[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

Tue Sep 9 11:20:36 PDT 2014

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:20 AM PDT TUE SEP 9, 2014

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is allowed from now until 1 p.m. with a 50 acre limit.

WEATHER DISCUSSION:

Under a dry northwesterly flow aloft, marine clouds are slowing giving way to sunshine across NW Oregon.  Cool air aloft will promote good mixing today, but other factors may limit burning opportunities.  If the "negatively-stacked" onshore pressure gradients become "balanced" this afternoon, transport winds will likely be northerly. A PIBAL is scheduled for 2 p.m.

TODAY'S FORECAST:

Becoming mostly sunny but cooler.

Salem's high temperature today will be near 76°F (average is 79°F).

Relative humidity:  Near 50%; dropping below 40% by 5 p.m.

Surface winds: NW 5-10 mph; becoming NNW 5-10 mph later this afternoon.

Transport winds: NW 5-10 mph; becoming NNW 10-15 mph later this afternoon.

Mixing height: Near 3000 feet; rising to 5000 feet by 5 p.m.

Salem's sunset tonight: 7:34 p.m.

(Salem Airport data for Monday, September 8th: High 81°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 75)

EXTENDED DISCUSSION:

An upper-level ridge is forecast to strengthen along the west coast Wednesday through Friday, with a continued dry northwesterly flow aloft over Oregon.  A building thermal trough along the coast will turn low-level winds northerly on Wednesday and northeasterly Thursday and Friday.  Valley temperatures will warm to near average on Wednesday, with highs reaching the upper-80s by Friday.  Burning opportunities are unlikely.

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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