[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

Fri Aug 15 11:45:30 PDT 2014

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT FRI AUG 15, 2014

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

A persistent upper-level low-pressure system, centered over SE Washington at midday, will continue to slowly migrate to the NE this afternoon.  Clouds still cover most of Washington and northern Oregon, but a drier westerly flow aloft should slowly begin to clear skies this afternoon across NW Oregon.

An extended period of favorable burning conditions appears likely today.  Residual cool air aloft and daytime heating will combine to yield high mixing heights along with gradually increasing onshore flow.  An 11 a.m. PIBAL confirmed southerly transport winds, which should slowly veer to SW, then west, and eventually WNW, over the course of the day.  The next PIBAL is scheduled for noon.

TODAY'S FORECAST:

Partial clearing this afternoon.

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

Relative humidity:  Dropping below 65% by noon and to near 45% by 5 p.m.

Surface winds: S 3-8 mph; veering to the SW then WNW 5-10 mph this afternoon.

Transport winds: S 4-8 mph; veering to SW then WNW 8-14 mph this afternoon.

Mixing height: Rising to above 5000 feet by 5 p.m.

Salem's sunset tonight: 8:18 p.m.

(Salem Airport data for Thursday, August 14th: High 80°F; Rainfall: Tr.)

(Maximum Ventilation Index expected today: 70)

EXTENDED DISCUSSION:

A dry and stable westerly flow aloft should clear skies by Saturday afternoon with temperatures warming to slightly above average.  A very weak upper-level trough will back the winds aloft to southwesterly on Sunday, which should provide additional slight warming under mostly sunny skies.  The flow aloft may turn briefly southerly on Monday, as the trough gets kicked onshore by a weather system cutting across SW Canada.  That may generate scattered afternoon thundershowers across SW Oregon and along the Cascades.

Long-range computer models show the polar jet stream becoming more active; forcing an early autumn-like trough into the region from the Gulf of Alaska.  Beginning next Tuesday, increasing onshore flow and progressively cooler air aloft may provide burning opportunities but also a chance of showers.

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/20140815/8c6d78c4/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Silverton Hills Midday Forecast_Pete.doc
Type: application/msword
Size: 34304 bytes
Desc: Silverton Hills Midday Forecast_Pete.doc
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20140815/8c6d78c4/attachment.doc>