[willamette-fcst] Forecast - Friday, August 21st, 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.

NOON UPDATE

Issued: 
     Friday, August 21st, 2009 at 11:50am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 12:00pm until 7:30pm.
     Preparatory burning is allowed from 12:00pm until 2:00pm with a 100 acre limit.
     Propane flaming is allowed from 12:00pm until 2:00pm.
     Stack burning is not allowed.

Weather Discussion:
     late-morning visible satellite imagery showed low clouds
     continuing to blanket western Washington and northwestern
     Oregon.  There were even pockets of drizzle in the
     Willamette Valley earlier this morning. The low clouds were
     beginning to clear away from the southern half of the Oregon
     Coast and coastal range.  Surface observations and pilot
     reports show the low clouds over the Willamette Valley are
     about 2000 feet thick...extending up to between 3500 and
     4000 feet.  They should persist until the mid to late
     afternoon, so I have lowered my high temperature forecast a
     few degrees.  Skies were sunny over extreme southwestern
     Oregon and east of the Cascades.

     Late-morning temperatures were in the low to mid 60s, under
     cloudy skies, across the Willamette Valley.  Mixing heights
     will climb to the base of the low clouds, around 3000 feet,
     when surface temperatures reach the upper 60s early this
     afternoon.  That will allow for some propane flaming and
     limited prep burning.

     As expected, the marine push overnight has created gradient-stacking
     conditions, which worsened from 3 millibars to more than 4 millibars,
     as the morning progressed.  Normally, that would be too much
     gradient-stacking to reverse with afternoon heating. However, a weak
     cold front is forecast to move onshore late this afternoon.  It may
     help to break up the marine low clouds and increase the onshore
     gradients west of the valley.

     There is a slight chance that the approaching dry cold front could
     create a brief burning opportunity in the north valley, since transport
     winds are forecast to be north-northwesterly. Winds will likely be too
     northerly for open burning, in the south valley, even if the
     gradient-stacking is reversed.  We plan to begin pibals at 1pm.

Surface Winds:
     NNW 5-15 this afternoon.
Transport Winds:
     NNW 8 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3700 feet.  Ventilation index 30.
High Temperature:
     Salem\'s high temperature today will be near 77.
Humidities:
     Relative humidity drops to 50% around 2pm.
     Minimum relative humidity will be near 46%.
Sunrise/Sunset:
     Salem sunset tonight: 8:08pm; sunrise tomorrow: 6:23am.

Extended Outlook:
     A weak trough is forecast to maintain southwesterly flow
     aloft and onshore flow at the surface, over western Oregon,
     Saturday and Sunday.  A transitory ridge will bring more
     sunshine and some warming Monday, before another weak trough
     increases the onshore flow again by late Tuesday.  That
     transition could be enough to create a burning opportunity
     Tuesday afternoon.  Another transitory ridge is forecast for
     next Wednesday, following by increasing onshore flow Thursday
     and Friday. 

Tomorrow (22 Aug):  AM Clouds...PM Sunshine.  53/80

Sun (23 Aug):  AM Clouds.  Partly Sunny in the Afternoon.   51/79

Mon (24 Aug):  Brief AM Clouds...Mostly Sunny and Warmer.   50/83

Tue (25 Aug):  Mostly Sunny. Increasing Onshore Flow in the Afternoon.  51/79

Wed (26 Aug):  AM Clouds...Afternoon Sunshine and a Touch Warmer.  54/83

Thu (27 Aug):  Mostly Sunny.  Onshore Flow Possibly Increasing Late.  54/85

Fri (28 Aug):  Mostly Cloudy and Cooler.  Chance of AM Drizzle.  54/77

ODA Meteorologist
weather at oda.state.or.us