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 2024-11-04.

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	12% 7% 3 6% 4 4 4 4 6% 8% 42%	101213
	Night	13% 8% 3 6% 4 4 4 3 5% 7% 43%	97872
Transparency	Day	38% 7% 12% 24% 17% 2	104820
	Night	39% 6% 11% 24% 18% 3	102395
Seeing	Day	14% 10% 26% 27% 18% 5%	15633
	Night	16% 9% 29% 31% 13% 1	25435

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	9% 12% 6% 12% 6% 5% 5% 3 6% 7% 29%	2527
	11th to 20th	Day	13% 8% 4 8% 6% 8% 6% 3 6% 6% 32%	2726
	21st to end	Day	21% 18% 5% 8% 5% 3 3 2 3 5% 27%	3135
February	1st to 10th	Day	15% 10% 5% 9% 5% 4 5% 3 5% 7% 32%	1710
	11th to 20th	Day	15% 9% 3 7% 6% 4 4 3 5% 6% 37%	1827
	21st to end	Day	15% 11% 3 8% 5% 3 3 4 4 7% 38%	1570
March	1st to 10th	Day	18% 11% 3 6% 4 3 3 3 3 5% 41%	3171
	11th to 20th	Day	12% 8% 2 4 4 3 4 3 5% 7% 48%	3480
	21st to end	Day	15% 8% 3 7% 5% 5% 5% 4 6% 7% 35%	4024
April	1st to 10th	Day	11% 8% 2 7% 5% 4 5% 4 6% 7% 41%	2280
	11th to 20th	Day	16% 9% 2 6% 4 4 4 3 5% 6% 42%	2254
	21st to end	Day	17% 7% 3 7% 5% 5% 4 4 5% 7% 37%	2280
May	1st to 10th	Day	14% 7% 3 7% 5% 5% 6% 5% 7% 9% 33%	3861
	11th to 20th	Day	17% 8% 3 6% 4 4 4 3 6% 8% 37%	4358
	21st to end	Day	9% 6% 2 6% 5% 5% 5% 4 6% 7% 45%	4824
June	1st to 10th	Day	8% 5% 2 5% 4 5% 5% 4 6% 8% 48%	2660
	11th to 20th	Day	7% 4 1 5% 3 4 5% 5% 6% 9% 50%	2660
	21st to end	Day	5% 4 2 5% 5% 4 5% 6% 8% 10% 46%	2660
July	1st to 10th	Day	13% 5% 2 6% 4 5% 5% 4 7% 9% 41%	4440
	11th to 20th	Day	5% 4 2 5% 4 4 5% 5% 8% 11% 48%	4440
	21st to end	Day	6% 5% 2 6% 5% 5% 6% 6% 7% 10% 41%	4576
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	10% 6% 2 4 4 4 3 3 4 6% 55%	1699
	11th to 20th	Day	14% 8% 2 5% 4 4 3 3 5% 6% 47%	1710
	21st to end	Day	16% 11% 3 7% 4 3 4 3 4 6% 40%	1636
December	1st to 10th	Day	13% 13% 3 7% 4 3 4 3 4 7% 39%	1520
	11th to 20th	Day	13% 11% 3 7% 4 4 5% 3 5% 7% 38%	1918
	21st to end	Day	20% 14% 5% 9% 5% 4 4 3 5% 6% 25%	2783
January	1st to 10th	Night	14% 11% 6% 10% 5% 4 4 3 4 5% 34%	4428
	11th to 20th	Night	13% 11% 4 12% 6% 6% 6% 4 4 5% 30%	4242
	21st to end	Night	24% 16% 4 8% 4 3 3 3 4 6% 26%	4532
February	1st to 10th	Night	15% 11% 5% 8% 5% 4 4 3 5% 6% 34%	2470
	11th to 20th	Night	15% 8% 3 9% 5% 3 4 3 4 6% 41%	2237
	21st to end	Night	15% 11% 3 8% 5% 4 3 3 4 5% 40%	1884
March	1st to 10th	Night	22% 10% 2 4 4 3 3 2 3 4 42%	3711
	11th to 20th	Night	14% 7% 2 5% 3 3 3 3 4 6% 51%	3480
	21st to end	Night	17% 10% 3 8% 5% 5% 4 3 5% 5% 34%	3606
April	1st to 10th	Night	12% 7% 2 7% 5% 3 3 3 4 7% 47%	1900
	11th to 20th	Night	13% 7% 3 5% 4 3 4 3 6% 7% 44%	1875
	21st to end	Night	18% 8% 3 6% 4 3 3 3 4 7% 41%	1900
May	1st to 10th	Night	17% 7% 3 6% 4 4 4 3 6% 8% 38%	3034
	11th to 20th	Night	15% 7% 2 6% 3 3 4 3 5% 7% 43%	2542
	21st to end	Night	9% 5% 2 7% 5% 4 5% 4 6% 10% 42%	2743
June	1st to 10th	Night	8% 5% 2 5% 4 4 4 3 7% 9% 49%	1520
	11th to 20th	Night	5% 3 2 4 4 3 4 4 6% 10% 54%	1520
	21st to end	Night	4 4 2 4 4 4 4 5% 5% 11% 53%	1520
July	1st to 10th	Night	12% 5% 2 5% 3 3 5% 3 6% 10% 45%	2530
	11th to 20th	Night	5% 4 1 5% 4 3 4 3 6% 10% 55%	2530
	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% 56%	2452
	11th to 20th	Night	14% 6% 2 5% 4 4 4 3 4 6% 49%	2470
	21st to end	Night	18% 9% 2 5% 3 3 3 3 5% 6% 44%	2541
December	1st to 10th	Night	15% 11% 4 7% 5% 4 4 4 5% 6% 35%	2660
	11th to 20th	Night	16% 10% 3 7% 4 4 3 3 4 5% 41%	3279
	21st to end	Night	19% 19% 5% 10% 5% 5% 3 3 4 4 23%	4884

