Teeter's Telescopes Workshop
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Teeter's Telescopes Workshop clear sky chart from 2005-11-06 to 2026-01-02.

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	17% 7% 2 6% 4 4 4 4 5% 7% 39%	127341
	Night	17% 7% 2 6% 4 4 4 3 5% 6% 42%	124022
Transparency	Day	42% 6% 11% 22% 16% 3	130855
	Night	41% 6% 11% 22% 16% 3	128582
Seeing	Day	23% 16% 30% 20% 9% 2	16381
	Night	21% 14% 31% 25% 8% 1	25609

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	13% 6% 2 5% 4 4 4 4 5% 6% 47%	3605
	11th to 20th	Day	14% 9% 3 8% 6% 5% 4 3 4 5% 39%	3570
	21st to end	Day	17% 8% 4 7% 4 4 4 3 4 5% 39%	4351
February	1st to 10th	Day	17% 8% 3 7% 5% 4 4 4 6% 6% 37%	1800
	11th to 20th	Day	14% 9% 3 7% 5% 4 4 4 4 6% 41%	1927
	21st to end	Day	18% 10% 2 7% 4 4 3 3 5% 5% 38%	1650
March	1st to 10th	Day	21% 7% 2 5% 4 4 3 2 4 5% 42%	4476
	11th to 20th	Day	12% 5% 3 6% 5% 5% 5% 4 6% 7% 42%	4837
	21st to end	Day	18% 7% 2 6% 4 3 4 3 5% 6% 42%	5878
April	1st to 10th	Day	18% 9% 3 6% 5% 3 5% 3 5% 6% 37%	2400
	11th to 20th	Day	17% 7% 2 7% 5% 3 5% 4 4 7% 39%	2374
	21st to end	Day	18% 6% 2 6% 5% 4 4 4 6% 6% 39%	2405
May	1st to 10th	Day	30% 7% 2 5% 3 4 4 3 5% 7% 28%	5932
	11th to 20th	Day	23% 8% 3 6% 4 4 4 4 5% 6% 33%	6318
	21st to end	Day	21% 6% 3 5% 4 4 4 4 6% 8% 35%	6949
June	1st to 10th	Day	17% 6% 2 6% 5% 5% 5% 4 7% 8% 35%	2800
	11th to 20th	Day	18% 6% 2 6% 5% 5% 6% 5% 6% 9% 34%	2800
	21st to end	Day	13% 7% 2 6% 5% 5% 5% 5% 7% 8% 38%	2800
July	1st to 10th	Day	11% 7% 2 8% 5% 5% 5% 4 7% 10% 36%	6360
	11th to 20th	Day	12% 6% 3 6% 5% 5% 7% 5% 8% 11% 31%	6360
	21st to end	Day	14% 6% 2 6% 5% 4 5% 4 6% 8% 39%	6926
August	1st to 10th	Day	21% 6% 2 7% 5% 5% 5% 4 6% 8% 32%	4314
	11th to 20th	Day	13% 6% 2 6% 4 4 4 4 6% 8% 42%	3850
	21st to end	Day	13% 5% 2 5% 3 3 4 3 5% 9% 48%	4312
September	1st to 10th	Day	15% 5% 2 6% 4 4 5% 4 5% 6% 42%	2400
	11th to 20th	Day	14% 5% 2 5% 3 4 3 3 5% 7% 50%	2333
	21st to end	Day	19% 6% 3 8% 4 4 4 4 5% 6% 39%	2200
October	1st to 10th	Day	19% 7% 2 5% 4 4 4 3 5% 6% 42%	2055
	11th to 20th	Day	15% 6% 2 5% 4 4 5% 2 5% 7% 46%	2000
	21st to end	Day	20% 5% 2 5% 3 3 4 4 5% 6% 42%	2060
November	1st to 10th	Day	14% 6% 2 5% 3 3 4 3 4 6% 51%	1851
	11th to 20th	Day	17% 6% 1 4 3 4 4 3 5% 7% 45%	1890
	21st to end	Day	16% 7% 2 5% 4 4 4 4 4 7% 41%	1764
December	1st to 10th	Day	15% 8% 2 6% 4 3 4 4 5% 6% 43%	2680
	11th to 20th	Day	22% 7% 2 4 3 3 3 3 4 5% 43%	3066
	21st to end	Day	17% 8% 3 7% 5% 4 5% 3 6% 8% 35%	4048
January	1st to 10th	Night	13% 6% 2 5% 4 4 4 4 5% 7% 47%	6364
	11th to 20th	Night	13% 7% 3 8% 5% 4 4 3 4 6% 44%	6315
	21st to end	Night	17% 9% 2 5% 4 4 4 3 5% 6% 40%	6600
February	1st to 10th	Night	17% 9% 3 5% 4 4 4 3 5% 6% 40%	2600
	11th to 20th	Night	16% 8% 3 6% 4 4 4 4 5% 6% 40%	2358
	21st to end	Night	18% 7% 3 6% 4 4 4 3 4 6% 40%	1980
