Ammon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ammon clear sky chart from 2005-11-06 to 2025-05-26.

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	7% 9% 3 6% 4 4 4 3 5% 6% 50%	117845
	Night	8% 10% 3 7% 4 4 4 3 5% 6% 46%	120220
Transparency	Day	37% 4 9% 22% 18% 10%	117594
	Night	40% 4 10% 22% 16% 8%	120059
Seeing	Day	13% 13% 27% 28% 16% 4	15976
	Night	14% 8% 23% 35% 17% 3	25710

By Month

Percentage Cloud Cover SW (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% 22% 7% 10% 5% 5% 4 3 5% 5% 23%	3529
	11th to 20th	Day	9% 14% 7% 14% 6% 4 4 2 4 4 32%	3778
	21st to end	Day	11% 15% 5% 9% 4 3 3 3 3 4 39%	4510
February	1st to 10th	Day	11% 16% 5% 13% 7% 5% 5% 4 4 5% 26%	1800
	11th to 20th	Day	12% 14% 5% 10% 6% 5% 5% 4 5% 7% 28%	1768
	21st to end	Day	7% 15% 5% 10% 6% 4 5% 4 5% 5% 33%	1650
March	1st to 10th	Day	8% 13% 4 10% 4 5% 4 3 5% 7% 36%	4755
	11th to 20th	Day	7% 13% 3 7% 5% 4 5% 3 4 6% 43%	5000
	21st to end	Day	8% 14% 4 10% 6% 6% 6% 4 6% 7% 28%	5486
April	1st to 10th	Day	9% 12% 3 7% 5% 5% 4 4 6% 7% 37%	2270
	11th to 20th	Day	7% 10% 4 7% 4 4 4 4 5% 7% 44%	2567
	21st to end	Day	10% 8% 4 7% 5% 4 5% 4 6% 8% 39%	2600
May	1st to 10th	Day	10% 10% 3 6% 4 4 5% 3 5% 7% 43%	4240
	11th to 20th	Day	5% 4 1 5% 4 4 4 4 5% 8% 56%	4201
	21st to end	Day	8% 8% 2 6% 4 4 5% 4 6% 6% 48%	4851
June	1st to 10th	Day	7% 4 2 4 5% 4 5% 4 7% 8% 49%	2775
	11th to 20th	Day	7% 5% 1 6% 4 4 3 4 6% 7% 54%	2850
	21st to end	Day	2 2 1 3 2 2 3 3 4 7% 71%	2850
July	1st to 10th	Day	2 2 1 2 2 2 2 2 3 5% 78%	4688
	11th to 20th	Day	1 2 1 3 2 2 3 3 5% 6% 72%	4375
	21st to end	Day	3 2 1 3 3 3 4 3 4 6% 68%	4454
August	1st to 10th	Day	4 3 1 4 3 3 5% 4 5% 7% 61%	4092
	11th to 20th	Day	2 2 1 2 3 3 3 2 4 6% 71%	4028
	21st to end	Day	2 2 1 3 2 3 3 3 4 6% 73%	4521
September	1st to 10th	Day	4 3 1 3 2 3 2 2 4 5% 71%	2205
	11th to 20th	Day	6% 4 1 4 3 3 3 3 4 6% 62%	2090
	21st to end	Day	7% 3 2 3 2 3 2 3 4 6% 64%	2090
October	1st to 10th	Day	7% 4 2 4 2 3 3 2 3 4 67%	3308
	11th to 20th	Day	5% 4 2 4 3 3 3 2 4 5% 63%	3150
	21st to end	Day	8% 9% 2 6% 4 4 4 3 6% 7% 46%	3289
November	1st to 10th	Day	13% 12% 3 7% 4 3 3 3 5% 6% 43%	1764
	11th to 20th	Day	11% 11% 3 7% 4 4 4 4 6% 7% 39%	1673
	21st to end	Day	9% 13% 5% 8% 4 4 4 3 4 5% 41%	1600
