[willamette-fcst] Silverton Hills AM Forecast_Tom

Fri Aug 28 08:45:33 PDT 2015

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:45 AM PDT FRI AUG 28, 2015

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

An upper-level trough is off the coast of Oregon, producing southwesterly flow across the Pacific Northwest. At the surface, a storm system with frontal boundaries has formed off the coast of California and will track northeast towards Oregon today. Cloudy skies will keep temperatures just below seasonal averages, with onshore flow keeping the atmosphere well-mixed throughout the day. Light rain at times will become more showery after sunset as a cold front approaches the Silverton Hills, but less than 0.10 of an inch is expected to fall today. Isolated thunderstorms are possible in the Cascades this evening.

TODAY'S FORECAST:

Cloudy with light rain showers.

Salem's high temperature today will be near 78°F (average is 81°F).

Relative humidity:  Dropping near 45% by 2 p.m.

Surface winds: SW 5-10 mph this morning; W-SW 5-10 mph this afternoon.

Transport winds: SW 10-15 mph this morning; SW 15-25 mph this afternoon.

Mixing height: 5000 feet throughout the day.

Salem's sunset tonight: 7:56 p.m.

(Salem Airport data for Thursday, August 27th: High 90°F; Rainfall: Trace")

(Maximum Ventilation Index expected today: 125)

EXTENDED DISCUSSION:

Foul weather sets in for the weekend, as a second upper-level trough off the coast of California taps into tropical moisture over the Pacific Ocean. A fast-moving surface frontal system will again bring scattered showers and isolated thunderstorms to western Oregon, with heavier showers in higher elevations. The heaviest rainfall is expected to occur on Saturday morning. Moderate showers move in again overnight into Sunday, with rainfall slowly tapering off by sunset. At this time, ~1.2 inches of rainfall are projected for the Silverton Hills over the weekend.

Westerly flow aloft sets up for Monday, with an area of higher pressure forming off the coast of Oregon. This will maintain onshore flow, while allowing the atmosphere to dry out as temperatures increase closer to seasonal averages. Another upper-level disturbance will be developing in the Gulf of Alaska, and may tap into remnant moisture from Tropical Storms Ignacio and Jimena for more late-summer showers ahead of the Labor Day weekend.

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

Tom Jenkins, AEM

ODF Meteorologist
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20150828/4c55dba6/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Silverton Hills AM Forecast_Tom.doc
Type: application/msword
Size: 36352 bytes
Desc: Silverton Hills AM Forecast_Tom.doc
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20150828/4c55dba6/attachment.doc>