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 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	17% 7% 2 6% 5% 4 4 4 5% 7% 38%	101524
	Night	17% 7% 2 6% 4 4 4 3 5% 7% 41%	97952
Transparency	Day	42% 7% 12% 22% 15% 2	105056
	Night	41% 7% 12% 23% 16% 2	102496
Seeing	Day	22% 16% 30% 20% 9% 2	15014
	Night	21% 14% 32% 25% 8% 1	24186

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% 7% 3 6% 4 4 4 3 5% 4 46%	2517
	11th to 20th	Day	15% 9% 3 8% 7% 6% 5% 3 4 5% 35%	2520
	21st to end	Day	21% 11% 5% 7% 4 4 3 3 4 5% 32%	3037
February	1st to 10th	Day	17% 8% 3 6% 5% 4 4 4 5% 6% 37%	1710
	11th to 20th	Day	13% 8% 3 7% 5% 4 4 4 4 6% 42%	1828
	21st to end	Day	19% 10% 2 7% 4 4 3 4 5% 5% 38%	1570
March	1st to 10th	Day	26% 9% 3 6% 4 4 3 2 4 5% 35%	3116
	11th to 20th	Day	9% 5% 2 5% 5% 5% 6% 4 7% 8% 43%	3379
	21st to end	Day	21% 8% 2 5% 4 3 3 3 4 6% 42%	4102
April	1st to 10th	Day	18% 9% 3 6% 5% 3 5% 3 5% 7% 38%	2280
	11th to 20th	Day	17% 7% 2 7% 5% 4 4 4 4 7% 40%	2254
	21st to end	Day	19% 7% 2 6% 5% 4 4 4 6% 6% 38%	2285
May	1st to 10th	Day	29% 8% 3 5% 3 4 4 3 5% 7% 30%	4138
	11th to 20th	Day	23% 8% 3 8% 5% 4 5% 4 5% 6% 29%	4398
	21st to end	Day	14% 5% 2 5% 4 4 4 4 6% 9% 44%	4837
June	1st to 10th	Day	16% 6% 2 6% 5% 5% 5% 4 7% 8% 36%	2660
	11th to 20th	Day	16% 6% 2 6% 5% 5% 6% 5% 6% 9% 34%	2660
	21st to end	Day	12% 7% 2 6% 5% 5% 5% 5% 6% 8% 39%	2660
July	1st to 10th	Day	10% 6% 2 8% 6% 6% 6% 4 6% 10% 35%	4440
	11th to 20th	Day	11% 6% 3 5% 5% 5% 6% 5% 7% 10% 38%	4440
	21st to end	Day	16% 8% 3 7% 6% 5% 6% 4 6% 7% 32%	4814
August	1st to 10th	Day	22% 6% 2 7% 5% 5% 5% 4 6% 8% 31%	4182
	11th to 20th	Day	13% 6% 2 6% 4 4 4 4 6% 8% 42%	3730
	21st to end	Day	13% 6% 2 5% 3 3 4 3 5% 9% 47%	4180
September	1st to 10th	Day	16% 5% 2 6% 4 4 5% 5% 5% 6% 42%	2280
	11th to 20th	Day	14% 5% 2 5% 3 3 3 3 5% 7% 50%	2217
	21st to end	Day	19% 6% 3 7% 4 4 4 4 4 6% 39%	2090
October	1st to 10th	Day	19% 7% 2 5% 4 4 4 4 5% 6% 41%	1952
	11th to 20th	Day	15% 6% 2 5% 4 3 5% 3 5% 7% 47%	1900
	21st to end	Day	20% 5% 2 5% 3 3 4 4 5% 6% 42%	1957
November	1st to 10th	Day	14% 6% 2 5% 3 3 3 2 3 6% 52%	1761
	11th to 20th	Day	18% 6% 1 4 3 3 4 3 5% 7% 45%	1800
	21st to end	Day	16% 7% 2 4 4 4 4 5% 4 7% 42%	1632
December	1st to 10th	Day	20% 8% 3 6% 5% 3 3 4 5% 6% 37%	1520
	11th to 20th	Day	21% 6% 2 4 3 4 4 3 5% 6% 41%	1906
	21st to end	Day	18% 9% 3 9% 6% 5% 5% 3 6% 7% 28%	2772
January	1st to 10th	Night	16% 7% 2 4 3 4 3 3 5% 6% 45%	4429
	11th to 20th	Night	15% 8% 3 8% 5% 4 4 3 4 6% 40%	4440
	21st to end	Night	24% 11% 2 5% 4 4 4 2 5% 6% 34%	4614
February	1st to 10th	Night	17% 9% 3 5% 5% 4 3 3 5% 6% 41%	2470
	11th to 20th	Night	16% 8% 3 6% 4 4 4 4 5% 6% 41%	2237
	21st to end	Night	19% 8% 3 6% 4 4 4 3 4 6% 41%	1884
March	1st to 10th	Night	23% 10% 3 6% 5% 3 3 2 4 5% 36%	3724
