[willamette-fcst] Forecast - Thursday, August 7th, 2008

[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: 
     Thursday, August 7th, 2008 at 9:00am.

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

Weather Discussion:
     A moist and unstable south-southwesterly flow aloft will
     continue today over Oregon.  Doppler radar showed showers
     and thundershowers this morning stretching from
     South-Central through NE Oregon.  The storms in Central
     Oregon, over Northern Deschutes, Eastern Jefferson, and
     Northern Crook Counties, appeared quite strong on radar. 
     Daytime heating will act to further destabilize the air mass
     and keep the showers and thundershowers going today...mainly
     from the Cascades eastward.

     The ODA surface analysis showed a broad thermal trough
     extending from South-Central Washington through Central
     Oregon.  That appears to be the focus of the thunderstorm
     development this morning.   Onshore flow is keeping low
     clouds against both the Washington and Oregon Coastlines
     with a greater penetration trough the coastal mountain gaps
     than on Wednesday morning.  Marine low clouds were making it
     into the Willamette Valley this morning.  They should give
     way to mostly sunny skies by midday.

     The Salem sounding this morning showed south-southwesterly
     winds aloft, and if those directions are maintained, then
     the showers and thundershowers will stay mainly east of the
     Cascades.  However, it is possible that showers or
     thundershowers could swing more westward, to over the
     Willamette Valley, if the flow aloft turns more southerly
     later this afternoon and evening.  The air aloft is only
     slightly cooler than on Wednesday, so mixing heights will
     remain below 3000 feet well into the afternoon.

     A filtering of marine air into the valley today should take
     a few degrees off of high temperatures this afternoon.  More
     cooing aloft may lift mixing heights to near 4000 feet later
     this afternoon.  If the flow aloft remains southwesterly,
     and the thunderstorm activity over Central Oregon moves
     further east, there is a chance that ventialtion conditions
     could become favorable for open burning this afternoon.  

Surface Winds:
     Var 0-5 this morning, NW 5-10 this afternoon.
Transport Winds:
     SW 5 this morning, NW 5 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4000 feet.  Ventilation index 20.
High Temperature:
     Salem\'s high temperature today will be near 85.
Humidities:
     Relative humidity drops to 50% by 2pm.
     Minimum relative humidity will be near 38%.
Sunrise/Sunset:
     Salem sunset tonight: 8:30pm; sunrise tomorrow: 6:06am.

Extended Outlook:
     As the upper-level ridge shifts east, to over Montana, the
     flow aloft over Oregon is forecast to become more
     southwesterly Friday.  The thermal trough will shift
     eastward, into Eastern Oregon and Idaho, with increasing
     onshore flow across Western Oregon.  Southwesterly flow
     aloft will also push the moist and unstable air east, with
     the thundershowers shifting to Eastern Oregon and Idaho.

     Southwesterly transport winds and higher mixing heights may
     create an open-burning opportunity Friday.  However, that
     could be dampened, if too much marine air invades the valley
     overnight tonight.  In addition, the low-level winds will be
     increasing Friday and may become too strong for good plume
     rise by the afternoon.

     The upper-level trough is forecast to move onshore over the
     weekend with the flow aloft turning westerly.  Temperatures
     will cool further with increasing onshore flow possibly
     leading to areas of drizzle or light rain Saturday morning. 
     A transitory ridge of high pressure is forecast for early
     next week.  A trough is forecast to approach the coastline
     Tuesday afternoon, which could create another burning
     opportunity.

Tomorrow (08 Aug):  Slight Chance of AM Showers/T-storms...Partly Cloudy and Cooler.  58/80

Sat (09 Aug):  Morning Clouds...Areas of Drizzle.  Afternoon Clearing.  56/75

Sun (10 Aug):  Morning Clouds.  Mostly Sunny in the Afternoon.  50/79

Mon (11 Aug):  Sunny and Warmer.  50/84

Tue (12 Aug):  Mostly Sunny and Warm.  Increasing Onshore Flow Late.  52/87

Wed (13 Aug):  Morning Clouds...Chance of Drizzle.  Afternoon Clearing.  54/75

Thu (14 Aug):  Morning Clouds.  Afternoon Clearing.  54/77

ODA Meteorologist
weather at oda.state.or.us