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 2026-05-02.

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% 5% 5% 4 5% 7% 34%	131270
	Night	15% 10% 4 8% 5% 4 4 3 5% 6% 35%	131403
Transparency	Day	48% 5% 11% 22% 13% 1	134869
	Night	48% 5% 10% 22% 13% 2	135877
Seeing	Day	17% 11% 27% 23% 15% 6%	17557
	Night	18% 10% 29% 29% 13% 1	27473

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	15% 16% 8% 15% 6% 4 4 3 4 5% 19%	4691
	11th to 20th	Day	11% 14% 8% 15% 7% 9% 6% 5% 4 3 18%	4710
	21st to end	Day	18% 16% 7% 14% 6% 4 4 4 4 5% 18%	5472
February	1st to 10th	Day	17% 15% 7% 11% 6% 5% 4 4 4 4 22%	2032
	11th to 20th	Day	15% 12% 5% 12% 7% 5% 4 3 4 6% 27%	2048
	21st to end	Day	15% 15% 5% 10% 5% 4 4 3 4 6% 29%	1730
March	1st to 10th	Day	19% 15% 6% 10% 4 3 3 2 3 4 30%	4580
	11th to 20th	Day	11% 11% 3 6% 5% 3 4 3 5% 7% 41%	4990
	21st to end	Day	17% 12% 5% 9% 6% 4 4 4 5% 7% 27%	5718
April	1st to 10th	Day	16% 11% 4 8% 6% 5% 5% 3 5% 7% 31%	2520
	11th to 20th	Day	17% 8% 3 7% 4 4 4 4 5% 7% 36%	2515
	21st to end	Day	19% 8% 2 7% 5% 4 4 4 6% 7% 34%	2730
May	1st to 10th	Day	21% 8% 2 9% 5% 5% 5% 4 6% 7% 28%	5875
	11th to 20th	Day	19% 7% 2 7% 4 4 4 4 5% 7% 37%	5861
	21st to end	Day	14% 6% 2 6% 5% 5% 5% 4 8% 9% 36%	6524
June	1st to 10th	Day	11% 6% 3 6% 5% 6% 4 4 5% 8% 41%	2800
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 4 7% 9% 42%	2800
	21st to end	Day	10% 5% 2 6% 6% 5% 6% 4 7% 9% 41%	2800
July	1st to 10th	Day	10% 6% 2 6% 5% 5% 4 5% 6% 10% 40%	6360
	11th to 20th	Day	9% 5% 2 6% 5% 5% 5% 5% 7% 11% 40%	6360
	21st to end	Day	10% 7% 2 7% 5% 5% 6% 5% 6% 8% 37%	6662
August	1st to 10th	Day	8% 5% 1 5% 4 5% 5% 4 7% 10% 45%	4234
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 4 6% 9% 43%	4118
	21st to end	Day	7% 5% 2 6% 4 4 4 4 6% 9% 49%	4312
September	1st to 10th	Day	11% 5% 1 7% 5% 4 4 3 6% 7% 49%	2340
	11th to 20th	Day	9% 5% 2 5% 4 4 5% 3 5% 9% 49%	2200
	21st to end	Day	16% 7% 2 4 4 4 4 3 5% 6% 46%	2200
October	1st to 10th	Day	12% 5% 3 6% 4 4 4 4 5% 6% 47%	2200
	11th to 20th	Day	13% 6% 1 6% 4 4 5% 4 6% 7% 43%	2030
	21st to end	Day	20% 9% 2 7% 4 5% 4 3 4 7% 34%	1980
November	1st to 10th	Day	10% 7% 2 6% 4 3 4 4 5% 7% 48%	1852
	11th to 20th	Day	17% 14% 3 8% 4 4 4 3 4 6% 32%	1890
	21st to end	Day	19% 13% 4 9% 5% 4 3 3 5% 4 31%	1890
December	1st to 10th	Day	12% 14% 5% 10% 5% 3 3 2 4 5% 38%	3020
	11th to 20th	Day	16% 16% 6% 12% 5% 5% 4 3 5% 5% 23%	3156
	21st to end	Day	25% 19% 8% 11% 5% 5% 4 3 4 5% 11%	4070
January	1st to 10th	Night	14% 15% 8% 13% 7% 5% 4 3 4 4 21%	8232
	11th to 20th	Night	9% 18% 8% 17% 7% 6% 5% 4 4 4 19%	8280
	21st to end	Night	18% 12% 5% 9% 5% 6% 5% 5% 5% 5% 26%	8722
February	1st to 10th	Night	17% 15% 5% 10% 6% 5% 4 3 5% 5% 26%	2584
	11th to 20th	Night	14% 12% 4 11% 6% 5% 4 3 4 5% 31%	2458
	21st to end	Night	17% 13% 5% 10% 5% 4 5% 3 4 6% 29%	2076
