[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

Mon Aug 22 11:54:43 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:55 AM PDT MON AUG 22, 2016

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

An upper-level trough, cutting across southern British Columbia, forced a dry cold front across Oregon on Sunday.  That brought an end to record-breaking warm temperatures across western Oregon.  Even with sunny skies, temperatures will struggle to reach 80°F today.  However, gusty north to NE winds and lowering humidity could push sections of the Willamette Valley into State Fire Marshal Burn-Ban Conditions late this afternoon.  A 1 p.m. PIBAL is scheduled to verify the predicted NNE transport winds.

TODAY'S FORECAST:

Sunny and breezy.

Salem's high temperature today will be near 79°F (average is 82°F).

Relative humidity:  Dropping to near 30% by 5 p.m.

Surface winds: North to NNE 10-15 mph with gusts to 20 mph.

Transport winds: NNE 15-20 mph.

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

Salem's sunset tonight: 8:06 p.m.

(Salem Airport data for Sunday, August 21st: High 86°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 100)

EXTENDED DISCUSSION:

The outlook for burning this week is bleak.  A building upper-level ridge, centered in the eastern Gulf of Alaska, will produce a dry northerly flow aloft over Oregon with increasing offshore transport winds and warming temperatures.  Valley highs should climb back into the 90s Wednesday through Friday.  State Fire Marshal Burn-Ban Conditions are possible in the afternoons.  Another dry cold front will likely bring cooling 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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