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 2024-03-18.

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% 6% 3 5% 5% 6% 7% 41%	78343
	Night	9% 8% 3 6% 6% 3 5% 5% 5% 7% 42%	81486
Transparency	Day	41% 7% 15% 25% 11% 1	78041
	Night	40% 7% 14% 24% 13% 2	81310
Seeing	Day	13% 9% 30% 32% 14% 2	15038
	Night	12% 7% 33% 37% 11% 1	25188

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% 14% 5% 8% 13% 6% 6% 7% 6% 6% 22%	2418
	11th to 20th	Day	5% 8% 4 10% 9% 6% 7% 9% 9% 9% 23%	2540
	21st to end	Day	4 11% 8% 18% 8% 3 5% 4 4 5% 28%	2825
February	1st to 10th	Day	9% 10% 5% 10% 7% 5% 5% 5% 7% 7% 30%	1710
	11th to 20th	Day	6% 10% 5% 11% 7% 5% 6% 5% 6% 6% 33%	1730
	21st to end	Day	8% 12% 5% 9% 7% 5% 7% 5% 6% 7% 30%	1570
March	1st to 10th	Day	11% 10% 5% 10% 8% 3 6% 4 5% 7% 32%	1924
	11th to 20th	Day	10% 10% 5% 8% 6% 4 4 4 5% 7% 37%	2057
	21st to end	Day	13% 12% 4 9% 8% 4 5% 5% 5% 8% 27%	2178
April	1st to 10th	Day	15% 8% 3 6% 4 3 4 3 5% 7% 41%	2114
	11th to 20th	Day	19% 9% 3 7% 5% 4 5% 4 5% 5% 35%	2309
	21st to end	Day	18% 9% 3 6% 5% 4 4 4 5% 6% 36%	2340
May	1st to 10th	Day	17% 8% 3 6% 6% 3 4 4 5% 6% 38%	2340
	11th to 20th	Day	13% 6% 3 4 5% 3 5% 5% 7% 7% 42%	2302
	21st to end	Day	15% 6% 3 5% 5% 3 5% 5% 5% 9% 39%	2877
June	1st to 10th	Day	10% 5% 2 5% 4 3 5% 5% 7% 9% 44%	2700
	11th to 20th	Day	10% 4 2 5% 5% 3 5% 5% 6% 9% 45%	2700
	21st to end	Day	8% 4 2 4 4 3 5% 5% 5% 8% 52%	2700
July	1st to 10th	Day	5% 3 1 4 5% 3 5% 6% 7% 9% 52%	2700
	11th to 20th	Day	5% 3 1 3 4 2 3 4 6% 8% 61%	2524
	21st to end	Day	6% 3 1 4 5% 3 4 6% 6% 9% 54%	2734
August	1st to 10th	Day	8% 5% 2 5% 6% 3 5% 5% 7% 7% 47%	2328
	11th to 20th	Day	10% 4 1 4 4 3 4 4 6% 8% 50%	2301
	21st to end	Day	7% 4 1 3 3 2 3 4 5% 8% 59%	2574
September	1st to 10th	Day	10% 4 2 3 4 3 3 4 5% 8% 54%	2109
	11th to 20th	Day	10% 4 2 4 4 3 3 4 6% 7% 53%	1980
	21st to end	Day	15% 6% 2 4 4 2 3 3 4 6% 52%	1980
October	1st to 10th	Day	15% 6% 2 5% 5% 3 3 3 4 7% 46%	1908
	11th to 20th	Day	14% 6% 3 5% 3 3 4 4 4 6% 48%	1789
	21st to end	Day	14% 7% 3 6% 4 3 3 4 5% 8% 43%	1782
November	1st to 10th	Day	11% 9% 3 6% 5% 3 3 5% 5% 7% 42%	1673
	11th to 20th	Day	8% 10% 4 7% 7% 4 5% 5% 6% 6% 40%	1596
	21st to end	Day	8% 9% 4 7% 5% 3 5% 5% 7% 8% 39%	1520
December	1st to 10th	Day	8% 9% 4 10% 7% 6% 7% 4 5% 7% 32%	1386
	11th to 20th	Day	8% 10% 5% 10% 8% 5% 6% 5% 5% 8% 29%	1683
	21st to end	Day	20% 11% 5% 8% 7% 3 5% 4 4 5% 29%	2442
January	1st to 10th	Night	6% 12% 5% 8% 10% 6% 7% 8% 7% 7% 24%	4534
	11th to 20th	Night	4 8% 4 9% 9% 5% 9% 8% 7% 9% 27%	4430
	21st to end	Night	5% 11% 7% 13% 7% 4 7% 6% 6% 6% 29%	4842
February	1st to 10th	Night	7% 9% 5% 10% 8% 5% 5% 5% 5% 7% 34%	2470
	11th to 20th	Night	6% 10% 4 7% 7% 3 5% 6% 6% 7% 39%	2352
	21st to end	Night	9% 9% 5% 7% 7% 3 5% 6% 5% 7% 37%	1884
March	1st to 10th	Night	10% 9% 4 8% 6% 4 5% 5% 5% 7% 37%	2256
	11th to 20th	Night	13% 8% 3 6% 6% 3 5% 4 5% 7% 40%	2068
	21st to end	Night	12% 8% 4 7% 6% 3 5% 5% 6% 8% 37%	2178
April	1st to 10th	Night	12% 9% 3 5% 5% 3 4 5% 5% 8% 42%	1842
	11th to 20th	Night	17% 8% 3 6% 6% 2 4 3 4 7% 41%	1599
