SkyShed Observatories
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the SkyShed Observatories clear sky chart from 2005-11-06 to 2024-11-25.

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	15% 11% 4 9% 5% 5% 5% 4 5% 7% 30%	101763
	Night	15% 13% 5% 10% 5% 4 4 3 5% 6% 29%	97715
Transparency	Day	51% 7% 12% 19% 10% 1	105353
	Night	54% 6% 11% 18% 10% 1	102215
Seeing	Day	19% 12% 28% 24% 13% 5%	15148
	Night	20% 11% 29% 28% 11% 1	24398

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	15% 21% 12% 15% 6% 4 3 2 4 5% 13%	2368
	11th to 20th	Day	11% 19% 11% 23% 8% 9% 6% 2 2 2 7%	2777
	21st to end	Day	18% 22% 8% 19% 7% 5% 4 3 3 3 8%	3124
February	1st to 10th	Day	14% 19% 7% 16% 11% 6% 4 3 3 4 13%	1710
	11th to 20th	Day	12% 13% 10% 15% 10% 7% 4 4 4 5% 17%	1663
	21st to end	Day	15% 17% 6% 12% 7% 5% 5% 3 5% 5% 21%	1563
March	1st to 10th	Day	16% 15% 6% 11% 5% 4 4 2 4 5% 27%	3336
	11th to 20th	Day	10% 16% 7% 12% 5% 5% 5% 3 5% 6% 26%	3480
	21st to end	Day	16% 13% 4 11% 6% 4 4 3 5% 6% 29%	3815
April	1st to 10th	Day	16% 17% 5% 7% 4 4 4 4 5% 7% 27%	2161
	11th to 20th	Day	18% 12% 2 6% 4 3 4 3 5% 7% 35%	2439
	21st to end	Day	19% 11% 4 7% 4 3 4 3 5% 7% 32%	2470
May	1st to 10th	Day	17% 9% 3 6% 5% 4 5% 4 6% 8% 33%	4108
	11th to 20th	Day	17% 9% 3 8% 5% 5% 5% 4 6% 8% 32%	4127
	21st to end	Day	14% 5% 2 5% 4 4 4 3 5% 8% 46%	4837
June	1st to 10th	Day	13% 7% 3 7% 5% 4 6% 4 6% 8% 37%	2701
	11th to 20th	Day	12% 6% 3 6% 4 4 5% 4 6% 9% 41%	2850
	21st to end	Day	15% 6% 2 6% 4 5% 5% 4 6% 8% 39%	2850
July	1st to 10th	Day	11% 6% 2 7% 4 4 6% 4 6% 9% 41%	4760
	11th to 20th	Day	11% 5% 2 6% 4 3 4 5% 7% 9% 44%	4354
	21st to end	Day	9% 5% 2 6% 5% 5% 5% 5% 6% 9% 43%	4466
August	1st to 10th	Day	13% 6% 2 6% 4 5% 5% 5% 7% 9% 37%	4104
	11th to 20th	Day	12% 6% 2 6% 5% 6% 6% 5% 8% 11% 34%	4044
	21st to end	Day	10% 6% 2 6% 4 5% 6% 5% 7% 9% 41%	4482
September	1st to 10th	Day	12% 6% 3 6% 5% 5% 5% 4 6% 9% 39%	2228
	11th to 20th	Day	11% 6% 2 6% 3 4 5% 4 7% 7% 43%	2090
	21st to end	Day	18% 7% 2 7% 4 5% 5% 4 7% 7% 34%	2090
October	1st to 10th	Day	18% 7% 3 8% 5% 5% 4 4 5% 6% 35%	1940
	11th to 20th	Day	21% 12% 4 8% 6% 5% 4 4 6% 6% 24%	1900
	21st to end	Day	25% 14% 4 8% 5% 5% 5% 4 6% 7% 17%	2038
November	1st to 10th	Day	15% 17% 4 9% 5% 4 4 3 6% 8% 26%	1762
	11th to 20th	Day	15% 18% 4 11% 6% 5% 5% 4 5% 6% 21%	1624
	21st to end	Day	18% 21% 7% 11% 7% 5% 4 4 4 5% 13%	1552
December	1st to 10th	Day	14% 26% 10% 14% 8% 5% 4 3 4 4 10%	1520
	11th to 20th	Day	18% 19% 7% 16% 8% 5% 4 3 5% 3 11%	1906
	21st to end	Day	27% 21% 8% 12% 5% 4 4 3 4 4 8%	2524
January	1st to 10th	Night	15% 20% 10% 20% 8% 5% 4 2 3 3 9%	4584
	11th to 20th	Night	13% 18% 9% 19% 11% 6% 6% 4 4 3 7%	4179
	21st to end	Night	19% 19% 9% 16% 7% 5% 4 3 4 4 11%	4532
February	1st to 10th	Night	15% 20% 6% 13% 10% 6% 4 3 4 4 15%	2470
