Al Meyers Airport
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Al Meyers Airport clear sky chart from 2005-11-06 to 2025-07-06.

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	14% 9% 3 8% 5% 5% 5% 4 6% 7% 34%	119677
	Night	15% 10% 4 8% 5% 4 4 3 5% 7% 35%	119220
Transparency	Day	47% 6% 12% 21% 13% 1	123290
	Night	47% 6% 11% 21% 13% 1	123745
Seeing	Day	17% 10% 28% 25% 15% 6%	16541
	Night	18% 9% 29% 30% 13% 1	26394

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% 14% 7% 17% 6% 5% 5% 4 5% 6% 21%	3617
	11th to 20th	Day	14% 14% 5% 15% 9% 6% 7% 5% 5% 6% 14%	3620
	21st to end	Day	21% 17% 6% 13% 6% 5% 4 3 5% 4 16%	4352
February	1st to 10th	Day	14% 15% 4 11% 8% 5% 5% 3 6% 6% 22%	1800
	11th to 20th	Day	15% 10% 4 11% 8% 6% 5% 4 5% 6% 25%	1936
	21st to end	Day	16% 13% 5% 11% 5% 4 5% 5% 5% 6% 27%	1650
March	1st to 10th	Day	16% 11% 5% 10% 6% 6% 5% 3 4 6% 29%	4540
	11th to 20th	Day	12% 11% 3 8% 5% 4 5% 4 5% 7% 37%	4980
	21st to end	Day	19% 15% 4 9% 5% 5% 4 4 5% 6% 26%	5465
April	1st to 10th	Day	16% 12% 4 7% 5% 4 5% 4 5% 7% 30%	2356
	11th to 20th	Day	17% 8% 2 8% 5% 5% 5% 4 5% 7% 34%	2502
	21st to end	Day	18% 9% 3 7% 5% 4 4 3 5% 8% 35%	2600
May	1st to 10th	Day	20% 8% 3 7% 4 4 4 4 5% 6% 34%	5862
	11th to 20th	Day	17% 7% 3 7% 5% 4 5% 4 6% 9% 34%	5861
	21st to end	Day	15% 6% 2 6% 4 4 5% 4 6% 7% 41%	6448
June	1st to 10th	Day	10% 6% 2 5% 5% 5% 5% 4 7% 8% 42%	2800
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 4 6% 9% 42%	2800
	21st to end	Day	9% 6% 2 6% 5% 5% 5% 5% 7% 10% 40%	2800
July	1st to 10th	Day	11% 5% 2 7% 5% 5% 5% 4 7% 10% 40%	4511
	11th to 20th	Day	7% 4 2 5% 4 4 5% 4 7% 9% 49%	4440
	21st to end	Day	7% 5% 2 7% 5% 5% 6% 5% 7% 9% 42%	4565
August	1st to 10th	Day	12% 5% 2 5% 4 4 4 4 6% 9% 45%	4104
	11th to 20th	Day	9% 6% 2 6% 5% 4 5% 4 7% 9% 42%	4044
	21st to end	Day	8% 4 2 7% 5% 5% 5% 5% 6% 10% 42%	4405
September	1st to 10th	Day	11% 6% 2 6% 5% 4 4 4 6% 8% 44%	2166
	11th to 20th	Day	9% 4 2 5% 4 4 5% 5% 7% 8% 47%	2090
	21st to end	Day	14% 6% 3 6% 5% 4 5% 4 5% 8% 40%	2090
October	1st to 10th	Day	12% 6% 3 7% 4 4 4 3 6% 8% 44%	2066
	11th to 20th	Day	17% 8% 2 7% 5% 4 5% 3 6% 7% 35%	1900
	21st to end	Day	19% 9% 3 8% 5% 5% 5% 4 6% 6% 32%	1914
November	1st to 10th	Day	12% 8% 3 8% 5% 4 4 4 6% 7% 40%	1762
	11th to 20th	Day	15% 14% 4 8% 6% 5% 5% 3 5% 6% 30%	1800
	21st to end	Day	18% 13% 4 9% 5% 5% 5% 4 5% 6% 27%	1800
December	1st to 10th	Day	12% 14% 7% 12% 6% 5% 5% 4 5% 6% 23%	2930
	11th to 20th	Day	20% 17% 5% 10% 7% 4 5% 4 5% 5% 18%	3119
	21st to end	Day	26% 20% 6% 11% 5% 5% 3 2 3 4 14%	3982
January	1st to 10th	Night	14% 15% 6% 14% 5% 4 4 3 4 6% 24%	6348
	11th to 20th	Night	12% 17% 7% 13% 7% 5% 5% 4 5% 7% 17%	6360
	21st to end	Night	19% 15% 6% 10% 5% 4 4 3 4 5% 24%	6605
February	1st to 10th	Night	16% 14% 5% 11% 8% 5% 4 2 5% 6% 24%	2600
