The Stellar Shed
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Stellar Shed clear sky chart from 2005-11-06 to 2024-11-30.

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	12% 8% 3 7% 5% 4 4 4 6% 8% 39%	101660
	Night	13% 9% 3 7% 4 4 4 3 5% 7% 40%	98024
Transparency	Day	41% 7% 13% 23% 15% 2	105240
	Night	42% 7% 12% 22% 15% 2	102584
Seeing	Day	15% 10% 29% 27% 15% 5%	15884
	Night	16% 9% 32% 30% 12% 1	25742

By Month

Percentage Cloud Cover SE (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% 12% 6% 15% 6% 6% 5% 4 5% 6% 25%	2527
	11th to 20th	Day	11% 11% 4 12% 9% 7% 7% 2 8% 5% 22%	2576
	21st to end	Day	16% 20% 10% 12% 7% 4 4 2 3 4 18%	3135
February	1st to 10th	Day	15% 13% 4 9% 5% 4 4 4 5% 6% 30%	1710
	11th to 20th	Day	14% 10% 3 8% 5% 5% 4 3 5% 6% 36%	1750
	21st to end	Day	13% 12% 5% 11% 4 4 3 3 5% 5% 35%	1570
March	1st to 10th	Day	15% 12% 4 7% 4 3 3 3 4 6% 39%	3176
	11th to 20th	Day	10% 7% 3 6% 4 5% 4 4 5% 7% 47%	3480
	21st to end	Day	20% 12% 4 10% 5% 4 4 3 5% 6% 26%	4000
April	1st to 10th	Day	14% 12% 3 8% 5% 4 5% 3 5% 6% 35%	2280
	11th to 20th	Day	17% 9% 3 7% 5% 3 4 3 4 7% 37%	2254
	21st to end	Day	20% 8% 3 8% 5% 4 4 3 5% 7% 33%	2280
May	1st to 10th	Day	14% 8% 3 7% 5% 5% 5% 4 6% 9% 34%	4160
	11th to 20th	Day	16% 7% 2 7% 4 4 4 4 5% 7% 40%	4399
	21st to end	Day	12% 6% 2 6% 5% 4 4 4 6% 7% 44%	4824
June	1st to 10th	Day	8% 6% 2 6% 4 5% 4 4 6% 9% 45%	2660
	11th to 20th	Day	8% 5% 2 5% 4 5% 5% 4 6% 9% 46%	2660
	21st to end	Day	10% 6% 2 6% 5% 4 5% 5% 7% 9% 41%	2660
July	1st to 10th	Day	8% 7% 3 8% 5% 6% 5% 5% 8% 9% 35%	4440
	11th to 20th	Day	6% 4 1 5% 4 4 5% 4 6% 10% 50%	4440
	21st to end	Day	6% 4 2 6% 5% 5% 6% 6% 8% 12% 40%	4752
August	1st to 10th	Day	6% 5% 2 6% 4 5% 5% 5% 8% 11% 44%	4104
	11th to 20th	Day	10% 5% 2 6% 4 5% 4 5% 7% 10% 41%	3860
	21st to end	Day	7% 5% 2 6% 4 3 4 3 6% 9% 50%	4180
September	1st to 10th	Day	11% 5% 1 6% 3 4 5% 3 5% 8% 49%	2280
	11th to 20th	Day	9% 4 2 5% 3 4 4 3 5% 8% 53%	2275
	21st to end	Day	10% 5% 2 6% 4 4 5% 5% 6% 8% 47%	2043
October	1st to 10th	Day	12% 7% 2 5% 4 3 3 3 5% 6% 50%	1900
	11th to 20th	Day	16% 8% 3 6% 4 3 3 3 4 6% 45%	1900
	21st to end	Day	19% 8% 2 5% 4 4 4 3 4 6% 41%	2028
November	1st to 10th	Day	12% 9% 2 5% 4 3 4 4 5% 6% 45%	1762
	11th to 20th	Day	15% 11% 3 7% 5% 3 3 3 6% 7% 37%	1777
	21st to end	Day	16% 11% 3 7% 5% 4 4 3 4 6% 38%	1597
December	1st to 10th	Day	14% 13% 4 10% 5% 4 4 3 4 5% 32%	1520
	11th to 20th	Day	13% 12% 4 8% 5% 5% 5% 3 6% 6% 34%	1918
	21st to end	Day	22% 20% 7% 12% 5% 3 3 3 4 4 17%	2783
January	1st to 10th	Night	13% 12% 6% 14% 5% 5% 4 3 4 5% 28%	4428
	11th to 20th	Night	13% 17% 7% 11% 5% 4 5% 4 7% 4 23%	4380
	21st to end	Night	18% 17% 6% 13% 5% 4 3 3 3 5% 23%	4532
February	1st to 10th	Night	14% 13% 4 9% 5% 4 4 3 5% 6% 33%	2470
	11th to 20th	Night	12% 11% 3 7% 4 5% 4 4 5% 6% 39%	2315
