[willamette-fcst] Silverton Hills Midday Forecast_Gary.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT FRI AUG 26, 2016


BURN ADVISORY:



***STATE FIRE MARSHAL CONDITIONS TO BEGIN BEFORE 1:00 P.M.***



Agricultural burning is not recommended.



Prep burning is not allowed.



WEATHER DISCUSSION:



A thermal trough is centered over Willamette Valley and will remain through today. It will cause State Fire Marshall conditions again with criteria being reached between noon and 1:00 p.m. in the temperature and relative humidity. However, winds will be weaker than they were on Thursday.



Sunny and very hot.



Salem's high temperature today will be near 99°F (average is 81°F).

Relative humidity:  Already below 30% and falling to near 15% by 4:00 p.m.

Surface winds: N 5-10 mph.

Transport winds: NNE 9-14 mph.

Mixing height: Rising to 2000 feet about 1:00 p.m. then 8000 feet by 5:00 p.m.

Salem's sunset tonight: 7:59 p.m.



(Salem Airport data for Thursday, August 25th: High 97°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 96)



EXTENDED DISCUSSION:



An upper level trough will push a developing cold front into NW Oregon on Saturday morning. This will be the beginning of a major pattern change in the weather over the area. A marine push early that evening will reinforce cooler air arriving in the valley, but little cloud cover is expected Saturday.

The extended outlook is for an upper trough to persist just offshore and to intensify through next week. West or southwest transport winds appear likely each afternoon on Monday through Wednesday along with good mixing levels. There is a slight chance of showers beginning Monday night. Pressure gradient stacking appears to be the most questionable factor which will require monitoring. Models indicate that they may balance on Monday afternoon.



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



Gary Votaw

ODF Meteorologist

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