[willamette-fcst] Forecast - Tuesday, July 7th, 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: 
     Tuesday, July 7th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 11:00am until 8:00pm.
     Preparatory burning is not allowed.
     Propane flaming is not allowed.
     Straw stack burning is allowed from 11:00am until 8:00pm.

Weather Discussion:
     An upper-level trough remains over the region this morning.
     Onshore flow is continuing at the surface with visible
     satellite imagery showing marine low clouds blanketing
     western Washington and most of western Oregon...extending
     southward into Douglas County.  Pilot reports this morning
     show cloud-tops between 3600 and 4200 feet, which is about
     2000 feet lower than Monday morning and favors more breaks
     this afternoon.  Some breaks in the low clouds were already
     visible off the coastline, where a weak upper-level
     disturbance is helping to create some instability.

     With cooler marine air spilling across the entire state,
     temperautures this morning were much cooler east of the
     Cascades.  Mid-morning readings were in the 50s and 60s.
     Western Oregon temperatures were mostly in the 50s.  Onshore
     gradients were stronger east of the Cascades than west of
     the Cascades but weaker than they were Monday morning.  As a
     weak upper-level disturbance moves moves onshore, it will
     aid in the break-up of the low clouds over the valley this
     afternoon.  That should help temperatures climb into the low
     70s, but cool air aloft will prevent more warming than that.

     The incoming weak upper-level disturbance is forecast to
     rotate another surge of cool marine air onshore late this
     afternoon and evening. It may be accompanied by a light
     shower. Cooling aloft and forecast westerly transport winds
     may create favorable ventilation conditions for burning this
     afternoon, for available fields.  However, the current
     pressure gradient-stacking would need to be reversed by the
     combination of daytime heating and the approaching weather
     system.  That may not happen and will be monitored this afternoon.

Surface Winds:
     WSW 3-8 this morning, W 5-15 this afternoon.
Transport Winds:
     WSW 5 this morning, WNW 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4500 feet.  Ventilation index 45.
High Temperature:
     Salem\'s high temperature today will be near 71.
Humidities:
     Relative humidity drops to 50% by 2pm.
     Minimum relative humidity will be near 44%.
Sunrise/Sunset:
     Salem sunset tonight: 9:00pm; sunrise tomorrow: 5:34am.

Extended Outlook:
     The forecast weather pattern maintains enough of a westerly
     component, through next week, for potential burning
     opportunities at times...

     An upper-level trough of low pressure will remain over the
     Pacific Northwest Wednesday and Thursday with weak
     disturbances rotating across the region.  That will maintain
     onshore flow across western Washington and western Oregon
     with considerable amounts of clouds and below normal
     temperatures.  There will also be at least a slight chance
     of sprinkles or light showers at times...especially north.     

     The trough is forecast to weaken and shift slightly offshore
     by Friday.  That would put Oregon under a slightly warmer
     southwesterly flow aloft.  Onshore flow at the surface would
     likely still be strong enough to keep considerable clouds
     across western Oregon with temperatures only warming a
     little closer to normal.  The trough is still forecast to
     move inland this weekend, which would increase the onshore
     flow, cool temperatures a few degrees, and heighten the
     threat of light showers.

     A transitory ridge is forecast to bring a drier
     northwesterly flow on Monday with more sunshine warming
     temperatures to around normal.  Another weak trough is
     forecast to turn to flow southwesterly again on Tuesday with
     increasing onshore flow. West-southwesterly flow aloft is
     forecast for the middle of next week, which would keep
     temperatures slightly below normal.

Tomorrow (08 Jul):  Mostly Cloudy.  Chance of Sprinkles or Light Showers.  52/68

Thu (09 Jul):  Mostly Cloudy.  Slight Chance of Sprinkles or Light Showers.  52/73

Fri (10 Jul):  Partly Sunny and a Little Warmer.  53/78

Sat (11 Jul):  Partly Sunny.  Increasing Onshore Flow Late.  54/79

Sun (12 Jul):  Mostly Cloudy and Cooler.  Chance of a Light Showers North.  53/73

Mon (13 Jul):  Becoming Mostly Sunny and Warmer.  53/82

Tue (14 Jul):  Partly Cloudy.  Increasing Onshore Flow Late.  54/81

ODA Meteorologist
weather at oda.state.or.us