Here is my weekly weather quiz question for the last time. What is a “Back-building thunderstorm?”  Here is the correct answer. A Back-building Thunderstorm is a  thunderstorm in which new development takes place on the upwind side (usually the west or southwest side), such that the storm seems to remain stationary or propagate in a backward direction. I’ll have a new weekly weather quiz question for you starting Monday. 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 is being replaced by high pressure (Shaded “Arch” shape with blue arrows) and that means the rain goes away again, but there’s a slight chance of rain yet today. The low is moving eastward as the high pressure takes over for the most of long Labor Day Holiday Weekend.

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Air Quality Index:

Eugene-Springfield: The Air Quality Index is 25 in the Good category measuring Particulate Matter.

Oakridge: The Air Quality Index is 7 in the Good category measuring Particulate Matter.

Cottage Grove: The Air Quality Index is 28 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:

• Mostly cloudy with a slight (20%) chance of morning rain, possible sun breaks with a slight (20%) chance of showers this afternoon, partly cloudy tonight and Monday AM, mostly sunny and a bit warmer Monday (Labor Day), mostly clear Monday night,
• Partly cloudy in the AM, mostly sunny and warmer Tuesday afternoon, then partly cloudy at night.
• highs 73-82 lows 50-52.
• Mostly sunny and warmer Wednesday, Thursday and Friday, mostly clear each night,
• Then sunny and warmer Saturday.
• highs 82-89 lows 50-53. (seasonal averages high 80 low 49)

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Forecast for the Umpqua Basin including Roseburg:

• Mostly cloudy with a slight (20%) chance of showers today, possible sun breaks late this afternoon, partly cloudy tonight and Monday AM (Labor Day), sunny and a bit warmer in the afternoon, clear Monday night,
• Sunny and a bit warmer Tuesday, then mostly clear at night.
• highs 77-87 lows 52-54.
• Sunny and a bit warmer Wednesday, clear at night,
• Then sunny and warmer Thursday, Friday and Saturday, clear Thursday night and Friday night.
• highs 90-95 lows 55-60. (seasonal averages high 81 low 53)

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

• Mostly cloudy with a slight (20%) chance of showers today, partly cloudy tonight and Monday AM, sunny and a bit cooler Monday afternoon (Labor Day), mostly clear at night,
• Sunny and a bit warmer Tuesday, then mostly clear at night.
• highs near 66 lows 53-56.
• Mostly sunny and a bit warmer Wednesday and Thursday, mostly clear each night,
• Then sunny and a bit cooler Friday and Saturday, clear at night.
• highs 65-70 lows 56-60. (seasonal averages high 66 low 51).

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Forecast for the Cascades in Lane County:

• Partly cloudy this AM, mostly cloudy this afternoon, partly cloudy tonight,
• Mostly sunny and warmer Monday (Labor Day), mostly clear at night,
• Mostly sunny and a bit warmer Tuesday, then mostly clear at night.
• free air freezing level 10,000 ft. today, 11,000 ft. tonight and Monday, 13,000 ft. Monday night, then 14,000 ft. Tuesday and Tuesday night.
• highs 58-72 lows 38-43.
• Mostly sunny Wednesday, mostly clear at night,
• Then sunny and warmer Thursday, Friday and Saturday, clear each night.
• free air freezing level 14,000 ft. Wednesday, 15,000 ft. Wednesday night through Friday, then 16,000 ft. Friday night and Saturday.
• highs 73-80 lows 44-48.

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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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