MIRA Weaver Student Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the MIRA Weaver Student Observatory clear sky chart from 2005-11-06 to 2026-03-03.

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	5% 7% 3 6% 4 4 4 3 6% 10% 49%	139575
	Night	7% 11% 3 7% 4 4 3 3 4 6% 48%	139077
Transparency	Day	24% 6% 10% 20% 24% 16%	134533
	Night	30% 8% 11% 16% 21% 14%	135104
Seeing	Day	9% 3 10% 27% 36% 15%	17182
	Night	14% 3 8% 27% 34% 15%	26710

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	10% 6% 2 5% 4 4 4 3 5% 7% 49%	5142
	11th to 20th	Day	7% 4 2 5% 3 3 3 3 4 5% 59%	5340
	21st to end	Day	10% 8% 3 7% 4 4 4 4 5% 7% 43%	5843
February	1st to 10th	Day	13% 7% 2 4 4 4 4 4 4 6% 48%	1890
	11th to 20th	Day	11% 8% 3 5% 4 4 5% 4 5% 7% 44%	1988
	21st to end	Day	10% 6% 3 6% 4 4 4 3 5% 7% 47%	1730
March	1st to 10th	Day	10% 8% 3 8% 5% 5% 6% 5% 7% 9% 33%	4862
	11th to 20th	Day	10% 5% 2 6% 4 4 4 3 5% 7% 50%	5000
	21st to end	Day	8% 8% 3 7% 4 5% 5% 5% 7% 9% 38%	5604
April	1st to 10th	Day	8% 7% 2 6% 4 3 4 3 5% 7% 49%	2400
	11th to 20th	Day	7% 8% 2 7% 4 4 3 3 4 7% 50%	2369
	21st to end	Day	5% 9% 3 5% 3 3 3 4 6% 9% 51%	2400
May	1st to 10th	Day	5% 4 1 3 2 2 2 2 4 8% 66%	5440
	11th to 20th	Day	3 5% 2 5% 3 2 3 3 5% 10% 58%	5914
	21st to end	Day	4 11% 3 7% 4 4 4 3 5% 10% 46%	6902
June	1st to 10th	Day	4 9% 3 6% 4 4 4 3 6% 9% 48%	2800
	11th to 20th	Day	3 6% 2 4 3 3 3 3 5% 11% 59%	2800
	21st to end	Day	3 7% 2 5% 3 3 4 3 6% 11% 53%	2800
July	1st to 10th	Day	1 5% 2 5% 3 3 4 4 7% 12% 55%	6243
	11th to 20th	Day	1 8% 4 7% 4 3 4 3 7% 16% 41%	5880
	21st to end	Day	1 17% 4 9% 5% 5% 5% 4 7% 14% 31%	6402
August	1st to 10th	Day	2 7% 4 8% 4 3 4 4 9% 16% 38%	5777
	11th to 20th	Day	2 9% 3 5% 3 2 3 3 7% 14% 49%	5407
	21st to end	Day	1 6% 3 6% 3 3 3 3 7% 13% 52%	5984
September	1st to 10th	Day	2 5% 1 4 3 3 3 3 5% 10% 62%	2400
	11th to 20th	Day	4 9% 2 4 3 4 3 3 6% 11% 52%	2400
	21st to end	Day	3 4 2 4 2 3 3 3 5% 9% 64%	2135
October	1st to 10th	Day	2 3 1 3 2 3 2 3 5% 9% 67%	3280
	11th to 20th	Day	3 8% 2 6% 4 3 3 3 4 7% 58%	3261
	21st to end	Day	3 5% 1 4 3 3 4 3 6% 7% 61%	3558
November	1st to 10th	Day	7% 4 1 4 3 3 4 3 5% 9% 56%	2033
	11th to 20th	Day	8% 7% 2 6% 4 3 4 2 5% 7% 52%	1890
	21st to end	Day	9% 5% 2 4 3 3 3 3 4 8% 57%	1801
December	1st to 10th	Day	6% 4 2 6% 4 3 3 3 6% 8% 55%	2700
	11th to 20th	Day	13% 8% 3 7% 5% 5% 4 4 4 7% 40%	3108
	21st to end	Day	15% 10% 3 8% 5% 4 4 4 5% 7% 34%	4092
January	1st to 10th	Night	11% 7% 3 7% 4 3 3 3 5% 7% 49%	7757
	11th to 20th	Night	8% 5% 2 5% 3 3 4 3 5% 8% 54%	7650
	21st to end	Night	11% 10% 3 9% 4 4 3 3 5% 7% 40%	8371
February	1st to 10th	Night	12% 8% 3 5% 4 3 4 3 4 5% 49%	2730
	11th to 20th	Night	12% 9% 3 7% 4 4 4 4 5% 7% 42%	2519
	21st to end	Night	11% 8% 2 5% 4 4 3 3 5% 7% 48%	2076
March	1st to 10th	Night	16% 13% 3 9% 5% 4 4 4 4 5% 33%	5060
