Whippoorwill Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Whippoorwill Hill Observatory clear sky chart from 2005-11-06 to 2026-03-03.

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	16% 10% 3 8% 5% 5% 4 3 5% 6% 32%	131358
	Night	17% 12% 4 9% 5% 4 4 3 5% 6% 31%	129796
Transparency	Day	52% 3 11% 22% 11% 1	134849
	Night	54% 3 11% 20% 11% 1	134392
Seeing	Day	24% 14% 31% 20% 9% 3	16059
	Night	24% 12% 30% 24% 9% 1	25336

By Month

Percentage Cloud Cover NE (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	13% 17% 5% 13% 6% 6% 4 3 4 5% 22%	4661
	11th to 20th	Day	12% 19% 8% 16% 6% 5% 5% 3 4 4 19%	4650
	21st to end	Day	11% 16% 6% 14% 8% 8% 5% 3 4 4 20%	5500
February	1st to 10th	Day	16% 14% 4 12% 8% 4 5% 4 5% 5% 24%	1890
	11th to 20th	Day	12% 15% 5% 11% 6% 5% 5% 3 4 6% 27%	1843
	21st to end	Day	20% 15% 5% 11% 5% 5% 4 4 4 5% 22%	1724
March	1st to 10th	Day	19% 14% 4 11% 5% 4 4 3 4 5% 28%	4578
	11th to 20th	Day	11% 13% 4 8% 5% 6% 5% 4 5% 7% 32%	4980
	21st to end	Day	18% 11% 3 7% 5% 4 3 3 3 4 38%	5729
April	1st to 10th	Day	21% 13% 3 6% 5% 4 4 2 4 5% 33%	2400
	11th to 20th	Day	21% 10% 2 6% 4 3 3 3 5% 5% 37%	2374
	21st to end	Day	22% 9% 3 8% 4 4 3 4 5% 5% 32%	2509
May	1st to 10th	Day	25% 10% 3 8% 5% 4 4 3 4 6% 27%	6346
	11th to 20th	Day	17% 8% 3 8% 5% 4 5% 3 5% 7% 34%	6318
	21st to end	Day	19% 8% 3 6% 4 5% 5% 3 5% 8% 34%	6949
June	1st to 10th	Day	21% 8% 2 7% 6% 4 5% 4 5% 7% 31%	2800
	11th to 20th	Day	15% 5% 2 6% 5% 5% 5% 4 6% 8% 38%	2800
	21st to end	Day	17% 8% 3 7% 5% 5% 4 5% 5% 7% 34%	2800
July	1st to 10th	Day	13% 6% 3 7% 5% 5% 6% 4 6% 10% 35%	6360
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 4 6% 9% 43%	6360
	21st to end	Day	10% 5% 2 6% 4 4 5% 4 7% 9% 45%	6926
August	1st to 10th	Day	17% 8% 3 6% 5% 4 4 3 6% 6% 38%	4402
	11th to 20th	Day	17% 7% 2 5% 4 4 4 4 6% 9% 38%	4141
	21st to end	Day	15% 5% 2 6% 4 4 5% 4 6% 9% 39%	4312
September	1st to 10th	Day	13% 5% 2 6% 4 5% 5% 3 6% 7% 43%	2400
	11th to 20th	Day	12% 4 2 6% 4 4 4 4 5% 7% 48%	2400
	21st to end	Day	19% 6% 2 6% 4 4 4 3 5% 6% 40%	2125
October	1st to 10th	Day	21% 7% 2 6% 5% 4 3 3 5% 6% 38%	2000
	11th to 20th	Day	20% 9% 3 7% 5% 5% 5% 3 5% 7% 31%	2000
	21st to end	Day	25% 10% 2 8% 4 4 5% 4 4 5% 28%	2074
November	1st to 10th	Day	15% 10% 3 8% 5% 5% 5% 4 5% 6% 33%	1851
	11th to 20th	Day	17% 13% 4 11% 4 5% 4 3 4 6% 30%	1682
	21st to end	Day	20% 16% 5% 9% 6% 5% 5% 3 5% 5% 22%	1680
December	1st to 10th	Day	21% 18% 5% 11% 6% 4 4 3 5% 4 17%	2680
	11th to 20th	Day	18% 19% 5% 11% 6% 4 4 3 3 4 24%	3066
	21st to end	Day	22% 17% 5% 12% 5% 4 3 2 3 4 22%	4048
January	1st to 10th	Night	14% 16% 7% 14% 7% 5% 4 3 4 5% 22%	8234
	11th to 20th	Night	12% 18% 7% 16% 7% 5% 5% 3 4 5% 18%	8235
	21st to end	Night	13% 15% 6% 12% 7% 6% 5% 3 5% 5% 23%	8665
February	1st to 10th	Night	14% 16% 5% 10% 6% 6% 4 4 6% 6% 23%	2730
