[willamette-fcst] Silverton Hills Forecast - Fri, Jul 09 2010

[Willamette Valley Ag/Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
12:00 PM PDT FRI JUL 09 2010

BURN ADVISORY:

…State Fire Marshal Conditions may be reached this afternoon due to high temperatures and
low relative humidities…

Recommended burn times for agricultural burning are from now to 6:00pm.
Prep burning is not allowed. 
Propane flaming burning is not allowed.									
										
MIDDAY WEATHER DISCUSSION:

A strong ridge of high pressure remains over the Pacific Northwest.  A broad surface
thermal trough extends from the Willamette Valley to the Cascades and northeastward across
the Columbia Gorge and into central Washington.  Temperatures continue to be very warm
across the Willamette Valley.  Late morning readings were in the upper 70s north and low
to mid 80s south.  The central and south valley is still running 3-8 degrees warmer than
24 hours ago, but temperatures in the extreme north valley are slightly cooler than at
this time yesterday.  Low clouds are continuing to hug much of the coastal strip, but some
of the beaches are beginning to see the sunshine.  Weak onshore flow is keeping coastal
temperatures from the upper 50s to mid 60s.

A very weak upper-level disturbance, just off the northern California coast, is continuing
to circulate considerable mid and high-level moisture northward over mainly the southern
half of Oregon. That has combined with daytime heating the past couple of days to produce
some fairly potent thunderstorms over southwestern and south-central Oregon.  Lightning
detection showed over 300 strikes Thursday with the bulk of the activity over Jackson and
eastern Douglas Counties.  That will be the case again later today, but the convective
activity should push slightly further north and east…staying east of the Willamette
Valley.

The surface thermal trough is forecast to shift into central Oregon this evening, which
will open the door for marine air to begin filtering into the Willamette Valley.  Before
then, valley temperatures should warm well into the 90s, especially south.  Sections of
the central and south valley may end up warmer today than yesterday, but the extreme north
valley will likely be a few degrees cooler.  

THIS AFTERNOON’S FORECAST:

Sunny and continued hot.  Light north winds will turn northwesterly and increase this
evening.  Valley highs today will climb to near 95 degrees.  Relative humidities should
fall below 30% in the mid to late afternoon.

Salem Sunset: 8:59 pm	
																	
EXTENDED DISCUSSION:

A dry northwesterly flow aloft will prevail during the extended forecast period.  Weak
onshore flow will cool temperatures back into the 80s over the weekend.  A stronger
upper-level trough is forecast to swing across southern British Columbia Monday, which
will increase the onshore flow across western Oregon and cool temperatures back to normal
or slightly below normal.  A similar system is forecast to bring another surge of marine
air into the valley late Thursday, which will keep hold temperatures around normal.

EXTENDED FORECAST:	
     
Saturday:  Mostly Sunny but cooler.  Wind: NW 5-15 mph.  57/85
Sunday:    Mostly Sunny.  Wind: NW 5-15 mph.  55/87
Monday:    Morning clouds with afternoon clearing. Breezy and cooler.  55/75
Tuesday:   Morning clouds.  Mostly Sunny in the afternoon.  53/78
Wednesday: Partly to mostly sunny.  52/81
Thursday:  Partly to mostly Sunny.  53/81
Friday:    Morning Clouds.  Mostly Sunny in the afternoon.  53/80
										
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 15mph.								
     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 times 
         the transport wind speed 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 and the Oregon Department of Forestry.  For information contact ODA at
503-986-4701.