Middleton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Middleton clear sky chart from 2005-11-06 to 2026-03-18.

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	7% 6% 2 6% 4 4 4 3 5% 6% 54%	139730
	Night	9% 7% 3 7% 4 4 4 4 5% 6% 47%	139088
Transparency	Day	31% 5% 11% 20% 20% 14%	134503
	Night	37% 5% 12% 19% 17% 11%	135313
Seeing	Day	9% 6% 18% 28% 25% 14%	16119
	Night	12% 5% 19% 39% 23% 3	25537

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	14% 15% 5% 12% 7% 6% 5% 5% 6% 5% 20%	4722
	11th to 20th	Day	8% 9% 3 10% 6% 5% 6% 4 6% 7% 35%	4740
	21st to end	Day	11% 10% 5% 10% 6% 5% 4 3 5% 6% 35%	5187
February	1st to 10th	Day	12% 11% 5% 10% 6% 4 5% 4 5% 7% 32%	1847
	11th to 20th	Day	11% 12% 3 8% 5% 5% 5% 5% 5% 6% 36%	2050
	21st to end	Day	10% 11% 3 6% 6% 5% 6% 4 6% 8% 36%	1730
March	1st to 10th	Day	7% 10% 4 10% 6% 5% 5% 5% 7% 8% 34%	4618
	11th to 20th	Day	7% 9% 3 7% 4 4 4 4 5% 5% 48%	4845
	21st to end	Day	8% 9% 3 8% 6% 7% 7% 5% 7% 8% 33%	5792
April	1st to 10th	Day	10% 8% 2 6% 5% 4 5% 4 6% 8% 42%	2400
	11th to 20th	Day	6% 7% 2 6% 4 5% 5% 4 5% 7% 48%	2398
	21st to end	Day	7% 6% 2 5% 5% 3 5% 4 6% 7% 50%	2600
May	1st to 10th	Day	7% 4 2 5% 3 4 4 3 5% 6% 58%	5880
	11th to 20th	Day	5% 4 2 4 3 3 3 3 5% 6% 62%	6097
	21st to end	Day	4 3 1 4 3 3 4 3 5% 8% 63%	6902
June	1st to 10th	Day	8% 4 2 6% 4 4 4 5% 6% 8% 48%	2800
	11th to 20th	Day	5% 4 2 4 3 3 3 3 6% 8% 60%	2800
	21st to end	Day	3 2 1 3 2 3 3 3 4 5% 72%	2800
July	1st to 10th	Day	2 1 2 1 2 2 2 3 4 80%	6319
	11th to 20th	Day	1 1 1 2 1 2 2 2 3 3 83%	6320
	21st to end	Day	2 2 1 3 2 2 3 3 4 7% 71%	6880
August	1st to 10th	Day	3 3 1 4 2 3 3 3 5% 8% 66%	6026
	11th to 20th	Day	1 1 2 2 2 2 2 2 4 82%	5761
	21st to end	Day	4 3 1 4 3 3 3 3 3 4 69%	5984
September	1st to 10th	Day	3 2 1 2 2 2 3 2 4 6% 74%	2400
	11th to 20th	Day	4 3 1 3 3 3 3 3 4 7% 66%	2235
	21st to end	Day	5% 3 2 4 4 3 3 3 3 6% 66%	2200
October	1st to 10th	Day	5% 3 1 4 2 3 3 2 3 5% 69%	3600
	11th to 20th	Day	8% 3 2 5% 3 4 4 3 5% 7% 56%	3131
	21st to end	Day	7% 7% 3 6% 4 4 4 4 6% 8% 48%	3200
November	1st to 10th	Day	13% 8% 2 7% 4 4 4 4 6% 8% 39%	1854
	11th to 20th	Day	13% 9% 3 7% 6% 5% 5% 3 6% 8% 34%	1890
	21st to end	Day	10% 10% 4 9% 7% 6% 5% 5% 6% 9% 30%	1822
December	1st to 10th	Day	10% 6% 3 9% 8% 7% 6% 4 6% 7% 34%	2700
	11th to 20th	Day	15% 13% 4 14% 7% 6% 4 4 5% 6% 21%	3108
	21st to end	Day	17% 11% 5% 11% 7% 6% 5% 4 6% 6% 23%	4092
January	1st to 10th	Night	16% 17% 5% 12% 6% 6% 5% 4 5% 6% 17%	8172
	11th to 20th	Night	10% 10% 3 8% 5% 5% 6% 4 7% 7% 34%	8220
	21st to end	Night	11% 9% 4 10% 5% 5% 4 3 5% 7% 37%	8994
February	1st to 10th	Night	15% 11% 4 8% 6% 5% 5% 4 5% 7% 31%	2768
	11th to 20th	Night	12% 10% 3 7% 6% 6% 5% 5% 6% 7% 34%	2458
	21st to end	Night	12% 11% 3 8% 5% 5% 5% 4 6% 7% 34%	2076