	11th to 20th	Night	14% 12% 5% 9% 6% 4 6% 4 5% 6% 28%	2348
	21st to end	Night	19% 10% 5% 9% 5% 4 4 3 4 7% 29%	1980
March	1st to 10th	Night	16% 11% 3 7% 4 4 4 3 5% 6% 37%	5311
	11th to 20th	Night	10% 7% 3 5% 4 4 5% 4 6% 7% 46%	4980
	21st to end	Night	17% 10% 3 8% 5% 4 4 3 5% 6% 36%	5467
April	1st to 10th	Night	17% 9% 4 7% 4 4 4 4 5% 6% 37%	2060
	11th to 20th	Night	18% 7% 2 6% 5% 4 4 3 5% 7% 38%	1847
	21st to end	Night	16% 8% 3 6% 4 4 5% 4 5% 6% 38%	1800
May	1st to 10th	Night	21% 9% 3 8% 5% 4 4 3 5% 6% 31%	4033
	11th to 20th	Night	19% 8% 2 6% 4 4 4 3 4 7% 38%	4032
	21st to end	Night	15% 5% 2 6% 4 4 4 4 5% 8% 44%	4390
June	1st to 10th	Night	10% 4 2 5% 5% 4 4 4 6% 9% 47%	1600
	11th to 20th	Night	10% 6% 2 6% 5% 3 5% 4 6% 9% 43%	1600
	21st to end	Night	9% 5% 1 6% 4 3 5% 5% 7% 9% 46%	1600
July	1st to 10th	Night	9% 4 2 4 4 4 4 4 6% 10% 51%	2570
	11th to 20th	Night	8% 4 2 4 4 3 4 4 6% 8% 54%	2530
	21st to end	Night	6% 4 1 5% 4 4 5% 4 7% 10% 48%	2987
August	1st to 10th	Night	12% 5% 2 6% 4 3 4 3 5% 8% 46%	2825
	11th to 20th	Night	8% 5% 1 5% 3 4 5% 4 6% 8% 49%	2785
	21st to end	Night	9% 4 2 6% 4 5% 5% 4 6% 7% 48%	3247
September	1st to 10th	Night	10% 5% 2 6% 4 4 4 3 5% 8% 50%	1995
	11th to 20th	Night	9% 5% 1 5% 4 4 3 2 5% 8% 54%	2090
	21st to end	Night	13% 7% 3 7% 4 4 4 3 5% 6% 44%	2090
October	1st to 10th	Night	11% 7% 2 6% 4 4 4 3 5% 7% 47%	2114
	11th to 20th	Night	16% 8% 3 7% 6% 4 5% 3 5% 5% 38%	2280
	21st to end	Night	20% 9% 3 6% 4 4 4 4 5% 6% 36%	2682
November	1st to 10th	Night	13% 9% 3 6% 4 4 4 4 4 6% 43%	2536
	11th to 20th	Night	16% 10% 3 7% 5% 4 4 4 6% 8% 32%	2600
	21st to end	Night	18% 13% 4 9% 5% 4 4 4 5% 6% 28%	2600
December	1st to 10th	Night	13% 12% 6% 12% 6% 5% 4 3 6% 7% 26%	4250
	11th to 20th	Night	17% 17% 5% 11% 6% 4 5% 4 4 6% 21%	5082
	21st to end	Night	27% 18% 5% 10% 5% 4 4 3 4 5% 15%	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	61% 8% 11% 15% 5%	3618
	11th to 20th	Day	66% 7% 11% 8% 7%	3620
	21st to end	Day	70% 5% 9% 10% 6%	4352
February	1st to 10th	Day	61% 6% 10% 15% 7%	1800
	11th to 20th	Day	58% 6% 8% 18% 9% 1	1946
	21st to end	Day	56% 6% 12% 17% 7% 2	1650
March	1st to 10th	Day	56% 5% 12% 18% 9% 1	4540
	11th to 20th	Day	45% 5% 17% 22% 9% 2	4980
	21st to end	Day	58% 6% 11% 15% 10% 1	5465
April	1st to 10th	Day	52% 6% 11% 18% 13%	2356
	11th to 20th	Day	49% 5% 11% 21% 12% 2	2502
	21st to end	Day	48% 6% 12% 20% 14% 1	2600
May	1st to 10th	Day	50% 6% 10% 19% 14% 2	5897
	11th to 20th	Day	46% 7% 12% 21% 12% 1	5865
	21st to end	Day	40% 6% 10% 22% 18% 4	6462
June	1st to 10th	Day	38% 7% 11% 26% 15% 3	2800
	11th to 20th	Day	37% 7% 12% 23% 18% 2	2800
	21st to end	Day	37% 8% 14% 21% 17% 2	2800
July	1st to 10th	Day	39% 7% 14% 22% 16% 3	4442
	11th to 20th	Day	29% 7% 13% 33% 17% 1	4365
	21st to end	Day	35% 9% 14% 20% 21% 2	4420
August	1st to 10th	Day	34% 8% 13% 28% 16% 1	4091
