Young's Astronomy Club and Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Young's Astronomy Club and Observatory clear sky chart from 2005-11-06 to 2024-11-10.

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	14% 11% 4 9% 5% 5% 5% 4 5% 7% 32%	101659
	Night	13% 11% 4 10% 5% 5% 4 4 5% 6% 32%	97633
Transparency	Day	50% 7% 12% 21% 10% 1	105107
	Night	50% 7% 12% 21% 9% 1	102272
Seeing	Day	21% 16% 33% 19% 8% 3	16079
	Night	20% 13% 32% 25% 9% 1	25951

By Month

Percentage Cloud Cover NE (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	10% 16% 8% 18% 7% 6% 5% 3 5% 6% 17%	2527
	11th to 20th	Day	9% 18% 5% 13% 10% 7% 7% 5% 6% 6% 15%	2530
	21st to end	Day	11% 16% 10% 19% 6% 4 5% 3 5% 5% 15%	2783
February	1st to 10th	Day	9% 13% 6% 12% 7% 7% 6% 4 6% 6% 26%	1642
	11th to 20th	Day	9% 13% 5% 12% 8% 7% 6% 4 6% 7% 26%	1762
	21st to end	Day	12% 15% 6% 11% 6% 6% 4 3 6% 6% 24%	1570
March	1st to 10th	Day	12% 13% 3 10% 4 4 4 3 4 6% 37%	3118
	11th to 20th	Day	8% 15% 4 14% 9% 4 4 4 5% 5% 27%	3275
	21st to end	Day	19% 14% 6% 15% 5% 4 3 3 4 5% 20%	4165
April	1st to 10th	Day	17% 14% 4 9% 5% 5% 5% 4 4 7% 26%	2280
	11th to 20th	Day	20% 13% 6% 10% 4 4 3 3 4 5% 29%	2254
	21st to end	Day	17% 12% 4 7% 6% 5% 5% 4 5% 6% 30%	2455
May	1st to 10th	Day	16% 10% 3 8% 5% 4 4 3 5% 5% 36%	4352
	11th to 20th	Day	14% 8% 3 7% 4 4 4 4 5% 6% 40%	4399
	21st to end	Day	13% 9% 4 8% 5% 5% 5% 3 6% 7% 35%	4837
June	1st to 10th	Day	13% 7% 3 7% 5% 5% 5% 5% 5% 8% 38%	2660
	11th to 20th	Day	14% 7% 3 7% 6% 5% 5% 4 6% 8% 35%	2660
	21st to end	Day	14% 7% 2 7% 6% 5% 6% 5% 7% 7% 34%	2660
July	1st to 10th	Day	13% 5% 2 6% 5% 5% 5% 5% 8% 9% 37%	4440
	11th to 20th	Day	7% 4 2 6% 4 5% 5% 4 7% 9% 47%	4440
	21st to end	Day	8% 6% 2 6% 4 4 5% 5% 6% 9% 45%	4814
August	1st to 10th	Day	11% 6% 2 8% 6% 5% 6% 5% 7% 7% 38%	4423
	11th to 20th	Day	13% 6% 2 6% 4 4 3 4 6% 7% 46%	4066
	21st to end	Day	16% 8% 2 6% 5% 4 4 3 4 7% 41%	4180
September	1st to 10th	Day	15% 6% 2 6% 4 5% 4 4 5% 8% 41%	2280
	11th to 20th	Day	13% 8% 3 8% 5% 4 5% 3 5% 7% 40%	2194
	21st to end	Day	16% 10% 3 8% 5% 4 5% 4 5% 7% 34%	2090
October	1st to 10th	Day	17% 10% 3 7% 5% 3 4 4 6% 8% 34%	1967
	11th to 20th	Day	21% 16% 4 10% 5% 5% 4 4 6% 5% 21%	1840
	21st to end	Day	21% 19% 4 9% 5% 4 4 3 3 6% 23%	1881
November	1st to 10th	Day	17% 15% 4 7% 5% 4 4 4 5% 6% 28%	1753
	11th to 20th	Day	16% 16% 7% 13% 7% 5% 4 3 5% 5% 19%	1625
