Mitchell School
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mitchell School clear sky chart from 2005-11-06 to 2024-10-24.

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	6% 9% 3 6% 4 4 4 3 5% 6% 49%	101422
	Night	7% 11% 3 7% 4 4 4 4 5% 6% 45%	97508
Transparency	Day	35% 8% 11% 19% 17% 10%	101165
	Night	37% 9% 13% 20% 15% 7%	97354
Seeing	Day	13% 14% 27% 26% 15% 4	14536
	Night	13% 10% 18% 34% 21% 4	23588

By Month

Percentage Cloud Cover SW (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	11% 18% 7% 10% 6% 5% 5% 4 6% 6% 21%	2539
	11th to 20th	Day	11% 17% 5% 11% 7% 6% 5% 4 4 6% 24%	2540
	21st to end	Day	9% 16% 5% 9% 6% 6% 5% 4 6% 7% 27%	2869
February	1st to 10th	Day	9% 15% 5% 9% 6% 5% 5% 6% 7% 7% 27%	1710
	11th to 20th	Day	9% 16% 4 8% 5% 5% 5% 4 5% 8% 31%	1718
	21st to end	Day	7% 17% 7% 11% 6% 5% 6% 5% 5% 6% 26%	1570
March	1st to 10th	Day	5% 10% 5% 10% 6% 6% 7% 5% 7% 9% 31%	3138
	11th to 20th	Day	4 11% 3 8% 5% 4 4 3 4 5% 49%	3414
	21st to end	Day	6% 17% 5% 12% 9% 7% 7% 5% 6% 6% 21%	4070
April	1st to 10th	Day	10% 16% 5% 10% 6% 5% 6% 4 6% 7% 27%	2280
	11th to 20th	Day	9% 14% 5% 8% 6% 5% 5% 4 5% 5% 34%	2249
	21st to end	Day	10% 13% 3 7% 4 5% 4 4 5% 7% 37%	2346
May	1st to 10th	Day	8% 12% 3 8% 5% 4 5% 3 4 5% 42%	4418
	11th to 20th	Day	7% 5% 2 5% 4 3 3 3 4 5% 60%	4377
	21st to end	Day	9% 12% 3 6% 4 3 4 4 5% 8% 41%	4813
June	1st to 10th	Day	12% 10% 2 7% 5% 5% 5% 4 5% 7% 38%	2660
	11th to 20th	Day	10% 7% 2 5% 4 3 4 3 7% 7% 48%	2660
	21st to end	Day	5% 4 1 4 3 3 3 3 6% 6% 63%	2660
July	1st to 10th	Day	1 1 1 1 1 2 2 2 3 4 82%	4420
	11th to 20th	Day	1 1 1 2 2 2 2 2 3 4 80%	4420
	21st to end	Day	1 1 1 2 2 2 2 2 4 4 78%	4790
August	1st to 10th	Day	3 3 1 4 3 3 3 3 4 5% 68%	4349
	11th to 20th	Day	2 2 1 3 2 2 3 3 4 6% 73%	3918
	21st to end	Day	3 2 1 3 3 3 3 2 4 5% 71%	4180
September	1st to 10th	Day	3 2 1 2 2 2 2 3 4 6% 73%	2280
	11th to 20th	Day	5% 4 2 5% 4 4 3 3 5% 6% 58%	2271
	21st to end	Day	8% 7% 2 5% 3 3 3 3 4 6% 57%	2069
October	1st to 10th	Day	11% 9% 2 5% 4 3 3 3 4 5% 50%	1900
	11th to 20th	Day	7% 7% 2 7% 4 5% 4 4 6% 8% 45%	1900
	21st to end	Day	10% 10% 3 8% 5% 5% 4 3 5% 6% 41%	1866
November	1st to 10th	Day	12% 14% 4 7% 4 4 4 4 6% 7% 33%	1674
	11th to 20th	Day	10% 13% 4 9% 7% 6% 6% 5% 7% 7% 28%	1592