	11th to 20th	Night	13% 16% 6% 15% 8% 6% 5% 4 5% 5% 18%	2403
	21st to end	Night	17% 13% 5% 14% 6% 5% 5% 3 5% 4 22%	1889
March	1st to 10th	Night	14% 13% 5% 8% 4 4 4 3 5% 5% 33%	3504
	11th to 20th	Night	11% 12% 6% 11% 5% 5% 4 3 5% 7% 31%	3479
	21st to end	Night	15% 11% 4 9% 5% 4 4 3 5% 4 38%	3817
April	1st to 10th	Night	19% 13% 3 7% 5% 4 4 3 5% 6% 31%	2019
	11th to 20th	Night	18% 9% 4 7% 4 4 4 3 5% 7% 35%	1706
	21st to end	Night	16% 12% 3 7% 5% 4 4 3 5% 7% 34%	1710
May	1st to 10th	Night	17% 8% 2 6% 4 4 4 3 5% 8% 39%	2833
	11th to 20th	Night	13% 9% 3 8% 5% 5% 5% 4 5% 8% 35%	2763
	21st to end	Night	11% 5% 2 5% 4 4 4 3 6% 8% 49%	2738
June	1st to 10th	Night	14% 6% 2 6% 5% 5% 4 4 5% 7% 42%	1474
	11th to 20th	Night	10% 7% 2 6% 4 5% 5% 4 8% 8% 41%	1330
	21st to end	Night	12% 6% 2 6% 5% 4 5% 3 5% 8% 45%	1330
July	1st to 10th	Night	7% 4 2 5% 4 4 5% 4 7% 9% 49%	2210
	11th to 20th	Night	10% 5% 2 5% 3 3 3 3 5% 9% 53%	2605
	21st to end	Night	6% 7% 2 6% 5% 5% 5% 5% 6% 7% 47%	3087
August	1st to 10th	Night	11% 6% 2 7% 5% 4 4 4 5% 7% 45%	2825
	11th to 20th	Night	12% 8% 2 7% 4 3 4 4 5% 7% 44%	2785
	21st to end	Night	11% 5% 3 6% 4 4 4 3 6% 7% 46%	3141
September	1st to 10th	Night	11% 5% 2 6% 5% 5% 5% 4 5% 6% 46%	1948
	11th to 20th	Night	11% 5% 2 4 3 3 4 3 5% 8% 52%	2090
	21st to end	Night	16% 8% 2 6% 5% 4 4 3 6% 6% 39%	2090
October	1st to 10th	Night	14% 8% 4 8% 5% 3 5% 3 6% 6% 38%	2238
	11th to 20th	Night	22% 12% 3 8% 5% 5% 4 3 4 6% 29%	2280
	21st to end	Night	25% 10% 4 9% 6% 5% 5% 4 5% 5% 23%	2557
November	1st to 10th	Night	15% 14% 3 9% 4 3 4 4 6% 6% 31%	2536
	11th to 20th	Night	16% 18% 5% 11% 5% 5% 6% 3 4 7% 20%	2775
	21st to end	Night	19% 20% 6% 11% 6% 5% 5% 3 4 4 17%	2723
December	1st to 10th	Night	18% 26% 8% 13% 6% 4 4 3 3 4 10%	2660
	11th to 20th	Night	14% 23% 8% 16% 6% 4 4 3 4 4 14%	3288
	21st to end	Night	25% 24% 9% 12% 5% 4 3 3 4 4 8%	5117

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	74% 5% 11% 8% 2	2369
	11th to 20th	Day	84% 6% 5% 3 2	2777
	21st to end	Day	82% 5% 6% 5% 2	3124
February	1st to 10th	Day	76% 5% 7% 10% 2	1710
	11th to 20th	Day	69% 6% 8% 12% 4	1672
	21st to end	Day	63% 6% 11% 13% 6% 1	1563
March	1st to 10th	Day	60% 6% 11% 18% 5% 1	3339
	11th to 20th	Day	57% 5% 14% 16% 7% 1	3480
	21st to end	Day	54% 6% 12% 17% 10% 2	3815
April	1st to 10th	Day	55% 6% 11% 17% 9%	2161
	11th to 20th	Day	47% 6% 12% 21% 12% 1	2439
	21st to end	Day	52% 6% 11% 19% 11% 2	2470
May	1st to 10th	Day	46% 6% 13% 21% 12% 2	4120
	11th to 20th	Day	46% 10% 14% 21% 7% 1	4131
	21st to end	Day	36% 8% 12% 19% 20% 5%	4837
June	1st to 10th	Day	41% 8% 13% 23% 13% 1	2701
	11th to 20th	Day	39% 7% 11% 24% 17% 1	2850
	21st to end	Day	41% 7% 12% 24% 14%	2850
July	1st to 10th	Day	38% 7% 14% 23% 16% 2	4686
	11th to 20th	Day	35% 5% 13% 33% 13% 1	4277
	21st to end	Day	36% 6% 15% 23% 18% 1	4324
