Taylor Dark Sky Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Taylor Dark Sky Site clear sky chart from 2005-11-06 to 2025-02-21.

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	13% 8% 3 7% 4 4 4 4 5% 7% 39%	108496
	Night	15% 8% 3 7% 4 4 4 3 5% 6% 41%	110262
Transparency	Day	41% 7% 12% 23% 15% 2	112113
	Night	42% 6% 11% 22% 17% 2	114773
Seeing	Day	15% 9% 26% 25% 18% 7%	15929
	Night	17% 8% 28% 31% 15% 2	25892

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	14% 11% 7% 12% 5% 5% 5% 4 5% 6% 28%	3617
	11th to 20th	Day	12% 10% 5% 14% 7% 7% 6% 4 5% 5% 26%	3620
	21st to end	Day	20% 15% 4 8% 5% 4 4 3 3 4 29%	4327
February	1st to 10th	Day	17% 12% 5% 9% 4 4 4 3 5% 6% 32%	1952
	11th to 20th	Day	16% 11% 3 9% 6% 5% 4 5% 5% 7% 32%	1948
	21st to end	Day	16% 12% 4 7% 5% 5% 5% 3 5% 5% 34%	1570
March	1st to 10th	Day	21% 15% 4 7% 4 4 3 2 3 5% 34%	3120
	11th to 20th	Day	12% 8% 3 6% 4 3 4 4 5% 7% 46%	3268
	21st to end	Day	15% 9% 3 8% 6% 5% 5% 4 6% 7% 32%	4165
April	1st to 10th	Day	15% 8% 2 7% 4 4 4 3 5% 8% 40%	2280
	11th to 20th	Day	15% 8% 2 7% 5% 4 3 4 5% 6% 41%	2254
	21st to end	Day	19% 7% 2 7% 4 5% 4 3 6% 6% 37%	2323
May	1st to 10th	Day	16% 7% 2 7% 4 4 5% 5% 8% 10% 31%	4082
	11th to 20th	Day	18% 8% 3 6% 4 4 4 3 5% 7% 39%	4081
	21st to end	Day	8% 5% 2 7% 5% 5% 5% 5% 6% 9% 42%	4782
June	1st to 10th	Day	11% 6% 2 5% 4 4 4 4 6% 8% 46%	2660
	11th to 20th	Day	7% 5% 2 6% 5% 5% 5% 4 6% 6% 49%	2660
	21st to end	Day	8% 6% 2 6% 4 4 5% 5% 7% 9% 44%	2660
July	1st to 10th	Day	12% 5% 2 6% 4 4 5% 4 6% 10% 40%	4440
	11th to 20th	Day	6% 4 2 6% 3 4 5% 5% 8% 12% 45%	4440
	21st to end	Day	9% 6% 2 7% 6% 6% 7% 6% 8% 9% 34%	4813
August	1st to 10th	Day	8% 4 2 4 4 3 4 4 6% 10% 53%	3992
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 4 8% 11% 41%	3729
	21st to end	Day	5% 4 2 4 4 4 4 4 7% 10% 52%	4180
September	1st to 10th	Day	12% 5% 3 6% 5% 4 4 4 6% 7% 46%	2280
	11th to 20th	Day	9% 4 2 5% 5% 5% 5% 4 6% 7% 50%	2138
	21st to end	Day	11% 5% 2 5% 4 3 3 3 5% 7% 51%	2090
October	1st to 10th	Day	11% 4 1 5% 3 3 4 3 5% 7% 54%	2088
	11th to 20th	Day	15% 5% 2 5% 3 4 4 3 5% 6% 48%	1900
	21st to end	Day	20% 7% 3 6% 3 4 4 3 5% 5% 43%	1910
November	1st to 10th	Day	10% 6% 2 6% 4 4 3 2 4 7% 52%	1762
	11th to 20th	Day	16% 10% 3 6% 5% 3 3 3 4 7% 42%	1800
	21st to end	Day	17% 10% 4 8% 4 4 4 3 5% 4 39%	1800
December	1st to 10th	Day	11% 10% 4 6% 4 3 4 3 4 5% 46%	2775
	11th to 20th	Day	14% 12% 5% 10% 5% 5% 5% 3 4 6% 30%	3008
	21st to end	Day	29% 16% 5% 10% 5% 4 3 3 3 4 18%	3982
January	1st to 10th	Night	16% 12% 7% 11% 4 4 4 3 4 5% 29%	6348
	11th to 20th	Night	14% 15% 5% 10% 5% 6% 7% 3 3 4 28%	6360
	21st to end	Night	21% 11% 5% 8% 6% 4 3 3 4 5% 32%	6649
February	1st to 10th	Night	20% 9% 4 9% 5% 4 4 4 5% 6% 31%	2445
	11th to 20th	Night	16% 10% 3 8% 6% 5% 3 4 4 6% 36%	2338
