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 2024-11-02.

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% 4 4 4 6% 7% 42%	101403
	Night	9% 8% 3 7% 5% 4 5% 4 6% 7% 43%	97759
Transparency	Day	40% 7% 14% 26% 12% 1	101141
	Night	39% 7% 15% 25% 13% 2	97611
Seeing	Day	13% 9% 30% 31% 14% 3	16026
	Night	12% 7% 33% 37% 11% 1	25915

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	6% 15% 5% 10% 11% 8% 6% 5% 6% 6% 22%	2418
	11th to 20th	Day	4 9% 4 12% 7% 7% 9% 6% 9% 9% 23%	2540
	21st to end	Day	4 11% 8% 20% 6% 5% 5% 3 4 5% 28%	2825
February	1st to 10th	Day	8% 12% 5% 11% 6% 7% 5% 3 7% 7% 30%	1710
	11th to 20th	Day	6% 10% 5% 11% 7% 7% 5% 4 6% 6% 33%	1730
	21st to end	Day	8% 13% 4 10% 6% 8% 5% 4 6% 7% 29%	1570
March	1st to 10th	Day	9% 10% 4 10% 5% 4 5% 3 5% 7% 40%	3178
	11th to 20th	Day	8% 10% 3 8% 4 4 4 3 5% 9% 42%	3480
	21st to end	Day	21% 14% 4 13% 6% 4 4 3 4 6% 23%	3814
April	1st to 10th	Day	15% 8% 3 7% 4 4 4 3 6% 7% 42%	2233
	11th to 20th	Day	18% 9% 3 8% 5% 5% 4 3 5% 5% 35%	2439
	21st to end	Day	19% 10% 2 6% 5% 4 4 4 5% 6% 35%	2470
May	1st to 10th	Day	17% 8% 3 6% 5% 4 4 3 4 6% 41%	4120
	11th to 20th	Day	11% 6% 3 5% 4 4 4 4 6% 7% 46%	4082
	21st to end	Day	16% 6% 2 6% 4 4 4 4 6% 8% 39%	5105
June	1st to 10th	Day	10% 5% 2 6% 4 4 4 4 7% 9% 44%	2850
	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	14% 7% 2 5% 4 4 3 3 4 7% 47%	2014
	11th to 20th	Day	14% 7% 2 5% 3 4 3 3 4 6% 49%	1888
	21st to end	Day	14% 8% 3 6% 4 3 3 3 5% 7% 43%	1881
November	1st to 10th	Day	11% 10% 3 8% 3 4 3 4 5% 7% 42%	1682
	11th to 20th	Day	8% 11% 3 9% 6% 5% 5% 3 6% 6% 40%	1596
	21st to end	Day	8% 10% 3 8% 5% 3 5% 5% 7% 8% 39%	1520
December	1st to 10th	Day	8% 10% 4 11% 7% 7% 6% 4 5% 7% 32%	1386
	11th to 20th	Day	8% 11% 5% 11% 7% 6% 6% 4 5% 8% 29%	1683
	21st to end	Day	20% 12% 5% 9% 6% 5% 4 3 4 5% 28%	2442
January	1st to 10th	Night	6% 13% 4 10% 8% 8% 7% 5% 7% 7% 24%	4534
	11th to 20th	Night	4 9% 3 10% 7% 7% 10% 6% 7% 9% 27%	4430
	21st to end	Night	5% 11% 6% 14% 6% 5% 7% 5% 6% 6% 29%	4842
February	1st to 10th	Night	7% 10% 4 11% 7% 7% 4 4 5% 7% 34%	2470
	11th to 20th	Night	6% 11% 3 9% 6% 4 5% 4 6% 7% 39%	2352
	21st to end	Night	9% 10% 4 9% 6% 5% 5% 5% 5% 7% 37%	1884
March	1st to 10th	Night	8% 8% 3 7% 5% 5% 5% 5% 6% 7% 42%	3684
	11th to 20th	Night	10% 7% 2 7% 4 4 5% 4 7% 8% 43%	3480
	21st to end	Night	22% 12% 4 8% 4 3 5% 4 6% 6% 27%	3817
April	1st to 10th	Night	12% 9% 3 6% 4 3 4 4 5% 8% 42%	1943
	11th to 20th	Night	16% 8% 3 7% 5% 3 4 3 4 7% 42%	1689
	21st to end	Night	16% 10% 4 7% 4 4 4 4 5% 7% 35%	1710
May	1st to 10th	Night	14% 6% 2 5% 3 4 4 3 5% 7% 47%	2850
	11th to 20th	Night	9% 5% 2 5% 4 4 5% 4 6% 8% 48%	2823
	21st to end	Night	12% 5% 2 6% 4 4 5% 4 6% 8% 45%	2476
June	1st to 10th	Night	10% 4 1 4 3 3 3 4 7% 8% 53%	1330
	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	14% 6% 2 4 3 3 3 3 5% 6% 50%	2147
	11th to 20th	Night	13% 7% 3 5% 3 3 3 3 4 5% 50%	2289
	21st to end	Night	12% 8% 2 6% 3 4 4 3 5% 7% 45%	2717
November	1st to 10th	Night	9% 7% 2 6% 4 4 4 3 6% 7% 48%	2431
	11th to 20th	Night	7% 9% 4 10% 6% 5% 5% 4 5% 6% 41%	2581
	21st to end	Night	8% 7% 3 6% 4 4 4 3 6% 8% 47%	2660
December	1st to 10th	Night	8% 10% 5% 11% 7% 5% 5% 4 4 6% 36%	2793
	11th to 20th	Night	8% 12% 4 8% 5% 6% 5% 5% 6% 7% 35%	3514
	21st to end	Night	19% 13% 4 9% 5% 3 4 3 4 5% 31%	5225