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	49% 9% 11% 22% 8% 1	2528
	11th to 20th	Day	48% 8% 14% 20% 11%	2726
	21st to end	Day	59% 5% 9% 16% 10% 1	3135
February	1st to 10th	Day	51% 6% 11% 21% 10% 1	1710
	11th to 20th	Day	47% 6% 11% 20% 14% 3	1837
	21st to end	Day	46% 6% 9% 22% 14% 4	1570
March	1st to 10th	Day	47% 4 8% 20% 18% 3	3171
	11th to 20th	Day	36% 6% 12% 25% 17% 5%	3480
	21st to end	Day	44% 10% 17% 22% 8% 1	4024
April	1st to 10th	Day	40% 6% 12% 25% 16% 1	2280
	11th to 20th	Day	44% 5% 11% 23% 15% 3	2254
	21st to end	Day	45% 8% 11% 22% 13% 1	2280
May	1st to 10th	Day	42% 10% 15% 22% 10%	3896
	11th to 20th	Day	44% 9% 11% 24% 12% 1	4362
	21st to end	Day	35% 9% 11% 22% 21% 1	4837
June	1st to 10th	Day	32% 8% 14% 26% 17% 2	2660
	11th to 20th	Day	28% 8% 13% 25% 23% 3	2660
	21st to end	Day	28% 10% 17% 24% 15% 5%	2660
July	1st to 10th	Day	38% 6% 12% 28% 13% 2	4371
	11th to 20th	Day	27% 8% 15% 31% 17% 2	4365
	21st to end	Day	35% 9% 18% 26% 11% 1	4432
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	32% 5% 12% 26% 21% 5%	1699
	11th to 20th	Day	38% 5% 10% 23% 20% 5%	1710
	21st to end	Day	46% 5% 9% 25% 14%	1636
December	1st to 10th	Day	44% 7% 12% 25% 12%	1520
	11th to 20th	Day	46% 6% 11% 23% 12% 2	1915
	21st to end	Day	59% 7% 11% 14% 8% 1	2783
January	1st to 10th	Night	50% 7% 11% 23% 9% 1	4428
	11th to 20th	Night	55% 8% 9% 19% 9% 1	4242
	21st to end	Night	59% 5% 10% 18% 7% 1	4532
February	1st to 10th	Night	52% 5% 10% 20% 12% 1	2470
	11th to 20th	Night	45% 5% 10% 21% 17% 2	2238
	21st to end	Night	47% 5% 11% 21% 13% 4	1884
March	1st to 10th	Night	47% 5% 7% 24% 15% 2	3711
	11th to 20th	Night	35% 5% 12% 23% 21% 4	3480
	21st to end	Night	49% 9% 11% 24% 7%	3606
April	1st to 10th	Night	38% 6% 9% 27% 17% 4	1900
	11th to 20th	Night	38% 5% 10% 23% 20% 4	1875
	21st to end	Night	44% 6% 8% 24% 17% 2	1900
May	1st to 10th	Night	40% 10% 16% 19% 13% 1	3064
	11th to 20th	Night	39% 9% 12% 27% 12% 1	2543
	21st to end	Night	33% 11% 14% 24% 16% 2	2751
June	1st to 10th	Night	30% 7% 15% 25% 18% 4	1520
	11th to 20th	Night	24% 8% 12% 27% 26% 4	1520
	21st to end	Night	24% 9% 16% 26% 18% 7%	1520
July	1st to 10th	Night	35% 6% 12% 29% 15% 3	2490
	11th to 20th	Night	24% 6% 12% 36% 20% 3	2482
	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	30% 5% 12% 25% 22% 6%	2452
	11th to 20th	Night	37% 4 9% 25% 21% 4	2470
	21st to end	Night	42% 5% 11% 24% 17% 2	2541
December	1st to 10th	Night	48% 6% 10% 24% 11% 1	2660
	11th to 20th	Night	45% 5% 11% 23% 15% 1	3281
	21st to end	Night	62% 8% 9% 13% 7% 1	4884

