[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:50 AM PDT TUE AUG 23, 2016



BURN ADVISORY:



Agricultural burning is not recommended.



Prep burning is not allowed.



WEATHER DISCUSSION:



An upper-level ridge is building into the eastern Gulf of Alaska and bringing a dry NW flow aloft to Oregon.  At the surface, northerly pressure gradients have weakened and will become increasingly offshore, maintaining a very dry air mass across the region today.  Temperatures will only warm into the mid-80s, but portions of the valley will be flirting with State Fire Marshal Burn-Ban Conditions, 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 near 30% by 5 p.m.

Surface winds: N 5-12 mph.

Transport winds: NNE 10-15 mph.

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:



As the flow aloft veers from NW to NE, later this week, a building coastal thermal through will turn transport winds increasingly offshore.  Valley temperatures will climb back into the 90s.  State Fire Marshal Burn-Ban Conditions are possible in the afternoons.  A dry cold front is predicted to turn transport winds onshore and drop temperatures back 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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