[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT WED JUL 2, 2014



...TEST MESSAGE...  ...CONTENT VALID...  ...TEST MESSAGE...  ...CONTENT VALID...



BURN ADVISORY:



Recommended times for agricultural burning are from now until 7 p.m.



WEATHER DISCUSSION:



An upper-level disturbance moved onshore overnight, initiating a cooling trend across western Oregon and producing thunderstorms over the Cascades.  That system will push east of the region this afternoon, replaced by a more stable but cooler SW flow aloft.



The strong surface thermal trough that brought near 100 degree heat to the Willamette Valley on Tuesday has moved into central Oregon with cooler onshore flow expected today west of the Cascades.



The air aloft has cooled significantly since yesterday, so mixing should be good this afternoon with increasing NW surface and transport winds.



TODAY'S FORECAST:



Mostly sunny this afternoon.  Much cooler but still warmer than average.



Salem's high temperature today will be near 83 degrees (average is 79).

Relative humidity:  Dropping to about 35% by 5 p.m.

Surface winds: NW increasing to 5-15 mph this afternoon.

Transport winds: NW increasing to 10-15 mph this afternoon.

Mixing height: Rising to near 6000 feet by 5 p.m.

Salem's sunset tonight: 9:02 p.m.



(Salem Airport data for Tuesday, July 1st: High 99°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 90)



EXTENDED DISCUSSION:



A stable southwesterly flow aloft and low-level onshore flow will bring dry weather and seasonal temperatures to the region Thursday and Friday.  Fairly extensive morning marine clouds should give way to afternoon sunshine. Expect valley highs in the mid to upper 70s.  Afternoon transport winds should be northwesterly with cool air aloft maintaining good daytime mixing.



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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