[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

Tue Jul 28 11:28:15 PDT 2015

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:30 AM PDT TUE JUL 28, 2015

BURN ADVISORY:

*** State Fire Marshal Burn-Ban Conditions may be reached this afternoon due to low humidity and wind. ***

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

A building upper-level ridge is producing a drying and warming NW flow aloft and sunny skies statewide.  At the surface, strengthening offshore flow should help temperatures climb to above average this afternoon.  A 2 p.m. pibal is scheduled to verify the expected NE transport winds.

TODAY'S FORECAST:

Sunny and much warmer.

Salem's high temperature today will be near 88°F (average is 84°F).

Relative humidity:  Dropping to near 35% by 2 p.m. and to near 25% by 5 p.m.

Surface winds: NNE increasing to 10-15 mph this afternoon.

Transport winds: NE 15 mph this afternoon.

Mixing height: Rising to 4000 feet by 2 p.m. to 5000 feet by 5 p.m.

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

(Salem Airport data for Monday, July 27th: High 79°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 75)

EXTENDED DISCUSSION:

A strong upper-level ridge is expected to produce near-record heat across western Oregon Wednesday through Friday.  Willamette Valley highs will range from 95-100°F, with Thursday likely being the warmest day.  Hot temperatures and low humidity levels will likely put the valley into State Fire Marshal Burn-Ban conditions in the afternoons.

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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