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	58% 9% 13% 14% 5% 1	2419
	11th to 20th	Day	52% 9% 16% 19% 4	2540
	21st to end	Day	58% 7% 12% 20% 3	2825
February	1st to 10th	Day	52% 8% 14% 19% 7% 1	1710
	11th to 20th	Day	49% 7% 13% 21% 8% 1	1739
	21st to end	Day	51% 7% 16% 17% 8% 1	1570
March	1st to 10th	Day	44% 8% 11% 28% 7% 1	3178
	11th to 20th	Day	38% 6% 17% 27% 10% 1	3480
	21st to end	Day	63% 7% 13% 12% 5%	3814
April	1st to 10th	Day	42% 5% 15% 25% 12% 1	2233
	11th to 20th	Day	50% 6% 11% 19% 12% 1	2442
	21st to end	Day	49% 6% 13% 23% 8% 1	2470
May	1st to 10th	Day	44% 5% 9% 25% 16% 1	4120
	11th to 20th	Day	34% 7% 12% 27% 16% 3	4086
	21st to end	Day	40% 8% 13% 28% 11%	5105
June	1st to 10th	Day	34% 8% 16% 29% 12% 2	2850
	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	37% 5% 14% 27% 15% 1	2014
	11th to 20th	Day	37% 6% 11% 31% 14% 2	1888
	21st to end	Day	40% 5% 16% 26% 11% 1	1881
November	1st to 10th	Day	40% 7% 15% 23% 13% 2	1682
	11th to 20th	Day	44% 6% 15% 24% 10% 1	1596
	21st to end	Day	41% 7% 18% 24% 8% 2	1520
December	1st to 10th	Day	51% 8% 15% 19% 6% 1	1386
	11th to 20th	Day	51% 9% 17% 19% 4	1680
	21st to end	Day	59% 7% 11% 19% 4	2442
January	1st to 10th	Night	54% 11% 13% 16% 6%	4534
	11th to 20th	Night	49% 9% 15% 18% 8%	4430
	21st to end	Night	51% 11% 14% 17% 6%	4842
February	1st to 10th	Night	49% 8% 14% 19% 11% 1	2470
	11th to 20th	Night	43% 7% 14% 23% 11% 2	2353
	21st to end	Night	44% 8% 14% 20% 12% 2	1884
March	1st to 10th	Night	40% 7% 15% 26% 10% 2	3684
	11th to 20th	Night	36% 7% 15% 31% 10% 1	3480
	21st to end	Night	55% 8% 15% 15% 6% 1	3817
April	1st to 10th	Night	41% 6% 13% 28% 12% 1	1943
	11th to 20th	Night	44% 5% 9% 24% 16% 3	1689
	21st to end	Night	47% 7% 10% 23% 11% 1	1710
May	1st to 10th	Night	34% 7% 13% 25% 17% 4	2850
	11th to 20th	Night	30% 9% 12% 29% 19% 2	2824
	21st to end	Night	34% 8% 14% 34% 9% 1	2476
June	1st to 10th	Night	28% 7% 16% 30% 15% 4	1330
	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	36% 5% 11% 26% 20% 2	2147
	11th to 20th	Night	36% 4 11% 29% 16% 3	2289
	21st to end	Night	38% 6% 14% 26% 15% 2	2717
November	1st to 10th	Night	34% 6% 15% 24% 18% 3	2431
	11th to 20th	Night	42% 7% 15% 22% 12% 2	2581
	21st to end	Night	35% 6% 20% 27% 11% 1	2660
December	1st to 10th	Night	49% 7% 15% 21% 8%	2793
	11th to 20th	Night	46% 7% 20% 19% 7%	3516
	21st to end	Night	57% 5% 11% 20% 7%	5225

