[willamette-fcst] Silverton Hills AM Forecast_doug.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

9:00 AM PDT THURS. JUL 11, 2013



BURN ADVISORY:



Recommended burn times for agricultural burning from 10:00 a.m. to 7:00 p.m.

Prep burning is allowed 10:00 a.m. until 3:00 p.m..



WEATHER DISCUSSION:



A moderately strong upper trough is centered along the Pacific coastline this morning, with generally dry southwesterly flow aloft over western Oregon. Some energy within the trough is trying to push eastward. Low-level onshore flow continues to be weak and disorganized, however. Some increased coastal low-cloud intrusions are over the lower elevations over the extreme northwestern corner of Oregon and portions of the Valley.



The upper trough remains in place for the next several days, with some waves of energy skirting western Oregon as they periodically progress eastward.



Cooling aloft over western Oregon will limit valley maximum temperatures to around 80 degrees this afternoon.  Transport winds should remain mostly northerly.



TODAY'S FORECAST:



Mostly sunny and cooler.



Salem's high temperature today will be around 80.

Relative humidity:  Will drop below 60% by 11:00 a.m. and to 40-45% by 5 p.m.

Surface winds:  N 5-10 mph this morning through the afternoon; N 7-15 mph this evening.

Transport winds: NNE 10-15 mph

Mixing height: Rising to near 5000 feet this afternoon.

Salem's sunset tonight: 8:58 p.m.



(Salem Airport data for Wednesday, July 10th: High 86°F; Rainfall .00")

(Maximum Ventilation index expected today: 60)



EXTENDED DISCUSSION:



The upper-level trough just to the west should persist through the weekend, with a wave within the trough progressing eastward into Montana and Idaho late on Friday.  Increasing onshore flow should bring more marine clouds into the Willamette Valley particularly early in the day and then again in the evening on Friday. Otherwise, expect partly cloudy conditions and continued cooler temperatures with maximums in the mid- and upper-70s.  Transport winds are forecast to turn northwesterly late in the day Saturday.



Upper-level troughing will persist just west of Oregon Sunday.  No showers are expected, but the threat of morning low clouds over the Willamette Valley persists. Mostly sunny conditions are likely in the afternoon.  Maximum temperatures will likely warm into the 80s.



The National Weather Service's digital forecast is available at:

http://forecast.weather.gov/MapClick.php?lat=44.90549606158295&lon=-122.8106689453125&site=pqr&unit=0&lg=en&FcstType=text



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 (ft) times

         the transport wind speed (mph) 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.



Doug Wesley

ODF Meteorologist

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