[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

Wed Jul 6 08:32:53 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:35 AM PDT WED JUL 6, 2016

BURN ADVISORY:

Recommended times for agricultural burning are from 11 a.m. until 7 p.m.

Prep burning is not allowed.

WEATHER DISCUSSION:

An upper-level trough will move across the northern Rockies today with a dry and stable NW flow aloft over Oregon.  Onshore flow is very weak this morning, so only patchy marine clouds have formed over the northern Willamette Valley.

Under mostly sunny skies, temperatures will warm to near average this afternoon.  Onshore gradients should become favorably-stacked to keep smoke elevated this afternoon with cool air aloft providing excellent mixing.  Northerly transport winds, this morning, may turn enough NW to provide a burning opportunity in the afternoon.

TODAY'S FORECAST:

Mostly sunny after patchy morning clouds.

Salem's high temperature today will be near 79°F (average is 80°F).

Relative humidity:  Dropping to 60% by 11 a.m. and to near 40% by 5 p.m.

Surface winds: N 5-10 mph; becoming NW 5-10 mph this afternoon.

Transport winds: N 5-10 mph; becoming NW 10-15 mph this afternoon.

Mixing height: Rising to 3000 feet at 11 a.m. and to 6000 feet by 5 p.m.

Salem's sunset tonight: 9:00 p.m.

(Salem Airport data for Tuesday, July 5th: High 77°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 90)

EXTENDED DISCUSSION:

On Thursday, an approaching upper-level trough will turn the winds mostly westerly.  Daytime mixing should be excellent with favorable onshore pressure-gradients for burning.  Light rain is expected to move onto the north coast in the afternoon and into the Willamette Valley Thursday night.

Rain will turn to showers on Friday, as an upper-level trough moves onshore.  Rainfall totals may exceed one-tenth of an inch. Showery and unseasonably cool weather is expected on Saturday with a chance of a thundershower.  Additional quarter-inch rain totals are possible.  A few light showers will linger into Sunday.  Another upper-level trough will renew the threat of showers on Monday with temperatures remaining well below average.

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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