	21st to end	Night	20% 9% 3 7% 4 3 4 3 4 5% 37%	1885
March	1st to 10th	Night	20% 14% 3 7% 4 3 3 3 5% 5% 33%	3733
	11th to 20th	Night	13% 7% 2 5% 4 3 3 3 4 6% 49%	3719
	21st to end	Night	18% 8% 2 6% 5% 4 4 4 5% 6% 38%	3466
April	1st to 10th	Night	12% 7% 3 7% 5% 4 4 3 5% 6% 44%	1900
	11th to 20th	Night	16% 7% 2 5% 4 4 3 3 5% 6% 44%	1875
	21st to end	Night	17% 8% 2 6% 5% 5% 4 4 5% 7% 36%	1857
May	1st to 10th	Night	15% 8% 3 7% 5% 5% 5% 4 6% 8% 34%	2813
	11th to 20th	Night	18% 6% 2 5% 3 4 3 4 6% 7% 42%	2812
	21st to end	Night	11% 5% 2 7% 4 5% 5% 4 7% 10% 41%	2780
June	1st to 10th	Night	9% 6% 2 5% 5% 4 3 3 6% 7% 49%	1520
	11th to 20th	Night	7% 4 2 5% 3 4 6% 3 6% 8% 52%	1520
	21st to end	Night	6% 4 2 5% 4 4 4 4 7% 10% 48%	1520
July	1st to 10th	Night	12% 5% 2 5% 4 4 3 4 5% 10% 47%	2530
	11th to 20th	Night	5% 4 2 5% 4 5% 4 4 6% 8% 55%	2530
	21st to end	Night	8% 7% 3 9% 5% 5% 5% 4 7% 9% 38%	2750
August	1st to 10th	Night	6% 3 1 5% 3 4 4 4 5% 9% 55%	2934
	11th to 20th	Night	7% 4 2 5% 4 4 5% 4 6% 8% 52%	3100
	21st to end	Night	4 3 1 4 3 4 4 4 6% 10% 57%	3476
September	1st to 10th	Night	11% 5% 2 5% 3 4 3 3 5% 7% 54%	1900
	11th to 20th	Night	7% 4 2 5% 4 3 4 3 6% 7% 56%	2021
	21st to end	Night	11% 5% 2 5% 3 4 4 3 5% 7% 51%	2090
October	1st to 10th	Night	8% 4 2 4 3 3 4 3 4 5% 59%	2090
	11th to 20th	Night	15% 5% 2 4 3 3 3 3 3 6% 53%	2278
	21st to end	Night	17% 8% 2 6% 4 4 3 3 5% 5% 43%	2687
November	1st to 10th	Night	11% 6% 2 6% 3 3 4 3 5% 5% 53%	2536
	11th to 20th	Night	13% 9% 2 5% 4 4 3 3 5% 6% 46%	2600
	21st to end	Night	19% 9% 3 6% 4 4 3 2 5% 6% 39%	2600
December	1st to 10th	Night	15% 9% 3 7% 4 3 3 3 4 5% 44%	4405
	11th to 20th	Night	18% 8% 3 7% 4 4 4 3 5% 6% 37%	5199
	21st to end	Night	30% 15% 4 7% 4 4 3 3 4 4 21%	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	55% 6% 10% 21% 8% 1	3618
	11th to 20th	Day	57% 6% 11% 14% 9% 2	3620
	21st to end	Day	58% 5% 7% 19% 8% 3	4327
February	1st to 10th	Day	53% 5% 11% 21% 9% 2	1952
	11th to 20th	Day	51% 6% 11% 20% 10% 2	1958
	21st to end	Day	51% 6% 9% 21% 10% 3	1570
March	1st to 10th	Day	55% 5% 7% 18% 13% 3	3120
	11th to 20th	Day	37% 6% 13% 26% 16% 2	3268
	21st to end	Day	46% 10% 14% 22% 7% 1	4165
April	1st to 10th	Day	41% 7% 13% 23% 15% 1	2280
	11th to 20th	Day	43% 6% 10% 24% 14% 3	2254
	21st to end	Day	46% 6% 11% 23% 11% 3	2323
May	1st to 10th	Day	43% 12% 17% 22% 7%	4120
	11th to 20th	Day	43% 8% 12% 26% 11%	4085
	21st to end	Day	34% 10% 13% 20% 20% 2	4795
June	1st to 10th	Day	33% 8% 14% 24% 17% 4	2660
	11th to 20th	Day	33% 7% 12% 22% 21% 4	2660
	21st to end	Day	34% 10% 15% 22% 15% 4	2660
July	1st to 10th	Day	37% 7% 12% 27% 15% 2	4371
	11th to 20th	Day	28% 9% 14% 31% 17% 1	4365
	21st to end	Day	41% 10% 16% 21% 11% 1	4662
August	1st to 10th	Day	26% 7% 14% 35% 16% 1	3977
	11th to 20th	Day	34% 8% 14% 26% 16% 1	3765