	21st to end	Day	15% 14% 7% 15% 7% 5% 4 3 5% 6% 18%	1520
December	1st to 10th	Day	10% 16% 6% 16% 10% 5% 4 4 5% 4 20%	1520
	11th to 20th	Day	15% 17% 6% 15% 9% 5% 5% 3 4 6% 15%	1914
	21st to end	Day	20% 26% 8% 11% 5% 4 3 2 3 4 13%	2783
January	1st to 10th	Night	14% 15% 6% 16% 7% 5% 4 3 4 6% 20%	4428
	11th to 20th	Night	9% 16% 7% 13% 9% 7% 6% 5% 6% 6% 16%	4440
	21st to end	Night	11% 16% 7% 17% 8% 6% 5% 4 5% 6% 18%	4884
February	1st to 10th	Night	9% 13% 5% 11% 6% 6% 6% 4 7% 7% 26%	2537
	11th to 20th	Night	9% 11% 4 12% 8% 6% 6% 5% 6% 7% 26%	2305
	21st to end	Night	12% 16% 5% 9% 6% 5% 4 4 5% 7% 26%	1884
March	1st to 10th	Night	9% 9% 4 9% 5% 5% 5% 4 6% 9% 36%	3722
	11th to 20th	Night	8% 11% 6% 14% 5% 4 5% 4 5% 7% 32%	3700
	21st to end	Night	17% 12% 6% 10% 7% 5% 4 3 4 6% 25%	3466
April	1st to 10th	Night	17% 13% 4 9% 5% 4 5% 4 5% 6% 29%	1900
	11th to 20th	Night	20% 10% 4 9% 4 4 2 3 5% 5% 34%	1875
	21st to end	Night	16% 10% 3 9% 5% 5% 4 3 4 6% 34%	1724
May	1st to 10th	Night	17% 9% 3 6% 4 4 3 3 4 6% 39%	2595
	11th to 20th	Night	13% 8% 3 7% 5% 3 4 4 5% 6% 43%	2506
	21st to end	Night	16% 8% 2 7% 5% 5% 5% 4 6% 7% 36%	2750
June	1st to 10th	Night	12% 8% 2 5% 5% 4 4 3 5% 8% 44%	1520
	11th to 20th	Night	13% 8% 2 7% 4 4 4 5% 5% 7% 40%	1520
	21st to end	Night	14% 7% 2 6% 4 4 4 4 7% 9% 41%	1520
July	1st to 10th	Night	14% 5% 2 6% 4 4 4 3 5% 8% 45%	2530
	11th to 20th	Night	6% 4 2 5% 3 3 4 4 6% 9% 55%	2530
	21st to end	Night	8% 6% 2 5% 3 4 3 3 5% 7% 53%	2750
August	1st to 10th	Night	11% 7% 2 7% 4 4 3 3 5% 8% 44%	2517
	11th to 20th	Night	13% 6% 2 5% 3 3 4 2 5% 7% 50%	2763
	21st to end	Night	15% 8% 3 6% 4 3 4 3 4 5% 46%	3476
September	1st to 10th	Night	11% 6% 2 5% 3 5% 3 3 5% 8% 49%	1900
	11th to 20th	Night	12% 6% 2 5% 4 4 4 3 5% 8% 46%	1966
	21st to end	Night	14% 9% 3 7% 5% 5% 4 4 4 6% 40%	2090
October	1st to 10th	Night	16% 10% 2 6% 4 5% 3 3 5% 6% 41%	2209
	11th to 20th	Night	17% 12% 4 9% 4 4 5% 4 5% 7% 30%	2338
	21st to end	Night	20% 15% 3 9% 6% 4 5% 3 5% 6% 25%	2717
November	1st to 10th	Night	16% 12% 4 8% 5% 5% 5% 3 6% 7% 30%	2530
	11th to 20th	Night	15% 14% 6% 13% 6% 5% 4 3 5% 6% 24%	2554
	21st to end	Night	15% 13% 6% 13% 7% 5% 4 4 6% 7% 21%	2660
December	1st to 10th	Night	12% 15% 6% 13% 7% 5% 4 4 6% 6% 23%	2660
	11th to 20th	Night	12% 14% 6% 14% 8% 5% 5% 4 4 6% 21%	3283
	21st to end	Night	22% 22% 7% 11% 5% 4 3 3 4 3 16%	4884

