[willamette-fcst] Forecast - Thursday, March 18th, 2010

[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: 
     Thursday, March 18th, 2010 at 9:00am.

Burn Advisory:
     Recommended burn times for agricultural burning are from 12:00pm until 4:30pm.
     Stack burning is not allowed.

Weather Discussion:
     Drier air filtering into the region cleared skies overnight
     and allowed for temperatures across the Willamette Valley to
     drop well down into the 30s, with patchy frost.  Both Salem
     and Eugene dipped to the freezing mark, and Hillsboro dropped
     to at least 33 degrees.  Mid-morning temperatures were still
     in the chilly low to mid 30s across virtually all of western
     Oregon.  The exception was along the south coast, at Brookings,
     where temperatures were in the low 50s.

     Dry northerly flow sent temperatures plummeting into the
     teens and 20s across most of central and eastern Oregon this
     morning, with brisk north-northwesterly winds making some
     areas, like Baker City, feel even colder.  Ontario was
     the warm spot east of the Cascades, with a temperature
     hovering near 40 degrees, but 20 mph winds were dropping
     windchill temperature below freezing (some warm spot).

     Satellite imagery showed mostly clear skies across all of
     Oregon this morning.  There were a few patches of valley low
     clouds and fog in southwestern Oregon.  As an upper-level
     ridge of high pressure builds just off the west coast today,
     a dry north-northwesterly flow aloft will prevail over
     Washington and Oregon.  The ODA surface analysis showed
     northerly gradients across all of Oregon, as pressures
     continued to build over Washington and north-central Oregon.
     A thermal trough was starting to push northward, just off
     the southern Oregon coast...turning the flow offshore along
     the central and southern coast. 

     Even with a full day of sunshine, increasing cool northerly
     winds should keep highs from climbing much above 60 degrees
     this afternoon along the northern and central coast and
     across the Willamette Valley.  However, downsloping
     north-northeasterly winds should lift temperatures on the
     south coast, around Brookings, into the low 70s. 
     North-northeasterly transport winds are not favorable for
     stack burning, so it is not allowed today.

Surface Winds:
     N 5-15 this morning, N 10-20 G25 this afternoon.
Transport Winds:
     NNE 12 this morning, NNE 20 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 2500 feet.  Ventilation index 50.
High Temperature:
     Salem\'s high temperature today will be near 60.
Humidities:
     Minimum relative humidity will be near 32%.
Sunrise/Sunset:
     Salem sunset tonight: 7:22pm; sunrise tomorrow: 7:17am.

Extended Outlook:
     There have been some significant timing changes to the
     extended forecast since yesterday.  Friday now appears as if
     it will be the warmest day of this dry spell, with the
     upper-level ridge forecast to move over western Oregon.  A
     building surface thermal trough, along the coast, will turn
     low-level winds offshore...further drying the air mass and
     leading to a large spread between morning minimums and
     afternoon maximums.  After another cold morning, with local
     areas of frost, afternoon highs should climb into the low to
     mid 60s in the Willamette Valley.  The northern and central
     coast could see high temperatures climb to near 70 degrees.

     The upper-level ridge is forecast to shift eastward on
     Saturday, to over eastern Oregon, with increasing
     southwesterly flow aloft initiating a marine push across
     western Oregon.  Temperatures will cool significantly along
     the coast, with afternoon onshore flow capping high
     temperatures a few degrees cooler across the Willammette
     Valley.  Clouds will also be on the increase Saturday
     afternoon, as a weak cold front comes onshore.  The latest
     computer guidance is suggesting that the cold front could be
     strong enough to bring some areas of light rain to western
     Oregon by Saturday evening...especially along the coast.

     A weak upper-level trough will turn the flow aloft westerly
     over Oregon on Sunday, with strong onshore flow producing
     mostly cloudy skies and some shower activity across western
     Oregon.  High temperatures will drop back below normal. 
     Snow levels may drop to the Cascade passes by late Sunday,
     with minor snow accumulations possible.  The upper-level
     trough will push east of the region late Monday with a weak
     ridge building over the west coast Tuesday.  Another weak
     weather system may bring back a chance of rain by later Wednesday.

Fri (19 Mar):  Possible Frosty Start...Sunny and Mild in the Afternoon. Offshore Flow.  31/63

Sat (20 Mar):  Increasing Clouds and Cooler.  Slight Chance of Rain late.   34/59

Sun (21 Mar):  Mostly Cloudy.  Scattered Showers.  Snow Level Dropping to 4000 Feet.  42/55

Mon (22 Mar):  Decreasing Showers.  Snow Level Dropping to 3000 Feet.  39/52

Tue (23 Mar):  Partly Sunny.  37/56

Wed (24 Mar):  Chance of Light Rain Late.  Snow Level Rising to 4-5000 Feet. 36/56

Thu (25 Mar):  Becoming Partly Sunny.  38/60

ODA Meteorologist
weather at oda.state.or.us