The Geek Shed
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Geek Shed 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% 8% 3 7% 5% 5% 5% 4 6% 7% 35%	101579
	Night	16% 8% 3 7% 5% 4 4 4 5% 7% 37%	97895
Transparency	Day	46% 6% 12% 22% 12% 2	105182
	Night	45% 6% 12% 22% 13% 2	102380
Seeing	Day	22% 19% 27% 19% 10% 3	14851
	Night	20% 16% 27% 26% 10% 1	24251

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	14% 12% 4 9% 5% 4 5% 3 4 5% 34%	2517
	11th to 20th	Day	11% 15% 7% 14% 9% 6% 5% 3 4 5% 21%	2747
	21st to end	Day	18% 14% 6% 11% 6% 5% 5% 3 4 5% 22%	3124
February	1st to 10th	Day	16% 14% 4 9% 6% 5% 5% 3 6% 7% 27%	1710
	11th to 20th	Day	12% 9% 4 10% 6% 5% 5% 5% 5% 7% 31%	1678
	21st to end	Day	17% 12% 4 9% 6% 5% 3 4 5% 6% 30%	1570
March	1st to 10th	Day	23% 10% 3 6% 4 3 4 4 5% 6% 32%	3334
	11th to 20th	Day	10% 9% 3 8% 6% 5% 5% 4 6% 6% 38%	3480
	21st to end	Day	15% 11% 3 7% 4 4 3 3 4 5% 40%	3898
April	1st to 10th	Day	15% 9% 3 9% 6% 5% 4 3 6% 6% 34%	2280
	11th to 20th	Day	15% 9% 3 7% 5% 5% 5% 4 5% 5% 37%	2254
	21st to end	Day	18% 8% 2 7% 5% 4 4 4 6% 6% 35%	2307
May	1st to 10th	Day	28% 6% 3 7% 5% 4 4 4 4 7% 30%	4135
	11th to 20th	Day	23% 9% 3 8% 5% 5% 5% 3 5% 6% 27%	4398
	21st to end	Day	12% 6% 2 5% 4 4 6% 5% 6% 9% 41%	4837
June	1st to 10th	Day	12% 6% 3 7% 5% 5% 5% 6% 6% 8% 37%	2660
	11th to 20th	Day	14% 6% 2 6% 5% 6% 5% 3 6% 9% 37%	2660
	21st to end	Day	11% 5% 2 5% 5% 5% 5% 5% 7% 11% 39%	2660
July	1st to 10th	Day	7% 6% 2 7% 6% 6% 7% 5% 7% 9% 38%	4440
	11th to 20th	Day	7% 5% 2 6% 5% 6% 6% 5% 8% 11% 38%	4440
	21st to end	Day	11% 6% 3 7% 6% 5% 6% 5% 7% 8% 34%	4534
August	1st to 10th	Day	20% 6% 2 7% 5% 5% 5% 4 7% 8% 31%	4104
	11th to 20th	Day	14% 6% 2 7% 4 6% 6% 5% 7% 8% 35%	3949
	21st to end	Day	16% 4 2 4 4 4 4 4 6% 9% 42%	4180
September	1st to 10th	Day	17% 5% 2 6% 5% 4 4 3 5% 6% 44%	2280
	11th to 20th	Day	14% 4 2 5% 4 4 3 3 5% 7% 50%	2280
	21st to end	Day	22% 7% 2 7% 3 4 3 3 4 6% 38%	1996
October	1st to 10th	Day	17% 7% 2 6% 5% 4 4 3 5% 7% 40%	1900
	11th to 20th	Day	18% 7% 2 6% 4 5% 4 4 5% 7% 39%	1900
	21st to end	Day	17% 7% 3 7% 5% 5% 5% 4 5% 6% 37%	2090
November	1st to 10th	Day	11% 7% 2 6% 4 3 4 4 6% 7% 46%	1792
	11th to 20th	Day	14% 9% 2 8% 4 5% 5% 4 6% 6% 36%	1695
	21st to end	Day	18% 7% 2 6% 5% 5% 5% 6% 6% 6% 32%	1552
December	1st to 10th	Day	17% 12% 5% 9% 7% 6% 4 3 4 7% 25%	1520
	11th to 20th	Day	18% 9% 4 9% 5% 5% 4 3 6% 7% 30%	1906
	21st to end	Day	19% 11% 4 13% 8% 5% 5% 4 5% 6% 21%	2772
January	1st to 10th	Night	14% 10% 4 8% 7% 5% 5% 4 6% 8% 31%	4429
	11th to 20th	Night	14% 12% 5% 11% 6% 5% 4 4 5% 6% 27%	4212
	21st to end	Night	22% 11% 4 9% 5% 5% 5% 4 4 6% 26%	4532
February	1st to 10th	Night	14% 10% 3 7% 6% 5% 4 4 6% 6% 33%	2470
	11th to 20th	Night	14% 9% 4 8% 6% 5% 5% 4 6% 7% 32%	2386
	21st to end	Night	16% 10% 4 9% 5% 5% 5% 4 4 6% 33%	1884
