[willamette-fcst] Forecast - Friday, July 18th, 2008

[Willamette Valley Ag/Burning Forecast]

Daily Smoke Management Forecast




Oregon Department of Agriculture
Smoke Management Program
Weather Outlook and Field Burning Advisory for Willamette Valley Growers and Fire Districts.

Issued: 
     Friday, July 18th, 2008 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 12:00pm until 8:00pm.
     Preparatory burning is allowed from 12:00pm until 2:00pm with a 100 acre limit.
     Propane flaming is allowed from 12:00pm until 5:00pm.
     Stack burning is not allowed.

Weather Discussion:
     An upper-level trough, moving across Southern British
     Columbia, helped turn the transport winds from northerly to
     north-northwesterly late Thursday, but not before surface
     winds became too strong for open burning.  Sunny skies
     helped valley temperatures climb into the low to mid 80s.

     Increased onshore flow overnight brought a thick blanket of
     low clouds into the coastline with some clouds penetrating
     into the extreme northern valley this morning.  Visible
     satellite imagery showed low clouds over most of Western
     Washington, along the Oregon Coast, and in the Northern
     Willamette Valley (from about Salem northward).  Some
     drizzle was also falling along section of the north coast. 
     With the exception of the north valley, skies were sunny
     across the interior of Oregon.

     The morning ODA surface analysis showed high pressure had
     built into Western Washington and Western Oregon with
     onshore flow now extending across both states.  Strong
     gradiant-stacking and Medford-Draw conditions exist and will
     likely persist today with the transport winds remaining more
     northerly.

     The Salem sounding this morning showed very slight cooling
     below about 8000 feet, so afternoon temperatures should only
     climb to about 80 today across the valley. Valley minimums
     this morning were in the mid 40s to mid 50s.  Mid-morning
     temperatures were in the mid to upper 50s with generally
     northwest winds about 4-8 mph.

     As the upper-level trough slides into Northern Idaho, the
     flow aloft will turn west-northwesterly this afternoon. 
     Weak subsidence aloft will slightly warm the air mass this
     afternoon.  Valley temperatures should top out near 80
     degrees with afternoon sunshine.  Transport winds were
     northeasterly this morning and will turn northerly this
     afternoon with a slight northwesterly component possible in
     the north valley. 

     Mixing heights should climb to near 3000 feet after about 2
     pm.  Daytime heating will probably not alleviate the
     significant gradient-stacking and Medford-Draw conditions,
     and transport winds will be mostly northerly.  That makes
     open burning unlikely this afternoon.

Surface Winds:
     NW 5-10 this morning, N 8-15 this afternoon.
Transport Winds:
     NNE 10 this morning, N 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4700 feet.  Ventilation index 47.
High Temperature:
     Salem\'s high temperature today will be near 80.
Humidities:
     Relative humidity drops to 50% by 12pm.
     Minimum relative humidity will be near 31%.
Sunrise/Sunset:
     Salem sunset tonight: 8:53pm; sunrise tomorrow: 5:44am.

Extended Outlook:
     A weak upper-level low pressure area will approach the
     Northern California Coast Saturday and turn the flow aloft
     southwesterly over Oregon.  That should bring a little
     warming to the region but also a slight chance of shower or
     thundershowers to the southern mountains.

     The long-range computer models have been very inconsistent
     in their handling of the weak upper-level low pressure area
     slated to move onshore Sunday.  It appears as if it will be
     too weak to produce much in the way of shower activity but
     should maintain the onshore flow pattern across Western
     Oregon.   A westerly flow aloft is forecast Monday through
     Friday for seasonal conditions.

Tomorrow (19 Jul):  Mostly Sunny and Warmer.  Wind: N 10-20 mph.  49/84

Sun (20 Jul):  Mostly Sunny.  50/85

Mon (21 Jul):  Morning Clouds.  Mostly Sunny.  53/85

Tue (22 Jul):  Morning Clouds.  Mostly Sunny.  54/83

Wed (23 Jul):  Morning Clouds...Sunny & Warmer.  52/82

Thu (24 Jul):  Mostly Sunny.  53/84

Fri (25 Jul):  Mostly Sunny.  53/82

ODA Meteorologist
weather at oda.state.or.us