[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

Fri Sep 5 08:55:55 PDT 2014

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:55 AM PDT FRI SEP 5, 2014

BURN ADVISORY:

***  State Fire Marshal Burn-Ban Conditions Are Likely This Afternoon ***

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

Northeasterly flow aloft will bring sunny and even warmer weather today.  The surface thermal trough will remain just offshore with NE winds extending the very warm temperatures all the way to the coast.  NE winds will increase across the Willamette Valley again this afternoon; significantly drying out the low-levels of the air mass.  Temperatures will top out about 5 degrees warmer than on Thursday.

TODAY'S FORECAST:

Sunny, breezy, and hot.  Very low humidity this afternoon.

Salem's high temperature today will be near 92°F (average is 80°F).

Relative humidity:  Dropping to 30% by noon and to below 20% by 5 p.m.

Surface winds: NNE 7-12 mph this morning; NE 15-25 mph this afternoon.

Transport winds: NE 15 mph this morning; NE 20-25 mph this afternoon.

Mixing height: Rising to 3000 feet around 2 p.m. and to 4500 feet by 5 p.m.

Salem's sunset tonight: 7:41 p.m.

(Salem Airport data for Thursday, September 4th: High 86°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 110)

EXTENDED DISCUSSION:

Weak southwesterly flow aloft will push the thermal trough inland, to over the Willamette Valley, on Saturday.  That should be the peak of this warm spell with temperatures topping out in the mid-90s but with less wind.  Onshore flow should begin by Sunday, which will cool valley temperatures back into the upper-80s.

Early next week, increasing NW flow aloft will push the thermal trough into eastern Oregon, with onshore flow bringing more significant cooling to NW Oregon.  No precipitation is expected, but temperatures will cool to near average by Tuesday, with possible burning opportunities Monday and Tuesday.

An upper-level ridge is predicted to strengthen over Oregon again later next week, bringing a return of offshore flow and warmer temperatures.  Longer-range models are maintaining a generally dry weather pattern, with above average temperatures, through the middle of September.

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
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