[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

Fri Jul 21 08:57:44 PDT 2017

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:55 AM PDT FRI JUL 21, 2017

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

Weaker westerly flow aloft and onshore flow at the surface have produced little in the way of marine low clouds this morning.  A full day of sunshine and warmer air aloft will allow temperatures to climb back into the 80s this afternoon.  Westerly transport winds and good mixing should be favorable for burning.  However, there is still some negative gradient-stacking this morning, which will need to get balanced by daytime heating.  Light transport wind speeds may also be a limiting factor for burning.

TODAY'S FORECAST:

Sunny and warmer.

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

Relative humidity:  Dropping to 60% by 11 a.m. and to near 30% by 5 p.m.

Surface winds: Light this morning; W 5 mph this afternoon.

Transport winds: W 5 mph this morning; W 5-10 mph this afternoon.

Mixing height: Rising to 3000 feet around 11 a.m. and to 5000 feet by 5 p.m.

Salem's sunset tonight: 8:50 p.m.

(Salem Airport data for Thursday, July 20th: High 77°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 50)

EXTENDED DISCUSSION:

Dry and warmer weather is expected over the weekend, with high temperatures climbing to around 90°F. Increasing SSW flow aloft will introduce a chance of thundershowers across SW Oregon late Sunday...possibly extending northward into the Willamette Valley Monday and Tuesday.

Increasing onshore flow should push the thundershower threat east of the region by Wednesday.  A pattern of morning clouds with afternoon sunshine and moderate temperatures is expected late 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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