[willamette-fcst] Forecast - Tuesday, July 21st, 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: 
     Tuesday, July 21st, 2009 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:
     An upper-level ridge of high pressure rebuilt over Oregon
     Monday with the development of a surface thermal trough
     helping high temperatures climb into the low 90s in the
     Willamette Valley.  The upper-level ridge shifted slightly
     eastward overnight, to over eastern Oregon, with the surface
     thermal trough following it into central Oregon.  Onshore
     flow has increased along the coast with visible satellite
     imagery showing marine low clouds penetrating into the
     coastal mountain gaps this morning. Skies remained clear,
     east of the coast range, this morning, with just a slight
     influx of onshore flow into the Willamette Valley overnight.

     Skies will be sunny again today, east of the coast range. 
     With the thermal trough staying east of the Cascades today,
     an afternoon seabreeze will likely cap high temperatures in
     the upper 80s across the Willamette Valley.  Light
     southwesterly transport this morning should increase and
     turn west-northwesterly, in respnose to the incoming
     seabreeze this afternoon.  Pressure gradients should become
     favorable this afternoon for smoke evacuation, from the
     valley, eastward over the Cascade passes.

Surface Winds:
     SW 5 this morning, NW 5-12 this afternoon.
Transport Winds:
     SW 5 this morning, WNW 8 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4500 feet.  Ventilation index 36.
High Temperature:
     Salem\'s high temperature today will be near 88.
Humidities:
     Relative humidity drops to 50% by 12pm.
     Minimum relative humidity will be near 33%.
Sunrise/Sunset:
     Salem sunset tonight: 8:50pm; sunrise tomorrow: 5:47am.

Extended Outlook:
     The upper-level ridge axis is forecast to continue to shift
     eastward Wednesday, to over Idaho and western Montana, with
     the surface thermal trough shifting to eastern Oregon. 
     Patchy morning clud may penetrate into the Willamette
     Valley.  Once again, an afternoon seabreeze will likely
     create favorable ventilation conditions for burning in the
     Willamette Valley.  Temperatures will likely be a couple of
     degrees cooler, with valley highs in the mid to upper 80s.

     The upper-level ridge axis is forecast to amplify over Idaho
     Thursday, with the flow aloft turning more southerly over
     Oregon.  That will open the door for more subtropical
     moisture to push northward into central and Eastern Oregon,
     which will enhance the threat of afternoon and evening
     thunderstorms there.  Onshore flow will decrease west of the
     Cascades Thursday, with temperatures starting to warm back
     up.  There may still be enough of an afternoon seabreeze to
     provide adequate ventilation for burning.

     A weak weather system is now forecast to ride over the ridge
     and into southern British Columbia Friday.  That may promote
     the continuation of the afternoon seabreeze pattern, but
     that is getting too far out to call that closely.  In any
     case, no major change to the weather pattern is forecast
     through this week, with possible burning opportunities each
     afternoon.

     The are still significant differences in the long-range
     models by this weekend, with the latest guidance suggesting
     that the weak system cutting across southern British
     Columbia will keep the thermal trough east of the Cascades
     and weak onshore flow across western Oregon.  That would
     maintain the sunny and dry pattern but keep temperatures
     from climing much higher than the low to mid 90s across the
     Willamette Valley.  The ridge is forecast to amplify over
     the region early next week, with the thermal trough coming
     back west of the Cascades and warming temperatures possibly
     to near the century mark in the Willamette Valley.

Tomorrow (22 Jul):  Patchy AM Clouds.  Sunny.  55/86

Thu (23 Jul):  Sunny.  55/88

Fri (24 Jul):  Sunny.  55/88

Sat (25 Jul):  Sunny and Warmer.  57/92

Sun (26 Jul):  Sunny and Very Warm.  58/93

Mon (27 Jul):  Sunny and Very Warm.  58/94

Tue (28 Jul):  Sunny and Hot.  59/97

ODA Meteorologist
weather at oda.state.or.us