[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

Tue Jul 22 08:48:00 PDT 2014

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:45 AM PDT TUE JUL 22, 2014

BURN ADVISORY:

Recommended times for agricultural burning are from 11 a.m. until 7 p.m.

Prep burning is not allowed.

WEATHER DISCUSSION:

An upper-level trough, centered just off the northern Vancouver Island coast, is producing a moist southwesterly flow aloft over Oregon. The first band of measurable precipitation since July 13th moved across the northern Willamette Valley early this morning.  The Salem Airport recorded one-tenth of an inch, with reports of up to one-quarter of an inch in the foothills east of Salem.

Radar is showing a general decrease in shower activity across the northern valley at mid-morning, but skies remain cloudy across virtually all of western Oregon.  Slightly cooler air aloft and more cloud-cover should continue the recent cooling trend, with temperatures only climbing into the mid to upper 70s this afternoon.  The air mass will remain moist and unstable enough for scattered showers.  Additional rainfall totals should be mostly less than one-tenth of an inch.

TODAY'S FORECAST:

Mostly cloudy and cooler.  Scattered showers.

Salem's high temperature today will be near 78°F (average is 84°F).

Relative humidity:  Dropping to 60% by noon and to near 45% by 5 p.m.

Surface winds: S 5 mph this morning; SW 5 mph this afternoon.

Transport winds: SSW 5-10 mph this morning; SW 10-15 mph this afternoon.

Mixing height: Rising to 3000 feet by 11 a.m. and to near 5000 feet by 5 p.m.

Salem's sunset tonight: 8:49 p.m.

(Salem Airport data for Monday, July 21st: High 81°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 75)

EXTENDED DISCUSSION:

A potent upper-level trough will approach the Oregon coast on Wednesday, which will increase the moisture and instability over the region.  Expect widespread showers with a chance of thunderstorms.  Rainfall totals will vary but should be on the order of one-quarter to one-half of an inch.  Temperatures will only reach the low to mid 70s.

Showers may linger through Thursday morning, followed by a drying and warming trend into the weekend.  Temperatures will recover into the upper 70s Thursday afternoon and into the mid 80s on Friday.  Expect sunny and quite warm conditions Saturday and Sunday, with highs in the low 90s.

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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