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 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	12% 6% 2 5% 4 4 4 3 5% 7% 48%	109178
	Night	13% 6% 2 5% 3 3 3 3 5% 6% 51%	109655
Transparency	Day	34% 6% 10% 21% 20% 9%	112973
	Night	33% 5% 10% 20% 20% 12%	113987
Seeing	Day	13% 7% 22% 29% 23% 7%	15217
	Night	14% 7% 26% 35% 15% 1	25279

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% 9% 3 5% 3 3 3 3 4 6% 48%	4077
	11th to 20th	Day	13% 6% 2 4 2 2 2 2 5% 6% 54%	4080
	21st to end	Day	25% 8% 3 6% 3 3 2 2 3 4 43%	4690
February	1st to 10th	Day	19% 8% 3 5% 3 3 3 3 3 6% 46%	2000
	11th to 20th	Day	17% 7% 2 5% 3 4 3 3 4 5% 46%	1949
	21st to end	Day	19% 6% 2 4 3 3 2 3 4 5% 50%	1570
March	1st to 10th	Day	15% 7% 3 7% 4 4 4 3 4 5% 43%	3428
	11th to 20th	Day	20% 8% 3 8% 5% 4 4 4 5% 6% 33%	3480
	21st to end	Day	13% 8% 3 6% 4 3 4 3 5% 6% 44%	3814
April	1st to 10th	Day	14% 9% 2 6% 4 3 4 3 5% 6% 42%	2090
	11th to 20th	Day	17% 7% 3 6% 5% 3 3 4 4 5% 43%	2066
	21st to end	Day	15% 6% 2 5% 5% 4 4 3 5% 6% 46%	2432
May	1st to 10th	Day	22% 9% 3 7% 4 4 4 4 5% 7% 31%	4082
	11th to 20th	Day	15% 6% 2 6% 4 4 4 3 5% 6% 44%	4082
	21st to end	Day	12% 6% 2 7% 6% 5% 6% 6% 8% 10% 33%	4477
June	1st to 10th	Day	5% 4 2 5% 4 5% 6% 4 6% 9% 50%	2470
	11th to 20th	Day	7% 4 1 4 4 4 5% 5% 7% 9% 49%	2470
	21st to end	Day	7% 5% 2 5% 6% 5% 6% 5% 7% 9% 42%	2470
July	1st to 10th	Day	6% 4 2 5% 5% 5% 5% 4 6% 8% 50%	4120
	11th to 20th	Day	4 3 1 4 4 4 4 4 7% 11% 53%	4120
	21st to end	Day	9% 6% 2 6% 5% 5% 5% 5% 8% 11% 39%	4465
August	1st to 10th	Day	1 1 1 2 2 3 3 2 5% 8% 71%	4104
	11th to 20th	Day	3 2 1 3 3 3 4 4 7% 11% 60%	3828
	21st to end	Day	4 2 1 5% 4 5% 6% 5% 8% 11% 49%	3970
September	1st to 10th	Day	9% 5% 2 5% 5% 4 5% 4 6% 8% 47%	2090
	11th to 20th	Day	10% 6% 2 5% 5% 6% 5% 3 6% 9% 43%	2090
	21st to end	Day	7% 4 2 5% 3 5% 4 4 5% 8% 53%	2090
October	1st to 10th	Day	6% 4 2 4 3 3 3 3 5% 6% 61%	2090
	11th to 20th	Day	12% 4 2 5% 3 3 3 3 4 6% 55%	1932
	21st to end	Day	11% 5% 1 4 3 3 2 2 4 5% 60%	2090
November	1st to 10th	Day	14% 8% 2 5% 3 4 4 3 5% 5% 49%	1958
	11th to 20th	Day	10% 5% 2 5% 4 4 4 3 4 6% 53%	1885
	21st to end	Day	16% 7% 2 5% 4 3 4 3 5% 5% 48%	1800
December	1st to 10th	Day	21% 7% 2 5% 4 3 4 3 4 5% 42%	2940
	11th to 20th	Day	16% 7% 2 5% 3 4 4 3 5% 5% 45%	3391
	21st to end	Day	14% 6% 2 4 3 2 2 2 4 4 58%	4488
January	1st to 10th	Night	17% 7% 2 4 2 2 2 2 3 5% 53%	5888
	11th to 20th	Night	11% 4 1 3 2 2 2 2 4 5% 65%	5900
	21st to end	Night	26% 7% 2 6% 3 2 2 2 4 5% 41%	6329
February	1st to 10th	Night	18% 8% 2 4 3 4 2 2 3 5% 49%	2400
	11th to 20th	Night	19% 6% 2 5% 2 3 3 2 4 5% 49%	2338
	21st to end	Night	19% 7% 2 4 3 3 3 3 3 5% 48%	1884
March	1st to 10th	Night	17% 8% 2 6% 4 4 5% 3 4 6% 42%	3425
	11th to 20th	Night	21% 9% 3 6% 4 4 4 4 5% 5% 34%	3480
