[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:55 AM PDT MON SEP 26, 2016



BURN ADVISORY:



Agricultural burning is not recommended.



Prep burning is not allowed.



WEATHER DISCUSSION:



A strong and broad upper-level ridge is centered over Idaho this morning with very warm and stable air aloft over Oregon. At the surface, a thermal trough extends northward along the coast with weak offshore pressure gradients across the Willamette Valley.



The upper-level ridge will progress eastward today with the surface thermal trough shifting over the Willamette Valley around midday and into central Oregon later this afternoon.  That may create a late-day burning opportunity, for remaining fields, as transport winds turn northwesterly and mixing heights creep upward, to between 3000 and 3500 feet.



TODAY'S FORECAST:



Sunny and warm.



Salem's high temperature today will be near 86°F (average is 74°F).

Relative humidity:  Dropping to 50% around noon and to near 30% by 5 p.m.

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

Transport winds: Var 5 mph this morning; becoming NW 10 mph this afternoon.

Mixing height: Rising to 3000 feet around 3 p.m.

Salem's sunset tonight: 7:01 p.m.



(Salem Airport data for Sunday, September 25th: High 84°F; Rainfall: 0.00")

(Maximum Ventilation Index expected today: 35)



EXTENDED DISCUSSION:



A weak cold front will push across SW British Columbia tonight with the trailing edge bringing some clouds and a marine push into NW Oregon.  Tuesday will be at least 10 degrees cooler with morning clouds giving way to partly sunny skies in the afternoon.  Gradient-stacking will likely be unfavorable for burning with northerly winds in the afternoon.



A continued dry SW flow aloft may turn transport winds northwesterly Wednesday afternoon with gradients becoming more favorable for burning.



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/20160926/6b1858c6/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Silverton Hills AM Forecast_Pete.doc
Type: application/msword
Size: 35840 bytes
Desc: Silverton Hills AM Forecast_Pete.doc
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20160926/6b1858c6/attachment.doc>