[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

Fri Aug 18 11:54:49 PDT 2017

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:50 AM PDT FRI AUG 18, 2017

*** Next Update 9 a.m. Tuesday, August 22nd ***

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

A weak weather system may spread some high clouds across the region today, but its main effect will be to increase the onshore flow.  That should cap afternoon temperatures in the middle-80s and push a fresh surge of marine air into the valley overnight.

TODAY'S FORECAST:

Sunny and seasonably warm.  Turning a little breezy this afternoon.

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: N 8-15 mph this afternoon.

Transport winds: N 15 mph this afternoon.

Mixing height: Rising to 5000 feet by 5 p.m.

Salem's sunset tonight: 8:13 p.m.

(Salem Airport data for Thursday, August 17th: High 85°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 75)

EXTENDED DISCUSSION:

Expect morning marine clouds and afternoon sunshine this weekend with high temperatures in the low-80s.  By Monday, a building upper-level ridge will inhibit morning clouds.  Sunny skies and warmer air aloft will allow temperatures to climb to near 90°F.

The ridge will progress eastward by Tuesday with developing SW flow aloft. Tuesday will likely still be near 90°F, but increasing onshore flow in the afternoon may provide a burning opportunity.  Even stronger onshore flow should provide favorable burning conditions on Wednesday.

An upper-level trough will bring additional cooling Thursday and Friday.  The latest computer guidance has backed off on the strength of this system but still gives the Salem area a few light showers Thursday morning.

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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