 September 2016...A thermal
trough will keep moderate north winds and wind driven seas going
over most of the area through tonight. The trough will weaken
briefly on Monday with lower winds and seas...but it will redevelop
Tuesday into Wednesday after a weak front moves onshore. Models are
consistent in showing low end gales over the southern outer waters
Tuesday afternoon through Wednesday afternoon. Given the models have
been showing this for the past few runs, decided to go with a gale
watch for zone 376 mainly south of Cape Blanco starting Tuesday
afternoon and going until Wednesday afternoon. Elsewhere, winds will
be weaker Tuesday afternoon through Wednesday afternoon, but will
still reach small craft conditions.
.FIRE WEATHER...Updated 800 PM PDT Sunday 25 September 2016...
Compared to Saturday night, easterly winds will be weaker tonight
but it will remain very dry with poorer recoveries at mid slopes
and ridges. With the weaker winds, red flag warning conditions are
not expected but the extreme dryness warrants headlining.
With an upper ridge in place and surface thermal trough moving
inland, it will be hot and very dry inland on Monday with highs
approaching though not exceeding record levels. Coastal humidities
will improve Monday afternoon, but gusty northerly winds will
develop at the coast on Tuesday.
With the thermal trough moving farther inland Tuesday, humidities
will creep up and inland temperatures get a modest start to a
cooling trend. After very slight additional cooling on Wednesday,
temperatures will be noticeably cooler Thursday. But, the most
notable aspect of conditions on Thursday will be increasing westerly
winds at 10 to 20 MPH on the east side in the afternoon. These winds
will likely trend stronger at 15 to 25 MPH on Friday but it will be
dramatically cooler with below normal temperatures.
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 next
weekend. 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. -DW
Pacific Coastal Waters...Small Craft Advisory for hazardous seas until
5 AM PDT Monday for PZZ350-356-370-376.
Gale Watch from Tuesday morning through Wednesday afternoon for
Small Craft Advisory until 5 AM PDT Monday for PZZ376.