Meadow View Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Meadow View Observatory clear sky chart from 2005-11-06 to 2025-05-26.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	10% 3 1 3 2 2 2 2 4 5% 64%	118158
	Night	13% 4 1 4 3 2 3 2 4 5% 59%	119986
Transparency	Day	23% 4 7% 18% 23% 24%	117912
	Night	27% 5% 8% 17% 21% 21%	119821
Seeing	Day	11% 7% 18% 28% 27% 10%	15785
	Night	12% 4 17% 36% 27% 3	25110

By Month

Percentage Cloud Cover SW (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	22% 6% 2 4 3 3 4 3 5% 7% 41%	3639
	11th to 20th	Day	19% 6% 2 5% 3 2 2 1 3 3 55%	3990
	21st to end	Day	23% 5% 2 4 3 2 2 2 4 6% 48%	4510
February	1st to 10th	Day	21% 5% 2 3 2 3 4 3 5% 5% 48%	1800
	11th to 20th	Day	17% 6% 2 5% 3 3 4 2 4 7% 47%	1820
	21st to end	Day	17% 5% 2 3 3 3 3 2 5% 7% 49%	1650
March	1st to 10th	Day	21% 9% 3 7% 3 3 3 3 4 6% 39%	4753
	11th to 20th	Day	20% 6% 1 4 3 3 3 2 4 6% 47%	5000
	21st to end	Day	17% 8% 2 5% 4 4 4 3 6% 7% 40%	5633
April	1st to 10th	Day	13% 6% 2 5% 4 3 4 3 5% 8% 48%	2400
	11th to 20th	Day	12% 4 1 4 3 2 2 4 5% 5% 57%	2369
	21st to end	Day	6% 3 2 3 2 3 3 3 5% 7% 63%	2400
May	1st to 10th	Day	6% 2 1 2 2 2 2 2 3 5% 73%	4140
	11th to 20th	Day	3 2 1 2 1 1 1 2 3 5% 79%	4516
	21st to end	Day	3 2 1 2 2 2 2 2 4 5% 76%	4886
June	1st to 10th	Day	5% 3 1 2 2 2 3 3 5% 8% 64%	2660
	11th to 20th	Day	2 1 2 2 2 2 2 3 5% 79%	2660
	21st to end	Day	2 1 1 1 1 1 2 1 2 3 84%	2660
July	1st to 10th	Day	1 1 1 1 1 2 93%	4420
	11th to 20th	Day	1 1 1 1 1 1 1 2 3 86%	4420
	21st to end	Day	1 1 1 1 1 1 2 2 90%	4463
August	1st to 10th	Day	2 2 1 2 2 1 2 3 4 5% 77%	4091
	11th to 20th	Day	1 1 1 1 1 1 2 3 90%	3882
	21st to end	Day	1 1 1 1 1 1 1 1 2 2 89%	4180
September	1st to 10th	Day	1 1 1 1 1 1 1 2 3 88%	2280
	11th to 20th	Day	3 2 1 3 2 2 3 2 3 5% 76%	2280
	21st to end	Day	3 1 2 1 1 1 2 3 5% 81%	2024
October	1st to 10th	Day	3 2 2 2 2 2 2 3 4 78%	3180
	11th to 20th	Day	6% 2 1 3 2 2 2 2 4 6% 70%	3161
	21st to end	Day	6% 3 1 4 3 3 4 3 6% 8% 58%	3448
November	1st to 10th	Day	14% 4 1 4 2 3 3 3 5% 7% 55%	1821
	11th to 20th	Day	15% 4 1 5% 3 3 4 3 5% 8% 49%	1770
	21st to end	Day	14% 4 1 4 3 3 4 3 4 6% 54%	1600
December	1st to 10th	Day	12% 3 1 3 2 3 3 2 5% 5% 60%	2620
	11th to 20th	Day	31% 6% 2 5% 4 4 3 3 5% 8% 29%	3028
	21st to end	Day	33% 7% 2 5% 3 3 3 2 4 6% 31%	4004
January	1st to 10th	Night	15% 6% 2 6% 4 4 4 4 6% 8% 42%	6306
	11th to 20th	Night	19% 4 1 4 2 2 2 2 4 4 55%	5968
	21st to end	Night	21% 6% 2 5% 3 3 3 2 3 5% 47%	6468
February	1st to 10th	Night	20% 4 1 4 3 3 3 3 5% 6% 49%	2600
	11th to 20th	Night	16% 5% 2 4 3 4 3 4 5% 7% 47%	2467
	21st to end	Night	16% 5% 2 4 4 3 3 3 4 6% 50%	1980
March	1st to 10th	Night	18% 9% 3 7% 4 4 3 3 4 7% 40%	5139
