[willamette-fcst] Silverton Hills Midday Forecast_Tom

Fri Jul 24 11:38:55 PDT 2015

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT FRI JUL 24, 2015

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is allowed between 12 p.m. to 2 p.m. with a 50 acre limit.

WEATHER DISCUSSION:

An upper-level ridge is passing over the Pacific Northwest, ahead of a strengthening upper-level low near Vancouver Island. This is forming a weak frontal system at the surface near the Canadian coastline, which will produce onshore southwesterly flow ahead of it today. Partly Cloudy skies will allow great heating, and gradients are onshore with +1.6mb from Newport to Salem and +2.5mb from Salem to Redmond. This points to a late day of potential open burning opportunities across the Silverton Hills, as light westerly winds, onshore gradients, and optimal mixing & ventilation of smoke all come together mid-afternoon. The surface frontal system will be offshore Washington by sunset, with a dry Cold Front passing over the Willamette Valley close to midnight tonight.

TODAY'S FORECAST:

Partly Cloudy becoming Mostly Cloudy skies this afternoon.

Salem's high temperature today will be near 80°F (average is 84°F).

Relative humidity:  Currently near 45% and dropping near 30% by 2 p.m.

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

Transport winds: SW 5-10 mph this afternoon.

Mixing height: Currently near 3000 feet and rising to 6000 feet by 3 p.m.

Salem's sunset tonight: 8:48 p.m.

(Salem Airport data for Thursday, July 23rd: High 83°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 60)

EXTENDED DISCUSSION:

Onshore flow with cooler temperatures arrive for the weekend. Moisture moving in from the Pacific Ocean will provide Mostly Cloudy to Overcast conditions, with pop-up showers and isolated thunderstorms possible in the Cascades. Rainfall will be very light, amounting to less than 0.10 of an inch for the entire weekend in areas affected.

An unsettled weather pattern will reach its apex on Monday, as the upper-level low that generated cool & cloudy weather for the weekend finally passes across the Washington/Oregon border. Onshore flow will build throughout the day, with northwesterly winds at all levels. Ample moisture will be pulled in from the Pacific Ocean, increasing the coverage of rainfall with isolated thunderstorms across the Oregon Cascades Monday afternoon. An upper-level ridge will begin to re-establish itself Monday evening, calming the atmosphere for the remainder of the week and improving the favorability for open field burning beyond Tuesday.

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

ODF Meteorologist
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20150724/cf4c8bcd/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Silverton Hills Midday Forecast_Tom.doc
Type: application/msword
Size: 36864 bytes
Desc: Silverton Hills Midday Forecast_Tom.doc
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20150724/cf4c8bcd/attachment.doc>