[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

Fri Aug 25 08:56:03 PDT 2017

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:50 AM PDT FRI AUG 25, 2017

BURN ADVISORY:

Agricultural burning is not recommended.

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

WEATHER DISCUSSION:

Onshore flow weakened overnight, and pressure gradients have turned mostly northerly this morning.  An upper-level ridge of high pressure will begin building over the region today.  As a result, a full day of sunshine is expected today with valley temperatures warming back into the low 80s.

Warming aloft will likely cap mixing heights just under 5000 feet this afternoon.  Mostly northerly winds should increase this afternoon.

TODAY'S FORECAST:

Sunny, warmer, and breezy.

Salem's high temperature today will be near 83°F (average is 81°F).

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

Surface winds: N 5-10 mph this morning; N 10-15 mph this afternoon.

Transport winds: NNE 10-15 mph this morning; N 14-18 mph this afternoon.

Mixing height: Rising to 3000 by noon and to near 4800 feet by 5 p.m.

Salem's sunset tonight: 8:01 p.m.

(Salem Airport data for Thursday, August 24th: High 78°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 86)

EXTENDED DISCUSSION:

A strong upper-level ridge is expected to warm temperatures to near 90°F on Saturday and the mid-90s Sunday and Monday.  In addition, offshore flow will likely transport wildfire smoke back into the region.

A very weak upper-level trough should turn winds onshore next Tuesday and Wednesday, which will bring some cooling, help to clear any wildfire smoke from the valley, and possibly create burning opportunities.

Another strong upper-level ridge is expected to build over the region later next week, with very warm temperatures and possibly more wildfire smoke.

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.

     5. In accordance with OAR 837-110-0090, all field burning shall be
         banned when any two of the following criteria are present:
         A. Temperature of 95 degrees Fahrenheit or above
         B. Relative humidity of 30 percent or below
         C. Wind speed of 15 miles per hour or higher

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

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