December	1st to 10th	Day	8% 9% 4 9% 3 2 3 2 3 4 51%	2620
	11th to 20th	Day	14% 18% 6% 10% 7% 5% 4 4 5% 6% 22%	2920
	21st to end	Day	15% 16% 4 10% 5% 4 5% 4 5% 7% 26%	3498
January	1st to 10th	Night	11% 17% 6% 13% 5% 4 4 3 5% 6% 27%	6444
	11th to 20th	Night	13% 18% 6% 14% 5% 3 3 2 4 5% 27%	6172
	21st to end	Night	12% 16% 4 7% 4 4 2 2 3 4 43%	6468
February	1st to 10th	Night	13% 15% 4 9% 5% 5% 4 4 5% 6% 30%	2600
	11th to 20th	Night	13% 16% 4 8% 4 4 4 2 5% 6% 34%	2517
	21st to end	Night	8% 13% 6% 11% 6% 5% 5% 5% 5% 6% 30%	1980
March	1st to 10th	Night	8% 14% 4 8% 5% 5% 4 3 5% 6% 39%	5125
	11th to 20th	Night	6% 10% 3 7% 5% 4 5% 4 6% 8% 44%	5000
	21st to end	Night	8% 10% 3 8% 5% 5% 5% 5% 6% 8% 37%	5489
April	1st to 10th	Night	9% 10% 3 7% 5% 4 4 4 7% 7% 40%	2126
	11th to 20th	Night	8% 11% 3 7% 5% 5% 5% 3 6% 7% 42%	1781
	21st to end	Night	9% 8% 2 6% 4 4 4 4 6% 7% 46%	1800
May	1st to 10th	Night	9% 13% 3 7% 3 4 4 3 5% 6% 43%	2950
	11th to 20th	Night	5% 4 2 5% 5% 4 4 4 6% 8% 54%	2924
	21st to end	Night	8% 6% 2 5% 4 4 5% 3 6% 9% 48%	2848
June	1st to 10th	Night	6% 4 2 5% 5% 4 5% 5% 6% 9% 50%	1401
	11th to 20th	Night	8% 5% 1 5% 3 5% 4 3 6% 7% 54%	1330
	21st to end	Night	2 3 2 4 1 3 3 3 5% 7% 69%	1330
July	1st to 10th	Night	3 1 1 2 2 2 3 2 4 6% 72%	2268
	11th to 20th	Night	1 1 1 3 2 3 4 3 5% 7% 70%	2572
	21st to end	Night	2 1 1 3 3 3 4 4 6% 8% 65%	3109
August	1st to 10th	Night	3 3 1 3 2 3 4 4 6% 8% 62%	2847
	11th to 20th	Night	2 2 1 3 3 3 4 3 5% 7% 66%	2811
	21st to end	Night	3 3 1 3 2 2 2 2 3 4 73%	3146
September	1st to 10th	Night	4 3 1 3 3 3 3 3 4 4 69%	1971
	11th to 20th	Night	7% 4 1 4 3 3 4 3 5% 7% 60%	2090
	21st to end	Night	8% 4 1 3 2 2 3 2 4 6% 64%	2090
October	1st to 10th	Night	6% 3 1 3 2 2 3 2 3 4 70%	3666
	11th to 20th	Night	10% 6% 2 6% 3 3 4 3 4 4 55%	3778
	21st to end	Night	8% 8% 3 6% 4 4 4 4 6% 7% 47%	4267
November	1st to 10th	Night	11% 9% 3 6% 3 3 4 4 5% 7% 45%	2535
	11th to 20th	Night	10% 12% 4 6% 5% 4 4 3 5% 6% 40%	2705
	21st to end	Night	9% 11% 4 8% 5% 4 4 3 5% 7% 40%	2800
December	1st to 10th	Night	8% 10% 3 7% 5% 3 3 3 4 5% 49%	4570
	11th to 20th	Night	13% 17% 4 9% 5% 4 4 3 4 7% 29%	5252
	21st to end	Night	14% 16% 5% 10% 5% 4 5% 3 4 5% 28%	7458

