Nutter Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Nutter Observatory 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	16% 11% 4 8% 5% 5% 5% 4 6% 7% 30%	101691
	Night	16% 11% 4 9% 5% 4 4 3 5% 6% 31%	97908
Transparency	Day	51% 7% 12% 20% 10% 1	105240
	Night	51% 7% 13% 19% 10% 1	102448
Seeing	Day	25% 17% 28% 18% 9% 3	14834
	Night	23% 15% 28% 24% 9% 1	24083

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% 18% 11% 12% 5% 4 3 3 4 4 23%	2517
	11th to 20th	Day	13% 16% 8% 17% 7% 5% 5% 3 4 4 18%	2524
	21st to end	Day	17% 17% 10% 12% 8% 5% 4 3 4 4 17%	3124
February	1st to 10th	Day	16% 15% 6% 13% 7% 5% 4 5% 4 5% 20%	1710
	11th to 20th	Day	13% 13% 7% 13% 7% 4 6% 4 5% 5% 23%	1724
	21st to end	Day	18% 14% 3 13% 8% 3 4 3 5% 5% 25%	1570
March	1st to 10th	Day	22% 16% 5% 11% 4 3 3 3 3 4 25%	3175
	11th to 20th	Day	10% 17% 5% 10% 6% 5% 4 3 4 5% 30%	3480
	21st to end	Day	18% 12% 4 9% 6% 4 4 3 5% 5% 31%	3997
April	1st to 10th	Day	17% 15% 3 8% 4 4 4 3 4 6% 31%	2280
	11th to 20th	Day	16% 11% 3 8% 5% 4 4 4 5% 5% 33%	2254
	21st to end	Day	18% 12% 4 7% 5% 4 4 3 4 6% 33%	2280
May	1st to 10th	Day	25% 10% 2 6% 4 3 4 4 5% 6% 30%	4307
	11th to 20th	Day	20% 9% 4 8% 7% 6% 5% 4 6% 8% 25%	4398
	21st to end	Day	13% 6% 2 6% 5% 5% 5% 4 7% 9% 40%	4837
June	1st to 10th	Day	17% 7% 2 7% 6% 5% 5% 4 7% 8% 32%	2660
	11th to 20th	Day	15% 7% 2 7% 5% 5% 5% 5% 7% 9% 33%	2660
	21st to end	Day	14% 7% 2 6% 5% 5% 5% 5% 8% 8% 35%	2660
July	1st to 10th	Day	9% 6% 2 7% 5% 5% 6% 5% 8% 11% 34%	4440
	11th to 20th	Day	8% 6% 3 7% 6% 6% 6% 5% 8% 10% 35%	4440
	21st to end	Day	13% 6% 3 7% 6% 5% 6% 6% 7% 8% 33%	4795
August	1st to 10th	Day	20% 8% 3 7% 4 4 5% 4 6% 8% 30%	4104
	11th to 20th	Day	16% 7% 3 7% 5% 5% 5% 4 7% 9% 31%	3871
	21st to end	Day	15% 8% 3 6% 4 4 5% 3 6% 7% 39%	4180
September	1st to 10th	Day	16% 7% 2 7% 5% 4 4 3 5% 7% 39%	2280
	11th to 20th	Day	13% 8% 2 6% 4 5% 3 3 5% 7% 44%	2280
	21st to end	Day	19% 8% 2 7% 5% 4 5% 4 5% 6% 34%	2033
October	1st to 10th	Day	16% 9% 3 8% 5% 4 4 4 5% 8% 34%	1900
	11th to 20th	Day	16% 11% 3 6% 6% 5% 4 4 5% 6% 33%	1900
	21st to end	Day	21% 14% 3 8% 5% 4 3 3 5% 6% 27%	2019
November	1st to 10th	Day	13% 11% 3 8% 4 4 4 3 5% 7% 38%	1761
	11th to 20th	Day	15% 16% 4 9% 5% 4 5% 3 4 5% 31%	1735
	21st to end	Day	18% 15% 5% 9% 5% 5% 4 4 5% 5% 25%	1598
December	1st to 10th	Day	17% 17% 6% 11% 6% 6% 4 4 4 5% 19%	1520
	11th to 20th	Day	20% 15% 9% 10% 4 3 3 2 4 5% 25%	1906
	21st to end	Day	21% 20% 8% 11% 5% 5% 4 2 4 4 15%	2772
January	1st to 10th	Night	15% 14% 8% 14% 5% 5% 4 3 5% 6% 21%	4429
	11th to 20th	Night	12% 15% 7% 15% 8% 6% 4 3 4 5% 21%	4431
	21st to end	Night	20% 17% 6% 14% 10% 5% 4 3 3 4 16%	4532
February	1st to 10th	Night	14% 13% 5% 11% 6% 6% 6% 3 5% 6% 24%	2470
	11th to 20th	Night	13% 13% 6% 14% 8% 5% 6% 4 5% 5% 21%	2342
