The HomCav Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The HomCav Observatory clear sky chart from 2005-11-06 to 2025-10-04.

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	17% 10% 4 9% 5% 5% 5% 4 5% 7% 29%	126830
	Night	17% 11% 4 10% 6% 5% 4 4 5% 6% 29%	122519
Transparency	Day	53% 6% 11% 19% 10% 1	130361
	Night	54% 6% 11% 18% 10% 1	127076
Seeing	Day	25% 16% 28% 18% 9% 3	15898
	Night	23% 15% 28% 24% 10% 1	25082

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	11% 17% 10% 23% 7% 3 3 2 3 4 15%	3597
	11th to 20th	Day	13% 17% 9% 20% 9% 6% 4 3 4 4 13%	3570
	21st to end	Day	15% 15% 7% 12% 7% 5% 5% 3 5% 5% 21%	4466
February	1st to 10th	Day	16% 15% 6% 14% 8% 5% 5% 4 5% 5% 18%	1800
	11th to 20th	Day	13% 15% 6% 14% 8% 5% 4 4 4 5% 20%	1808
	21st to end	Day	21% 12% 4 12% 8% 5% 3 4 4 4 24%	1650
March	1st to 10th	Day	21% 14% 5% 10% 6% 5% 3 3 4 4 26%	4568
	11th to 20th	Day	13% 13% 5% 8% 6% 4 4 3 4 6% 34%	4980
	21st to end	Day	16% 11% 4 12% 6% 5% 5% 4 5% 5% 28%	5729
April	1st to 10th	Day	19% 14% 4 8% 5% 4 5% 3 4 6% 29%	2400
	11th to 20th	Day	19% 12% 3 7% 4 4 5% 3 5% 5% 33%	2374
	21st to end	Day	19% 12% 3 8% 5% 4 3 3 5% 6% 33%	2400
May	1st to 10th	Day	30% 10% 3 7% 3 4 4 3 4 6% 26%	6218
	11th to 20th	Day	20% 10% 3 8% 5% 5% 5% 3 5% 7% 29%	6318
	21st to end	Day	20% 9% 3 7% 4 4 5% 4 7% 8% 30%	6949
June	1st to 10th	Day	17% 7% 4 6% 5% 4 5% 4 6% 8% 33%	2800
	11th to 20th	Day	16% 7% 2 6% 6% 5% 5% 4 7% 9% 33%	2800
	21st to end	Day	14% 7% 2 7% 6% 5% 5% 5% 7% 9% 33%	2800
July	1st to 10th	Day	9% 7% 2 6% 5% 5% 6% 5% 8% 10% 36%	6360
	11th to 20th	Day	9% 6% 2 8% 6% 5% 7% 5% 9% 11% 32%	6360
	21st to end	Day	12% 6% 3 7% 5% 5% 5% 4 6% 8% 39%	6913
August	1st to 10th	Day	19% 6% 3 8% 4 5% 5% 5% 6% 8% 31%	4234
	11th to 20th	Day	17% 6% 3 7% 5% 6% 6% 5% 7% 10% 27%	4019
	21st to end	Day	17% 6% 2 6% 4 5% 5% 4 7% 9% 36%	4312
September	1st to 10th	Day	16% 6% 3 6% 5% 4 4 4 5% 8% 39%	2400
	11th to 20th	Day	14% 6% 2 6% 4 4 5% 3 5% 7% 43%	2400
	21st to end	Day	19% 8% 3 7% 5% 4 4 4 6% 7% 33%	2137
October	1st to 10th	Day	18% 8% 3 7% 4 5% 5% 4 6% 7% 32%	1930
	11th to 20th	Day	20% 9% 4 7% 5% 4 4 3 5% 6% 32%	1900
	21st to end	Day	22% 13% 2 9% 5% 4 5% 3 4 6% 26%	2016
November	1st to 10th	Day	14% 12% 3 8% 4 4 5% 3 5% 7% 35%	1761
	11th to 20th	Day	15% 14% 4 11% 5% 4 4 3 5% 6% 28%	1715
	21st to end	Day	19% 16% 4 9% 6% 5% 4 4 4 7% 20%	1600
December	1st to 10th	Day	19% 16% 8% 15% 6% 5% 5% 4 4 5% 13%	2600
	11th to 20th	Day	20% 18% 7% 11% 4 4 3 3 3 4 23%	2986
	21st to end	Day	20% 19% 7% 12% 5% 5% 4 3 4 5% 17%	3960
January	1st to 10th	Night	14% 13% 6% 25% 8% 5% 4 4 4 5% 13%	6349
	11th to 20th	Night	11% 14% 7% 17% 9% 6% 5% 4 5% 6% 17%	6299
	21st to end	Night	16% 12% 5% 13% 9% 6% 5% 4 5% 5% 19%	6490
February	1st to 10th	Night	16% 13% 4 11% 7% 6% 6% 4 5% 6% 22%	2600
	11th to 20th	Night	14% 12% 5% 14% 8% 6% 6% 4 5% 5% 20%	2478
