[willamette-fcst] Willamette Valley - Silverton Hills Field Burning Forecast July 8, 2010

[Willamette Valley Ag/Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
9:00 AM PDT THU JUL 08 2010

BURN ADVISORY:

Agricultural burning is not recommended.
Prep burning is not allowed.
Propane flaming burning is not allowed.

WEATHER DISCUSSION:

A strong ridge of high pressure remains over the Pacific Northwest this morning.  A strong surface thermal trough shifted just inland overnight and induced an onshore flow onto the immediate coastline.  Visible satellite imagery this morning showed low clouds banked up along the entire length of the Oregon coast and most of the Washington coast.  Some low cloudiness was trying to penetrate into the coastal range gaps but was not making it past the coast range crest.  Skies were sunny over the remainder of Oregon, except for some debris clouds left over from some last night's thunderstorm activity near the California border.

Another near record warm day is in store, for the Willamette Valley.  The surface thermal trough forecast to remain over the interior of western Oregon through mid-afternoon, then possibly shift eastward to over the Cascades this evening.  A weak upper-level trough just off the northern California coastline will continue to circulate enough moisture northward for a chance of afternoon thunderstorms over mainly southern Oregon.  A few storms could develop as far north as the central Cascades.  Winds in the valley will be mostly northerly today but could turn northwesterly late this afternoon and evening, with some marine air beginning to filter into the valley.

TODAY:

Sunny and hot.  Light north winds this afternoon.  High near 99 degrees.
Minimum relative humidity will be near 19%.

Salem Sunset: 8:55 pm


THREE-HOURLY DATA:

                                 11am     2pm     5pm     8pm
     Temperature:                 81       94      98      88
     Relative Humidity:           38%      25%     22%     30%
     Surface Wind Direction:     120      350     340     330
     Surface Wind Speed:           5        7       7       7
     Transport Wind Direction:   120      360     350     340
     Transport Wind Speed:         5        5      10       7
     Estimated Mixing Height:   1800     3000    3800    1500
     Ventilation Index:            9       15      38      10

EXTENDED DISCUSSION:

A weak upper-level trough is forecast to push across Oregon Friday with a return of onshore flow cooling temperatures several degrees.  There is also an increased chance for thunderstorms over the Cascades.  A dry northwesterly flow aloft will prevail for the remainder of the extended forecast period with varying degrees of onshore flow holding temperatures closer to seasonal normals.

EXTENDED FORECAST:

Friday:    Mostly Sunny and continued hot.  Slight chance of pm t-storms,
           mainly near the Cascades.  Wind: NW 5-10 mph.  63/94
Saturday:  Mostly Sunny and a little cooler.  Wind: NW 5-15 mph.  59/87
Sunday:    Morning clouds.  Sunny in the afternoon.  56/85
Monday:    Patchy morning clouds.  Sunny in the afternoon.  55/85
Tuesday:   Patchy morning clouds.  Sunny in the afternoon.  53/82
Wednesday: Morning clouds with afternoon clearing.  Cooler.  52/77
Thursday:  Brief morning clouds...becoming mostly sunny and warmer.  51/85


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.
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