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 2026-09-29.

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	6% 7% 3 6% 4 4 4 3 5% 6% 52%	158052
	Night	8% 9% 3 7% 4 4 4 3 5% 7% 48%	150786
Transparency	Day	34% 4 9% 22% 20% 11%	152759
	Night	38% 4 11% 21% 17% 10%	147085
Seeing	Day	13% 13% 27% 28% 16% 4	17864
	Night	14% 8% 24% 36% 17% 2	27377

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	13% 22% 6% 10% 5% 5% 4 3 4 6% 24%	4586
	11th to 20th	Day	7% 11% 5% 11% 5% 4 3 2 3 5% 44%	4920
	21st to end	Day	9% 13% 5% 9% 4 4 3 3 4 6% 40%	5844
February	1st to 10th	Day	11% 15% 5% 12% 7% 5% 5% 4 4 5% 27%	1890
	11th to 20th	Day	12% 14% 5% 10% 6% 5% 5% 4 5% 7% 27%	1859
	21st to end	Day	7% 15% 5% 10% 6% 4 5% 4 5% 5% 34%	1730
March	1st to 10th	Day	9% 13% 4 10% 4 4 4 3 5% 7% 36%	4860
	11th to 20th	Day	6% 13% 3 7% 5% 4 5% 3 4 6% 44%	5110
	21st to end	Day	8% 14% 4 9% 6% 6% 6% 4 6% 7% 28%	5607
April	1st to 10th	Day	9% 12% 3 7% 5% 5% 4 4 6% 7% 38%	2383
	11th to 20th	Day	7% 10% 4 7% 4 4 4 4 5% 7% 44%	2697
	21st to end	Day	9% 9% 4 7% 5% 4 5% 4 6% 8% 39%	2730
May	1st to 10th	Day	6% 6% 2 4 3 3 3 3 5% 7% 57%	7626
	11th to 20th	Day	6% 6% 2 7% 5% 4 5% 4 6% 7% 48%	7596
	21st to end	Day	7% 6% 2 5% 3 3 4 3 5% 7% 54%	8926
June	1st to 10th	Day	7% 4 2 4 5% 4 5% 4 7% 8% 51%	3067
	11th to 20th	Day	7% 4 1 5% 4 4 3 3 5% 7% 56%	3150
	21st to end	Day	3 2 1 3 2 3 3 3 4 7% 69%	3150
July	1st to 10th	Day	1 2 1 3 2 3 3 3 5% 6% 71%	8725
	11th to 20th	Day	1 2 1 2 2 2 3 3 5% 6% 72%	8149
	21st to end	Day	2 2 1 4 3 3 4 3 5% 7% 65%	8304
August	1st to 10th	Day	3 2 1 3 2 3 3 3 4 5% 71%	7549
	11th to 20th	Day	3 2 1 3 3 3 4 3 5% 7% 64%	7565
	21st to end	Day	5% 3 1 4 3 3 3 3 5% 7% 62%	8374
September	1st to 10th	Day	3 3 1 3 2 2 2 2 4 6% 71%	2437
	11th to 20th	Day	6% 4 1 4 3 3 3 3 4 7% 63%	2310
	21st to end	Day	7% 3 2 4 3 3 2 3 4 6% 64%	2289
October	1st to 10th	Day	7% 4 2 4 2 3 3 2 3 3 67%	3412
	11th to 20th	Day	6% 4 2 4 4 3 4 2 4 5% 62%	3250
	21st to end	Day	8% 8% 2 6% 4 4 4 3 6% 7% 46%	3394
November	1st to 10th	Day	12% 12% 3 6% 4 3 3 3 5% 6% 43%	1854
	11th to 20th	Day	11% 11% 3 7% 5% 4 4 4 6% 7% 39%	1756
	21st to end	Day	9% 13% 5% 8% 3 4 4 3 4 5% 41%	1680
December	1st to 10th	Day	8% 9% 5% 9% 3 2 3 2 3 4 50%	2700
	11th to 20th	Day	14% 18% 6% 10% 6% 4 4 4 5% 6% 23%	2998
	21st to end	Day	15% 16% 4 10% 5% 4 5% 4 5% 7% 26%	3575
January	1st to 10th	Night	13% 18% 6% 13% 6% 4 4 3 5% 6% 23%	8348
	11th to 20th	Night	10% 14% 4 11% 4 3 3 2 4 5% 41%	8033
	21st to end	Night	9% 14% 5% 7% 4 4 3 2 4 6% 43%	8370
February	1st to 10th	Night	12% 15% 4 9% 5% 5% 4 4 5% 6% 30%	2730
	11th to 20th	Night	13% 16% 4 8% 5% 4 4 3 4 6% 34%	2646
	21st to end	Night	9% 13% 5% 10% 6% 5% 4 5% 5% 6% 31%	2076
March	1st to 10th	Night	8% 14% 4 8% 5% 5% 4 3 5% 6% 38%	5240
