Aberdeen Regional Airport
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Aberdeen Regional Airport clear sky chart from 2005-11-06 to 2025-06-10.

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	11% 7% 3 7% 5% 5% 4 4 5% 7% 42%	122907
	Night	9% 7% 3 8% 5% 4 5% 4 6% 7% 43%	124103
Transparency	Day	41% 6% 14% 25% 13% 1	122646
	Night	40% 6% 15% 25% 14% 2	123955
Seeing	Day	13% 9% 30% 31% 14% 3	16815
	Night	12% 7% 33% 37% 10% 1	26808

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	5% 14% 5% 15% 11% 9% 8% 5% 6% 5% 17%	3476
	11th to 20th	Day	5% 8% 4 11% 8% 9% 9% 6% 9% 9% 23%	3640
	21st to end	Day	3 8% 8% 18% 9% 6% 5% 3 3 4 33%	4048
February	1st to 10th	Day	8% 12% 5% 11% 6% 7% 4 3 7% 7% 30%	1800
	11th to 20th	Day	6% 10% 5% 11% 6% 7% 5% 4 6% 7% 33%	1824
	21st to end	Day	8% 12% 4 10% 6% 8% 5% 4 7% 7% 30%	1650
March	1st to 10th	Day	8% 8% 3 8% 4 4 4 3 5% 7% 47%	4561
	11th to 20th	Day	9% 8% 2 8% 4 4 4 3 6% 9% 42%	4980
	21st to end	Day	18% 13% 4 12% 6% 4 5% 3 4 6% 23%	5464
April	1st to 10th	Day	15% 8% 3 6% 4 4 4 2 6% 7% 42%	2351
	11th to 20th	Day	18% 9% 3 8% 5% 5% 4 3 5% 6% 35%	2569
	21st to end	Day	19% 10% 2 6% 4 4 4 4 5% 6% 36%	2600
May	1st to 10th	Day	12% 6% 2 5% 4 3 3 3 5% 7% 51%	5900
	11th to 20th	Day	19% 7% 2 5% 3 3 3 3 4 6% 44%	5862
	21st to end	Day	15% 7% 2 6% 4 4 5% 4 6% 8% 39%	7332
June	1st to 10th	Day	10% 5% 2 6% 4 4 4 4 8% 9% 44%	2987
	11th to 20th	Day	11% 5% 2 5% 5% 4 4 4 7% 8% 45%	2850
	21st to end	Day	9% 4 2 4 4 4 5% 4 6% 8% 51%	2850
July	1st to 10th	Day	11% 4 2 5% 4 5% 5% 5% 7% 9% 44%	4750
	11th to 20th	Day	4 3 1 3 3 3 4 3 6% 8% 62%	4434
	21st to end	Day	5% 3 1 5% 5% 4 5% 5% 7% 10% 49%	4782
August	1st to 10th	Day	11% 5% 2 5% 4 4 4 4 6% 8% 48%	4103
	11th to 20th	Day	13% 6% 2 6% 4 5% 5% 3 6% 9% 41%	4041
	21st to end	Day	8% 4 2 5% 3 4 4 3 5% 8% 54%	4532
September	1st to 10th	Day	10% 4 1 4 3 3 3 4 5% 8% 56%	2225
	11th to 20th	Day	9% 4 2 5% 4 4 3 3 6% 8% 53%	2090
	21st to end	Day	14% 6% 2 4 3 3 3 2 4 6% 54%	2090
October	1st to 10th	Day	12% 5% 2 4 3 3 3 2 4 6% 58%	3352
	11th to 20th	Day	11% 5% 2 5% 3 3 3 3 4 6% 54%	3117
	21st to end	Day	13% 7% 3 6% 4 4 4 3 5% 7% 44%	3091
November	1st to 10th	Day	12% 10% 3 8% 3 4 3 4 5% 7% 41%	1763
	11th to 20th	Day	8% 11% 3 8% 5% 5% 5% 3 6% 6% 40%	1680
	21st to end	Day	8% 11% 3 8% 5% 3 5% 5% 7% 8% 38%	1600
December	1st to 10th	Day	7% 10% 4 12% 8% 7% 6% 3 5% 6% 31%	2372
	11th to 20th	Day	7% 14% 6% 13% 7% 7% 6% 4 5% 7% 23%	2643
	21st to end	Day	15% 12% 4 12% 6% 5% 5% 4 4 5% 28%	3498
January	1st to 10th	Night	5% 11% 5% 13% 9% 8% 7% 5% 7% 7% 22%	6486
	11th to 20th	Night	4 8% 3 10% 7% 8% 9% 6% 8% 8% 28%	6340
	21st to end	Night	4 9% 6% 12% 5% 5% 6% 4 6% 5% 37%	6917
February	1st to 10th	Night	8% 10% 4 11% 6% 7% 4 4 5% 7% 34%	2600
	11th to 20th	Night	6% 10% 3 9% 6% 4 5% 4 6% 7% 39%	2479