March	1st to 10th	Night	19% 8% 3 5% 4 3 4 3 4 5% 43%	5364
	11th to 20th	Night	13% 8% 3 5% 4 3 3 3 4 6% 47%	5118
	21st to end	Night	17% 9% 3 6% 4 3 4 3 5% 6% 41%	5054
April	1st to 10th	Night	19% 8% 2 6% 4 4 5% 4 6% 6% 36%	2000
	11th to 20th	Night	18% 8% 2 6% 4 4 4 3 5% 7% 39%	1975
	21st to end	Night	19% 6% 2 5% 4 3 4 3 5% 6% 42%	1995
May	1st to 10th	Night	30% 9% 2 6% 4 3 4 3 5% 7% 27%	4037
	11th to 20th	Night	23% 9% 4 6% 3 4 4 2 5% 6% 34%	3575
	21st to end	Night	22% 7% 2 5% 4 4 4 3 5% 8% 36%	3926
June	1st to 10th	Night	16% 5% 2 5% 4 5% 4 3 5% 8% 43%	1600
	11th to 20th	Night	14% 7% 2 5% 5% 4 4 4 6% 9% 40%	1600
	21st to end	Night	13% 4 2 5% 5% 4 5% 4 7% 8% 44%	1600
July	1st to 10th	Night	12% 6% 2 6% 4 5% 5% 4 6% 9% 40%	3600
	11th to 20th	Night	17% 8% 3 6% 5% 4 5% 4 7% 9% 33%	3600
	21st to end	Night	13% 6% 2 5% 3 4 4 4 5% 7% 46%	3926
August	1st to 10th	Night	21% 5% 3 6% 5% 4 4 4 6% 8% 34%	2806
	11th to 20th	Night	15% 6% 3 7% 5% 4 4 4 5% 7% 40%	3192
	21st to end	Night	12% 4 2 5% 3 3 4 3 4 7% 53%	3586
September	1st to 10th	Night	16% 6% 2 7% 4 4 4 4 4 6% 45%	2000
	11th to 20th	Night	13% 5% 2 4 3 4 4 2 5% 6% 52%	2066
	21st to end	Night	19% 6% 2 6% 4 3 4 3 4 7% 43%	2200
October	1st to 10th	Night	20% 6% 3 6% 4 3 3 3 4 6% 43%	2340
	11th to 20th	Night	17% 6% 2 5% 3 2 3 3 4 6% 50%	2400
	21st to end	Night	19% 7% 2 4 3 2 3 3 4 5% 46%	2779
November	1st to 10th	Night	12% 6% 2 4 3 3 4 3 5% 6% 51%	2667
	11th to 20th	Night	18% 7% 2 4 4 3 3 3 4 5% 47%	2730
	21st to end	Night	15% 5% 2 5% 4 4 4 4 6% 7% 44%	2851
December	1st to 10th	Night	13% 7% 2 6% 4 4 4 3 5% 6% 46%	4720
	11th to 20th	Night	24% 7% 2 4 3 3 3 3 4 6% 41%	5348
	21st to end	Night	18% 10% 3 7% 4 4 4 3 4 5% 38%	7150

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	35% 5% 10% 30% 18% 3	3606
	11th to 20th	Day	45% 5% 9% 21% 14% 6%	3600
	21st to end	Day	47% 6% 9% 21% 16% 1	4351
February	1st to 10th	Day	46% 6% 12% 22% 13% 1	1800
	11th to 20th	Day	43% 6% 10% 22% 16% 2	1936
	21st to end	Day	47% 5% 10% 21% 13% 3	1650
March	1st to 10th	Day	44% 4 10% 20% 14% 8%	4479
	11th to 20th	Day	38% 7% 13% 28% 10% 4	4837
	21st to end	Day	43% 4 11% 12% 24% 6%	5878
April	1st to 10th	Day	46% 6% 9% 19% 15% 5%	2400
	11th to 20th	Day	43% 6% 12% 20% 17% 3	2374
	21st to end	Day	43% 6% 10% 21% 16% 4	2405
May	1st to 10th	Day	54% 7% 13% 15% 10% 1	5943
	11th to 20th	Day	50% 7% 9% 19% 13% 1	6322
	21st to end	Day	44% 8% 11% 22% 14% 1	6949
June	1st to 10th	Day	43% 9% 14% 19% 15% 1	2800
	11th to 20th	Day	45% 8% 12% 22% 11% 2	2800
	21st to end	Day	41% 8% 13% 22% 15% 1	2800
July	1st to 10th	Day	42% 10% 11% 21% 14% 1	6290
	11th to 20th	Day	41% 10% 17% 21% 10% 1	6285
	21st to end	Day	41% 7% 10% 21% 20% 1	6728
August	1st to 10th	Day	49% 8% 12% 21% 9% 1	4300
	11th to 20th	Day	38% 7% 14% 28% 13% 1	3886
	21st to end	Day	34% 6% 9% 29% 20% 2	4312
