[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

Thu Jul 27 11:43:04 PDT 2017

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:40 AM PDT THU JUL 27, 2017

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is allowed from noon until 2 p.m. with a 50 acre limit.

WEATHER DISCUSSION:

Low clouds continue to blanket the northern Willamette Valley at midday.  Due to an ongoing marine push, skies will be slow to clear this afternoon.  Negative gradient-stacking and northerly winds are likely to persist this afternoon, making burning unlikely.  A PIBAL is scheduled for 2 p.m., but it will be postponed, if skies are still cloudy at that time.

TODAY'S FORECAST:

Afternoon clearing.  Cooler.

Salem's high temperature today will be near 81°F (average is 84°F).

Relative humidity:  Dropping to near 60% by 1 p.m. and to near 40% by 5 p.m.

Surface winds: N 5-10 mph.

Transport winds: NNW 10-15 mph.

Mixing height: Rising to 3000 feet by 2 p.m. and to 5000 feet by 5 p.m.

Salem's sunset tonight: 8:44 p.m.

(Salem Airport data for Wednesday, July 26th: High 91°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 75)

EXTENDED DISCUSSION:

Onshore flow will weaken on Friday.  Patchy morning clouds should give way to sunshine and seasonal temperatures.  Although gradient-stacking should become more balanced, transport winds may stay too northerly to allow for burning.

Sunny and warmer weather is expected this weekend and the first half of next week, with temperatures climbing back into the lower 90s by Monday.  There is hope for a burning opportunity, around the middle of next week, if we get an increase in onshore flow at the right time of day.

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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