	11th to 20th	Night	6% 10% 3 7% 5% 4 5% 4 6% 8% 44%	5110
	21st to end	Night	8% 9% 3 8% 5% 6% 5% 5% 7% 9% 37%	5610
April	1st to 10th	Night	9% 10% 3 7% 5% 4 4 4 7% 7% 40%	2233
	11th to 20th	Night	8% 11% 2 7% 5% 5% 5% 3 6% 7% 42%	1871
	21st to end	Night	9% 8% 2 6% 4 4 4 4 6% 7% 47%	1890
May	1st to 10th	Night	7% 8% 2 5% 3 4 3 3 5% 7% 54%	5321
	11th to 20th	Night	6% 5% 2 5% 4 4 4 3 6% 7% 54%	5296
	21st to end	Night	8% 4 2 4 3 3 4 4 6% 9% 52%	5264
June	1st to 10th	Night	6% 4 2 5% 5% 4 5% 5% 6% 9% 50%	1548
	11th to 20th	Night	7% 5% 1 5% 3 4 3 3 6% 7% 56%	1470
	21st to end	Night	3 3 1 4 1 3 3 3 5% 6% 68%	1470
July	1st to 10th	Night	3 2 1 3 3 4 4 3 5% 7% 66%	4216
	11th to 20th	Night	1 1 1 3 2 3 4 3 6% 8% 70%	4800
	21st to end	Night	1 1 1 4 3 4 4 4 6% 8% 63%	5805
August	1st to 10th	Night	2 2 1 2 2 3 3 3 5% 7% 70%	5273
	11th to 20th	Night	2 2 1 4 4 4 5% 4 6% 8% 61%	5291
	21st to end	Night	7% 4 1 5% 3 3 4 4 5% 6% 56%	5842
September	1st to 10th	Night	4 3 2 3 3 3 3 3 4 4 69%	2179
	11th to 20th	Night	7% 4 1 4 3 4 4 3 5% 6% 59%	2310
	21st to end	Night	7% 4 1 3 2 3 3 2 5% 6% 64%	2288
October	1st to 10th	Night	6% 3 1 3 2 2 3 2 3 4 70%	3782
	11th to 20th	Night	10% 6% 2 6% 3 3 4 3 5% 4 55%	3898
	21st to end	Night	8% 8% 3 6% 4 3 4 4 6% 7% 47%	4404
November	1st to 10th	Night	11% 9% 3 6% 3 3 4 4 5% 7% 45%	2665
	11th to 20th	Night	10% 12% 4 6% 6% 4 4 3 5% 7% 39%	2840
	21st to end	Night	9% 11% 4 8% 5% 4 4 3 5% 6% 40%	2940
December	1st to 10th	Night	8% 11% 3 7% 5% 3 3 3 4 5% 48%	4710
	11th to 20th	Night	13% 17% 4 9% 5% 4 4 3 5% 7% 29%	5394
	21st to end	Night	14% 16% 5% 10% 5% 4 5% 4 4 5% 28%	7623

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 16% 13% 4	4587
	11th to 20th	Day	45% 3 20% 19% 10% 3	4920
	21st to end	Day	47% 4 14% 22% 12% 1	5844
February	1st to 10th	Day	61% 5% 12% 18% 5% 1	1890
	11th to 20th	Day	57% 5% 13% 18% 6% 1	1868
	21st to end	Day	53% 7% 10% 20% 9% 1	1730
March	1st to 10th	Day	50% 4 10% 24% 8% 4	4860
	11th to 20th	Day	44% 4 8% 31% 12% 1	5110
	21st to end	Day	57% 6% 14% 20% 4	5607
April	1st to 10th	Day	46% 5% 13% 21% 13% 2	2383
	11th to 20th	Day	41% 5% 9% 27% 16% 2	2700
	21st to end	Day	43% 5% 10% 26% 15%	2730
May	1st to 10th	Day	28% 4 7% 28% 29% 4	7626
	11th to 20th	Day	35% 5% 5% 24% 24% 7%	7599
	21st to end	Day	30% 5% 6% 34% 23% 2	8927
June	1st to 10th	Day	32% 4 11% 31% 20% 2	3067
	11th to 20th	Day	29% 4 7% 23% 25% 11%	3150
	21st to end	Day	17% 3 3 24% 37% 16%	3150
July	1st to 10th	Day	14% 3 3 13% 27% 39%	8653
	11th to 20th	Day	13% 3 3 16% 30% 35%	8074
	21st to end	Day	19% 3 4 14% 35% 25%	8120
August	1st to 10th	Day	17% 3 2 11% 27% 39%	5978
	11th to 20th	Day	23% 4 6% 20% 32% 15%	5964
	21st to end	Day	20% 3 6% 26% 25% 20%	6569
September	1st to 10th	Day	17% 3 6% 19% 33% 22%	2437
	11th to 20th	Day	24% 3 7% 26% 29% 12%	2310
