Arrow Heights Astroimaging Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Arrow Heights Astroimaging Observatory clear sky chart from 2005-11-06 to 2025-07-21.

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% 8% 3 6% 4 4 4 4 5% 7% 42%	120111
	Night	14% 8% 3 7% 4 4 4 3 5% 6% 42%	119217
Transparency	Day	39% 6% 11% 24% 17% 2	123721
	Night	40% 6% 10% 23% 18% 3	123740
Seeing	Day	15% 10% 26% 27% 17% 5%	16599
	Night	16% 9% 29% 31% 13% 1	26412

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% 12% 6% 14% 6% 4 4 3 5% 6% 28%	3617
	11th to 20th	Day	10% 8% 4 8% 6% 7% 5% 4 5% 6% 37%	3914
	21st to end	Day	18% 14% 4 9% 4 4 3 3 3 5% 34%	4488
February	1st to 10th	Day	16% 10% 5% 9% 5% 4 5% 3 5% 7% 32%	1800
	11th to 20th	Day	15% 10% 3 8% 6% 4 4 3 5% 6% 37%	1926
	21st to end	Day	14% 10% 3 8% 5% 4 3 4 4 7% 39%	1650
March	1st to 10th	Day	16% 11% 2 5% 3 3 2 2 3 5% 49%	4545
	11th to 20th	Day	9% 7% 2 4 4 3 4 3 6% 7% 51%	4980
	21st to end	Day	13% 8% 3 8% 5% 5% 5% 4 6% 8% 36%	5770
April	1st to 10th	Day	13% 8% 2 7% 5% 4 5% 4 6% 6% 41%	2400
	11th to 20th	Day	16% 9% 3 6% 4 4 4 3 5% 6% 41%	2374
	21st to end	Day	16% 7% 3 7% 5% 5% 4 4 5% 8% 37%	2400
May	1st to 10th	Day	16% 8% 3 8% 5% 5% 5% 4 7% 8% 31%	5543
	11th to 20th	Day	16% 8% 3 6% 4 5% 5% 4 6% 8% 37%	6264
	21st to end	Day	13% 7% 3 6% 5% 5% 5% 4 6% 7% 40%	6935
June	1st to 10th	Day	9% 6% 2 5% 4 4 5% 4 6% 7% 48%	2800
	11th to 20th	Day	8% 4 1 5% 3 4 5% 5% 6% 9% 49%	2800
	21st to end	Day	5% 4 2 5% 5% 4 5% 6% 8% 10% 47%	2800
July	1st to 10th	Day	12% 5% 2 6% 4 4 5% 4 7% 8% 42%	4580
	11th to 20th	Day	5% 4 2 5% 4 4 5% 5% 8% 11% 47%	4580
	21st to end	Day	6% 5% 2 6% 5% 5% 6% 6% 7% 10% 41%	4577
August	1st to 10th	Day	5% 4 2 4 4 5% 4 5% 7% 10% 50%	4086
	11th to 20th	Day	12% 5% 2 6% 4 5% 5% 4 7% 9% 41%	3729
	21st to end	Day	6% 4 2 4 4 4 5% 4 6% 9% 52%	4180
September	1st to 10th	Day	13% 5% 2 4 3 3 3 3 5% 7% 50%	2280
	11th to 20th	Day	9% 5% 2 5% 5% 3 4 3 6% 9% 49%	2256
	21st to end	Day	8% 6% 2 5% 4 4 4 3 5% 7% 52%	2085
October	1st to 10th	Day	9% 5% 2 5% 4 3 3 2 4 6% 56%	1900
	11th to 20th	Day	14% 6% 2 4 3 3 3 3 3 6% 53%	1900
	21st to end	Day	18% 8% 3 4 3 4 3 2 3 6% 46%	2068
November	1st to 10th	Day	11% 6% 2 5% 4 4 3 3 4 6% 53%	1762
	11th to 20th	Day	14% 9% 2 5% 4 4 3 3 5% 6% 47%	1800
	21st to end	Day	16% 11% 3 7% 4 3 4 3 4 6% 40%	1722
December	1st to 10th	Day	9% 10% 3 6% 4 3 3 3 4 6% 50%	2610
	11th to 20th	Day	13% 9% 5% 9% 4 4 4 3 5% 6% 37%	3008
	21st to end	Day	23% 17% 5% 10% 4 4 3 2 4 5% 22%	3982
January	1st to 10th	Night	15% 11% 6% 12% 5% 4 4 3 4 5% 32%	6348
	11th to 20th	Night	11% 10% 4 12% 5% 6% 5% 3 4 5% 36%	6064
	21st to end	Night	18% 13% 4 8% 4 3 3 3 4 6% 34%	6490
February	1st to 10th	Night	16% 12% 5% 8% 5% 4 4 3 5% 6% 34%	2600
	11th to 20th	Night	16% 8% 3 9% 5% 3 4 3 3 5% 40%	2358