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	11% 9% 29% 43% 7% 2	270
	11th to 20th	Day	12% 9% 36% 30% 12% 1	270
	21st to end	Day	15% 8% 34% 25% 16% 2	297
February	1st to 10th	Day	11% 12% 41% 33% 3	270
	11th to 20th	Day	12% 11% 41% 25% 10% 1	270
	21st to end	Day	12% 10% 40% 32% 5%	225
March	1st to 10th	Day	16% 12% 35% 27% 7% 2	270
	11th to 20th	Day	13% 11% 33% 27% 13% 2	270
	21st to end	Day	17% 12% 28% 24% 14% 5%	297
April	1st to 10th	Day	20% 15% 31% 27% 7%	413
	11th to 20th	Day	22% 15% 27% 26% 8% 1	640
	21st to end	Day	21% 12% 29% 27% 10% 1	650
May	1st to 10th	Day	17% 12% 28% 29% 12% 1	653
	11th to 20th	Day	16% 12% 26% 28% 16% 2	675
	21st to end	Day	17% 9% 28% 29% 15% 3	734
June	1st to 10th	Day	8% 8% 27% 32% 18% 6%	680
	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% 21% 8% 2	330
November	1st to 10th	Day	21% 11% 28% 33% 8% 1	273
	11th to 20th	Day	14% 10% 41% 24% 10% 1	270
	21st to end	Day	15% 14% 37% 26% 7% 1	270
December	1st to 10th	Day	13% 7% 35% 33% 11% 1	270
	11th to 20th	Day	13% 6% 46% 30% 4	270
	21st to end	Day	21% 11% 33% 25% 10%	297
January	1st to 10th	Night	11% 7% 38% 35% 8% 1	950
	11th to 20th	Night	12% 8% 33% 39% 7%	950
	21st to end	Night	13% 8% 34% 38% 7% 1	1045
February	1st to 10th	Night	10% 9% 35% 36% 8% 1	950
	11th to 20th	Night	11% 6% 39% 33% 9% 1	878
	21st to end	Night	13% 7% 32% 33% 12% 3	628
March	1st to 10th	Night	13% 10% 33% 34% 9%	736
	11th to 20th	Night	17% 7% 33% 33% 9%	570
	21st to end	Night	16% 7% 32% 33% 10% 1	627
April	1st to 10th	Night	15% 10% 38% 29% 7%	570
	11th to 20th	Night	20% 12% 29% 28% 11%	563
	21st to end	Night	18% 8% 34% 29% 9% 1	570
May	1st to 10th	Night	12% 8% 35% 34% 11%	570
	11th to 20th	Night	11% 6% 32% 40% 10%	561
	21st to end	Night	12% 8% 33% 35% 11%	617
June	1st to 10th	Night	10% 5% 26% 44% 15%	570
	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% 8% 34% 35% 11%	935
	11th to 20th	Night	10% 9% 37% 33% 10% 1	950
	21st to end	Night	11% 9% 35% 38% 8%	950
December	1st to 10th	Night	11% 7% 37% 34% 9% 1	950
	11th to 20th	Night	15% 8% 34% 35% 8%	950
	21st to end	Night	21% 7% 35% 29% 7% 1	1045

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