[willamette-fcst] Field Burning Forecast - August 3, 2017

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
8:45 AM PDT THU AUG 3, 2017

BURN ADVISORY:

***State Fire Marshal Burn-Ban conditions are expected this afternoon***

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

The upper-level ridge over the Oregon coast has weakened overnight, and flow aloft is becoming NW; as the atmosphere cools, it will trigger a slow end to our current heat wave. Offshore flow persists at the surface, with transport winds continuing to trap regional wildfire smoke throughout the Willamette Valley. State Fire Marshall Burn-Ban conditions will develop early this afternoon, with temperatures again peaking in the triple-digits. A mild sea breeze is expected to push in around sunset and improve air quality throughout the night, but a strong marine push is not expected.

TODAY'S FORECAST:

Hazy with layers of smoke aloft becoming Mostly Clear this evening.

Salem's high temperature today will be near 106°F (average is 84°F).
Relative humidity:  Below 30% by 1 p.m. and nearing 17% by 5 p.m.
Surface winds: Variable 5 mph or less this morning, becoming N 5-10 mph this afternoon and NW 10-15 mph this evening.
Transport winds: N-NE 5-10 mph this morning, becoming N-NW 5-10 mph this afternoon and NW 15-20 mph this evening.
Mixing height: Rising to 3000 feet around 3 p.m. and reaching 4,000 feet by 6 p.m.
Salem's sunset tonight: 8:35 p.m.

(Salem Airport data for Tuesday, August 1st: High 107°F; Rainfall: .00")
(Maximum Ventilation Index expected today: 70)

EXTENDED DISCUSSION:

The upper-level ridge will continue to break down and retreat out to sea on Friday, turning flow aloft W-NW and allowing better mixing to occur with daytime heating. Onshore gradients may develop by mid-afternoon ahead of another mild sea breeze, but overall cooling may not be enough to reduce the threat of State Fire Marshal conditions. Saturday is expected to be the coolest day of the weekend, as a limited marine push brings morning clouds to the northern and southern ends of the Willamette Valley. Sunday, the upper-level ridge will begin to rebuild over western Oregon; this will cause gradients to flatten out and northerly flow to prevail across the Willamette Valley. Field burning opportunities will be determined by development of onshore gradients in the afternoon hours next week, but appear to trend positive as the week progresses and daily sea breezes further cool the atmosphere.

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/20170803/b215eaa4/attachment.html>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20170803/b215eaa4/attachment.htm>