[willamette-fcst] Willamette Valley Ag/Burning Forecast/Backup Mailing Method

[Willamette Valley Ag/Burning Forecast]

Oregon Department of Agriculture
Smoke Management Program
Weather Outlook and Field Burning Advisory for Willamette 
Valley Growers and Fire Districts.

Issued:
      Friday, August 14th, 2009 at 8:50am.

Burn Advisory:
      Agricultural burning is not recommended.
      Preparatory burning is allowed from 11:00am until 
2:00pm with a 100 acre limit.
      Propane flaming is allowed from 11:00am until 
2:00pm.
      Stack burning is not allowed.

Weather Discussion:
      An unseasonably cool upper-level trough is over the 
Pacific
      Northwest this morning.  The upper-level trough axis 
moved
      across western Oregon Thursday evening but did not 
produce
      much in the way of shower activity.  Most of the 
moisture
      from this system is well north and east of western 
Oregon,
      but the air aloft is quite cool for mid-August.  The
      freezing level over Salem was measured at just 7500 
feet,
      compared with a mid-August average of 12,400 feet.

      The cool and unstable atmosphere helped to keep 
skies at
      least partially clear overnight, across western 
Oregon, with
      early morning temperatures locally dropping into the 
mid to
      upper 40s.  Eugene and Corvallis both dipped down to 
47
      degrees.  Mid-morning readings were mostly in the 
low to mid
      50s with numerous sunbreaks and light winds.  Skies 
should
      be partly to mostly sunny this afternoon, with a 
drier
      northwesterly flow aloft.  Willamette Valley highs 
will only
      climb into the low 70s, with increasing 
northwesterly winds
      this afternoon.

      The air mass is cool and moist enough for convective 
cloud
      development, once surface temperatures reach about 
62
      degrees, which should occur late this morning.  I do 
not
      expect the convection to be strong enough to develop
      showers, but the development of \"fair weather\" 
cumulus
      clouds will be a good indicator of mixing height 
(they shoud
      form between 2500 and 3000 feet late this morning).

      Cold air aloft will likely combine with daytime 
heating to
      lift mixing heights to over 5000 feet this 
afternoon. High
      mixing heights, combined with northwesterly 
transport winds,
      should provide adequate ventilation to allow for 
open
      burning in the north valley this afternoon. Winds 
may be too
      northerly to allow for burning in the south valley 
today.
      Winds are expected to turn more northerly overnight.

Surface Winds:
      NW 5-10 this morning, NW 5-15 this afternoon.
Transport Winds:
      NW 5 this morning, NW 10 this afternoon.
Atmospheric Ventilation Conditions:
      Maximum mixing height today will be near 5500 feet. 
 Ventilation index 55.
High Temperature:
      Salem's high temperature today will be near 72.
Humidities:
      Relative humidity drops to 50% around 2pm.
      Minimum relative humidity will be near 43%.
Sunrise/Sunset:
      Salem sunset tonight: 8:19pm; sunrise tomorrow: 
6:14am.

Extended Outlook:
      The flow aloft is forecast to become northerly 
Saturday and
      Sunday, as a strong upper-level ridge builds along 
the west
      coast.  Temperatures will rapidly warm across 
western Oregon
      through Tuesday, as a surface thermal trough builds
      northward, into western Oregon.  Low-level winds 
will turn
      offshore early next week, even along the northern 
and
      central coast.

      It appears as if a slow cooling trend will begin 
around the
      middle of next week, as the upper-level ridge, and
      associated surface thermal trough, both shift east 
of the
      Cascades.  That may create a burning opportunity, as 
soon as
      Wednesday afternoon, with the low-level winds 
turning back onshore.

Tomorrow (15 Aug):  Mostly Sunny.  48/78

Sun (16 Aug):  Sunny and Warmer.  50/84

Mon (17 Aug):  Sunny and Very Warm.  52/88

Tue (18 Aug):  Sunny and Very Warm.  54/92

Wed (19 Aug):  Mostly Sunny and Warm.  Possible Onshore 
Flow Late.  56/89

Thu (20 Aug):  Mostly Sunny and a Little Cooler.  Onshore 
Flow in the Afternoon.  55/86

Fri (21 Aug):  Patchy AM Clouds.  Afternoon Sunshine. 
55/84

ODA Meteorologist
weather at oda.state.or.us