[willamette-fcst] Forecast - Friday, September 5th, 2008

Fri Sep 5 07:59:17 PDT 2008

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: 
     Friday, September 5th, 2008 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 12:00pm until 2:00pm.
     Preparatory burning is allowed from 12:00pm until 2:00pm with a 100 acre limit.
     Propane flaming is allowed from 12:00pm until 2:00pm.
     Stack burning is not allowed.

Weather Discussion:
     A strong upper-level ridge offshore will move closer to the
     coastline today and continue the dry northwesterly flow
     aloft over Oregon.  Satellite imagery showed high clouds
     circulating clockwise over the ridge, across Washington...then 
     southeastward over much of Eastern Oregon.

     Onshore flow had brought low clouds onto the Washington
     coast...extending southward to the central Oregon Coast.  A few low
     clouds had managed to form, in the extreme northern Willamette Valley,
     along with patchy areas of fog.  Otherwise, skies were mostly clear
     over the interior of Western Oregon and along the south coast.

     The ODA surface analysis showed a low-pressure trough over
     East-Central Washington with weak onshore flow across Western
     Washington.  The flow turned northerly across Western Oregon, in
     response to a thermal trough of low-pressure building northward
     along the southern Oregon Coast.  Valley winds were light northerly
     and strongest near Eugene.

     The Salem sounding this morning showed more warming aloft
     since Thursday, so mixing heights will be about 500-1000
     feet lower today (maximum of about 3500 feet).  Temperatures
     will continue their upward trend with afternoon highs in the
     low to mid 80s.

     Low relative humidity levels and increasing northerly winds
     pushed the south valley into State Fire Marshal conditions
     again late Thursday afternoon.  The northerly winds should
     be even stronger today, and humidtiy levels may drop enough
     for areas of the valley to meet State Fire Marshal
     conditions by mid-afternoon.

     With the upper-level ridge buildng closer to the coastline
     today, transport winds should take on more of an offshore
     component.  That may allow for the burning of remaining
     fields on the west side of the valley around midday.  Other
     open burning is highly unlikely today.

Surface Winds:
     N 5-15 G20 South this morning, N 12-22 G30 South this afternoon.
Transport Winds:
     NNE 15 this morning, NNE 17 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3500 feet.  Ventilation index 60.
High Temperature:
     Salem\'s high temperature today will be near 83.
Humidities:
     Relative humidity drops to 50% by 12pm.
     Minimum relative humidity will be near 29%.
Sunrise/Sunset:
     Salem sunset tonight: 7:41pm; sunrise tomorrow: 6:41am.

Extended Outlook:
     The dry weather pattern is forecast to continue during the
     extended forecast period and possibly through the first half
     of September.  That is consistent with the ODA long-range
     climate prediction of a drier than normal September.  The
     ODA Seasonal Climate Forecast is updated monthly, on our
     website, at:
     http://oregon.gov/ODA/NRD/weather.shtml#Weather_forecasts.

     A weak weather system is forecast to ride over the top of
     the offshore ridge and drop into Western Montana Saturday. 
     That will hold the ridge in place with little change in
     temperatures across Western Oregon.  The ridge is forecast
     to build over Oregon Sunday with a surface thermal trough
     building northward into SW Oregon.  That will turn transport
     winds even more offshore with warming temperatures under
     sunny skies.

     The ridge is forecast to weaken, and shift more offshore,
     Monday and Tuesday.  That will allow a couple of weather
     systems to slide over the ridge and drop closer the Pacific
     Northwest.   The  thermal trough may shift east of the
     Cascades Monday afternoon with onshore flow developing
     across the Willamette Valley.  That process could be delayed
     until the second weather system moves north of the region
     Tuesday.  Depending on the timing of these changes, there
     could be burning opportunities Monday afternooon and/or
     Tuesday of next week.

     The upper-level ridge is forecast to push back closer to the
     coastline Wednesday, with the flow aloft and transport winds
     becoming northerly.  Temperatures will climb to normal.  The
     ridge is forecast to build over the region Thursday and
     Friday for continued sunny and warm weather.  Transport winds
     are forecast to turn offshore with well above normal temperatures.

Tomorrow (06 Sep):  Sunny.  North winds.  51/83

Sun (07 Sep):  Sunny and Warmer.  NE winds.  53/87

Mon (08 Sep):  Sunny.  Onshore flow possibly increasing late.  53/84

Tue (09 Sep):  Mostly Sunny.  Cooler with onshore flow.  51/77

Wed (10 Sep):  Mostly Sunny.  Winds becoming northerly.  48/79

Thu (11 Sep):  Sunny and Warm.  49/83

Fri (12 Sep):  Sunny and Warm.  50/87

ODA Meteorologist
weather at oda.state.or.us