	11th to 20th	Day	35% 9% 11% 30% 14% 1	4083
	21st to end	Day	35% 7% 13% 31% 12% 2	4404
September	1st to 10th	Day	38% 6% 16% 22% 16% 2	2166
	11th to 20th	Day	32% 7% 9% 32% 18% 1	2090
	21st to end	Day	42% 5% 13% 24% 16%	2090
October	1st to 10th	Day	29% 5% 11% 31% 23% 1	3430
	11th to 20th	Day	39% 5% 10% 26% 20%	3140
	21st to end	Day	43% 5% 13% 25% 13% 1	3126
November	1st to 10th	Day	42% 6% 12% 26% 14% 1	1762
	11th to 20th	Day	55% 4 12% 18% 9% 2	1800
	21st to end	Day	57% 5% 13% 17% 7% 1	1800
December	1st to 10th	Day	59% 8% 16% 12% 5%	2930
	11th to 20th	Day	67% 6% 11% 13% 3	3116
	21st to end	Day	75% 5% 7% 9% 4	3982
January	1st to 10th	Night	60% 6% 9% 17% 8% 1	6348
	11th to 20th	Night	65% 5% 12% 11% 7%	6360
	21st to end	Night	61% 5% 12% 11% 10%	6605
February	1st to 10th	Night	62% 5% 11% 14% 7% 1	2600
	11th to 20th	Night	56% 6% 10% 19% 8% 1	2349
	21st to end	Night	55% 5% 12% 17% 9% 2	1980
March	1st to 10th	Night	46% 5% 13% 25% 11% 1	5311
	11th to 20th	Night	36% 6% 14% 27% 16% 1	4980
	21st to end	Night	48% 5% 11% 20% 14% 2	5467
April	1st to 10th	Night	47% 6% 10% 22% 14% 2	2060
	11th to 20th	Night	46% 5% 10% 20% 18% 1	1847
	21st to end	Night	45% 7% 11% 19% 16% 3	1800
May	1st to 10th	Night	53% 6% 9% 16% 13% 3	4060
	11th to 20th	Night	45% 7% 9% 25% 12% 2	4033
	21st to end	Night	37% 6% 13% 23% 19% 3	4398
June	1st to 10th	Night	33% 5% 11% 28% 20% 3	1600
	11th to 20th	Night	37% 7% 11% 26% 16% 3	1600
	21st to end	Night	32% 7% 14% 26% 20% 1	1600
July	1st to 10th	Night	29% 6% 13% 29% 16% 6%	2530
	11th to 20th	Night	27% 6% 15% 28% 21% 2	2482
	21st to end	Night	28% 9% 18% 19% 23% 2	2892
August	1st to 10th	Night	35% 8% 13% 27% 16% 1	2814
	11th to 20th	Night	30% 8% 13% 33% 14% 2	2812
	21st to end	Night	34% 7% 11% 29% 17% 2	3247
September	1st to 10th	Night	32% 6% 12% 27% 20% 3	1995
	11th to 20th	Night	29% 5% 10% 30% 24% 2	2090
	21st to end	Night	40% 6% 10% 27% 15% 1	2090
October	1st to 10th	Night	25% 4 9% 32% 28% 1	3530
	11th to 20th	Night	39% 5% 10% 24% 22%	3779
	21st to end	Night	37% 4 9% 33% 16% 1	4420
November	1st to 10th	Night	41% 5% 11% 25% 17% 1	2536
	11th to 20th	Night	48% 6% 13% 21% 10% 2	2600
	21st to end	Night	56% 5% 12% 19% 7%	2600
December	1st to 10th	Night	56% 7% 15% 16% 5%	4250
	11th to 20th	Night	63% 6% 12% 13% 6% 1	5084
	21st to end	Night	71% 6% 9% 8% 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	23% 13% 37% 20% 6% 1	300
	11th to 20th	Day	22% 13% 42% 19% 3 1	300
	21st to end	Day	25% 12% 33% 23% 6%	330
February	1st to 10th	Day	22% 14% 39% 19% 4 1	300
	11th to 20th	Day	23% 16% 39% 20% 3	300
	21st to end	Day	24% 18% 39% 16% 2	249
March	1st to 10th	Day	21% 18% 37% 19% 4	321
	11th to 20th	Day	22% 12% 34% 25% 7% 1	500
	21st to end	Day	27% 14% 32% 21% 6% 1	550
April	1st to 10th	Day	21% 13% 35% 21% 10%	500
	11th to 20th	Day	22% 18% 30% 17% 9% 4	492
	21st to end	Day	22% 10% 34% 21% 11% 2	500