March	1st to 10th	Night	9% 11% 3 8% 7% 5% 5% 4 6% 7% 35%	5496
	11th to 20th	Night	12% 10% 3 6% 4 3 3 3 5% 6% 44%	5309
	21st to end	Night	10% 9% 3 7% 6% 5% 6% 5% 7% 9% 34%	5169
April	1st to 10th	Night	10% 8% 2 6% 4 3 4 4 6% 8% 44%	2000
	11th to 20th	Night	9% 7% 2 6% 5% 6% 5% 3 6% 6% 46%	1949
	21st to end	Night	7% 5% 2 6% 4 3 4 4 5% 7% 52%	1800
May	1st to 10th	Night	9% 4 2 4 3 3 3 3 5% 7% 58%	4100
	11th to 20th	Night	5% 5% 2 5% 4 4 5% 4 5% 6% 57%	3800
	21st to end	Night	5% 4 2 4 3 3 3 3 4 5% 63%	3972
June	1st to 10th	Night	8% 6% 2 6% 5% 4 4 4 6% 8% 48%	1600
	11th to 20th	Night	6% 5% 1 5% 4 3 3 3 3 7% 60%	1600
	21st to end	Night	2 2 1 3 3 3 4 3 4 6% 69%	1600
July	1st to 10th	Night	2 2 1 3 2 2 2 2 3 5% 77%	3640
	11th to 20th	Night	1 1 2 2 2 3 4 83%	3640
	21st to end	Night	1 2 1 4 3 4 4 4 6% 8% 62%	3970
August	1st to 10th	Night	2 3 1 4 3 3 4 4 6% 7% 63%	3761
	11th to 20th	Night	1 1 1 2 1 2 2 2 3 5% 79%	4087
	21st to end	Night	5% 3 1 3 2 3 3 3 4 5% 68%	5015
September	1st to 10th	Night	3 2 1 3 2 2 3 3 3 6% 74%	2000
	11th to 20th	Night	4 3 1 4 3 3 3 3 4 6% 65%	2165
	21st to end	Night	7% 3 1 3 2 3 3 2 4 4 68%	2200
October	1st to 10th	Night	4 2 1 4 3 3 3 3 3 4 70%	3600
	11th to 20th	Night	6% 4 1 4 3 3 4 3 4 6% 61%	4017
	21st to end	Night	9% 6% 2 6% 4 3 5% 4 6% 8% 48%	4600
November	1st to 10th	Night	14% 6% 2 6% 4 4 4 3 4 6% 44%	2665
	11th to 20th	Night	16% 7% 3 7% 5% 5% 5% 4 5% 7% 37%	2730
	21st to end	Night	13% 8% 3 8% 5% 5% 5% 3 5% 8% 37%	2793
December	1st to 10th	Night	11% 8% 4 7% 5% 5% 6% 5% 6% 8% 37%	4700
	11th to 20th	Night	16% 14% 5% 13% 7% 6% 6% 4 5% 6% 19%	5316
	21st to end	Night	16% 12% 4 11% 7% 7% 6% 4 6% 6% 22%	7106

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	61% 9% 16% 12% 2	4723
	11th to 20th	Day	46% 8% 21% 21% 4	4740
	21st to end	Day	49% 7% 15% 22% 6% 1	5187
February	1st to 10th	Day	51% 9% 19% 16% 5% 1	1847
	11th to 20th	Day	48% 8% 15% 20% 8%	2060
	21st to end	Day	45% 6% 17% 20% 11% 1	1730
March	1st to 10th	Day	45% 5% 15% 22% 11% 1	4618
	11th to 20th	Day	36% 5% 11% 33% 14% 1	4845
	21st to end	Day	44% 8% 18% 20% 8% 2	5792
April	1st to 10th	Day	38% 5% 16% 23% 14% 3	2400
	11th to 20th	Day	34% 5% 12% 25% 19% 5%	2401
	21st to end	Day	32% 5% 12% 28% 19% 4	2600
May	1st to 10th	Day	25% 3 8% 23% 33% 7%	5880
	11th to 20th	Day	22% 4 8% 26% 29% 11%	6100
	21st to end	Day	20% 4 10% 28% 30% 8%	6904
June	1st to 10th	Day	31% 6% 12% 25% 23% 4	2800
	11th to 20th	Day	22% 4 9% 23% 30% 12%	2800
	21st to end	Day	14% 3 7% 19% 32% 24%	2800
July	1st to 10th	Day	9% 2 4 9% 24% 52%	6251
	11th to 20th	Day	8% 2 2 5% 22% 61%	6245
	21st to end	Day	13% 3 4 14% 32% 34%	6681
August	1st to 10th	Day	20% 3 5% 11% 26% 35%	4384
	11th to 20th	Day	9% 2 3 16% 36% 34%	4172
	21st to end	Day	15% 2 3 18% 35% 27%	4311