	11th to 20th	Night	13% 16% 5% 10% 7% 5% 4 3 4 6% 28%	2663
	21st to end	Night	14% 16% 5% 9% 5% 5% 4 3 5% 6% 28%	2081
March	1st to 10th	Night	21% 14% 4 9% 5% 4 3 3 3 4 30%	5305
	11th to 20th	Night	14% 12% 3 7% 4 4 5% 4 7% 8% 31%	4979
	21st to end	Night	19% 11% 3 8% 4 4 4 3 4 5% 35%	5202
April	1st to 10th	Night	21% 10% 3 8% 5% 4 4 3 4 5% 33%	2000
	11th to 20th	Night	21% 9% 2 7% 4 4 4 3 4 5% 37%	1975
	21st to end	Night	20% 10% 3 7% 5% 3 4 3 4 6% 33%	1905
May	1st to 10th	Night	25% 10% 3 8% 4 4 5% 3 5% 6% 25%	3594
	11th to 20th	Night	15% 8% 2 7% 4 4 4 3 5% 7% 40%	3575
	21st to end	Night	18% 8% 3 7% 4 4 4 4 6% 7% 34%	3926
June	1st to 10th	Night	16% 7% 3 7% 5% 5% 5% 4 7% 6% 35%	1600
	11th to 20th	Night	14% 7% 2 5% 4 4 5% 4 6% 7% 42%	1600
	21st to end	Night	17% 7% 2 7% 5% 5% 5% 5% 6% 7% 35%	1600
July	1st to 10th	Night	12% 6% 2 8% 5% 5% 6% 5% 7% 9% 36%	3600
	11th to 20th	Night	12% 6% 2 6% 4 4 5% 4 6% 7% 46%	3600
	21st to end	Night	9% 6% 2 6% 4 4 4 4 5% 7% 49%	3926
August	1st to 10th	Night	11% 7% 2 7% 4 4 4 3 6% 7% 44%	2744
	11th to 20th	Night	12% 7% 2 8% 5% 4 4 4 5% 7% 43%	2875
	21st to end	Night	11% 5% 2 6% 4 5% 5% 4 6% 9% 43%	3586
September	1st to 10th	Night	12% 6% 2 6% 5% 4 4 3 5% 7% 47%	2000
	11th to 20th	Night	12% 4 2 5% 3 3 4 4 5% 6% 52%	2000
	21st to end	Night	17% 7% 2 6% 4 4 4 3 5% 7% 43%	2271
October	1st to 10th	Night	17% 8% 3 6% 4 4 4 4 5% 7% 39%	2400
	11th to 20th	Night	21% 8% 2 7% 5% 4 4 4 5% 6% 32%	2400
	21st to end	Night	23% 9% 3 7% 5% 4 4 4 5% 6% 30%	2765
November	1st to 10th	Night	18% 11% 3 6% 4 3 5% 4 5% 6% 35%	2667
	11th to 20th	Night	17% 11% 4 8% 4 4 4 4 4 6% 33%	2935
	21st to end	Night	21% 13% 4 10% 5% 4 5% 4 5% 6% 24%	2940
December	1st to 10th	Night	19% 18% 5% 12% 6% 6% 4 3 4 5% 18%	4720
	11th to 20th	Night	22% 14% 4 9% 5% 4 4 3 3 4 26%	5348
	21st to end	Night	26% 16% 4 12% 4 3 3 3 5% 4 19%	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	64% 2 13% 15% 4 1	4662
	11th to 20th	Day	71% 2 8% 10% 9% 1	4680
	21st to end	Day	68% 3 9% 10% 10% 1	5500
February	1st to 10th	Day	62% 3 8% 20% 6% 1	1890
	11th to 20th	Day	59% 2 9% 19% 9% 1	1852
	21st to end	Day	67% 2 8% 12% 10% 1	1724
March	1st to 10th	Day	61% 1 9% 14% 12% 3	4581
	11th to 20th	Day	52% 3 16% 15% 12% 2	4980
	21st to end	Day	51% 2 5% 20% 19% 3	5729
April	1st to 10th	Day	55% 3 6% 19% 14% 3	2400
	11th to 20th	Day	51% 3 5% 21% 17% 2	2374
	21st to end	Day	54% 3 8% 17% 14% 4	2509
May	1st to 10th	Day	60% 3 8% 18% 10% 2	6357
	11th to 20th	Day	51% 3 12% 20% 13% 1	6322
	21st to end	Day	49% 3 12% 23% 11% 1	6949
June	1st to 10th	Day	53% 4 9% 21% 13% 1	2800
	11th to 20th	Day	43% 4 10% 27% 13% 2	2800
	21st to end	Day	49% 4 13% 21% 12% 1	2800
July	1st to 10th	Day	42% 5% 13% 28% 11%	6290
	11th to 20th	Day	37% 5% 14% 30% 15%	6285
	21st to end	Day	35% 5% 13% 37% 10%	6728
