[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

Tue Aug 2 11:32:38 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:30 AM PDT TUE AUG 2, 2016

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is allowed from now until 2 p.m. with a 50 acre limit.

WEATHER DISCUSSION:

A compact upper-level low pressure area, centered over extreme NW Washington, will slowly slide eastward this afternoon.  Cool air aloft will provide excelling mixing today and aid in the break-up of marine clouds covering NW Oregon.  Shower activity will stay mostly in Washington but could extend southward into the northern Willamette Valley.

With excellent mixing and NW transport winds expected this afternoon, the limiting factor for open burning is the negative gradient stacking left over from last night's marine push (11 a.m.: Newport-to-Salem 1.1 mb and Salem-to-Redmond 5.1 mb), which was about 4 millibars late this morning.  That will be hard to overcome this afternoon.  The first PIBAL is scheduled for 2 p.m.

TODAY'S FORECAST:

Partly sunny and cooler.  Risk of a light shower.

Salem's high temperature today will be near 77°F (average is 84°F).

Relative humidity:  Dropping to near 35% by 5 p.m.

Surface winds: W 3-8 mph; becoming NW 7-12 mph late this afternoon.

Transport winds: W 5-10 mph; becoming NW 10-15 mph late this afternoon.

Mixing height: Rising to 5500 feet by 5 p.m.

Salem's sunset tonight: 8:36 p.m.

(Salem Airport data for Monday, August 1st: High 85°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 85)

EXTENDED DISCUSSION:

A transitory ridge will bring dry and warmer conditions Wednesday and Thursday with northerly transport winds.  Another upper-level trough will turn transport winds onshore Friday, bringing cooler air into the region and possibly providing a burning opportunity.

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/20160802/5c0098bd/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Silverton Hills Midday Forecast_Pete.doc
Type: application/msword
Size: 35840 bytes
Desc: Silverton Hills Midday Forecast_Pete.doc
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20160802/5c0098bd/attachment.doc>