[willamette-fcst] Forecast - Tuesday, December 23rd, 2008
Willamette Valley Ag/Burning Forecast
willamette-fcst at listsmart.osl.state.or.us
Tue Dec 23 08:59:52 PST 2008
Daily Smoke Management Forecast
Oregon Department of Agriculture
Smoke Management Program
Weather Outlook and Field Burning Advisory for Willamette Valley Growers and Fire Districts.
Issued:
Tuesday, December 23rd, 2008 at 9:00am.
Burn Advisory:
Agricultural burning is not recommended.
Stack burning is not allowed.
Weather Discussion:
Snow showers tapered off Monday afternoon, but not before
dropping several more inches of snow over northwestern
Oregon, adding to the most significant snowfall for the
region since the winter of 1968-69. The cold Arctic air was
drawn a little further south, in the Willamette Valley,
Monday, with Corvallis finally seeing about one inch of
snow. Eugene bounced in and out of the cold dome of
low-level air Monday, with temperatures dropping into the
mid 30s and then climbing to the mid 40s.
A comprehensive summary of snow and ice totals, since
Saturday morning, for western Oregon and southwestern
Washington is available, from the Portland National Weather
Service, at:
http://www.wrh.noaa.gov/total_forecast/getprod.php?wfo=pqr&pil=PNS&sid=PQR
A weather system offshore was headed mainly towards
California this morning, but it dropped the pressures enough
to create northeasterly gradients across western Oregon.
The surface analysis showed that the Arctic cold front was
able to dip further southwest this morning, with
sub-freezing temperatures covering the entire Willamette
Valley. Valley temperatures ranged from 31 degrees, in
Eugene, to 24 degrees in Hillsboro. The low-level cold air
is very shallow over Eugene and progressively deeper down
the valley, towards Portland, and deeper yet in the Columbia
Gorge. That will play in big role when the next Pacific
storm makes it into the region Wednesday.
Satellite imagery this morning showed a large area of
clouds, associated with the offshore weather system. Some
clouds and light snow flurries were making it onto the
northern Oregon Coast. Mostof the state had generally cloudy
and dry conditions. Today should bring a brief break from
the heavy snow, although skies will stay mostly cloudy.
Some snow flurries are likely along the north coast and the
Willamette Valley, from the weather system headed into
California. Some sprinkles are likely along the central and
south coast. Light northeasterly gradients will keep cold
air in place across the entire Willamette Valley today, with
high temperatures only climbing into the mid 30s in the
south valley and staying below freezing from Salem north to
Portland.
Many roadways acrosss the region remained snow-packed this
morning, with some travel restrictions are in place. Before
traveling, please check the latest road conditions and
requirements, from the Oregon Department of Transportation,
at:
http://167.131.0.179/Pages/RCMap.asp?curRegion=1&mainNav=RoadConditions
Cloudy skies are expected tonight with one system headed
into California and another moving southward, along the
British Columbia Coastline, towards Washington and Oregon.
There is an increasing chance for light snow, in the
pre-dawn hours Wednesday, along the north coast and in the
northern Willamette Valley. The National Weather Service
has issued a Winter Storm Watch for Wednesday, in the
greater Portand area, where the potential for more heavy
snow and/or ice exists. More on that in the extended
discussion...
The latest weather warnings, advisories, and forecasts, from
the Portland National Weather Service, are available at:
http://www.wrh.noaa.gov/pqr/
Surface Winds:
NE 2-5 this morning, NE 3-6 this afternoon.
Transport Winds:
NE 3 this morning, NE 4 this afternoon.
Atmospheric Ventilation Conditions:
Maximum mixing height today will be near 800 feet. Ventilation index 3.
High Temperature:
Salem\'s high temperature today will be near 31.
Humidities:
Minimum relative humidity will be near 78%.
Sunrise/Sunset:
Salem sunset tonight: 4:35pm; sunrise tomorrow: 7:49am.
Extended Outlook:
The next significant weather event will involve a system
dropping into the region, from the Gulf of Alaska on
Wednesday. Enough cold air will be in place, ahead of this
storm, for precipitation to begin in the form of snow for
most of the Willamette Valley, especially from Salem north.
This system has the potential to turn the surface winds more
southerly in the valley by Wednesday afternoon, which would
eliminate the cold influence of the Columbia Gorge winds and
warm the lowest levels of the atmosphere above freezing.
That would lift the snow level to about 500-1000 feet over
most of the valley. However, that transition may be very
slow in the Portland area, where cold outflow from the
Columbia Gorge could enable significant snow and ice to
accumulate, before the warmer southerly winds lift surface
temperatures abve freezing.
The system coming in Wednesday does not have as much warm
air aloft associated with it, as the one over the weekend,
so the threat of significant freezing rain is not as great.
Most likely, precipitation will start as snow in the valley
and transition mostly to plain rain, wher the warmer
southerly winds send surface temperatures above freezing.
Snow levels are not expected to climb above 2000 feet,
before dropping back to about 500-1000 feet by Wednesday
night. There could still be areas of briefsleet or freezing
rain, but I would not expect significant ice accumulations
from this storm. On the other hand, if the transition to
warmer air is slow, in the north valley, significant snow
accumulations are a real possibility.
A cold upper-level trough will bring showers to the region
for Christmas, with the snow level between 500 and 1000
feet. It will likely be a White Christmas for the north
valley, because of the snow already on the ground. Locally
heavy new snow is possible in the coast range and in the
Cascades. Another system will move onshore Friday. It will
pull some easterly winds, from the Gorge, ahead of it. If
enough cold air is still trapped there, then precipitation
may begin in the form of snow in the Portland area and in
the Gorge. This system appears strong enough to fairly
quickly lift the snow level to about 3000 feet by Friday
afternoon.
A strong westerly jet stream is forecast for next weekend
and early next week with rain in the valleys and snow for
the mountains. Snow levels will be around 3-4000 feet.
Temperatures will return to near seasonal normals.
Wed (24 Dec): AM Snow North; Rain or Snow South. PM Rain South...Wintry Mix North. 28/37
Thu (25 Dec): Showers. Snow Level 500-1000 Feet...near the Surface in the Gorge. 32/38
Fri (26 Dec): Rain or Snow North...Turning to Rain. Rain South. Snow levels Rising. 32/39
Sat (27 Dec): Rain at Times. Snow Levels near 4000 Feet. 39/46
Sun (28 Dec): Rain at Times. Snow Levels 3-4000 Feet. 37/44
Mon (29 Dec): Rain at Times. Snow levels 3000 Feet. 36/43
Tue (30 Dec): Rain at Times. Snow Level 4000 Feet. 38/47
ODA Meteorologist
weather at oda.state.or.us
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