[willamette-fcst] Forecast - Wednesday, July 22nd, 2009

Wed Jul 22 09:00:54 PDT 2009

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, July 22nd, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is not recommended.
     Preparatory burning is allowed from 11:00am until 2:00pm with a 100 acre limit.
     Propane flaming is allowed from 11:00am until 2:00pm.
     Straw stack burning is allowed from 11:00am until 8:00pm.

Weather Discussion:
     The upper-level ridge of high pressure that has been over
     the region shifted far enough to the east to allow an influx
     of cooler ocean air into the Willamette Valley overnight.
     Visible satellite imagery this morning showed that marine
     low clouds were able to penetrate east of the coast range
     and into sections of the Willamette Valley...especially in
     the extreme north valley, near the Columbia River, and in
     the south valley, across most of Lane County.  That helped
     cool Willamette Valley temperatures well down into the 50s
     this morning, after maximums on Tuesday near 90 degrees. 
     The coastline was blanketed with low clouds again this
     morning, and there were some pockets of drizzle and/or light
     rain.  Astoria and Newport both picked up .01 inches this
     morning.  There were no reports of rain east of the coast
     range.  Skies were clear this morning over the interior of
     southwestern Oregon and all areas east of the Cascade crest.

     The Salem sounding this morning showed a few degrees of
     cooling, from the surface up to about 12,000 feet, in
     response to the increase in onshore flow.  The ODA surface
     analysis showed the thermal trough had shifted further
     eastward overnight...extending from east-central Washington
     southward through south-central Oregon.  The weak marnine
     push overnight resulted in a gradient-stacking pattern this
     morning, with onshore gradients stronger across central
     Oregon than over western Oregon.  That pressure pattern does
     not promote good lifting of smoke over the Cascade passes. 
     However, the gradient-stacking is not severe, so it is
     likely that daytime heating overcome it by mid-afternoon.

     The upper-level ridge will weaken and shift slightly further
     east today, with continued onshore flow at the surface. 
     Areas of valley low clouds this morning should give way to
     sunshine this afternoon. With stronger onshore flow,
     temperatures will be cooler today. Valley highs should top
     out in the mid 80s.  Transport winds are light southwesterly
     this morning and are forecast to become northwesterly this
     afternoon...increasing in response to the seabreeze this
     evening. Mixing heights should climb to near 3000 feet
     around midday and above 4000 feet by late this afternoon.

Surface Winds:
     SW 5 this morning, NW 5-15 this afternoon.
Transport Winds:
     W 5 this morning, NW 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4500 feet.  Ventilation index 45.
High Temperature:
     Salem\'s high temperature today will be near 85.
Humidities:
     Relative humidity drops to 50% by 12pm.
     Minimum relative humidity will be near 37%.
Sunrise/Sunset:
     Salem sunset tonight: 8:49pm; sunrise tomorrow: 5:48am.

Extended Outlook:
     The upper-level ridge axis is forecast to remain over
     eastern Idaho and western Montana Thursday, as a weak
     upper-level disturbance slides across Washington.  Onshore
     flow could become strong enough to produce morning drizzle
     along the coast again Thursday morning. Marine low clouds
     will likely penetrate into the Willamette Valley, Thursday
     morning, but no rain is expected east of the coast range. 
     Skies should clear Thursday afternoon over the Willamette
     Valley, but high temperatures will likely be a few degrees
     cooler.  There may be an open burning opportunity again
     Thursday afternoon, if daytime heating can overcome morning
     gradient-stacking.

     The upper-level disturbance is forecast to weaken over
     eastern Washington Friday and Saturday with onshore flow
     weakening across western Oregon.  Any morning clouds should
     quickly give way to sunshine, with temperatures rebouding
     back above normal.  Northwesterly transport winds may become
     too northerly to allow for open burning.

     The ridge is forecast to amplify over Washington and Oregon
     Sunday, as the weak upper-level disturbance drops
     southeastward to over Idaho.  That would force the thermal
     trough back west of the Cascades...shutting off the onshore
     flow.  Temperatures will likely climb well into the 90s with
     sunny skies.  There is some indication that the upper-level
     ridge may become strong enough to send Willamette Valley
     temperatures to the century mark early next week, but that
     is still uncertain at this time.

Tomorrow (23 Jul):  AM Clouds...Becoming Sunny.  A Little Cooler.  52/82

Fri (24 Jul):  Brief AM Clouds...Sunny and Warmer.  52/85

Sat (25 Jul):  Patchy AM Clouds...Sunny and Warmer.  55/91

Sun (26 Jul):  Sunny and Hot.  57/96

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

Tue (28 Jul):  Sunny and Hot.  62/100

Wed (29 Jul):  Sunny and Hot.  62/100

ODA Meteorologist
weather at oda.state.or.us