[willamette-fcst] Forecast - Wednesday, September 10th, 2008

[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.

Issued: 
     Wednesday, September 10th, 2008 at 9:00am.

Burn Advisory:

  ...State Fire Marshal conditions may be reached, after 2:30pm, due to low humidities
     and increasing northerly winds...

     Agricultural burning is allowed.  Suggested burn times are from 12:30pm until 2:30pm.
     Preparatory burning is allowed from 12:30pm until 2:30pm with a 100 acre limit.
     Propane flaming is allowed from 12:30pm until 2:30pm.
     Stack burning is not allowed.

Weather Discussion:
     A weak upper-level disturbance moved across Northern
     Washington Tuesday evening and was over Northern Idaho this
     morning.  That induced weak onshore flow Tuesday evening
     which brought cooler air into the Willamette Valley. 
     However, the air mass remains very dry this morning with
     virtually no penetration of marine clouds into the interior
     of Western Oregon overnight.  Clear skies allowed for a
     chilly morning with valley minimums dropping into the low 40s.

     The Salem sounding this morning also showed considerable cooling
     aloft since Tuesday, so mixing heights should climb to near 3000 feet
     by early afternoon, when surface temperatures reach the low 70s.

     Northeasterly transport winds may allow for the burning of
     remaining fields, on the west side of the valley, later this
     morning.  Other open burning is highly unlikely today with
     north-northeasterly transport winds forecast for this
     afternoon.  Skies should be sunny today with valley highs
     recovering into the low 80s.

     A building ridge of high pressure is turning the flow aloft
     northerly and keeping the air mass very dry over Western
     Oregon.  The ODA surface analysis showed flat pressure
     gradients over Western Oregon this morning.  However, a
     thermal trough is forecast to begin building into SW oregon
     this afternoon and increase the northerly gradients across
     the Willamette Valley.  Low humidties and increasing
     northerly winds may push the Willamette Valley into State
     Fire Marshal conditions after about 2:30pm...especially south.

Surface Winds:
     N 5-12 this morning, N 10-17 G25 south this afternoon.
Transport Winds:
     NE 12 this morning, NNE 17 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4100 feet.  Ventilation index 70.
High Temperature:
     Salem\'s high temperature today will be near 82.
Humidities:
     Minimum relative humidity will be near 27%.
Sunrise/Sunset:
     Salem sunset tonight: 7:31pm; sunrise tomorrow: 6:47am.

Extended Outlook:
     High pressure will push over Oregon Thursday with the air
     mass warming a few more degrees.  That will lower mixing
     heights slightly with north-northeasterly transport winds
     making open burning unlikely.  Very dry conditions and
     northerly surface winds may put much of the valley into Fire
     Marshal Conditions in the afternoon.

     A weak upper-level disturbance is forecast to flatten the
     ridge and turn the flow weakly onshore Friday.  That will
     bring another cool-down to the region and a potential
     burning opportunity, especially for the north valley.

     A strong upper-level ridge is forecast to build over the
     Pacific Northwest this weekend for sunny and warmer weather.
     Surface and transport winds are forcast to turn offshore
     Sunday and Monday.  A weak westerly flow aloft is forecast
     to undercut the ridge and push into Northern California late
     Monday and Tuesday of next week.  That may advance the
     thermal trough into Eastern Oregon and initiate a slow
     cooling trend across Western Oregon.

     The split-flow pattern in the jet stream that is forecast
     during the second half of next week would maintain dry
     condtions for Western Oregon with above normal temperatures.
     Weak onshore flow at times may create some limited burning
     opportunities, but no significant burning opportunity is
     forecast at this time.

Tomorrow (11 Sep):  Sunny and Warmer.  47/88

Fri (12 Sep):  Mostly Sunny but Cooler with Increasing Onshore Flow.  49/81

Sat (13 Sep):  Sunny and Warmer.  North Winds.  49/84

Sun (14 Sep):  Sunny and Very Warm.  Northeast Winds.  53/90

Mon (15 Sep):  Mostly Sunny and Continued Very Warm.  Northeast Winds.  54/91

Tue (16 Sep):  Mostly Sunny and Slightly Cooler.  52/86

Wed (17 Sep):  Moslty Sunny and a Little Cooler.  50/82

ODA Meteorologist
weather at oda.state.or.us