[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

Tue Aug 23 08:56:32 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:50 AM PDT TUE AUG 23, 2016

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

A building upper-level ridge, in the eastern Gulf of Alaska, is bringing a dry NW flow aloft to Oregon.  At the surface, pressure gradients have weakened and turning mostly northerly, with a developing offshore component.  The air mass is slowly warming, so valley highs today will climb back into the 80s.  Warming aloft will suppress daytime mixing.  State Fire Marshal Conditions may be reached late this afternoon, based on wind and humidity.

TODAY'S FORECAST:

Sunny and warmer.  Not as windy.

Salem's high temperature today will be near 84°F (average is 82°F).

Relative humidity:  Dropping to 50% around 11 a.m. and to near 30% by 5 p.m.

Surface winds: NNE 5-10 mph this morning; N 5-12 mph this afternoon.

Transport winds: NNE 5-10 mph this morning; NNE 10-15 mph this afternoon.

Mixing height: Rising to 3000 feet around 1 p.m. and to 4500 feet by 5 p.m.

Salem's sunset tonight: 8:04 p.m.

(Salem Airport data for Monday, August 22nd: High 78°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 68)

EXTENDED DISCUSSION:

The flow aloft will veer to northerly and eventually northeasterly later this week.  A building thermal through along the coast will turn transport winds offshore and allow valley temperatures to climb back into the 90s.  State Fire Marshal Burn-Ban Conditions are possible in the afternoons.  A dry cold front will drop temperatures into the upper-70s this weekend.

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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