[willamette-fcst] Silverton Hills AM Forecast_Tom (CORRECTION)

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:45 AM PDT THU SEP 10, 2015


BURN ADVISORY:



Agricultural burning is not recommended.



Prep burning is not allowed.



WEATHER DISCUSSION:



An upper-level ridge is currently off the coast of Oregon, suppressing mixing as it warms the air aloft. At the surface, higher pressure over central Oregon is producing light offshore flow, keeping skies clear this morning. Heating will rapidly occur throughout western Oregon, with winds becoming breezy as the morning inversion quickly dissipates. A thermal trough will form over the Silverton Hills, but the very warm air aloft will cap mixing heights and produce hazy conditions this afternoon as temperatures rise well above seasonal averages. Conditions are likely to remain unfavorable for open burning as a result.



TODAY'S FORECAST:



Sunny becoming hazy and very warm this afternoon.



Salem's high temperature today will be near 89°F (average is 79°F).

Relative humidity:  Dropping near 25% by 5 p.m.

Surface winds: N-NE 5-15 mph this morning; N-NE 5-15 mph this afternoon.

Transport winds: N-NE 5-15 mph this morning; N-NE 5-15 mph this afternoon.

Mixing height: Below 3000 feet all day.

Salem's sunset tonight: 7:32 p.m.



(Salem Airport data for Wednesday, September 9th: High 86°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 60)



EXTENDED DISCUSSION:



The upper-level ridge will continue to strengthen as the week progresses, remaining stationary off the coast of Oregon through Friday afternoon. Higher pressure will maintain northerly winds over the Silverton Hills, warming air further above seasonal averages and producing summer-like conditions. Skies will remain mostly clear during the day, with no rainfall expected at this time. Onshore gradients will be weak, and are likely to be the key factor to determine whether favorable open burning conditions develop later this week.



Early Saturday morning, an upper-level trough will approach the southern coast of Oregon and switch the flow aloft to southwesterly. This will begin to cool the air aloft and weaken the upper-level ridge over our region, pushing it further east into Idaho by Sunday.



Monday will see onshore flow with increasing clouds throughout the day, as a second upper-level trough approaches the Pacific Northwest from the Gulf of Alaska. An area of lower pressure will form off the coast of Washington, with a cold front sweeping across the Silverton Hills Monday evening with isolated showers. Onshore flow persists for the remainder of the week, leaving the door open for additional field burning operations.



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



Tom Jenkins, AEM

ODF Meteorologist
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