	21st to end	Night	15% 11% 3 7% 5% 4 2 3 5% 5% 40%	1884
March	1st to 10th	Night	18% 9% 3 7% 4 4 4 3 4 5% 40%	3705
	11th to 20th	Night	11% 6% 2 6% 4 4 3 3 5% 6% 50%	3480
	21st to end	Night	21% 12% 6% 11% 6% 4 4 3 5% 5% 24%	3629
April	1st to 10th	Night	15% 9% 4 6% 4 4 3 3 5% 7% 40%	1900
	11th to 20th	Night	16% 9% 3 6% 4 3 3 3 5% 6% 43%	1875
	21st to end	Night	16% 7% 3 7% 5% 4 4 4 6% 8% 38%	1900
May	1st to 10th	Night	18% 9% 3 7% 4 4 4 4 5% 7% 34%	2738
	11th to 20th	Night	13% 5% 2 7% 4 5% 4 4 6% 8% 42%	2506
	21st to end	Night	7% 6% 2 5% 4 4 5% 4 6% 8% 48%	2743
June	1st to 10th	Night	7% 5% 2 5% 5% 4 5% 3 6% 9% 49%	1520
	11th to 20th	Night	7% 5% 3 5% 4 3 5% 5% 7% 10% 47%	1520
	21st to end	Night	9% 7% 1 5% 5% 4 4 4 5% 9% 47%	1520
July	1st to 10th	Night	13% 5% 2 6% 5% 5% 5% 5% 7% 9% 40%	2530
	11th to 20th	Night	4 3 1 4 3 3 4 3 6% 9% 58%	2530
	21st to end	Night	5% 4 2 5% 5% 5% 5% 5% 7% 10% 46%	2807
August	1st to 10th	Night	4 3 1 5% 3 4 5% 4 6% 11% 55%	2836
	11th to 20th	Night	7% 4 2 5% 4 4 4 3 5% 7% 54%	2973
	21st to end	Night	5% 4 2 5% 4 4 4 3 5% 8% 56%	3476
September	1st to 10th	Night	10% 4 2 5% 3 3 3 2 5% 6% 57%	1900
	11th to 20th	Night	9% 5% 2 5% 3 4 4 4 5% 8% 51%	1900
	21st to end	Night	7% 5% 2 6% 4 4 4 4 5% 7% 52%	2120
October	1st to 10th	Night	10% 6% 2 6% 4 4 3 3 4 6% 54%	2280
	11th to 20th	Night	14% 7% 2 6% 4 3 3 2 5% 6% 49%	2280
	21st to end	Night	17% 7% 3 7% 4 4 5% 3 5% 6% 40%	2569
November	1st to 10th	Night	13% 7% 2 5% 3 2 3 3 4 6% 52%	2536
	11th to 20th	Night	15% 8% 3 6% 4 4 4 3 5% 7% 40%	2620
	21st to end	Night	16% 11% 3 8% 4 4 3 3 4 5% 39%	2799
December	1st to 10th	Night	12% 12% 4 8% 5% 5% 4 3 5% 6% 35%	2660
	11th to 20th	Night	15% 12% 3 8% 5% 4 3 4 4 5% 35%	3279
	21st to end	Night	22% 17% 6% 11% 5% 4 4 3 4 4 19%	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	57% 9% 12% 16% 6% 1	2528
	11th to 20th	Day	61% 6% 12% 14% 7%	2576
	21st to end	Day	70% 5% 9% 10% 5%	3135
February	1st to 10th	Day	55% 6% 14% 17% 7% 1	1710
	11th to 20th	Day	48% 7% 12% 22% 10% 1	1759
	21st to end	Day	51% 5% 12% 21% 9% 2	1570
March	1st to 10th	Day	45% 7% 12% 20% 15% 2	3176
	11th to 20th	Day	34% 8% 14% 26% 17% 1	3480
	21st to end	Day	56% 9% 15% 17% 3 1	4000
April	1st to 10th	Day	49% 6% 12% 22% 11%	2280
	11th to 20th	Day	46% 6% 10% 23% 13% 2	2254
	21st to end	Day	49% 7% 11% 18% 13% 2	2280
May	1st to 10th	Day	43% 9% 13% 19% 15%	4196
	11th to 20th	Day	42% 8% 11% 28% 11%	4403
	21st to end	Day	36% 9% 12% 22% 20% 2	4837
June	1st to 10th	Day	33% 9% 16% 23% 16% 2	2660
	11th to 20th	Day	34% 8% 11% 23% 21% 3	2660
	21st to end	Day	37% 9% 15% 22% 15% 2	2660
July	1st to 10th	Day	41% 8% 14% 24% 11% 2	4371
	11th to 20th	Day	28% 8% 16% 30% 17% 2	4365
	21st to end	Day	31% 11% 20% 20% 16% 1	4602
August	1st to 10th	Day	30% 9% 20% 29% 12% 1	4090
	11th to 20th	Day	35% 8% 15% 26% 15% 1	3899