	21st to end	Night	14% 11% 3 8% 4 3 3 3 4 5% 41%	1980
March	1st to 10th	Night	19% 11% 3 5% 3 3 3 2 3 4 43%	5337
	11th to 20th	Night	12% 8% 2 5% 3 3 3 3 4 6% 50%	4980
	21st to end	Night	16% 10% 3 9% 5% 5% 4 3 5% 6% 35%	5158
April	1st to 10th	Night	12% 7% 2 7% 5% 3 3 4 4 7% 46%	2000
	11th to 20th	Night	13% 7% 3 5% 4 3 4 3 6% 7% 44%	1975
	21st to end	Night	18% 7% 3 6% 4 3 3 3 4 7% 41%	2000
May	1st to 10th	Night	17% 8% 3 7% 4 4 4 4 6% 8% 34%	4352
	11th to 20th	Night	14% 7% 2 5% 4 4 4 4 6% 8% 42%	3645
	21st to end	Night	13% 7% 2 7% 4 4 5% 4 6% 9% 39%	3942
June	1st to 10th	Night	8% 5% 2 5% 5% 4 4 3 7% 9% 48%	1600
	11th to 20th	Night	6% 4 2 4 4 3 4 4 6% 10% 53%	1600
	21st to end	Night	4 4 2 4 4 4 4 5% 5% 11% 54%	1600
July	1st to 10th	Night	12% 5% 3 5% 3 3 4 3 6% 10% 46%	2610
	11th to 20th	Night	5% 4 1 5% 4 3 4 3 6% 10% 55%	2610
	21st to end	Night	7% 6% 3 8% 5% 5% 5% 5% 7% 10% 40%	2970
August	1st to 10th	Night	5% 4 1 4 3 4 4 4 6% 8% 57%	2853
	11th to 20th	Night	11% 5% 2 6% 4 4 4 4 6% 7% 47%	3100
	21st to end	Night	5% 2 1 4 3 4 4 3 6% 9% 58%	3476
September	1st to 10th	Night	11% 5% 2 5% 4 3 3 3 5% 6% 53%	1900
	11th to 20th	Night	8% 5% 2 5% 4 4 4 3 6% 7% 51%	1905
	21st to end	Night	10% 4 2 5% 3 4 4 4 4 6% 53%	2091
October	1st to 10th	Night	8% 5% 2 5% 3 3 3 4 4 6% 59%	2280
	11th to 20th	Night	14% 5% 2 4 3 3 3 3 5% 7% 53%	2280
	21st to end	Night	18% 7% 2 5% 3 3 4 2 5% 5% 47%	2527
November	1st to 10th	Night	10% 6% 2 4 4 3 4 3 5% 5% 55%	2536
	11th to 20th	Night	14% 6% 2 6% 4 4 4 3 4 6% 48%	2600
	21st to end	Night	18% 9% 3 5% 3 3 3 3 5% 6% 43%	2675
December	1st to 10th	Night	12% 9% 3 6% 4 4 4 3 4 6% 46%	4580
	11th to 20th	Night	14% 9% 3 6% 4 4 4 3 5% 6% 41%	5199
	21st to end	Night	25% 17% 4 9% 5% 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	54% 7% 10% 18% 9% 1	3618
	11th to 20th	Day	44% 6% 12% 21% 14% 4	3914
	21st to end	Day	54% 4 8% 16% 15% 4	4488
February	1st to 10th	Day	52% 5% 12% 21% 10% 1	1800
	11th to 20th	Day	48% 5% 10% 19% 14% 3	1936
	21st to end	Day	45% 5% 9% 22% 15% 4	1650
March	1st to 10th	Day	41% 3 6% 22% 25% 3	4545
	11th to 20th	Day	32% 5% 9% 25% 24% 5%	4980
	21st to end	Day	43% 8% 14% 26% 8% 1	5772
April	1st to 10th	Day	41% 6% 12% 25% 16% 1	2400
	11th to 20th	Day	44% 5% 11% 23% 14% 3	2374
	21st to end	Day	45% 8% 11% 23% 12% 1	2400
May	1st to 10th	Day	46% 8% 13% 21% 11%	5578
	11th to 20th	Day	43% 8% 11% 24% 13% 1	6268
	21st to end	Day	41% 7% 10% 22% 19% 1	6949
June	1st to 10th	Day	33% 8% 14% 26% 17% 2	2800
	11th to 20th	Day	29% 8% 13% 24% 23% 3	2800
	21st to end	Day	28% 10% 18% 24% 16% 5%	2800
July	1st to 10th	Day	37% 6% 12% 29% 14% 2	4511
	11th to 20th	Day	28% 8% 15% 31% 17% 2	4505
	21st to end	Day	35% 9% 18% 26% 11% 1	4433
August	1st to 10th	Day	26% 7% 15% 36% 14%	4072
	11th to 20th	Day	38% 7% 14% 24% 16% 1	3765
	21st to end	Day	27% 7% 14% 34% 15% 3	4179