	21st to end	Day	7% 14% 3 8% 6% 5% 6% 5% 6% 7% 33%	1520
December	1st to 10th	Day	6% 14% 4 8% 5% 4 5% 4 6% 7% 36%	1520
	11th to 20th	Day	8% 16% 5% 10% 5% 5% 5% 4 6% 8% 27%	1928
	21st to end	Day	8% 16% 6% 11% 6% 6% 5% 4 6% 7% 27%	2794
January	1st to 10th	Night	7% 17% 7% 12% 7% 6% 6% 5% 5% 6% 22%	4406
	11th to 20th	Night	14% 19% 6% 9% 6% 5% 4 3 5% 6% 23%	4420
	21st to end	Night	10% 16% 4 10% 6% 6% 6% 4 6% 6% 25%	4786
February	1st to 10th	Night	8% 15% 6% 9% 6% 6% 5% 4 5% 6% 30%	2470
	11th to 20th	Night	7% 15% 6% 9% 5% 4 5% 4 6% 6% 33%	2347
	21st to end	Night	7% 17% 6% 10% 7% 6% 5% 4 5% 7% 25%	1884
March	1st to 10th	Night	4 10% 4 8% 4 5% 6% 5% 8% 10% 36%	3736
	11th to 20th	Night	4 9% 3 7% 4 4 4 4 5% 6% 49%	3564
	21st to end	Night	6% 17% 5% 10% 6% 6% 6% 6% 8% 7% 23%	3581
April	1st to 10th	Night	9% 15% 4 8% 5% 5% 4 3 5% 6% 35%	1900
	11th to 20th	Night	8% 13% 4 9% 6% 5% 4 3 5% 6% 38%	1879
	21st to end	Night	8% 13% 3 6% 5% 3 4 5% 7% 8% 38%	1833
May	1st to 10th	Night	8% 15% 5% 8% 4 3 4 3 5% 5% 40%	2540
	11th to 20th	Night	7% 7% 2 4 3 2 2 3 4 5% 61%	2516
	21st to end	Night	11% 14% 2 4 2 3 3 3 4 5% 48%	2762
June	1st to 10th	Night	11% 7% 2 4 4 3 3 4 6% 8% 46%	1520
	11th to 20th	Night	10% 8% 2 5% 3 2 2 3 4 6% 55%	1520
	21st to end	Night	5% 3 1 4 3 3 3 4 4 5% 66%	1520
July	1st to 10th	Night	1 1 1 2 1 2 2 3 3 84%	2540
	11th to 20th	Night	1 1 2 3 2 3 2 3 4 79%	2540
	21st to end	Night	2 1 1 2 2 2 2 2 3 4 80%	2761
August	1st to 10th	Night	2 2 1 4 4 3 4 3 4 6% 67%	2580
	11th to 20th	Night	2 2 1 2 2 2 2 3 4 5% 75%	2922
	21st to end	Night	2 3 1 3 2 2 2 2 3 5% 75%	3498
September	1st to 10th	Night	2 2 1 3 2 2 2 2 4 4 76%	1900
	11th to 20th	Night	6% 4 1 3 3 3 4 4 5% 6% 62%	1909
	21st to end	Night	7% 5% 2 5% 3 3 4 3 4 6% 58%	2109
October	1st to 10th	Night	9% 9% 2 5% 3 3 3 3 4 6% 54%	2280
	11th to 20th	Night	8% 8% 2 5% 4 3 3 3 6% 7% 51%	2280
	21st to end	Night	9% 11% 3 8% 5% 6% 3 3 4 6% 42%	2556
November	1st to 10th	Night	11% 14% 3 6% 5% 5% 5% 4 6% 6% 34%	2405
	11th to 20th	Night	11% 12% 3 8% 5% 5% 5% 5% 7% 7% 32%	2586
	21st to end	Night	7% 14% 3 7% 5% 4 5% 4 7% 8% 36%	2660
December	1st to 10th	Night	8% 14% 4 8% 5% 5% 5% 3 6% 7% 35%	2660
	11th to 20th	Night	7% 12% 5% 10% 6% 7% 6% 5% 8% 8% 27%	3276
	21st to end	Night	8% 15% 5% 10% 5% 5% 5% 4 6% 6% 31%	4862