	21st to end	Day	31% 6% 14% 31% 16% 3	4179
September	1st to 10th	Day	32% 8% 11% 25% 20% 4	2280
	11th to 20th	Day	29% 6% 12% 28% 22% 3	2275
	21st to end	Day	33% 7% 12% 27% 20% 2	2043
October	1st to 10th	Day	22% 4 6% 27% 39% 2	3160
	11th to 20th	Day	27% 3 10% 23% 31% 5%	3140
	21st to end	Day	38% 4 9% 28% 17% 3	3318
November	1st to 10th	Day	38% 6% 15% 24% 14% 3	1762
	11th to 20th	Day	46% 5% 14% 21% 13% 2	1777
	21st to end	Day	48% 5% 15% 22% 10%	1597
December	1st to 10th	Day	54% 5% 13% 20% 8% 1	1520
	11th to 20th	Day	49% 7% 13% 22% 7% 2	1915
	21st to end	Day	71% 6% 8% 10% 5%	2783
January	1st to 10th	Night	56% 7% 11% 17% 8%	4428
	11th to 20th	Night	60% 4 12% 13% 9% 1	4380
	21st to end	Night	64% 5% 10% 15% 5% 1	4532
February	1st to 10th	Night	51% 5% 12% 19% 11% 1	2470
	11th to 20th	Night	45% 6% 12% 24% 13% 1	2316
	21st to end	Night	46% 4 10% 22% 14% 3	1884
March	1st to 10th	Night	46% 7% 10% 23% 13% 1	3705
	11th to 20th	Night	34% 6% 11% 30% 16% 4	3480
	21st to end	Night	60% 9% 12% 14% 5%	3629
April	1st to 10th	Night	44% 5% 11% 25% 14% 2	1900
	11th to 20th	Night	43% 5% 9% 22% 17% 4	1875
	21st to end	Night	43% 7% 12% 20% 14% 3	1900
May	1st to 10th	Night	45% 9% 13% 17% 14% 1	2767
	11th to 20th	Night	37% 10% 15% 25% 13% 1	2507
	21st to end	Night	29% 10% 13% 23% 22% 2	2751
June	1st to 10th	Night	31% 8% 15% 25% 18% 4	1520
	11th to 20th	Night	30% 9% 11% 23% 23% 5%	1520
	21st to end	Night	33% 8% 16% 20% 20% 3	1520
July	1st to 10th	Night	40% 7% 14% 23% 13% 2	2490
	11th to 20th	Night	21% 6% 16% 34% 22% 1	2482
	21st to end	Night	29% 10% 18% 21% 18% 3	2718
August	1st to 10th	Night	23% 8% 19% 31% 18% 2	2826
	11th to 20th	Night	28% 7% 16% 31% 17% 1	3000
	21st to end	Night	26% 7% 14% 31% 17% 4	3476
September	1st to 10th	Night	27% 6% 10% 26% 26% 4	1900
	11th to 20th	Night	30% 6% 12% 26% 20% 6%	1900
	21st to end	Night	30% 6% 12% 25% 24% 3	2120
October	1st to 10th	Night	23% 4 7% 27% 36% 4	3800
	11th to 20th	Night	26% 4 9% 23% 34% 5%	3779
	21st to end	Night	42% 5% 8% 21% 20% 4	4229
November	1st to 10th	Night	33% 5% 13% 26% 19% 4	2536
	11th to 20th	Night	43% 6% 11% 24% 14% 2	2620
	21st to end	Night	47% 5% 11% 23% 13% 1	2799
December	1st to 10th	Night	49% 6% 13% 22% 9% 1	2660
	11th to 20th	Night	49% 5% 13% 24% 8% 1	3281
	21st to end	Night	66% 8% 10% 11% 5%	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% 16% 35% 20% 7% 1	270
	11th to 20th	Day	21% 19% 41% 15% 4 1	270
	21st to end	Day	22% 18% 37% 18% 5% 1	297
February	1st to 10th	Day	24% 16% 41% 14% 4	270
	11th to 20th	Day	25% 16% 34% 19% 4 1	270
	21st to end	Day	21% 18% 43% 16% 2 1	225
March	1st to 10th	Day	18% 20% 39% 19% 3	270
	11th to 20th	Day	20% 20% 33% 20% 6% 2	270
	21st to end	Day	27% 19% 33% 15% 5% 1	406
April	1st to 10th	Day	22% 15% 35% 21% 6%	460
	11th to 20th	Day	21% 17% 30% 20% 11% 1	452
