Taylor University Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Taylor University Observatory clear sky chart from 2005-11-06 to 2025-01-07.

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	14% 9% 4 8% 5% 4 4 4 5% 7% 35%	104884
	Night	15% 11% 4 8% 4 4 4 3 5% 6% 36%	104187
Transparency	Day	47% 6% 11% 22% 13% 1	108526
	Night	47% 5% 10% 22% 14% 2	108685
Seeing	Day	17% 10% 27% 24% 16% 6%	15790
	Night	19% 9% 29% 29% 13% 1	25687

By Month

Percentage Cloud Cover SE (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	16% 17% 10% 11% 5% 4 4 3 4 5% 21%	2575
	11th to 20th	Day	16% 16% 9% 13% 5% 6% 7% 6% 5% 3 14%	2530
	21st to end	Day	28% 22% 8% 11% 3 3 2 2 3 4 14%	2945
February	1st to 10th	Day	18% 15% 6% 11% 7% 5% 5% 3 4 5% 22%	1838
	11th to 20th	Day	16% 11% 4 12% 7% 5% 3 3 4 6% 28%	1848
	21st to end	Day	16% 15% 5% 9% 6% 4 4 4 4 6% 27%	1570
March	1st to 10th	Day	22% 19% 5% 9% 3 3 3 3 4 4 25%	3120
	11th to 20th	Day	13% 9% 3 7% 5% 4 4 3 5% 7% 39%	3410
	21st to end	Day	18% 11% 6% 10% 6% 4 4 3 5% 6% 29%	3904
April	1st to 10th	Day	15% 12% 4 8% 6% 5% 5% 3 5% 7% 32%	2280
	11th to 20th	Day	18% 8% 3 7% 4 4 4 4 5% 7% 36%	2273
	21st to end	Day	20% 9% 2 7% 5% 4 3 4 6% 7% 33%	2470
May	1st to 10th	Day	20% 9% 2 8% 5% 5% 5% 4 6% 8% 28%	4082
	11th to 20th	Day	19% 6% 2 6% 4 4 4 4 5% 8% 37%	4081
	21st to end	Day	11% 6% 2 6% 5% 4 6% 4 8% 9% 40%	4539
June	1st to 10th	Day	10% 6% 3 6% 6% 6% 4 4 5% 8% 41%	2660
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 4 7% 9% 43%	2660
	21st to end	Day	11% 5% 2 6% 5% 5% 6% 4 7% 9% 40%	2660
July	1st to 10th	Day	13% 7% 3 6% 5% 5% 4 5% 7% 10% 35%	4440
	11th to 20th	Day	7% 4 2 5% 4 4 5% 5% 7% 11% 46%	4440
	21st to end	Day	9% 7% 2 7% 5% 6% 6% 5% 6% 9% 38%	4634
August	1st to 10th	Day	9% 5% 1 5% 4 5% 5% 4 7% 11% 44%	4104
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 4 6% 9% 44%	3990
	21st to end	Day	8% 5% 2 6% 4 4 4 4 6% 9% 49%	4180
September	1st to 10th	Day	11% 5% 2 7% 5% 4 4 3 6% 7% 47%	2223
	11th to 20th	Day	9% 5% 2 5% 5% 4 5% 3 5% 9% 47%	2090
	21st to end	Day	16% 7% 2 4 4 4 4 3 5% 6% 46%	2090
October	1st to 10th	Day	12% 5% 3 7% 4 4 4 4 5% 6% 47%	2090
	11th to 20th	Day	14% 6% 2 6% 4 5% 5% 4 6% 7% 43%	1929
	21st to end	Day	20% 9% 2 7% 5% 5% 5% 3 5% 7% 33%	1881
November	1st to 10th	Day	10% 6% 2 6% 4 3 4 4 5% 7% 49%	1762
	11th to 20th	Day	17% 14% 4 8% 5% 4 4 3 5% 6% 32%	1800
	21st to end	Day	19% 14% 3 9% 5% 4 3 3 5% 4 31%	1800
December	1st to 10th	Day	12% 14% 5% 9% 5% 3 3 2 4 5% 38%	2930
	11th to 20th	Day	16% 16% 6% 12% 5% 4 4 3 5% 5% 23%	3074
	21st to end	Day	26% 19% 8% 11% 5% 5% 4 3 4 5% 11%	3982
January	1st to 10th	Night	17% 17% 9% 12% 5% 4 3 3 3 4 22%	4513
	11th to 20th	Night	14% 21% 7% 15% 6% 5% 5% 4 4 4 15%	4440
	21st to end	Night	26% 18% 8% 9% 4 4 3 2 3 4 19%	4714
February	1st to 10th	Night	18% 16% 5% 9% 5% 5% 4 3 4 5% 26%	2338