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	17% 22% 36% 17% 7% 1	270
	11th to 20th	Day	27% 16% 38% 18% 2	270
	21st to end	Day	19% 21% 37% 19% 4	297
February	1st to 10th	Day	23% 18% 35% 21% 3	270
	11th to 20th	Day	21% 22% 31% 19% 6% 1	270
	21st to end	Day	23% 19% 37% 19% 2	225
March	1st to 10th	Day	17% 20% 45% 16% 3	270
	11th to 20th	Day	28% 18% 32% 17% 4 1	270
	21st to end	Day	29% 16% 31% 19% 5%	417
April	1st to 10th	Day	17% 14% 39% 20% 9% 1	460
	11th to 20th	Day	20% 17% 30% 21% 12%	452
	21st to end	Day	22% 15% 35% 20% 7% 1	460
May	1st to 10th	Day	17% 14% 30% 28% 9% 1	463
	11th to 20th	Day	16% 10% 28% 27% 16% 3	647
	21st to end	Day	12% 6% 30% 30% 16% 6%	734
June	1st to 10th	Day	9% 6% 21% 30% 24% 9%	680
	11th to 20th	Day	9% 3 21% 37% 24% 7%	680
	21st to end	Day	4 6% 28% 36% 21% 5%	680
July	1st to 10th	Day	11% 3 14% 27% 31% 14%	671
	11th to 20th	Day	6% 3 17% 38% 28% 8%	668
	21st to end	Day	9% 4 16% 33% 30% 8%	739
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	13% 10% 32% 29% 13% 4	279
	11th to 20th	Day	19% 19% 28% 21% 13% 1	270
	21st to end	Day	23% 16% 27% 24% 9% 1	270
December	1st to 10th	Day	13% 19% 39% 19% 7% 3	270
	11th to 20th	Day	19% 16% 34% 26% 4	270
	21st to end	Day	24% 21% 39% 13% 4	297
January	1st to 10th	Night	17% 15% 38% 24% 5%	950
	11th to 20th	Night	21% 17% 35% 22% 4	950
	21st to end	Night	19% 14% 39% 26% 2	1045
February	1st to 10th	Night	22% 12% 38% 25% 3	950
	11th to 20th	Night	19% 14% 39% 26% 2	762
	21st to end	Night	21% 15% 40% 23% 2	628
March	1st to 10th	Night	19% 15% 39% 23% 4	751
	11th to 20th	Night	22% 11% 34% 27% 5%	570
	21st to end	Night	23% 12% 34% 26% 6%	627
April	1st to 10th	Night	15% 14% 38% 26% 6%	570
	11th to 20th	Night	15% 13% 34% 28% 10%	563
	21st to end	Night	20% 11% 38% 26% 6%	570
May	1st to 10th	Night	16% 7% 35% 33% 9%	570
	11th to 20th	Night	17% 5% 28% 32% 17% 1	561
	21st to end	Night	10% 4 25% 39% 19% 3	617
June	1st to 10th	Night	9% 2 20% 41% 26% 1	570
	11th to 20th	Night	6% 2 20% 49% 21% 1	570
	21st to end	Night	5% 1 25% 44% 23% 2	570
July	1st to 10th	Night	10% 2 10% 39% 33% 6%	555
	11th to 20th	Night	5% 2 15% 43% 32% 3	552
	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	13% 8% 35% 32% 12% 1	755
	11th to 20th	Night	16% 14% 34% 29% 7%	760
	21st to end	Night	22% 10% 34% 27% 6%	831
December	1st to 10th	Night	21% 12% 35% 27% 5% 1	950
	11th to 20th	Night	23% 9% 29% 32% 6% 1	950
	21st to end	Night	25% 15% 34% 24% 2	1045

Page generated at 2024-11-01 21:47:50. Version ac07

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