[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

Mon Aug 1 11:57:21 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:55 AM PDT MON AUG 1, 2016

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

Marine clouds, which extended southward into Marion County this morning, have mostly given way to sunshine.  However, continued onshore flow will keep temperatures slightly below average today.  Winds were mostly northerly late this morning.  Daytime heating should balance the, slightly negatively-stacked, pressure gradients this afternoon.  In addition, an approaching upper-level trough may turn transport winds northwesterly and provide a burning opportunity. PIBALS are scheduled to begin at 1 p.m.

TODAY'S FORECAST:

Sunny and warm this afternoon.

Salem's high temperature today will be near 81°F (average is 84°F).

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

Surface winds: Becoming NW 5-10 mph this afternoon.

Transport winds: Becoming NW 10-15 mph this afternoon.

Mixing height: Rising to 3000 feet around 2 p.m. to 4500 feet by 5 p.m.

Salem's sunset tonight: 8:38 p.m.

(Salem Airport data for Sunday, July 31st: High 80°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 80)

EXTENDED DISCUSSION:

Showers from the incoming weather system will stay mostly in Washington, but a few could make it into extreme NW Oregon on Tuesday.  Temperatures will cool into the mid-70s with extensive morning clouds across the Willamette Valley.  Good mixing and westerly transport winds should be favorable for burning, but unfavorable gradient stacking may be an issue.

A transitory ridge will bring dry and warmer conditions on Wednesday with transport winds reverting to northerly.  However, another upper-level trough may turn transport winds enough northwesterly for a burning opportunity Thursday and/or Friday.

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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