[willamette-fcst] Forecast - Wednesday, July 29th, 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: 
     Wednesday, July 29th, 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:
     Slightly drier air allowed temperatures to dip a couple of
     degrees lower than Tuesday morning across the northern
     Willamette Valley.  Portland dipped to 71 this morning,
     after tying the all-time record warm minimum Tuesday morning
     with 74.  Salem was also a touch cooler this morning with a
     low of 68, after tying the all-time record warm minimum of
     70 the past two mornings.  Minimums were mostly in the mid
     60s across the rest of the Willamette Valley.

     No major changes are forecast to the general weather pattern
     today, so one more ridiculously hot day is in store, before
     a slow cooling trend begins. The late-morning ODA surface
     analysis showed a well-developed surface thermal trough
     extending northward from southwestern Oregon through western
     Washington.  The trough had moved just inland over western
     Oregon but continued to extend to the coastline in western
     Washington and extreme northern Oregon.  Midday visible
     satellite imagery showed a shallow layer of low clouds and
     fog extending northward, along the Oregon Coast, to just south
     of the mouth of the Columbia River.  Skies were sunny over the
     remainder of the state with only a few cumulus clouds beginning
     to develop...mainly over the mountains of eastern Oregon.

     Midday coastal conditions ranged from the cloudy and cool
     upper 50s in Brookings (extreme south coast)to sunny skies and
     near 70 degrees at Astoria (extreme north coast).  Due to the
     increase in onshore flow, the central and southern beaches
     will be cooler today, with highs staying in the 60s.  The
     north coast will climb into the 70s and locally the 80s. 
     Temperatures were much warmer just inland, with most of the
     Willamette Valley already in the low 90s.  Many Willamette 
     Valley locations are running a degree or two warmer than 24
     hours ago, so all-time high temperature records of 107 degrees
     in Portland and 108 degrees in Salem and Eugene could be
     reached late this afternoon.

     Like yesterday, State Fire Marshal conditions will likely be
     met across the Willamette Valley early this afternoon, due
     to high temperatures and low relative humidity.  With the
     thermal trough directly over the Willamette Valley, the hot
     and dry northerly winds will be lighter this afternoon.

Surface Winds:
     N 5-10 this afternoon.
Transport Winds:
     NNW 8 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5500 feet.  Ventilation index 44.
High Temperature:
     Salem\'s high temperature today will be near 107.
Humidities:
     Minimum relative humidity will be near 20%.
Sunrise/Sunset:
     Salem sunset tonight: 8:42pm; sunrise tomorrow: 5:56am.

Extended Outlook:
     Some minor cooling is forecast for late Thursday, as the
     thermal trough begins shifting eastward.  Willamette Valley
     highs should only back off to the 95-100 degree range. 
     Overnight minimums will also cool back into the upper 50s and
     60s...making it feel a little more confortable.  The upper-level 
     ridge is forecast to shift over eastern Oregon Friady, with the
     broad surface thermal trough finally sliding east of the Cascades.
     Weak onshore flow will cool western Oregon temperatures a bit more.

     By the weekend, an approaching upper-level trough is forecast to
     turn the flow aloft south-southesterly...introducing at least a
     chance of thunderstorms to the state by Saturday evening...especially
     south and over the Cascades.  Southeasetery flow aloft is expected to
     continue strengthening Sunday, which would expand the thunderstorm
     threat across the state.  That would be a typical scenario following
     an intense heat-wave and will be closely monitored for wildfire potential.
     
     The speed of the upcoming cool-down appears as if it will be gradual,
     with a little more marine air seeping into the western valleys each day.
     It is unlikely that any burning opportunities will be created later this
     week, but we will keep a close eye on things.

Tomorrow (30 Jul):  Sunny and Hot.  66/100

Fri (31 Jul):  Sunny.  A Little Cooler with Weak Onshore Flow Developing.  64/95

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

Sun (02 Aug):  Mostly Cloudy.  Muggy.  Good Chance of T-Storms.  60/89

Mon (03 Aug):  Mostly Cloudy.  Chance of Showers or T-Storms.  Cooler.  57/86

Tue (04 Aug):  Mostly Cloudy.  Chance of Showers and T-Storms.  56/83

Wed (05 Aug):  Mostly Cloudy.  Chance of Showers and T-Storms.  55/83

ODA Meteorologist
weather at oda.state.or.us