	21st to end	Night	18% 11% 3 14% 6% 5% 4 4 5% 6% 23%	1980
March	1st to 10th	Night	18% 11% 6% 10% 8% 5% 4 3 5% 6% 25%	5258
	11th to 20th	Night	16% 13% 4 8% 5% 3 3 3 5% 6% 34%	4979
	21st to end	Night	18% 12% 3 10% 6% 5% 5% 3 4 5% 27%	5202
April	1st to 10th	Night	20% 13% 4 7% 5% 4 4 3 5% 6% 29%	2000
	11th to 20th	Night	20% 12% 3 7% 5% 3 4 3 5% 6% 34%	1975
	21st to end	Night	19% 9% 3 5% 5% 4 4 3 6% 6% 36%	2000
May	1st to 10th	Night	33% 9% 3 7% 4 4 4 2 4 5% 25%	3750
	11th to 20th	Night	19% 9% 3 6% 4 4 4 4 6% 6% 34%	3575
	21st to end	Night	21% 9% 3 7% 5% 4 4 4 5% 6% 30%	3926
June	1st to 10th	Night	17% 8% 2 6% 4 3 4 4 5% 9% 38%	1600
	11th to 20th	Night	15% 7% 2 5% 5% 4 3 5% 6% 9% 38%	1600
	21st to end	Night	12% 4 2 5% 5% 5% 5% 3 6% 9% 43%	1600
July	1st to 10th	Night	9% 7% 3 8% 5% 4 5% 4 6% 9% 40%	3600
	11th to 20th	Night	12% 7% 2 6% 5% 5% 5% 4 6% 10% 38%	3600
	21st to end	Night	12% 6% 2 6% 4 4 4 4 6% 8% 46%	3926
August	1st to 10th	Night	19% 6% 3 7% 4 5% 5% 4 6% 6% 36%	2912
	11th to 20th	Night	17% 8% 2 6% 5% 4 3 4 4 6% 41%	2997
	21st to end	Night	14% 6% 2 6% 4 5% 4 3 5% 9% 43%	3586
September	1st to 10th	Night	14% 6% 2 5% 4 4 4 4 5% 7% 44%	2000
	11th to 20th	Night	12% 5% 2 5% 4 4 4 3 5% 6% 50%	2000
	21st to end	Night	18% 6% 2 7% 5% 4 5% 4 5% 8% 37%	2260
October	1st to 10th	Night	18% 8% 3 8% 4 4 4 3 5% 6% 36%	2317
	11th to 20th	Night	20% 8% 3 7% 4 4 4 3 5% 6% 36%	2280
	21st to end	Night	23% 12% 3 8% 5% 4 3 2 5% 6% 27%	2579
November	1st to 10th	Night	13% 9% 4 9% 5% 4 5% 4 5% 6% 37%	2537
	11th to 20th	Night	19% 11% 3 8% 5% 4 5% 4 5% 6% 30%	2680
	21st to end	Night	15% 14% 5% 7% 6% 5% 5% 5% 7% 7% 24%	2800
December	1st to 10th	Night	15% 14% 6% 13% 6% 5% 5% 4 6% 7% 18%	4580
	11th to 20th	Night	23% 14% 5% 10% 4 3 4 3 4 5% 25%	5208
	21st to end	Night	23% 17% 6% 9% 7% 4 4 3 4 6% 17%	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	74% 3 7% 13% 3	3598
	11th to 20th	Day	74% 4 7% 9% 5% 1	3600
	21st to end	Day	63% 5% 9% 16% 6%	4466
February	1st to 10th	Day	67% 6% 9% 13% 5%	1800
	11th to 20th	Day	65% 6% 6% 16% 6%	1817
	21st to end	Day	63% 4 10% 16% 6% 1	1650
March	1st to 10th	Day	62% 4 10% 14% 9% 1	4571
	11th to 20th	Day	51% 4 17% 17% 8% 3	4980
	21st to end	Day	57% 4 8% 15% 14% 2	5729
April	1st to 10th	Day	56% 5% 7% 21% 9% 2	2400
	11th to 20th	Day	52% 5% 10% 17% 14% 1	2374
	21st to end	Day	52% 5% 9% 19% 13% 3	2400
May	1st to 10th	Day	60% 5% 9% 15% 10% 1	6229
	11th to 20th	Day	53% 7% 9% 20% 10% 1	6322
	21st to end	Day	50% 7% 12% 19% 11% 1	6949
June	1st to 10th	Day	47% 7% 12% 20% 14% 1	2800
	11th to 20th	Day	46% 8% 14% 22% 10% 1	2800
	21st to end	Day	44% 9% 14% 21% 11% 1	2800
July	1st to 10th	Day	39% 9% 15% 25% 11% 1	6290
	11th to 20th	Day	41% 10% 15% 25% 10%	6285
	21st to end	Day	41% 7% 12% 25% 15%	6715
August	1st to 10th	Day	50% 8% 13% 18% 11% 1	4221