March	1st to 10th	Night	21% 13% 3 6% 4 4 4 3 4 5% 33%	3503
	11th to 20th	Night	9% 7% 4 8% 5% 5% 5% 4 6% 7% 39%	3479
	21st to end	Night	15% 9% 2 7% 4 4 3 3 4 6% 43%	3733
April	1st to 10th	Night	17% 9% 4 8% 6% 4 5% 4 5% 7% 33%	1900
	11th to 20th	Night	16% 7% 2 7% 5% 4 4 5% 6% 7% 37%	1875
	21st to end	Night	18% 5% 2 6% 4 4 4 4 5% 6% 40%	1890
May	1st to 10th	Night	28% 9% 3 6% 4 3 3 4 4 6% 30%	2803
	11th to 20th	Night	24% 10% 3 7% 4 4 4 4 5% 6% 30%	2495
	21st to end	Night	13% 6% 2 7% 5% 5% 4 3 6% 9% 40%	2738
June	1st to 10th	Night	13% 6% 2 6% 5% 4 4 3 5% 9% 42%	1520
	11th to 20th	Night	12% 5% 2 7% 5% 3 5% 4 6% 8% 42%	1520
	21st to end	Night	11% 5% 2 6% 5% 4 5% 4 7% 10% 42%	1520
July	1st to 10th	Night	8% 6% 2 6% 5% 5% 5% 4 6% 8% 44%	2520
	11th to 20th	Night	7% 5% 2 6% 5% 5% 6% 4 8% 10% 43%	2520
	21st to end	Night	13% 7% 2 6% 4 4 5% 3 5% 7% 42%	3015
August	1st to 10th	Night	18% 6% 2 6% 4 5% 4 4 7% 8% 37%	2825
	11th to 20th	Night	15% 7% 2 7% 5% 4 3 4 5% 6% 43%	2846
	21st to end	Night	16% 4 1 4 3 3 4 4 5% 9% 46%	3476
September	1st to 10th	Night	16% 5% 2 6% 4 4 4 3 5% 6% 46%	1900
	11th to 20th	Night	13% 5% 2 5% 3 3 3 3 5% 6% 52%	1900
	21st to end	Night	20% 6% 3 5% 4 4 4 3 5% 7% 41%	2177
October	1st to 10th	Night	19% 6% 2 6% 3 3 3 3 5% 7% 43%	2280
	11th to 20th	Night	15% 7% 1 6% 4 3 4 4 5% 8% 42%	2280
	21st to end	Night	19% 8% 2 6% 4 3 4 3 6% 6% 40%	2508
November	1st to 10th	Night	9% 8% 3 6% 4 4 4 3 5% 5% 51%	2504
	11th to 20th	Night	17% 8% 2 5% 5% 4 4 4 6% 7% 38%	2700
	21st to end	Night	15% 8% 3 8% 4 4 4 4 6% 8% 36%	2723
December	1st to 10th	Night	16% 10% 4 8% 5% 5% 5% 4 6% 8% 29%	2660
	11th to 20th	Night	17% 9% 3 7% 6% 5% 5% 4 5% 6% 33%	3288
	21st to end	Night	18% 10% 4 9% 6% 6% 5% 4 6% 7% 26%	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	50% 4 16% 21% 6% 2	2518
	11th to 20th	Day	64% 4 9% 12% 9% 1	2747
	21st to end	Day	63% 5% 9% 17% 5% 1	3124
February	1st to 10th	Day	56% 5% 12% 18% 8% 1	1710
	11th to 20th	Day	51% 6% 10% 24% 9% 1	1687
	21st to end	Day	55% 5% 11% 19% 8% 2	1570
March	1st to 10th	Day	52% 5% 9% 25% 7% 1	3337
	11th to 20th	Day	44% 5% 15% 22% 11% 3	3480
	21st to end	Day	46% 5% 9% 22% 16% 2	3898
April	1st to 10th	Day	50% 5% 9% 20% 13% 3	2280
	11th to 20th	Day	46% 6% 9% 21% 15% 3	2254
	21st to end	Day	46% 6% 10% 21% 13% 4	2307
May	1st to 10th	Day	54% 5% 9% 20% 11% 2	4147
	11th to 20th	Day	55% 8% 12% 15% 8% 1	4402
	21st to end	Day	37% 8% 13% 24% 15% 2	4837
June	1st to 10th	Day	42% 7% 12% 22% 14% 2	2660
	11th to 20th	Day	42% 8% 14% 21% 13% 2	2660
	21st to end	Day	37% 8% 13% 28% 14% 1	2660
July	1st to 10th	Day	39% 8% 15% 25% 11% 1	4370
	11th to 20th	Day	35% 8% 17% 25% 15% 1	4365
	21st to end	Day	43% 8% 12% 21% 15% 1	4389
August	1st to 10th	Day	49% 7% 13% 20% 10%	4091
	11th to 20th	Day	43% 7% 11% 28% 10% 1	3988
