[willamette-fcst] Silverton Hills Forecast - Wed, Jul 07 2010

[Willamette Valley Ag/Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
12:00 PM PDT WED JUL 07 2010

BURN ADVISORY:

...Fire Marshal Conditions are likely this afternoon...

Agricultural burning is allowed.  Suggested burn times are from now to 7:00pm.
Prep burning is not allowed.
Propane flaming burning is not allowed.


WEATHER DISCUSSION:

A strong ridge of high pressure will bring near record warm temperatures to the Willamette Valley today.  Skies were sunny across Oregon at midday, with the exception of low clouds advancing northward along the southern and central coast.  Most western valley locations had already warmed well into the 80s by late this morning and were 10-15 degrees warmer than 24 hours ago.  Salem's record high, of 100 degrees, is within reach this afternoon.

The late-morning surface analysis showed a thermal trough extending from southwestern Oregon to the northern Oregon coast.  The interior of western Oregon was getting offshore winds, while winds on the central and southern coast had turned onshore.  Winds were still offshore along the northern coast, where Astoria was in the mid 80s.  In contrast, temperatures were in the mid 50s on the south coast and only in the low 60s along the central coast.  The coastal onshore flow will continue to creep northward this afternoon.  Winds will stay offshore in the Willamette Valley, helping temperatures approach record highs.  Fields are not ready for burning.

Salem's high temperature today will be near 98 degrees.
Minimum relative humidity this afternoon will be near 17%.

Sunset: 8:55 pm


THREE-HOURLY DATA:

                                  2pm     5pm     8pm
     Temperature:                  93      98      92
     Relative Humidity:            22%     17%     21%
     Surface Wind Direction:       360     360     340
     Surface Wind Speed:            9      10       9
     Transport Wind Direction:     30      20      30
     Transport Wind Speed:         13      17      17
     Estimated Mixing Height:    3500    5000    3000
     Ventilation Index:            46      85      51

EXTENDED DISCUSSION:

The strong ridge of high pressure will continue to bring near record heat to the valley Thursday and Friday with weak onshore flow bring some minor cooling over the weekend.

EXTENDED FORECAST:

Thursday:  Sunny with near record warmth.  Light north winds.  62/100
Friday:    Sunny and continued hot.  Wind: NW 5-10 mph.  63/96
Saturday:  Sunny and slightly cooler.  Wind: NW 5-15 mph.  57/87
Sunday:    Patchy morning clouds.  Sunny and warm.  56/86
Monday:    Patchy morning clouds.  Sunny and warm.  56/88
Tuesday:   Morning clouds.  Sunny in the afternoon.  54/84
Wednesday: Morning clouds.  Sunny in the afternoon.  52/82

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.

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.

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