[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

Fri Jul 21 11:55:32 PDT 2017

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:55 AM PDT FRI JUL 21, 2017

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

Only patchy morning clouds developed in the Willamette Valley this morning, due to weakening westerly flow aloft and onshore flow at the surface.  Sunny skies and warming air aloft will allow temperatures to climb into the 80s this afternoon.  The mixing height, wind direction, and pressure gradient-stacking should all be favorable for burning today, but light wind speeds may be a limiting factor.

TODAY'S FORECAST:

Sunny and warmer.

Salem's high temperature today will be near 83°F (average is 83°F).

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

Surface winds: Light...becoming W 5-10 mph later this afternoon.

Transport winds: W 5-10 mph.

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

Salem's sunset tonight: 8:50 p.m.

(Salem Airport data for Thursday, July 20th: High 77°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 50)

EXTENDED DISCUSSION:

Dry and warmer weather is expected over the weekend, with high temperatures climbing to around 90°F. Increasing SSW flow aloft will introduce a chance of thundershowers across SW Oregon late Sunday.  There is a slight chance that the thundershower activity will migrate as far north as Salem, on Monday, but it should stay mostly south and east of the region.

A marine push is expected to initiate a cooling trend on Tuesday, pushing any threat of thundershowers east of the Cascades and possibly creating a significant burning opportunity.  Onshore flow will bring morning clouds and afternoon sunshine the remainder of next week with moderate temperatures.

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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