Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Medford or
824 PM PDT Wednesday may 6 2015
Update...after staring at the local radar returns and waiting
patiently this afternoon, a few isolated cells have managed to
throw out some lightning strikes in our area. As of this writing,
the most impressive of these is a cell along Highway 140 just
northwest of Klamath Falls. Due to this cell, and others across
the east side and along the coastal ranges west of Interstate 5,
have made adjustments to the forecast, mostly to bump up
precipitation chances and sky cover, and to spread the area of
showers and thunderstorms a bit further south. Otherwise, the
previous forecast looks on track...with showers quickly weakening
and mostly coming to an end over the next several hours. See the
previous discussion below for more details. -Bpn
Aviation...for the 07/00z taf cycle...scattered showers and
isolated thunderstorms currently over portions of the east side
and Douglas County this evening should weaken once the sun sets.
VFR conditions will prevail for the next 24 hours for most
areas...but low clouds along the coast and in the Umpqua basin
could create MVFR/IFR conditions overnight. Light north winds
tonight will increase tomorrow afternoon...and winds could become
especially gusty across the east side. -Schaaf/bpn
Marine...updated 800 PM PDT Wednesday 6 may 2015...offshore high
pressure will persist into this weekend. A thermal trough near the
coast will strengthen through Thursday evening...then weaken into
this weekend. A weak front will move onshore Sunday night. Moderate
north winds and steep wind driven seas will persist through Friday
evening. Winds and seas will remain small craft...except for an area
of hazardous seas over the southern waters through Thursday
Previous discussion... /issued 452 PM PDT Wednesday may 6 2015/
Short term...a cool and unstable air mass is overhead this
afternoon...and showers are affecting areas along and east of the
Cascades. A few thunderstorms are possible too. As clouds diminish
some tonight...frost conditions will be possible in the
Applegate...Shasta...and rogue valleys...and a frost advisory at
npwmfr has been issued. Freezing temperatures are not
expected...but given the current dew point temperatures and model
guidance trends...have bumped the temperatures lower and the middle
30s seem likely in sheltered locations near Ruch...Weed...Shady
Cove...and potentially the hills surrounding the Rogue Valley. In
more exposed areas...gusty north winds will keep temperatures in
the upper 30s...as is expected to be the case in the Illinois
The upper low moves south of the area tomorrow and
initiates a warmup...moreso west of the Cascades than east.
Instability and dynamics with the upper low continue to affect
mainly Modoc and lake counties Thursday and Friday afternoon.
Friday will continue the warming trend as temperatures reach about
10 degrees above normal.
Winds will ramp up significantly tomorrow as the low pushes to the
south. Instability...combined with surface winds that align with
700mb flow...will result in gusty winds from eastern
Siskiyou...through Modoc...Klamath...and lake counties.
Elsewhere...winds should be less significant but still breezy
conditions are expected. A Special Weather Statement at spsmfr has
been issued to highlight these winds. Any burning operations
should certainly take note of the expected gusty winds from
Thursday morning through the afternoon. Model guidance is showing
a wide range of solutions in terms of wind speeds...and we have
nudged wind speeds up some to get closer to higher end guidance.
Future shifts will be evaluating whether a Wind Advisory is
Long term...Saturday may 9th through Wednesday may 13th...the upper
level ridge continues the warm tranquil weather into the extended
through Sunday afternoon. High temperatures away from the coast will
be about 10 to 15 degrees above normal for Saturday and only
slightly cooler on Sunday by about 5 degrees.
By Sunday afternoon, the ridge breaks down as an upper level trough
digs south just off the Oregon coast. Both the GFS and European model (ecmwf) are in
fairly good agreement with this system aside from slight positional
differences. The GFS keeps the low closer to the Oregon coast than
the European model (ecmwf) through Monday before both models show the low moving over
northern California by Tuesday afternoon. During this time, both
solutions show enough instability to warrant a mention of
thunderstorms during the late afternoon and early evening through
Tuesday. The focus of the instability is mainly from the Cascade
crest eastward and the Trinity Alps, Mount Shasta, Medicine Lake
area in Siskiyou County. Given the decent model consensus in the
extended...confidence is moderate to high on this unsettled pattern.
The low will get kicked off to the east by Wednesday night as
ridging begins to build in. The European model (ecmwf) would end all remaining
showers by Wednesday night while the GFS continues showers into
Thursday morning. Sven/mnd
or...frost advisory from 3 am to 8 am PDT Thursday for
Frost advisory from 3 am to 8 am PDT Thursday for orz024-620.
California...frost advisory from 3 am to 8 am PDT Thursday for caz081-281.
Pacific coastal waters...Small Craft Advisory for winds until 11 PM PDT Friday for
Hazardous seas warning until 11 am PDT Thursday for pzz356-376.
Small Craft Advisory for hazardous seas until 11 PM PDT Friday