September	1st to 10th	Day	39% 8% 10% 21% 19% 3	2400
	11th to 20th	Day	34% 6% 10% 23% 25% 3	2333
	21st to end	Day	46% 6% 10% 18% 17% 3	2200
October	1st to 10th	Day	38% 6% 8% 19% 23% 6%	3341
	11th to 20th	Day	28% 5% 10% 25% 28% 5%	3240
	21st to end	Day	27% 4 15% 24% 26% 4	3311
November	1st to 10th	Day	34% 5% 12% 24% 22% 3	1851
	11th to 20th	Day	38% 5% 11% 23% 19% 3	1890
	21st to end	Day	41% 5% 13% 27% 11% 2	1764
December	1st to 10th	Day	40% 5% 15% 27% 12% 2	2680
	11th to 20th	Day	43% 4 14% 23% 14% 2	3066
	21st to end	Day	46% 6% 10% 21% 15% 2	4048
January	1st to 10th	Night	35% 5% 11% 25% 21% 4	6364
	11th to 20th	Night	40% 6% 14% 20% 15% 5%	6360
	21st to end	Night	44% 5% 10% 19% 17% 5%	6600
February	1st to 10th	Night	44% 6% 13% 23% 12% 2	2600
	11th to 20th	Night	44% 5% 11% 19% 17% 5%	2360
	21st to end	Night	45% 4 8% 24% 16% 3	1980
March	1st to 10th	Night	42% 5% 10% 21% 13% 8%	5374
	11th to 20th	Night	38% 6% 15% 24% 13% 4	5119
	21st to end	Night	44% 5% 7% 16% 23% 5%	5054
April	1st to 10th	Night	46% 6% 11% 19% 14% 4	2000
	11th to 20th	Night	44% 7% 9% 20% 18% 2	1975
	21st to end	Night	42% 6% 9% 21% 18% 4	1995
May	1st to 10th	Night	55% 7% 12% 14% 10% 1	4043
	11th to 20th	Night	50% 7% 12% 14% 14% 1	3576
	21st to end	Night	45% 8% 13% 23% 10% 2	3927
June	1st to 10th	Night	40% 6% 11% 21% 20% 1	1600
	11th to 20th	Night	40% 9% 14% 25% 12% 1	1600
	21st to end	Night	34% 10% 15% 25% 15% 1	1600
July	1st to 10th	Night	39% 10% 14% 19% 16% 2	3560
	11th to 20th	Night	46% 8% 13% 21% 11% 1	3552
	21st to end	Night	35% 7% 13% 23% 20% 1	3809
August	1st to 10th	Night	48% 9% 15% 18% 9% 1	2796
	11th to 20th	Night	42% 9% 12% 27% 10%	3222
	21st to end	Night	31% 6% 9% 32% 20% 1	3586
September	1st to 10th	Night	40% 6% 10% 24% 19% 1	2000
	11th to 20th	Night	33% 6% 10% 22% 25% 3	2066
	21st to end	Night	42% 4 10% 21% 21% 1	2200
October	1st to 10th	Night	39% 5% 10% 23% 21% 2	3821
	11th to 20th	Night	26% 5% 9% 28% 28% 4	3899
	21st to end	Night	30% 4 13% 31% 19% 3	4478
November	1st to 10th	Night	33% 6% 12% 24% 22% 4	2667
	11th to 20th	Night	39% 3 10% 23% 20% 4	2730
	21st to end	Night	38% 6% 12% 28% 14% 1	2851
December	1st to 10th	Night	38% 5% 13% 30% 11% 2	4720
	11th to 20th	Night	46% 4 11% 21% 15% 3	5348
	21st to end	Night	47% 6% 10% 18% 16% 4	7150

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	30% 27% 29% 12% 1	202
	11th to 20th	Day	33% 30% 29% 7% 2	200
	21st to end	Day	24% 29% 32% 10% 3 1	305
February	1st to 10th	Day	30% 29% 32% 9% 1	300
	11th to 20th	Day	31% 24% 35% 9% 1	475
	21st to end	Day	31% 23% 32% 12% 2	414
March	1st to 10th	Day	28% 23% 32% 14% 3	500
	11th to 20th	Day	26% 23% 34% 13% 3 1	500
	21st to end	Day	31% 24% 28% 13% 4 1	550
April	1st to 10th	Day	31% 24% 28% 13% 5%	500
	11th to 20th	Day	26% 22% 33% 12% 6% 1	492
	21st to end	Day	30% 20% 30% 15% 3 2	500
