[willamette-fcst] Silverton Hills Midday Forecast_Gary.doc

Thu Sep 8 11:49:55 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT THU SEPT 8, 2016

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

NW flow aloft will continue today over the valley but with due N surface and transport winds. A 2:00 p.m. PIBAL is expected to verify if this wind direction is accurate. Otherwise good drying and mixing heights are already ongoing. Pressure gradients remain negatively stacked but still may balance this afternoon. The primary factor preventing burning today would be the N wind, and possibly gradients.

Sunny.

Salem's high temperature today will be near 80°F (average is 79°F).

Relative humidity:  Below 50% at noon dropping to a low of 30% around 5:00 p.m.

Surface winds: N 8-12 mph.

Transport winds: N 8-12 mph increasing to 12-15 mph during the afternoon.

Mixing height: Near 4000 feet at noon rising to 5000 feet by 5:00 p.m.

Salem's sunset tonight: 7:35 p.m.

(Salem Airport data for Wednesday, September 7th: High 77°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 75)

EXTENDED DISCUSSION:

A weak ridge will cause air flow will turn offshore on Friday for a NNE transport wind. A marine push is expected late on Saturday afternoon as a trough approaches. But the models do not agree on winds becoming conducive for burning, and no cloud cover is expected. N transports are expected again Sunday. Models agree well in the outlook for the first half of next week which calls for an upper low developing over California and a ridge from the Pacific building into British Columbia. This combination will turn the wind NE again on Monday and Tuesday and possibly Wednesday too.

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

Gary Votaw

ODF Meteorologist

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