[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

Fri Aug 29 11:57:52 PDT 2014

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:55 AM PDT FRI AUG 29, 2014

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

Moring low clouds are giving way to increasing middle and high clouds.  An approaching weather system is currently bringing sprinkles to NW Washington and will spread more middle and high clouds across the region this afternoon.  Increasing onshore flow and cooling aloft will likely combine to hold high temperatures below 80°F.

Conditions have become very favorable for burning.  An 11 a.m. PIBAL revealed mostly westerly transport winds.  Cooling aloft and frontal forcing will promote good lifting of smoke plumes with minimal down-mixing.  WSW transport winds should slowly veer to the NW by late afternoon.  Transport winds will continue to be closely monitored today.

TODAY'S FORECAST:

Increasing middle and high clouds this afternoon and evening.

Salem's high temperature today will be near 78°F (average is 81°F).

Relative humidity:  Dropping below 50% by 2 p.m.

Surface winds: W 5-10 mph; veering to NW 10 mph late this afternoon.

Transport winds: W 10 mph; veering to NW 15 mph late this afternoon.

Mixing height: Rising to near 5000 feet by 2 p.m.

Salem's sunset tonight: 7:54 p.m.

(Salem Airport data for Thursday, August 28th: High 87°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 75)

EXTENDED DISCUSSION:

An upper-level trough is forecast to move across Oregon tonight, which will aid in the evacuation of smoke.  A cool NW flow aloft will set up Saturday through Monday.  Areas of morning drizzle are possible Saturday with a chance of light showers.  Precipitation totals will range from nothing to just a few hundredths of an inch.  Sunday and Monday look dry, with morning clouds giving way to partly sunny afternoons.  Temperatures will top out in the mid-70s Saturday, then slowly warm to the upper-70s by Monday.  An approaching weak weather system may bring favorable burning conditions next Tuesday.

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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