	21st to end	Night	14% 8% 3 7% 4 4 4 3 4 6% 43%	3817
April	1st to 10th	Night	12% 7% 2 4 5% 3 4 4 5% 6% 47%	2090
	11th to 20th	Night	17% 7% 3 5% 3 3 4 4 5% 6% 44%	2063
	21st to end	Night	14% 7% 2 5% 4 3 3 4 4 6% 48%	1743
May	1st to 10th	Night	24% 9% 3 5% 3 3 3 3 5% 7% 36%	2823
	11th to 20th	Night	11% 6% 2 5% 4 4 4 3 5% 7% 50%	2823
	21st to end	Night	13% 6% 2 5% 4 4 5% 4 6% 8% 42%	3090
June	1st to 10th	Night	5% 3 1 3 3 3 4 4 6% 10% 59%	1710
	11th to 20th	Night	5% 3 1 4 3 3 4 4 6% 9% 58%	1710
	21st to end	Night	5% 4 2 4 3 4 4 4 6% 10% 53%	1710
July	1st to 10th	Night	4 4 1 4 3 3 4 4 6% 10% 56%	2850
	11th to 20th	Night	3 4 1 4 3 3 4 3 7% 10% 59%	2850
	21st to end	Night	7% 6% 3 6% 4 4 5% 5% 6% 10% 43%	3098
August	1st to 10th	Night	1 1 2 1 1 2 2 4 7% 78%	2836
	11th to 20th	Night	3 2 1 3 2 3 3 4 7% 10% 62%	3006
	21st to end	Night	4 3 1 4 4 3 4 3 6% 10% 57%	3690
September	1st to 10th	Night	8% 6% 2 5% 4 4 4 3 6% 8% 51%	2090
	11th to 20th	Night	9% 6% 2 6% 5% 4 4 3 5% 8% 46%	2090
	21st to end	Night	8% 4 1 4 3 3 3 3 6% 8% 57%	2090
October	1st to 10th	Night	7% 3 1 3 3 3 3 2 4 6% 64%	2090
	11th to 20th	Night	12% 4 1 4 3 2 3 3 4 6% 58%	2228
	21st to end	Night	13% 5% 2 3 2 3 3 3 3 4 60%	2508
November	1st to 10th	Night	14% 6% 2 5% 3 3 2 3 3 6% 53%	2340
	11th to 20th	Night	9% 5% 2 5% 3 3 3 2 5% 5% 58%	2510
	21st to end	Night	17% 6% 2 5% 3 4 3 3 4 5% 49%	2600
December	1st to 10th	Night	19% 8% 2 5% 3 3 4 3 5% 5% 43%	4250
	11th to 20th	Night	17% 10% 3 5% 3 3 2 2 3 4 47%	4816
	21st to end	Night	16% 6% 2 4 2 2 2 2 3 4 57%	6490

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	38% 4 5% 23% 20% 10%	4078
	11th to 20th	Day	31% 2 5% 17% 26% 17%	4080
	21st to end	Day	48% 2 3 10% 23% 14%	4690
February	1st to 10th	Day	42% 4 6% 11% 22% 15%	2000
	11th to 20th	Day	41% 4 6% 18% 19% 12%	1959
	21st to end	Day	40% 5% 4 17% 19% 15%	1570
March	1st to 10th	Day	43% 5% 7% 14% 21% 11%	3428
	11th to 20th	Day	50% 8% 8% 10% 16% 8%	3480
	21st to end	Day	39% 6% 10% 16% 22% 8%	3814
April	1st to 10th	Day	43% 5% 7% 18% 14% 13%	2090
	11th to 20th	Day	42% 6% 7% 16% 19% 11%	2066
	21st to end	Day	39% 6% 6% 20% 21% 9%	2432
May	1st to 10th	Day	52% 7% 10% 14% 13% 5%	4120
	11th to 20th	Day	39% 7% 9% 16% 24% 5%	4086
	21st to end	Day	40% 11% 13% 24% 10% 2	4489
June	1st to 10th	Day	29% 8% 12% 27% 19% 4	2470
	11th to 20th	Day	29% 7% 13% 27% 17% 6%	2470
	21st to end	Day	34% 9% 13% 23% 18% 3	2470
July	1st to 10th	Day	29% 7% 17% 38% 8% 1	4056
	11th to 20th	Day	24% 7% 16% 32% 18% 2	4051
	21st to end	Day	35% 10% 18% 28% 9% 1	4325
August	1st to 10th	Day	12% 4 12% 37% 33% 2	4090
	11th to 20th	Day	17% 6% 22% 38% 14% 3	3867
	21st to end	Day	25% 11% 18% 26% 18% 2	3969
September	1st to 10th	Day	36% 7% 11% 20% 17% 10%	2090
	11th to 20th	Day	37% 7% 12% 19% 18% 6%	2090