	11th to 20th	Night	10% 7% 3 7% 5% 4 4 3 4 6% 47%	5000
	21st to end	Night	13% 11% 3 8% 5% 4 4 3 5% 6% 38%	5369
April	1st to 10th	Night	9% 8% 3 5% 4 4 3 4 5% 7% 48%	2000
	11th to 20th	Night	9% 9% 2 5% 3 3 3 3 5% 6% 52%	1979
	21st to end	Night	5% 8% 3 5% 4 3 3 3 5% 9% 53%	2000
May	1st to 10th	Night	3 6% 2 6% 3 3 3 2 4 5% 62%	4546
	11th to 20th	Night	2 13% 6% 9% 4 4 4 2 3 6% 45%	3989
	21st to end	Night	4 12% 2 7% 4 3 3 1 3 4 56%	3972
June	1st to 10th	Night	5% 13% 3 6% 4 3 3 3 4 6% 50%	1600
	11th to 20th	Night	3 9% 2 6% 3 3 3 2 4 6% 58%	1600
	21st to end	Night	3 10% 2 7% 3 4 3 2 4 7% 55%	1600
July	1st to 10th	Night	11% 3 8% 4 4 3 2 4 5% 55%	3701
	11th to 20th	Night	1 20% 9% 11% 4 4 3 2 4 5% 36%	4100
	21st to end	Night	2 40% 3 12% 3 3 3 2 3 5% 24%	4472
August	1st to 10th	Night	2 16% 8% 16% 4 4 4 3 5% 5% 34%	4035
	11th to 20th	Night	2 16% 4 10% 3 3 3 2 4 4 50%	4458
	21st to end	Night	2 12% 4 8% 4 4 4 2 4 6% 49%	5015
September	1st to 10th	Night	3 8% 3 5% 3 4 3 3 5% 7% 57%	2000
	11th to 20th	Night	4 11% 3 6% 3 4 3 2 4 8% 52%	2000
	21st to end	Night	3 7% 2 4 3 2 3 2 4 7% 62%	2259
October	1st to 10th	Night	3 4 2 3 2 2 2 2 3 5% 70%	3920
	11th to 20th	Night	4 14% 2 7% 3 3 3 2 3 5% 53%	3897
	21st to end	Night	4 7% 2 4 3 3 3 2 4 6% 61%	4253
November	1st to 10th	Night	7% 7% 2 5% 3 4 3 3 5% 7% 56%	2483
	11th to 20th	Night	9% 7% 2 6% 4 3 3 3 5% 8% 51%	2730
	21st to end	Night	7% 5% 2 4 3 3 3 3 5% 6% 57%	2814
December	1st to 10th	Night	7% 4 1 4 3 3 4 3 5% 7% 59%	4700
	11th to 20th	Night	13% 9% 3 8% 4 4 5% 4 7% 8% 35%	5316
	21st to end	Night	16% 9% 4 9% 5% 6% 5% 4 5% 6% 31%	7106

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	32% 9% 14% 25% 16% 4	5143
	11th to 20th	Day	27% 5% 7% 11% 21% 29%	5340
	21st to end	Day	37% 7% 7% 16% 22% 11%	5843
February	1st to 10th	Day	37% 6% 8% 18% 19% 12%	1890
	11th to 20th	Day	38% 8% 11% 18% 17% 7%	1998
	21st to end	Day	37% 8% 9% 22% 18% 6%	1730
March	1st to 10th	Day	40% 13% 12% 16% 17% 2	4862
	11th to 20th	Day	31% 8% 13% 29% 12% 8%	5000
	21st to end	Day	36% 14% 16% 22% 11% 1	5604
April	1st to 10th	Day	35% 8% 13% 25% 16% 4	2400
	11th to 20th	Day	33% 7% 12% 25% 17% 6%	2372
	21st to end	Day	28% 8% 14% 26% 20% 4	2400
May	1st to 10th	Day	16% 5% 10% 29% 32% 9%	5440
	11th to 20th	Day	14% 5% 10% 33% 29% 8%	5917
	21st to end	Day	21% 8% 12% 25% 29% 4	6904
June	1st to 10th	Day	25% 8% 12% 25% 24% 7%	2800
	11th to 20th	Day	15% 4 11% 23% 32% 16%	2800
	21st to end	Day	14% 4 5% 18% 32% 27%	2800
July	1st to 10th	Day	7% 4 6% 12% 22% 49%	6176
	11th to 20th	Day	12% 6% 9% 7% 25% 41%	5811
	21st to end	Day	19% 7% 12% 22% 24% 16%	6217
August	1st to 10th	Day	13% 4 11% 14% 32% 26%	4206
	11th to 20th	Day	8% 3 8% 15% 40% 26%	3911
	21st to end	Day	12% 4 8% 13% 35% 29%	4311
September	1st to 10th	Day	12% 3 4 14% 28% 40%	2400
	11th to 20th	Day	18% 4 9% 23% 30% 16%	2400