August	1st to 10th	Day	41% 8% 13% 24% 14% 1	4091
	11th to 20th	Day	41% 8% 17% 24% 9%	4083
	21st to end	Day	38% 5% 15% 29% 12% 1	4482
September	1st to 10th	Day	40% 8% 14% 25% 12% 1	2228
	11th to 20th	Day	36% 8% 13% 29% 14% 1	2090
	21st to end	Day	46% 8% 14% 23% 9% 1	2090
October	1st to 10th	Day	41% 6% 12% 24% 16% 1	3226
	11th to 20th	Day	45% 6% 12% 21% 15%	3140
	21st to end	Day	54% 6% 17% 17% 5%	3340
November	1st to 10th	Day	56% 8% 11% 18% 7% 1	1762
	11th to 20th	Day	63% 6% 13% 10% 7% 1	1624
	21st to end	Day	73% 7% 10% 9% 2	1552
December	1st to 10th	Day	77% 6% 9% 6% 1	1520
	11th to 20th	Day	75% 7% 9% 7% 1	1906
	21st to end	Day	79% 7% 9% 5%	2524
January	1st to 10th	Night	79% 6% 8% 5% 2	4584
	11th to 20th	Night	79% 9% 7% 4 2	4179
	21st to end	Night	77% 7% 8% 6% 2 1	4532
February	1st to 10th	Night	72% 6% 8% 11% 2	2470
	11th to 20th	Night	67% 5% 12% 12% 4	2405
	21st to end	Night	63% 6% 11% 14% 6%	1889
March	1st to 10th	Night	52% 6% 14% 23% 6%	3514
	11th to 20th	Night	49% 6% 17% 18% 9% 1	3480
	21st to end	Night	48% 5% 12% 21% 12% 2	3817
April	1st to 10th	Night	53% 6% 9% 18% 12% 1	2019
	11th to 20th	Night	49% 5% 11% 18% 16% 2	1706
	21st to end	Night	49% 6% 10% 17% 15% 3	1710
May	1st to 10th	Night	43% 7% 12% 19% 16% 4	2840
	11th to 20th	Night	45% 9% 12% 22% 11% 2	2764
	21st to end	Night	31% 7% 13% 23% 22% 4	2739
June	1st to 10th	Night	39% 6% 10% 26% 16% 2	1474
	11th to 20th	Night	36% 8% 13% 24% 17% 3	1330
	21st to end	Night	37% 6% 13% 25% 18% 2	1330
July	1st to 10th	Night	30% 6% 14% 26% 18% 6%	2175
	11th to 20th	Night	30% 5% 13% 32% 19% 1	2560
	21st to end	Night	35% 7% 14% 23% 19% 2	2988
August	1st to 10th	Night	38% 6% 12% 27% 16% 1	2814
	11th to 20th	Night	39% 6% 15% 25% 14% 1	2812
	21st to end	Night	36% 7% 11% 32% 15% 1	3141
September	1st to 10th	Night	36% 9% 12% 24% 17% 2	1948
	11th to 20th	Night	31% 6% 13% 29% 20% 1	2090
	21st to end	Night	44% 7% 13% 23% 12%	2090
October	1st to 10th	Night	35% 6% 9% 26% 23% 1	3732
	11th to 20th	Night	47% 5% 15% 19% 14%	3779
	21st to end	Night	49% 6% 15% 21% 9%	4205
November	1st to 10th	Night	51% 7% 12% 20% 10%	2536
	11th to 20th	Night	64% 7% 10% 13% 5% 1	2775
	21st to end	Night	69% 7% 13% 9% 2	2723
December	1st to 10th	Night	78% 6% 8% 6% 2	2660
	11th to 20th	Night	74% 6% 11% 8% 2	3288
	21st to end	Night	82% 5% 9% 4 1	5117

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	20% 22% 32% 16% 7% 2	225
	11th to 20th	Day	22% 18% 43% 12% 4 1	270
	21st to end	Day	26% 13% 36% 21% 3 1	297
February	1st to 10th	Day	23% 21% 37% 14% 3	270
	11th to 20th	Day	21% 22% 41% 13% 2	270
	21st to end	Day	26% 28% 31% 15% 1	225
March	1st to 10th	Day	23% 15% 37% 19% 6% 1	398
	11th to 20th	Day	20% 15% 33% 24% 7% 1	460
	21st to end	Day	25% 15% 31% 23% 6% 1	506
April	1st to 10th	Day	22% 17% 33% 21% 6% 1	460
	11th to 20th	Day	27% 16% 25% 19% 9% 3	452
