[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:55 AM PDT MON AUG 1, 2016



BURN ADVISORY:



Agricultural burning is not recommended.



Prep burning is not allowed.



WEATHER DISCUSSION:



Westerly flow aloft has produced enough onshore flow at low levels to push a layer of marine low clouds into the northern Willamette Valley this morning.  Skies should clear by midday with sunshine and moderate temperatures this afternoon.



An upper-level trough, advancing southward along the British Columbia coastline, will bring increasing westerly flow aloft to Oregon today.  If it approaches quickly enough, it may turn transport winds enough northwesterly for a burning opportunity this afternoon.



TODAY'S FORECAST:



Brief morning clouds, then sunny and warm.



Salem's high temperature today will be near 81°F (average is 84°F).

Relative humidity:  Dropping to 60% by 11 a.m. and to near 35% by 5 p.m.

Surface winds: N 5-10 mph this morning; NW 5-10 mph this afternoon.

Transport winds: NNE 10-15 mph this morning; NW 10-15 mph this afternoon.

Mixing height: Rising to 3000 feet around 2 p.m. to 4500 feet by 5 p.m.

Salem's sunset tonight: 8:38 p.m.



(Salem Airport data for Sunday, July 31st: High 80°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 80)



EXTENDED DISCUSSION:



Precipitation from the incoming weather system will be limited and mainly impact Washington, but a few showers are possible across extreme NW Oregon, late tonight Tuesday.  Temperatures will cool into the mid-70s with more extensive clouds across the Willamette Valley.  Good mixing and westerly transport winds will likely be countered by unfavorable gradient stacking.



A transitory ridge will bring dry and warmer conditions on Wednesday with transport winds reverting to northerly.  However, another upper-level trough may turn transport winds enough northwesterly for a burning opportunity Thursday and/or Friday.



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 15 mph.



     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 (ODA) and the Oregon Department of Forestry (ODF).  For

information contact ODA at 503-986-4701.



To add/remove your email address from this list, please go to:



http://listsmart.osl.state.or.us/mailman/listinfo/willamette-fcst



Pete Parsons

ODF Meteorologist

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