September	1st to 10th	Day	32% 6% 11% 26% 21% 5%	2280
	11th to 20th	Day	32% 6% 10% 25% 24% 3	2256
	21st to end	Day	31% 5% 9% 28% 23% 3	2085
October	1st to 10th	Day	18% 3 6% 19% 47% 7%	3160
	11th to 20th	Day	23% 3 7% 21% 37% 9%	3140
	21st to end	Day	33% 4 7% 28% 26% 3	3382
November	1st to 10th	Day	33% 5% 11% 26% 20% 5%	1762
	11th to 20th	Day	38% 5% 10% 23% 20% 5%	1800
	21st to end	Day	46% 5% 9% 26% 14%	1722
December	1st to 10th	Day	36% 5% 14% 31% 15%	2610
	11th to 20th	Day	48% 5% 12% 21% 13% 1	3005
	21st to end	Day	65% 5% 12% 12% 6% 1	3982
January	1st to 10th	Night	55% 5% 10% 22% 8%	6348
	11th to 20th	Night	50% 6% 7% 21% 13% 3	6064
	21st to end	Night	53% 4 8% 18% 16% 1	6490
February	1st to 10th	Night	52% 5% 11% 20% 12% 1	2600
	11th to 20th	Night	47% 5% 9% 20% 17% 2	2359
	21st to end	Night	45% 4 10% 23% 14% 3	1980
March	1st to 10th	Night	46% 4 5% 22% 21% 2	5337
	11th to 20th	Night	35% 4 10% 23% 21% 6%	4980
	21st to end	Night	49% 7% 10% 23% 11% 1	5158
April	1st to 10th	Night	38% 6% 9% 26% 17% 3	2000
	11th to 20th	Night	39% 5% 10% 23% 19% 4	1975
	21st to end	Night	44% 6% 9% 24% 16% 2	2000
May	1st to 10th	Night	46% 9% 14% 19% 12% 1	4382
	11th to 20th	Night	39% 8% 12% 25% 15% 2	3646
	21st to end	Night	39% 9% 13% 23% 15% 2	3950
June	1st to 10th	Night	31% 7% 15% 25% 18% 4	1600
	11th to 20th	Night	25% 8% 12% 26% 25% 4	1600
	21st to end	Night	23% 9% 16% 27% 19% 7%	1600
July	1st to 10th	Night	35% 6% 11% 28% 16% 3	2570
	11th to 20th	Night	24% 6% 12% 36% 19% 3	2562
	21st to end	Night	37% 8% 17% 24% 13% 2	2876
August	1st to 10th	Night	23% 7% 16% 35% 17% 1	2843
	11th to 20th	Night	35% 6% 13% 24% 19% 2	3130
	21st to end	Night	22% 6% 16% 35% 18% 3	3476
September	1st to 10th	Night	31% 6% 10% 24% 23% 7%	1900
	11th to 20th	Night	31% 6% 9% 24% 25% 5%	1905
	21st to end	Night	30% 7% 9% 23% 27% 4	2091
October	1st to 10th	Night	16% 4 6% 17% 49% 7%	3800
	11th to 20th	Night	22% 4 7% 22% 36% 10%	3779
	21st to end	Night	31% 4 9% 25% 26% 6%	4151
November	1st to 10th	Night	31% 5% 11% 25% 22% 6%	2536
	11th to 20th	Night	37% 4 9% 24% 22% 4	2600
	21st to end	Night	42% 5% 11% 24% 17% 2	2675
December	1st to 10th	Night	40% 4 9% 32% 14% 1	4580
	11th to 20th	Night	43% 4 13% 22% 17%	5201
	21st to end	Night	65% 6% 11% 12% 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	18% 22% 36% 17% 6% 1	300
	11th to 20th	Day	26% 16% 38% 18% 2	300
	21st to end	Day	18% 21% 38% 19% 3	330
February	1st to 10th	Day	23% 18% 37% 19% 2	300
	11th to 20th	Day	25% 23% 30% 17% 5% 1	300
	21st to end	Day	23% 20% 37% 19% 2	249
March	1st to 10th	Day	19% 19% 44% 16% 3	300
	11th to 20th	Day	28% 20% 32% 16% 4 1	300
	21st to end	Day	29% 17% 32% 18% 5%	457
April	1st to 10th	Day	20% 15% 37% 19% 9% 1	500
	11th to 20th	Day	22% 17% 29% 20% 11%	492
	21st to end	Day	21% 15% 36% 20% 7% 1	500