September	1st to 10th	Day	14% 3 4 18% 32% 29%	2400
	11th to 20th	Day	19% 4 8% 25% 30% 14%	2235
	21st to end	Day	22% 3 7% 24% 34% 11%	2200
October	1st to 10th	Day	21% 2 7% 20% 41% 9%	3600
	11th to 20th	Day	28% 4 12% 29% 23% 4	3131
	21st to end	Day	34% 4 13% 32% 17% 1	3200
November	1st to 10th	Day	42% 6% 15% 26% 10%	1854
	11th to 20th	Day	49% 6% 18% 22% 4 1	1890
	21st to end	Day	48% 9% 19% 20% 5%	1822
December	1st to 10th	Day	46% 9% 21% 20% 3	2700
	11th to 20th	Day	62% 7% 17% 11% 2	3108
	21st to end	Day	60% 6% 17% 14% 3	4092
January	1st to 10th	Night	66% 8% 15% 9% 2	8172
	11th to 20th	Night	45% 8% 19% 21% 7%	8220
	21st to end	Night	46% 7% 15% 21% 10% 2	8994
February	1st to 10th	Night	52% 7% 18% 19% 4 1	2768
	11th to 20th	Night	46% 8% 17% 21% 9% 1	2459
	21st to end	Night	47% 6% 15% 20% 10% 2	2076
March	1st to 10th	Night	43% 6% 14% 23% 12% 1	5496
	11th to 20th	Night	41% 3 7% 29% 19% 1	5309
	21st to end	Night	43% 8% 15% 25% 10%	5169
April	1st to 10th	Night	36% 5% 13% 25% 19% 3	2000
	11th to 20th	Night	35% 5% 10% 25% 22% 3	1949
	21st to end	Night	30% 5% 10% 27% 24% 4	1800
May	1st to 10th	Night	25% 3 9% 20% 33% 10%	4097
	11th to 20th	Night	27% 4 7% 22% 32% 8%	3800
	21st to end	Night	24% 4 8% 26% 30% 9%	3972
June	1st to 10th	Night	33% 6% 12% 22% 24% 3	1600
	11th to 20th	Night	26% 4 8% 20% 32% 11%	1600
	21st to end	Night	16% 3 7% 17% 32% 25%	1600
July	1st to 10th	Night	12% 2 4 8% 18% 57%	3600
	11th to 20th	Night	6% 2 2 6% 20% 64%	3592
	21st to end	Night	19% 3 4 12% 30% 32%	3857
August	1st to 10th	Night	22% 3 5% 10% 23% 36%	2732
	11th to 20th	Night	10% 2 5% 9% 28% 46%	2951
	21st to end	Night	15% 2 3 12% 33% 35%	3608
September	1st to 10th	Night	13% 3 4 13% 31% 37%	2000
	11th to 20th	Night	21% 3 7% 20% 26% 24%	2165
	21st to end	Night	21% 2 4 20% 33% 20%	2200
October	1st to 10th	Night	20% 3 6% 17% 33% 22%	3600
	11th to 20th	Night	24% 4 8% 29% 29% 5%	4017
	21st to end	Night	33% 5% 11% 30% 20% 2	4600
November	1st to 10th	Night	40% 5% 13% 25% 16% 1	2665
	11th to 20th	Night	46% 6% 14% 25% 8%	2730
	21st to end	Night	44% 7% 18% 23% 7%	2793
December	1st to 10th	Night	44% 7% 24% 21% 4	4700
	11th to 20th	Night	64% 7% 16% 10% 2	5316
	21st to end	Night	59% 8% 17% 12% 5%	7106

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	20% 10% 15% 29% 18% 8%	220
	11th to 20th	Day	12% 10% 18% 28% 24% 9%	220
	21st to end	Day	14% 5% 12% 30% 29% 10%	242
February	1st to 10th	Day	16% 7% 26% 24% 19% 8%	348
	11th to 20th	Day	17% 9% 21% 32% 16% 5%	535
	21st to end	Day	16% 10% 27% 26% 15% 6%	446
March	1st to 10th	Day	13% 15% 26% 30% 13% 4	540
	11th to 20th	Day	12% 9% 25% 30% 17% 6%	529
	21st to end	Day	13% 12% 25% 26% 18% 5%	550
April	1st to 10th	Day	14% 11% 21% 22% 19% 12%	500
	11th to 20th	Day	9% 12% 28% 26% 16% 9%	492
