Here is my new weekly weather quiz question. What is a “Back-building thunderstorm?” Please remember to post your answer as a comment by clicking on “no comments /comments” in the upper right hand portion of this page under the caption, then add your comment. The first person to post the correct answer will win a week of free personalized weather forecasts tailored to your needs. The answer has to be a comment to win. An email answer will not count. Good luck.

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An upper level low (Shaded “U” shape with blue arrows) that has been controlling our weather will be replaced by high pressure (Shaded “Arch” shape with blue arrows) and that means the rain goes away again, but not quite yet. The low will move southward through Oregon bring the slight chance of showers and thunderstorms Friday, then the high pressure takes over for the long Labor Day Holiday Weekend. Weather will be good, but chilly for the Duck game Saturday evening. There is a slight chance of a shower or thunderstorm though for the Beaver game Friday evening.

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Air Quality Index:

Eugene-Springfield: The Air Quality Index is 26 in the Good category measuring Particulate Matter.

Oakridge: The Air Quality Index is 5 in the Good category measuring Particulate Matter.

Cottage Grove: The Air Quality Index is 25 in the Good category measuring Particulate Matter.

Data courtesy of Lane Regional Air Protection Agency (LRAPA).

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Advisories:

• A HEALTH ADVISORY CONTINUES FOR SUNSET BAY STATE PARK BEACH LOCATED IN COOS COUNTY FOR HIGHER-THAN-NORMAL FECAL BACTERIA WHICH CAN RESULT IN DIARRHEA, STOMACH CRAMPS, SKIN RASHES, UPPER RESPIRATORY INFECTIONS AND OTHER ILLNESSES. DIRECT CONTACT WITH THE WATER – ESPECIALLY BY CHILDREN AND THE ELDERLY, WHO MAY BE VULNERABLE TO WATERBORNE BACTERIA – SHOULD BE AVOIDED IN THIS AREA UNTIL THE ADVISORY IS LIFTED. VISITORS SHOULD AVOID WADING IN NEARBY CREEKS, POOLS OF WATER ON THE BEACH, OR IN DISCOLORED WATER AND STAY CLEAR OF WATER RUNOFF FLOWING INTO THE OCEAN.
• A HEALTH ADVISORY CONTINUES FOR UPPER KLAMATH LAKE AND AGENCY LAKE DOWN TO KENO DAM, LOCATED JUST NORTH OF KLAMATH FALLS ALONG HIGHWAY 97 IN KLAMATH COUNTY. WATER MONITORING BY THE USGS HAS CONFIRMED THE PRESENCE OF BLUE-GREEN ALGAE TOXINS WHICH CAN BE HARMFUL TO HUMANS AND ANIMALS. SWALLOWING, INHALING OR SKIN CONTACT WITH WATER DROPLETS SHOULD BE AVOIDED.

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Forecast for the Southern and lower Mid Willamette Valley including Eugene-Springfield and Albany-Corvallis:

• Partly cloudy tonight,
• A mix of clouds and sun Friday with a slight (20%) chance of AM showers, a slight (20%) chance of showers and thunderstorms in the afternoon, partly cloudy with a slight (20%) chance of showers and thunderstorms in the evening, partly cloudy late Friday night and Saturday AM, mostly sunny and warmer in the afternoon, partly cloudy Saturday night,
• A mix of clouds and sun with a slight (20%) chance of showers Sunday afternoon, mostly cloudy in the evening, then partly cloudy late Sunday night.
• lows 46-50 highs 70-75.
• Partly cloudy in the AM, mostly sunny and a bit warmer Monday afternoon (Labor Day), partly cloudy Monday night through Wednesday AM, mostly sunny in the afternoon, mostly clear at night,
• Mostly sunny Thursday AM, then partly cloudy and a bit cooler in the afternoon.
• highs 77-83 cooling to 82 Thursday lows 48-53. (seasonal averages high 80 low 49)

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Forecast for the Umpqua Basin including Roseburg:

• Mostly clear this evening, partly cloudy late tonight,
• Mostly cloudy with a slight (20%) chance of showers Friday AM, a (30%) chance of showers and a slight (20%) chance of afternoon thunderstorms,  partly cloudy with a slight (20%) chance of showers and thunderstorms in the evening, mostly cloudy with a slight (20%) chance of showers late Friday night,
• Partly cloudy in the AM, sunny and warmer Saturday afternoon, mostly clear Saturday night,
• Partly cloudy and  warmer Sunday, then mostly clear at night.
• lows 48-54 highs 70-80.
• Mostly sunny Monday (Labor Day), mostly clear Monday night,
• Mostly sunny and a bit warmer Tuesday and Wednesday, mostly clear at night,
• Then sunny and a bit warmer Thursday.
• highs 82-88 lows 52-57. (seasonal averages high 82 low 54)

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Forecast for the South Oregon Coast including Coos Bay and North Bend:

• Mostly clear this evening, mostly cloudy late tonight,
• Mostly cloudy with a slight (20%) chance of AM showers, partly cloudy with a slight (20%) chance of showers Friday afternoon, partly cloudy in the evening with a slight (20%) chance of showers, just partly cloudy late Friday night and Saturday AM, sunny in the afternoon, mostly clear in the evening, then partly cloudy Saturday night through Sunday night.
• lows 52-54 highs 64-66.
• Partly cloudy in the AM, sunny Monday afternoon (Labor Day), clear at night,
• Sunny Tuesday, mostly clear at night,
• Mostly sunny Wednesday, clear Wednesday night,
• Then sunny and a bit warmer Thursday.
• highs 65-70 lows 54-56. (seasonal averages high 66 low 52).

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Forecast for the Cascades in Lane County:

• Partly cloudy tonight,
• A mix of clouds and sun Friday with a slight (20%) chance of AM showers, showers and a slight (20%) chance of thunderstorms Friday afternoon (0.25 in. of rain possible, more in storms), mostly cloudy with a good (50%) chance of showers and a slight (20%) chance of showers and thunderstorms in the evening, partly cloudy with a good (50%) chance of showers late Friday night,
  Then partly cloudy and warmer Saturday through Sunday night.
• free air freezing level 8,000 ft. tonight, snow level 6,500 ft. Friday and Friday night, free air freezing level 7,500 ft. Saturday, 9,000 ft. Saturday night, 10,000 ft. Sunday, then 11,000 ft. Sunday night.
• lows 34-40 highs 52-64.
• Partly cloudy in the AM, mostly sunny and warmer Monday afternoon (Labor Day), mostly clear Monday night,
• Mostly sunny and a bit warmer Tuesday, Wednesday and Thursday, partly cloudy Tuesday night, mostly clear Wednesday night.
• free air freezing level 9,000 ft. Monday, 10,000 ft. Monday night, 11,000 ft. Tuesday and Tuesday night, then 12,000 ft. Wednesday through Thursday.
• highs 66-70 lows 43-49.

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**Because weather forecasting is a combination of science, intuition, and timing there can be no absolute guarantees that individual forecasts will be 100% accurate. Nature is in a constant state of flux and sudden unexpected weather events can happen.

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Get your local Eugene-Springfield and Lane County news on-line at eugenedailynews.com.

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