May	1st to 10th	Day	18% 14% 31% 27% 9% 1	503
	11th to 20th	Day	17% 10% 28% 26% 16% 3	696
	21st to end	Day	13% 7% 30% 29% 15% 6%	789
June	1st to 10th	Day	11% 6% 22% 30% 23% 8%	730
	11th to 20th	Day	9% 3 22% 36% 23% 7%	730
	21st to end	Day	5% 5% 27% 37% 21% 5%	730
July	1st to 10th	Day	11% 2 15% 27% 31% 14%	721
	11th to 20th	Day	6% 3 17% 38% 27% 8%	718
	21st to end	Day	9% 4 16% 33% 30% 8%	740
August	1st to 10th	Day	8% 2 15% 37% 28% 10%	671
	11th to 20th	Day	12% 4 15% 29% 30% 11%	479
	21st to end	Day	8% 2 13% 30% 35% 12%	539
September	1st to 10th	Day	12% 3 15% 30% 30% 10%	490
	11th to 20th	Day	8% 3 13% 30% 32% 14%	490
	21st to end	Day	10% 9% 20% 27% 24% 9%	485
October	1st to 10th	Day	10% 9% 24% 34% 17% 5%	300
	11th to 20th	Day	14% 16% 31% 28% 10% 1	300
	21st to end	Day	30% 18% 25% 20% 7%	330
November	1st to 10th	Day	15% 10% 34% 26% 12% 3	300
	11th to 20th	Day	20% 19% 28% 19% 12% 2	300
	21st to end	Day	26% 16% 27% 22% 9% 1	300
December	1st to 10th	Day	15% 19% 38% 19% 6% 3	300
	11th to 20th	Day	19% 18% 33% 25% 4	300
	21st to end	Day	26% 20% 37% 13% 4	330
January	1st to 10th	Night	18% 15% 38% 24% 4	1000
	11th to 20th	Night	20% 18% 36% 22% 4	1000
	21st to end	Night	19% 14% 40% 26% 2	1100
February	1st to 10th	Night	22% 13% 38% 24% 3	1000
	11th to 20th	Night	21% 14% 38% 24% 2	803
	21st to end	Night	20% 14% 41% 23% 2	660
March	1st to 10th	Night	20% 15% 38% 23% 4	790
	11th to 20th	Night	23% 12% 34% 26% 5%	600
	21st to end	Night	24% 13% 33% 25% 5%	660
April	1st to 10th	Night	16% 14% 38% 26% 6%	600
	11th to 20th	Night	17% 13% 34% 27% 9%	593
	21st to end	Night	20% 11% 38% 25% 6%	600
May	1st to 10th	Night	16% 7% 34% 33% 9%	600
	11th to 20th	Night	17% 6% 28% 31% 17% 1	591
	21st to end	Night	11% 5% 26% 38% 19% 2	650
June	1st to 10th	Night	9% 3 21% 41% 25% 1	600
	11th to 20th	Night	7% 2 21% 48% 21% 1	600
	21st to end	Night	5% 1 25% 44% 23% 2	600
July	1st to 10th	Night	10% 2 10% 39% 33% 6%	585
	11th to 20th	Night	5% 2 15% 43% 32% 3	582
	21st to end	Night	7% 2 15% 40% 34% 2	624
August	1st to 10th	Night	7% 3 11% 41% 35% 3	567
	11th to 20th	Night	7% 2 14% 40% 33% 3	564
	21st to end	Night	6% 1 12% 40% 37% 4	627
September	1st to 10th	Night	12% 3 14% 36% 30% 5%	570
	11th to 20th	Night	10% 4 13% 33% 35% 5%	575
	21st to end	Night	11% 5% 23% 32% 25% 4	760
October	1st to 10th	Night	9% 4 26% 34% 23% 4	760
	11th to 20th	Night	16% 10% 28% 33% 12% 1	760
	21st to end	Night	21% 13% 32% 28% 6%	836
November	1st to 10th	Night	14% 8% 35% 31% 11% 1	780
	11th to 20th	Night	16% 14% 34% 29% 7%	800
	21st to end	Night	22% 11% 34% 26% 6%	875
December	1st to 10th	Night	21% 12% 35% 27% 5% 1	1000
	11th to 20th	Night	23% 11% 29% 31% 6% 1	1000
	21st to end	Night	26% 15% 34% 23% 2	1100

Page generated at 2025-07-18 00:10:01. Version ac07

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