August	1st to 10th	Day	46% 3 15% 25% 11% 1	4388
	11th to 20th	Day	43% 4 14% 28% 10% 1	4180
	21st to end	Day	41% 3 15% 30% 11%	4312
September	1st to 10th	Day	40% 4 14% 29% 12% 1	2400
	11th to 20th	Day	36% 4 12% 32% 16%	2400
	21st to end	Day	46% 4 13% 26% 12%	2125
October	1st to 10th	Day	44% 3 11% 32% 9%	3260
	11th to 20th	Day	46% 3 15% 26% 10% 1	3240
	21st to end	Day	49% 4 15% 25% 7%	3325
November	1st to 10th	Day	51% 3 14% 23% 9%	1851
	11th to 20th	Day	56% 3 12% 17% 10% 1	1682
	21st to end	Day	65% 3 12% 12% 8%	1680
December	1st to 10th	Day	70% 3 14% 9% 3	2680
	11th to 20th	Day	66% 3 11% 14% 6%	3066
	21st to end	Day	68% 2 8% 15% 6%	4048
January	1st to 10th	Night	67% 2 13% 13% 5%	8234
	11th to 20th	Night	71% 2 9% 10% 7%	8280
	21st to end	Night	64% 2 8% 13% 12% 1	8665
February	1st to 10th	Night	62% 3 9% 18% 7% 1	2730
	11th to 20th	Night	59% 3 9% 20% 9% 1	2665
	21st to end	Night	59% 3 9% 17% 10% 1	2081
March	1st to 10th	Night	60% 2 6% 17% 11% 4	5315
	11th to 20th	Night	51% 3 18% 17% 9% 3	4980
	21st to end	Night	53% 3 6% 23% 14% 2	5202
April	1st to 10th	Night	54% 2 7% 20% 14% 2	2000
	11th to 20th	Night	51% 3 7% 21% 17% 1	1975
	21st to end	Night	53% 3 8% 17% 16% 3	1905
May	1st to 10th	Night	60% 3 8% 17% 9% 3	3600
	11th to 20th	Night	45% 3 14% 22% 14% 1	3576
	21st to end	Night	49% 3 13% 19% 14% 1	3927
June	1st to 10th	Night	48% 5% 11% 23% 13% 1	1600
	11th to 20th	Night	41% 4 13% 23% 18% 2	1600
	21st to end	Night	46% 6% 12% 22% 13% 1	1600
July	1st to 10th	Night	42% 5% 16% 20% 16% 1	3560
	11th to 20th	Night	37% 5% 13% 33% 12%	3552
	21st to end	Night	35% 5% 12% 32% 15% 1	3809
August	1st to 10th	Night	40% 5% 14% 27% 13% 1	2734
	11th to 20th	Night	40% 4 14% 31% 10% 1	2902
	21st to end	Night	38% 5% 15% 30% 11% 1	3586
September	1st to 10th	Night	37% 4 12% 31% 15% 1	2000
	11th to 20th	Night	33% 4 13% 35% 14% 1	2000
	21st to end	Night	43% 3 11% 30% 13% 1	2271
October	1st to 10th	Night	41% 3 11% 30% 15%	3920
	11th to 20th	Night	45% 3 15% 27% 10%	3899
	21st to end	Night	48% 4 14% 25% 8%	4464
November	1st to 10th	Night	50% 3 13% 22% 11% 1	2667
	11th to 20th	Night	53% 3 11% 20% 11% 2	2935
	21st to end	Night	62% 3 12% 17% 5%	2940
December	1st to 10th	Night	69% 4 11% 12% 3	4720
	11th to 20th	Night	62% 4 10% 14% 10% 1	5348
	21st to end	Night	70% 2 7% 12% 9%	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	28% 15% 40% 13% 4	220
	11th to 20th	Day	36% 14% 33% 13% 3	220
	21st to end	Day	23% 21% 33% 17% 5%	311
February	1st to 10th	Day	32% 20% 34% 12% 2	330
	11th to 20th	Day	29% 24% 38% 8% 1	330
	21st to end	Day	35% 17% 36% 10% 2	440
March	1st to 10th	Day	28% 20% 31% 16% 4	508
	11th to 20th	Day	31% 17% 32% 15% 5%	500
	21st to end	Day	33% 19% 28% 12% 7% 1	550
April	1st to 10th	Day	32% 20% 28% 13% 6%	500
	11th to 20th	Day	35% 17% 23% 14% 8% 2	492
	21st to end	Day	31% 16% 34% 12% 5% 2	500
