[willamette-fcst] Forecast - Tuesday, February 10th, 2009

[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: 
     Tuesday, February 10th, 2009 at 12:00pm.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from now until 3:30pm.
     Straw stack burning is allowed from now until 3:30pm.

Weather Discussion:
     Another in a series of cold weather systems brought light snow to most
     of western Washington and the interior of western Oregon this morning,
     north of about Roseburg.  There was little accumulation below 500 feet
     with an inch or two of snow at elevations above about 1000 feet.  The
     first band of precipitation moved east of the Cascades around mid-morning,
     with the snow tapering off and mixing with rain across the Willamette
     Valley.  Rain was beginning to increase again, along with the south wind,
     by late this morning.

     Satellite imagery showed the main cold front nearing the coastline late
     this morning, with Doppler radar showing a more substantial surge of
     moisture moving onshore. The ODA surface analysis showed rapidly increasing
     southeasterly pressure gradients across western Oregon, in response to the
     approaching cold front.  South-southeasterly winds had increased to between
     10 and 15 mph in the Willamette Valley, with gusts to near 25 mph in the Salem
     area.  Southerly winds were also rapidly increasing along the coast, with
     Lincoln City getting gusts to more than 40 mph.  Southerly winds were helping
     to warm temperaures into the mid and upper 30s across western Oregon.

     The air mass aloft is still very cold.  The freezing level over Salem early
     this morning was measured at just 900 feet, and that is forecast to only rise
     to about 2500 feet by late this afternoon.  That puts the snow level at or
     below about 1500 feet for the duration of this storm system, and the bulk of
     the precipitation is yet to come.  That means the mountains are going to get
     a fair amount of new snow later today.

     Satellite imagery showed a fairly intense low-pressure center a litle more
     than 300 miles west of the central Washington Coast and continuing to drift
     southeastward.  It is forecast to be just off the central Oregon coast by
     Wednesday morning.  Cool outflow from the Columbia Gorge will increase
     this afternoon, as the low-pressure center moves close to the northern
     Oregon Coast.  That will maintain very low snow levels in and near the
     Columbia Gorge...perhaps down to river level. However, increasing southerly
     winds should help snow levels stay above the valley floor, south of the
     Portland area, as the main surge of moisture rolls onshore this afternoon.

     Precipitation will remain as snow at elevations above about
     1500 feet with 3-6 inches of snow likely this afternoon and
     evening. The steady rain and snow will turn showery, in the
     wake of the front, tonight, with snow levels dropping very
     near the valley floors.  The National Weather Service has
     issued a Winter Storm Warning for the western Columbia
     Gorge, where wet snow may accumulate down the river level
     later today.  Winter Weather Advisories are still in effect
     for the coastal range, the Portland/Vancouver area, the
     western Cascade foothills (above 1500 feet), and the Cascades.

     Temperatures are marginal for sticking snow in the lower
     elevations around Portland, because outflow from the
     Columbia Gorge is not that cold.  It will likely barely get
     cold enough in the Gorge for snow to accumulate down to the
     Columbia River level.  only a couple of degrees can make the
     difference between wet pavement and several inches of wet
     snow, so check road conditions before planning trevel in
     these areas later today and tonight.  At the very least,
     expect winter driving conditions today over all western
     Oregon and western Washington mountain passes...including
     the coastal range passes.

     Temperatures in the valley should warm into the low 40s this
     afternoon, as southerly winds increase and become rather
     blustery (gusts to near 30 mph are possible).  Southerly
     winds will continue to increase along the northern and
     central Oregon Coast this afternoon, where High Wind
     Warnings have been issued, until 4pm, for gusts to near 65
     mph.  Very cold air aloft will yield reasonably high mixing
     heights this afternoon.  That, combined with brisk southerly
     transport winds, will make for good ventilation conditions
     this afternoon across the region.

     The latest weather advisories from the National Weather
     Service are at:

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

     The latest road conditions across Oregon may be found at:

     http://167.131.0.179/Pages/RCmap.asp?curRegion=0&mainNav=RoadConditions

Surface Winds:
     S 12-25 G30 this afternoon.
Transport Winds:
     S 25 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3000 feet.  Ventilation index 75.
High Temperature:
     Salem\'s high temperature today will be near 41.
Humidities:
     Minimum relative humidity will be near 73%.
Sunrise/Sunset:
     Salem sunset tonight: 5:34pm; sunrise tomorrow: 7:18am.

Extended Outlook:
     The rain and snow should taper off Wednesday, from north to
     south across western Oregon, as the low-pressure center
     moves inland near the southern Oregon/northern California
     border.  The snow level should hover around 500-1000 feet. 
     Wednesday morning temperatures will be near freezing with
     cool northerly winds only allowing afternoon highs to warm
     into the low to mid 40s.  Some clearing is likely Wednesday
     night and early Thursday.  That will allow temperatures to
     fall below the freezing mark Thursday morning.  The next system
     is forecast to take a slightly more of a southerly track, but
     it should bring more rain and snow to western Oregon Thursday
     afternoon through early Friday.  The snow level should be near
     the valley floors again with significant snow accumulations
     possible above about 1000 feet, especially south.

     Computer models are fairly consistent in forecasting a
     split-flow jet stream pattern Saturday and Sunday, with
     weather systems moving by both north and south of Oregon. 
     It is unlikely that the region will stay completely dry
     during that time period, so I have kept a chane of showers
     in the forecast with continued very low snow levels.  A more
     organized system may move onshore Monday night and Tuesday,
     but that is getting too far out to call at this point. 
     Temperatures will stay well below normal through the weekend
     and possible warm to near normal by next Tuesday.

Tomorrow (11 Feb):  Decreasing Areas of light Rain/Snow.  Partial PM Clearing.  32/46

Thu (12 Feb):  Increasing Clouds.  Chance of PM Rain/Snow Mix.  28/45

Fri (13 Feb):  Decreasing Rain and Snow.  Snow Level Near 1000 Feet.  32/45

Sat (14 Feb):  Partial Clearing and Cool.  28/47

Sun (15 Feb):  Chance of Showers and Cool.  Snow Level Near 2000 Feet. 28/48

Mon (16 Feb):  Increasing Clouds.  Chance of Rain Late.  Snow Level 3000 feet.  32/48

Tue (17 Feb):  Increasing Rain and Warmer.  Snow Level 4000 Feet.  36/50

ODA Meteorologist
weather at oda.state.or.us