	21st to end	Day	37% 5% 12% 31% 13% 2	4180
September	1st to 10th	Day	40% 7% 10% 23% 18% 3	2280
	11th to 20th	Day	35% 4 12% 25% 22% 3	2280
	21st to end	Day	47% 4 10% 19% 17% 2	1996
October	1st to 10th	Day	39% 5% 8% 25% 18% 4	3160
	11th to 20th	Day	37% 5% 9% 26% 21% 1	3140
	21st to end	Day	30% 4 15% 31% 18% 1	3428
November	1st to 10th	Day	36% 5% 15% 24% 17% 3	1792
	11th to 20th	Day	46% 4 12% 23% 12% 2	1695
	21st to end	Day	48% 7% 13% 23% 8% 1	1552
December	1st to 10th	Day	58% 6% 15% 15% 7%	1520
	11th to 20th	Day	53% 5% 15% 20% 6% 1	1906
	21st to end	Day	62% 6% 14% 14% 4	2772
January	1st to 10th	Night	51% 5% 13% 21% 7% 1	4429
	11th to 20th	Night	56% 5% 15% 15% 7% 1	4212
	21st to end	Night	59% 5% 10% 17% 7% 1	4532
February	1st to 10th	Night	49% 6% 14% 22% 8% 1	2470
	11th to 20th	Night	49% 6% 12% 20% 12% 1	2388
	21st to end	Night	52% 4 10% 20% 12% 2	1884
March	1st to 10th	Night	54% 4 9% 22% 10% 1	3513
	11th to 20th	Night	43% 5% 13% 27% 10% 1	3480
	21st to end	Night	43% 4 8% 21% 19% 4	3733
April	1st to 10th	Night	51% 5% 9% 19% 14% 2	1900
	11th to 20th	Night	43% 7% 10% 22% 16% 3	1875
	21st to end	Night	43% 6% 11% 22% 15% 3	1890
May	1st to 10th	Night	56% 6% 7% 20% 10% 2	2810
	11th to 20th	Night	53% 11% 11% 13% 10% 1	2496
	21st to end	Night	39% 8% 15% 20% 13% 5%	2739
June	1st to 10th	Night	39% 7% 12% 23% 17% 2	1520
	11th to 20th	Night	39% 8% 14% 23% 15% 2	1520
	21st to end	Night	35% 7% 14% 28% 15% 1	1520
July	1st to 10th	Night	38% 8% 13% 20% 17% 4	2480
	11th to 20th	Night	35% 9% 14% 26% 15% 1	2472
	21st to end	Night	41% 8% 11% 17% 22% 2	2919
August	1st to 10th	Night	45% 9% 13% 23% 10%	2814
	11th to 20th	Night	41% 5% 12% 26% 16%	2873
	21st to end	Night	35% 6% 11% 31% 15% 2	3476
September	1st to 10th	Night	39% 6% 10% 24% 18% 3	1900
	11th to 20th	Night	32% 4 11% 30% 21% 2	1900
	21st to end	Night	43% 5% 11% 22% 19% 2	2177
October	1st to 10th	Night	39% 4 11% 24% 21% 1	3800
	11th to 20th	Night	32% 5% 10% 28% 23% 3	3779
	21st to end	Night	31% 3 14% 29% 20% 2	4120
November	1st to 10th	Night	35% 4 12% 26% 19% 3	2504
	11th to 20th	Night	45% 5% 10% 23% 14% 3	2700
	21st to end	Night	45% 5% 15% 23% 9% 1	2723
December	1st to 10th	Night	51% 6% 15% 19% 9%	2660
	11th to 20th	Night	52% 5% 12% 21% 10% 1	3288
	21st to end	Night	56% 6% 15% 19% 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	29% 32% 26% 11% 1 2	180
	11th to 20th	Day	28% 31% 31% 9% 1	245
	21st to end	Day	24% 35% 29% 8% 3	297
February	1st to 10th	Day	27% 35% 27% 10% 1	270
	11th to 20th	Day	31% 31% 34% 4	285
	21st to end	Day	34% 24% 25% 15% 2	382
March	1st to 10th	Day	30% 24% 29% 12% 4	460
	11th to 20th	Day	29% 28% 27% 12% 3 1	460
	21st to end	Day	28% 26% 28% 13% 4 2	506
April	1st to 10th	Day	25% 29% 26% 14% 5% 1	460
	11th to 20th	Day	22% 29% 22% 16% 7% 3	452
	21st to end	Day	28% 21% 31% 11% 7% 2	460
