[willamette-fcst] Forecast - Monday, December 22nd, 2008

[Willamette Valley Ag/Burning Forecast]

Daily Smoke Management Forecast




Oregon Department of Agriculture
Smoke Management Program
Weather Outlook and Field Burning Advisory for Willamette Valley Growers and Fire Districts.

NOON UPDATE

Issued: 
     Monday, December 22nd, 2008 at 12:00pm.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from now until 2:30pm.
     Straw stack burning is allowed from now until 2:30pm.

Weather Discussion:
     A moist Pacifc storm system approached the coastline
     Saturday, inducing strong easterly winds through the
     Columbia Gorge, gusting over 60 mph at the west end of the
     Gorge and to about 40 mph in the Portland area.  That pulled
     low-level Arctic air, from the Columbia basin, into
     northwestern Oregon.  Temperatures dropped into the 20s,
     from about Salem northward in the Willamette Valley, as
     abundant warm and moist air circulated onshore over the top
     of the cold dome.  That brought a substantial amount of snow
     and ice to northwestern Oregon.  There was enough warming
     aloft, by Saturday night, for the snow to turn to sleet and
     freezing rain across much of the northern Willamette Valley,
     with many areas receiving about one-quarter of an inch of
     ice over the top of 6-10 inches of snow.  Meanwhile, the
     cold Arcitc air was not able to penetrate southward in the
     Willamette Valley much beyond Salem, where just plain rain
     fell from this system.

     The storm was not able to scour out the low-level cold air
     from the Columbia Basin nor from over northwestern Oregon. 
     As the associated upper-level trough approached the
     coastline Sunday, cooling aloft wiped out the above freezing
     layer of air over the Arctic dome and turned precipitation
     mostly back to snow over northwestern Oregon.  Most areas
     received another 2-3 inches of snow accumulation, with the
     snow showers Sunday afternoon and evening.  Once again,
     areas south of about Salem received plain rain showers with
     temperatures just above freezing.

     A summary of snow and ice totals for western Oregon is
     available, from the Portland National Weather Service, at:

     http://www.wrh.noaa.gov/total_forecast/getprod.php?wfo=pqr&pil=PNS&sid=PQR

     The cold upper-level trough will move over western Oregon
     this morning.  Snow shower acticity increased early this
     morning across the northern Willamette Valley with an
     additional couple of inches of snow falling from about Salem
     north to Portland.  Satellite and radar imagery showed an
     organized band of showers rotating across the eastern half
     of the Willamette Valley late this morning with snow showers
     continuing from Portland to Salem.

     The surface analysis showed a low-pressure center near
     Newport with an Arctic frontal boundary extending eastard,
     from the low-pressure center, across the central Willamette
     Valley.  Arctic air was being drawn further south, into the
     Willamette Valley, than it has been during this entire
     episode.  Temperatures were nearing the freezing mark in
     Corvallis and had dropped into the mid and upper 30s in
     Eugene.  Rain showers could mix with or turn to snow in the
     Albany and Corvallis areas this afternoon, and possibly as
     far south as Eugene.  However, showers will be taping off
     this afternoon.  A couple of inches of new snow are locally
     possible, from Salem north, this afternoon, mainly on the
     east side of the valley.

     Midday temperatures ranged from the mid 20s, near Portland,
     to the upper 20s around Salem.  Corvallis was just above
     freezing and Eugene was in the upper 30s.  Temperatures will
     not warm much this afternoon across the valley.  The north
     coast was also seeing snow showers this morning with
     temperatures near freezing.  Newport was just south of the
     Arctic front with temperatures in the low 40s.  Rain and
     snow showers will taper off along the north coast this
     afternoon, with snow showers possibly extending as far south
     as Lincoln City.  Rain showers will fall along the central
     and south coast.  Locally heavy snow showers will continue
     over the Cascades today and taper off over the coast range. 
     Showers will taper off across all of western Oregon tonight,
     as the upper-level trough pushes into eastern Oregon. 
     Overnight temperatures should range from the low 20s near
     Portland to the low 30s near Eugene.

     At midday, roads were sonw-packed in the Cascades, coast
     range, Columbia Gorge, and the Willamette Valley (from
     Portland to Salem).  Roads in the southern Willamette Valley
     remained wet.  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

     The latest weather warnings, advisories, and forecasts, from
     the Portland National Weather Service, are available at:
 
     http://www.wrh.noaa.gov/pqr/

Surface Winds:
     This afternoon:  SW 5-10 south valley; NW 5-10 north valley.
Transport Winds:
     This afternoon:  NNW 10.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 1800 feet.  Ventilation index 27.
High Temperature:
     Salem\'s high temperature today will be near 36.
Humidities:
     Minimum relative humidity will be near 82%.
Sunrise/Sunset:
     Salem sunset tonight: 4:34pm; sunrise tomorrow: 7:48am.

Extended Outlook:
     Tuesday should bring a small break in the weather, with a
     transitory ridge of high pressure bringing some partial
     clearing to western Oregon.  The cold air mass will remain
     in place over the region with high temperatures not likely
     goin above freezing in the Portland area and struggling into
     the mid to upper 30s in the central and southern Willamette Valley.

     The next significant weather event will involve a system
     dropping into the region, from the Gulf of Alaska, Tuesday
     night and Wednesday morning.  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.  However, this system had the
     potential to turn the surface winds southerly in the valley
     by Wednesday afternoon...warming the lowest levels above
     freezing and lifting the snow level to about 500-1000 feet. 
     That transition will be slowest in the Portland area, where
     significant snow and ice may first accumulate.

     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 progressively drop from around
     4000 feet Saturday to 1-3000 feet by Monday. Temperatures will
     return to near seasonal normals.

Tomorrow (23 Dec):  Mostly Cloudy.  Slight Chance of Snow Showers. 26/35

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 1-3000 Feet.  36/43

ODA Meteorologist
weather at oda.state.or.us