[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:55 AM PDT MON AUG 17, 2015



BURN ADVISORY:



***State Fire Marshal Burn-Ban Conditions should be reached this afternoon   (due to low humidity and wind).***



Agricultural burning is not recommended.



Prep burning is not allowed.



WEATHER DISCUSSION:



A building upper-level ridge, centered in the Gulf of Alaska, is producing a dry NW flow aloft over Oregon and keeping weather systems too far to the north to have a significant impact on our weather.  Warming aloft will suppress afternoon mixing and allow temperatures to climb to around 90°F.



At the surface, a thermal trough will strengthen over SW Oregon today, which will lead to increasing north winds in the Willamette Valley this afternoon.  The combination of brisk north winds and low humidity will likely put the valley into State Fire Marshal Burn-Ban Conditions around mid-afternoon.



TODAY'S FORECAST:



Sunny and very warm.  Hazy at times due to wildfire smoke.



Salem's high temperature today will be near 91°F (average is 82°F).

Relative humidity:  Dropping below 50% by 11 a.m. and below 30% by 3 p.m.

Surface winds: N 10-15 mph this morning; N 10-20 mph this afternoon.

Transport winds: NNE 10-15 mph this morning; N 15-20 mph this afternoon.

Mixing height: Rising to 3000 feet about 2 p.m. and to 3500 feet by 5 p.m.

Salem's sunset tonight: 8:15 p.m.



(Salem Airport data for Sunday, August 16th: High 86°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 70)



EXTENDED DISCUSSION:



The upper-level ridge is predicted to strengthen over the region on Tuesday. Further warming aloft will keep mixing heights suppressed with afternoon temperatures climbing into the upper 90s (possibly breaking daily records).  Dry north winds will continue with State Fire Marshal Conditions likely being reached again Tuesday afternoon.



On Wednesday, the upper-level ridge will retreat slightly into the Gulf of Alaska with minor cooling aloft over Oregon.  The surface thermal trough is expected to shift east of the Cascades in the afternoon...initiating onshore flow into NW Oregon and capping temperatures in the mid-90s.  It is unlikely that this transition will occur soon enough in the day to create a burning opportunity.



On Thursday, a strengthening NW flow aloft will bring stronger onshore flow and more significant cooling to western Oregon.  Any burning opportunities will depend on the timing and strength of this marine push, with temperatures expected to drop back close to average Thursday afternoon.



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



Pete Parsons

ODF Meteorologist
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20150817/7b4f6855/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Silverton Hills AM Forecast_Pete.doc
Type: application/msword
Size: 36352 bytes
Desc: Silverton Hills AM Forecast_Pete.doc
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20150817/7b4f6855/attachment.doc>