Weekly Weather Briefing January 14th, 2013

Uploaded by nwsspokane on 14.01.2013

Welcome to the National Weather Service Spokane, WA weekly weather briefing.
The most active weather for the week will come during the next 12 hours associated with light
wintry precipitation mainly across the ID Panhandle. By Tuesday, high pressure will
begin to build into the region and persist well into the start of next week. Expect
strengthening temperature inversions leading to air stagnation, persistent low
clouds, fog, and potentially riming of ice.
On this graphic, the area shaded in grey outlines the locations where areas of light wintry
precipitation will impact through the evening.
High pressure will begin to build into the region on Tuesday and persist well into
next week. This will shield the Inland NW from the main storm track leading to an
extended dry period.
Under these weather regimes...strong temperature inversions develop resulting in
mild temperatures for the Middle and upper slopes of the mountains while cool air stays
trapped in the valleys. This will act as a lid to trap airborne pollutants and lead to
air stagnation and decreasing air quality. The mild temperatures in the mountains
will also lead to some melting snow.
As a result, an air stagnation advisory has been issued for much of Central WA. The winter
weather advisory for the ID Panhandle will expire this evening.
Given the cold temperatures experienced over the last few days and potential for some
mountain snowmelt, it is urged to closely monitor any frozen rivers for potential ice-jams
and relay any related information to the NWS.
This pattern will also lead to potential riming of ice on surfaces where fog and low
clouds are most persistent. For those who are unaware, riming is the process when
super-cooled water droplets within the fog freeze to surfaces. In an event back in
2009, a similar pattern lead to pseudo ice-storm without any precipitation actually falling
from the sky shown in this picture from near Davenport.
During the event 2009, the hardest hit areas were along the highway 2 corridor between
Spokane and the Waterville Plateau at elevations between 2 and 3 thousand feet.
While the upper-level pattern is remarkably similar...it is still uncertain whether we have
identical moisture and temperature profiles at the surface to support such a high
impact icing event.
Current model guidance suggest the area shaded in grey would have the highest probability
for boundary layer moisture supportive of fog and low and clouds and will need to be
monitored closely.
The 8 to 14 day outlook issued by the Climate Prediction Center shows a better than
average chance of near to above normal temperatures coupled with near to below normal
precipitation during the week of January 21th through the 27th. This would imply high
pressure will persist but become less amplified.
In summary, this week will be rather quiet weather-wise after tonight. Strong high pressure
will be the dominate weather feature. This will promote warming in the mountains,
continued cool for the valleys, and increasing risk for air stagnation. Bitterly cold
temperatures over the last few days would also raise some concern for icing on rivers and
potential for ice Jams in the coming days.
Here is how you can stay informed and get the latest information from the National
Weather Service Spokane Forecast Office. Our forecasts and various winter weather
products are available on our website weather.gov/spokane. Like us on facebook, follow us
on twitter, and subscribe to us on youtube. And as always, you can listen to us on NOAA Weather
Radio. Thank you for tuning in for this weekly weather briefing.