	21st to end	Night	16% 9% 4 6% 5% 3 4 5% 4 7% 36%	1620
May	1st to 10th	Night	12% 6% 2 5% 4 4 5% 5% 6% 7% 44%	1620
	11th to 20th	Night	9% 6% 3 5% 5% 3 5% 5% 6% 10% 44%	1593
	21st to end	Night	11% 4 3 6% 5% 3 6% 5% 7% 8% 41%	1393
June	1st to 10th	Night	10% 3 2 3 3 2 3 5% 7% 8% 52%	1260
	11th to 20th	Night	7% 3 3 6% 5% 3 4 4 6% 9% 50%	1260
	21st to end	Night	5% 3 1 3 3 2 3 5% 5% 9% 61%	1260
July	1st to 10th	Night	5% 3 2 3 5% 3 4 4 6% 7% 58%	1260
	11th to 20th	Night	4 2 1 2 3 2 3 4 5% 7% 69%	1431
	21st to end	Night	4 2 2 3 3 2 3 4 5% 9% 64%	1581
August	1st to 10th	Night	6% 3 2 4 5% 3 5% 5% 7% 8% 53%	1611
	11th to 20th	Night	8% 4 1 3 4 2 3 4 6% 7% 59%	1600
	21st to end	Night	5% 2 1 2 3 2 4 4 4 7% 67%	1782
September	1st to 10th	Night	9% 4 2 4 2 2 3 4 5% 6% 60%	1846
	11th to 20th	Night	8% 4 1 4 4 3 3 4 4 6% 58%	1980
	21st to end	Night	11% 4 2 4 4 2 3 4 4 6% 56%	1980
October	1st to 10th	Night	15% 6% 3 3 4 3 4 4 5% 7% 47%	2034
	11th to 20th	Night	14% 6% 3 5% 4 2 3 4 4 5% 50%	2168
	21st to end	Night	12% 8% 3 5% 4 3 4 4 5% 8% 45%	2574
November	1st to 10th	Night	9% 6% 3 5% 5% 2 4 4 5% 8% 48%	2405
	11th to 20th	Night	7% 8% 4 8% 7% 4 5% 4 5% 6% 41%	2581
	21st to end	Night	8% 6% 3 6% 5% 3 4 4 5% 8% 47%	2660
December	1st to 10th	Night	8% 9% 5% 10% 8% 4 5% 5% 4 6% 36%	2793
	11th to 20th	Night	8% 11% 4 7% 6% 4 5% 6% 6% 7% 36%	3514
	21st to end	Night	19% 13% 5% 8% 6% 2 4 4 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	52% 7% 14% 19% 6% 1	1924
	11th to 20th	Day	47% 7% 14% 23% 11%	2057
	21st to end	Day	55% 8% 16% 16% 4	2178
April	1st to 10th	Day	42% 6% 15% 25% 11% 1	2114
	11th to 20th	Day	51% 5% 11% 19% 12% 1	2312
	21st to end	Day	49% 6% 14% 23% 8%	2340
May	1st to 10th	Day	47% 6% 10% 23% 13% 1	2340
	11th to 20th	Day	39% 7% 16% 24% 14% 1	2306
	21st to end	Day	41% 7% 16% 24% 11% 1	2877
June	1st to 10th	Day	34% 8% 16% 29% 12% 1	2700
	11th to 20th	Day	33% 9% 15% 26% 15% 2	2700
	21st to end	Day	28% 9% 17% 30% 15% 2	2700
July	1st to 10th	Day	25% 8% 17% 32% 16% 2	2626
	11th to 20th	Day	21% 6% 15% 30% 22% 6%	2448
	21st to end	Day	25% 7% 17% 27% 20% 3	2582
August	1st to 10th	Day	32% 9% 14% 27% 14% 4	2314
	11th to 20th	Day	30% 8% 16% 31% 14% 2	2301
	21st to end	Day	23% 6% 14% 33% 18% 4	2574
September	1st to 10th	Day	28% 7% 13% 32% 18% 1	2109
	11th to 20th	Day	30% 7% 16% 31% 15% 1	1980
	21st to end	Day	34% 6% 13% 30% 15% 2	1980
October	1st to 10th	Day	39% 5% 15% 27% 13% 1	1908
	11th to 20th	Day	37% 6% 11% 30% 13% 3	1789
	21st to end	Day	41% 5% 15% 26% 11% 2	1782
November	1st to 10th	Day	40% 7% 15% 23% 13% 2	1673
	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	45% 7% 18% 22% 7% 1	2256
	11th to 20th	Night	44% 6% 12% 25% 12% 1	2068
	21st to end	Night	45% 8% 16% 22% 8% 1	2178
April	1st to 10th	Night	41% 6% 13% 28% 12% 1	1842
	11th to 20th	Night	44% 5% 9% 23% 15% 3	1599
	21st to end	Night	47% 7% 10% 24% 10% 1	1620
May	1st to 10th	Night	37% 7% 14% 23% 17% 1	1620
	11th to 20th	Night	35% 8% 14% 25% 16% 2	1594
	21st to end	Night	36% 10% 16% 25% 12% 1	1393
