Hi, this is Colby Neuman and Bill Schneider
of the National Weather Service in Portland, Oregon here to discuss the storm expected
to occur tonight into Thursday as well as some information on the increasing potential
for heavy rain next week. An approaching strong storm will bring increasing
winds and seas this evening along the coast. Gusts of 50-55 mph appear likely along the
north Oregon coast and southwest Washington coast with gusts of 60-65 mph along the central
Oregon coast. In addition, scattered showers with prolonged breaks in the wet weather will
move across the rest of the area with snow levels generally near 6000 feet. However,
cold air trapped in primarily the upper Hood River valley around Parkdale will lead to
areas of freezing rain and snow. Areas of hazardous travel conditions will result.
For Thursday, winds should peak in the morning with the highest gusts expected to occur along
the central and southern Oregon coast. Breezy conditions will also develop across much of
the Willamette Valley, but high winds are NOT expected. In addition, widespread rain
will move into western Oregon with precipitation likely to fall as snow above about 5500 feet.
The front responsible for the strong winds will push ashore around midday resulting in
a noticeable decrease in the wind gusts along the coast.
It should be noted that there is some uncertainty in regards to the wind forecast along the
north Oregon coast for Thursday. This is due to a mini low pressure the models are depicting
to develop along the front and move northeastward into western Oregon. Strong south winds with
gusts to 65 mph will occur south of this area of low pressure and depending on where it
makes landfall will determine the extent of the high winds along the coast. Our confidence
is growing that this mini low pressure will make landfall across the central Oregon coast,
and thus spare the north Oregon coast from high winds. However, this is by no means guaranteed,
and the situation will be closely monitored over the next 24 hours so please monitor NOAA
Weather Radio or http://www.weather.gov/portland for the latest watches and warnings.
Thanks Colby, this is Bill Schneider, Science and Operations Officer with information on
potential a wet first week of December. Most of the focus for storms this week will be
on California and southwest Oregon. However, there is an increasing possibility that very
wet conditions will return to the Pacific Northwest early next week. An upper trough
with strong jet stream will direct storms and moisture into northern California and
southern Oregon, beginning tomorrow, but early next week ridging may shift the action to
the north. What’s important here is how moisture will be moving into the west coast.
Here’s a graphic that shows water content of the atmosphere for this Saturday morning.
The thing to focus on is the band of higher values (the yellows and oranges overlaid by
gray dots) off the coast. In the weather community we refer to this as a tropical moisture plume,
or and “Atmospheric River.” Atmospheric Rivers are relatively narrow bands, where
moisture is being transported out of the tropics and into the higher latitudes.
By early next week, say Monday, Tuesday and Wednesday our computer forecast models are
giving indications that the jet stream will shift north. There is a chance that an Atmospheric
River may reach the Pacific Northwest. This is significant because it is these Atmospheric
Rivers that are largely responsible for flooding events in the Pacific Northwest, although
not all Atmospheric Rivers produce flooding. Here is a graphic that shows water content
of the atmosphere for the morning of December 4th, 2012. Notice the higher values off the
coast and how the band extends up from the subtropics.
Now, if we look at how that moisture content from the previous image is being transported
or moved, we see it’s directed right toward Oregon and Washington! This is definitely
something to watch. Especially since we are expecting a series of moderate rain events
over the next few days which will likely result in periodic minor rises on our rivers but
an overall rising trend. There is still a lot on uncertainty in this forecast and it’s
too soon to talk about details this far out, but keep apprised of the forecasts in the
coming days. Thanks for joining us and we hope you found
this information useful.