	21st to end	Day	24% 3 7% 28% 31% 8%	2289
October	1st to 10th	Day	25% 2 6% 22% 33% 12%	3412
	11th to 20th	Day	28% 3 9% 38% 18% 6%	3250
	21st to end	Day	38% 5% 13% 28% 16% 1	3394
November	1st to 10th	Day	44% 4 15% 24% 11% 2	1854
	11th to 20th	Day	46% 4 17% 24% 7% 2	1756
	21st to end	Day	46% 3 18% 23% 9% 2	1680
December	1st to 10th	Day	40% 4 22% 30% 4 2	2700
	11th to 20th	Day	65% 4 14% 14% 3	2996
	21st to end	Day	60% 3 12% 18% 7%	3575
January	1st to 10th	Night	62% 5% 10% 19% 5%	8349
	11th to 20th	Night	47% 4 22% 20% 6% 1	8033
	21st to end	Night	44% 3 15% 23% 11% 3	8370
February	1st to 10th	Night	55% 5% 15% 18% 7% 1	2730
	11th to 20th	Night	54% 4 13% 20% 9% 1	2647
	21st to end	Night	54% 5% 12% 20% 7% 2	2076
March	1st to 10th	Night	47% 5% 9% 24% 12% 4	5240
	11th to 20th	Night	39% 3 11% 28% 17% 1	5110
	21st to end	Night	45% 4 15% 28% 8% 1	5610
April	1st to 10th	Night	44% 5% 11% 23% 14% 3	2233
	11th to 20th	Night	42% 4 12% 24% 17% 2	1871
	21st to end	Night	39% 4 10% 28% 18% 1	1890
May	1st to 10th	Night	31% 4 6% 23% 32% 4	5319
	11th to 20th	Night	29% 5% 6% 24% 26% 10%	5297
	21st to end	Night	27% 5% 7% 28% 31% 3	5265
June	1st to 10th	Night	31% 5% 12% 24% 24% 4	1548
	11th to 20th	Night	27% 4 8% 20% 29% 12%	1470
	21st to end	Night	19% 2 4 19% 32% 24%	1470
July	1st to 10th	Night	18% 4 3 12% 21% 42%	4180
	11th to 20th	Night	13% 3 4 13% 26% 41%	4752
	21st to end	Night	18% 4 5% 14% 30% 30%	5677
August	1st to 10th	Night	15% 2 3 9% 23% 48%	4168
	11th to 20th	Night	24% 4 8% 17% 28% 18%	4168
	21st to end	Night	25% 4 6% 19% 23% 24%	4578
September	1st to 10th	Night	20% 2 4 13% 33% 27%	2179
	11th to 20th	Night	26% 4 6% 23% 26% 16%	2310
	21st to end	Night	24% 3 5% 26% 32% 10%	2288
October	1st to 10th	Night	20% 2 6% 20% 36% 16%	3782
	11th to 20th	Night	33% 3 7% 33% 17% 8%	3898
	21st to end	Night	37% 4 11% 29% 18% 2	4404
November	1st to 10th	Night	40% 4 13% 26% 14% 2	2665
	11th to 20th	Night	47% 4 14% 24% 9% 2	2840
	21st to end	Night	46% 3 16% 23% 10% 2	2940
December	1st to 10th	Night	41% 4 20% 30% 4 1	4710
	11th to 20th	Night	56% 5% 19% 17% 4	5395
	21st to end	Night	60% 3 12% 18% 8% 1	7623

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% 19% 16% 23% 10% 4	220
	11th to 20th	Day	17% 9% 28% 25% 20% 2	253
	21st to end	Day	17% 9% 26% 34% 13% 2	363
February	1st to 10th	Day	22% 18% 29% 22% 7% 2	330
	11th to 20th	Day	20% 18% 32% 19% 9% 1	344
	21st to end	Day	17% 21% 30% 22% 8% 1	446
March	1st to 10th	Day	20% 21% 29% 21% 7% 1	540
	11th to 20th	Day	15% 21% 28% 26% 9% 1	540
	21st to end	Day	20% 22% 32% 18% 8% 1	594
April	1st to 10th	Day	18% 18% 27% 24% 10% 2	540
	11th to 20th	Day	17% 18% 33% 22% 9% 1	532
	21st to end	Day	17% 15% 28% 27% 11% 3	540
May	1st to 10th	Day	11% 14% 28% 30% 13% 3	543
	11th to 20th	Day	13% 18% 28% 24% 15% 3	568