	21st to end	Night	8% 10% 3 8% 6% 4 5% 5% 5% 7% 38%	1980
March	1st to 10th	Night	8% 7% 2 7% 5% 5% 5% 4 6% 7% 44%	5310
	11th to 20th	Night	9% 6% 2 7% 4 4 5% 4 7% 8% 43%	4980
	21st to end	Night	18% 11% 3 8% 5% 4 5% 4 6% 7% 30%	5467
April	1st to 10th	Night	13% 9% 3 5% 4 3 4 4 5% 8% 42%	2045
	11th to 20th	Night	16% 8% 3 7% 5% 3 4 3 4 7% 42%	1779
	21st to end	Night	17% 10% 4 7% 4 4 4 4 5% 7% 35%	1800
May	1st to 10th	Night	12% 5% 2 4 2 3 3 3 5% 6% 55%	4080
	11th to 20th	Night	16% 7% 2 5% 3 3 4 3 5% 6% 47%	4053
	21st to end	Night	15% 6% 2 6% 4 4 4 4 6% 8% 41%	3559
June	1st to 10th	Night	10% 4 1 4 3 3 3 4 7% 8% 53%	1397
	11th to 20th	Night	8% 4 2 6% 4 5% 4 3 6% 9% 49%	1330
	21st to end	Night	5% 3 1 3 3 3 3 4 5% 9% 60%	1330
July	1st to 10th	Night	7% 5% 2 5% 6% 5% 4 4 7% 9% 47%	2220
	11th to 20th	Night	3 2 1 2 2 2 3 3 4 6% 72%	2531
	21st to end	Night	4 3 1 4 4 3 4 4 8% 10% 54%	2778
August	1st to 10th	Night	7% 5% 2 5% 4 4 4 4 6% 8% 52%	2836
	11th to 20th	Night	10% 6% 2 5% 4 3 4 3 5% 7% 51%	2798
	21st to end	Night	7% 4 2 4 4 4 4 3 5% 8% 55%	3135
September	1st to 10th	Night	8% 4 1 4 2 2 3 3 4 6% 61%	1950
	11th to 20th	Night	8% 4 2 5% 4 3 3 4 4 6% 58%	2090
	21st to end	Night	11% 4 2 5% 3 3 3 3 4 6% 57%	2090
October	1st to 10th	Night	9% 4 2 3 2 2 3 2 4 5% 65%	3576
	11th to 20th	Night	11% 5% 2 5% 3 3 3 3 6% 7% 52%	3800
	21st to end	Night	11% 6% 2 6% 4 5% 4 3 5% 7% 47%	4467
November	1st to 10th	Night	9% 7% 2 6% 4 4 4 3 6% 7% 47%	2535
	11th to 20th	Night	7% 9% 3 9% 6% 5% 5% 4 5% 6% 42%	2717
	21st to end	Night	8% 7% 3 7% 4 4 4 3 6% 8% 46%	2800
December	1st to 10th	Night	5% 8% 5% 11% 7% 6% 5% 4 4 7% 38%	4804
	11th to 20th	Night	6% 12% 5% 10% 7% 6% 5% 4 6% 7% 32%	5564
	21st to end	Night	14% 12% 4 11% 7% 4 4 3 5% 5% 29%	7480

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	65% 8% 11% 11% 4	3477
	11th to 20th	Day	52% 7% 16% 16% 9%	3640
	21st to end	Day	55% 6% 15% 20% 5%	4048
February	1st to 10th	Day	53% 7% 13% 19% 7% 1	1800
	11th to 20th	Day	49% 7% 13% 21% 9% 1	1833
	21st to end	Day	51% 7% 16% 17% 8% 1	1650
March	1st to 10th	Day	38% 6% 11% 34% 10% 1	4561
	11th to 20th	Day	38% 5% 15% 28% 13% 1	4980
	21st to end	Day	62% 6% 13% 15% 5%	5464
April	1st to 10th	Day	42% 5% 15% 25% 12% 1	2351
	11th to 20th	Day	49% 6% 11% 20% 12% 1	2572
	21st to end	Day	49% 6% 13% 23% 8% 1	2600
May	1st to 10th	Day	34% 4 9% 30% 22% 1	5900
	11th to 20th	Day	41% 5% 9% 21% 20% 5%	5866
	21st to end	Day	42% 7% 12% 27% 13%	7333
June	1st to 10th	Day	34% 8% 16% 28% 12% 2	2987
	11th to 20th	Day	34% 8% 15% 25% 15% 2	2850
	21st to end	Day	29% 8% 16% 30% 15% 2	2850
July	1st to 10th	Day	35% 6% 17% 27% 13% 1	4676
	11th to 20th	Day	21% 5% 15% 36% 21% 3	4358
	21st to end	Day	29% 6% 18% 29% 16% 2	4631
August	1st to 10th	Day	33% 6% 13% 30% 16% 2	4090
	11th to 20th	Day	40% 6% 16% 28% 8% 1	4080