	21st to end	Day	14% 4 7% 23% 33% 19%	2135
October	1st to 10th	Day	14% 3 7% 13% 28% 36%	3280
	11th to 20th	Day	20% 5% 10% 21% 28% 16%	3261
	21st to end	Day	19% 4 8% 23% 29% 16%	3558
November	1st to 10th	Day	25% 6% 11% 21% 25% 12%	2033
	11th to 20th	Day	31% 6% 12% 18% 23% 10%	1890
	21st to end	Day	27% 6% 10% 17% 27% 13%	1801
December	1st to 10th	Day	26% 5% 8% 20% 33% 9%	2700
	11th to 20th	Day	41% 8% 12% 17% 14% 8%	3108
	21st to end	Day	46% 10% 13% 18% 9% 4	4092
January	1st to 10th	Night	34% 10% 15% 21% 17% 3	7757
	11th to 20th	Night	27% 7% 10% 10% 25% 21%	7650
	21st to end	Night	39% 8% 7% 15% 19% 12%	8371
February	1st to 10th	Night	37% 7% 9% 15% 19% 13%	2730
	11th to 20th	Night	39% 8% 10% 16% 19% 6%	2520
	21st to end	Night	36% 8% 10% 25% 15% 6%	2076
March	1st to 10th	Night	50% 9% 10% 15% 13% 2	5060
	11th to 20th	Night	34% 9% 12% 22% 15% 7%	5000
	21st to end	Night	42% 13% 15% 19% 10% 2	5369
April	1st to 10th	Night	33% 10% 14% 23% 14% 5%	2000
	11th to 20th	Night	33% 8% 12% 24% 16% 6%	1979
	21st to end	Night	28% 11% 14% 24% 19% 5%	2000
May	1st to 10th	Night	19% 13% 11% 20% 27% 10%	4543
	11th to 20th	Night	22% 8% 17% 22% 23% 8%	3990
	21st to end	Night	24% 12% 10% 21% 29% 4	3972
June	1st to 10th	Night	30% 9% 11% 20% 22% 9%	1600
	11th to 20th	Night	20% 7% 11% 14% 30% 19%	1600
	21st to end	Night	16% 4 6% 14% 31% 30%	1600
July	1st to 10th	Night	11% 7% 12% 9% 18% 43%	3660
	11th to 20th	Night	24% 10% 14% 7% 13% 31%	4046
	21st to end	Night	40% 13% 10% 9% 15% 14%	4345
August	1st to 10th	Night	19% 6% 24% 11% 20% 20%	2929
	11th to 20th	Night	15% 3 9% 8% 37% 27%	3221
	21st to end	Night	18% 4 9% 12% 32% 25%	3608
September	1st to 10th	Night	17% 3 5% 11% 24% 39%	2000
	11th to 20th	Night	21% 6% 8% 18% 28% 18%	2000
	21st to end	Night	16% 4 7% 17% 35% 20%	2259
October	1st to 10th	Night	13% 3 6% 14% 25% 38%	3920
	11th to 20th	Night	25% 10% 6% 18% 25% 16%	3897
	21st to end	Night	20% 5% 6% 24% 28% 17%	4253
November	1st to 10th	Night	26% 6% 10% 20% 24% 15%	2483
	11th to 20th	Night	31% 6% 12% 20% 22% 9%	2730
	21st to end	Night	27% 7% 9% 18% 24% 15%	2814
December	1st to 10th	Night	24% 5% 7% 23% 29% 12%	4700
	11th to 20th	Night	43% 8% 10% 15% 17% 6%	5316
	21st to end	Night	50% 12% 13% 13% 8% 4	7106

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	21% 4 10% 30% 26% 10%	367
	11th to 20th	Day	14% 2 9% 27% 35% 13%	430
	21st to end	Day	13% 3 9% 31% 32% 13%	473
February	1st to 10th	Day	14% 2 14% 28% 28% 13%	430
	11th to 20th	Day	14% 7% 15% 34% 25% 6%	502
	21st to end	Day	9% 5% 14% 39% 26% 8%	446
March	1st to 10th	Day	18% 5% 17% 33% 24% 5%	509
	11th to 20th	Day	16% 5% 13% 30% 26% 10%	500
	21st to end	Day	12% 5% 19% 35% 21% 8%	550
April	1st to 10th	Day	12% 4 16% 30% 27% 9%	500
	11th to 20th	Day	10% 6% 19% 27% 27% 11%	492
	21st to end	Day	6% 3 20% 31% 26% 14%	500