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% 16% 13% 11% 3	2539
	11th to 20th	Day	59% 10% 12% 12% 5% 2	2540
	21st to end	Day	54% 14% 12% 13% 5% 2	2869
February	1st to 10th	Day	52% 11% 14% 16% 7% 1	1710
	11th to 20th	Day	50% 11% 12% 16% 9% 2	1727
	21st to end	Day	57% 10% 13% 11% 7% 1	1570
March	1st to 10th	Day	45% 12% 14% 18% 11% 1	3138
	11th to 20th	Day	35% 9% 10% 33% 14%	3414
	21st to end	Day	54% 16% 13% 14% 4	4070
April	1st to 10th	Day	55% 8% 13% 14% 8% 1	2280
	11th to 20th	Day	49% 8% 12% 17% 11% 2	2252
	21st to end	Day	45% 8% 12% 22% 11% 1	2346
May	1st to 10th	Day	40% 9% 11% 26% 12% 1	4418
	11th to 20th	Day	27% 4 9% 29% 27% 4	4380
	21st to end	Day	37% 11% 20% 23% 8% 1	4814
June	1st to 10th	Day	44% 7% 11% 27% 11% 1	2660
	11th to 20th	Day	34% 7% 12% 27% 17% 3	2660
	21st to end	Day	21% 5% 12% 27% 26% 9%	2660
July	1st to 10th	Day	9% 2 6% 12% 21% 50%	4351
	11th to 20th	Day	10% 2 6% 7% 23% 52%	4345
	21st to end	Day	11% 2 4 16% 39% 27%	4639
August	1st to 10th	Day	19% 3 6% 13% 33% 26%	4333
	11th to 20th	Day	13% 4 4 27% 37% 15%	3957
	21st to end	Day	16% 4 7% 28% 25% 20%	4179
September	1st to 10th	Day	14% 4 7% 25% 32% 19%	2280
	11th to 20th	Day	27% 5% 10% 22% 24% 12%	2271
	21st to end	Day	29% 6% 11% 23% 22% 10%	2069
October	1st to 10th	Day	38% 5% 9% 19% 19% 9%	1900
	11th to 20th	Day	37% 7% 12% 22% 19% 4	1900
	21st to end	Day	43% 8% 12% 20% 16% 2	1866
November	1st to 10th	Day	50% 8% 13% 19% 10% 1	1674
	11th to 20th	Day	52% 11% 13% 16% 8%	1592
	21st to end	Day	48% 10% 12% 14% 15% 2	1520
December	1st to 10th	Day	45% 13% 15% 16% 10% 2	1520
	11th to 20th	Day	53% 11% 16% 13% 7% 1	1928
	21st to end	Day	55% 12% 15% 14% 4 1	2794
January	1st to 10th	Night	53% 17% 14% 11% 4	4406
	11th to 20th	Night	58% 12% 11% 11% 5% 3	4420
	21st to end	Night	53% 14% 14% 11% 6% 1	4786
February	1st to 10th	Night	51% 12% 14% 14% 9%	2470
	11th to 20th	Night	48% 10% 13% 17% 8% 3	2349
	21st to end	Night	55% 11% 10% 15% 8% 1	1884
March	1st to 10th	Night	37% 12% 14% 24% 11% 1	3736
	11th to 20th	Night	32% 10% 13% 34% 10% 1	3564
	21st to end	Night	49% 19% 15% 13% 5%	3581
April	1st to 10th	Night	48% 8% 18% 18% 7% 1	1900
	11th to 20th	Night	46% 8% 14% 21% 9% 1	1879
	21st to end	Night	41% 10% 16% 21% 11% 2	1833
May	1st to 10th	Night	37% 11% 14% 26% 11%	2540
	11th to 20th	Night	21% 6% 13% 39% 19% 1	2516
	21st to end	Night	32% 11% 26% 25% 6%	2762
June	1st to 10th	Night	36% 8% 14% 28% 13% 1	1520
	11th to 20th	Night	31% 5% 15% 31% 15% 4	1520
	21st to end	Night	20% 5% 13% 29% 26% 8%	1520
July	1st to 10th	Night	7% 3 7% 14% 22% 47%	2500
	11th to 20th	Night	11% 2 6% 13% 22% 47%	2492
	21st to end	Night	10% 2 4 18% 37% 29%	2674
August	1st to 10th	Night	19% 3 7% 15% 35% 21%	2572
	11th to 20th	Night	12% 4 6% 34% 33% 10%	2949
	21st to end	Night	13% 4 10% 28% 26% 19%	3498
September	1st to 10th	Night	14% 3 7% 27% 33% 18%	1900
	11th to 20th	Night	22% 6% 10% 24% 25% 13%	1909
	21st to end	Night	27% 5% 9% 25% 22% 12%	2109
October	1st to 10th	Night	32% 5% 10% 24% 23% 7%	2280
	11th to 20th	Night	32% 7% 13% 21% 21% 5%	2280
	21st to end	Night	40% 10% 12% 16% 18% 4	2556
November	1st to 10th	Night	48% 10% 11% 15% 13% 2	2405
	11th to 20th	Night	48% 12% 12% 18% 10% 1	2586
	21st to end	Night	44% 10% 13% 15% 18% 2	2660
December	1st to 10th	Night	46% 12% 16% 15% 9% 2	2660
	11th to 20th	Night	52% 13% 13% 14% 8%	3276
	21st to end	Night	49% 13% 17% 13% 7% 1	4862