	21st to end	Day	28% 6% 10% 21% 20% 14%	2090
October	1st to 10th	Day	15% 3 7% 13% 24% 38%	3480
	11th to 20th	Day	20% 3 8% 18% 31% 20%	3185
	21st to end	Day	24% 4 5% 20% 34% 14%	3428
November	1st to 10th	Day	37% 5% 9% 17% 21% 11%	1958
	11th to 20th	Day	33% 5% 8% 17% 21% 16%	1885
	21st to end	Day	39% 4 6% 17% 20% 14%	1800
December	1st to 10th	Day	45% 3 6% 17% 19% 9%	2940
	11th to 20th	Day	41% 5% 7% 11% 23% 13%	3389
	21st to end	Day	31% 4 4 17% 28% 15%	4488
January	1st to 10th	Night	36% 3 4 21% 24% 12%	5888
	11th to 20th	Night	24% 2 4 19% 31% 20%	5900
	21st to end	Night	47% 3 4 11% 20% 15%	6329
February	1st to 10th	Night	40% 4 5% 13% 21% 18%	2400
	11th to 20th	Night	40% 3 6% 17% 19% 14%	2338
	21st to end	Night	40% 4 6% 14% 18% 17%	1884
March	1st to 10th	Night	42% 7% 7% 15% 19% 10%	3425
	11th to 20th	Night	50% 7% 10% 11% 14% 8%	3480
	21st to end	Night	41% 6% 8% 15% 21% 8%	3817
April	1st to 10th	Night	37% 6% 9% 17% 17% 15%	2090
	11th to 20th	Night	40% 6% 10% 13% 17% 14%	2063
	21st to end	Night	38% 5% 10% 19% 20% 9%	1743
May	1st to 10th	Night	48% 6% 9% 17% 14% 5%	2850
	11th to 20th	Night	33% 7% 10% 24% 17% 8%	2824
	21st to end	Night	37% 8% 13% 28% 9% 4	3099
June	1st to 10th	Night	21% 7% 16% 30% 23% 3	1710
	11th to 20th	Night	22% 7% 15% 30% 20% 6%	1710
	21st to end	Night	26% 7% 16% 28% 18% 4	1710
July	1st to 10th	Night	22% 9% 24% 37% 7% 1	2805
	11th to 20th	Night	20% 7% 19% 36% 16% 1	2796
	21st to end	Night	34% 8% 22% 28% 7%	2999
August	1st to 10th	Night	8% 4 14% 42% 31% 1	2826
	11th to 20th	Night	18% 5% 29% 33% 13% 2	3033
	21st to end	Night	21% 10% 21% 28% 17% 2	3690
September	1st to 10th	Night	30% 7% 14% 24% 16% 8%	2090
	11th to 20th	Night	34% 8% 14% 22% 15% 7%	2090
	21st to end	Night	25% 7% 14% 23% 19% 13%	2090
October	1st to 10th	Night	14% 3 7% 15% 20% 41%	3480
	11th to 20th	Night	19% 3 9% 16% 32% 22%	3701
	21st to end	Night	24% 3 6% 19% 31% 17%	4120
November	1st to 10th	Night	34% 5% 8% 18% 22% 14%	2340
	11th to 20th	Night	30% 4 7% 20% 22% 17%	2510
	21st to end	Night	39% 4 7% 16% 18% 16%	2600
December	1st to 10th	Night	43% 4 6% 17% 19% 10%	4250
	11th to 20th	Night	42% 3 6% 9% 23% 16%	4817
	21st to end	Night	34% 3 4 16% 29% 16%	6490

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	19% 13% 38% 23% 6% 1	300
	11th to 20th	Day	21% 13% 32% 26% 7% 1	300
	21st to end	Day	23% 13% 34% 23% 6%	330
February	1st to 10th	Day	25% 14% 33% 20% 8%	300
	11th to 20th	Day	23% 16% 37% 19% 4	300
	21st to end	Day	27% 13% 40% 18% 1	225
March	1st to 10th	Day	20% 16% 36% 23% 5%	270
	11th to 20th	Day	20% 19% 37% 17% 7%	270
	21st to end	Day	20% 13% 39% 21% 7%	297
April	1st to 10th	Day	19% 22% 37% 17% 4 1	270
	11th to 20th	Day	19% 14% 38% 20% 8%	264
	21st to end	Day	18% 12% 36% 24% 8% 1	612