	11th to 20th	Night	11% 6% 3 5% 4 4 4 3 5% 7% 48%	3576
	21st to end	Night	18% 9% 3 6% 3 3 3 3 4 5% 43%	3530
April	1st to 10th	Night	18% 8% 2 6% 4 4 5% 4 6% 6% 37%	1900
	11th to 20th	Night	18% 7% 2 6% 4 4 4 3 5% 7% 39%	1875
	21st to end	Night	20% 6% 2 5% 4 3 3 3 5% 6% 41%	1895
May	1st to 10th	Night	26% 9% 3 7% 4 4 5% 3 5% 6% 29%	2817
	11th to 20th	Night	24% 10% 4 7% 4 4 4 2 4 6% 32%	2495
	21st to end	Night	15% 6% 2 6% 4 4 4 3 5% 9% 42%	2738
June	1st to 10th	Night	17% 5% 2 5% 4 5% 4 3 5% 8% 43%	1520
	11th to 20th	Night	13% 7% 2 5% 5% 4 4 4 6% 9% 41%	1520
	21st to end	Night	12% 4 2 5% 5% 4 5% 4 7% 8% 44%	1520
July	1st to 10th	Night	10% 5% 2 6% 4 5% 6% 5% 6% 9% 41%	2520
	11th to 20th	Night	14% 5% 2 6% 4 4 5% 5% 7% 10% 38%	2520
	21st to end	Night	18% 7% 2 6% 4 4 5% 5% 6% 8% 37%	2739
August	1st to 10th	Night	22% 5% 3 6% 5% 4 5% 4 6% 8% 33%	2719
	11th to 20th	Night	15% 6% 3 7% 5% 4 4 4 5% 7% 40%	3092
	21st to end	Night	11% 4 2 5% 3 3 4 3 4 7% 52%	3476
September	1st to 10th	Night	15% 6% 2 7% 4 4 4 4 4 7% 45%	1900
	11th to 20th	Night	13% 5% 2 4 3 3 3 2 5% 6% 53%	1962
	21st to end	Night	19% 6% 2 6% 3 3 4 3 4 7% 44%	2090
October	1st to 10th	Night	20% 6% 3 6% 4 3 3 3 4 6% 42%	2223
	11th to 20th	Night	16% 6% 2 5% 3 2 3 3 4 6% 50%	2280
	21st to end	Night	20% 8% 2 4 3 2 3 3 4 5% 45%	2640
November	1st to 10th	Night	12% 6% 2 4 3 3 4 3 5% 6% 51%	2537
	11th to 20th	Night	19% 7% 2 4 3 3 3 3 4 5% 47%	2600
	21st to end	Night	15% 5% 2 5% 4 4 4 4 6% 7% 44%	2638
December	1st to 10th	Night	18% 7% 2 6% 5% 4 4 3 5% 7% 38%	2660
	11th to 20th	Night	18% 8% 2 5% 4 3 4 3 5% 7% 40%	3288
	21st to end	Night	19% 10% 3 7% 4 4 4 3 4 6% 35%	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	38% 6% 12% 31% 11% 2	2518
	11th to 20th	Day	49% 6% 11% 21% 11% 2	2520
	21st to end	Day	54% 6% 9% 20% 10% 1	3037
February	1st to 10th	Day	46% 6% 12% 22% 12% 1	1710
	11th to 20th	Day	42% 6% 10% 22% 17% 3	1837
	21st to end	Day	48% 5% 10% 21% 13% 3	1570
March	1st to 10th	Day	52% 4 10% 23% 9% 2	3119
	11th to 20th	Day	34% 8% 14% 29% 13% 2	3379
	21st to end	Day	44% 4 9% 15% 23% 5%	4102
April	1st to 10th	Day	45% 6% 9% 19% 15% 4	2280
	11th to 20th	Day	43% 6% 12% 20% 17% 3	2254
	21st to end	Day	43% 6% 10% 20% 16% 4	2285
May	1st to 10th	Day	53% 7% 12% 15% 11% 2	4152
	11th to 20th	Day	53% 9% 11% 18% 8% 2	4402
	21st to end	Day	35% 8% 12% 25% 18% 2	4837
June	1st to 10th	Day	42% 9% 14% 19% 15% 1	2660
	11th to 20th	Day	44% 9% 13% 22% 10% 2	2660
	21st to end	Day	41% 8% 13% 22% 15% 1	2660
July	1st to 10th	Day	43% 9% 12% 21% 13% 2	4370
	11th to 20th	Day	38% 9% 16% 22% 13% 1	4365
	21st to end	Day	49% 8% 10% 16% 16% 2	4661
August	1st to 10th	Day	49% 8% 13% 20% 9%	4168
	11th to 20th	Day	38% 7% 14% 28% 13% 1	3766
	21st to end	Day	35% 6% 9% 28% 20% 2	4180
September	1st to 10th	Day	40% 8% 10% 21% 19% 2	2280
