[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

Wed Aug 26 11:54:59 PDT 2015

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:50 AM PDT WED AUG 26, 2015

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

Little change is expected in the overall weather pattern today.  A nearly stationary upper-level trough, centered about 800 miles off of the northern Oregon coast, is maintaining a dry SW flow aloft over Oregon.  Very weak onshore flow (Newport to Salem +1.7mb and Salem to Redmond +0.7mb) is keeping area wildfire smoke mostly east of the valley, but some haze and elevated smoke is still visible over the Cascades.

Skies will be mostly sunny today with above average temperatures.  Isolated thunderstorms are possible over the Cascades.  The air aloft is warm, so mixing heights will not likely climb above 3000 feet until after 2 p.m.

Although State Fire Marshal Burn-Ban conditions are not expected this afternoon, relative humidity levels should drop below 30%, and the risk of wildfires remains elevated. A PIBAL is schedule for 2 p.m.

TODAY'S FORECAST:

Partly cloudy and seasonably warm.

Salem's high temperature today will be near 86°F (average is 81°F).

Relative humidity:  Dropping below 30% by 5 p.m.

Surface winds: Light...becoming W 3-8 mph this afternoon.

Transport winds: Light...becoming SW 5-15 mph this afternoon.

Mixing height: Rising to 3000 feet by 3 p.m. and to 4000 feet by 5 p.m.

Salem's sunset tonight: 8:00 p.m.

(Salem Airport data for Tuesday, August 25th: High 85°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 60)

EXTENDED DISCUSSION:

The offshore upper-level trough will move very little through Thursday.  Continued dry SW flow aloft will maintain mostly sunny and warm weather with a chance for isolated afternoon thundershowers over the Cascades. Increasing onshore flow should keep wildfire smoke east of the valley.

A major change in the weather pattern will begin on Friday, as the upper-level trough advances towards the coast.  Increasing SW flow aloft and onshore flow at the surface will bring clouds and cooler temperatures.

Wetting rains are expected to move into the region Friday night and Saturday, with over one-half inch possible in the Silverton Hills (the most significant rain for the area since June 1st).  Additional weather systems are expected to move across the region Sunday and Tuesday, bringing lighter amounts of rain and keeping temperatures cool.

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/20150826/7dde1400/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/20150826/7dde1400/attachment.doc>