[willamette-fcst] Forecast - Friday, August 14th, 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 14th, 2009 at 12:00pm.

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

Weather Discussion:
     An unseasonably cool upper-level trough is over the Pacific
     Northwest this morning.  The main upper-level trough axis
     moved across western Oregon Thursday evening and was pusing
     across Idaho late this morning.  On the back side of the
     parent trough, a smaller spoke of upper-level energy was
     visible on satellite imagery, late this morning, rotating
     southeastwawrd onto the Washington and extreme northern
     Oregon Coast late this morning.  That weak disturbance is
     forcast to rotate over the Willamette Valley this
     afternoon...maintaining the cool pool of air aloft and weak
     convective cloud development.  It is unlikely that the
     convection will be strong enough to produce showers over the
     Willamette Valley, but an isolated shower is possible over
     the coastal range and western slopes of the Cascades.

     Once surface temperatures climbed into the low 60s, late
     this morning, convective clouds began developing, between
     3000 and 3500 feet over northwestern Oregon, due to very
     cold air and cyclonic flow aloft.  As a result, skies had
     become mostly cloudy over the valley.  Late-morning
     temperatures had only warmed into the mid 60s with light and
     variable surface winds.  Mixing down of colder air aloft
     will slow the rate of warming for the remainder of the day,
     with high temperatures only climbing into the low 70s. 
     Daytime heating should drop relative humidities to near 50
     percent, and raise mixing heights to near 5000 feet, by
     about 2pm.  Transport winds are forecast to be about 330
     degrees this afternoon, which should allow for open burning
     in the north valley.  Some limited burning may be possible
     in the south valley.  Pibals will begin at 1pm.

Surface Winds:
     NW 5-15 this afternoon.
Transport Winds:
     NW 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5500 feet.  Ventilation index 55.
High Temperature:
     Salem\'s high temperature today will be near 72.
Humidities:
     Relative humidity drops to 50% by 2pm.
     Minimum relative humidity will be near 43%.
Sunrise/Sunset:
     Salem sunset tonight: 8:19pm; sunrise tomorrow: 6:14am.

Extended Outlook:
     The flow aloft is forecast to become northerly Saturday and
     Sunday, as a strong upper-level ridge builds along the west
     coast.  Temperatures will rapidly warm across western Oregon
     through Tuesday, as a surface thermal trough builds northward,
     into western Oregon.  Low-level winds will turn offshore early
     next week, even along the northern and central coast.  That may
     allow for the burning of fields on extreme west side of the valley.

     It appears as if a slow cooling trend will begin around the
     middle of next week, as the upper-level ridge, and associated
     surface thermal trough, both shift east of the Cascades.  That
     may create afternoon burning opportunities, beginning as soon
     as Wednesday, with the low-level winds turning back onshore.

Tomorrow (15 Aug):  Mostly Sunny.  48/78

Sun (16 Aug):  Sunny and Warmer.  49/84

Mon (17 Aug):  Sunny and Very Warm.  52/88

Tue (18 Aug):  Sunny and Very Warm.  54/92

Wed (19 Aug):  Mostly Sunny and Warm.  Possible Onshore Flow Late.  56/89

Thu (20 Aug):  Mostly Sunny and a Little Cooler.  Onshore Flow in the Afternoon.  55/86

Fri (21 Aug):  Patchy AM Clouds.  Afternoon Sunshine. 55/84

ODA Meteorologist
weather at oda.state.or.us