	11th to 20th	Night	22% 6% 2 5% 2 2 2 2 4 5% 48%	5000
	21st to end	Night	19% 8% 3 6% 4 3 4 3 5% 7% 38%	5341
April	1st to 10th	Night	10% 5% 2 5% 4 4 4 4 6% 9% 48%	2000
	11th to 20th	Night	10% 5% 1 4 3 3 3 2 4 7% 58%	1979
	21st to end	Night	7% 4 2 3 2 2 3 3 4 6% 64%	2000
May	1st to 10th	Night	5% 4 2 4 3 2 2 2 4 5% 67%	3049
	11th to 20th	Night	2 2 1 2 2 2 3 2 3 5% 75%	2596
	21st to end	Night	3 3 1 2 2 2 2 2 3 5% 74%	2805
June	1st to 10th	Night	5% 3 1 4 3 3 3 3 5% 9% 61%	1520
	11th to 20th	Night	2 1 2 2 2 2 2 3 6% 78%	1520
	21st to end	Night	1 1 1 2 1 1 2 2 3 3 82%	1520
July	1st to 10th	Night	1 1 1 1 1 2 93%	2540
	11th to 20th	Night	1 2 1 2 1 1 1 1 2 2 85%	2540
	21st to end	Night	1 1 1 1 1 1 2 3 88%	3098
August	1st to 10th	Night	3 2 1 2 2 2 2 2 4 3 76%	2848
	11th to 20th	Night	1 1 1 1 1 2 2 91%	2962
	21st to end	Night	2 1 1 1 1 1 1 2 89%	3498
September	1st to 10th	Night	1 1 1 1 1 1 1 2 3 88%	1900
	11th to 20th	Night	3 2 1 2 2 2 2 2 3 5% 76%	1900
	21st to end	Night	3 1 1 1 1 2 1 4 5% 80%	2150
October	1st to 10th	Night	3 1 1 2 2 2 2 1 3 3 80%	3800
	11th to 20th	Night	4 2 1 2 1 2 2 2 4 5% 75%	3777
	21st to end	Night	8% 2 1 3 2 2 4 2 5% 6% 64%	4121
November	1st to 10th	Night	13% 4 1 3 2 3 4 3 5% 7% 55%	2478
	11th to 20th	Night	13% 4 1 4 3 3 3 4 6% 8% 52%	2628
	21st to end	Night	14% 5% 2 4 2 3 3 3 4 5% 55%	2800
December	1st to 10th	Night	12% 3 1 3 2 2 3 2 5% 7% 61%	4560
	11th to 20th	Night	32% 6% 2 4 3 4 5% 4 5% 8% 27%	5176
	21st to end	Night	32% 6% 2 6% 4 3 3 3 3 5% 33%	6952

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	43% 7% 12% 22% 11% 5%	3639
	11th to 20th	Day	37% 4 5% 16% 23% 13%	3990
	21st to end	Day	39% 5% 8% 13% 19% 15%	4510
February	1st to 10th	Day	38% 5% 11% 18% 19% 9%	1800
	11th to 20th	Day	37% 6% 9% 20% 21% 7%	1829
	21st to end	Day	34% 5% 11% 26% 17% 7%	1650
March	1st to 10th	Day	46% 7% 7% 20% 17% 3	4753
	11th to 20th	Day	39% 4 9% 23% 16% 8%	5000
	21st to end	Day	40% 9% 13% 24% 12% 2	5633
April	1st to 10th	Day	34% 6% 11% 23% 19% 6%	2400
	11th to 20th	Day	28% 5% 11% 23% 23% 10%	2372
	21st to end	Day	21% 5% 13% 29% 24% 8%	2400
May	1st to 10th	Day	15% 4 11% 24% 26% 21%	4140
	11th to 20th	Day	11% 3 7% 22% 35% 23%	4519
	21st to end	Day	11% 4 12% 31% 29% 13%	4887
June	1st to 10th	Day	18% 6% 11% 25% 26% 15%	2660
	11th to 20th	Day	8% 3 9% 20% 32% 27%	2660
	21st to end	Day	8% 2 4 13% 32% 42%	2660
July	1st to 10th	Day	3 1 2 6% 16% 73%	4351
	11th to 20th	Day	7% 1 2 7% 18% 65%	4345
	21st to end	Day	3 1 1 6% 28% 60%	4322
August	1st to 10th	Day	10% 2 2 7% 26% 52%	4076
	11th to 20th	Day	4 1 1 10% 41% 43%	3921
	21st to end	Day	5% 1 3 14% 38% 39%	4179
September	1st to 10th	Day	4 1 3 8% 26% 57%	2280
	11th to 20th	Day	12% 3 6% 21% 36% 22%	2280
	21st to end	Day	10% 2 6% 20% 30% 33%	2024
