[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 MON JUL 25, 2016



BURN ADVISORY:



Agricultural burning is not recommended.



Prep burning is allowed from 11 a.m. until 1 p.m. with a 50 acre limit.



WEATHER DISCUSSION:



A dry upper-level trough has initiated a weak marine push into western Oregon this morning.  Low clouds and spotty drizzle blanket the coastline.  Patchy low clouds will penetrate into the Willamette Valley this morning but should evaporate by midday.



The prospects for open burning today are marginal.  Onshore flow has creating minor negative gradient stacking, which should further increase this morning, before slowly balancing this afternoon.  Wind speeds may also get too strong for burning this afternoon, even if the gradients become positively stacked.  That said, today may be the best opportunity for open burning this week.



TODAY'S FORECAST:



Brief patchy morning clouds, then sunny and slightly cooler.



Salem's high temperature today will be near 86°F (average is 84°F).

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

Surface winds: NW 5-10 mph this morning; NW 7-12 mph this afternoon.

Transport winds: NW 5-12 mph this morning; NW 12-18 mph this afternoon.

Mixing height: Rising to 3000 feet at 11 a.m. to 4500 feet by 5 p.m.

Salem's sunset tonight: 8:46 p.m.



(Salem Airport data for Sunday, July 24th: High 89°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 80)



EXTENDED DISCUSSION:



A building upper-level ridge will bring a warming trend through the week with temperatures climbing into the low-to-mid 90s by Friday.  Transport winds will turn mostly northerly.  A cool-down is expected this weekend with a series of upper-level troughs providing better burning potential next week.



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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