Aztalan State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Aztalan State Park clear sky chart from 2005-11-06 to 2025-08-05.

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	13% 8% 3 8% 5% 4 4 4 5% 7% 38%	125947
	Night	13% 10% 4 8% 5% 4 4 3 5% 6% 39%	122374
Transparency	Day	43% 6% 12% 24% 13% 1	129429
	Night	45% 5% 11% 23% 14% 2	126953
Seeing	Day	16% 10% 29% 25% 14% 5%	16946
	Night	18% 9% 31% 31% 11% 1	26774

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	8% 12% 6% 14% 8% 6% 5% 3 5% 6% 27%	3617
	11th to 20th	Day	8% 12% 6% 11% 4 4 6% 7% 6% 7% 28%	3620
	21st to end	Day	12% 15% 8% 9% 4 2 3 2 4 5% 35%	4099
February	1st to 10th	Day	12% 13% 6% 10% 5% 5% 4 4 4 6% 31%	1800
	11th to 20th	Day	13% 12% 3 7% 5% 5% 5% 3 5% 5% 36%	1908
	21st to end	Day	12% 14% 4 10% 7% 4 5% 3 4 5% 32%	1650
March	1st to 10th	Day	14% 7% 2 6% 4 3 4 3 5% 6% 45%	4480
	11th to 20th	Day	12% 6% 2 7% 4 5% 5% 3 4 7% 44%	4722
	21st to end	Day	22% 12% 4 10% 5% 4 4 3 4 5% 28%	5957
April	1st to 10th	Day	18% 13% 4 7% 5% 4 4 3 5% 6% 31%	2400
	11th to 20th	Day	17% 10% 4 7% 4 5% 5% 4 6% 6% 34%	2374
	21st to end	Day	19% 9% 3 7% 5% 5% 4 4 5% 7% 33%	2495
May	1st to 10th	Day	14% 8% 2 7% 4 4 4 3 6% 8% 40%	5988
	11th to 20th	Day	14% 6% 3 7% 5% 4 5% 4 6% 7% 41%	6319
	21st to end	Day	16% 6% 2 6% 4 4 4 4 6% 9% 39%	6935
June	1st to 10th	Day	10% 5% 2 6% 5% 4 5% 4 7% 8% 44%	2800
	11th to 20th	Day	12% 6% 3 6% 5% 4 5% 4 7% 8% 42%	2800
	21st to end	Day	12% 6% 3 6% 4 4 5% 4 6% 9% 41%	2800
July	1st to 10th	Day	11% 6% 2 7% 4 5% 5% 4 7% 10% 40%	6360
	11th to 20th	Day	7% 5% 2 5% 4 4 5% 4 6% 9% 47%	6360
	21st to end	Day	9% 6% 3 6% 4 5% 4 4 7% 9% 42%	6924
August	1st to 10th	Day	9% 5% 3 7% 5% 5% 6% 4 7% 8% 41%	4480
	11th to 20th	Day	11% 5% 2 5% 4 4 4 4 6% 9% 47%	3771
	21st to end	Day	9% 6% 2 6% 4 5% 5% 4 6% 8% 44%	4180
September	1st to 10th	Day	13% 5% 2 6% 4 4 5% 4 6% 8% 45%	2280
	11th to 20th	Day	12% 5% 2 5% 3 4 5% 2 5% 7% 50%	2195
	21st to end	Day	13% 6% 2 6% 4 4 4 4 5% 8% 43%	2090
October	1st to 10th	Day	14% 5% 2 7% 4 4 4 3 5% 7% 46%	1975
	11th to 20th	Day	19% 9% 3 8% 4 4 4 3 5% 8% 34%	1900
	21st to end	Day	17% 10% 3 7% 5% 3 4 3 4 6% 38%	1886
November	1st to 10th	Day	13% 9% 3 6% 3 4 5% 3 4 6% 45%	1762
	11th to 20th	Day	14% 11% 3 10% 6% 5% 4 3 6% 6% 31%	1800
	21st to end	Day	17% 13% 4 9% 5% 4 3 2 5% 5% 35%	1620
December	1st to 10th	Day	8% 9% 5% 9% 6% 5% 5% 4 6% 8% 36%	2610
	11th to 20th	Day	13% 15% 5% 11% 6% 5% 5% 5% 6% 6% 24%	3008
	21st to end	Day	20% 22% 8% 12% 5% 4 3 3 3 4 14%	3982
January	1st to 10th	Night	9% 12% 6% 13% 7% 4 4 3 4 5% 33%	6348
	11th to 20th	Night	10% 14% 6% 14% 6% 5% 5% 5% 5% 6% 24%	6360
	21st to end	Night	12% 16% 7% 10% 5% 4 4 3 4 5% 30%	6876
February	1st to 10th	Night	11% 15% 5% 9% 6% 4 4 3 5% 5% 33%	2600
	11th to 20th	Night	11% 12% 3 8% 5% 4 4 3 4 5% 40%	2376
