[willamette-fcst] Forecast - Wednesday, August 5th, 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: 
     Wednesday, August 5th, 2009 at 8:20am.

Burn Advisory:
     Agricultural burning is not recommended.
     Preparatory burning is not allowed.
     Propane flaming is not allowed.
     Stack burning is not allowed.

Weather Discussion:
     An upper-level low pressure center was about 200 miles off
     the northern California coastline and drifting slowly
     eastward this morning. It will continue the weak southerly
     flow aloft over Oregon today, along with a chance of
     afternoon and evening thunderstorms...mainly from the
     Cascades eastward.

     Marine low clouds penetrated across most of the Willamette
     Valley this morning but should give way to mostly sunny
     skies this afternoon.  Mid-morning temperatures were in the
     comfortable 55-60 degree range across most of western
     Oregon.  Willamette Valley highs only climbed to near-normal
     Tuesday and will be similar today (the normal high for Salem
     today is 83 degrees).

     The Salem sounding this morning showed a few degrees more
     cooling aloft, compared to Tuesday morning, so mixing
     heights should climb to just over 4000 feet by late this
     afternoon (compared to a maximum of about 3700 feet Tuesday
     afternoon). Forecast northwesterly transport winds should
     allow for limited open burning this afternoon, assuming the
     weak gradient-stacking from last night\'s marine influx is
     reversed by daytime heating.  Once again, thunderstorm
     development over the Cascades, and across central Oregon,
     will need to be closely monitored.

     By this evening, enough moisture may feed far enough north
     and west to include a slight chance for a shower or
     thunderstorm over the Willamette Valley, but it appears that
     the bulk of the shower activity will stay east of the region.

Surface Winds:
     W 0-6 this morning, NW 5-15 this afternoon.
Transport Winds:
     SW 4 this morning, NW 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4200 feet.  Ventilation index 42.
High Temperature:
     Salem\'s high temperature today will be near 82.
Humidities:
     Relative humidity drops to 50% by 12pm.
     Minimum relative humidity will be near 33%.
Sunrise/Sunset:
     Salem sunset tonight: 8:33pm; sunrise tomorrow: 6:04am.

Extended Outlook:
     A weak weather system, cutting across southern British
     Columbia on Thursday, will finally force the upper-level
     trough off the California coast onshore.  That will initiate
     a significant increase in onshore flow across western Oregon
     with much cooler temperatures.  A burning opportunity is
     possible with this transition to a cooler air mass, because
     most of the moisture is forecast to stay south and east of
     the Willamette Valley. There will be considerable clouds and
     at least a slight chance of showers...especially over the
     southern Willamette Valley.

     The threat of showers and thunderstorms will increase, from
     the Cascades eastward, Thursday and Friday, with some storms
     possibly becoming quite strong.  Due to the recent hot and
     dry weather, these storms have the potential to start many
     wildfires.  The trough is forecast to continue eastward,
     into Idaho, Friday with a drier northwesterly flow aloft
     spreading from west to east across Oregon.  A weak system is
     forecast to move across southern British Columbia over the
     weekend...maintining onshore flow, and below normal
     temperatures, across the interior of western Oregon.

     The long-range models differ on their timing and strength of
     a system coming onshore early next week.  It should maintain
     below normal temperatures across western Oregon and could
     introduce a chance of rain...especially in the northern
     Willamette Valley.

Tomorrow (06 Aug):  Mostly Cloudy and Cooler.  Slight Chance of Showers.  52/75

Fri (07 Aug):  AM Clouds.  Slight Chance of a Shower.  Partial PM Clearing.  52/72

Sat (08 Aug):  AM Clouds.  Partly Sunny.  51/77

Sun (09 Aug):  Partly Sunny and Continued Seasonably Cool.  52/77

Mon (10 Aug):  Mostly Cloudy.  Chance of Rain...Mainly North.  54/74

Tue (11 Aug):  Mostly Cloudy.  Chance of Showers...Mainly North.  54/78

Wed (12 Aug):  Mostly Cloudy.  Chance of Showers...Mainly North.  54/78

ODA Meteorologist
weather at oda.state.or.us