	11th to 20th	Day	35% 6% 10% 22% 25% 3	2217
	21st to end	Day	46% 6% 10% 18% 18% 3	2090
October	1st to 10th	Day	38% 6% 8% 18% 23% 6%	3238
	11th to 20th	Day	27% 5% 10% 25% 29% 5%	3140
	21st to end	Day	27% 4 15% 24% 26% 4	3208
November	1st to 10th	Day	35% 5% 12% 24% 22% 3	1761
	11th to 20th	Day	38% 5% 11% 23% 20% 3	1800
	21st to end	Day	40% 5% 13% 28% 11% 2	1632
December	1st to 10th	Day	46% 6% 15% 19% 13% 1	1520
	11th to 20th	Day	42% 5% 16% 23% 11% 2	1906
	21st to end	Day	52% 7% 12% 21% 8%	2772
January	1st to 10th	Night	39% 5% 12% 29% 11% 4	4429
	11th to 20th	Night	45% 6% 12% 24% 12% 2	4440
	21st to end	Night	51% 5% 9% 21% 12% 1	4614
February	1st to 10th	Night	44% 6% 13% 23% 12% 2	2470
	11th to 20th	Night	44% 5% 11% 19% 17% 5%	2239
	21st to end	Night	45% 4 8% 24% 16% 3	1884
March	1st to 10th	Night	50% 5% 10% 21% 11% 3	3734
	11th to 20th	Night	35% 7% 15% 26% 16% 2	3577
	21st to end	Night	43% 5% 8% 16% 21% 6%	3530
April	1st to 10th	Night	45% 6% 12% 19% 14% 3	1900
	11th to 20th	Night	43% 7% 9% 20% 19% 2	1875
	21st to end	Night	43% 6% 10% 21% 17% 4	1895
May	1st to 10th	Night	53% 8% 11% 17% 10% 1	2823
	11th to 20th	Night	52% 8% 14% 14% 10% 1	2496
	21st to end	Night	37% 10% 14% 24% 12% 3	2739
June	1st to 10th	Night	40% 6% 12% 22% 19% 1	1520
	11th to 20th	Night	38% 9% 14% 25% 12% 1	1520
	21st to end	Night	34% 10% 15% 25% 15% 1	1520
July	1st to 10th	Night	37% 11% 16% 19% 15% 2	2480
	11th to 20th	Night	40% 9% 14% 24% 13% 1	2472
	21st to end	Night	42% 8% 15% 15% 18% 2	2651
August	1st to 10th	Night	48% 9% 16% 17% 9% 1	2709
	11th to 20th	Night	42% 9% 12% 27% 10% 1	3122
	21st to end	Night	32% 7% 10% 32% 19% 1	3476
September	1st to 10th	Night	40% 6% 10% 24% 19% 1	1900
	11th to 20th	Night	33% 6% 10% 23% 25% 3	1962
	21st to end	Night	42% 4 9% 21% 22% 1	2090
October	1st to 10th	Night	40% 5% 10% 22% 21% 2	3704
	11th to 20th	Night	25% 5% 9% 28% 29% 4	3779
	21st to end	Night	30% 4 13% 31% 19% 3	4339
November	1st to 10th	Night	33% 6% 12% 23% 22% 4	2537
	11th to 20th	Night	40% 3 10% 23% 20% 4	2600
	21st to end	Night	38% 6% 13% 28% 13% 1	2638
December	1st to 10th	Night	44% 6% 13% 22% 12% 1	2660
	11th to 20th	Night	43% 6% 13% 19% 15% 3	3288
	21st to end	Night	48% 8% 12% 21% 11%	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	28% 27% 29% 14% 2	180
	11th to 20th	Day	33% 28% 30% 7% 2	180
	21st to end	Day	24% 27% 33% 12% 3 1	274
February	1st to 10th	Day	29% 28% 33% 9% 1	270
	11th to 20th	Day	28% 25% 37% 9% 1	436
	21st to end	Day	31% 23% 31% 12% 3	382
March	1st to 10th	Day	28% 23% 32% 15% 3	460
	11th to 20th	Day	26% 24% 32% 13% 3 1	460
	21st to end	Day	30% 23% 28% 14% 4 1	506
April	1st to 10th	Day	29% 24% 29% 13% 5%	460
	11th to 20th	Day	25% 22% 33% 13% 6% 1	452
	21st to end	Day	30% 20% 30% 15% 3 2	460
May	1st to 10th	Day	34% 18% 27% 14% 5% 2	463
