[willamette-fcst] Forecast - Monday, July 20th, 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 may be met this afternoon due to low humidities and wind...

Issued: 
     Monday, July 20th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 2:00pm until 8:00pm.
     Preparatory burning is not allowed.
     Propane flaming is not allowed.
     Stack burning is not allowed.

Weather Discussion:
     The broad upper-level ridge of high pressure that was over the
     region last week pushed east and allowed a weak influx of marine
     air into the Willamette Valley over the weekend.  That cooled
     temperatures from the low 90s Thursday and Friday back into
     the upper 80s Saturday and low to mid 80s (near-normal) Sunday.

     The upper-level ridge is rebuilding over the region today.
     Satellite imagery showed considerable low clouds and fog
     banked up against most ot the Washington and Oregon
     coastlines this morning, with some high clouds sweeping
     northward over western Oregon and southwestern Washington. 
     Otherwise, skies were sunny over the region.  The onshore
     flow along the coastal strip will turn northerly this
     afternoon with skies clearing there.  Mostly sunny skies are
     forecast over the remainder of Oregon today.  After starting
     off mostly in the 50s this morning, Willamette Vally high
     temperatures will likely hit the low 90s this afternoon.

     The mid-morning ODA surface analysis showed a thermal trough
     building northward, from northern California, into western
     Oregon.  Northeasterly transport winds this morning are
     forecast to increase and turn northerly this afternoon. The
     combination of low humidities and increasing northerly winds
     may locally push sections of the Willamette Valley into
     State Fire Marshal conditions this afternoon...especially south.

Surface Winds:
     N 5-12 this morning, N 7-15 this afternoon.
Transport Winds:
     NNE 12 this morning, N 12 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3700 feet.  Ventilation index 44.
High Temperature:
     Salem\'s high temperature today will be near 91.
Humidities:
     Relative humidity drops to 50% by 10am.
     Minimum relative humidity will be near 25%.
Sunrise/Sunset:
     Salem sunset tonight: 8:51pm; sunrise tomorrow: 5:46am.

Extended Outlook:
     The upper-level ridge axis is forecast to shift eastward, to
     near the Oregon/Idaho border, by Tuesday afternoon, with
     increasing southwesterly flow aloft over western Oregon. 
     That should keep temperatures from climbing much higher
     across western Oregon and may promote a weak afternoon
     seabreeze into the Willamette Valley.  The upper-level ridge
     axis is forecast to continue to shift eastward Wednesday, to
     over Idaho and western Montana, but the ridge is also
     forecast to become more broad, so only a slight increase in
     southwesterly flow aloft is forecast over western Oregon. 
     That may cool Willamette Valley temperatures a couple of
     degrees with a possible afternoon seabreeze again.

     The upper-level ridge axis is forecast to amplify over Idaho
     Thursday and Friday, with the flow aloft turning more
     southerly, and warming, 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.  However, there
     should be enough southwesterly flow aloft over western Oregon
     to keep thunderstorms mainly from the Cascades eastward.  The
     afternoon seabreezes will turn more northerly with Willamette
     Valley temperatures warming again by Friday.

     The are significant differences in the long-range models by
     this weekend, but they all indicate that a strong upper-level
     ridge of high pressure will develop somewhere near the west
     coast of North America.  Depending on the exact location of
     the ridge, temperatures across western Oregon have the
     potential to reach the century mark.  The flow aloft may also
     turn southerly enough to allow for thunderstorm development,
     west of the Cascades, by early next week.

Tomorrow (21 Jul):  Mostly Sunny.  59/91

Wed (22 Jul):  Mostly Sunny.  56/88

Thu (23 Jul):  Sunny.  55/88

Fri (24 Jul):  Sunny and Warmer.  56/91

Sat (25 Jul):  Sunny and Hot.  58/95

Sun (26 Jul):  Mostly Sunny and Hot.  Slight Chance of Thunderstorms Late.  60/97

Mon (27 Jul):  Mostly Sunny and Hot.  Chance of PM Thunderstorms.  61/92

ODA Meteorologist
weather at oda.state.or.us