[willamette-fcst] Silverton Hills Midday Forecast_Tom

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
11:45 AM PDT WED JUL 26, 2017

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is allowed from 10 a.m. to 1 p.m. with a 50 acre limit.

WEATHER DISCUSSION:

An upper-level disturbance approaches the northern coast today, enhancing surface onshore flow throughout the Willamette Valley. Mixing conditions will continue to develop through late afternoon and persist into the evening as the disturbance nears. Positive gradient stacking is developing mid-valley, and onshore flow up the Columbia River has weakened west of the Gorge, indicating that a mid-valley marine push is more likely tonight. Field burning possibilities remain, though the timeframe will be later in the day as a result.

TODAY'S FORECAST:

Partly Cloudy skies with afternoon haze.

Salem's high temperature today will be near 89°F (average is 84°F).
Relative humidity:  Currently 50% and dropping near 30% by 5 p.m.
Surface winds: N 5-7 mph shifting NW 7-12 mph late afternoon.
Transport winds: N 10 mph shifting W-NW 10-15 mph late afternoon.
Mixing height: Near 3,000 feet currently and reaching 5,000 feet by 3 p.m.
Salem's sunset tonight: 8:45 p.m.

(Salem Airport data for Tuesday, July 25th: High 93°F; Rainfall: .00")
(Maximum Ventilation Index expected today: 75)

EXTENDED DISCUSSION:

Weakened upper-level disturbances push through on Thursday with SW flow aloft, and surface flow remains onshore with a mild sea breeze bringing more clouds into Willamette Valley overnight. Field burning opportunities may be limited if stubborn marine air can't be pushed out by these transient features aloft. W flow aloft develops overnight into Friday as one of these disturbances enters the southern Willamette Valley, which should allow mixing and surface flow to improve rapidly after sunrise; it will also help build clouds over the Cascades Friday afternoon, causing positive gradients to fade out as mountain showers push into central Oregon, so potential field burning would begin and likely end early ahead of the weekend. Upper-level ridging builds over Oregon for the weekend, helping to warm the atmosphere and elevate temperatures back above seasonal averages. Mild mornings and balmy afternoons persist under mostly sunny skies, with onshore flow producing early evening sea breezes to close out the month of July.

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/20170726/9e746c29/attachment.html>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20170726/9e746c29/attachment.htm>