[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

Fri Jul 28 11:55:12 PDT 2017

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:55 AM PDT FRI JUL 28, 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:

A dry and stable WSW flow aloft will bring a full day of sunshine with temperatures warming into the mid-80s.  Daytime heating may balance the existing negative onshore gradient stacking later this afternoon.  However, transport winds may be too northerly and/or become too brisk to allow for burning.  A PIBAL scheduled for 2 p.m.

TODAY'S FORECAST:

Sunny and seasonably warm.

Salem's high temperature today will be near 85°F (average is 84°F).

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

Surface winds: Becoming NNW 5-15 mph this afternoon.

Transport winds: Becoming NNW 10-20 mph this afternoon.

Mixing height: Near 3000 feet at noon; rising to around 4500 feet by 5 p.m.

Salem's sunset tonight: 8:43 p.m.

(Salem Airport data for Thursday, July 27th: High 81°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 90)

EXTENDED DISCUSSION:

A building upper-level ridge will bring sunny and hot weather this weekend through much of next week.  Temperatures will warm to near 90°F by Sunday and possibly to near 100°F early next week. As the upper-level ridge progresses east of the region, increasing SSW flow aloft will initiate a cooling trend later next week and introduce a threat of thundershowers.

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
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