	21st to end	Day	29% 6% 17% 31% 15% 2	4531
September	1st to 10th	Day	27% 6% 13% 34% 18% 1	2225
	11th to 20th	Day	30% 7% 17% 32% 15% 1	2090
	21st to end	Day	32% 6% 12% 30% 17% 2	2090
October	1st to 10th	Day	29% 4 9% 29% 27% 4	3352
	11th to 20th	Day	33% 4 9% 35% 17% 2	3117
	21st to end	Day	40% 4 15% 23% 17% 1	3091
November	1st to 10th	Day	40% 7% 15% 23% 12% 2	1763
	11th to 20th	Day	43% 6% 15% 24% 10% 1	1680
	21st to end	Day	42% 7% 17% 24% 8% 2	1600
December	1st to 10th	Day	53% 6% 17% 19% 4 1	2372
	11th to 20th	Day	60% 8% 15% 15% 3	2640
	21st to end	Day	59% 5% 14% 17% 5%	3498
January	1st to 10th	Night	58% 8% 13% 16% 6%	6486
	11th to 20th	Night	48% 7% 17% 16% 12%	6340
	21st to end	Night	45% 8% 17% 20% 10%	6917
February	1st to 10th	Night	48% 7% 14% 18% 11% 1	2600
	11th to 20th	Night	43% 7% 14% 23% 13% 1	2480
	21st to end	Night	44% 7% 14% 22% 12% 2	1980
March	1st to 10th	Night	37% 6% 14% 30% 10% 2	5310
	11th to 20th	Night	37% 5% 15% 30% 12% 1	4980
	21st to end	Night	52% 6% 15% 21% 6%	5467
April	1st to 10th	Night	41% 6% 13% 28% 12% 1	2045
	11th to 20th	Night	43% 5% 9% 24% 16% 3	1779
	21st to end	Night	48% 7% 10% 23% 11% 1	1800
May	1st to 10th	Night	29% 6% 12% 26% 24% 4	4080
	11th to 20th	Night	37% 6% 10% 21% 23% 4	4054
	21st to end	Night	39% 7% 13% 32% 9%	3559
June	1st to 10th	Night	28% 6% 16% 30% 15% 4	1397
	11th to 20th	Night	30% 7% 17% 25% 17% 4	1330
	21st to end	Night	21% 7% 21% 30% 19% 2	1330
July	1st to 10th	Night	33% 7% 20% 23% 16% 2	2185
	11th to 20th	Night	14% 4 12% 46% 21% 3	2484
	21st to end	Night	24% 6% 21% 29% 17% 3	2691
August	1st to 10th	Night	29% 7% 16% 28% 17% 3	2826
	11th to 20th	Night	34% 5% 16% 31% 12% 2	2825
	21st to end	Night	29% 5% 15% 28% 20% 3	3135
September	1st to 10th	Night	23% 5% 13% 34% 22% 3	1950
	11th to 20th	Night	28% 5% 15% 31% 18% 2	2090
	21st to end	Night	29% 4 11% 31% 21% 3	2090
October	1st to 10th	Night	24% 3 7% 26% 37% 3	3576
	11th to 20th	Night	31% 3 10% 33% 21% 2	3800
	21st to end	Night	37% 5% 14% 26% 17% 1	4467
November	1st to 10th	Night	35% 6% 15% 24% 18% 3	2535
	11th to 20th	Night	42% 7% 15% 22% 13% 2	2717
	21st to end	Night	36% 6% 20% 27% 10% 1	2800
December	1st to 10th	Night	46% 5% 18% 23% 8%	4804
	11th to 20th	Night	50% 6% 19% 19% 5%	5566
	21st to end	Night	57% 4 14% 18% 6%	7480

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	10% 8% 29% 42% 8% 3	300
	11th to 20th	Day	12% 9% 36% 30% 11% 1	300
	21st to end	Day	14% 10% 36% 24% 15% 2	330
February	1st to 10th	Day	12% 14% 40% 32% 3	300
	11th to 20th	Day	12% 10% 41% 25% 10% 2	300
	21st to end	Day	13% 10% 39% 33% 5%	249
March	1st to 10th	Day	16% 11% 35% 29% 7% 2	300
	11th to 20th	Day	13% 13% 34% 25% 13% 2	300
	21st to end	Day	18% 11% 30% 24% 13% 5%	330
April	1st to 10th	Day	21% 14% 31% 27% 6%	451
	11th to 20th	Day	22% 15% 28% 26% 8% 1	690
	21st to end	Day	22% 11% 29% 27% 9% 1	700