May	1st to 10th	Day	35% 19% 27% 13% 5% 1	503
	11th to 20th	Day	24% 18% 32% 18% 7% 1	527
	21st to end	Day	22% 11% 29% 25% 10% 2	573
June	1st to 10th	Day	20% 13% 32% 24% 11% 1	530
	11th to 20th	Day	21% 15% 29% 24% 11% 1	530
	21st to end	Day	15% 13% 33% 27% 11% 1	530
July	1st to 10th	Day	15% 6% 29% 30% 16% 4	525
	11th to 20th	Day	12% 6% 27% 35% 17% 2	524
	21st to end	Day	14% 9% 32% 29% 13% 2	576
August	1st to 10th	Day	16% 7% 27% 29% 15% 6%	526
	11th to 20th	Day	15% 6% 25% 32% 17% 5%	519
	21st to end	Day	13% 9% 31% 26% 14% 6%	583
September	1st to 10th	Day	18% 13% 25% 25% 13% 6%	530
	11th to 20th	Day	16% 7% 29% 23% 15% 10%	530
	21st to end	Day	22% 13% 30% 21% 10% 4	530
October	1st to 10th	Day	24% 10% 29% 20% 12% 5%	530
	11th to 20th	Day	20% 19% 31% 20% 10% 1	530
	21st to end	Day	26% 17% 30% 18% 8% 1	506
November	1st to 10th	Day	21% 16% 31% 22% 8% 2	425
	11th to 20th	Day	26% 21% 30% 18% 3	430
	21st to end	Day	26% 25% 31% 14% 4	304
December	1st to 10th	Day	29% 26% 28% 12% 5%	220
	11th to 20th	Day	36% 22% 28% 10% 3	220
	21st to end	Day	30% 19% 34% 12% 4	242
January	1st to 10th	Night	21% 23% 38% 16% 3	805
	11th to 20th	Night	26% 19% 32% 21% 3	800
	21st to end	Night	21% 20% 39% 18% 2	880
February	1st to 10th	Night	23% 18% 37% 20% 2	800
	11th to 20th	Night	25% 22% 39% 13% 1	783
	21st to end	Night	26% 20% 34% 17% 3	660
March	1st to 10th	Night	24% 20% 35% 17% 4	800
	11th to 20th	Night	23% 22% 33% 18% 3 1	800
	21st to end	Night	23% 19% 37% 16% 4 1	880
April	1st to 10th	Night	25% 19% 36% 16% 4	800
	11th to 20th	Night	23% 17% 35% 20% 4	791
	21st to end	Night	23% 15% 33% 24% 5%	795
May	1st to 10th	Night	28% 14% 35% 18% 6%	596
	11th to 20th	Night	21% 13% 35% 24% 7%	394
	21st to end	Night	19% 7% 26% 34% 12% 1	433
June	1st to 10th	Night	18% 6% 30% 34% 12% 1	400
	11th to 20th	Night	16% 7% 31% 35% 11%	400
	21st to end	Night	13% 6% 26% 44% 11%	400
July	1st to 10th	Night	11% 6% 26% 37% 20% 1	390
	11th to 20th	Night	13% 4 23% 41% 18% 1	388
	21st to end	Night	13% 4 25% 43% 14% 1	438
August	1st to 10th	Night	12% 2 21% 41% 21% 2	527
	11th to 20th	Night	14% 4 22% 36% 23% 2	785
	21st to end	Night	16% 5% 21% 38% 18% 2	880
September	1st to 10th	Night	18% 4 25% 34% 17% 2	800
	11th to 20th	Night	16% 6% 22% 34% 19% 4	800
	21st to end	Night	21% 6% 25% 33% 13% 2	800
October	1st to 10th	Night	22% 8% 29% 24% 16% 2	800
	11th to 20th	Night	20% 15% 28% 29% 9% 1	800
	21st to end	Night	24% 13% 35% 21% 7%	880
November	1st to 10th	Night	18% 13% 32% 26% 9% 1	820
	11th to 20th	Night	24% 17% 31% 22% 6%	840
	21st to end	Night	19% 19% 34% 22% 5%	840
December	1st to 10th	Night	24% 18% 33% 21% 4 1	840
	11th to 20th	Night	25% 16% 35% 22% 3	840
	21st to end	Night	25% 17% 35% 20% 3	924

Page generated at 2025-12-30 01:14:06. Version ac07

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