[willamette-fcst] Forecast - Thursday, August 13th, 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.

Issued: 
     Thursday, August 13th, 2009 at 8:50am.

Burn Advisory:
     Agricultural burning is not recommended.
     Preparatory burning is not allowed.
     Propane flaming is allowed from 11:00am until 5:00pm.
     Stack burning is not allowed.

Weather Discussion:
     The Pacific frontal system, that brought significant rain to
     much of the northern Willamette Valley Tuesday night, pushed
     southeastward across Oregon Wednesday afternoon. It brought
     a few more showers to mainly the extreme southern Willamette
     Valley last night. Blustery west winds aided in the drying
     of damp fields Wednesday afternoon.  Some sunshine helped
     valley high temperatures climb int the upper 70s.

     The cold front had pushed south and east of Oregon by this
     morning, with only residual low clouds over the Willamette
     Valley. Mid-morning valley temperatures were mostly in the
     upper 50s with northwest winds around 5 mph.  The low clouds
     should give way to some sunshine later this morning, through
     early this afternoon, but temperatures will only climb into
     the mid 70s due to very cool air aloft.  That should be
     enough warming to overcome about 3 millibars of
     gradient-stacking, from Salem to Redmond, this morning, but
     that will need to be monitored this afternoon.

     An upper-level trough is forecast to drop southeastward,
     along the southern British Columbia and Washington coastlines,
     this afternoon...resulting in west-northwesterly transport winds
     and very high mixing heights over western Oregon. That should
     create favorable conditions, early this afternoon, for open
     burning, if relative humidities can drop below 50%.

     There are other potential limiting factors to open burning this
     afternoon...First of all, damp fields will need to be fluffed,
     before they can be burned.  In addition, the upper-level trough
     is quite vigorous and may get close enough to bring showers into
     the north valley by mid to late afternoon.  The southward progression
     of shower activity will need to be closely monitored this afternoon.
     Surface winds may also become too strong for safe ignition and/or good
     plume rise by late this afternoon and will also be closely watched.

     The upper-level trough is forecast to move onshore this
     evening with a good chance of showers over the north valley
     and a slight chance of showers in the south valley. 
     Rainfall amounts from this system are forecast to be spotty
     and much less than with the leading cold front that came
     through earlier this week.  The south valley may stay dry,
     with north-valley totals likely less than one-tenth of an inch.

Surface Winds:
     NW 5-10 this morning, W 5-15 this afternoon.
Transport Winds:
     NNW 7 this morning, WNW 12 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 6000 feet.  Ventilation index 72.
High Temperature:
     Salem\'s high temperature today will be near 74.
Humidities:
     Relative humidity drops to 50% by 2pm.
     Minimum relative humidity will be near 40%.
Sunrise/Sunset:
     Salem sunset tonight: 8:21pm; sunrise tomorrow: 6:13am.

Extended Outlook:
     As the upper-level trough pushes east, to over eastern
     Oregon Friday afternoon, a drier northwesterly flow aloft is
     forecast to move over western Oregon.  That may also create
     a burning opportunity, if surface winds are not too strong,
     and there is not too much gradient-stacking.

     The flow aloft is forecast to become northerly Saturday and
     Sunday, and offshore early next week, as a strong
     upper-level ridge builds along the west coast.  Temperatures
     will rapidly warm across western Oregon Sunday through
     Tuesday.  With a surface thermal trough building into
     western Oregon, low-level winds will turn offshore, except
     along the immediate coastline. The long-range computer
     models differ on how and when the ridge will eventually
     break down, but it appears as if some cooling will begin by
     next Wednesday.  That may create a burning opportunity, as
     the windflow turns back onshore.

Tomorrow (14 Aug):  Mostly Cloudy AM.  Chance Shower...Mainly North.  PM Clearing.  50/76

Sat (15 Aug):  Mostly Sunny.  49/80

Sun (16 Aug):  Sunny and Warmer.  51/85

Mon (17 Aug):  Sunny and Very Warm.  54/90

Tue (18 Aug):  Sunny and Very Warm.  58/95

Wed (19 Aug):  Mostly Sunny and Warm.  Slight Chance of PM T-Storms.  58/91

Thu (20 Aug):  Mostly Sunny and Warm.  Slight Chance of T-Storms.  55/88

ODA Meteorologist
weather at oda.state.or.us