Whitetail Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Whitetail Observatory clear sky chart from 2005-11-06 to 2026-06-16.

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	12% 6% 2 5% 4 4 4 3 5% 7% 47%	137750
	Night	13% 6% 2 5% 3 3 3 3 5% 7% 51%	134652
Transparency	Day	35% 6% 10% 21% 19% 10%	141506
	Night	33% 5% 10% 20% 20% 12%	138963
Seeing	Day	13% 7% 22% 29% 23% 6%	17009
	Night	14% 7% 26% 35% 15% 1	26939

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	12% 8% 3 6% 3 3 3 3 4 6% 50%	5289
	11th to 20th	Day	12% 6% 2 4 3 2 3 3 5% 5% 56%	5310
	21st to end	Day	23% 8% 3 8% 4 3 2 2 3 5% 40%	6083
February	1st to 10th	Day	18% 8% 3 5% 3 3 3 3 3 6% 46%	2100
	11th to 20th	Day	17% 7% 2 5% 3 4 3 3 4 6% 46%	2049
	21st to end	Day	18% 6% 2 4 2 3 2 3 3 5% 51%	1730
March	1st to 10th	Day	13% 6% 3 6% 3 3 3 3 4 5% 51%	5038
	11th to 20th	Day	14% 6% 2 5% 3 3 3 3 4 6% 50%	5090
	21st to end	Day	13% 8% 3 6% 4 3 4 3 5% 6% 46%	5583
April	1st to 10th	Day	15% 9% 2 6% 4 3 4 4 5% 6% 42%	2310
	11th to 20th	Day	17% 7% 3 6% 5% 4 4 4 4 5% 42%	2286
	21st to end	Day	16% 6% 2 5% 5% 4 4 3 6% 6% 44%	2689
May	1st to 10th	Day	21% 8% 3 6% 3 4 4 3 6% 7% 35%	7617
	11th to 20th	Day	12% 7% 3 7% 4 4 5% 4 6% 8% 42%	7627
	21st to end	Day	13% 6% 2 7% 5% 5% 6% 5% 7% 10% 33%	8392
June	1st to 10th	Day	5% 4 2 6% 5% 5% 6% 4 6% 9% 48%	2730
	11th to 20th	Day	7% 4 1 5% 4 5% 5% 5% 7% 9% 48%	2666
	21st to end	Day	7% 5% 2 5% 6% 5% 6% 5% 7% 9% 43%	2600
July	1st to 10th	Day	10% 6% 2 7% 5% 5% 5% 4 6% 9% 40%	5900
	11th to 20th	Day	4 3 2 5% 4 5% 5% 5% 7% 11% 49%	5900
	21st to end	Day	6% 5% 2 5% 4 5% 5% 5% 8% 11% 44%	6422
August	1st to 10th	Day	1 1 1 2 2 3 3 2 5% 8% 71%	4234
	11th to 20th	Day	3 2 1 3 3 3 4 4 7% 11% 60%	3951
	21st to end	Day	4 2 1 5% 4 5% 6% 5% 8% 11% 49%	4096
September	1st to 10th	Day	9% 5% 2 5% 5% 4 5% 4 5% 8% 47%	2200
	11th to 20th	Day	10% 5% 2 5% 5% 5% 4 3 6% 9% 45%	2200
	21st to end	Day	6% 4 2 5% 3 5% 5% 4 5% 8% 54%	2200
October	1st to 10th	Day	6% 4 2 4 3 3 3 3 4 6% 62%	2200
	11th to 20th	Day	11% 4 1 5% 3 3 3 3 4 6% 57%	2033
	21st to end	Day	10% 5% 1 4 3 3 2 2 3 5% 60%	2200
November	1st to 10th	Day	13% 7% 2 5% 3 3 4 3 4 5% 51%	2058
	11th to 20th	Day	10% 5% 2 5% 4 4 4 3 4 6% 54%	1979
	21st to end	Day	16% 7% 2 5% 4 3 4 3 5% 5% 47%	1890
December	1st to 10th	Day	21% 7% 2 5% 4 3 3 3 4 5% 43%	3030
	11th to 20th	Day	16% 7% 2 6% 3 4 4 3 5% 5% 45%	3481
	21st to end	Day	14% 6% 2 4 3 2 3 2 4 4 58%	4587
January	1st to 10th	Night	14% 6% 2 4 3 3 3 3 3 5% 55%	7634
	11th to 20th	Night	9% 4 1 3 2 2 2 2 5% 5% 64%	7680
	21st to end	Night	26% 7% 2 6% 3 3 2 2 4 5% 40%	8186
February	1st to 10th	Night	17% 8% 2 4 3 3 2 2 3 5% 50%	2520
	11th to 20th	Night	18% 7% 2 5% 3 3 3 2 4 5% 49%	2458
	21st to end	Night	18% 7% 2 4 3 3 3 2 3 5% 49%	2076
March	1st to 10th	Night	15% 7% 2 5% 4 4 4 3 4 7% 46%	5035
