[willamette-fcst] Forecast - Tuesday, March 23rd, 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: 
     Tuesday, March 23rd, 2010 at 12:00pm.

Burn Advisory:
     Recommended burn times for agricultural burning are from now until 5:30pm.
     Stack burning is not allowed.

Weather Discussion:
     Light winds, clearing skies, and cool air aloft, allowed temperatures to drop well into the
     30s across western Oregon this morning.  Some spots dropped to near the freezing mark with
     patchy frost in the Willamette Valley.  Hillsboro recorded a minimum of 32 degrees,
     McMinnville and Salem dropped to 33, Eugene dipped to 34, and Corvallis cooled to 36.
     Even the normally warmer Portland Airport temperature fell into the upper 30s. Those
     temperatures were warm, compared with the 16 degree minimum recorded at Burns, and the
     morning low of 18 degrees at Baker City.  Meacham, Redmond, and Klamath Falls dropped into
     the teens this morning, all recording minimums of 19 degrees.

     Late-morning infrared satellite imagery showed only a few high clouds drifting over
     Washington and Oregon, in a dry northwesterly flow aloft. However, visible satellite imagery
     showed areas of western valley low clouds stretching from the Columbia River to Roseburg.
     The low clouds were more prevalent in Douglas County, with Roseburg reporting a solid
     overcast cloud-deck at about 2000 feet above the ground.  Low clouds were beginning to
     give way to sunshine across the Willamette Valley, with sunny skies along the entire
     stretch of the Oregon coast.
 
     The ODA surface analysis showed high pressure centered over eastern Washington, with a
     thermal trough pushing northward along the southern Oregon coast.  Offshore flow was
     beginning to develop from southwestern Oregon to the central and southern coast.  Dry
     northeasterly winds, gusting over 15 mph, were clearing the skies over Newport, where
     temperatures had jumped into the low 50s. Late-morning temperatures in the Willamette
     Valley ranged from the low 40s, in the Eugene area, to near 50 in the north valley.
     North-northeasterly winds were just beginning to increase in the Willamette Valley but
     were still mostly under 10 mph.

     As an upper-level ridge continues to build over western Oregon today, the surface thermal
     trough will push further north into southwestern Oregon.  Increasing north-northeasterly
     pressure gradients will help dry the low-level air mass over western Oregon, with areas of
     morning fog and low clouds giving way to mostly sunny skies.  After the chilly start this
     morning, afternoon highs should rebound into the low 60s across most of the Willamette
     Valley.  The south valley will likely stay in the 50s, due to a slower start to the
     sunshine and a cool northerly afternoon breeze.

     Warming aloft will lift afternoon freezing levels to around 10,000 feet...with mixing
     heights significantly lower than on Monday. Even though general ventilation conditions
     will be fair this afternoon, north-northeasterly transport winds are not conducive to
     good ventilation for stack burning, so it is not allowed today.

Surface Winds:
     North wind increasing to 5-15 mph this afternoon.
Transport Winds:
     NNE 12 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 2500 feet.  Ventilation index 30.
High Temperature:
     Salem\'s high temperature today will be near 62.
Humidities:
     Minimum relative humidity will be near 39%.
Sunrise/Sunset:
     Salem sunset tonight: 7:29pm; sunrise tomorrow: 7:08am.

Extended Outlook:
     The upper-level ridge will weaken and shift eastward, to
     over Idaho, by Wednesday afternoon.  Increasing southwesterly
     flow aloft will initiate a push of cooling marine air into the
     Willamette Valley in the afternoon but likely after temperatures
     climb into the low to mid 60s. Increasing southwesterly transport
     winds and high mixing heights will likely provide excellent
     ventilation for stack burning.

     A cold front is forecast to spread rain across western
     Oregon late Wednesday night and Thursday morning, followed
     by an upper-level trough Thursday afternoon through perhaps
     much of Friday.  Another upper-level ridge is forecast to
     bring drying conditions late Friday and Saturday.  The next
     weather system, on Sunday, does not look very
     strong...bringing a chance of light rain and high elevation
     snow...mainly north.  A stronger system is forecast to come
     onshore Monday, with more significant rain and possibly
     windy conditions...especially along the coast.  That will be
     followed by a cold upper-level trough Tuesday and Wednesday,
     with showers and mountain snow.

Tomorrow (24 Mar):  Increasing Clouds in the Afternoon.  Rain Late.  35/64

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

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

Sat (27 Mar):  Chilly Start...Becoming Mostly Sunny and Warmer.  35/63

Sun (28 Mar):  Chance of Light Rain...Mainly North.  Snow Level 5-6000 Feet.  44/58

Mon (29 Mar):  Increasing Rain and Wind.  Snow Level 5-6000 Feet.  43/59

Tue (30 Mar):  Showers.  Snow Level Dropping to 3000 Feet.  40/56

ODA Meteorologist
weather at oda.state.or.us