[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.

...Corrected Surface Winds Today...

Issued: 
     Friday, August 21st, 2009 at 9:00am.

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:
     Increasing south-southwesterly flow aloft pushed the surface
     thermal trough east of the Cascades Thursday.  A significant
     surge of cool marine air poured into the Willamette Valley
     Thursday and Thursday night.  After topping out near the
     century mark Wednesday, valley highs cooled into the low to
     mid 80s Thursdsay.  By this morning, the marine layer had
     deepened to about 3700 feet thick over the Willamette
     Valley.  Visible satellite imagery showed low clouds had
     pushed inland and extended from the coast to the crest of
     the Cascades.  Skies were mostly clear over extreme
     southwestern Oregon and east of the Cascades.  There were a
     few high clouds over northeastern Oregon, in association
     with the weak weather system that intiated the onshore flow.

     Onshore flow will continue today, cooling valley
     temperatures a few more degrees. Morning clouds should give
     way to some sunshine this afternoon, but highs will struggle
     to reach 80 degrees.  Mixing heights will climb to the top
     of the marine layer by about noon, which will allow for some
     propane flaming and limited prep burning.

     As expected, the marine push overnight has created
     gradient-stacking conditions this morning, with about 3
     millabars more onshore gradient east of The valley than west
     of the valley.  The unbalance in gradients will likely
     increase later this morning, as central Oregon heats up, and
     the western valleys stay cool under cloud-cover.  It is
     doubtful that the western valleys will get enough afternoon
     heating to overcome that much gradient-stacking.  However, a
     little stronger weather system, about 150 miles offshore at
     mid-morning, is forecast to move onshore late this
     afternoon.  There is a slight chance that the timing of that
     system may help reverse the gradient-stacking, late this
     afternoon, which could give the north-valley a burning
     opportunity with north-northwesterly transport winds.

Surface Winds:
     N 3-8 this morning, NNW 5-15 this afternoon.
Transport Winds:
     N 5 this morning, 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 81.
Humidities:
     Relative humidity drops to 50% by 2pm.
     Minimum relative humidity will be near 41%.
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 and Thursday, following by increasing onshore
     flow by Friday. 

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

Sun (23 Aug):  AM Clouds.  PM Sunshine.   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 Warmer.  54/85

Thu (27 Aug):  Mostly Sunny and Warm.  54/87

Fri (28 Aug):  Increasing Clouds and Cooler.  54/79

ODA Meteorologist
weather at oda.state.or.us