[willamette-fcst] Silverton Hills Midday Forecast.doc

Fri Jul 20 11:35:59 PDT 2012

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:35 AM PDT FRI JUL 20, 2012

BURN ADVISORY:

Recommended burn times for agricultural burning are from now to 7:00 p.m.

Prep burning is not allowed.

Propane flaming is not allowed.

WEATHER DISCUSSION:

A slow-moving upper-level trough pushed northeastward, across western Oregon, early this morning and was advancing into southern Washington at midday.  Bands of showers and thundershowers are continuing to rotate around mainly the north side of circulation center, across western Washington. A few light showers are still evident on radar, over the northern Oregon Cascades and the northern Willamette Valley, but the treat of thundershowers is over.  Moist onshore flow is maintaining generally cloudy skies and cool temperatures across most of western Oregon.

The upper-level trough is forecast to push northeastward...into eastern Washington by late this afternoon.  A drier west-southwesterly flow aloft should bring at least partial clearing to the Willamette Valley late this afternoon and evening.  Temperatures will remain well below average.

TODAY'S FORECAST:

Cloudy and cool, with a chance of a lingering light shower, through early this afternoon.  Slowly clearing skies in the late-afternoon and evening.

Salem's high temperature today will be near 75 degrees (normal is 83).

Relative humidity drops to 50% around 5 p.m.

Surface winds:  SSW 5-10 mph; becoming W 5-10 mph late this afternoon.

Transport winds: SSW 8-12 mph; becoming WSW 8-12 mph late this afternoon.

Mixing height: Rising to near 3500 feet around 2 p.m. and 4500 feet by 5 p.m.

Salem's sunset tonight: 8:51 p.m.

THREE-HOURLY DATA:

                                2 p.m.  5 p.m.  8 p.m.

     Temperature:                 71      74      70

     Relative Humidity:           57%     50%     57%

     Surface Wind Direction:     210     270     290

     Surface Wind Speed:           8       8       6

     Transport Wind Direction:   220     250     280

     Transport Wind Speed:        12      10      10

     Mixing Height:             3500    4500    2300

     Ventilation Index:           42      45      23

EXTENDED DISCUSSION:

Another upper-level trough is forecast to drop southeastward, from the Gulf of Alaska to just off the Washington coast, over the weekend.  That will maintain an onshore flow pattern with morning clouds and afternoon clearing.  Temperatures should recover close to normal on Saturday and then drop back a few degrees on Sunday. The trough is forecast to move across Washington and extreme northern Oregon on Monday, introducing a slight chance of light showers and cooling temperatures to as much as 10 degrees below normal.

A return to a more typical summer-time pattern is forecast for Tuesday through Friday of next week.  Look for morning clouds and afternoon sunshine, with temperatures recovering to near 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 15mph.

     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 times

         the transport wind speed 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 and the Oregon Department of Forestry.  For information contact ODA at 503-986-4701.

Pete Parsons

ODF Meteorologist
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20120720/76029240/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Silverton Hills Midday Forecast.doc
Type: application/msword
Size: 33280 bytes
Desc: Silverton Hills Midday Forecast.doc
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20120720/76029240/attachment.doc>