May	1st to 10th	Day	17% 11% 36% 28% 8%	653
	11th to 20th	Day	18% 6% 29% 31% 15% 2	675
	21st to end	Day	16% 6% 26% 33% 16% 3	734
June	1st to 10th	Day	6% 2 15% 41% 29% 6%	680
	11th to 20th	Day	7% 2 16% 46% 24% 5%	680
	21st to end	Day	5% 2 13% 38% 32% 10%	680
July	1st to 10th	Day	6% 2 8% 38% 36% 11%	671
	11th to 20th	Day	3 1 6% 34% 47% 10%	668
	21st to end	Day	4 1 4 32% 47% 11%	739
August	1st to 10th	Day	2 4 31% 50% 14%	676
	11th to 20th	Day	5% 1 4 31% 46% 14%	543
	21st to end	Day	5% 5% 22% 41% 25%	420
September	1st to 10th	Day	8% 1 5% 21% 42% 24%	300
	11th to 20th	Day	7% 8% 24% 42% 19%	300
	21st to end	Day	10% 1 6% 28% 37% 18%	300
October	1st to 10th	Day	3 3 13% 33% 36% 13%	300
	11th to 20th	Day	10% 4 22% 33% 25% 6%	300
	21st to end	Day	20% 12% 22% 24% 19% 4	330
November	1st to 10th	Day	20% 7% 24% 33% 12% 4	300
	11th to 20th	Day	17% 7% 30% 27% 15% 4	300
	21st to end	Day	18% 17% 32% 20% 11% 2	300
December	1st to 10th	Day	17% 8% 32% 27% 13% 3	300
	11th to 20th	Day	19% 14% 33% 24% 10%	300
	21st to end	Day	18% 12% 38% 22% 7% 2	330
January	1st to 10th	Night	20% 10% 32% 30% 7%	1000
	11th to 20th	Night	18% 11% 33% 31% 7%	1000
	21st to end	Night	20% 11% 33% 29% 6%	1030
February	1st to 10th	Night	24% 10% 33% 28% 5%	800
	11th to 20th	Night	24% 13% 36% 24% 2	784
	21st to end	Night	24% 14% 41% 19% 3	628
March	1st to 10th	Night	20% 14% 36% 25% 4	576
	11th to 20th	Night	19% 10% 34% 32% 4	570
	21st to end	Night	15% 12% 43% 25% 4	627
April	1st to 10th	Night	14% 11% 42% 30% 3	570
	11th to 20th	Night	20% 12% 39% 24% 5%	563
	21st to end	Night	16% 10% 42% 23% 8% 1	570
May	1st to 10th	Night	16% 11% 39% 28% 6%	570
	11th to 20th	Night	13% 7% 33% 35% 12% 1	561
	21st to end	Night	11% 7% 33% 35% 14%	617
June	1st to 10th	Night	4 3 22% 45% 25% 1	570
	11th to 20th	Night	6% 1 30% 47% 16% 1	570
	21st to end	Night	6% 2 15% 47% 27% 3	570
July	1st to 10th	Night	6% 2 11% 48% 29% 4	555
	11th to 20th	Night	4 9% 57% 28% 2	552
	21st to end	Night	4 1 10% 51% 33% 2	624
August	1st to 10th	Night	1 6% 56% 32% 5%	567
	11th to 20th	Night	7% 1 6% 50% 33% 4	564
	21st to end	Night	4 1 5% 43% 42% 5%	627
September	1st to 10th	Night	9% 3 8% 41% 35% 5%	570
	11th to 20th	Night	10% 2 6% 40% 39% 3	570
	21st to end	Night	10% 10% 38% 37% 4	570
October	1st to 10th	Night	6% 1 12% 48% 28% 5%	570
	11th to 20th	Night	13% 4 22% 40% 20% 2	708
	21st to end	Night	14% 8% 25% 30% 21% 1	836
November	1st to 10th	Night	14% 5% 23% 38% 18% 1	780
	11th to 20th	Night	12% 7% 28% 37% 15% 1	910
	21st to end	Night	19% 9% 30% 30% 11% 1	1000
December	1st to 10th	Night	17% 8% 32% 33% 10% 1	1000
	11th to 20th	Night	22% 10% 29% 32% 6% 1	1000
	21st to end	Night	20% 9% 30% 32% 8%	1100

Page generated at 2025-02-18 02:26:29. Version ac07

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