	11th to 20th	Night	13% 13% 4 11% 7% 5% 4 3 4 5% 32%	2218
	21st to end	Night	18% 14% 5% 9% 5% 4 5% 3 4 5% 28%	1884
March	1st to 10th	Night	19% 13% 3 6% 4 4 4 3 4 5% 35%	3733
	11th to 20th	Night	12% 8% 3 5% 4 4 4 3 5% 7% 44%	3549
	21st to end	Night	20% 8% 3 7% 4 4 4 3 5% 6% 36%	3754
April	1st to 10th	Night	14% 10% 3 6% 6% 4 4 4 5% 7% 36%	1900
	11th to 20th	Night	17% 9% 2 6% 4 5% 5% 4 5% 6% 37%	1854
	21st to end	Night	20% 9% 2 6% 4 4 4 4 6% 6% 36%	1710
May	1st to 10th	Night	20% 9% 3 8% 5% 4 5% 4 6% 7% 29%	2813
	11th to 20th	Night	21% 7% 2 5% 3 4 4 3 5% 7% 39%	2812
	21st to end	Night	10% 5% 2 7% 4 4 5% 4 6% 9% 44%	3002
June	1st to 10th	Night	8% 5% 2 6% 5% 4 4 3 4 8% 49%	1520
	11th to 20th	Night	8% 6% 2 6% 5% 3 5% 3 6% 10% 47%	1520
	21st to end	Night	9% 5% 2 5% 5% 4 5% 3 8% 9% 45%	1520
July	1st to 10th	Night	9% 5% 2 6% 4 5% 4 3 5% 9% 48%	2530
	11th to 20th	Night	7% 3 1 4 3 3 4 4 6% 8% 56%	2530
	21st to end	Night	11% 7% 2 7% 4 4 5% 4 6% 9% 42%	2920
August	1st to 10th	Night	11% 5% 3 6% 4 4 4 4 5% 7% 47%	2825
	11th to 20th	Night	7% 6% 2 6% 4 5% 5% 3 5% 9% 48%	2835
	21st to end	Night	7% 4 2 6% 4 4 4 4 5% 7% 52%	3476
September	1st to 10th	Night	12% 4 2 6% 4 3 4 3 6% 7% 50%	1938
	11th to 20th	Night	9% 4 2 4 4 2 3 3 4 8% 56%	2090
	21st to end	Night	13% 5% 1 5% 4 3 4 3 5% 7% 50%	2090
October	1st to 10th	Night	10% 6% 2 6% 3 3 3 3 5% 6% 53%	2090
	11th to 20th	Night	17% 8% 3 6% 4 3 3 3 4 6% 44%	2244
	21st to end	Night	19% 7% 2 6% 4 4 4 3 5% 6% 38%	2717
November	1st to 10th	Night	13% 9% 3 5% 3 3 3 3 5% 6% 46%	2536
	11th to 20th	Night	15% 11% 3 7% 5% 4 4 2 5% 7% 36%	2600
	21st to end	Night	18% 14% 4 9% 5% 5% 4 3 4 6% 29%	2600
December	1st to 10th	Night	14% 11% 4 8% 5% 5% 4 3 6% 7% 34%	4250
	11th to 20th	Night	18% 16% 7% 11% 5% 4 4 3 4 5% 22%	5126
	21st to end	Night	26% 19% 7% 11% 5% 4 4 3 4 5% 13%	6996

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	66% 5% 7% 16% 6%	2576
	11th to 20th	Day	74% 4 9% 9% 5%	2530
	21st to end	Day	78% 2 6% 11% 3	2945
February	1st to 10th	Day	66% 4 9% 12% 9% 1	1838
	11th to 20th	Day	58% 4 10% 20% 7% 1	1858
	21st to end	Day	58% 5% 11% 17% 6% 2	1570
March	1st to 10th	Day	63% 4 8% 17% 8%	3120
	11th to 20th	Day	44% 5% 10% 30% 11% 1	3410
	21st to end	Day	56% 7% 15% 18% 4	3904
April	1st to 10th	Day	53% 5% 11% 19% 12% 1	2280
	11th to 20th	Day	48% 5% 10% 23% 11% 3	2273
	21st to end	Day	50% 5% 12% 20% 10% 3	2470
May	1st to 10th	Day	53% 7% 11% 21% 8% 1	4120
	11th to 20th	Day	44% 7% 14% 25% 9% 1	4085
	21st to end	Day	37% 8% 12% 24% 18% 2	4552
June	1st to 10th	Day	40% 7% 10% 25% 16% 2	2660
	11th to 20th	Day	37% 6% 11% 25% 19% 2	2660
	21st to end	Day	39% 7% 15% 20% 15% 4	2660
July	1st to 10th	Day	44% 6% 13% 20% 15% 2	4371
	11th to 20th	Day	29% 7% 15% 28% 20% 1	4365
	21st to end	Day	40% 8% 15% 17% 17% 3	4487
August	1st to 10th	Day	33% 7% 18% 27% 14% 1	4091
