[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

Wed Aug 20 08:54:07 PDT 2014

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:50 AM PDT WED AUG 20, 2014

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is allowed from 11 a.m. until 1 p.m. with a 50 acre limit.

WEATHER DISCUSSION:

A moderate marine push into western Oregon overnight produced a fairly solid deck of marine low clouds across the Willamette Valley this morning, with areas of light drizzle.  The cooler and moist marine air will knock about 10 degrees off of valley high temperatures today, even with afternoon clearing.

Mixing heights and transport winds should be favorable for burning again today.  However, negative pressure gradient-stacking, this morning, will need to be balanced by daytime heating, before smoke will stay elevated.  That is not likely to happen until at least mid-afternoon.  Like yesterday, low-level winds may strengthen enough late this afternoon to inhibit good vertical plume development.

TODAY'S FORECAST:

Cloudy this morning with areas of light drizzle. Afternoon clearing.

Salem's high temperature today will be near 79°F (average is 82°F).

Relative humidity:  Dropping below 60% by 11 a.m. and to near 35% by 5 p.m.

Surface winds: NW 5-10 mph this morning; NW 5-15 mph this afternoon.

Transport winds: NW 10 mph this morning; NW 10-18 mph this afternoon.

Mixing height: Rising to near 3000 feet at 11 a.m.; to 5000 feet by 2 p.m.

Salem's sunset tonight: 8:10 p.m.

(Salem Airport data for Tuesday, August 19th: High 89°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 110)

EXTENDED DISCUSSION:

A cool NW flow aloft will continue through the week, as an upper-level trough slowly strengthens over the Pacific Northwest. Temperatures should remain a few degrees below average with varying amounts of morning marine clouds.  The combination of high afternoon mixing heights and NW transport winds may provide additional burning opportunities.  However, gradient-stacking will continue to be a limiting factor for burning.  There is also an increased risk of light showers by 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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20140820/2d82b3f9/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Silverton Hills AM Forecast_Pete.doc
Type: application/msword
Size: 34304 bytes
Desc: Silverton Hills AM Forecast_Pete.doc
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20140820/2d82b3f9/attachment.doc>