	21st to end	Day	14% 9% 23% 30% 17% 6%	809
June	1st to 10th	Day	8% 13% 27% 28% 18% 6%	780
	11th to 20th	Day	13% 13% 28% 31% 13% 2	780
	21st to end	Day	6% 7% 28% 34% 19% 6%	780
July	1st to 10th	Day	4 7% 23% 38% 24% 4	743
	11th to 20th	Day	3 7% 25% 41% 20% 4	564
	21st to end	Day	3 3 23% 35% 28% 7%	619
August	1st to 10th	Day	5% 5% 28% 32% 23% 5%	567
	11th to 20th	Day	6% 5% 25% 34% 24% 7%	557
	21st to end	Day	6% 11% 24% 29% 21% 8%	627
September	1st to 10th	Day	4 8% 25% 29% 26% 8%	570
	11th to 20th	Day	9% 12% 26% 30% 19% 5%	570
	21st to end	Day	9% 9% 25% 27% 23% 7%	563
October	1st to 10th	Day	12% 10% 19% 29% 24% 6%	420
	11th to 20th	Day	11% 17% 22% 22% 19% 9%	330
	21st to end	Day	15% 14% 25% 31% 12% 3	363
November	1st to 10th	Day	22% 11% 25% 25% 10% 5%	330
	11th to 20th	Day	15% 15% 30% 25% 12% 3	330
	21st to end	Day	16% 12% 28% 30% 12% 2	330
December	1st to 10th	Day	23% 13% 23% 25% 12% 5%	330
	11th to 20th	Day	26% 11% 31% 21% 10% 1	307
	21st to end	Day	27% 14% 24% 19% 12% 3	242
January	1st to 10th	Night	22% 9% 21% 30% 16% 1	903
	11th to 20th	Night	21% 7% 23% 30% 15% 3	840
	21st to end	Night	20% 6% 21% 38% 14% 2	924
February	1st to 10th	Night	20% 12% 28% 27% 12% 1	840
	11th to 20th	Night	21% 11% 26% 29% 11% 2	824
	21st to end	Night	15% 13% 27% 32% 11% 2	692
March	1st to 10th	Night	15% 13% 27% 31% 12% 2	840
	11th to 20th	Night	13% 9% 30% 32% 14% 2	840
	21st to end	Night	13% 11% 30% 35% 10% 1	924
April	1st to 10th	Night	15% 11% 26% 34% 13% 1	790
	11th to 20th	Night	14% 11% 31% 34% 8% 1	623
	21st to end	Night	13% 8% 25% 36% 16% 1	630
May	1st to 10th	Night	11% 9% 24% 35% 19% 1	630
	11th to 20th	Night	11% 8% 22% 34% 21% 3	621
	21st to end	Night	12% 7% 22% 38% 17% 3	683
June	1st to 10th	Night	8% 8% 23% 35% 22% 3	498
	11th to 20th	Night	10% 7% 30% 35% 17% 1	420
	21st to end	Night	6% 3 22% 41% 23% 6%	420
July	1st to 10th	Night	3 1 21% 46% 24% 5%	410
	11th to 20th	Night	2 1 22% 50% 25% 1	429
	21st to end	Night	2 2 17% 48% 27% 3	690
August	1st to 10th	Night	6% 3 18% 48% 23% 2	627
	11th to 20th	Night	3 2 20% 46% 27% 3	624
	21st to end	Night	6% 3 21% 42% 24% 3	693
September	1st to 10th	Night	5% 4 21% 41% 24% 4	735
	11th to 20th	Night	7% 4 21% 38% 25% 5%	840
	21st to end	Night	9% 3 20% 39% 22% 6%	832
October	1st to 10th	Night	12% 6% 20% 38% 22% 2	800
	11th to 20th	Night	13% 9% 21% 35% 19% 4	800
	21st to end	Night	11% 9% 22% 40% 13% 4	880
November	1st to 10th	Night	15% 10% 26% 31% 16% 2	820
	11th to 20th	Night	17% 10% 28% 32% 12% 1	950
	21st to end	Night	14% 9% 23% 35% 16% 2	1050
December	1st to 10th	Night	20% 10% 24% 34% 11% 1	1050
	11th to 20th	Night	24% 10% 24% 29% 12% 1	1050
	21st to end	Night	26% 12% 23% 27% 9% 2	1155

Page generated at 2026-09-26 01:18:44. Version ac07

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