[willamette-fcst] Forecast - Friday, December 26th, 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.

Issued: 
     Friday, December 26th, 2008 at 9:00am.

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:
     Christmas 2008 set snowfall records in the northern
     Willamette Valley.  It was the snowiest in Portland history,
     with 10 inches on the ground at the National Weather Service
     offices in northeast Portland.  In addition, December 2008
     will go into the record books as the snowiest December, in
     Portland, since at least 1940 (when records started at the
     Portland Airport), with 18.9 inches of snowfall.

     More on this record-setting snowy month can be found at:

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

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

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

     More snow showers fell in the northern Willamette Valley on
     Christmas, with .8 inches of snow falling at the Portland
     National Weather Service.  A cold upper-level trough was
     responsible for the rain and snow showers Christmas Day,
     with valley high temperatures only climbing into the mid to
     upper 30s.  Partial clearing overnight allowed areas of icy
     fog to form in the valley with low temperatures generally
     falling below freezing.  That allowed slushy streets to
     refreeze in many areas, with visibilities locally less than
     one-half mile.  That made for difficult travel conditions
     again this morning.

     There are major changes in store beginning later today.  The
     first in a long seris of warmer weather systems will move
     onshore later today.  A warm front will spread rain onto the
     coastline by midday and into the Willamette Valley this
     afternoon.  Initially, the air mass over the valley may be
     cold enough for some to fall at very low elevations.  No
     accumulation is expected below 1000 feet.  The snow level
     should rise to around 2500 feet by this evening.

     Cold air remains trapped in the Columbia Gorge, so
     precipitation there will begin as snow.  The National
     Weather Service has issued a Winter Storm Warning for later
     this afternoon and tonight, in the Columbia Gorge.  The snow
     in the Gorge will slowly change to rain, from west to east,
     overnight, as the trapped low-level cold air gets scoured out.

     The incoming storm will also produce strong southerly winds
     along the coast, so the National Weather Service has issues
     a High Wind Warning for the northern and central Oregon
     Coast for later this afternoon and tnight.  Southerly winds
     will increase later today with gusts to 60 mph possible late
     this afternoon and tonight.  Rain and southerly winds will
     also increase in the Willamette Valley later today with
     temperatures climbing into the low 40s by this evening.  The
     combination of increasing rain melting snow will make for
     local hazardous ponding of water on roadways in the north valley.

     Continued rain and brisk southerly winds will keep valley
     temperatures steady or slowly rising overnight with the cold
     front not coming onshore until Saturday morning.

Surface Winds:
     S 5-15 this morning, S 5-15 G20 this afternoon.
Transport Winds:
     S 15 this morning, S 25 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 2000 feet.  Ventilation index 50.
High Temperature:
     Salem\'s high temperature today will be near 42.
Humidities:
     Minimum relative humidity will be near 89%.
Sunrise/Sunset:
     Salem sunset tonight: 4:37pm; sunrise tomorrow: 7:50am.

Extended Outlook:
     A strong westerly jet stream is forecast for this weekend
     and much of next week with rain in the valleys and snow for
     the mountains.  Snow levels will rise to around 3-4000 feet.
     Temperatures will return to near seasonal normals.  Run-off
     from rain, combined with the significant melting of
     low-elevation snow, raises the concern for flooding.  At
     this time, major flooding is not expected, but rivers and
     streams will need to be closely monitored.

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

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

     The Nortwest River Forecast Center will have the latest
     river levels, forecasts, watches and warnings at:

     http://www.nwrfc.noaa.gov/

Tomorrow (27 Dec):  Rain at Times.  Snow Levels Rising to 5000 Feet. 40/46

Sun (28 Dec):  Rain at Times.  Snow Levels 3-4000 Feet. 40/46

Mon (29 Dec):  Rain at Times.  Snow levels 2-3000 Feet. 39/43

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

Thu (01 Jan):  Rain at Times.  37/44

Fri (02 Jan):  Rain at Times.  35/46

ODA Meteorologist
weather at oda.state.or.us