October	1st to 10th	Day	12% 3 3 12% 23% 47%	3180
	11th to 20th	Day	17% 3 5% 24% 30% 22%	3161
	21st to end	Day	23% 4 7% 22% 30% 14%	3448
November	1st to 10th	Day	28% 5% 11% 23% 20% 14%	1821
	11th to 20th	Day	34% 7% 11% 22% 17% 9%	1770
	21st to end	Day	31% 6% 9% 20% 21% 14%	1600
December	1st to 10th	Day	26% 4 6% 24% 28% 12%	2620
	11th to 20th	Day	55% 4 11% 16% 11% 3	3028
	21st to end	Day	53% 7% 12% 18% 8% 2	4004
January	1st to 10th	Night	39% 7% 17% 18% 13% 6%	6306
	11th to 20th	Night	34% 7% 7% 15% 23% 14%	5968
	21st to end	Night	42% 5% 7% 8% 17% 20%	6468
February	1st to 10th	Night	36% 5% 9% 21% 17% 13%	2600
	11th to 20th	Night	35% 5% 9% 20% 22% 8%	2469
	21st to end	Night	35% 5% 9% 23% 20% 8%	1980
March	1st to 10th	Night	42% 9% 11% 19% 14% 5%	5139
	11th to 20th	Night	38% 5% 9% 20% 19% 9%	5000
	21st to end	Night	43% 8% 13% 22% 12% 3	5341
April	1st to 10th	Night	31% 6% 14% 22% 19% 8%	2000
	11th to 20th	Night	25% 6% 12% 25% 20% 12%	1979
	21st to end	Night	21% 5% 13% 27% 26% 8%	2000
May	1st to 10th	Night	15% 7% 11% 17% 29% 21%	3049
	11th to 20th	Night	12% 4 9% 19% 32% 24%	2596
	21st to end	Night	12% 5% 10% 33% 24% 16%	2805
June	1st to 10th	Night	19% 7% 12% 25% 25% 12%	1520
	11th to 20th	Night	9% 4 9% 19% 30% 29%	1520
	21st to end	Night	9% 2 4 13% 29% 42%	1520
July	1st to 10th	Night	3 1 2 7% 14% 74%	2500
	11th to 20th	Night	9% 1 2 6% 17% 65%	2492
	21st to end	Night	5% 1 1 7% 26% 60%	3001
August	1st to 10th	Night	14% 2 2 8% 24% 51%	2839
	11th to 20th	Night	4 2 2 9% 36% 48%	2989
	21st to end	Night	6% 1 2 11% 35% 44%	3498
September	1st to 10th	Night	5% 2 2 7% 27% 58%	1900
	11th to 20th	Night	12% 3 6% 17% 36% 26%	1900
	21st to end	Night	9% 2 5% 16% 31% 37%	2150
October	1st to 10th	Night	12% 2 3 10% 18% 54%	3800
	11th to 20th	Night	14% 3 7% 23% 30% 24%	3777
	21st to end	Night	20% 3 5% 23% 28% 20%	4121
November	1st to 10th	Night	28% 6% 10% 23% 17% 16%	2478
	11th to 20th	Night	29% 7% 14% 22% 19% 10%	2628
	21st to end	Night	31% 5% 7% 21% 22% 14%	2800
December	1st to 10th	Night	25% 3 8% 24% 23% 17%	4560
	11th to 20th	Night	55% 4 9% 16% 13% 3	5176
	21st to end	Night	55% 6% 10% 14% 11% 3	6952

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	41% 8% 15% 22% 15% 1	200
	11th to 20th	Day	23% 9% 19% 28% 14% 7%	355
	21st to end	Day	21% 5% 20% 23% 23% 7%	440
February	1st to 10th	Day	25% 9% 19% 25% 18% 5%	400
	11th to 20th	Day	22% 13% 22% 24% 15% 4	428
	21st to end	Day	15% 12% 25% 28% 16% 3	414
March	1st to 10th	Day	25% 17% 25% 20% 12% 2	500
	11th to 20th	Day	26% 9% 22% 22% 15% 5%	500
	21st to end	Day	21% 15% 23% 25% 13% 3	550
April	1st to 10th	Day	17% 13% 25% 24% 16% 5%	500
	11th to 20th	Day	14% 12% 24% 25% 19% 6%	492
	21st to end	Day	7% 12% 21% 30% 23% 7%	500