May	1st to 10th	Day	30% 21% 27% 12% 7% 3	463
	11th to 20th	Day	22% 23% 25% 18% 9% 3	487
	21st to end	Day	18% 13% 29% 20% 16% 4	529
June	1st to 10th	Day	16% 18% 28% 24% 11% 2	490
	11th to 20th	Day	18% 16% 26% 26% 12% 2	490
	21st to end	Day	14% 14% 34% 25% 10% 2	490
July	1st to 10th	Day	13% 8% 27% 30% 17% 6%	485
	11th to 20th	Day	8% 9% 27% 34% 18% 4	484
	21st to end	Day	13% 10% 30% 28% 14% 5%	532
August	1st to 10th	Day	14% 6% 28% 27% 20% 5%	486
	11th to 20th	Day	15% 8% 25% 25% 19% 7%	479
	21st to end	Day	15% 9% 26% 25% 17% 9%	539
September	1st to 10th	Day	20% 11% 20% 23% 17% 8%	490
	11th to 20th	Day	15% 7% 24% 25% 22% 7%	490
	21st to end	Day	28% 12% 24% 17% 14% 4	490
October	1st to 10th	Day	23% 13% 23% 21% 17% 3	490
	11th to 20th	Day	21% 17% 30% 21% 9% 1	490
	21st to end	Day	23% 19% 30% 20% 8%	539
November	1st to 10th	Day	19% 19% 28% 21% 11% 1	410
	11th to 20th	Day	24% 26% 27% 18% 5%	295
	21st to end	Day	25% 30% 30% 12% 2 1	188
December	1st to 10th	Day	28% 32% 26% 11% 4 1	180
	11th to 20th	Day	31% 27% 28% 13% 2	180
	21st to end	Day	26% 29% 30% 12% 2	198
January	1st to 10th	Night	19% 28% 34% 16% 3	760
	11th to 20th	Night	24% 22% 30% 19% 4	760
	21st to end	Night	17% 26% 36% 20% 2	836
February	1st to 10th	Night	23% 21% 33% 21% 1	760
	11th to 20th	Night	23% 28% 33% 15% 1	743
	21st to end	Night	25% 25% 31% 17% 3	628
March	1st to 10th	Night	24% 23% 30% 20% 3	760
	11th to 20th	Night	24% 23% 29% 19% 5%	760
	21st to end	Night	22% 20% 35% 18% 5% 1	836
April	1st to 10th	Night	22% 23% 31% 18% 5%	760
	11th to 20th	Night	20% 20% 31% 21% 7% 1	751
	21st to end	Night	22% 17% 29% 26% 6%	750
May	1st to 10th	Night	25% 12% 26% 25% 12%	553
	11th to 20th	Night	20% 10% 30% 30% 10%	374
	21st to end	Night	17% 9% 22% 34% 17%	411
June	1st to 10th	Night	14% 6% 26% 37% 17%	380
	11th to 20th	Night	13% 9% 23% 40% 15%	380
	21st to end	Night	11% 3 30% 43% 13% 1	380
July	1st to 10th	Night	12% 5% 24% 39% 20% 1	370
	11th to 20th	Night	7% 4 20% 45% 24% 1	368
	21st to end	Night	13% 3 21% 42% 21% 1	578
August	1st to 10th	Night	13% 2 18% 41% 24% 2	567
	11th to 20th	Night	14% 5% 17% 33% 27% 3	599
	21st to end	Night	15% 3 18% 35% 27% 2	836
September	1st to 10th	Night	19% 5% 22% 30% 23% 2	760
	11th to 20th	Night	15% 5% 19% 29% 26% 5%	760
	21st to end	Night	23% 8% 20% 28% 19% 2	760
October	1st to 10th	Night	22% 10% 22% 25% 18% 3	760
	11th to 20th	Night	19% 15% 27% 29% 10% 1	760
	21st to end	Night	24% 14% 28% 27% 7%	836
November	1st to 10th	Night	15% 15% 29% 28% 11% 1	780
	11th to 20th	Night	24% 21% 24% 24% 7% 1	800
	21st to end	Night	21% 22% 30% 22% 4 1	779
December	1st to 10th	Night	25% 22% 31% 16% 5%	760
	11th to 20th	Night	23% 22% 31% 20% 4	760
	21st to end	Night	23% 22% 30% 23% 2	836

Page generated at 2024-11-22 08:02:27. Version ac07

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