[willamette-fcst] Forecast - Wednesday, December 24th, 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: 
     Wednesday, December 24th, 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 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 dropped 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 continued this
     morning, with snow changing to rain, at the Salem Airport,
     around daybreak, and northward, to the Portland area, by
     late this morning.

     Increasing southerly winds had warmed late-morning
     temperatures into the mid 40s along the northern and central
     coast, the low 40s in the southern Willamette Valley, and to
     just above freezing on the south and west sides of the
     greater Portland area.  Temperatures were still below
     freezing, and snow was still falling, from the east side of
     the Portland area, north into southwestern Washington, and
     east into the Columbia Gorge (areas still exposed to cold
     easterly outflow, from the Columbia Gorge).

     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 just above the
     freezing mark in the Portland area.

     Mountain roadways remained snow-packed late this morning,
     and some melting snow on low-elevation roads will make for
     locally slippery conditions.  Use extreme care when
     traveling.  The latest road conditions, and requirements,
     may be found 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 and early Christmas morning.  That may turn surface
     winds easterly and pull more cold air from 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 locally 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 10-20 G 30 this afternoon.
Transport Winds:
     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. Have a
     Merry Christmas.

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