	21st to end	Night	17% 11% 3 7% 4 4 3 3 5% 6% 36%	1980
March	1st to 10th	Night	16% 8% 2 6% 5% 4 4 3 4 4 44%	5373
	11th to 20th	Night	10% 6% 2 5% 4 4 4 4 6% 8% 47%	5266
	21st to end	Night	20% 13% 4 9% 4 4 4 3 4 5% 30%	4971
April	1st to 10th	Night	17% 11% 2 7% 4 4 4 3 5% 6% 37%	2000
	11th to 20th	Night	20% 9% 3 6% 4 4 4 3 5% 5% 38%	1975
	21st to end	Night	18% 8% 3 6% 4 4 4 3 5% 7% 38%	1903
May	1st to 10th	Night	16% 8% 3 7% 4 4 4 3 5% 7% 40%	3911
	11th to 20th	Night	11% 5% 2 7% 4 4 6% 4 5% 7% 45%	3596
	21st to end	Night	17% 8% 3 6% 4 4 4 3 6% 7% 39%	3942
June	1st to 10th	Night	10% 4 2 5% 4 4 5% 4 7% 8% 47%	1600
	11th to 20th	Night	13% 5% 1 5% 5% 3 4 4 6% 9% 46%	1600
	21st to end	Night	10% 6% 2 7% 4 3 4 3 5% 7% 48%	1600
July	1st to 10th	Night	12% 7% 2 5% 4 4 4 3 6% 9% 43%	3618
	11th to 20th	Night	6% 5% 2 5% 4 4 5% 3 6% 8% 52%	3617
	21st to end	Night	7% 4 2 6% 4 5% 5% 4 6% 8% 50%	3947
August	1st to 10th	Night	10% 5% 2 4 4 4 4 4 7% 8% 49%	2549
	11th to 20th	Night	9% 6% 2 6% 4 3 4 4 5% 8% 49%	3056
	21st to end	Night	8% 5% 2 5% 4 4 5% 4 6% 9% 48%	3476
September	1st to 10th	Night	8% 5% 2 5% 3 3 4 3 6% 7% 55%	1900
	11th to 20th	Night	11% 5% 1 5% 3 4 4 3 5% 7% 51%	1964
	21st to end	Night	10% 6% 3 6% 4 3 4 4 5% 7% 49%	2090
October	1st to 10th	Night	10% 6% 3 6% 4 3 3 3 4 6% 50%	2202
	11th to 20th	Night	16% 8% 2 6% 4 4 4 3 4 5% 43%	2280
	21st to end	Night	19% 9% 3 6% 4 4 4 3 5% 7% 36%	2712
November	1st to 10th	Night	12% 8% 3 6% 4 3 4 4 5% 6% 46%	2536
	11th to 20th	Night	14% 12% 4 8% 6% 4 4 4 4 5% 35%	2600
	21st to end	Night	17% 10% 3 8% 5% 4 4 3 5% 5% 36%	2775
December	1st to 10th	Night	9% 9% 3 8% 4 5% 5% 4 5% 7% 41%	4580
	11th to 20th	Night	17% 17% 5% 10% 5% 4 4 3 4 4 26%	5199
	21st to end	Night	21% 19% 7% 11% 5% 4 4 3 4 5% 18%	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	59% 4 13% 18% 5%	3618
	11th to 20th	Day	54% 5% 11% 13% 16% 1	3620
	21st to end	Day	53% 4 11% 20% 12%	4099
February	1st to 10th	Day	55% 5% 11% 18% 10% 1	1800
	11th to 20th	Day	49% 5% 11% 24% 9% 2	1918
	21st to end	Day	54% 5% 10% 18% 10% 2	1650
March	1st to 10th	Day	40% 5% 12% 28% 12% 4	4480
	11th to 20th	Day	39% 4 13% 29% 13% 1	4722
	21st to end	Day	58% 5% 11% 15% 10% 1	5959
April	1st to 10th	Day	54% 6% 11% 19% 10%	2400
	11th to 20th	Day	48% 7% 11% 20% 12% 2	2374
	21st to end	Day	50% 6% 13% 19% 11% 1	2495
May	1st to 10th	Day	41% 6% 11% 24% 16% 2	6023
	11th to 20th	Day	41% 7% 10% 27% 15% 1	6323
	21st to end	Day	40% 7% 11% 27% 13% 2	6949
June	1st to 10th	Day	36% 7% 14% 26% 16% 1	2800
	11th to 20th	Day	38% 7% 14% 23% 17% 1	2800
	21st to end	Day	39% 7% 15% 23% 15% 2	2800
July	1st to 10th	Day	39% 6% 14% 30% 10% 1	6291
	11th to 20th	Day	32% 6% 15% 31% 14% 1	6285
	21st to end	Day	36% 7% 16% 22% 17% 1	6728
August	1st to 10th	Day	38% 7% 13% 29% 12% 1	4465
	11th to 20th	Day	33% 7% 13% 34% 13% 1	3807