	11th to 20th	Night	15% 6% 2 5% 3 3 3 3 4 5% 50%	5090
	21st to end	Night	16% 10% 3 6% 4 3 3 3 3 6% 44%	5588
April	1st to 10th	Night	13% 7% 2 5% 5% 3 4 4 5% 6% 46%	2310
	11th to 20th	Night	17% 7% 3 5% 4 3 4 4 5% 6% 44%	2283
	21st to end	Night	16% 7% 2 5% 4 3 3 3 4 6% 46%	1925
May	1st to 10th	Night	22% 8% 2 6% 4 3 3 3 5% 7% 35%	5266
	11th to 20th	Night	10% 6% 2 7% 5% 5% 5% 3 6% 7% 45%	5265
	21st to end	Night	13% 7% 3 7% 4 4 5% 4 6% 9% 36%	5793
June	1st to 10th	Night	6% 4 1 3 3 3 4 4 6% 9% 58%	1890
	11th to 20th	Night	5% 3 1 4 3 3 4 4 6% 9% 57%	1845
	21st to end	Night	5% 4 2 4 3 4 4 4 6% 10% 53%	1800
July	1st to 10th	Night	8% 6% 2 6% 4 4 4 4 7% 11% 43%	4078
	11th to 20th	Night	3 3 1 4 3 3 4 3 7% 12% 56%	4077
	21st to end	Night	5% 5% 2 5% 4 4 5% 5% 7% 10% 48%	4449
August	1st to 10th	Night	1 1 2 1 1 2 2 4 7% 78%	2926
	11th to 20th	Night	3 2 1 3 2 3 3 4 7% 10% 62%	3102
	21st to end	Night	4 3 1 4 4 3 4 3 6% 11% 57%	3806
September	1st to 10th	Night	8% 6% 2 5% 4 4 4 3 6% 8% 51%	2200
	11th to 20th	Night	9% 6% 2 6% 5% 4 4 3 5% 8% 47%	2200
	21st to end	Night	8% 4 1 4 3 3 3 3 6% 8% 58%	2200
October	1st to 10th	Night	6% 3 1 3 3 3 3 3 4 6% 65%	2200
	11th to 20th	Night	11% 4 1 4 3 2 3 2 4 6% 59%	2345
	21st to end	Night	13% 4 2 3 2 3 3 2 3 4 60%	2640
November	1st to 10th	Night	13% 6% 2 5% 3 3 2 3 3 5% 55%	2460
	11th to 20th	Night	9% 5% 2 5% 3 3 3 2 5% 5% 58%	2636
	21st to end	Night	17% 6% 2 5% 3 4 3 3 4 5% 49%	2730
December	1st to 10th	Night	19% 8% 2 5% 3 3 4 3 4 5% 44%	4380
	11th to 20th	Night	17% 10% 3 5% 3 3 2 2 3 4 47%	4946
	21st to end	Night	16% 6% 2 4 2 2 2 2 3 4 57%	6633

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	36% 4 5% 24% 22% 9%	5290
	11th to 20th	Day	31% 2 5% 16% 28% 19%	5310
	21st to end	Day	49% 2 4 12% 23% 11%	6083
February	1st to 10th	Day	42% 4 6% 12% 22% 15%	2100
	11th to 20th	Day	40% 4 7% 18% 19% 11%	2059
	21st to end	Day	38% 4 4 18% 21% 15%	1730
March	1st to 10th	Day	36% 4 5% 18% 17% 20%	5038
	11th to 20th	Day	35% 5% 6% 9% 16% 28%	5090
	21st to end	Day	39% 5% 8% 20% 21% 8%	5585
April	1st to 10th	Day	44% 5% 7% 17% 14% 13%	2310
	11th to 20th	Day	43% 6% 7% 15% 18% 11%	2286
	21st to end	Day	40% 6% 7% 19% 19% 8%	2689
May	1st to 10th	Day	47% 6% 11% 19% 14% 3	7655
	11th to 20th	Day	40% 6% 10% 17% 23% 5%	7631
	21st to end	Day	43% 9% 12% 23% 11% 2	8405
June	1st to 10th	Day	30% 9% 13% 26% 19% 3	2730
	11th to 20th	Day	30% 7% 14% 26% 18% 6%	2666
	21st to end	Day	33% 9% 14% 23% 18% 3	2600
July	1st to 10th	Day	39% 7% 19% 29% 6% 1	5836
	11th to 20th	Day	26% 8% 17% 32% 15% 2	5831
	21st to end	Day	31% 9% 16% 26% 15% 3	6240
August	1st to 10th	Day	12% 4 11% 38% 33% 1	4220
	11th to 20th	Day	17% 6% 22% 38% 13% 3	3990
	21st to end	Day	25% 11% 18% 26% 18% 2	4095
September	1st to 10th	Day	36% 7% 10% 20% 17% 10%	2200