	21st to end	Day	26% 7% 17% 31% 15% 4	4179
September	1st to 10th	Day	36% 7% 11% 22% 19% 5%	2280
	11th to 20th	Day	32% 6% 12% 25% 23% 3	2138
	21st to end	Day	32% 4 11% 24% 25% 4	2090
October	1st to 10th	Day	19% 4 8% 25% 40% 4	3465
	11th to 20th	Day	26% 4 8% 24% 35% 3	3140
	21st to end	Day	36% 3 8% 24% 28% 1	3122
November	1st to 10th	Day	33% 4 10% 29% 17% 6%	1762
	11th to 20th	Day	43% 4 9% 22% 17% 5%	1800
	21st to end	Day	48% 6% 9% 21% 15% 1	1800
December	1st to 10th	Day	41% 5% 13% 27% 13% 1	2775
	11th to 20th	Day	56% 5% 9% 22% 7% 1	3005
	21st to end	Day	70% 6% 10% 11% 3	3982
January	1st to 10th	Night	55% 5% 11% 21% 8%	6348
	11th to 20th	Night	60% 4 8% 13% 11% 3	6360
	21st to end	Night	55% 4 8% 20% 11% 1	6649
February	1st to 10th	Night	53% 7% 12% 18% 9% 1	2445
	11th to 20th	Night	50% 5% 11% 19% 14% 2	2339
	21st to end	Night	49% 5% 11% 21% 11% 2	1885
March	1st to 10th	Night	52% 7% 8% 21% 11% 2	3733
	11th to 20th	Night	35% 7% 11% 24% 22% 2	3719
	21st to end	Night	45% 7% 12% 27% 7% 1	3466
April	1st to 10th	Night	40% 7% 11% 26% 14% 3	1900
	11th to 20th	Night	38% 6% 10% 22% 20% 4	1875
	21st to end	Night	45% 7% 10% 21% 13% 3	1857
May	1st to 10th	Night	44% 12% 16% 20% 7% 1	2840
	11th to 20th	Night	40% 7% 15% 25% 12%	2813
	21st to end	Night	34% 11% 14% 19% 17% 4	2788
June	1st to 10th	Night	33% 6% 11% 25% 22% 3	1520
	11th to 20th	Night	28% 8% 11% 24% 23% 6%	1520
	21st to end	Night	29% 9% 14% 22% 19% 7%	1520
July	1st to 10th	Night	34% 7% 11% 24% 21% 4	2490
	11th to 20th	Night	25% 7% 12% 31% 22% 2	2482
	21st to end	Night	40% 8% 15% 20% 14% 2	2662
August	1st to 10th	Night	24% 7% 16% 37% 15% 1	2925
	11th to 20th	Night	29% 8% 13% 29% 20% 1	3130
	21st to end	Night	23% 7% 15% 30% 21% 4	3476
September	1st to 10th	Night	30% 5% 10% 27% 21% 6%	1900
	11th to 20th	Night	26% 5% 9% 28% 27% 5%	2021
	21st to end	Night	33% 5% 11% 21% 25% 5%	2090
October	1st to 10th	Night	17% 4 7% 22% 45% 5%	3480
	11th to 20th	Night	24% 3 7% 26% 36% 4	3777
	21st to end	Night	32% 5% 8% 24% 25% 6%	4425
November	1st to 10th	Night	33% 4 11% 24% 22% 5%	2536
	11th to 20th	Night	38% 4 10% 23% 21% 3	2600
	21st to end	Night	47% 4 11% 22% 15% 1	2600
December	1st to 10th	Night	43% 4 11% 26% 16%	4405
	11th to 20th	Night	47% 6% 13% 21% 13%	5201
	21st to end	Night	67% 5% 10% 13% 5% 1	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% 16% 34% 20% 7% 1	300
	11th to 20th	Day	26% 17% 34% 20% 3	300
	21st to end	Day	22% 17% 38% 18% 5%	330
February	1st to 10th	Day	25% 16% 39% 16% 5%	300
	11th to 20th	Day	23% 22% 32% 17% 3 2	300
	21st to end	Day	28% 14% 34% 20% 4	225
March	1st to 10th	Day	22% 19% 36% 20% 3	270
	11th to 20th	Day	24% 19% 37% 15% 5%	302
	21st to end	Day	26% 15% 35% 17% 6% 1	506
April	1st to 10th	Day	18% 14% 35% 25% 7% 2	460
	11th to 20th	Day	18% 16% 28% 22% 14% 2	452
	21st to end	Day	21% 13% 35% 21% 7% 3	460
