[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:35 AM PDT TUE SEP 9, 2014



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 significant surge of marine air poured into western Oregon overnight.  Low clouds cover most of the Willamette Valley this morning.  Spotty light drizzle is possible.  As is typically the case after a "marine push," onshore pressure gradients are negatively-stacked this morning and may not balance out this afternoon.



A dry northwesterly flow aloft should slowly clear skies today.  Cool air aloft will make for good afternoon mixing, but poor gradient-stacking and afternoon winds veering to more northerly will limit burning opportunities.



TODAY'S FORECAST:



Cloudy this morning with possible light drizzle.  Afternoon clearing.



Salem's high temperature today will be near 76°F (average is 79°F).

Relative humidity:  Dropping to 60% around 11 a.m. and to near 40% by 5 p.m.

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

Transport winds: NW 5-10 mph this morning; NNW 10-15 mph this afternoon.

Mixing height: Rising to 3000 feet at 11 a.m. and to 5000 feet by 5 p.m.

Salem's sunset tonight: 7:34 p.m.



(Salem Airport data for Monday, September 8th: High 81°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 75)



EXTENDED DISCUSSION:



An upper-level ridge is forecast to strengthen along the west coast Wednesday through Friday, with a continued dry northwesterly flow aloft over Oregon.  A building thermal trough along the coast will turn low-level winds northerly on Wednesday and offshore Thursday and Friday.  Valley temperatures will warm to near average on Wednesday, with highs reaching the upper-80s by Friday.  Burning opportunities are unlikely.



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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