March	1st to 10th	Night	19% 12% 3 6% 4 3 4 3 4 5% 37%	5493
	11th to 20th	Night	12% 8% 3 6% 4 4 4 3 5% 7% 43%	5189
	21st to end	Night	19% 8% 3 8% 5% 4 4 3 5% 6% 35%	5495
April	1st to 10th	Night	15% 10% 3 6% 6% 4 4 4 5% 7% 35%	2100
	11th to 20th	Night	16% 8% 2 6% 4 6% 5% 4 5% 7% 38%	2052
	21st to end	Night	18% 8% 2 6% 4 4 4 4 6% 6% 37%	1890
May	1st to 10th	Night	22% 10% 4 8% 5% 4 4 3 5% 6% 29%	4042
	11th to 20th	Night	17% 7% 3 6% 4 4 4 4 6% 8% 39%	4032
	21st to end	Night	14% 7% 3 7% 4 4 4 4 6% 8% 40%	4318
June	1st to 10th	Night	9% 5% 2 6% 5% 4 4 3 4 9% 48%	1600
	11th to 20th	Night	8% 6% 2 6% 5% 4 5% 3 6% 10% 46%	1600
	21st to end	Night	9% 5% 2 5% 5% 4 5% 3 8% 9% 47%	1600
July	1st to 10th	Night	9% 5% 2 5% 4 4 4 4 6% 9% 49%	3618
	11th to 20th	Night	9% 4 2 6% 4 4 5% 4 7% 10% 47%	3617
	21st to end	Night	11% 7% 2 8% 4 4 5% 4 6% 8% 41%	4195
August	1st to 10th	Night	11% 5% 3 6% 4 4 4 3 5% 8% 47%	2915
	11th to 20th	Night	7% 6% 2 6% 4 5% 5% 3 5% 9% 49%	2926
	21st to end	Night	7% 4 2 6% 4 4 4 4 5% 7% 52%	3586
September	1st to 10th	Night	12% 4 2 6% 4 3 4 3 5% 7% 51%	2040
	11th to 20th	Night	9% 4 2 4 4 3 3 3 4 8% 57%	2200
	21st to end	Night	13% 5% 1 5% 4 3 4 3 4 7% 50%	2200
October	1st to 10th	Night	10% 6% 2 5% 3 3 3 3 5% 6% 54%	2200
	11th to 20th	Night	16% 8% 3 6% 4 3 3 3 4 5% 44%	2363
	21st to end	Night	19% 7% 2 7% 4 4 5% 4 5% 6% 38%	2860
November	1st to 10th	Night	12% 9% 3 6% 3 3 3 3 5% 6% 46%	2666
	11th to 20th	Night	15% 11% 3 7% 5% 4 4 2 5% 7% 37%	2730
	21st to end	Night	18% 14% 5% 9% 5% 5% 4 2 4 6% 29%	2730
December	1st to 10th	Night	14% 11% 4 8% 5% 5% 4 3 6% 6% 34%	4380
	11th to 20th	Night	18% 16% 8% 11% 5% 4 4 3 4 5% 22%	5264
	21st to end	Night	26% 19% 7% 11% 5% 4 4 3 4 5% 13%	7150

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	67% 5% 10% 14% 4	4692
	11th to 20th	Day	72% 3 8% 9% 7% 2	4710
	21st to end	Day	70% 2 8% 12% 6%	5472
February	1st to 10th	Day	66% 4 9% 13% 8% 1	2032
	11th to 20th	Day	60% 4 9% 20% 7%	2058
	21st to end	Day	57% 5% 12% 17% 7% 2	1730
March	1st to 10th	Day	60% 3 6% 20% 10% 1	4580
	11th to 20th	Day	42% 4 10% 33% 10% 1	4990
	21st to end	Day	57% 6% 13% 16% 6% 2	5720
April	1st to 10th	Day	53% 5% 11% 19% 12%	2520
	11th to 20th	Day	48% 5% 11% 23% 11% 3	2515
	21st to end	Day	48% 5% 12% 22% 10% 3	2730
May	1st to 10th	Day	54% 6% 11% 17% 11%	5910
	11th to 20th	Day	46% 6% 13% 23% 12% 1	5865
	21st to end	Day	41% 7% 12% 25% 14% 1	6538
June	1st to 10th	Day	40% 7% 10% 24% 16% 2	2800
	11th to 20th	Day	38% 6% 11% 24% 18% 2	2800
	21st to end	Day	38% 7% 15% 21% 15% 4	2800
July	1st to 10th	Day	39% 6% 11% 25% 17% 2	6291
	11th to 20th	Day	35% 8% 16% 25% 15% 1	6285
	21st to end	Day	41% 8% 13% 19% 16% 2	6472
August	1st to 10th	Day	32% 7% 18% 28% 14% 1	4221
	11th to 20th	Day	34% 7% 13% 30% 15% 1	4157