June	1st to 10th	Night	28% 7% 17% 31% 16% 2	1260
	11th to 20th	Night	30% 7% 17% 25% 17% 4	1260
	21st to end	Night	20% 7% 21% 30% 19% 3	1260
July	1st to 10th	Night	23% 8% 16% 32% 19% 3	1225
	11th to 20th	Night	16% 6% 14% 34% 25% 5%	1384
	21st to end	Night	18% 6% 16% 31% 24% 5%	1493
August	1st to 10th	Night	27% 9% 17% 29% 15% 3	1601
	11th to 20th	Night	24% 8% 16% 34% 16% 3	1600
	21st to end	Night	18% 6% 12% 36% 24% 4	1782
September	1st to 10th	Night	24% 6% 13% 32% 23% 3	1846
	11th to 20th	Night	28% 6% 15% 31% 18% 2	1980
	21st to end	Night	30% 5% 12% 31% 19% 3	1980
October	1st to 10th	Night	37% 5% 12% 25% 18% 2	2034
	11th to 20th	Night	36% 4 11% 29% 16% 4	2168
	21st to end	Night	37% 7% 14% 25% 15% 2	2574
November	1st to 10th	Night	34% 6% 15% 23% 19% 3	2405
	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% 28% 13% 2	261
	21st to end	Day	17% 10% 28% 25% 15% 6%	264
April	1st to 10th	Day	21% 14% 31% 26% 7% 1	374
	11th to 20th	Day	23% 14% 28% 26% 9% 1	590
	21st to end	Day	21% 12% 28% 28% 10% 1	600
May	1st to 10th	Day	18% 11% 28% 29% 12% 1	603
	11th to 20th	Day	17% 11% 27% 28% 16% 2	625
	21st to end	Day	18% 8% 28% 29% 15% 3	679
June	1st to 10th	Day	8% 8% 26% 33% 19% 7%	630
	11th to 20th	Day	9% 9% 38% 29% 14% 3	630
	21st to end	Day	9% 8% 31% 33% 16% 2	630
July	1st to 10th	Day	6% 5% 24% 39% 21% 5%	621
	11th to 20th	Day	6% 5% 32% 40% 15% 2	618
	21st to end	Day	5% 5% 26% 42% 20% 3	684
August	1st to 10th	Day	8% 3 21% 42% 22% 4	626
	11th to 20th	Day	11% 5% 25% 36% 19% 5%	615
	21st to end	Day	8% 3 26% 36% 23% 4	693
September	1st to 10th	Day	12% 8% 27% 36% 14% 3	399
	11th to 20th	Day	11% 4 36% 33% 14% 2	270
	21st to end	Day	19% 13% 31% 24% 10% 3	270
October	1st to 10th	Day	19% 8% 30% 29% 12% 3	270
	11th to 20th	Day	16% 13% 33% 30% 8%	270
	21st to end	Day	17% 14% 39% 21% 7% 2	297
November	1st to 10th	Day	20% 11% 28% 33% 8% 1	270
	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% 34% 9%	564
	21st to end	Night	15% 7% 32% 34% 11% 1	594
April	1st to 10th	Night	15% 10% 39% 29% 7%	540
	11th to 20th	Night	20% 12% 28% 28% 12%	533
	21st to end	Night	18% 8% 34% 29% 10% 1	540
May	1st to 10th	Night	12% 7% 35% 34% 11%	540
	11th to 20th	Night	11% 6% 32% 41% 9%	531
	21st to end	Night	12% 8% 34% 35% 11%	584
June	1st to 10th	Night	10% 4 25% 44% 16%	540
	11th to 20th	Night	8% 6% 35% 42% 9%	540
	21st to end	Night	6% 3 29% 50% 11% 1	540
July	1st to 10th	Night	5% 3 27% 48% 17% 1	525
	11th to 20th	Night	5% 3 28% 50% 15%	522
	21st to end	Night	5% 2 24% 56% 13% 1	591
August	1st to 10th	Night	6% 3 20% 53% 17%	537
	11th to 20th	Night	9% 2 24% 44% 20% 1	534
	21st to end	Night	5% 4 26% 47% 18%	594
September	1st to 10th	Night	10% 3 30% 42% 14% 2	540
	11th to 20th	Night	9% 5% 28% 44% 13% 1	540
	21st to end	Night	12% 6% 34% 36% 12% 1	540
October	1st to 10th	Night	18% 8% 31% 32% 11%	594
	11th to 20th	Night	17% 9% 32% 34% 8%	728
	21st to end	Night	16% 8% 35% 31% 9%	990
November	1st to 10th	Night	12% 8% 34% 35% 11%	925
	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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