	21st to end	Night	18% 12% 3 12% 6% 4 5% 3 5% 6% 26%	1884
March	1st to 10th	Night	20% 15% 6% 9% 4 4 3 3 4 4 28%	3662
	11th to 20th	Night	12% 16% 6% 10% 6% 4 4 3 4 6% 29%	3479
	21st to end	Night	14% 14% 3 9% 5% 5% 4 4 4 5% 33%	3634
April	1st to 10th	Night	17% 14% 4 8% 5% 4 5% 3 4 6% 30%	1900
	11th to 20th	Night	20% 11% 3 7% 4 4 3 3 4 7% 34%	1875
	21st to end	Night	17% 9% 3 7% 4 5% 4 2 4 6% 37%	1900
May	1st to 10th	Night	25% 9% 3 6% 5% 4 3 3 4 5% 32%	2658
	11th to 20th	Night	18% 9% 4 8% 5% 4 5% 4 6% 7% 32%	2495
	21st to end	Night	10% 9% 3 7% 5% 4 5% 4 6% 8% 38%	2738
June	1st to 10th	Night	16% 8% 2 6% 5% 4 3 3 6% 9% 38%	1520
	11th to 20th	Night	14% 7% 2 5% 5% 4 5% 3 6% 9% 40%	1520
	21st to end	Night	13% 5% 2 5% 5% 4 5% 4 5% 8% 43%	1520
July	1st to 10th	Night	9% 7% 3 8% 6% 5% 5% 4 7% 8% 39%	2520
	11th to 20th	Night	10% 5% 2 6% 4 4 5% 4 7% 10% 42%	2520
	21st to end	Night	14% 8% 3 7% 4 5% 5% 4 5% 7% 39%	2755
August	1st to 10th	Night	20% 7% 3 7% 5% 5% 4 4 5% 7% 34%	2825
	11th to 20th	Night	16% 8% 3 7% 5% 4 4 3 4 6% 41%	2912
	21st to end	Night	13% 8% 2 5% 4 4 4 3 6% 7% 44%	3476
September	1st to 10th	Night	14% 6% 3 6% 4 4 4 4 5% 7% 44%	1900
	11th to 20th	Night	13% 6% 2 4 4 3 4 3 5% 6% 51%	1900
	21st to end	Night	18% 7% 3 6% 4 5% 4 4 5% 7% 38%	2142
October	1st to 10th	Night	16% 9% 3 7% 5% 4 5% 4 5% 6% 37%	2280
	11th to 20th	Night	18% 8% 3 6% 5% 3 4 4 5% 7% 38%	2280
	21st to end	Night	22% 13% 3 7% 4 5% 4 2 4 6% 30%	2579
November	1st to 10th	Night	12% 12% 3 7% 5% 4 4 3 5% 7% 39%	2537
	11th to 20th	Night	17% 12% 3 7% 4 4 5% 4 5% 5% 33%	2663
	21st to end	Night	14% 13% 4 9% 5% 5% 5% 4 6% 7% 27%	2798
December	1st to 10th	Night	16% 16% 7% 10% 6% 5% 4 4 5% 6% 21%	2660
	11th to 20th	Night	18% 15% 5% 10% 6% 4 5% 4 5% 5% 24%	3288
	21st to end	Night	24% 15% 7% 10% 5% 4 4 3 4 5% 18%	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	62% 4 14% 15% 4 1	2518
	11th to 20th	Day	68% 6% 8% 12% 5% 1	2524
	21st to end	Day	70% 5% 10% 11% 4	3124
February	1st to 10th	Day	64% 7% 10% 13% 6% 1	1710
	11th to 20th	Day	60% 7% 8% 18% 7%	1733
	21st to end	Day	60% 5% 10% 16% 7% 1	1570
March	1st to 10th	Day	62% 5% 9% 16% 6% 1	3178
	11th to 20th	Day	53% 8% 12% 18% 8% 1	3480
	21st to end	Day	54% 6% 8% 17% 14% 2	3997
April	1st to 10th	Day	54% 6% 8% 22% 9% 2	2280
	11th to 20th	Day	50% 6% 11% 18% 13% 2	2254
	21st to end	Day	51% 5% 9% 19% 12% 3	2280
May	1st to 10th	Day	53% 6% 10% 19% 10% 2	4321
	11th to 20th	Day	55% 8% 11% 18% 6% 1	4402
	21st to end	Day	38% 9% 14% 24% 15% 1	4837
June	1st to 10th	Day	47% 9% 12% 19% 13%	2660
	11th to 20th	Day	45% 9% 13% 21% 10% 1	2660
	21st to end	Day	43% 9% 14% 24% 10% 1	2660
July	1st to 10th	Day	40% 9% 17% 23% 10% 1	4370
	11th to 20th	Day	39% 9% 17% 24% 10%	4365
	21st to end	Day	46% 8% 15% 19% 11% 1	4642
August	1st to 10th	Day	52% 8% 14% 18% 9%	4091
	11th to 20th	Day	45% 9% 15% 24% 6%	3910
