[willamette-fcst] Forecast - Thursday, July 23rd, 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: 
     Thursday, July 23rd, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 11:00am until 8:00pm.
     Preparatory burning is allowed from 11:00am until 2:00pm with a 50 acre limit.
     Propane flaming is allowed from 11:00am until 2:00pm.
     Stack burning is not allowed.

Weather Discussion:
     A very weak upper-level trough will cut across Washington
     today and maintain onshore flow across western Oregon.
     Satellite imagery showed the marine low clouds extended from
     the coast to the crest of the Cascades this morning and will
     be slower to give way to sunshine than they were yesterday.
     As a result, valley temperatures will be a few degrees
     cooler today. Highs will peak in the upper 70s to low 80s,
     after hitting the low to mid 80s Wednesday.

     The morning sounding over Salem was a few degrees cooler,
     everywhere below 35,000 feet, compared with yesterday
     morning.  Transport winds were light north-northwesterly and
     are forecast to be mostly northerly this afternoon. The
     mid-morning ODA surface analysis showed high pressure
     building into the Oregon coast and slightly more significant
     gradient-stacking than yesterday morning, due to the strong
     surge of marine air into the Willamette Valley last night.
     The thermal trough, which was over central Oregon yesterday,
     had shifted into Idaho.

     With cooler air aloft, mixing heights should climb to near
     3000 feet by midday, which will provide adequate ventilation
     for propane flaming and limited prep burning.  However, a
     later break-out from the marine low clouds today will not
     give the sun as much chance to warm the valley and reverse
     the gradient-stacking pattern this afternoon. In addition,
     transport winds are forecast to be more northerly than
     yesterday afternoon.  We will, of course, monitor both the
     transport winds and pressure gradients this afternoon, on
     the outside chance they turn more favorable for open burning.

Surface Winds:
     NNW 5-12 this morning, NW 8-15 G20 south this afternoon.
Transport Winds:
     NNW 8 this morning, N 12 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4100 feet.  Ventilation index 49.
High Temperature:
     Salem\'s high temperature today will be near 80.
Humidities:
     Relative humidity drops to 50% by 1pm.
     Minimum relative humidity will be near 39%.
Sunrise/Sunset:
     Salem sunset tonight: 8:48pm; sunrise tomorrow: 5:49am.

Extended Outlook:
     The upper-level disturbance, over Washington, is forecast to
     weaken and drift slowly eastward, to over northern Idaho,
     Friday and Saturday.  That should weaken the onshore flow
     across western Oregon, allowing any morning clouds to more
     quickly give way to sunshine with warming temperatures.
     Transport winds will likely be too northerly to allow for
     open burning.  The upper-level ridge is forecast to amplify
     over Washington and Oregon Sunday, as a weak upper-level
     disturbance drops southeastward across Idaho.  That may
     force the thermal trough back west of the Cascades...shutting
     off the onshore flow for continued warming temperatures.

     It now appears likely that the upper-level ridge will
     further strengthen along the west coast of North America
     early next week, with the surface thermal trough building
     northward over western Oregon.  That would help Willamette
     Valley temperatures climb to near, or above, the century
     mark...perhaps for several days.  The latest comuter guidance
     is even suggesting that the thermal trough may eventually
     move offshore and allow very warm temperatures to extend
     westward to the coastline.  Those details will become more
     clear by Monday.

Tomorrow (24 Jul):  Brief AM Clouds...Sunny and Warmer.  52/86

Sat (25 Jul):  Brief Patchy AM Clouds...Sunny and Even Warmer.  56/92

Sun (26 Jul):  Sunny and Hot.  58/96

Mon (27 Jul):  Sunny and Hot.  60/100

Tue (28 Jul):  Sunny and Hot.  62/102

Wed (29 Jul):  Sunny and Hot.  60/101

Thu (30 Jul):  Sunny and Hot.  59/98

ODA Meteorologist
weather at oda.state.or.us