	21st to end	Day	23% 14% 32% 20% 8% 2	460
May	1st to 10th	Day	22% 11% 26% 28% 9% 3	463
	11th to 20th	Day	20% 7% 28% 24% 16% 5%	487
	21st to end	Day	15% 7% 25% 28% 18% 7%	529
June	1st to 10th	Day	12% 9% 31% 29% 14% 5%	531
	11th to 20th	Day	14% 9% 30% 30% 14% 3	680
	21st to end	Day	15% 8% 29% 32% 13% 3	680
July	1st to 10th	Day	9% 6% 25% 29% 23% 8%	671
	11th to 20th	Day	15% 4 25% 28% 21% 7%	583
	21st to end	Day	8% 4 23% 36% 20% 8%	532
August	1st to 10th	Day	12% 4 22% 26% 23% 13%	486
	11th to 20th	Day	13% 4 17% 31% 22% 13%	479
	21st to end	Day	16% 5% 22% 24% 23% 10%	539
September	1st to 10th	Day	14% 6% 23% 27% 18% 12%	490
	11th to 20th	Day	9% 5% 19% 25% 28% 14%	490
	21st to end	Day	17% 11% 26% 24% 14% 8%	490
October	1st to 10th	Day	19% 11% 27% 22% 17% 5%	490
	11th to 20th	Day	22% 17% 31% 21% 7% 1	490
	21st to end	Day	29% 17% 31% 18% 5%	487
November	1st to 10th	Day	26% 20% 27% 19% 7% 1	300
	11th to 20th	Day	25% 20% 33% 15% 5% 1	212
	21st to end	Day	26% 20% 38% 13% 3	188
December	1st to 10th	Day	26% 26% 33% 12% 4	180
	11th to 20th	Day	28% 28% 27% 12% 4	180
	21st to end	Day	33% 23% 30% 13% 1	198
January	1st to 10th	Night	23% 18% 36% 17% 5% 1	950
	11th to 20th	Night	29% 16% 31% 20% 4	793
	21st to end	Night	20% 13% 38% 23% 6%	836
February	1st to 10th	Night	24% 16% 35% 23% 2	760
	11th to 20th	Night	22% 15% 32% 25% 5%	743
	21st to end	Night	24% 17% 35% 22% 3	628
March	1st to 10th	Night	20% 13% 36% 24% 7%	760
	11th to 20th	Night	19% 16% 36% 23% 6% 1	760
	21st to end	Night	22% 12% 32% 25% 8% 1	836
April	1st to 10th	Night	24% 14% 30% 27% 4	760
	11th to 20th	Night	21% 14% 31% 23% 10% 1	582
	21st to end	Night	21% 12% 29% 29% 8%	570
May	1st to 10th	Night	19% 8% 31% 30% 12% 1	570
	11th to 20th	Night	18% 5% 29% 34% 12% 1	538
	21st to end	Night	11% 5% 28% 39% 17% 1	411
June	1st to 10th	Night	16% 4 29% 36% 15%	380
	11th to 20th	Night	11% 6% 27% 43% 13%	380
	21st to end	Night	12% 4 24% 46% 13% 1	380
July	1st to 10th	Night	6% 2 19% 49% 22% 1	370
	11th to 20th	Night	10% 2 21% 40% 24% 2	512
	21st to end	Night	9% 3 17% 47% 23% 1	624
August	1st to 10th	Night	10% 2 14% 42% 29% 2	567
	11th to 20th	Night	10% 2 15% 39% 29% 4	564
	21st to end	Night	13% 3 20% 36% 26% 2	631
September	1st to 10th	Night	13% 5% 21% 34% 20% 5%	760
	11th to 20th	Night	11% 4 18% 36% 26% 4	760
	21st to end	Night	19% 6% 22% 33% 16% 4	760
October	1st to 10th	Night	18% 8% 29% 29% 15% 2	760
	11th to 20th	Night	25% 15% 25% 25% 9% 1	760
	21st to end	Night	29% 12% 31% 24% 4	836
November	1st to 10th	Night	24% 13% 27% 28% 8% 1	780
	11th to 20th	Night	25% 16% 36% 17% 5% 1	800
	21st to end	Night	29% 13% 32% 22% 4	779
December	1st to 10th	Night	29% 19% 30% 18% 4	760
	11th to 20th	Night	24% 21% 36% 16% 3	760
	21st to end	Night	30% 15% 36% 17% 2	978

Page generated at 2024-11-22 08:02:23. Version ac07

Copyright © 2024 Attilla Danko.