[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

Fri Jul 25 11:51:00 PDT 2014

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:50 AM PDT FRI JUL 25, 2014

BURN ADVISORY:

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

Prep burning is not allowed.

WEATHER DISCUSSION:

Patchy marine clouds quickly cleared from the valley this morning.  By midday, sunny skies had already helped temperatures climb to 3-7 degrees warmer than 24 hours ago.  High temperatures will be about 10 degrees warmer than on Thursday but still slightly below average.  Northerly winds should increase this afternoon, which will aid in the drying of damp fields.

TODAY'S FORECAST:

Sunny and warmer.

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

Relative humidity:  Dropping to near 35% by 5 p.m.

Surface winds: N 7-15 mph.

Transport winds: N 10-15 mph.

Mixing height: Rising to 4000 feet by 2 p.m. and to 5000 feet by 5 p.m.

Salem's sunset tonight: 8:46 p.m.

(Maximum Ventilation Index expected today: 75)

EXTENDED DISCUSSION:

A drying and warming trend will continue this weekend, as an upper-level ridge of high pressure builds over the western US.  Sunny skies will help temperatures warm into the mid 80s on Saturday and to near 90 on Sunday.  Northerly surface winds will continue to aid in the drying of fields.

By Sunday, southerly flow aloft will begin circulating monsoonal moisture northward over Oregon.  Very little change in that pattern is predicted though next week, as a strong upper-level ridge of high pressure builds over the Rockies.  As the week progresses, both the humidity and the threat of thundershowers will increase.  High temperatures should be mostly in the low to mid 90s.  Onshore flow will be minimal; reducing burning opportunities.

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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