	11th to 20th	Day	48% 9% 14% 22% 6%	4058
	21st to end	Day	43% 7% 11% 31% 7% 1	4312
September	1st to 10th	Day	43% 6% 11% 26% 13% 1	2400
	11th to 20th	Day	40% 6% 11% 24% 18% 1	2400
	21st to end	Day	49% 7% 11% 21% 11% 1	2137
October	1st to 10th	Day	45% 7% 10% 24% 13% 1	3190
	11th to 20th	Day	46% 5% 11% 22% 15% 1	3140
	21st to end	Day	42% 5% 16% 25% 10% 1	3306
November	1st to 10th	Day	47% 6% 13% 20% 12% 1	1761
	11th to 20th	Day	55% 4 12% 18% 9% 2	1715
	21st to end	Day	62% 6% 13% 14% 4	1600
December	1st to 10th	Day	72% 5% 9% 11% 2	2600
	11th to 20th	Day	65% 5% 10% 12% 8%	2986
	21st to end	Day	70% 3 10% 11% 5%	3960
January	1st to 10th	Night	72% 5% 9% 9% 4	6349
	11th to 20th	Night	66% 6% 11% 12% 5% 1	6344
	21st to end	Night	66% 4 8% 9% 11% 1	6490
February	1st to 10th	Night	61% 6% 12% 14% 7%	2600
	11th to 20th	Night	65% 5% 9% 13% 6% 1	2480
	21st to end	Night	60% 6% 11% 15% 8% 1	1980
March	1st to 10th	Night	60% 4 12% 14% 10%	5268
	11th to 20th	Night	51% 4 19% 17% 6% 3	4980
	21st to end	Night	58% 4 7% 19% 11% 1	5202
April	1st to 10th	Night	57% 4 10% 18% 9% 2	2000
	11th to 20th	Night	50% 6% 11% 18% 15%	1975
	21st to end	Night	47% 6% 11% 20% 13% 4	2000
May	1st to 10th	Night	62% 6% 7% 14% 9% 2	3756
	11th to 20th	Night	48% 9% 13% 18% 11% 1	3576
	21st to end	Night	52% 8% 10% 18% 11% 1	3927
June	1st to 10th	Night	42% 7% 11% 24% 15%	1600
	11th to 20th	Night	42% 8% 14% 23% 11% 2	1600
	21st to end	Night	37% 8% 14% 26% 13% 1	1600
July	1st to 10th	Night	41% 7% 15% 22% 14% 1	3560
	11th to 20th	Night	40% 8% 14% 24% 14% 1	3552
	21st to end	Night	36% 7% 12% 26% 18% 1	3809
August	1st to 10th	Night	48% 8% 14% 22% 9% 1	2902
	11th to 20th	Night	44% 7% 14% 25% 10%	3024
	21st to end	Night	38% 7% 11% 32% 11% 1	3586
September	1st to 10th	Night	40% 7% 13% 24% 16% 1	2000
	11th to 20th	Night	34% 7% 11% 30% 17% 1	2000
	21st to end	Night	46% 7% 11% 21% 14% 1	2260
October	1st to 10th	Night	50% 7% 9% 22% 11% 1	3837
	11th to 20th	Night	42% 6% 13% 21% 14% 3	3779
	21st to end	Night	43% 5% 15% 27% 9% 1	4239
November	1st to 10th	Night	46% 6% 11% 20% 14% 2	2537
	11th to 20th	Night	53% 5% 12% 19% 10% 2	2680
	21st to end	Night	55% 8% 14% 18% 5%	2800
December	1st to 10th	Night	63% 7% 11% 17% 2	4580
	11th to 20th	Night	61% 4 11% 13% 10%	5208
	21st to end	Night	69% 5% 8% 12% 6% 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	30% 25% 31% 11% 3 1	200
	11th to 20th	Day	40% 25% 27% 7% 2 1	200
	21st to end	Day	27% 31% 28% 10% 4	330
February	1st to 10th	Day	34% 28% 31% 7% 1	300
	11th to 20th	Day	37% 32% 26% 5% 1	355
	21st to end	Day	36% 22% 30% 9% 2	414
March	1st to 10th	Day	34% 21% 30% 11% 4 1	500
	11th to 20th	Day	34% 22% 27% 13% 4	500
	21st to end	Day	33% 25% 27% 10% 3 2	550
April	1st to 10th	Day	37% 19% 26% 13% 4 1	500
	11th to 20th	Day	31% 24% 25% 10% 6% 3	492
	21st to end	Day	33% 17% 28% 15% 5% 2	500