	21st to end	Day	36% 6% 13% 27% 17% 1	4179
September	1st to 10th	Day	36% 7% 12% 25% 18% 1	2280
	11th to 20th	Day	33% 5% 12% 31% 18% 2	2195
	21st to end	Day	40% 5% 11% 30% 14% 1	2090
October	1st to 10th	Day	24% 3 6% 40% 25% 2	3274
	11th to 20th	Day	36% 4 10% 28% 21% 1	3140
	21st to end	Day	42% 4 10% 29% 12% 2	3086
November	1st to 10th	Day	41% 6% 14% 24% 13% 2	1762
	11th to 20th	Day	53% 6% 13% 19% 9% 1	1800
	21st to end	Day	53% 4 14% 23% 6%	1620
December	1st to 10th	Day	46% 5% 20% 22% 5% 1	2610
	11th to 20th	Day	59% 5% 11% 18% 6% 2	3005
	21st to end	Day	74% 4 6% 10% 6%	3982
January	1st to 10th	Night	54% 4 8% 22% 11%	6348
	11th to 20th	Night	60% 5% 9% 10% 16% 1	6360
	21st to end	Night	56% 4 12% 16% 11%	6876
February	1st to 10th	Night	52% 5% 11% 19% 11% 2	2600
	11th to 20th	Night	47% 5% 10% 22% 14% 1	2377
	21st to end	Night	49% 4 13% 20% 11% 3	1980
March	1st to 10th	Night	44% 4 12% 23% 11% 5%	5373
	11th to 20th	Night	33% 5% 13% 32% 13% 4	5266
	21st to end	Night	58% 5% 9% 16% 12% 1	4971
April	1st to 10th	Night	48% 6% 9% 20% 16% 1	2000
	11th to 20th	Night	48% 4 8% 21% 17% 3	1975
	21st to end	Night	45% 6% 12% 22% 14% 2	1903
May	1st to 10th	Night	43% 6% 12% 18% 20% 2	3938
	11th to 20th	Night	36% 7% 16% 22% 16% 2	3597
	21st to end	Night	43% 7% 10% 23% 13% 4	3950
June	1st to 10th	Night	31% 8% 14% 27% 19% 1	1600
	11th to 20th	Night	34% 7% 12% 24% 21% 2	1600
	21st to end	Night	35% 6% 15% 22% 19% 2	1600
July	1st to 10th	Night	37% 6% 14% 30% 11% 2	3580
	11th to 20th	Night	30% 5% 14% 31% 19% 1	3572
	21st to end	Night	31% 8% 14% 24% 21% 2	3832
August	1st to 10th	Night	31% 7% 15% 26% 20% 1	2540
	11th to 20th	Night	33% 6% 12% 33% 16% 1	3086
	21st to end	Night	32% 6% 13% 27% 19% 3	3476
September	1st to 10th	Night	28% 6% 13% 27% 23% 2	1900
	11th to 20th	Night	31% 6% 11% 31% 19% 2	1964
	21st to end	Night	35% 5% 11% 30% 18% 1	2090
October	1st to 10th	Night	25% 4 6% 37% 26% 1	3670
	11th to 20th	Night	34% 4 12% 27% 21% 2	3779
	21st to end	Night	43% 4 9% 27% 15% 1	4462
November	1st to 10th	Night	40% 5% 10% 27% 16% 2	2536
	11th to 20th	Night	50% 6% 12% 20% 11% 2	2600
	21st to end	Night	50% 5% 14% 21% 9% 1	2775
December	1st to 10th	Night	42% 6% 16% 27% 8% 2	4580
	11th to 20th	Night	62% 5% 10% 14% 9% 1	5201
	21st to end	Night	70% 4 8% 13% 5%	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	19% 11% 35% 26% 7% 2	300
	11th to 20th	Day	16% 16% 38% 23% 6% 1	300
	21st to end	Day	22% 13% 35% 24% 5% 1	330
February	1st to 10th	Day	15% 18% 42% 18% 5% 1	300
	11th to 20th	Day	19% 21% 37% 17% 6%	300
	21st to end	Day	21% 18% 43% 16% 2	249
March	1st to 10th	Day	18% 19% 45% 14% 4	300
	11th to 20th	Day	20% 22% 32% 15% 10% 1	300
	21st to end	Day	27% 12% 31% 22% 6% 2	540
April	1st to 10th	Day	23% 14% 34% 23% 4	500
	11th to 20th	Day	26% 16% 26% 20% 9% 3	492
	21st to end	Day	25% 13% 26% 23% 12% 1	500