	11th to 20th	Day	36% 7% 13% 21% 18% 5%	2200
	21st to end	Day	28% 6% 10% 21% 20% 15%	2200
October	1st to 10th	Day	15% 3 7% 13% 25% 37%	3590
	11th to 20th	Day	19% 3 8% 18% 31% 20%	3286
	21st to end	Day	24% 4 5% 20% 33% 14%	3538
November	1st to 10th	Day	35% 5% 9% 16% 23% 11%	2058
	11th to 20th	Day	33% 5% 8% 18% 21% 16%	1979
	21st to end	Day	40% 4 6% 17% 20% 13%	1890
December	1st to 10th	Day	45% 3 6% 16% 20% 9%	3030
	11th to 20th	Day	40% 5% 7% 11% 24% 13%	3479
	21st to end	Day	31% 4 5% 17% 28% 15%	4587
January	1st to 10th	Night	34% 3 5% 20% 25% 13%	7635
	11th to 20th	Night	23% 2 4 18% 31% 22%	7680
	21st to end	Night	49% 3 3 11% 21% 13%	8186
February	1st to 10th	Night	39% 3 5% 13% 22% 18%	2520
	11th to 20th	Night	40% 3 6% 17% 19% 14%	2458
	21st to end	Night	39% 4 6% 14% 20% 17%	2076
March	1st to 10th	Night	38% 6% 6% 16% 21% 14%	5035
	11th to 20th	Night	37% 5% 8% 10% 15% 25%	5090
	21st to end	Night	42% 5% 7% 17% 20% 9%	5588
April	1st to 10th	Night	38% 6% 9% 17% 16% 15%	2310
	11th to 20th	Night	41% 6% 10% 13% 16% 14%	2283
	21st to end	Night	40% 5% 11% 18% 18% 9%	1925
May	1st to 10th	Night	48% 6% 9% 20% 13% 4	5293
	11th to 20th	Night	38% 7% 10% 19% 19% 8%	5266
	21st to end	Night	43% 7% 15% 24% 8% 3	5805
June	1st to 10th	Night	22% 7% 16% 30% 22% 3	1890
	11th to 20th	Night	23% 7% 16% 29% 19% 6%	1845
	21st to end	Night	26% 7% 17% 28% 18% 4	1800
July	1st to 10th	Night	35% 9% 24% 27% 5% 1	4035
	11th to 20th	Night	21% 7% 23% 35% 13% 1	4026
	21st to end	Night	29% 9% 21% 25% 13% 4	4320
August	1st to 10th	Night	8% 4 13% 43% 31% 1	2916
	11th to 20th	Night	18% 5% 30% 33% 13% 2	3129
	21st to end	Night	21% 10% 21% 28% 17% 2	3806
September	1st to 10th	Night	31% 7% 14% 23% 16% 9%	2200
	11th to 20th	Night	34% 8% 14% 23% 15% 7%	2200
	21st to end	Night	24% 6% 13% 25% 18% 13%	2200
October	1st to 10th	Night	14% 3 7% 15% 20% 40%	3590
	11th to 20th	Night	19% 3 8% 17% 32% 22%	3818
	21st to end	Night	24% 3 6% 19% 31% 17%	4252
November	1st to 10th	Night	33% 5% 7% 17% 23% 14%	2460
	11th to 20th	Night	30% 4 7% 20% 22% 16%	2636
	21st to end	Night	39% 4 7% 16% 18% 15%	2730
December	1st to 10th	Night	43% 4 6% 17% 20% 10%	4380
	11th to 20th	Night	42% 3 6% 9% 23% 17%	4947
	21st to end	Night	34% 3 4 16% 28% 15%	6633

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	18% 13% 37% 24% 7% 1	330
	11th to 20th	Day	20% 13% 32% 26% 8% 1	330
	21st to end	Day	22% 14% 36% 22% 6%	363
February	1st to 10th	Day	24% 13% 34% 21% 8%	330
	11th to 20th	Day	22% 16% 37% 21% 4	330
	21st to end	Day	26% 13% 40% 18% 3	273
March	1st to 10th	Day	19% 16% 36% 24% 5%	330
	11th to 20th	Day	17% 20% 38% 18% 6%	330
	21st to end	Day	18% 11% 37% 24% 8% 1	363
April	1st to 10th	Day	19% 20% 35% 19% 5% 1	330
	11th to 20th	Day	19% 14% 39% 21% 7%	324
	21st to end	Day	21% 13% 35% 24% 7% 1	709