	21st to end	Day	30% 7% 13% 30% 17% 3	4311
September	1st to 10th	Day	35% 5% 12% 26% 18% 4	2340
	11th to 20th	Day	33% 6% 10% 27% 23% 3	2200
	21st to end	Day	39% 5% 9% 24% 22% 1	2200
October	1st to 10th	Day	25% 5% 11% 32% 26% 2	3590
	11th to 20th	Day	32% 5% 11% 25% 25% 1	3285
	21st to end	Day	43% 4 9% 25% 18% 2	3180
November	1st to 10th	Day	36% 5% 13% 28% 17% 2	1852
	11th to 20th	Day	53% 4 10% 20% 11% 3	1890
	21st to end	Day	57% 5% 10% 20% 8% 1	1890
December	1st to 10th	Day	51% 3 13% 23% 10%	3020
	11th to 20th	Day	64% 5% 10% 18% 4	3153
	21st to end	Day	76% 4 7% 9% 4	4070
January	1st to 10th	Night	66% 4 8% 16% 6%	8233
	11th to 20th	Night	69% 4 6% 11% 9% 1	8280
	21st to end	Night	59% 4 11% 18% 7% 1	8722
February	1st to 10th	Night	61% 4 11% 15% 7% 1	2584
	11th to 20th	Night	56% 4 10% 19% 10% 1	2459
	21st to end	Night	57% 4 11% 16% 10% 2	2076
March	1st to 10th	Night	51% 3 7% 26% 11% 2	5493
	11th to 20th	Night	40% 5% 12% 28% 13% 2	5189
	21st to end	Night	50% 4 10% 25% 9% 1	5495
April	1st to 10th	Night	47% 6% 11% 22% 12% 1	2100
	11th to 20th	Night	45% 6% 10% 21% 15% 4	2052
	21st to end	Night	45% 6% 10% 24% 12% 3	1890
May	1st to 10th	Night	56% 7% 8% 16% 12% 2	4069
	11th to 20th	Night	42% 7% 11% 26% 13% 1	4033
	21st to end	Night	41% 8% 13% 23% 13% 2	4326
June	1st to 10th	Night	35% 4 10% 27% 21% 3	1600
	11th to 20th	Night	33% 7% 12% 25% 20% 3	1600
	21st to end	Night	31% 9% 16% 23% 17% 4	1600
July	1st to 10th	Night	32% 6% 12% 27% 17% 5%	3580
	11th to 20th	Night	32% 7% 16% 26% 18% 2	3572
	21st to end	Night	39% 7% 14% 20% 16% 3	4072
August	1st to 10th	Night	35% 7% 14% 29% 15% 1	2904
	11th to 20th	Night	32% 7% 12% 30% 18% 1	2953
	21st to end	Night	30% 6% 13% 27% 21% 3	3586
September	1st to 10th	Night	32% 6% 12% 25% 20% 6%	2040
	11th to 20th	Night	27% 5% 8% 29% 28% 3	2200
	21st to end	Night	35% 5% 10% 24% 23% 3	2200
October	1st to 10th	Night	21% 3 6% 31% 36% 2	3590
	11th to 20th	Night	31% 4 10% 23% 31% 1	3847
	21st to end	Night	35% 4 8% 29% 22% 2	4610
November	1st to 10th	Night	38% 4 10% 27% 20% 2	2666
	11th to 20th	Night	48% 4 9% 22% 15% 3	2730
	21st to end	Night	58% 3 10% 20% 8%	2730
December	1st to 10th	Night	50% 4 12% 25% 8% 1	4380
	11th to 20th	Night	64% 5% 11% 13% 6% 1	5266
	21st to end	Night	74% 4 9% 10% 3	7150

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	25% 17% 35% 15% 6% 1	330
	11th to 20th	Day	25% 24% 35% 13% 4	330
	21st to end	Day	28% 20% 33% 15% 5%	363
February	1st to 10th	Day	25% 17% 35% 19% 5%	330
	11th to 20th	Day	24% 16% 40% 15% 5% 1	330
	21st to end	Day	24% 19% 43% 11% 2	273
March	1st to 10th	Day	22% 21% 38% 17% 2	330
	11th to 20th	Day	26% 17% 31% 19% 6% 1	492
	21st to end	Day	28% 16% 33% 17% 5% 1	594
April	1st to 10th	Day	22% 17% 33% 18% 9% 1	540
	11th to 20th	Day	20% 22% 27% 19% 9% 3	532
	21st to end	Day	23% 13% 31% 21% 10% 2	540