May	1st to 10th	Day	7% 6% 15% 31% 32% 10%	503
	11th to 20th	Day	10% 2 15% 29% 32% 12%	528
	21st to end	Day	10% 4 12% 26% 34% 14%	573
June	1st to 10th	Day	8% 3 10% 28% 37% 14%	530
	11th to 20th	Day	6% 2 13% 30% 38% 11%	530
	21st to end	Day	7% 2 6% 24% 48% 14%	530
July	1st to 10th	Day	9% 1 4 21% 45% 20%	526
	11th to 20th	Day	6% 1 1 14% 55% 24%	524
	21st to end	Day	7% 3 2 17% 53% 19%	575
August	1st to 10th	Day	8% 2 3 23% 46% 18%	527
	11th to 20th	Day	5% 1 2 22% 48% 21%	517
	21st to end	Day	8% 2 2 16% 48% 24%	583
September	1st to 10th	Day	5% 2 4 17% 50% 22%	530
	11th to 20th	Day	8% 2 5% 27% 40% 18%	530
	21st to end	Day	6% 2 7% 21% 40% 24%	530
October	1st to 10th	Day	4 1 9% 25% 37% 23%	530
	11th to 20th	Day	7% 2 9% 24% 35% 23%	530
	21st to end	Day	8% 2 5% 28% 37% 21%	583
November	1st to 10th	Day	7% 2 7% 28% 36% 21%	509
	11th to 20th	Day	10% 4 6% 32% 32% 16%	330
	21st to end	Day	9% 1 5% 35% 34% 15%	283
December	1st to 10th	Day	13% 2 5% 26% 35% 19%	220
	11th to 20th	Day	12% 2 8% 27% 37% 15%	220
	21st to end	Day	18% 4 13% 31% 23% 12%	242
January	1st to 10th	Night	18% 2 10% 38% 25% 6%	840
	11th to 20th	Night	13% 1 11% 34% 33% 8%	840
	21st to end	Night	15% 2 8% 37% 33% 5%	924
February	1st to 10th	Night	18% 3 11% 32% 28% 8%	840
	11th to 20th	Night	16% 6% 14% 30% 28% 6%	824
	21st to end	Night	13% 3 12% 39% 28% 4	692
March	1st to 10th	Night	20% 4 13% 31% 26% 6%	808
	11th to 20th	Night	15% 3 11% 33% 30% 8%	800
	21st to end	Night	16% 3 13% 32% 30% 6%	880
April	1st to 10th	Night	13% 3 12% 32% 32% 7%	800
	11th to 20th	Night	14% 3 12% 31% 29% 10%	791
	21st to end	Night	9% 2 12% 32% 31% 14%	800
May	1st to 10th	Night	10% 1 11% 33% 34% 12%	799
	11th to 20th	Night	12% 1 7% 26% 35% 18%	559
	21st to end	Night	14% 3 8% 26% 33% 16%	433
June	1st to 10th	Night	12% 1 8% 26% 39% 15%	400
	11th to 20th	Night	10% 2 8% 25% 45% 12%	400
	21st to end	Night	9% 2 2 20% 43% 24%	400
July	1st to 10th	Night	13% 4 2 13% 43% 26%	411
	11th to 20th	Night	14% 3 1 6% 38% 39%	582
	21st to end	Night	22% 5% 3 7% 35% 27%	657
August	1st to 10th	Night	19% 4 1 12% 41% 24%	597
	11th to 20th	Night	12% 4 2 14% 41% 26%	769
	21st to end	Night	16% 4 2 8% 41% 29%	880
September	1st to 10th	Night	8% 2 2 13% 46% 30%	800
	11th to 20th	Night	11% 3 3 19% 43% 22%	800
	21st to end	Night	7% 1 5% 18% 43% 26%	800
October	1st to 10th	Night	9% 2 4 25% 38% 22%	800
	11th to 20th	Night	10% 2 7% 23% 37% 22%	800
	21st to end	Night	11% 1 5% 25% 35% 23%	880
November	1st to 10th	Night	10% 2 8% 27% 38% 15%	820
	11th to 20th	Night	13% 2 5% 30% 40% 10%	840
	21st to end	Night	9% 1 8% 39% 35% 8%	840
December	1st to 10th	Night	14% 2 8% 39% 31% 6%	840
	11th to 20th	Night	20% 2 11% 36% 26% 6%	840
	21st to end	Night	20% 4 15% 37% 21% 3	924

Page generated at 2026-02-27 22:40:22. Version ac07

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