[willamette-fcst] Forecast - Monday, March 22nd, 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: 
     Monday, March 22nd, 2010 at 9:00am.

Burn Advisory:
     Recommended burn times for agricultural burning are from now until 4:30pm.
     Straw stack burning is allowed from now until 4:30pm.

Weather Discussion:
     Winter ended on a sunny and mild note, with temperatures last Friday climbing to near 70
     degrees both along the coast and in the Willamette Valley.  On Saturday, the first day of
     spring, strong onshore flow cooled the immediate coastline back into the 50s and low 60s,
     with some rain moving onshore by Saturday evening.  However, the western valleys enjoyed
     another mostly sunny and quite mild day, with highs topping out near the 70 degree mark.

     A cold front pushed the cooler and breezy conditions inland by Saturday evening, with some
     rain making it into the Willamette Valley Sunday morning.  Mostly cloudy and showery
     conditions prevailed on Sunday across western Oregon. Temperatures cooled into the mid 50s
     along the coast and into the mid to upper 50s in the Willamete Valley (close to seasonal
     normals).  The snow level dropped to 4-5000 feet by Sunday afternoon, with wintry conditions
     returning to the Cascade passes and ski areas.

     Mid-morning satellite imagery showed a weak upper-level disturbance dropping into
     northwestern Oregon.  Doppler radar and surface reports showed scattered showers
     continuing to circulate onshore, as far south as Roseburg, across western Oregon.  The 
     snow level has dropped to about 2500 feet, with ODOT road cameras showing snow-packed road
     surfaces over the Cascade passes and a few inches of new snow.  The ODA surface analysis
     showed high pressure beginning to build into western Oregon with a weak trough moving onto
     the extreme northern coast.  That was producing light south to southwesterly winds across
     the Willamette Valley.  Temperatures were mostly in the low to mid 40s along the coast and
     in the interior valleys of western Oregon.

     The weak upper-level disturbance is forecast to dive southeastward across Oregon during the
     day, taking some scattered showers with it along the way.  As the system moves into
     southeastern Oregon this afternoon, showers will taper off across western Oregon.  Surface
     winds will veer from southwesterly to northwesterly by late this afternoon, as drier air
     begins pouring into western Oregon.  The snow level will only rise to about 3000 feet this
     afternoon, so a couple of additional inches of snow are possible over the Cascade passes,
     before the snow showers end later today. Cool air aloft and daytime heating will combine to
     produce high mixing heights over western Oregon this afternoon.  Northwesterly flow aloft
     will begin to subdue convective overturning of the atmosphere later this afternoon, in spite
     of the destabilizing effects of daytime heating.  Valley highs should climb to near normal
     this afternoon with some sunbreaks.

Surface Winds:
     S 3-8 this morning, becoming NW 5-10 by late this afternoon.
Transport Winds:
     SW 6 this morning, becoming W 6 by late this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5000 feet.  Ventilation index 30.
High Temperature:
     Salem\'s high temperature today will be near 56.
Humidities:
     Minimum relative humidity will be near 53%.
Sunrise/Sunset:
     Salem sunset tonight: 7:27pm; sunrise tomorrow: 7:09am.

Extended Outlook:
     An upper-level ridge of high pressure is forecast to build over Oregon and Washington on
     Tuesday, with a building surface thermal trough along the southern Oregon coast helping to
     turn the low-level winds offshore.  That will further warm and dry the air mass across
     western Oregon, with skies becoming mostly sunny by the afternoon.  After a chilly morning,
     with mimimums locally near freezing, afternoon highs should rebound into the low 60s.

     The upper-level ridge will weakend and shift eastward, to over Idaho, on Wednesday.
     Increasing southwesterly flow aloft will turn the surface winds onshore along the coast,
     leading to cooler temperatures there. However, highs in the Willamette Valley should climb
     into the 60s again, before a push of cooler marine air penetrates east of the coast range
     Wednesday afternoon.  A cold front is forecast to spread rain onshore Wednesday night and
     into the Willamette Valley Thursday morning.

     Another upper-level ridge is forecast to bring drier conditions late Friday and Saturday.
     The next weather system, on Sunday, does not look as strong...bringing just a chance of
     light rain and mountain snow.  A stronger system is forecast to come onshore by late Monday.

Tomorrow (23 Mar):  Chilly Start...Becoming Mostly Sunny and Mild in the Afternoon.  34/62

Wed (24 Mar):  Mostly Sunny. Increasing Clouds in the Afternoon.  35/65

Thu (25 Mar):  Rain Likely and Much Cooler.  Snow Level Dropping to 3-4000 Feet.  44/56

Fri (26 Mar):  Showers Ending with Partial Clearing.  Snow Level 3-4000 Feet.  40/56

Sat (27 Mar):  Becoming Mostly Sunny and Warmer.  36/63

Sun (28 Mar):  Mostly Cloudy.  Chance of Light Rain.  Snow Level 4-5000 Feet.  41/58

Mon (29 Mar):  Mostly Cloudy.  Increasing Rain Late.  Snow Level 5000 Feet.  41/59

ODA Meteorologist
weather at oda.state.or.us