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	67% 6% 10% 13% 3	2528
	11th to 20th	Day	67% 8% 11% 10% 3	2530
	21st to end	Day	70% 6% 11% 9% 3 1	2783
February	1st to 10th	Day	57% 6% 11% 17% 8%	1642
	11th to 20th	Day	57% 6% 11% 19% 7%	1771
	21st to end	Day	59% 6% 9% 15% 9% 1	1570
March	1st to 10th	Day	48% 6% 13% 18% 14% 1	3120
	11th to 20th	Day	56% 7% 12% 17% 8% 1	3275
	21st to end	Day	66% 6% 9% 13% 6%	4165
April	1st to 10th	Day	58% 6% 10% 17% 9%	2280
	11th to 20th	Day	58% 6% 7% 20% 9% 1	2254
	21st to end	Day	53% 6% 8% 19% 12% 2	2455
May	1st to 10th	Day	47% 6% 9% 21% 15% 1	4364
	11th to 20th	Day	42% 7% 11% 28% 11% 1	4403
	21st to end	Day	47% 8% 10% 17% 16% 1	4837
June	1st to 10th	Day	42% 7% 13% 24% 13% 1	2660
	11th to 20th	Day	44% 8% 13% 19% 14% 1	2660
	21st to end	Day	44% 9% 13% 22% 10% 1	2660
July	1st to 10th	Day	40% 8% 15% 24% 12% 1	4371
	11th to 20th	Day	31% 8% 13% 32% 15% 2	4365
	21st to end	Day	33% 7% 12% 32% 16% 1	4662
August	1st to 10th	Day	42% 7% 15% 24% 11% 1	4408
	11th to 20th	Day	36% 7% 16% 30% 11%	4108
	21st to end	Day	44% 5% 15% 23% 13% 1	4179
September	1st to 10th	Day	41% 6% 13% 29% 11%	2280
	11th to 20th	Day	42% 7% 19% 24% 6%	2194
	21st to end	Day	48% 7% 13% 24% 8%	2090
October	1st to 10th	Day	37% 5% 11% 33% 14%	3266
	11th to 20th	Day	58% 5% 10% 16% 11%	3030
	21st to end	Day	59% 5% 15% 17% 4	3081
November	1st to 10th	Day	56% 6% 11% 19% 8% 1	1753
	11th to 20th	Day	67% 6% 10% 11% 6%	1625
	21st to end	Day	67% 6% 13% 10% 3 1	1520
December	1st to 10th	Day	66% 5% 10% 14% 4	1520
	11th to 20th	Day	69% 7% 9% 10% 4	1915
	21st to end	Day	75% 4 6% 10% 4	2783
January	1st to 10th	Night	64% 6% 10% 15% 4	4428
	11th to 20th	Night	65% 9% 12% 11% 3	4440
	21st to end	Night	67% 6% 11% 13% 3	4884
February	1st to 10th	Night	55% 5% 11% 17% 11% 1	2537
	11th to 20th	Night	55% 8% 11% 19% 6% 1	2306
	21st to end	Night	56% 6% 13% 17% 8%	1884
March	1st to 10th	Night	42% 8% 20% 20% 9% 1	3733
	11th to 20th	Night	49% 7% 11% 23% 9% 1	3701
	21st to end	Night	59% 8% 9% 15% 9% 1	3466
April	1st to 10th	Night	54% 6% 11% 16% 12% 1	1900
	11th to 20th	Night	52% 5% 9% 21% 11% 2	1875
	21st to end	Night	51% 5% 10% 18% 14% 1	1724
May	1st to 10th	Night	44% 6% 12% 24% 13% 1	2602
	11th to 20th	Night	40% 8% 11% 24% 15% 2	2507
	21st to end	Night	45% 10% 13% 16% 13% 3	2751
June	1st to 10th	Night	37% 8% 14% 27% 12% 1	1520
	11th to 20th	Night	42% 8% 13% 22% 14% 1	1520
	21st to end	Night	39% 7% 16% 26% 11% 2	1520
July	1st to 10th	Night	38% 7% 18% 22% 13% 3	2490
	11th to 20th	Night	24% 8% 15% 39% 13% 1	2482
	21st to end	Night	29% 6% 14% 30% 20% 1	2662
August	1st to 10th	Night	38% 6% 15% 23% 17% 2	2508
	11th to 20th	Night	35% 7% 17% 27% 13% 3	2787
	21st to end	Night	40% 6% 12% 26% 14% 1	3476
September	1st to 10th	Night	34% 7% 14% 31% 14% 1	1900
	11th to 20th	Night	37% 7% 14% 32% 9%	1966
	21st to end	Night	44% 8% 14% 25% 8% 1	2090
October	1st to 10th	Night	35% 4 9% 36% 15% 1	3690
	11th to 20th	Night	44% 5% 12% 26% 12%	3887
	21st to end	Night	57% 6% 11% 21% 5%	4467
November	1st to 10th	Night	52% 6% 13% 19% 9%	2530
	11th to 20th	Night	60% 7% 13% 12% 7% 1	2554
	21st to end	Night	61% 8% 15% 13% 3 1	2660
December	1st to 10th	Night	60% 7% 14% 15% 4	2660
	11th to 20th	Night	63% 6% 11% 15% 5%	3281
	21st to end	Night	73% 5% 6% 12% 4	4884