	21st to end	Day	42% 6% 11% 33% 8% 1	4180
September	1st to 10th	Day	44% 7% 12% 24% 12% 1	2280
	11th to 20th	Day	39% 6% 12% 22% 20% 1	2280
	21st to end	Day	48% 6% 12% 20% 12% 1	2033
October	1st to 10th	Day	45% 8% 10% 22% 14% 1	3160
	11th to 20th	Day	44% 6% 10% 23% 15% 3	3140
	21st to end	Day	40% 5% 17% 26% 12% 1	3309
November	1st to 10th	Day	45% 6% 14% 20% 13% 2	1761
	11th to 20th	Day	53% 6% 12% 18% 9% 2	1735
	21st to end	Day	58% 7% 14% 15% 5% 1	1598
December	1st to 10th	Day	66% 5% 13% 10% 5%	1520
	11th to 20th	Day	63% 4 15% 13% 4	1906
	21st to end	Day	72% 6% 8% 10% 3	2772
January	1st to 10th	Night	60% 7% 15% 13% 5% 1	4429
	11th to 20th	Night	63% 7% 12% 13% 4	4431
	21st to end	Night	73% 4 7% 12% 4	4532
February	1st to 10th	Night	59% 6% 13% 15% 7%	2470
	11th to 20th	Night	61% 6% 12% 14% 6% 1	2344
	21st to end	Night	57% 5% 12% 17% 9% 1	1884
March	1st to 10th	Night	60% 5% 10% 17% 8%	3672
	11th to 20th	Night	55% 8% 13% 18% 6%	3480
	21st to end	Night	50% 7% 9% 20% 12% 2	3634
April	1st to 10th	Night	56% 6% 9% 17% 10% 2	1900
	11th to 20th	Night	49% 6% 11% 19% 15% 1	1875
	21st to end	Night	48% 5% 10% 20% 13% 3	1900
May	1st to 10th	Night	54% 5% 9% 21% 9% 2	2664
	11th to 20th	Night	50% 8% 16% 17% 8% 1	2496
	21st to end	Night	40% 11% 14% 19% 15% 1	2739
June	1st to 10th	Night	41% 7% 14% 23% 14% 1	1520
	11th to 20th	Night	39% 9% 15% 25% 10% 1	1520
	21st to end	Night	37% 8% 15% 27% 13% 1	1520
July	1st to 10th	Night	41% 8% 16% 19% 15% 1	2480
	11th to 20th	Night	35% 8% 18% 25% 14%	2472
	21st to end	Night	43% 7% 13% 20% 16% 1	2667
August	1st to 10th	Night	50% 7% 16% 20% 7%	2814
	11th to 20th	Night	44% 6% 15% 25% 10%	2939
	21st to end	Night	38% 7% 13% 31% 11% 1	3476
September	1st to 10th	Night	40% 7% 13% 24% 14% 1	1900
	11th to 20th	Night	34% 6% 12% 28% 19% 1	1900
	21st to end	Night	44% 6% 12% 22% 15% 1	2142
October	1st to 10th	Night	50% 7% 10% 21% 11% 1	3800
	11th to 20th	Night	39% 5% 14% 21% 15% 6%	3779
	21st to end	Night	41% 5% 17% 25% 11% 1	4239
November	1st to 10th	Night	43% 7% 14% 20% 15% 2	2537
	11th to 20th	Night	50% 6% 12% 18% 10% 2	2663
	21st to end	Night	52% 8% 16% 18% 6%	2798
December	1st to 10th	Night	62% 7% 14% 14% 4	2660
	11th to 20th	Night	60% 7% 13% 16% 5%	3288
	21st to end	Night	66% 7% 11% 13% 2	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% 27% 31% 9% 4 1	180
	11th to 20th	Day	41% 26% 25% 5% 2 1	182
	21st to end	Day	28% 28% 30% 11% 2	297
February	1st to 10th	Day	34% 30% 29% 7%	270
	11th to 20th	Day	37% 29% 29% 5%	331
	21st to end	Day	37% 22% 29% 10% 2	382
March	1st to 10th	Day	34% 20% 31% 12% 4	460
	11th to 20th	Day	37% 20% 27% 12% 3 1	460
	21st to end	Day	34% 25% 25% 10% 3 2	506
April	1st to 10th	Day	34% 23% 27% 12% 4	460
	11th to 20th	Day	30% 24% 26% 11% 6% 3	452
	21st to end	Day	30% 23% 28% 12% 6% 1	460
