[willamette-fcst] Forecast - Monday, July 27th, 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.

...State Fire Marshal Conditions will likely be met this afternoon...

Issued: 
     Monday, July 27th, 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:
     A heat-wave pattern is developing for most of Oregon, with a
     strong upper-level ridge of high pressure rapidly building
     along the west coast of North America.  The morning ODA
     surface analysis showed a thermal trough extending from
     southwestern Oregon northward through the Willamette Valley.
     Minimum temperatures in the Willamette Valley this morning
     were quite warm...especially in urban regions.  The Salem
     Airport recorded a preliminary low temperature this morning of
     a balmy 70 degrees, and Portland only dropped to 68.  Eugene
     did manage to fall down to 62 degrees and Corvallis dipped to
     63.  Mid-morning temperatures had already warmed into the mid
     70s in some sections of the valley.

     The Salem sounding this morning showed several degrees of
     warming aloft, compared with Sunday afternoon, with offshore
     flow.  Since high temperatures Sunday warmed into the low to
     mid 90s across the Willamette Valley, it is reasonable to
     expect high temperatures today to hit the century mark in
     many valley locations.  Maximums will soar well over 100
     degrees in southwestern Oregon, with 90s and low 100 common
     across central and eastern Oregon.

     The immediate coastline will get some relief from the heat
     today.  Weak onshore flow was pushing a shallow layer of low
     clouds and fog onto the beaches, with mid-morning
     temperatures in the low to mid 50s.  The low clouds should
     back away from the beaches this afternoon, with high
     temperatures ranging from the mid 60s along the south coast
     to near 80 on the extreme north coast.

Surface Winds:
     N 3-8 this morning, N 5-15 this afternoon.
Transport Winds:
     NNE 10 this morning, N 12 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3200 feet.  Ventilation index 38.
High Temperature:
     Salem\'s high temperature today will be near 100.
Humidities:
     Minimum relative humidity will be near 26%.
Sunrise/Sunset:
     Salem sunset tonight: 8:44pm; sunrise tomorrow: 5:54am.

Extended Outlook:
     The long-range computer models are consistent in forecasting
     a prolonged period of hot weather...lasting at least through
     most of this week.  Willamette Valley high temperatures will
     likely top 100 degrees for several straight days, and overnight
     minimums will struggle to get much below 70 degrees in urban
     areas.  It also appears that the thermal trough may move far
     enough west to allow the hot offshore surface winds to
     extend to sections of the coast, especially north, Tuesday
     and Wednesday.

     The impressively strong upper-level ridge may shift eastward
     enough by Thursday to return onshore flow, and much cooler
     temperatures, to the immediate coastline.  Some weak onshore
     flow may begin seeping into the Willamette Valley Thursday
     afternoon, but not likely in time to keep much of the valley
     from seeing a fourth straight 100-degree afternoon.  The long-range
     computer models are indicating that the upper-level ridge will
     shift far enough east to send the thermal surface trough east
     of the Cascades by Friday afternoon...beginning a cool-down
     across the interior of western Oregon.

     By the weekend, increasing southerly flow aloft may introduce
     a chance of thunderstorms to most of the state, especially south,
     along with cooling temperatures.  That would be a typical scenario
     following an intense heat-wave, but the computer models are still
     not clear on the details of how this hot pattern will break down.

Tomorrow (28 Jul):  Sunny and Hot.  69/103

Wed (29 Jul):  Sunny and Hot.  69/104

Thu (30 Jul):  Sunny and Hot.  67/101

Fri (31 Jul):  Sunny and Not as Hot.  Increasing onshore flow.  62/93

Sat (01 Aug):  Partly Cloudy.  Muggy.  Chance of T-Storms.  Cooler.  60/88

Sun (02 Aug):  Mostly Cloudy.  Muggy.  Chance of T-Storms.  59/87

Mon (03 Aug):  Mostly Cloudy.  Chance of Showers or T-Storms.  59/82

ODA Meteorologist
weather at oda.state.or.us