May	1st to 10th	Day	19% 11% 31% 26% 10% 3	551
	11th to 20th	Day	21% 9% 29% 26% 12% 3	725
	21st to end	Day	17% 9% 29% 24% 15% 6%	789
June	1st to 10th	Day	10% 7% 28% 33% 17% 5%	730
	11th to 20th	Day	13% 8% 28% 32% 13% 5%	730
	21st to end	Day	13% 8% 30% 28% 16% 4	730
July	1st to 10th	Day	8% 3 18% 32% 26% 13%	721
	11th to 20th	Day	8% 6% 26% 30% 22% 9%	718
	21st to end	Day	7% 3 24% 35% 21% 9%	794
August	1st to 10th	Day	8% 3 20% 33% 25% 12%	697
	11th to 20th	Day	12% 6% 16% 25% 25% 15%	506
	21st to end	Day	12% 5% 18% 31% 25% 10%	539
September	1st to 10th	Day	14% 6% 22% 26% 23% 8%	490
	11th to 20th	Day	12% 2 21% 29% 24% 12%	490
	21st to end	Day	15% 11% 27% 23% 17% 8%	490
October	1st to 10th	Day	19% 8% 23% 29% 16% 5%	375
	11th to 20th	Day	23% 14% 32% 22% 8% 1	300
	21st to end	Day	26% 13% 34% 21% 5% 2	330
November	1st to 10th	Day	15% 16% 38% 21% 10% 1	300
	11th to 20th	Day	20% 14% 41% 16% 9%	300
	21st to end	Day	26% 11% 38% 19% 5%	300
December	1st to 10th	Day	17% 16% 43% 17% 6% 1	300
	11th to 20th	Day	20% 14% 39% 17% 9% 1	300
	21st to end	Day	23% 18% 37% 18% 4 1	330
January	1st to 10th	Night	16% 15% 36% 25% 7% 1	1000
	11th to 20th	Night	19% 13% 36% 26% 5% 1	1000
	21st to end	Night	19% 11% 36% 27% 6%	1100
February	1st to 10th	Night	20% 10% 38% 26% 6% 1	1000
	11th to 20th	Night	18% 14% 35% 29% 4	821
	21st to end	Night	23% 12% 38% 23% 4	660
March	1st to 10th	Night	21% 10% 35% 27% 7% 1	800
	11th to 20th	Night	17% 12% 35% 30% 6%	730
	21st to end	Night	22% 11% 30% 30% 7% 1	660
April	1st to 10th	Night	23% 11% 36% 25% 5%	600
	11th to 20th	Night	23% 12% 30% 28% 6%	593
	21st to end	Night	22% 9% 33% 29% 8%	600
May	1st to 10th	Night	19% 8% 35% 33% 6%	600
	11th to 20th	Night	18% 5% 34% 31% 12%	591
	21st to end	Night	14% 5% 27% 37% 16%	650
June	1st to 10th	Night	11% 4 27% 43% 14% 1	600
	11th to 20th	Night	14% 3 32% 39% 12% 1	600
	21st to end	Night	12% 3 28% 43% 15%	600
July	1st to 10th	Night	9% 2 15% 40% 31% 3	585
	11th to 20th	Night	8% 3 18% 45% 23% 3	582
	21st to end	Night	7% 2 17% 51% 22% 2	657
August	1st to 10th	Night	9% 1 15% 47% 25% 3	579
	11th to 20th	Night	10% 2 15% 41% 29% 4	564
	21st to end	Night	11% 2 18% 40% 25% 3	627
September	1st to 10th	Night	8% 3 22% 37% 24% 5%	570
	11th to 20th	Night	12% 4 20% 35% 26% 3	634
	21st to end	Night	13% 6% 27% 31% 21% 2	760
October	1st to 10th	Night	14% 7% 29% 32% 17% 1	760
	11th to 20th	Night	21% 9% 32% 29% 9%	760
	21st to end	Night	24% 9% 31% 27% 7% 1	836
November	1st to 10th	Night	17% 10% 36% 26% 11% 1	780
	11th to 20th	Night	20% 13% 38% 23% 6%	800
	21st to end	Night	22% 12% 34% 24% 7%	975
December	1st to 10th	Night	21% 12% 39% 21% 6% 1	1000
	11th to 20th	Night	25% 11% 33% 25% 5%	1000
	21st to end	Night	29% 11% 33% 22% 4	1100

Page generated at 2025-08-02 00:32:24. Version ac07

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