May	1st to 10th	Day	23% 12% 31% 19% 13% 3	503
	11th to 20th	Day	21% 10% 27% 22% 14% 6%	527
	21st to end	Day	13% 7% 25% 25% 19% 10%	575
June	1st to 10th	Day	11% 9% 28% 30% 19% 3	730
	11th to 20th	Day	12% 6% 29% 33% 15% 5%	730
	21st to end	Day	10% 6% 29% 33% 15% 6%	730
July	1st to 10th	Day	8% 4 20% 28% 27% 13%	697
	11th to 20th	Day	9% 6% 22% 30% 21% 13%	668
	21st to end	Day	8% 3 21% 31% 23% 13%	592
August	1st to 10th	Day	9% 4 15% 29% 25% 17%	486
	11th to 20th	Day	11% 6% 14% 31% 25% 13%	479
	21st to end	Day	10% 2 17% 28% 29% 14%	539
September	1st to 10th	Day	14% 5% 18% 26% 23% 15%	490
	11th to 20th	Day	8% 4 16% 25% 31% 16%	490
	21st to end	Day	17% 9% 21% 23% 20% 9%	490
October	1st to 10th	Day	13% 7% 27% 27% 18% 10%	490
	11th to 20th	Day	19% 13% 28% 27% 10% 3	490
	21st to end	Day	24% 13% 39% 17% 6% 1	363
November	1st to 10th	Day	12% 16% 34% 24% 11% 3	300
	11th to 20th	Day	20% 20% 31% 22% 5% 2	300
	21st to end	Day	22% 15% 38% 21% 5%	300
December	1st to 10th	Day	22% 21% 31% 18% 7% 1	300
	11th to 20th	Day	21% 15% 42% 17% 5%	300
	21st to end	Day	29% 20% 29% 18% 3	330
January	1st to 10th	Night	22% 14% 35% 22% 6% 1	1000
	11th to 20th	Night	25% 12% 35% 23% 5%	1000
	21st to end	Night	21% 12% 36% 26% 6%	930
February	1st to 10th	Night	23% 12% 35% 26% 4	800
	11th to 20th	Night	22% 13% 35% 27% 4	783
	21st to end	Night	23% 13% 40% 21% 3	660
March	1st to 10th	Night	20% 11% 34% 27% 7%	800
	11th to 20th	Night	20% 13% 36% 26% 6% 1	800
	21st to end	Night	23% 9% 33% 28% 7%	880
April	1st to 10th	Night	21% 12% 34% 28% 5%	660
	11th to 20th	Night	20% 10% 35% 24% 9% 1	593
	21st to end	Night	21% 7% 33% 30% 9%	600
May	1st to 10th	Night	19% 7% 30% 33% 9% 1	600
	11th to 20th	Night	23% 4 27% 32% 14% 1	591
	21st to end	Night	13% 4 24% 36% 21% 2	650
June	1st to 10th	Night	12% 3 27% 42% 17%	600
	11th to 20th	Night	12% 4 21% 44% 19% 1	600
	21st to end	Night	10% 2 21% 41% 24% 2	600
July	1st to 10th	Night	9% 2 15% 41% 27% 5%	570
	11th to 20th	Night	9% 2 18% 40% 27% 4	552
	21st to end	Night	6% 2 16% 44% 31% 2	624
August	1st to 10th	Night	8% 2 14% 45% 27% 3	567
	11th to 20th	Night	9% 3 15% 38% 30% 4	564
	21st to end	Night	11% 3 14% 34% 34% 5%	627
September	1st to 10th	Night	12% 3 18% 34% 28% 4	665
	11th to 20th	Night	9% 4 14% 36% 32% 5%	760
	21st to end	Night	16% 6% 19% 33% 22% 4	760
October	1st to 10th	Night	13% 7% 25% 34% 18% 3	760
	11th to 20th	Night	21% 10% 32% 26% 10% 1	760
	21st to end	Night	23% 11% 33% 27% 6%	836
November	1st to 10th	Night	19% 11% 32% 25% 13% 1	780
	11th to 20th	Night	21% 13% 35% 23% 7% 1	800
	21st to end	Night	24% 11% 34% 25% 7%	800
December	1st to 10th	Night	22% 13% 36% 22% 7%	800
	11th to 20th	Night	23% 12% 37% 22% 5% 1	922
	21st to end	Night	31% 11% 33% 23% 3	1100

Page generated at 2025-07-03 01:30:15. Version ac07

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