	11th to 20th	Day	34% 7% 12% 30% 15% 1	4029
	21st to end	Day	30% 6% 13% 29% 18% 3	4179
September	1st to 10th	Day	36% 5% 12% 25% 18% 4	2223
	11th to 20th	Day	33% 6% 10% 26% 22% 3	2090
	21st to end	Day	39% 5% 9% 24% 21% 1	2090
October	1st to 10th	Day	25% 5% 11% 32% 25% 2	3480
	11th to 20th	Day	32% 5% 11% 25% 25% 1	3184
	21st to end	Day	43% 4 9% 25% 17% 2	3081
November	1st to 10th	Day	35% 5% 13% 28% 17% 2	1762
	11th to 20th	Day	54% 4 10% 20% 11% 3	1800
	21st to end	Day	56% 5% 10% 20% 8% 1	1800
December	1st to 10th	Day	50% 3 13% 24% 10%	2930
	11th to 20th	Day	64% 5% 10% 17% 4	3071
	21st to end	Day	76% 4 7% 9% 4	3982
January	1st to 10th	Night	67% 4 8% 14% 7%	4513
	11th to 20th	Night	73% 4 7% 12% 4	4440
	21st to end	Night	71% 3 7% 14% 5%	4714
February	1st to 10th	Night	61% 4 11% 15% 8% 1	2338
	11th to 20th	Night	55% 4 11% 19% 11% 1	2219
	21st to end	Night	59% 4 10% 16% 9% 2	1884
March	1st to 10th	Night	53% 4 9% 23% 10% 1	3733
	11th to 20th	Night	39% 6% 10% 28% 15% 2	3549
	21st to end	Night	50% 5% 12% 26% 7% 1	3754
April	1st to 10th	Night	46% 6% 11% 22% 13% 1	1900
	11th to 20th	Night	46% 6% 10% 20% 15% 4	1854
	21st to end	Night	46% 6% 10% 22% 12% 4	1710
May	1st to 10th	Night	52% 8% 9% 20% 9% 2	2840
	11th to 20th	Night	43% 7% 12% 28% 9% 1	2813
	21st to end	Night	34% 9% 14% 23% 16% 3	3010
June	1st to 10th	Night	35% 5% 10% 28% 20% 3	1520
	11th to 20th	Night	31% 8% 12% 26% 20% 3	1520
	21st to end	Night	32% 9% 15% 24% 16% 4	1520
July	1st to 10th	Night	34% 6% 11% 26% 16% 6%	2490
	11th to 20th	Night	24% 6% 15% 29% 23% 2	2482
	21st to end	Night	38% 7% 15% 18% 18% 5%	2827
August	1st to 10th	Night	35% 7% 14% 28% 15% 2	2814
	11th to 20th	Night	33% 7% 12% 29% 18% 1	2862
	21st to end	Night	30% 6% 13% 27% 21% 3	3476
September	1st to 10th	Night	33% 6% 12% 24% 20% 6%	1938
	11th to 20th	Night	28% 5% 9% 29% 27% 3	2090
	21st to end	Night	34% 5% 11% 24% 22% 3	2090
October	1st to 10th	Night	21% 3 7% 32% 35% 2	3480
	11th to 20th	Night	31% 4 10% 23% 31% 1	3728
	21st to end	Night	34% 4 8% 29% 22% 3	4467
November	1st to 10th	Night	39% 4 9% 26% 20% 2	2536
	11th to 20th	Night	48% 4 9% 21% 15% 3	2600
	21st to end	Night	58% 3 10% 21% 8%	2600
December	1st to 10th	Night	49% 4 12% 25% 8% 1	4250
	11th to 20th	Night	65% 5% 10% 13% 6% 1	5128
	21st to end	Night	74% 4 9% 10% 3	6996

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	23% 18% 37% 15% 7% 1	288
	11th to 20th	Day	27% 19% 36% 14% 5%	270
	21st to end	Day	32% 17% 32% 15% 5%	297
February	1st to 10th	Day	28% 17% 34% 17% 4	270
	11th to 20th	Day	24% 17% 38% 15% 5% 1	270
	21st to end	Day	26% 19% 40% 12% 3	225
March	1st to 10th	Day	23% 20% 36% 18% 2	270
	11th to 20th	Day	25% 16% 32% 20% 6% 1	416
	21st to end	Day	30% 14% 31% 18% 6% 1	506
April	1st to 10th	Day	19% 17% 33% 20% 9% 2	460
	11th to 20th	Day	20% 19% 28% 19% 11% 3	452