May	1st to 10th	Day	32% 18% 29% 12% 6% 3	503
	11th to 20th	Day	25% 16% 29% 18% 9% 3	527
	21st to end	Day	21% 12% 29% 22% 12% 4	573
June	1st to 10th	Day	20% 16% 31% 20% 11% 3	530
	11th to 20th	Day	21% 13% 26% 25% 13% 2	530
	21st to end	Day	19% 11% 35% 25% 8% 3	530
July	1st to 10th	Day	14% 8% 32% 26% 16% 5%	525
	11th to 20th	Day	11% 8% 28% 30% 17% 6%	524
	21st to end	Day	15% 7% 34% 28% 14% 3	576
August	1st to 10th	Day	14% 8% 25% 25% 21% 8%	526
	11th to 20th	Day	18% 8% 22% 27% 17% 7%	519
	21st to end	Day	14% 12% 25% 25% 14% 10%	583
September	1st to 10th	Day	19% 12% 23% 21% 18% 8%	530
	11th to 20th	Day	15% 8% 22% 23% 21% 12%	530
	21st to end	Day	24% 12% 28% 21% 12% 5%	530
October	1st to 10th	Day	23% 13% 25% 19% 15% 6%	502
	11th to 20th	Day	24% 17% 30% 20% 7% 2	490
	21st to end	Day	32% 16% 28% 18% 5%	499
November	1st to 10th	Day	25% 19% 25% 20% 10% 2	395
	11th to 20th	Day	32% 20% 25% 17% 6%	315
	21st to end	Day	35% 24% 30% 9% 3	200
December	1st to 10th	Day	35% 22% 29% 11% 3 1	200
	11th to 20th	Day	40% 21% 25% 12% 3	200
	21st to end	Day	37% 18% 32% 10% 3	220
January	1st to 10th	Night	25% 25% 33% 15% 2	800
	11th to 20th	Night	28% 19% 30% 20% 4	800
	21st to end	Night	21% 22% 37% 17% 3	880
February	1st to 10th	Night	27% 19% 33% 19% 1	800
	11th to 20th	Night	28% 23% 32% 16% 1	783
	21st to end	Night	32% 19% 31% 15% 3	660
March	1st to 10th	Night	27% 21% 30% 20% 3	800
	11th to 20th	Night	27% 21% 31% 17% 4	800
	21st to end	Night	25% 21% 30% 17% 6%	880
April	1st to 10th	Night	31% 18% 29% 19% 3	800
	11th to 20th	Night	28% 18% 28% 19% 6%	791
	21st to end	Night	26% 14% 29% 25% 6%	800
May	1st to 10th	Night	28% 9% 25% 28% 9%	478
	11th to 20th	Night	18% 11% 31% 30% 8% 1	394
	21st to end	Night	15% 8% 27% 36% 14%	433
June	1st to 10th	Night	18% 9% 27% 34% 11% 1	400
	11th to 20th	Night	19% 7% 25% 34% 15% 1	400
	21st to end	Night	12% 7% 26% 42% 13% 1	400
July	1st to 10th	Night	9% 5% 21% 43% 20% 2	390
	11th to 20th	Night	11% 4 22% 41% 22% 1	388
	21st to end	Night	13% 5% 18% 45% 18% 2	438
August	1st to 10th	Night	11% 4 23% 35% 25% 2	594
	11th to 20th	Night	15% 5% 16% 31% 29% 4	664
	21st to end	Night	16% 4 19% 34% 25% 1	880
September	1st to 10th	Night	17% 6% 23% 32% 20% 2	800
	11th to 20th	Night	14% 7% 19% 29% 27% 4	800
	21st to end	Night	20% 10% 24% 26% 18% 2	800
October	1st to 10th	Night	21% 11% 24% 25% 17% 2	773
	11th to 20th	Night	25% 12% 26% 28% 7% 1	760
	21st to end	Night	31% 13% 27% 22% 5%	836
November	1st to 10th	Night	20% 15% 29% 27% 8% 1	780
	11th to 20th	Night	27% 15% 31% 20% 6% 1	800
	21st to end	Night	25% 18% 32% 20% 5%	800
December	1st to 10th	Night	28% 22% 28% 18% 4	800
	11th to 20th	Night	29% 21% 30% 18% 3	800
	21st to end	Night	30% 20% 30% 18% 3	880

Page generated at 2025-10-01 01:39:08. Version ac07

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