May	1st to 10th	Day	18% 11% 36% 27% 7% 1	753
	11th to 20th	Day	16% 8% 31% 29% 14% 2	775
	21st to end	Day	15% 6% 26% 34% 16% 3	844
June	1st to 10th	Day	7% 3 16% 41% 27% 6%	780
	11th to 20th	Day	8% 2 16% 45% 24% 5%	756
	21st to end	Day	5% 2 13% 38% 32% 10%	730
July	1st to 10th	Day	7% 2 9% 37% 35% 11%	721
	11th to 20th	Day	3 1 6% 35% 46% 9%	718
	21st to end	Day	4 1 4 32% 47% 11%	794
August	1st to 10th	Day	2 4 31% 49% 14%	726
	11th to 20th	Day	4 1 4 31% 46% 15%	586
	21st to end	Day	5% 1 5% 22% 41% 26%	458
September	1st to 10th	Day	9% 1 5% 22% 42% 22%	330
	11th to 20th	Day	6% 8% 23% 44% 18%	330
	21st to end	Day	10% 1 6% 29% 36% 18%	330
October	1st to 10th	Day	2 2 12% 32% 37% 14%	330
	11th to 20th	Day	9% 4 23% 32% 25% 7%	330
	21st to end	Day	19% 11% 21% 25% 20% 4	363
November	1st to 10th	Day	19% 7% 24% 33% 13% 5%	330
	11th to 20th	Day	16% 6% 30% 29% 15% 4	330
	21st to end	Day	18% 15% 32% 20% 12% 2	330
December	1st to 10th	Day	17% 9% 32% 28% 12% 3	330
	11th to 20th	Day	19% 14% 32% 24% 10% 2	330
	21st to end	Day	17% 13% 37% 23% 9% 2	363
January	1st to 10th	Night	19% 10% 32% 31% 7%	1050
	11th to 20th	Night	17% 11% 34% 31% 7%	1050
	21st to end	Night	21% 12% 33% 29% 6%	1081
February	1st to 10th	Night	24% 10% 33% 28% 5%	840
	11th to 20th	Night	24% 13% 36% 25% 3	824
	21st to end	Night	23% 13% 40% 21% 3	692
March	1st to 10th	Night	20% 15% 36% 25% 3	636
	11th to 20th	Night	19% 11% 35% 32% 4	630
	21st to end	Night	16% 11% 42% 26% 4	693
April	1st to 10th	Night	15% 12% 41% 29% 3	630
	11th to 20th	Night	21% 12% 39% 24% 4	623
	21st to end	Night	18% 10% 41% 22% 8%	630
May	1st to 10th	Night	16% 11% 38% 29% 6%	630
	11th to 20th	Night	13% 8% 33% 33% 11% 1	621
	21st to end	Night	11% 6% 33% 34% 14%	683
June	1st to 10th	Night	4 4 23% 44% 23% 1	630
	11th to 20th	Night	6% 1 30% 48% 15% 1	615
	21st to end	Night	6% 2 15% 48% 26% 3	600
July	1st to 10th	Night	7% 2 11% 48% 29% 3	585
	11th to 20th	Night	4 9% 57% 27% 2	582
	21st to end	Night	4 1 10% 51% 33% 2	657
August	1st to 10th	Night	1 6% 56% 33% 5%	597
	11th to 20th	Night	6% 1 6% 51% 32% 4	594
	21st to end	Night	4 1 5% 42% 42% 5%	660
September	1st to 10th	Night	9% 3 8% 41% 35% 5%	600
	11th to 20th	Night	10% 2 6% 41% 39% 3	600
	21st to end	Night	10% 1 10% 40% 36% 4	600
October	1st to 10th	Night	6% 1 12% 47% 30% 5%	600
	11th to 20th	Night	12% 3 21% 40% 21% 2	745
	21st to end	Night	14% 9% 25% 31% 20% 1	880
November	1st to 10th	Night	14% 5% 23% 39% 18% 1	820
	11th to 20th	Night	12% 7% 28% 38% 14% 1	956
	21st to end	Night	19% 9% 29% 30% 12% 1	1050
December	1st to 10th	Night	17% 8% 32% 32% 9% 1	1050
	11th to 20th	Night	22% 10% 29% 33% 6%	1050
	21st to end	Night	20% 9% 30% 33% 8%	1155

Page generated at 2026-06-13 01:31:41. Version ac07

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