[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

Thu Aug 14 11:55:45 PDT 2014

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:50 AM PDT THU AUG 14, 2014

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

A slow-moving upper-level low-pressure system, centered over north-central Oregon at midday, is continuing to spin considerable shower activity across Washington and mainly just a lot of clouds across Oregon.  Daytime heating will enhance the shower activity somewhat this afternoon, especially over higher terrain.

High mixing heights and a predicted westerly component to the transport winds may allow for burning this afternoon.  However, some fields are likely too wet (for burning), and shower development could dampen additional fields and cause smoke down-mixing.  Conditions will need to be closely monitored.

TODAY'S FORECAST:

Mostly cloudy.  Chance of showers and thundershowers.

Salem's high temperature today will be near 80°F (average is 83°F).

Relative humidity:  Dropping to near 50% by 5 p.m.

Surface winds: S 2-6 mph; becoming W 5-10 mph later this afternoon.

Transport winds: SW 4-8 mph; becoming W 5-10 mph later this afternoon.

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

Salem's sunset tonight: 8:20 p.m.

(Salem Airport data for Wednesday, August 13th: High 80°F; Rainfall: Tr.)

(Maximum Ventilation Index expected today: 60)

EXTENDED DISCUSSION:

The upper-level trough is forecast to move over eastern Washington on Friday.  The moist circulation around it should maintain mostly cloudy skies early, with afternoon clearing.  Increasing onshore flow and continued high afternoon mixing heights should provide some opportunity for burning.

A drier westerly flow aloft is forecast for Saturday through Monday.  Mostly sunny skies will help temperatures recover to slightly above average. Weak onshore flow may provide burning opportunities early next week.

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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