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	63% 4 12% 16% 5% 1	3529
	11th to 20th	Day	57% 4 14% 14% 7% 3	3778
	21st to end	Day	51% 3 12% 22% 11% 1	4510
February	1st to 10th	Day	62% 4 11% 17% 5% 1	1800
	11th to 20th	Day	57% 4 13% 19% 6% 1	1777
	21st to end	Day	55% 7% 10% 18% 8% 1	1650
March	1st to 10th	Day	50% 4 10% 24% 8% 4	4755
	11th to 20th	Day	45% 4 8% 31% 12% 1	5000
	21st to end	Day	57% 6% 14% 19% 4	5486
April	1st to 10th	Day	47% 5% 14% 19% 13% 2	2270
	11th to 20th	Day	41% 5% 9% 27% 15% 3	2570
	21st to end	Day	44% 5% 10% 26% 14% 1	2600
May	1st to 10th	Day	41% 5% 5% 26% 19% 3	4240
	11th to 20th	Day	29% 5% 5% 34% 21% 7%	4204
	21st to end	Day	38% 5% 7% 34% 15% 1	4851
June	1st to 10th	Day	34% 4 12% 32% 18% 1	2775
	11th to 20th	Day	31% 4 8% 23% 23% 11%	2850
	21st to end	Day	16% 3 3 24% 37% 17%	2850
July	1st to 10th	Day	11% 2 3 11% 30% 44%	4615
	11th to 20th	Day	14% 3 3 10% 26% 45%	4300
	21st to end	Day	19% 3 3 12% 33% 30%	4314
August	1st to 10th	Day	24% 3 3 15% 29% 25%	4078
	11th to 20th	Day	16% 3 3 20% 38% 21%	4067
	21st to end	Day	14% 3 4 21% 30% 28%	4520
September	1st to 10th	Day	18% 3 5% 18% 33% 23%	2205
	11th to 20th	Day	24% 3 7% 25% 27% 13%	2090
	21st to end	Day	23% 3 7% 28% 30% 9%	2090
October	1st to 10th	Day	25% 2 6% 22% 33% 13%	3308
	11th to 20th	Day	27% 3 9% 37% 18% 6%	3150
	21st to end	Day	38% 5% 13% 27% 17% 1	3289
November	1st to 10th	Day	45% 4 14% 23% 12% 2	1764
	11th to 20th	Day	46% 4 17% 24% 8% 2	1673
	21st to end	Day	47% 3 17% 22% 9% 2	1600
December	1st to 10th	Day	38% 4 22% 30% 4 2	2620
	11th to 20th	Day	66% 4 13% 14% 3	2918
	21st to end	Day	60% 3 12% 17% 7%	3498
January	1st to 10th	Night	58% 4 10% 21% 6%	6444
	11th to 20th	Night	60% 4 13% 17% 4 2	6172
	21st to end	Night	47% 2 14% 21% 13% 3	6468
February	1st to 10th	Night	56% 5% 14% 18% 7% 1	2600
	11th to 20th	Night	53% 4 13% 20% 9% 1	2518
	21st to end	Night	55% 5% 12% 19% 7% 2	1980
March	1st to 10th	Night	47% 5% 9% 24% 12% 4	5125
	11th to 20th	Night	40% 3 11% 28% 17% 1	5000
	21st to end	Night	45% 4 15% 28% 7%	5489
April	1st to 10th	Night	44% 5% 12% 21% 14% 3	2126
	11th to 20th	Night	42% 4 11% 24% 16% 2	1781
	21st to end	Night	39% 4 10% 28% 18% 1	1800
May	1st to 10th	Night	42% 5% 6% 25% 19% 3	2950
	11th to 20th	Night	27% 5% 8% 31% 22% 7%	2925
	21st to end	Night	33% 4 7% 31% 21% 3	2848
June	1st to 10th	Night	31% 5% 13% 25% 24% 2	1401
	11th to 20th	Night	29% 4 8% 20% 27% 11%	1330
	21st to end	Night	18% 2 4 19% 33% 24%	1330
July	1st to 10th	Night	14% 3 3 11% 24% 45%	2232
	11th to 20th	Night	13% 3 2 11% 22% 49%	2524
	21st to end	Night	16% 3 4 13% 31% 33%	3011
August	1st to 10th	Night	21% 3 4 13% 28% 32%	2838
	11th to 20th	Night	19% 3 3 18% 34% 23%	2838
	21st to end	Night	16% 3 4 16% 29% 32%	3146
September	1st to 10th	Night	20% 2 4 13% 32% 29%	1971
	11th to 20th	Night	25% 3 6% 23% 26% 17%	2090
	21st to end	Night	24% 3 4 26% 32% 11%	2090
October	1st to 10th	Night	20% 1 6% 20% 36% 17%	3666
	11th to 20th	Night	33% 2 7% 32% 17% 8%	3778
	21st to end	Night	37% 4 11% 28% 18% 2	4267
November	1st to 10th	Night	41% 4 13% 26% 14% 2	2535
	11th to 20th	Night	46% 4 14% 25% 10% 2	2705
	21st to end	Night	46% 3 15% 23% 11% 2	2800
December	1st to 10th	Night	40% 4 21% 30% 4 1	4570
	11th to 20th	Night	56% 5% 19% 16% 3	5253
	21st to end	Night	60% 3 12% 17% 8% 1	7458