	21st to end	Day	24% 13% 32% 19% 10% 2	460
May	1st to 10th	Day	23% 14% 30% 22% 9% 3	463
	11th to 20th	Day	21% 7% 28% 25% 12% 7%	487
	21st to end	Day	11% 5% 29% 27% 18% 9%	566
June	1st to 10th	Day	11% 6% 28% 29% 21% 5%	680
	11th to 20th	Day	12% 6% 25% 32% 20% 5%	680
	21st to end	Day	12% 7% 27% 28% 19% 7%	680
July	1st to 10th	Day	11% 3 19% 27% 24% 15%	671
	11th to 20th	Day	6% 3 23% 31% 24% 13%	668
	21st to end	Day	10% 3 15% 32% 27% 13%	635
August	1st to 10th	Day	7% 4 15% 29% 29% 16%	486
	11th to 20th	Day	9% 5% 18% 29% 28% 12%	479
	21st to end	Day	9% 4 14% 26% 34% 13%	539
September	1st to 10th	Day	13% 4 16% 25% 32% 10%	490
	11th to 20th	Day	9% 3 14% 24% 32% 18%	490
	21st to end	Day	19% 8% 22% 22% 22% 7%	490
October	1st to 10th	Day	12% 6% 26% 30% 19% 8%	490
	11th to 20th	Day	15% 17% 29% 26% 11% 2	452
	21st to end	Day	26% 15% 35% 21% 3 1	330
November	1st to 10th	Day	12% 14% 34% 26% 11% 4	300
	11th to 20th	Day	25% 15% 30% 21% 7% 2	300
	21st to end	Day	30% 13% 35% 19% 3	300
December	1st to 10th	Day	20% 21% 36% 16% 7%	300
	11th to 20th	Day	24% 17% 38% 14% 6% 1	300
	21st to end	Day	31% 17% 32% 18% 2	330
January	1st to 10th	Night	24% 17% 34% 21% 4	981
	11th to 20th	Night	25% 15% 37% 19% 4	950
	21st to end	Night	23% 16% 36% 22% 3	940
February	1st to 10th	Night	26% 11% 34% 25% 3	760
	11th to 20th	Night	20% 15% 38% 26% 2	743
	21st to end	Night	26% 12% 39% 19% 4	628
March	1st to 10th	Night	21% 14% 33% 25% 7%	760
	11th to 20th	Night	18% 13% 38% 24% 7% 1	760
	21st to end	Night	26% 11% 31% 27% 5% 1	798
April	1st to 10th	Night	17% 11% 36% 29% 7% 1	570
	11th to 20th	Night	20% 11% 33% 27% 8% 1	563
	21st to end	Night	23% 8% 35% 24% 8% 1	570
May	1st to 10th	Night	22% 8% 31% 31% 8%	570
	11th to 20th	Night	22% 4 23% 32% 17% 2	561
	21st to end	Night	10% 3 26% 40% 19% 3	617
June	1st to 10th	Night	10% 3 25% 45% 16% 1	570
	11th to 20th	Night	10% 3 24% 42% 21% 1	570
	21st to end	Night	10% 2 24% 37% 26% 1	570
July	1st to 10th	Night	10% 2 17% 35% 32% 3	555
	11th to 20th	Night	8% 3 15% 41% 30% 4	552
	21st to end	Night	8% 3 13% 42% 32% 2	624
August	1st to 10th	Night	8% 1 13% 44% 30% 5%	567
	11th to 20th	Night	7% 1 15% 40% 32% 5%	564
	21st to end	Night	8% 2 13% 33% 39% 6%	627
September	1st to 10th	Night	14% 3 13% 36% 30% 5%	608
	11th to 20th	Night	10% 2 15% 35% 33% 5%	760
	21st to end	Night	14% 5% 23% 34% 21% 3	760
October	1st to 10th	Night	12% 5% 26% 34% 19% 4	760
	11th to 20th	Night	21% 11% 29% 26% 13% 1	760
	21st to end	Night	21% 12% 34% 26% 7%	836
November	1st to 10th	Night	16% 10% 36% 25% 11% 1	780
	11th to 20th	Night	19% 16% 33% 25% 6% 1	800
	21st to end	Night	25% 14% 31% 23% 7%	800
December	1st to 10th	Night	25% 13% 35% 22% 5% 1	800
	11th to 20th	Night	26% 12% 33% 23% 6%	953
	21st to end	Night	31% 15% 31% 20% 3	1100

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