[willamette-fcst] Forecast - Tuesday, December 8th, 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.

...Next Update Not Until Thursday, December 10th, 2009 at 9:00am...

Issued: 
     Tuesday, December 8th, 2009 at 12:00pm.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from now until 2:30pm.
     Stack burning is not allowed.

Weather Discussion:
     Washington and Oregon remain under the influence of a dry and cold northerly flow
     aloft today, with a low-level dome of cold Arctic air blanketing the region.  A weak
     upper-level disturbance was visible on satellite imagery dropping southward just off
     the Washington Coast late this morning.  Cloudiness associated with this system was
     staying offshore, with dry north-northeasterly winds keeping skies sunny across western
     Washington and western Oregon.

     Although some increase in middle high clouds is is possible along the Oregon Coast,
     later today, it does not appear as if any precipitation will move onshore.  Offshore
     pressure gradients haved relaxed since Monday, with north-northeasterly winds
     generally in the 5-15 mph range across western Oregon.  The exception was in the
     extreme northern Willamette Valley, where outflow from the Columbia Gorge was
     generating easterly gusts to around 25 mph.

     It was the coldest morning of the year across most of the state.  Many spots east of the
     Cascades fell well below zero.  Meacham (northeastern Oregon) was the cold spot in the
     state this morning at -14 degrees.  Burns (southeastern Oregon) dropped down to -12 degrees,
     Lakeview (south-central Oregon) hit -11, and Redmond (central Oregon) dipped to -10 degrees.

     Most of western Oregon dropped into the teens overnight.  Eugene bottomed out at just 10
     degrees.  Hillsboro dipped down to 12, and Corvallis slid to 13.  Both Portland and Salem
     recorded a minimum of 14 degrees.  With sunny skies today, afternoon highs will struggle to
     around the freezing mark in the Willamette Valley.  Temperatures will quickly drop back into
     the teens, under mostly clear skies, this evening.

Surface Winds:
     NNE 5-15 this afternoon.
Transport Winds:
     NNE 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 2700 feet.  Ventilation index 27.
High Temperature:
     Salem\'s high temperature today will be near 30.
Humidities:
     Minimum relative humidity will be near 25%.
Sunrise/Sunset:
     Salem sunset tonight: 4:31pm; sunrise tomorrow: 7:39am.

Extended Outlook:
     Cold and dry northerly flow aloft will continue Wednesday and Thursday.  Decreasing
     surface winds will allow for even colder overnight temperatures across western Oregon,
     single-digit readings likely in sections of the Willamette Valley.  Sunny skies will
     help afternoon highs recover to around freezing on Wednesday and possibly the mid 30s
     on Thursday.  

     By Friday, a westerly flow aloft will begin to undercut the offshore ridge...directing
     Pacific moisture into California.  The flow aloft over Oregon will back from northerly
     to northwesterly, with clouds increasing across extreme southern Oregon.  Skies should
     remain mostly sunny over the Willamette Valley with highs climbing in the mid to upper 30s.

     By Saturday morning, moisture is forecast to spread northward into the Willamette Valley.
     The air mass aloft will be warming, but continued offshore flow at the surface should
     allow enough low-level cold air to remain in place for precipitation to begin as snow,
     sleet, or freezing rain. There will likely be enough warming for much of the central
     and southern valley to changeover to plain old rain by late Saturday, but expect
     wintry conditions to hold fast in the Portland area and in the Columbia Gorge.

     Precipitation is expected to taper off Sunday, with most of the Willamette Valley just
     getting plain old rain.  However, there could still be enough cold air coming out of the
     Columbia Gorge to keep wintry precipitation in the immediate Portland area. A much
     warmer weather system is forecast to come onshore late Monday, which should scour out the
     remaining low-level cold air trapped in the Gorge.

Tomorrow (09 Dec):  Mostly Sunny and Cold.  11/32

Thu (10 Dec):  Mostly Sunny and Cold.  15/34

Fri (11 Dec):  Mostly Sunny and Cold.  19/38

Sat (12 Dec):  Snow, Sleet, or Freezing Rain...Likely Changing to Rain South.  28/35

Sun (13 Dec):  Chance of Rain...Possible Wintry Mix Near the Gorge.  32/42

Mon (14 Dec):  Rain Increasing Late.  Turning Warmer.  36/50

Tue (15 Dec):  Rain Likely.  Mild.  42/52

ODA Meteorologist
weather at oda.state.or.us