[willamette-fcst] Forecast - Monday, July 13th, 2009

[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: 
     Monday, July 13th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 12:00pm until 7:00pm.
     Preparatory burning is not allowed.
     Propane flaming is not allowed.
     Stack burning is not allowed.

Weather Discussion:
     An impressively moist upper-level low pressure system moved
     onto the central Oregon Coast Sunday morning, across the
     central Willamette Valley Sunday afternoon and evening.  It
     continued to track northeastward overnight and was centered
     over northeastern Oregon this morning.  Significant rainfall
     accompanied this system, with numerous showers and
     thundershowers dropping between one-quarter and
     three-quarters of an inch across the Willamette Valley.

     Doppler radar showed the shower activity had mostly moved
     mostly east of the Cascades by mid-morning, with the
     greatest concentration near and north of the low-pressure
     center, over eastern Washington, northern Idaho, western
     Montana, and extreme northeastern Oregon.  Satellite imagery
     showed a blanket of low clouds continuing to cover most of
     western Oregon, from the coast to the creast of the
     Cascades.  The only areas in Oregon seeing much sunshine
     were the extreme southwestern and south-central sections of
     the state.

     The upper-level trough is forecast to continue moving
     northeastward today, to over cenral Montana by this evening.
     The flow aloft over western Oregon had already turned
     northwesterly by 5am, when the Salem sounding was taken. 
     The ODA surface analysis showed high pressure building into
     the central Oregon Coast, with southerly winds in the
     Willamette Valley and onshore flow extending eastward into
     Idaho.  Onshore gradients were stronger over eastern Oregon
     than across western Oregon...indicating that the air aloft
     over the Willamette Valley was beginning to sink and warm.

     As an upper-level ridge moves onshore this afternoon,
     sinking northwesterly flow flow aloft should gradually clear
     the skies over western Oregon with high temperatures
     recoving into the mid 70s (Highs Sunday only reached the mid
     60s).  Southerly surface winds should veer to northwesterly
     by late this afternoon.  More clearing tonight will combine
     with the cool air mass over the region to locally drop
     Willamette Valley temperatures into the 40s.

Surface Winds:
     S 5-10 this morning, NW 5-12 this afternoon.
Transport Winds:
     SW 10 this morning, W 8 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4300 feet.  Ventilation index 43.
High Temperature:
     Salem\'s high temperature today will be near 75.
Humidities:
     Relative humidity drops to 50% by 2pm.
     Minimum relative humidity will be near 43%.
Sunrise/Sunset:
     Salem sunset tonight: 8:57pm; sunrise tomorrow: 5:39am.

Extended Outlook:
     The upper-level ridge will build close to the coastline
     Tuesday, with a dry northwesterly flow aloft and increasing
     northerly winds at the surface.  That will aid in the drying
     of damp fields across the Willamette Valley.  Patchy morning
     clouds should quickly give way to sunny skies with high
     temperatures recovering to near-normal.

     In a change from what was advertised last week by the
     long-range computer models, the upper-level ridge is now
     forecast to shift only slightly eastward Wednesday and
     Thursday, with very weak southwesterly flow aloft developing
     over western Oregon.  That pattern would allow temperatures
     to continue warming slightly, as surface winds stay
     northerly.

     Friday and Saturday, southwesterly flow aloft is forecast to
     increase enough to shift the surface thermal trough into
     eastern Oregon.  That would increase the onshore flow into
     western Oregon and begin cooling temperatures.  It is too
     far out to tell when or if this pattern change may create a
     burning opportunity, but that is at least possible, late
     this week.  In the very long-range, a little stronger system
     is forecast bring increased onshore flow and more cooling
     early next week.

Tue (14 Jul):  Ppatchy AM Clouds...Sunny and Warmer.  Northerly Winds.  49/84

Wed (15 Jul):  Mostly Sunny and Warmer.  53/88

Thu (16 Jul):  Mostly Sunny and Warm.  54/89

Fri (17 Jul):  Mostly Sunny and Warm.  54/87

Sat (18 Jul):  Partly Cloudy.  Not Quite as Warm.  54/82

Sun (19 Jul):  Partly Cloudy.  54/82

Mon (20 Jul):  Partly Cloudy.  54/82

ODA Meteorologist
weather at oda.state.or.us