May	1st to 10th	Day	20% 13% 29% 25% 12% 2	463
	11th to 20th	Day	19% 8% 24% 27% 14% 8%	487
	21st to end	Day	9% 5% 29% 29% 18% 10%	705
June	1st to 10th	Day	11% 6% 23% 28% 24% 8%	680
	11th to 20th	Day	8% 5% 23% 34% 25% 7%	680
	21st to end	Day	9% 5% 28% 27% 22% 9%	680
July	1st to 10th	Day	10% 3 13% 26% 27% 21%	671
	11th to 20th	Day	7% 3 14% 36% 26% 15%	668
	21st to end	Day	9% 3 14% 31% 32% 11%	739
August	1st to 10th	Day	10% 4 10% 28% 33% 15%	515
	11th to 20th	Day	11% 3 15% 29% 28% 14%	479
	21st to end	Day	6% 1 12% 24% 40% 18%	539
September	1st to 10th	Day	11% 3 15% 26% 33% 13%	490
	11th to 20th	Day	8% 1 11% 29% 33% 17%	490
	21st to end	Day	14% 5% 23% 23% 23% 12%	490
October	1st to 10th	Day	9% 3 25% 31% 24% 8%	488
	11th to 20th	Day	12% 13% 36% 23% 12% 4	300
	21st to end	Day	25% 17% 30% 23% 5% 1	330
November	1st to 10th	Day	14% 10% 33% 24% 14% 5%	300
	11th to 20th	Day	16% 21% 31% 21% 9% 2	300
	21st to end	Day	20% 14% 30% 25% 9%	300
December	1st to 10th	Day	12% 20% 39% 20% 6% 3	300
	11th to 20th	Day	22% 14% 36% 20% 8%	300
	21st to end	Day	30% 16% 31% 16% 5% 1	330
January	1st to 10th	Night	19% 14% 37% 26% 4	1000
	11th to 20th	Night	24% 13% 37% 21% 4	1000
	21st to end	Night	20% 13% 38% 26% 3	1100
February	1st to 10th	Night	24% 11% 38% 24% 2	845
	11th to 20th	Night	22% 16% 35% 25% 3	783
	21st to end	Night	24% 13% 39% 23% 1	629
March	1st to 10th	Night	22% 12% 36% 26% 4	760
	11th to 20th	Night	20% 12% 37% 24% 6%	751
	21st to end	Night	24% 9% 32% 28% 6%	627
April	1st to 10th	Night	15% 13% 32% 33% 7%	570
	11th to 20th	Night	19% 10% 27% 31% 12% 1	563
	21st to end	Night	21% 8% 32% 31% 6% 1	570
May	1st to 10th	Night	16% 7% 34% 33% 9% 1	570
	11th to 20th	Night	16% 5% 25% 36% 17% 2	561
	21st to end	Night	12% 4 19% 37% 26% 2	617
June	1st to 10th	Night	11% 5% 20% 41% 22% 1	570
	11th to 20th	Night	8% 3 18% 47% 23% 1	570
	21st to end	Night	7% 2 22% 40% 28% 1	570
July	1st to 10th	Night	9% 3 12% 33% 35% 8%	555
	11th to 20th	Night	5% 3 14% 39% 35% 5%	552
	21st to end	Night	7% 2 12% 42% 33% 4	624
August	1st to 10th	Night	8% 2 9% 42% 35% 5%	567
	11th to 20th	Night	7% 1 10% 43% 35% 4	564
	21st to end	Night	6% 1 11% 33% 43% 6%	627
September	1st to 10th	Night	12% 2 12% 35% 33% 5%	570
	11th to 20th	Night	8% 2 13% 35% 38% 4	691
	21st to end	Night	13% 4 20% 31% 27% 4	760
October	1st to 10th	Night	9% 5% 22% 38% 23% 4	760
	11th to 20th	Night	18% 9% 28% 29% 15% 1	760
	21st to end	Night	21% 10% 33% 28% 8%	836
November	1st to 10th	Night	14% 8% 34% 31% 12% 1	780
	11th to 20th	Night	17% 11% 32% 31% 9%	800
	21st to end	Night	23% 12% 30% 27% 8%	800
December	1st to 10th	Night	21% 10% 38% 25% 6%	890
	11th to 20th	Night	24% 9% 33% 28% 6% 1	1000
	21st to end	Night	31% 13% 31% 21% 4	1100

Page generated at 2025-02-18 02:26:28. Version ac07

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