Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Medford or
926 am PST Friday Jan 30 2015

Discussion...once again low clouds and areas of fog are mostly
confined to the Westside valleys in the same locations as
previous mornings. However the one change from yesterday morning
is the extent of low clouds in Lake County and northern Klamath
County. The morning sounding shows a deeper moisture layer
compared to yesterday so it could take longer for the low clouds
and fog to burn off. Thus have adjusted the sky cover and fog
forecast to represent this idea for today.

Much of the same is expected Saturday, then the first of a couple
of fronts will move into the area Sunday morning. This front may
finally be enough to mix out the atmosphere. -Petrucelli

&&

Aviation...IFR and local LIFR ceilings will persist in the Westside
valleys through the morning. Current guidance shows clouds breaking
up around 21z, but it's possible it does not break out at all in
rosegurg and Grants Pass. Also low clouds with mountain obscurations
will impact most of Lake County north and east of Lakeview through
early afternoon. Elsewhere VFR conditions will continue including
the coast and 5 nm from shore. -Petrucelli

&&

Marine...updated 0830 am Friday 30 January 2015...high pressure
will persist offshore today and a thermal trough will strengthen
along the coast, resulting in moderate northerly winds with steep
seas over portions of the area today and tonight. Strongest winds
are expected south of Cape Blanco and steep seas are expected from
Bandon south. Winds will gradually weaken tonight into Saturday,
then a front will approach Saturday night and Sunday, bringing weak
south winds. Moderate west swell will build into the waters late
Sunday through Monday night. Additional fronts are expected early
next week, then late in the week, models indicate the potential for
a strong front to slowly move into the waters bringing possible gale
force winds with very steep seas. -Cc/bpn



&&

Previous discussion... /issued 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
Tuesday. /Dw

&&

Mfr watches/warnings/advisories...
or...air stagnation advisory until 1 PM PST Sunday for
orz023-024-026-616-620-622.
Air stagnation advisory until 1 PM PST Sunday for
orz029>031-623>625.

California...none.

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
pzz376.
Small Craft Advisory for hazardous seas until 7 am PST Saturday
for pzz376.

$$

Map/map/map

National Weather Service Glossary of Abbreviations