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	27% 19% 15% 25% 11% 4	200
	11th to 20th	Day	19% 10% 28% 23% 18% 2	230
	21st to end	Day	18% 9% 27% 32% 13% 2	330
February	1st to 10th	Day	23% 20% 30% 21% 6% 1	300
	11th to 20th	Day	21% 18% 33% 19% 9% 1	313
	21st to end	Day	17% 21% 29% 23% 9% 1	414
March	1st to 10th	Day	18% 22% 30% 22% 8% 1	500
	11th to 20th	Day	14% 20% 29% 27% 9% 1	500
	21st to end	Day	20% 21% 33% 18% 7% 1	550
April	1st to 10th	Day	18% 19% 26% 24% 10% 2	500
	11th to 20th	Day	17% 18% 33% 22% 9% 1	492
	21st to end	Day	16% 15% 29% 26% 11% 3	500
May	1st to 10th	Day	12% 15% 27% 30% 12% 3	503
	11th to 20th	Day	13% 16% 29% 24% 16% 3	528
	21st to end	Day	15% 9% 22% 30% 18% 6%	727
June	1st to 10th	Day	9% 13% 25% 27% 19% 7%	680
	11th to 20th	Day	14% 13% 28% 30% 13% 2	680
	21st to end	Day	5% 6% 28% 34% 20% 6%	680
July	1st to 10th	Day	4 7% 22% 37% 25% 4	646
	11th to 20th	Day	3 7% 26% 40% 20% 4	484
	21st to end	Day	4 3 21% 34% 30% 8%	531
August	1st to 10th	Day	6% 5% 28% 32% 23% 6%	487
	11th to 20th	Day	5% 5% 25% 34% 24% 7%	477
	21st to end	Day	5% 11% 25% 29% 22% 8%	539
September	1st to 10th	Day	4 7% 25% 29% 27% 7%	490
	11th to 20th	Day	9% 12% 26% 29% 19% 5%	490
	21st to end	Day	10% 9% 26% 26% 23% 6%	490
October	1st to 10th	Day	12% 11% 18% 29% 25% 6%	386
	11th to 20th	Day	11% 17% 19% 22% 20% 10%	300
	21st to end	Day	16% 15% 26% 29% 11% 3	330
November	1st to 10th	Day	22% 11% 27% 25% 9% 6%	300
	11th to 20th	Day	16% 15% 30% 24% 12% 3	300
	21st to end	Day	17% 12% 29% 30% 12% 2	300
December	1st to 10th	Day	21% 11% 23% 26% 14% 5%	300
	11th to 20th	Day	26% 10% 32% 20% 11% 1	279
	21st to end	Day	26% 14% 25% 20% 10% 3	220
January	1st to 10th	Night	22% 9% 20% 31% 17% 1	860
	11th to 20th	Night	22% 7% 23% 29% 16% 3	800
	21st to end	Night	21% 6% 21% 37% 14% 2	880
February	1st to 10th	Night	20% 12% 28% 27% 12% 1	800
	11th to 20th	Night	21% 10% 25% 30% 11% 3	784
	21st to end	Night	14% 13% 27% 32% 11% 2	660
March	1st to 10th	Night	16% 12% 27% 32% 12% 2	800
	11th to 20th	Night	12% 9% 29% 34% 15% 2	800
	21st to end	Night	13% 10% 29% 36% 11% 1	880
April	1st to 10th	Night	15% 10% 26% 35% 13% 1	752
	11th to 20th	Night	15% 11% 31% 34% 8% 2	593
	21st to end	Night	13% 9% 25% 36% 16% 2	600
May	1st to 10th	Night	12% 8% 24% 35% 19% 1	600
	11th to 20th	Night	11% 7% 22% 34% 22% 3	591
	21st to end	Night	12% 8% 21% 38% 18% 3	634
June	1st to 10th	Night	9% 8% 22% 34% 24% 4	451
	11th to 20th	Night	11% 7% 30% 33% 18% 1	380
	21st to end	Night	4 2 21% 42% 25% 6%	380
July	1st to 10th	Night	3 1 20% 44% 26% 6%	370
	11th to 20th	Night	2 1 22% 49% 25% 1	387
	21st to end	Night	3 3 16% 46% 29% 4	624
August	1st to 10th	Night	6% 2 16% 47% 26% 2	567
	11th to 20th	Night	3 2 18% 46% 28% 3	564
	21st to end	Night	5% 4 21% 41% 26% 3	627
September	1st to 10th	Night	5% 3 20% 42% 25% 5%	665
	11th to 20th	Night	7% 4 21% 37% 26% 6%	760
	21st to end	Night	10% 3 21% 38% 21% 7%	760
October	1st to 10th	Night	12% 5% 19% 39% 23% 2	760
	11th to 20th	Night	12% 8% 20% 36% 20% 4	760
	21st to end	Night	12% 9% 22% 40% 13% 4	836
November	1st to 10th	Night	16% 10% 25% 31% 16% 2	780
	11th to 20th	Night	17% 10% 29% 31% 13% 1	905
	21st to end	Night	15% 9% 23% 35% 16% 2	1000
December	1st to 10th	Night	19% 9% 24% 35% 12% 1	1000
	11th to 20th	Night	24% 9% 23% 30% 12% 1	1000
	21st to end	Night	27% 12% 23% 28% 9% 2	1100

Page generated at 2025-05-23 06:21:04. Version ac07

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