[willamette-fcst] Mon, 20 Sep 10

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
9:00 AM PDT MON SEP 20 2010

BURN ADVISORY:

     Recommended burn times for agricultural burning are from 11:00am to 5:00pm.
     Prep burning is allowed from 12:00pm to 5:00pm with a 50 acre limit.
     Propane flaming is allowed from 12:00pm to 5:00pm.

WEATHER DISCUSSION:

     Satellite pictures this morning show solid cloud cover over western Oregon, from
     the coast to the Cascade crest. Rainfall amounts in the past 24 hours include
     .16 at the Salem Airport and .13 at the Oregon Gardens in Silverton.

     Upper air charts show a trough covering much of the Pacific Northwest with a
     significant upper level disturbence just off the southern British Columbia coast
     embedded in the through. This will rotate across northern Washington but be
     close enough to keep some showers going as far south as the mid-Willamette
     Valley.

     The morning Salem sounding showed an inversion from 4900 to 5500 feet. This will
     cap mixing heights today, but at a fairly high elevation above ground level.
     Maximum mixing height will be around 5100 feet this afternoon. The sounding also
     showed SSW winds near the surface veering to WSW by about 2000 feet. This is a
     favorable direction for open field burning.

     Computer models suggest smoke trajectories would be to the NE or ENE this
     afternoon.

     Finding dry fields will be the limiting factor on open field burning this
     afternoon.

     Salem's high temperature today will be near 69. Minimum relative humidity will
     be down to 51%.

     Sunset tonight: 7:08 pm

THREE-HOURLY DATA:

                                 11am     2pm     5pm     8pm
     Temperature:                 63       68      68      60
     Relative Humidity:           72%      57%     51%     64%
     Surface Wind Direction:     190      220     230     270
     Surface Wind Speed:          11        7       7       5
     Transport Wind Direction:   190      220     250     280
     Transport Wind Speed:        15       10       8       5
     Estimated Mixing Height:   2200     5000    5100     500
     Ventilation Index:           33       50      41       2

EXTENDED DISCUSSION:

     The upper level trough moves east overnight tonight and weak ridging aloft
     should dry the area tomorrow and Wednesday. Another Pacific front moves across
     the area Thursday then Friday looks dry. By next weekend another major upper
     level trough moves across the Pacific Ocean to just off the Pacific Northwest
     coast to bring renewed rain to the region.

EXTENDED FORECAST:

     Tuesday: Patchy morning fog then partly sunny, 72. SW 4-7 mph.
     Wednesday: Patchy morning fog then mostly sunny. SW 4-7 mph.
     Thursday: Patchy morning fog then mostly cloudy with a chance of rain. 73.
     Friday: Partly sunny, with a high near 74.
     Saturday: A chance of rain. Partly sunny, with a high near 73.
     Sunday: A chance of rain. Mostly cloudy, with a high near 72.

Notes:
     1.  Mixing height, as used here, is the lowest height at which the
         potential temperature exceeds the potential temperature at the surface.
         As a practical matter it is the approximate height to which a
         smoke plume will rise assuming good ignition, dry fuels, and
         winds less than about 15mph.
     2.  Transport winds are a layer average through the mixing height,
         weighted slightly toward the winds at the top of the layer.
     3.  Ventilation Index is the height of the mixing layer times
         the transport wind speed divided by 1000.
     4.  Surface wind direction is the general expected wind direction.
         At a specific point surface winds are highly dependent on
         local terrain conditions.

This forecast is provided under an agreement between the Oregon Department of
Agriculture and the Oregon Department of Forestry.  For information contact ODA
at 503-986-4701.







-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20100920/ed508c6c/attachment.html>