[willamette-fcst] Forecast - Wednesday, December 24th, 2008

Wed Dec 24 08:58:39 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: 
     Wednesday, December 24th, 2008 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 10:00am until 2:30pm.
     Straw stack burning is allowed from 10:00am until 2:30pm.

Weather Discussion:
     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

     You can see how the current snowstorm compares with past
     northwestern Oregon snowstorms at:

     http://www.wrh.noaa.gov/pqr/info/2008_December_snowstorm.txt

     Another weather system is dropping into the region this
     morning, from the Gulf of Alaska.  Enough cold air was in
     place for valley floor precipitation to begin in the form of
     light snow, from about Salem north, in the pre-dawn hours. 
     The Salem sounding from early this morning showed southerly
     winds and warming aloft with temperatures slightly above
     freezing around 2000 feet.  That warming has continued this
     morning, with snow changing to rain, at the Salem Airport,
     around daybreak.

     Increasing southerly winds had warmed mid-morning
     temperatures into the upper 30s to mid 40s, with rain, along
     the northern and central coast.  Cloudy skies covered the
     southern Willamette Valley, where increasing southerly winds
     had warmed temperatures into the mid to upper 30s.  Snow was
     still falling in the extreme north valley, where easterly
     outflow, from the Columbia Gorge, was keeping the low levels
     of the atmosphere below freezing. Temperatures ranged from
     the mid 20s near the Gorge to near freezing at
     McMinnville.

     Southerly surface winds will slowly increase today, even in
     the north valley.  That will warm the lower levels of the
     atmosphere above freezing and turn the snow to rain. Snow
     levels will lift to about 1000 feet over the north valley
     and to 2000 feet over the south valley.  However, that
     transition will be delayed for areas close to, and in, the
     Columbia Gorge, where continued cold easterly winds could
     enable significant snow to accumulate.  Valley highs will
     range from the low 40s, in Eugene, to near the freezing mark
     in the Portland area.

     This weather system will not produce as much warming aloft
     as the one did this past weekend, so the threat of
     significant freezing rain is low and will mainly be for
     areas in and near the Columbia Gorge, where the low-level
     cold air is more persistent.  For the most part,
     precipitation will turn from snow to rain today, from south
     to north, on the Willamette Valley floors, with snow
     continuing to fall above 1-2000 feet.  There could be areas
     of brief sleet or freezing rain during that transition.

     Many roadways across the region remained snow-packed this
     morning, and some travel restrictions are in place. 
     Additional snow will likely accumulate this morning on
     extreme north valley roadways (several inches are possible
     in the Portland area...especially near the Columbia Gorge
     and in the higher hills).  In addition, melting snow, later
     today, could make slushy road surfaces even more slick. 
     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

     A cold upper-level trough will bring frequent showers
     tonight with the snow level dropping back down to between
     500 and 1000 feet.  Snow accumulations are likely in the
     higher hills, around the Willamette Valley, with locally
     heavy snow over the coast range passes and in the Cascades. 
     Computer forecast models show a surface low-pressure system
     dropping south, to off the northern Oregon Coast, later
     tonight.  That may turn surface winds easterly and pull cold
     air back out of the Columbia Gorge, into the north valley. 
     There is a good chance that enough cold air will come out of
     the Gorge to drop snow levels back to the valley floors in
     the greater Portland area, and possibly as far south as
     Salem, late tonight and Christmas Day.

     The latest weather warnings, advisories, and forecasts, from
     the Portland National Weather Service, are available at:

     http://www.wrh.noaa.gov/pqr/

Surface Winds:
     S 5-15 G 25 this morning, S 10-20 G 30 this afternoon.
Transport Winds:
     S 25 this morning, S 30 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 2000 feet.  Ventilation index 60.
High Temperature:
     Salem\'s high temperature today will be near 39.
Humidities:
     Minimum relative humidity will be near 79%.
Sunrise/Sunset:
     Salem sunset tonight: 4:36pm; sunrise tomorrow: 7:49am.

Extended Outlook:
     A cold upper-level trough will bring showers to the region
     for Christmas, with the snow level generally between 500 and
     1000 feet.  As previously mentioned, there is a good chance
     that snow levels will drop to the valley floor, once again,
     in the extreme north valley.  Accumulations of wet snow are
     possible, on the valley floor, as far south as Salem.

     Historical information regarding Willamette Valley snow on
     Christmas is available at:

     http://www.wrh.noaa.gov/pqr/info/2008_December_Christmas.txt

     Locally heavy snow is likely Christmas Day 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.

Thu (25 Dec):  Showers.  Snow Level 500-1000 Feet...Near the Surface North Valley.  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 3-4000 Feet. 36/43

Tue (30 Dec):  Rain at Times.  Snow Level 3-4000 Feet.  38/47

Wed (31 Dec):  Rain at Times.  Snow Level 3-4000 Feet.  38/46

ODA Meteorologist
weather at oda.state.or.us