May	1st to 10th	Day	26% 15% 31% 19% 7% 2	503
	11th to 20th	Day	20% 13% 37% 20% 8% 2	527
	21st to end	Day	21% 13% 32% 23% 10% 2	573
June	1st to 10th	Day	24% 11% 34% 22% 7% 2	530
	11th to 20th	Day	17% 14% 32% 22% 12% 2	530
	21st to end	Day	21% 12% 31% 22% 11% 3	530
July	1st to 10th	Day	14% 6% 31% 31% 13% 3	525
	11th to 20th	Day	16% 8% 32% 27% 14% 4	524
	21st to end	Day	14% 8% 32% 29% 13% 4	576
August	1st to 10th	Day	16% 5% 29% 32% 14% 4	526
	11th to 20th	Day	14% 6% 28% 30% 16% 7%	519
	21st to end	Day	17% 9% 31% 25% 12% 6%	583
September	1st to 10th	Day	16% 11% 29% 24% 12% 7%	530
	11th to 20th	Day	12% 7% 24% 27% 19% 11%	530
	21st to end	Day	21% 9% 29% 23% 14% 4	530
October	1st to 10th	Day	25% 13% 27% 19% 12% 4	530
	11th to 20th	Day	29% 16% 31% 16% 6% 2	530
	21st to end	Day	30% 18% 28% 20% 4	513
November	1st to 10th	Day	27% 17% 28% 20% 7%	425
	11th to 20th	Day	28% 14% 37% 12% 6% 2	222
	21st to end	Day	32% 20% 34% 11% 3	220
December	1st to 10th	Day	34% 16% 33% 12% 5%	220
	11th to 20th	Day	36% 20% 32% 7% 4	220
	21st to end	Day	36% 15% 31% 12% 5%	242
January	1st to 10th	Night	28% 16% 33% 19% 3	840
	11th to 20th	Night	31% 16% 29% 20% 4	840
	21st to end	Night	22% 15% 34% 23% 6%	924
February	1st to 10th	Night	24% 18% 34% 20% 3	840
	11th to 20th	Night	24% 18% 37% 18% 3	823
	21st to end	Night	25% 17% 35% 18% 4	692
March	1st to 10th	Night	27% 15% 31% 22% 4	809
	11th to 20th	Night	27% 19% 28% 22% 4	800
	21st to end	Night	26% 15% 31% 21% 7%	880
April	1st to 10th	Night	29% 14% 32% 22% 3	800
	11th to 20th	Night	28% 18% 27% 19% 7% 1	791
	21st to end	Night	26% 12% 29% 25% 7% 1	705
May	1st to 10th	Night	26% 9% 26% 28% 10% 2	400
	11th to 20th	Night	15% 11% 33% 32% 9% 1	394
	21st to end	Night	13% 11% 37% 28% 11%	433
June	1st to 10th	Night	17% 7% 30% 36% 10% 1	400
	11th to 20th	Night	17% 9% 29% 31% 14% 1	400
	21st to end	Night	19% 6% 26% 36% 14% 1	400
July	1st to 10th	Night	12% 4 32% 35% 16% 1	390
	11th to 20th	Night	14% 3 27% 39% 15% 1	388
	21st to end	Night	10% 5% 29% 41% 14% 1	438
August	1st to 10th	Night	13% 4 24% 36% 21% 1	491
	11th to 20th	Night	14% 3 22% 35% 24% 2	594
	21st to end	Night	13% 6% 29% 33% 17% 2	880
September	1st to 10th	Night	15% 6% 31% 30% 18% 1	800
	11th to 20th	Night	16% 5% 20% 30% 24% 5%	800
	21st to end	Night	20% 8% 26% 25% 19% 2	800
October	1st to 10th	Night	22% 10% 27% 23% 16% 2	800
	11th to 20th	Night	27% 11% 31% 24% 7% 1	800
	21st to end	Night	29% 13% 27% 25% 6%	880
November	1st to 10th	Night	29% 13% 29% 21% 8%	820
	11th to 20th	Night	26% 16% 31% 17% 9%	840
	21st to end	Night	31% 16% 27% 19% 6%	840
December	1st to 10th	Night	30% 16% 32% 18% 4	840
	11th to 20th	Night	28% 19% 32% 17% 3 1	840
	21st to end	Night	35% 15% 29% 19% 3	924

Page generated at 2026-02-28 01:40:26. Version ac07

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