Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Medford or
814 PM PST Monday Jan 26 2015
Update...expecting another night of fog in the west side valleys
tonight, and current observations show areas of fog already
developing in the rogue and Umpqua valleys, and along the coast.
However, some middle and high level clouds could inhibit formation.
The end result should still be the same a the past few mornings.
All other areas should remain clear.
Have not made any changes or updates, as the inherited forecast
appears to be on track. See the previous discussion below for more
Aviation...based on the 27/00z taf cycle...VFR conditions are
expected to prevail over the area this afternoon throughout the County Warning Area.
During the evening, ceilings are expected to lower to IFR/LIFR in west
side valleys, with fog expected to develop early in the morning and
continue through early Tuesday afternoon. Coastal area ceilings expected
to lower this evening to IFR as boundary layer winds develop an
onshore component ahead of a weakening front. As a low moves up into
east-central California and Nevada, high and middle clouds will
increase during the afternoon, possibly causing isolated mountain
obscurations in eastern Siskiyou and Modoc counties Tuesday
Marine...updated at 800 PM Monday 26 January 2015...west swell will
gradually diminish and south winds will stay below advisory criteria
at 10 to 15 knots through Wednesday. A weak front moves over the waters
Tuesday...then dissipates over the area on Wednesday. Moderate
northerly winds are expected Thursday into Friday with the strongest
winds in the southern outer waters as high pressure builds in to the
north...resulting in increased chop. -MSC/bpn
Previous discussion... /issued 448 PM PST Monday Jan 26 2015/
Discussion...current visible image shows scattered high clouds
moving up from the south. Low clouds are gradually breaking up in
the Rogue Valley near Medford and it has cleared out in Roseburg.
However Grants Pass remains overcast and it may only break out
briefly late this afternoon, if at all. A weak front will move
towards the area tonight, but there will not be enough middle or high
clouds to prevent fog and low clouds from developing in the
Westside valleys. Therefore we expect both to form again this
evening and continue through most of Tuesday morning for the same
The aforementioned front will bring little of any precipitation.
Could not rule out some patchy drizzle north of Cape Blanco, but
that's it. At the same time a weak upper trough is expected to
move north into Nevada Tuesday and the models show some quantitative precipitation forecast
barely making it into southern Modoc and Siskiyou County. Previous
forecast had a slight mention of showers which looked reasonable.
The front on Tuesday may be enough to weaken or break the
inversion for a brief time west of the Cascades Tuesday afternoon,
then the inversion will strengthen Wednesday and continue into
the end of the week as an upper ridge moves back into the region.
So have decided to extend the air stagnation advisory until 10 am
PST Thursday for west of the Cascades. Confidence is higher the
inversion will break east of the Cascades Tuesday afternoon with
mixing heights expected to be much higher. So did not change the
end time of the air stagnation there.
Little change in the weather is expected from Wednesday into start
of next weekend. It will remain dry with patchy to areas of fog
at night into the morning hours for the Westside valleys. The GFS
and ec show the upper ridge flattening out some Sunday and a
frontal boundary will move south bringing light rain to the
northwest part of the area Sunday afternoon. -Petrucelli
or...air stagnation advisory until 10 am PST Thursday for
Air stagnation advisory until 11 am PST Tuesday for
Pacific coastal waters...none.