[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 10, 2015



BURN ADVISORY:



Agricultural burning is not recommended.



Prep burning is not allowed.



WEATHER DISCUSSION:



An upper-level trough, parked off of the Oregon Coast this morning, is producing a strong and unstable SSW flow aloft over the region.  Daytime heating will further destabilize the air mass, which will lead to shower and thundershower development over the Cascades, and possibly the Willamette Valley, this afternoon and evening.  Light S-SW surface and transport winds will veer to the south at the mixing height.



TODAY'S FORECAST:



Partly cloudy.  Chance of afternoon and evening showers or thundershowers.



Salem's high temperature today will be near 86°F (average is 83°F).

Relative humidity:  Dropping to near 50% by 11 a.m. and to near 35% by 5 p.m.

Surface winds: S 3-6 mph this morning; SW 3-8 mph this afternoon.

Transport winds: SSW 5-10 mph this morning; SW 5-10 mph this afternoon.

Mixing height: Rising to 3000 feet about noon and to 5000 feet by 5 p.m.

Salem's sunset tonight: 8:26 p.m.



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

(Maximum Ventilation Index expected today: 75)



EXTENDED DISCUSSION:



The offshore upper-level trough will slowly drift south, to off the northern California coastline, Tuesday and Wednesday.  S-SE winds aloft will maintain a threat of mainly afternoon and evening showers and thundershowers.  Temperatures should warm into the upper-80s on Tuesday with minor cooling on Wednesday.



The upper-level trough is predicted to come onshore and move across the region Thursday and Friday.  That will bring much cooler onshore flow along with scattered showers.  Temperatures should drop back into the mid-to-upper 70s.  Rainfall totals are generally expected to be less than .10".



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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