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	24% 21% 22% 17% 13% 2	180
	11th to 20th	Day	21% 19% 23% 19% 14% 3	180
	21st to end	Day	14% 24% 26% 21% 14% 1	247
February	1st to 10th	Day	23% 21% 27% 20% 8% 1	370
	11th to 20th	Day	24% 21% 29% 18% 8% 1	390
	21st to end	Day	21% 19% 27% 26% 5% 2	382
March	1st to 10th	Day	17% 22% 32% 22% 7%	460
	11th to 20th	Day	17% 19% 28% 22% 12% 2	460
	21st to end	Day	20% 20% 29% 23% 8%	506
April	1st to 10th	Day	20% 21% 26% 19% 11% 3	460
	11th to 20th	Day	17% 21% 29% 19% 11% 3	452
	21st to end	Day	15% 20% 30% 18% 13% 3	460
May	1st to 10th	Day	13% 17% 30% 22% 14% 3	463
	11th to 20th	Day	20% 15% 25% 22% 13% 5%	488
	21st to end	Day	16% 11% 23% 28% 15% 7%	529
June	1st to 10th	Day	14% 12% 25% 26% 17% 6%	490
	11th to 20th	Day	14% 15% 32% 23% 12% 3	490
	21st to end	Day	4 10% 28% 33% 18% 6%	490
July	1st to 10th	Day	3 9% 32% 35% 15% 6%	486
	11th to 20th	Day	1 10% 37% 29% 15% 8%	484
	21st to end	Day	2 10% 32% 32% 18% 7%	531
August	1st to 10th	Day	4 7% 28% 33% 18% 11%	487
	11th to 20th	Day	3 6% 24% 32% 23% 12%	477
	21st to end	Day	5% 9% 25% 31% 23% 7%	539
September	1st to 10th	Day	4 7% 28% 29% 27% 6%	490
	11th to 20th	Day	8% 8% 25% 32% 22% 6%	490
	21st to end	Day	11% 10% 25% 31% 20% 3	490
October	1st to 10th	Day	14% 12% 21% 29% 20% 4	490
	11th to 20th	Day	14% 13% 23% 25% 21% 4	490
	21st to end	Day	15% 16% 26% 20% 18% 4	363
November	1st to 10th	Day	16% 18% 25% 27% 13%	270
	11th to 20th	Day	19% 15% 23% 22% 18% 2	214
	21st to end	Day	16% 17% 23% 27% 13% 4	180
December	1st to 10th	Day	16% 22% 20% 23% 13% 6%	180
	11th to 20th	Day	26% 15% 34% 18% 7% 1	180
	21st to end	Day	20% 21% 23% 21% 13% 2	198
January	1st to 10th	Night	19% 17% 23% 22% 15% 3	760
	11th to 20th	Night	21% 16% 18% 24% 18% 4	760
	21st to end	Night	19% 10% 19% 31% 17% 3	836
February	1st to 10th	Night	17% 15% 21% 30% 15% 2	760
	11th to 20th	Night	16% 13% 23% 29% 18% 2	744
	21st to end	Night	16% 17% 25% 31% 10% 1	628
March	1st to 10th	Night	15% 15% 24% 31% 12% 2	760
	11th to 20th	Night	13% 13% 22% 34% 16% 2	760
	21st to end	Night	14% 14% 26% 31% 13% 2	836
April	1st to 10th	Night	17% 13% 21% 30% 17% 3	760
	11th to 20th	Night	15% 10% 23% 31% 18% 4	751
	21st to end	Night	14% 11% 20% 34% 18% 3	693
May	1st to 10th	Night	11% 9% 21% 36% 20% 3	380
	11th to 20th	Night	15% 5% 11% 38% 27% 4	374
	21st to end	Night	17% 7% 14% 35% 24% 4	411
June	1st to 10th	Night	12% 4 16% 40% 25% 3	380
	11th to 20th	Night	15% 7% 16% 41% 20% 1	380
	21st to end	Night	6% 3 13% 48% 27% 3	380
July	1st to 10th	Night	2 2 9% 55% 29% 3	370
	11th to 20th	Night	1 1 12% 56% 27% 3	368
	21st to end	Night	2 1 9% 50% 32% 5%	416
August	1st to 10th	Night	2 8% 46% 40% 3	403
	11th to 20th	Night	3 1 8% 36% 42% 10%	622
	21st to end	Night	2 4 12% 44% 33% 5%	836
September	1st to 10th	Night	4 2 10% 40% 38% 5%	760
	11th to 20th	Night	7% 4 11% 36% 31% 11%	760
	21st to end	Night	10% 4 13% 35% 31% 7%	760
October	1st to 10th	Night	14% 3 15% 37% 26% 5%	760
	11th to 20th	Night	11% 9% 18% 35% 21% 7%	760
	21st to end	Night	15% 9% 18% 32% 18% 7%	804
November	1st to 10th	Night	18% 10% 18% 35% 17% 1	740
	11th to 20th	Night	18% 16% 19% 29% 16% 2	760
	21st to end	Night	17% 13% 19% 29% 17% 6%	760
December	1st to 10th	Night	17% 9% 22% 30% 19% 3	760
	11th to 20th	Night	18% 13% 24% 29% 15% 2	760
	21st to end	Night	22% 17% 27% 22% 11% 1	836

Page generated at 2024-10-20 23:20:03. Version ac07

Copyright © 2024 Attilla Danko.