May	1st to 10th	Day	33% 17% 28% 11% 9% 2	463
	11th to 20th	Day	22% 16% 32% 18% 8% 3	487
	21st to end	Day	20% 11% 31% 21% 12% 4	529
June	1st to 10th	Day	20% 16% 31% 19% 12% 1	490
	11th to 20th	Day	18% 13% 27% 28% 12% 1	490
	21st to end	Day	19% 14% 33% 23% 8% 3	490
July	1st to 10th	Day	13% 8% 31% 28% 14% 6%	485
	11th to 20th	Day	12% 8% 27% 31% 18% 4	484
	21st to end	Day	15% 9% 36% 26% 12% 3	532
August	1st to 10th	Day	15% 10% 27% 22% 19% 6%	486
	11th to 20th	Day	18% 8% 24% 29% 14% 8%	479
	21st to end	Day	13% 11% 26% 27% 13% 10%	539
September	1st to 10th	Day	18% 12% 25% 20% 17% 7%	490
	11th to 20th	Day	14% 9% 25% 22% 19% 10%	490
	21st to end	Day	23% 13% 29% 20% 10% 5%	490
October	1st to 10th	Day	25% 13% 24% 20% 13% 4	490
	11th to 20th	Day	23% 20% 28% 20% 7% 2	490
	21st to end	Day	32% 17% 28% 16% 7%	502
November	1st to 10th	Day	27% 17% 25% 21% 9% 2	395
	11th to 20th	Day	30% 23% 25% 15% 7%	335
	21st to end	Day	39% 20% 33% 7% 1 1	200
December	1st to 10th	Day	35% 21% 32% 8% 3 1	180
	11th to 20th	Day	36% 24% 26% 13% 1	180
	21st to end	Day	34% 28% 27% 11% 1	198
January	1st to 10th	Night	25% 25% 32% 15% 2	760
	11th to 20th	Night	27% 20% 29% 21% 3	760
	21st to end	Night	20% 24% 36% 17% 2	836
February	1st to 10th	Night	28% 20% 33% 17% 1	760
	11th to 20th	Night	27% 24% 36% 13% 1	743
	21st to end	Night	35% 18% 32% 14% 2	628
March	1st to 10th	Night	28% 23% 28% 18% 3	760
	11th to 20th	Night	28% 22% 30% 17% 4	760
	21st to end	Night	26% 21% 30% 17% 5% 1	836
April	1st to 10th	Night	28% 21% 31% 18% 3	760
	11th to 20th	Night	27% 19% 29% 17% 7%	751
	21st to end	Night	25% 15% 32% 23% 6%	760
May	1st to 10th	Night	28% 11% 25% 28% 8%	472
	11th to 20th	Night	17% 11% 35% 27% 8% 1	374
	21st to end	Night	13% 9% 30% 35% 12% 1	411
June	1st to 10th	Night	18% 8% 24% 36% 14%	380
	11th to 20th	Night	17% 8% 25% 34% 14% 1	380
	21st to end	Night	13% 6% 29% 42% 9%	380
July	1st to 10th	Night	9% 5% 22% 44% 17% 2	370
	11th to 20th	Night	12% 5% 20% 43% 19% 1	368
	21st to end	Night	16% 5% 21% 43% 14% 1	420
August	1st to 10th	Night	11% 4 22% 38% 24% 2	567
	11th to 20th	Night	17% 4 15% 32% 29% 4	639
	21st to end	Night	15% 6% 19% 35% 24% 2	836
September	1st to 10th	Night	18% 6% 24% 33% 17% 3	760
	11th to 20th	Night	16% 6% 19% 32% 23% 5%	760
	21st to end	Night	20% 9% 25% 27% 16% 2	760
October	1st to 10th	Night	22% 10% 26% 24% 17% 2	760
	11th to 20th	Night	24% 14% 28% 26% 7% 1	760
	21st to end	Night	30% 15% 28% 21% 6%	836
November	1st to 10th	Night	20% 17% 30% 25% 7%	780
	11th to 20th	Night	27% 18% 32% 17% 5% 1	800
	21st to end	Night	25% 19% 32% 20% 4	800
December	1st to 10th	Night	28% 23% 29% 17% 3	760
	11th to 20th	Night	27% 22% 30% 18% 3	760
	21st to end	Night	29% 20% 33% 16% 2	836

Page generated at 2024-11-27 17:30:54. Version ac07

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