May	1st to 10th	Day	17% 12% 28% 29% 14% 1	703
	11th to 20th	Day	18% 11% 26% 28% 15% 2	725
	21st to end	Day	17% 8% 26% 29% 16% 3	789
June	1st to 10th	Day	9% 8% 27% 32% 18% 6%	726
	11th to 20th	Day	10% 10% 37% 28% 13% 2	680
	21st to end	Day	11% 8% 31% 33% 16% 2	680
July	1st to 10th	Day	7% 5% 24% 38% 20% 6%	671
	11th to 20th	Day	6% 5% 31% 39% 16% 3	668
	21st to end	Day	5% 5% 26% 41% 20% 4	739
August	1st to 10th	Day	8% 4 21% 41% 21% 4	676
	11th to 20th	Day	11% 5% 25% 37% 18% 4	665
	21st to end	Day	8% 4 27% 35% 22% 4	748
September	1st to 10th	Day	11% 8% 27% 36% 14% 5%	435
	11th to 20th	Day	10% 5% 36% 32% 15% 2	300
	21st to end	Day	17% 13% 33% 22% 10% 5%	300
October	1st to 10th	Day	18% 8% 29% 28% 13% 4	300
	11th to 20th	Day	15% 12% 34% 31% 7%	300
	21st to end	Day	16% 15% 38% 22% 7% 2	330
November	1st to 10th	Day	21% 10% 27% 33% 8% 1	300
	11th to 20th	Day	15% 10% 41% 24% 10% 1	300
	21st to end	Day	15% 13% 37% 26% 8% 1	300
December	1st to 10th	Day	13% 7% 34% 34% 11% 1	300
	11th to 20th	Day	14% 6% 46% 29% 5%	300
	21st to end	Day	19% 10% 33% 27% 10%	330
January	1st to 10th	Night	11% 7% 38% 35% 8% 1	1000
	11th to 20th	Night	12% 8% 34% 39% 7%	1000
	21st to end	Night	12% 8% 35% 38% 7% 1	1100
February	1st to 10th	Night	11% 9% 36% 36% 8% 1	1000
	11th to 20th	Night	11% 6% 40% 33% 9% 2	925
	21st to end	Night	13% 7% 33% 33% 12% 3	660
March	1st to 10th	Night	13% 10% 33% 35% 9%	775
	11th to 20th	Night	18% 8% 33% 33% 9%	600
	21st to end	Night	16% 7% 33% 33% 10% 1	660
April	1st to 10th	Night	16% 10% 38% 29% 7%	600
	11th to 20th	Night	19% 13% 29% 28% 10%	593
	21st to end	Night	19% 8% 34% 29% 9% 1	600
May	1st to 10th	Night	12% 8% 35% 35% 12%	600
	11th to 20th	Night	13% 6% 32% 39% 10%	591
	21st to end	Night	13% 7% 32% 35% 12%	650
June	1st to 10th	Night	10% 6% 25% 44% 15% 1	599
	11th to 20th	Night	9% 6% 36% 41% 8%	570
	21st to end	Night	7% 4 29% 49% 12% 1	570
July	1st to 10th	Night	5% 3 27% 47% 17% 1	555
	11th to 20th	Night	5% 3 27% 50% 15%	552
	21st to end	Night	4 1 24% 55% 14% 1	624
August	1st to 10th	Night	7% 3 21% 53% 17%	567
	11th to 20th	Night	9% 2 23% 45% 19% 1	564
	21st to end	Night	5% 4 26% 47% 18%	627
September	1st to 10th	Night	9% 2 31% 42% 14% 2	570
	11th to 20th	Night	9% 5% 29% 43% 13% 1	570
	21st to end	Night	11% 6% 34% 36% 13% 1	570
October	1st to 10th	Night	17% 8% 32% 31% 11%	627
	11th to 20th	Night	17% 8% 33% 34% 8%	769
	21st to end	Night	16% 8% 36% 31% 9%	1045
November	1st to 10th	Night	12% 7% 34% 35% 11%	975
	11th to 20th	Night	10% 10% 37% 32% 10% 1	1000
	21st to end	Night	11% 9% 34% 38% 8%	1000
December	1st to 10th	Night	11% 7% 37% 35% 9% 1	1000
	11th to 20th	Night	15% 8% 34% 35% 8%	1000
	21st to end	Night	20% 7% 36% 29% 7% 1	1100

Page generated at 2025-06-07 09:28:15. Version ac07

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