May	1st to 10th	Day	7% 9% 34% 25% 20% 6%	503
	11th to 20th	Day	8% 9% 20% 25% 25% 12%	528
	21st to end	Day	4 8% 19% 28% 30% 11%	550
June	1st to 10th	Day	5% 7% 18% 28% 32% 10%	490
	11th to 20th	Day	4 6% 20% 34% 29% 7%	490
	21st to end	Day	1 3 15% 35% 33% 13%	490
July	1st to 10th	Day	1 2 10% 36% 39% 12%	486
	11th to 20th	Day	1 8% 33% 43% 14%	484
	21st to end	Day	1 6% 34% 45% 14%	531
August	1st to 10th	Day	2 1 12% 30% 40% 15%	487
	11th to 20th	Day	1 2 10% 27% 41% 18%	477
	21st to end	Day	2 1 9% 29% 45% 15%	539
September	1st to 10th	Day	1 2 10% 31% 43% 14%	490
	11th to 20th	Day	4 4 18% 28% 32% 14%	490
	21st to end	Day	3 4 19% 34% 30% 11%	490
October	1st to 10th	Day	4 7% 20% 25% 30% 15%	490
	11th to 20th	Day	8% 6% 18% 24% 31% 14%	490
	21st to end	Day	12% 7% 20% 27% 24% 10%	539
November	1st to 10th	Day	16% 7% 18% 23% 25% 11%	357
	11th to 20th	Day	15% 5% 16% 29% 23% 11%	285
	21st to end	Day	15% 6% 20% 27% 26% 8%	200
December	1st to 10th	Day	23% 6% 20% 22% 15% 15%	200
	11th to 20th	Day	28% 4 19% 26% 17% 8%	200
	21st to end	Day	24% 9% 19% 24% 20% 3	220
January	1st to 10th	Night	22% 5% 17% 35% 19% 2	800
	11th to 20th	Night	21% 5% 15% 39% 18% 2	800
	21st to end	Night	19% 4 19% 35% 21% 3	880
February	1st to 10th	Night	21% 4 17% 38% 19% 2	800
	11th to 20th	Night	18% 7% 20% 33% 20% 2	784
	21st to end	Night	18% 5% 24% 37% 14% 1	660
March	1st to 10th	Night	22% 10% 20% 30% 16% 3	800
	11th to 20th	Night	21% 7% 19% 28% 22% 2	800
	21st to end	Night	19% 9% 23% 33% 16% 1	880
April	1st to 10th	Night	12% 8% 27% 34% 18% 2	800
	11th to 20th	Night	12% 7% 23% 34% 21% 3	791
	21st to end	Night	8% 6% 22% 37% 24% 3	800
May	1st to 10th	Night	7% 6% 30% 32% 23% 1	660
	11th to 20th	Night	5% 4 23% 39% 27% 2	394
	21st to end	Night	5% 8% 19% 40% 27% 1	422
June	1st to 10th	Night	7% 3 19% 43% 27% 2	380
	11th to 20th	Night	1 4 22% 48% 24% 1	380
	21st to end	Night	2 2 17% 46% 31% 2	380
July	1st to 10th	Night	1 11% 48% 36% 2	370
	11th to 20th	Night	1 1 13% 50% 34% 2	368
	21st to end	Night	1 7% 39% 49% 4	613
August	1st to 10th	Night	2 2 9% 38% 47% 3	567
	11th to 20th	Night	1 1 9% 42% 44% 5%	649
	21st to end	Night	1 1 6% 38% 51% 3	836
September	1st to 10th	Night	1 1 8% 38% 48% 4	760
	11th to 20th	Night	4 2 11% 39% 38% 7%	760
	21st to end	Night	4 3 14% 36% 36% 8%	760
October	1st to 10th	Night	5% 4 17% 35% 33% 6%	760
	11th to 20th	Night	7% 3 15% 34% 36% 5%	760
	21st to end	Night	9% 4 15% 36% 29% 7%	836
November	1st to 10th	Night	14% 6% 14% 32% 30% 4	780
	11th to 20th	Night	14% 2 19% 39% 24% 2	800
	21st to end	Night	15% 4 17% 39% 22% 3	800
December	1st to 10th	Night	21% 4 14% 35% 22% 4	800
	11th to 20th	Night	29% 4 16% 30% 20% 2	800
	21st to end	Night	25% 6% 19% 33% 16% 1	880

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