[willamette-fcst] Forecast - Tuesday, July 29th, 2008

Tue Jul 29 08:02:15 PDT 2008

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 29th, 2008 at 9:00am.

Burn Advisory:
     Agricultural burning is not recommended.
     Preparatory burning is allowed from 12:00pm until 2:00pm with a 100 acre limit.
     Propane flaming is allowed from 12:00pm until 5:00pm.
     Stack burning is not allowed.

Weather Discussion:
     Today will bring the first measurable rain, for much of the
     north valley, since June 10th (50 days).  Satellite imagery
     showed clouds, associated with an upper-level cold front,
     rotating onshore across Western Oregon this morning. 
     Doppler radar and surface reports indicated areas of light
     rain...mainly along the coast and in the Willamette Valley
     (north of about Corvallis).  Skies were sunny east of the
     Cascades with clouds just starting to make their way into
     Central Oregon.

     Cloudy skies held temperatures up overnight across Western
     Oregon with minimums generally in the low 50s.  At
     mid-morning, most of the valley was in the mid 50s.  The
     Salem sounding this morning showed little change from Monday
     morning below 5000 feet with minor cooling aloft. Winds were
     southerly near the surface and turned strong southwesterly,
     for late July, above 3000 feet.

     The ODA surface analysis showed high pressure over Western
     Oregon...nosing into Western Washington with a troughs
     extending from Eastern Washington to SW Oregon and just off
     the Washington and Northern Oregon Coast.  Gradients were
     mainly southerly with valley winds from the south at 5-10 mph.

     The upper-level cold front is forecast to push east of the
     region late this morning with the spotty light showers
     tapering off for a few hours across the valley.  The surface
     cold front was still offshore this morning and will
     eventually bring a renewed threat of rain to the valley by
     this evening.  If things do dry out, there may be an
     opportunity for some prep burning and propane flaming, of
     dry fields, early tis afternoon.  Transport winds are
     forecast to turn southwesterly by midday, and mixing heights
     will rise above 3000 feet when surface temperatures reach
     about 70 degrees.

     If the cold front is delayed enough this afternoon, there is
     a chance that conditions could become favorable for limited
     open burning...especially for dry south-valley fields. 
     Southwesterly transport winds are forecast through the
     afternoon with mixing heights potentially rising to about
     4500 feet.  We will begin pibal readings at 12:45pm.

     The cold front is forecast to bring light rain to much of
     the valley this evening...followed by an upper-level trough
     with a chance of showers overnight.  The north valley could
     pick up as much as one-tenth of an ince of rain with lighter
     amounts further south.

Surface Winds:
     S 5-10 this morning, SW 5-15 this afternoon.
Transport Winds:
     SSW 12 this morning, SW 18 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4500 feet.  Ventilation index 81.
High Temperature:
     Salem\'s high temperature today will be near 75.
Humidities:
     Relative humidity drops to 50% by 12pm.
     Minimum relative humidity will be near 42%.
Sunrise/Sunset:
     Salem sunset tonight: 8:41pm; sunrise tomorrow: 5:56am.

Extended Outlook:
     A dry westerly flow aloft is forecast for Wednesday through
     early Thursday with onshore surface flow.  Temperatures will
     slowly recover to near normal by Thursday.  There is
     uncertainty in the long-range models regarding the timing
     and strength of weather system forecast to approach the
     coastline late Thursday.  It may be strong enough to bring
     some sprinkles as far south as Western Oregon Thursday
     night.  It may create another open burning opportunity for
     the Willamette Valley Thursday afternoon.

     A weak trough will resume the dry westerly flow aloft over
     the region Friday wtih a building ridge of pressure turning
     the flow aloft northwesterly over the weekend.  Temperatures
     will recover to near normal by Saturday and likely go above
     normal Sunday through early next week.

Tomorrow (30 Jul):  Morning Clouds...Becoming Partly Cloudy in the Afternooon.  53/77

Thu (31 Jul):  Mostly Sunny...Increasing Clouds with a Chance of Rain North Late.  51/79

Fri (01 Aug):  Morning Clouds...Becoming Partly Sunny in the Afternoon.  52/79

Sat (02 Aug):  Mostly Sunny.  51/83

Sun (03 Aug):  Sunny and Warmer.  52/87

Mon (04 Aug):  Sunny and Very Warm.  55/90

Tue (05 Aug):  Sunny and Very Warm.  56/90

ODA Meteorologist
weather at oda.state.or.us