[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

Mon Aug 24 11:57:17 PDT 2015

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:55 AM PDT MON AUG 24, 2015

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

SW flow aloft and weak onshore flow at the surface are working together to push wildfire smoke out of NW Oregon.  Air quality is continuing to improve, from the NW to SE, across the Willamette Valley.  "Good" air quality is being observed as far south as Silverton along the Cascade foothills and all the way to Eugene in the heart of the valley.  Decreasing smoke levels are still somewhat elevated from Lyons to Sweet Home.

SW flow aloft may destabilize the air mass enough for some thunderstorm development over the Cascades this afternoon.  Otherwise, expect partly cloudy skies and slightly above average temperatures.  Increasing NW winds in the transport layer will shear to the SW above the mixing height this afternoon.  A PIBAL is scheduled for 2 p.m.

TODAY'S FORECAST:

Mostly sunny.  Wildfire smoke clearing, from west to east, across the region.

Salem's high temperature today will be near 84°F (average is 82°F).

Relative humidity:  Dropping to near 30% by 5 p.m.

Surface winds: NNW 5-10 mph this afternoon.

Transport winds: NW 10 mph this afternoon.

Mixing height: Rising to 3000 feet about 1 p.m. and to 5000 feet by 5 p.m.

Salem's sunset tonight: 8:03 p.m.

(Salem Airport data for Sunday, August 23rd: High 88°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 50)

EXTENDED DISCUSSION:

Only minor changes in the weather pattern are expected through Wednesday.  A SW flow aloft should keep temperatures above average.  Skies will be partly cloudy with a slight chance of afternoon and evening thunderstorms over the Cascades.  Most of the wildfire smoke will stay east of the region, but nighttime drainage of smoke into the western Cascade foothills is possible.

Thursday and Friday, increasing onshore flow will bring slow cooling and should clear any remaining wildfire smoke from NW Oregon.  Some computer models are showers spreading across western Oregon on Friday, but that is still uncertain.

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/20150824/a97dfa11/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/20150824/a97dfa11/attachment.doc>