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	21% 17% 35% 21% 4 2	270
	11th to 20th	Day	24% 18% 36% 18% 4	270
	21st to end	Day	21% 13% 46% 16% 3	297
February	1st to 10th	Day	22% 22% 40% 11% 4 1	270
	11th to 20th	Day	20% 33% 31% 13% 3	270
	21st to end	Day	26% 29% 37% 8%	225
March	1st to 10th	Day	20% 25% 41% 12% 1	270
	11th to 20th	Day	26% 23% 32% 15% 4	276
	21st to end	Day	28% 20% 29% 14% 8% 1	506
April	1st to 10th	Day	30% 16% 32% 17% 4 1	460
	11th to 20th	Day	30% 19% 29% 15% 5% 1	452
	21st to end	Day	29% 20% 23% 21% 5% 3	460
May	1st to 10th	Day	24% 20% 32% 16% 6% 2	603
	11th to 20th	Day	22% 18% 34% 17% 6% 3	675
	21st to end	Day	20% 16% 34% 19% 8% 3	734
June	1st to 10th	Day	19% 18% 32% 21% 7% 4	680
	11th to 20th	Day	21% 11% 37% 21% 8% 2	680
	21st to end	Day	19% 12% 32% 23% 10% 3	680
July	1st to 10th	Day	10% 11% 37% 24% 13% 5%	671
	11th to 20th	Day	14% 11% 34% 24% 12% 6%	668
	21st to end	Day	10% 11% 35% 24% 14% 6%	739
August	1st to 10th	Day	14% 11% 32% 24% 16% 4	676
	11th to 20th	Day	16% 8% 24% 28% 18% 6%	567
	21st to end	Day	22% 12% 23% 22% 15% 5%	539
September	1st to 10th	Day	19% 12% 27% 23% 14% 4	490
	11th to 20th	Day	14% 12% 32% 28% 11% 3	490
	21st to end	Day	21% 14% 27% 23% 11% 3	490
October	1st to 10th	Day	26% 13% 32% 19% 8% 2	367
	11th to 20th	Day	28% 23% 36% 11% 2	300
	21st to end	Day	32% 25% 34% 7% 2	330
November	1st to 10th	Day	29% 20% 33% 14% 4 1	297
	11th to 20th	Day	26% 25% 36% 9% 4 1	270
	21st to end	Day	26% 20% 39% 10% 4	270
December	1st to 10th	Day	20% 19% 39% 15% 6% 1	270
	11th to 20th	Day	31% 24% 31% 11% 3	270
	21st to end	Day	32% 23% 30% 13% 1	297
January	1st to 10th	Night	18% 18% 41% 19% 3 1	950
	11th to 20th	Night	20% 17% 39% 15% 7% 1	950
	21st to end	Night	19% 13% 40% 21% 6%	1045
February	1st to 10th	Night	18% 17% 40% 18% 7% 1	950
	11th to 20th	Night	19% 21% 33% 21% 6%	831
	21st to end	Night	21% 19% 40% 17% 3	628
March	1st to 10th	Night	19% 15% 35% 24% 7% 1	760
	11th to 20th	Night	18% 19% 35% 23% 5%	720
	21st to end	Night	20% 12% 30% 28% 8% 1	627
April	1st to 10th	Night	23% 15% 33% 24% 5% 1	570
	11th to 20th	Night	26% 14% 28% 26% 6% 1	563
	21st to end	Night	21% 13% 32% 25% 8%	570
May	1st to 10th	Night	22% 13% 30% 28% 6% 1	570
	11th to 20th	Night	20% 10% 34% 28% 7% 1	561
	21st to end	Night	15% 11% 29% 33% 11%	617
June	1st to 10th	Night	16% 10% 28% 34% 12%	570
	11th to 20th	Night	17% 9% 29% 34% 10% 1	570
	21st to end	Night	18% 8% 27% 34% 12% 1	570
July	1st to 10th	Night	11% 5% 27% 40% 17%	555
	11th to 20th	Night	11% 7% 30% 35% 18% 1	552
	21st to end	Night	8% 4 30% 38% 19% 2	624
August	1st to 10th	Night	13% 4 26% 37% 18% 2	567
	11th to 20th	Night	14% 3 20% 34% 27% 2	564
	21st to end	Night	17% 6% 27% 31% 19% 1	627
September	1st to 10th	Night	15% 7% 24% 33% 18% 2	570
	11th to 20th	Night	16% 6% 27% 34% 15% 1	636
	21st to end	Night	20% 9% 28% 29% 13% 1	760
October	1st to 10th	Night	22% 12% 31% 24% 11% 1	760
	11th to 20th	Night	24% 16% 29% 24% 6%	760
	21st to end	Night	30% 13% 27% 24% 6%	836
November	1st to 10th	Night	23% 13% 37% 20% 6% 1	779
	11th to 20th	Night	24% 20% 34% 18% 5%	844
	21st to end	Night	24% 20% 30% 22% 4	950
December	1st to 10th	Night	21% 19% 38% 17% 5% 1	950
	11th to 20th	Night	20% 16% 36% 20% 5% 2	950
	21st to end	Night	30% 17% 34% 16% 4	1045

Page generated at 2024-11-07 06:55:48. Version ac07

Copyright © 2024 Attilla Danko.