[willamette-fcst] Forecast - Tuesday, April 13th, 2010

Tue Apr 13 12:10:50 PDT 2010

Daily Smoke Management Forecast

Oregon Department of Agriculture
Smoke Management Program
Weather Outlook and Field Burning Advisory for Willamette Valley Growers and Fire Districts.

     This daily Willamette Valley Agricultural Weather Forecast will become a seasonal product,
     as of Friday April 16th. The last broadcast and email of this forecast will be Thursday,
     April 15th. It will return as the \"Willamette Valley Field Burning Weather Forecast,\"
     issued daily via email and broadcast on WPOZ 585, beginning Thursday July 1st.

Issued: 
     Tuesday, April 13th, 2010 at 12:00pm.

Burn Advisory:
     Recommended burn times for agricultural burning are from now until 6:00pm.
     Stack burning is not allowed.

Weather Discussion:
     The upper-level trough that was centered over southwestern Oregon and northern California
     on Monday has ejected eastward, into the Rockies.  However, the counterclockwise circulation
     around it is still spinning moisture back across western Oregon.  A narow band of light rain
     slowly pushed southeastward, across the Willamette Valley, this morning.  Most locations
     picked up a few hundredths of an inch.  Doppler radar showed the rain moving east of the
     northern and central valley at midday, but it was over the south valley and extended
     southwestward to over southwestern Oregon and the southern Oregon coast.

     Visible satellite imagery showed some partial clearing, in the wake of the light rain, over
     the northern and central coast and northern coastal range.  The late-morning ODA surface
     analysis showed high pressure trying to build into the coast with low pressure over eastern
     Washington.  That was resulting in 5-15 mph west-southwesterly winds across western Oregon.
     Temperatures were in the 50-55 degree range.

     The band of light rain extending from the northern Cascades to the southern Oregon coast
     will continue to slide slowly eastward this afternoon.  However, the shower threat will not
     completely end across northwestern Oregon.  Daytime heating will act to destabilize the
     atmosphere, while another upper-level disturbance, dropping southward from Vancouver Island,
     British Columbia, maintains a moist onshore flow into the region. 

     The freezing level has dropped slightly since Monday and is near 5000 feet over western
     Oregon.  That puts the snow level near 4000 feet, so some minor snow accumulation is
     possible over the higher elevations of the Cascades this afternoon.  ODOT road cameras
     showed just wet pavement over the passes at midday.  After reaching highs Monday in the
     low to mid 60s, more clouds and slightly cooler air aloft will likely keep valley highs
     from climbing much above 60 degrees this afternoon.

Surface Winds:
     W 5-15 this afternoon.
Transport Winds:
     W 12 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5000 feet.  Ventilation index 60.
High Temperature:
     Salem\'s high temperature today will be near 60.
Humidities:
     Minimum relative humidity will be near 41%.
Sunrise/Sunset:
     Salem sunset tonight: 7:55pm; sunrise tomorrow: 6:29am.

Extended Outlook:
     Another upper-level trough is forecast to set up camp just off the Oregon and northern
     California coast tomorrow, which will turn the flow aloft more southerly and warm
     temperatures slightly.  Daytime heating will act to destabilize the moist air mass enough
     to maintain a threat of showers across western Oregon, aided by an upper-level
     disturbance forecast to rotate onshore Wednesday evening.

     Not much chance in the overall circulation pattern is forecast Thursday or Friday, with
     another weak upper-level disturbance forecast to rotate onshore by Friday.  There are
     signs the entire upper-level trough may finally move onshore Saturday, but that is too
     far out to call at this time.     

     We may get a break from the showers on Sunday, but that is also too far out to call.  The
     long-range models are consistent in forecasting a strong cold frontto come onshore next
     Monday, with a return of cool valley rain and mountain snow.

Tomorrow (14 Apr):  Increasing Chance of Showers PM.  Snow Level Rising to 5000 Feet.  37/61

Thu (15 Apr):  Mostly Cloudy.  Chance of Showers.  Snow Level 5000 Feet.  38/63

Fri (16 Apr):  Mostly Cloudy.  Chance of Showers.  Snow Level 6000 Feet.  43/63

Sat (17 Apr):  Showers Likely. Snow Level 5000 Feet. 45/62

Sun (18 Apr):  Partly Cloudy.  Slight Chance of Showers.  Snow Level 6-7000 Feet.  44/65

Mon (19 Apr):  Rain Developing. Cooler. Snow Level Dropping to 4000 Feet.  44/59

Tue (20 Apr):  Showers Likely...Decreasing Late.  Snow Level 3-4000 Feet.  41/57

ODA Meteorologist
weather at oda.state.or.us