	21st to end	Day	21% 13% 35% 22% 7% 2	460
May	1st to 10th	Day	17% 11% 37% 26% 8% 2	571
	11th to 20th	Day	19% 14% 26% 27% 13% 2	675
	21st to end	Day	15% 7% 30% 26% 15% 7%	734
June	1st to 10th	Day	6% 7% 27% 32% 20% 8%	680
	11th to 20th	Day	8% 5% 30% 33% 20% 4	680
	21st to end	Day	10% 10% 30% 30% 16% 4	680
July	1st to 10th	Day	9% 4 18% 31% 23% 14%	671
	11th to 20th	Day	9% 4 22% 35% 22% 8%	668
	21st to end	Day	6% 1 22% 36% 29% 7%	739
August	1st to 10th	Day	6% 3 22% 36% 24% 8%	676
	11th to 20th	Day	9% 6% 18% 31% 25% 12%	562
	21st to end	Day	6% 2 18% 35% 28% 11%	539
September	1st to 10th	Day	11% 6% 18% 32% 25% 7%	490
	11th to 20th	Day	7% 2 19% 34% 27% 11%	490
	21st to end	Day	11% 9% 26% 26% 21% 8%	443
October	1st to 10th	Day	16% 7% 27% 28% 16% 5%	300
	11th to 20th	Day	17% 20% 30% 21% 11%	300
	21st to end	Day	30% 13% 30% 20% 5% 1	330
November	1st to 10th	Day	14% 12% 40% 23% 8% 3	300
	11th to 20th	Day	23% 16% 30% 23% 7% 2	300
	21st to end	Day	24% 11% 36% 23% 5%	299
December	1st to 10th	Day	13% 17% 40% 23% 5% 3	270
	11th to 20th	Day	16% 15% 38% 22% 9%	270
	21st to end	Day	25% 22% 34% 17% 2	297
January	1st to 10th	Night	16% 15% 39% 23% 6% 1	950
	11th to 20th	Night	19% 14% 38% 23% 5%	950
	21st to end	Night	19% 13% 37% 27% 4	1045
February	1st to 10th	Night	22% 12% 39% 23% 4	950
	11th to 20th	Night	17% 16% 36% 28% 3	841
	21st to end	Night	21% 15% 40% 21% 2 1	628
March	1st to 10th	Night	20% 12% 40% 24% 4	745
	11th to 20th	Night	16% 12% 35% 29% 7%	570
	21st to end	Night	21% 16% 36% 22% 4	627
April	1st to 10th	Night	19% 15% 38% 25% 3	570
	11th to 20th	Night	19% 13% 33% 28% 6%	563
	21st to end	Night	17% 11% 35% 30% 7%	570
May	1st to 10th	Night	18% 8% 37% 29% 7% 1	570
	11th to 20th	Night	17% 6% 30% 37% 11%	561
	21st to end	Night	10% 6% 30% 35% 17% 1	617
June	1st to 10th	Night	9% 4 25% 46% 15% 1	570
	11th to 20th	Night	8% 4 28% 42% 18%	570
	21st to end	Night	11% 5% 26% 39% 17% 1	570
July	1st to 10th	Night	10% 2 11% 42% 31% 4	555
	11th to 20th	Night	4 2 21% 42% 28% 3	552
	21st to end	Night	7% 1 17% 44% 30% 1	624
August	1st to 10th	Night	5% 3 14% 46% 30% 2	567
	11th to 20th	Night	6% 2 15% 44% 28% 5%	564
	21st to end	Night	8% 16% 44% 29% 3	627
September	1st to 10th	Night	11% 4 18% 37% 27% 3	570
	11th to 20th	Night	10% 3 20% 36% 25% 6%	570
	21st to end	Night	8% 7% 24% 35% 23% 2	745
October	1st to 10th	Night	12% 6% 30% 31% 19% 2	760
	11th to 20th	Night	17% 12% 32% 29% 11%	760
	21st to end	Night	21% 11% 34% 26% 7%	836
November	1st to 10th	Night	17% 8% 39% 27% 8% 1	780
	11th to 20th	Night	19% 13% 38% 24% 6%	820
	21st to end	Night	21% 12% 37% 25% 5%	1000
December	1st to 10th	Night	18% 12% 40% 24% 5% 1	950
	11th to 20th	Night	22% 11% 34% 26% 6%	950
	21st to end	Night	26% 14% 34% 23% 3	1045

Page generated at 2024-11-27 16:30:54. Version ac07

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