[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:45 AM PDT WED JUL 19, 2017



BURN ADVISORY:



Agricultural burning is not recommended.



Prep burning is not allowed.



WEATHER DISCUSSION:



This morning's sounding over Salem showing a few degrees of cooling below 7000 feet, compared to Tuesday, and continued SW flow aloft.  Onshore pressure gradients are slightly negatively stacked this morning but should become favorable this afternoon, as an approaching upper-level trough increases the onshore flow.  Westerly transport winds and high afternoon mixing heights should be quite favorable for field-burning, once gradients become positively stacked.  A significant marine push is expected tonight.



TODAY'S FORECAST:



Sunny and slightly cooler.



Salem's high temperature today will be near 82°F (average is 83°F).

Relative humidity:  Dropping to 50% by 11 a.m. and to near 30% by 5 p.m.

Surface winds: SW 5 mph this morning; becoming W 5-10 mph this afternoon.

Transport winds: SW 5 mph this morning; becoming W 5-15 mph this afternoon.

Mixing height: Rising to 3000 feet around 11 a.m. and to 6000 feet by 5 p.m.

Salem's sunset tonight: 8:52 p.m.



(Salem Airport data for Tuesday, July 18th: High 86°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 90)



EXTENDED DISCUSSION:



Thursday will be cooler with widespread morning clouds and a chance for local drizzle.  Afternoon clearing will help temperatures reach the upper 70s, but strongly negative gradient-stacking will inhibit burning opportunities.



Dry westerly flow aloft will maintain onshore flow at the surface on Friday with some morning clouds and afternoon sunshine.  Westerly transport winds could create a burning opportunity, if onshore gradients can become balanced.



Dry and warmer weather is expected over the weekend, with temperatures possibly climbing to near 90°F. Dry conditions should prevail through next week with renewed onshore flow keeping temperatures moderate and likely creating more burning opportunities.



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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