May	1st to 10th	Day	24% 14% 29% 21% 9% 3	507
	11th to 20th	Day	21% 8% 28% 25% 12% 6%	527
	21st to end	Day	12% 6% 29% 27% 17% 9%	612
June	1st to 10th	Day	12% 6% 28% 28% 20% 5%	730
	11th to 20th	Day	12% 7% 25% 32% 20% 5%	730
	21st to end	Day	11% 7% 26% 29% 20% 7%	730
July	1st to 10th	Day	11% 3 19% 28% 24% 15%	721
	11th to 20th	Day	6% 3 23% 32% 24% 13%	718
	21st to end	Day	11% 3 15% 32% 27% 13%	684
August	1st to 10th	Day	7% 4 14% 29% 31% 16%	526
	11th to 20th	Day	9% 5% 17% 28% 28% 12%	519
	21st to end	Day	8% 4 14% 27% 33% 13%	583
September	1st to 10th	Day	12% 5% 16% 24% 31% 12%	530
	11th to 20th	Day	8% 3 13% 24% 32% 19%	530
	21st to end	Day	18% 8% 22% 22% 22% 8%	530
October	1st to 10th	Day	11% 5% 24% 31% 20% 9%	530
	11th to 20th	Day	14% 17% 28% 27% 12% 2	490
	21st to end	Day	26% 15% 34% 22% 2 1	363
November	1st to 10th	Day	13% 15% 33% 25% 10% 3	330
	11th to 20th	Day	26% 17% 30% 19% 6% 2	330
	21st to end	Day	30% 13% 36% 18% 3	330
December	1st to 10th	Day	19% 20% 38% 17% 6%	330
	11th to 20th	Day	25% 17% 38% 14% 5% 1	330
	21st to end	Day	30% 18% 33% 17% 2	363
January	1st to 10th	Night	23% 16% 34% 22% 4	1050
	11th to 20th	Night	24% 16% 39% 18% 3	1050
	21st to end	Night	22% 17% 37% 21% 3	1038
February	1st to 10th	Night	25% 12% 34% 25% 4	840
	11th to 20th	Night	20% 15% 38% 26% 1	823
	21st to end	Night	24% 13% 41% 19% 3	692
March	1st to 10th	Night	22% 15% 33% 24% 6%	840
	11th to 20th	Night	18% 14% 38% 23% 6% 1	840
	21st to end	Night	25% 12% 32% 26% 4 1	882
April	1st to 10th	Night	18% 12% 36% 27% 7%	630
	11th to 20th	Night	19% 13% 33% 27% 8% 1	623
	21st to end	Night	22% 8% 36% 25% 9% 1	630
May	1st to 10th	Night	23% 8% 31% 31% 8%	603
	11th to 20th	Night	21% 5% 24% 31% 16% 2	591
	21st to end	Night	10% 3 26% 40% 18% 2	650
June	1st to 10th	Night	11% 4 25% 44% 16% 1	600
	11th to 20th	Night	10% 4 23% 43% 20% 1	600
	21st to end	Night	10% 2 23% 38% 27% 1	600
July	1st to 10th	Night	10% 2 17% 35% 33% 4	585
	11th to 20th	Night	8% 3 15% 41% 30% 4	582
	21st to end	Night	8% 3 13% 42% 33% 2	657
August	1st to 10th	Night	7% 1 13% 44% 30% 4	597
	11th to 20th	Night	7% 2 14% 40% 32% 5%	594
	21st to end	Night	7% 2 13% 35% 38% 6%	660
September	1st to 10th	Night	13% 3 13% 35% 31% 5%	640
	11th to 20th	Night	10% 2 14% 36% 33% 5%	800
	21st to end	Night	14% 5% 22% 34% 22% 3	800
October	1st to 10th	Night	12% 5% 25% 34% 20% 4	800
	11th to 20th	Night	20% 11% 28% 28% 13% 1	800
	21st to end	Night	21% 12% 34% 26% 7%	880
November	1st to 10th	Night	16% 10% 37% 26% 11% 1	820
	11th to 20th	Night	19% 17% 33% 24% 6% 1	840
	21st to end	Night	26% 15% 30% 23% 7%	840
December	1st to 10th	Night	25% 13% 36% 21% 4	840
	11th to 20th	Night	25% 13% 34% 23% 5%	1001
	21st to end	Night	31% 15% 31% 20% 3	1155

Page generated at 2026-04-29 02:21:43. Version ac07

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