[willamette-fcst] Forecast - Tuesday, December 16th, 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: 
     Tuesday, December 16th, 2008 at 12:00pm.

Burn Advisory:
     Agricultural burning is not recommended.
     Stack burning is not allowed.

Weather Discussion:
     Cold and dry Arctic air, clear skies, and lighter winds made
     for the coldest morning in many years across most of Oregon.
     Coastal areas fell into the mid 20s, with freezing temperatures
     extending south to the California border.  The interior valleys
     dropped mostly into the teens in areas away from the Gorge winds.
     Below zero readings were common across central and eastern Oregon.
     The following are some morning low temperatures:

     Coast:

     Newport.....  23 degrees

     Astoria.....  24 degrees

     North Bend..  25 degrees

     Brookings...  31 degrees

     Willamette Valley:

     Corvallis...   9 degrees

     Eugene......  10 degrees

     Hillsboro...  12 degrees

     Salem.......  18 degrees

     Aurora......  20 degrees

     Portland....  20 degrees

     Central and Eastern Oregon:

     Hermiston... -16 degrees

     Redmond..... -12 degrees

     Meacham..... -11 degrees

     Pendleton... -10 degrees

     Baker City..  -9 degrees

     Burns.......   6 degrees

     The Dalles..   7 degrees

     Late-morning satellite imagery showed sunny skies across
     western Oregon with areas of valley low clouds east of the
     Cascades.  The ODA surface analysis showed the Arctic cold
     front had pushed south into northern California and a very
     cold high-pressure area was centered over northeastern
     Oregon.  Northerly gradients prevailed across eastern Oregon
     with offshore flow across western Oregon, extending off the
     coast to the Arctic frontal boundary.

     Today will be a break from the snow but not from the cold. 
     Midday temperatures had only warmed into the 30s along the
     coast and the mid 20s in the Willamette Valley.  It was
     still very cold east of the Cascades with much of
     northeastern Oregon still near zero. Even with plenty of
     sunshine, valley highs should only climb to near 30 degrees
     this afternoon with north-northeasterly winds.

Surface Winds:
     N 5-10 this afternoon.
Transport Winds:
     NNE 12 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 1600 feet.  Ventilation index 19.
High Temperature:
     Salem\'s high temperature today will be near 29.
Humidities:
     Minimum relative humidity will be near 40%.
Sunrise/Sunset:
     Salem sunset tonight: 4:32pm; sunrise tomorrow: 7:45am.

Extended Outlook:
     The next weather system is forecast to drop down the British
     Columbia coastline, and into the Pacific Northwest, tomorrow
     morning.  The air mass will initially be cold enough for the
     precipitation to begin as snow across all of western Oregon,
     with the possible exception of the central and south coast. 
     Snow will likely begin along the north coast in the early
     morning hours, and spread into the northern Willamette
     Valley by mid-morning.  The snow should increase, from
     north-to-south across the Willamette Valley during the
     late-morning hours tomorrow.  Accumulating snow in the
     Willamette Valley is likely with greater amounts in the
     north valley. 

     The forecast track of the storm brings low-pressure inland,
     across southwestern Washington, late Wednesday.  If that
     occurs, then enough southerly wind may develop to change the
     snow to sleet, freezing rain, and eventually rain in the
     lowest elevations in the southern and central Willamette
     Valley.  That transition is likely to occur quickly along
     the immediate coast.  It appears that cold outflow, from the
     Columbia Gorge, may be sufficient to keep precipitation in
     the Portland area entirely as snow, and it is likely that
     snow will previal across southwestern Washington.  Total
     snowfall amounts will be highly dependent on whether and
     when a transition to rain occurs.  The north valley will
     likely see around 2-4 inches, and perhaps more, if the
     precipitation stays entirely as snow.  The south valley will
     likely transition to a wintry mix and then rain Wednesday
     evening, but not before picking up from 1-3 inches of snow.

     Any transition to above freezing air will be brief...lasting
     at most about 12 hours.  Another cold Arctic front is
     forecast to drop south across Washington late Wednesday and
     into northern Oregon Thursday morning.  The Arctic cold
     front will advance south across western Oregon during the
     day Thurssday...changing all precipitation back to snow with
     additional accumulations on the order of 2-4 inches
     possible.  An even colder surge of Arctic air will pour into
     the region Friday, with skies gradually clearing and
     easterly winds increasing...especially in the Portland area.

     Saturday looks to be mostly sunny, cold, and windy with
     temperatures staying below freezing across the valley. 
     Another weather system is forecast to approach the coastline
     Sunday.  The track of that system is crucial in regards to
     how much snow and/or ice western Oregon will receive.  The
     latest comuter models suggest that the low-pressure center
     will track to near the central Oregon coast, which would
     keep precipitation mainly in the form of snow across the
     Willamette Valley.  Snow totals from that system could
     potentially be significant.  If the storm tracks a little
     farther north than currently forecast, then sleet and
     freezing rain chances increase. It appears that another
     reinforcing shot of Arctic air may invade the region early
     next week, for a continuation of cold conditions.

Wed (17 Dec):  Snow Spreading South...Wintry Mix Changing to Rain South of Portland.  15/35

Thu (18 Dec):  Rain or Snow Showers Turning to Snow Showers.  Accumulations Likely.  31/35

Fri (19 Dec):  Snow Showers Ending...Becoming Partly Cloudy. Continued Cold.  18/27

Sat (20 Dec):  Mostly Sunny, Cold, and Windy.  12/25

Sun (21 Dec):  Snow and Windy...Possible Wintry Mix.  Significant Accumulations Likely. 20/32

Mon (22 Dec):  Decreasing Snow Showers...Continued Cold.  20/27

Tue (23 Dec):  Partly Cloudy and Cold.  15/27

ODA Meteorologist
weather at oda.state.or.us