Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Medford or
337 am PST Friday Jan 30 2015
Discussion...upper ridging will build over the area the next few
days as weak upper troughing is nudged out by high pressure. The
troughing has cooled the air mass some...weakening inversions a
touch...but for all practical purposes we are still in a stagnant
weather pattern in most valley locations. Yesterday morning was
the shortest-duration of low clouds and fog in Medford in more
than a week...and believe clearing will follow a similar pattern today.
Most locations should see a similar amount...if not a bit more...sunshine
today than previous days...with the Grants Pass area and Umpqua
valley featuring the longest period of low clouds and fog
today...with Medford expected to clear out later this morning.
East of the Cascades...stagnant air will continue for most
places...but a tight northeast to southwest presure gradient is
generating breezy conditions in Southern Lake County...so have
canceled the air stagnation advisory due to the winds mixing up the
atmosphere enough to clear the air. Other valley locations will keep
stagnant air through Sunday morning at least...and this product is
found at npwmfr. Guidance is half-hearted in bringing a sustained
period of breezy conditions to Klamath Falls...so have kept the air
stagnation advisory going there.
Away from these inland valleys...the coast and mountains will warm
up the next couple days...with peak warmth on Saturday. Offshore
flow at the Curry County coast was highlighted well on previous
shift so have left 70 degree temperatures at Brookings on Saturday.
Inland valley temperatures will be highly dependent on the evolution
of low clouds and fog...and dayshift may have to consider increasing
Medford-area temperatures if the trend of earlier clearing
continues...especially with the air mass warming on Saturday.
On Sunday the weather pattern changes...with widespread rain chances
for the first time in two weeks. The first front on Sunday will
likely drop most of its rainfall at the coast and Umpqua basin as it
rides over the leftover ridging. Monday through Wednesday a series
fronts ride over a gradually flattening ridge...which simply means
snow levels will be high with these systems and precipitation
generally won't be heavy. Snow levels are forecast to remain 6500
feet or higher through the middle of the week.
The latest few runs of the European model (ecmwf) and GFS show an atmospheric river
event Thursday into Friday...bringing the potential for significant
rainfall and gusty winds to a large part of southern Oregon and
northern California. Unfortunately for the drought situation...snow
levels are forecast to remain high through this system. We have
increased probability of precipitation and winds some for this event...but will wait for a
few more runs of consistency to bring these elements up event
further. One thing is fairly clear...the upper ridge does look like
it's moving into the Great Basin area...leaving the West Coast more
vulnerable to several rounds of significant precipitation...something
we haven't seen in quite a while.
Aviation...based on the 30/06z taf cycle...IFR/LIFR low
clouds/fog in the umqua basin and Illinois and rogue valleys will
expand to many of the other west side valleys this morning,
including at kmfr. Also...IFR conditions are expected to continue
at the coast north of Cape Blanco. Areas near the coast can
expect to improve to VFR quickly after sunrise...but break out
times will be later over the interior valleys...generally between
18z (kmfr) and 21z (krbg). Confidence in the break out at krbg is
a bit lower than at other locations since IFR stratus persisted on
Thursday. Elsewhere, expect VFR through tonight.
Marine...updated at 330 am Friday 30 January 2015...high
pressure offshore will build through the afternoon and produce
moderate northerly winds with increased wind chop...especially
south of Cape Blanco. Winds will weaken slightly tonight then
more noticeably Saturday through Saturday night before a front
approaches. The front will usher in a change in the pattern. Wind
direction will back to south and west swell will become moderate
on Sunday then another front may bring winds that would be
hazardous to small craft on Monday with seas increasing into
or...air stagnation advisory until 1 PM PST Sunday for
Air stagnation advisory until 1 PM PST Sunday for
Pacific coastal waters...Small Craft Advisory for hazardous seas until 10 PM PST this
evening for pzz350-356-370.
Small Craft Advisory for winds from noon today to 7 PM PST this
evening for pzz356.
Small Craft Advisory for winds until 1 am PST Saturday for
Small Craft Advisory for hazardous seas until 7 am PST Saturday