	11th to 20th	Day	23% 17% 33% 19% 8% 1	487
	21st to end	Day	20% 11% 29% 27% 11% 2	529
June	1st to 10th	Day	19% 13% 33% 23% 11% 1	490
	11th to 20th	Day	19% 14% 30% 25% 12% 1	490
	21st to end	Day	14% 13% 34% 26% 11% 1	490
July	1st to 10th	Day	16% 6% 28% 30% 16% 5%	485
	11th to 20th	Day	12% 5% 28% 35% 18% 2	484
	21st to end	Day	14% 9% 32% 28% 14% 2	532
August	1st to 10th	Day	16% 7% 26% 29% 15% 6%	486
	11th to 20th	Day	15% 6% 25% 31% 18% 4	479
	21st to end	Day	14% 9% 29% 27% 14% 6%	539
September	1st to 10th	Day	18% 12% 24% 25% 14% 6%	490
	11th to 20th	Day	16% 7% 29% 22% 15% 10%	490
	21st to end	Day	22% 13% 30% 20% 10% 4	490
October	1st to 10th	Day	25% 10% 29% 20% 12% 4	490
	11th to 20th	Day	18% 18% 31% 21% 10% 1	490
	21st to end	Day	25% 17% 30% 19% 8% 1	469
November	1st to 10th	Day	20% 15% 32% 22% 9% 2	395
	11th to 20th	Day	26% 21% 32% 18% 4 1	400
	21st to end	Day	24% 22% 33% 16% 4	268
December	1st to 10th	Day	27% 27% 27% 12% 7%	180
	11th to 20th	Day	36% 22% 29% 11% 3	180
	21st to end	Day	29% 20% 34% 12% 5%	198
January	1st to 10th	Night	20% 22% 38% 16% 3	760
	11th to 20th	Night	26% 19% 32% 21% 3	760
	21st to end	Night	21% 20% 38% 18% 2	836
February	1st to 10th	Night	22% 18% 38% 20% 2	760
	11th to 20th	Night	23% 23% 40% 13% 1	743
	21st to end	Night	27% 20% 33% 18% 3	628
March	1st to 10th	Night	24% 20% 35% 17% 4	760
	11th to 20th	Night	22% 23% 33% 18% 3 1	760
	21st to end	Night	23% 19% 37% 16% 5% 1	836
April	1st to 10th	Night	24% 19% 37% 16% 4	760
	11th to 20th	Night	23% 17% 35% 21% 4	751
	21st to end	Night	24% 15% 33% 24% 5%	755
May	1st to 10th	Night	27% 13% 35% 18% 6%	566
	11th to 20th	Night	20% 13% 37% 24% 7%	374
	21st to end	Night	18% 7% 25% 36% 13% 1	411
June	1st to 10th	Night	18% 6% 29% 34% 12% 1	380
	11th to 20th	Night	14% 7% 32% 36% 11%	380
	21st to end	Night	12% 6% 26% 45% 10%	380
July	1st to 10th	Night	11% 6% 26% 37% 19% 1	370
	11th to 20th	Night	13% 4 24% 42% 17% 1	368
	21st to end	Night	14% 4 24% 43% 14% 1	416
August	1st to 10th	Night	12% 2 22% 41% 20% 2	500
	11th to 20th	Night	14% 3 23% 36% 22% 2	745
	21st to end	Night	15% 4 21% 39% 19% 2	836
September	1st to 10th	Night	18% 4 25% 34% 17% 2	760
	11th to 20th	Night	16% 6% 23% 32% 19% 4	760
	21st to end	Night	21% 6% 26% 33% 12% 2	760
October	1st to 10th	Night	23% 8% 29% 24% 14% 2	760
	11th to 20th	Night	20% 14% 28% 29% 8% 1	760
	21st to end	Night	24% 13% 34% 21% 8%	836
November	1st to 10th	Night	17% 13% 32% 26% 10% 1	780
	11th to 20th	Night	24% 15% 31% 23% 7% 1	800
	21st to end	Night	18% 19% 35% 22% 6% 1	779
December	1st to 10th	Night	25% 17% 33% 21% 4 1	760
	11th to 20th	Night	22% 16% 36% 22% 3	760
	21st to end	Night	24% 17% 36% 20% 3	836

Page generated at 2024-11-22 08:02:28. Version ac07

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