[willamette-fcst] Forecast - Tuesday, July 28th, 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.

NOON UPDATE

Issued: 
     Tuesday, July 28th, 2009 at 12:00pm.

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

Weather Discussion:
     Two all-time records were tied this morning.  Portland
     recorded a minimum of 74 degrees and Salem only dipped down
     to 70, for the second straight morning.  Both cities tied
     their all-time record warm minimum temperature.  It is
     possible that one or both records could be broken tomorrow,
     as the air mass continues to heat up. Of course, the growth
     of those cities, over the past century, makes that
     particular record less meaningful, because of the urban
     heat-island effect.  However, those very warm overnight
     temperatures highlight the significance of this summer
     heat-have across western Oregon.  Temperatures were able to
     drop into the 60s across much of the Willamette Valley this
     morning.  Eugene dropped to 62 degrees, Corvallis fell to
     63, and McMinnville dipped to 65 degrees.

     A strong upper-level ridge of high pressure remains parked
     along the west coast of North America today.  On the
     surface, a well-developed thermal heat-low extends northward
     across the Willamette Valley and into southwestern
     Washington.  It is expanding eastward, into the Columbia
     Gorge, and westward, to the Oregon Coast.  Dry northerly or
     northeasterly flow and clear skies prevailed across all of
     western Oregon late this morning.  Morning low clouds and
     fog had even cleard from the southern coast.

     Midday temperatures ranged from the low 60s on the south
     coast to the upper 70s on the north coast.  Coastal
     temperatures should climb into the 70s south and 80s north
     today.  Inland valley locations were running 3-6 degrees
     warmer than 24 hours ago with much of the Willamette Valley
     already in the low 90s.  Willamette Valley highs should
     climb to around 105 degrees today...easily breaking daily
     records and approaching the all-time records for Portland
     (107 degrees), Salem (108 degrees) and Eugene (108 degrees),
     which were set in August, 1981.  Hot temperatures and low
     humidities will push the Willamette Valley into State Fire
     Marshal Conditions early this afternoon.

Surface Winds:
     N 5-15 this afternoon.
Transport Winds:
     N 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5000 feet.  Ventilation index 50.
High Temperature:
     Salem\'s high temperature today will be near 105.
Humidities:
     Minimum relative humidity will be near 21%.
Sunrise/Sunset:
     Salem sunset tonight: 8:43pm; sunrise tomorrow: 5:55am.

Extended Outlook:
     Computer models show little change in the weather pattern
     Wednesday, with more record high temperatures likely across
     western Oregon.  Some minor cooling is forecast for late
     Thursday, as the thermal trough begins shifting eastward. 
     Overnight minimums will continue to stay near or above 70
     degrees in places like Portland and Salem, with mid 60s
     common across the valley.  

     The upper-level ridge is forecast weaken a little on Friday
     with increasing westerly flow aloft.  That should shift the
     surface thermal trough east of the Cascades and bring enough
     onshore flow into western Oregon to cool Willamette Valley
     highs back into the 90s.  By the weekend, an approaching
     upper-level trough may increase the southerly flow aloft
     enough to introduce a chance of thunderstorms to most of the
     state.  That would be a typical scenario following an
     intense heat-wave.  The speed of the ultimate cool-down
     appears as if it will be gradual, but that is still in
     question.  Also in question is whether or not the cool-down
     will present a burning opportunity.

Tomorrow (29 Jul):  Sunny and Hot.  70/105

Thu (30 Jul):  Sunny and Hot.  67/100

Fri (31 Jul):  Sunny.  A Little Cooler with Weak Onshore Flow.  62/95

Sat (01 Aug):  Partly Cloudy.  Muggy.  Chance of T-Storms.  62/93

Sun (02 Aug):  Mostly Cloudy.  Muggy.  Chance of T-Storms.  60/90

Mon (03 Aug):  Mostly Cloudy.  Chance of Showers or T-Storms.  Cooler.  58/86

Tue (04 Aug):  Mostly Cloudy.  Chance of Showers and T-Storms.  57/83

ODA Meteorologist
weather at oda.state.or.us