	21st to end	Day	7% 10% 28% 26% 20% 8%	500
May	1st to 10th	Day	5% 12% 25% 28% 18% 12%	503
	11th to 20th	Day	13% 7% 19% 28% 21% 12%	528
	21st to end	Day	8% 4 15% 25% 27% 20%	573
June	1st to 10th	Day	7% 5% 16% 28% 25% 18%	530
	11th to 20th	Day	7% 6% 22% 33% 25% 9%	530
	21st to end	Day	3 3 18% 30% 27% 18%	530
July	1st to 10th	Day	2 3 14% 32% 32% 17%	526
	11th to 20th	Day	1 2 14% 35% 33% 15%	524
	21st to end	Day	3 1 10% 29% 37% 20%	575
August	1st to 10th	Day	4 2 12% 31% 35% 16%	527
	11th to 20th	Day	2 1 11% 28% 34% 23%	517
	21st to end	Day	4 3 12% 26% 31% 24%	583
September	1st to 10th	Day	4 2 10% 20% 35% 28%	530
	11th to 20th	Day	5% 4 11% 26% 28% 26%	530
	21st to end	Day	4 3 15% 27% 32% 20%	530
October	1st to 10th	Day	8% 4 15% 24% 26% 24%	530
	11th to 20th	Day	9% 5% 17% 27% 23% 19%	432
	21st to end	Day	12% 4 18% 29% 28% 10%	363
November	1st to 10th	Day	18% 5% 16% 27% 25% 8%	330
	11th to 20th	Day	13% 7% 15% 32% 25% 8%	330
	21st to end	Day	14% 4 14% 32% 26% 10%	294
December	1st to 10th	Day	20% 3 14% 30% 17% 16%	220
	11th to 20th	Day	20% 7% 20% 29% 20% 5%	220
	21st to end	Day	18% 9% 19% 29% 19% 6%	242
January	1st to 10th	Night	21% 7% 20% 30% 18% 3	840
	11th to 20th	Night	18% 5% 19% 31% 25% 2	840
	21st to end	Night	17% 3 14% 38% 24% 3	924
February	1st to 10th	Night	20% 6% 19% 36% 16% 3	840
	11th to 20th	Night	14% 5% 21% 40% 18% 2	824
	21st to end	Night	16% 6% 26% 37% 14% 1	692
March	1st to 10th	Night	15% 7% 28% 35% 14% 2	840
	11th to 20th	Night	15% 7% 21% 39% 16% 2	828
	21st to end	Night	15% 8% 25% 38% 13% 1	880
April	1st to 10th	Night	12% 6% 22% 38% 21% 1	800
	11th to 20th	Night	11% 8% 26% 35% 19% 1	761
	21st to end	Night	9% 7% 24% 40% 18% 1	600
May	1st to 10th	Night	8% 8% 25% 39% 19% 2	600
	11th to 20th	Night	9% 5% 24% 32% 26% 3	474
	21st to end	Night	7% 7% 17% 38% 26% 5%	433
June	1st to 10th	Night	11% 6% 20% 36% 26% 3	400
	11th to 20th	Night	9% 8% 23% 37% 22% 2	400
	21st to end	Night	3 3 23% 40% 29% 2	400
July	1st to 10th	Night	1 1 17% 52% 28% 2	390
	11th to 20th	Night	1 1 18% 54% 25%	388
	21st to end	Night	3 1 16% 45% 34% 1	438
August	1st to 10th	Night	4 1 14% 49% 30% 2	477
	11th to 20th	Night	1 2 13% 48% 35% 2	604
	21st to end	Night	4 3 13% 42% 34% 5%	880
September	1st to 10th	Night	3 1 11% 43% 38% 5%	800
	11th to 20th	Night	5% 2 12% 37% 39% 4	800
	21st to end	Night	8% 3 14% 36% 32% 8%	800
October	1st to 10th	Night	8% 3 17% 41% 28% 4	800
	11th to 20th	Night	8% 4 16% 40% 27% 5%	800
	21st to end	Night	11% 3 18% 41% 24% 3	880
November	1st to 10th	Night	15% 5% 16% 38% 24% 2	820
	11th to 20th	Night	19% 5% 18% 39% 17% 2	840
	21st to end	Night	16% 4 16% 38% 21% 5%	840
December	1st to 10th	Night	21% 4 17% 36% 18% 4	840
	11th to 20th	Night	22% 6% 15% 38% 17% 2	840
	21st to end	Night	25% 6% 21% 35% 11% 2	924

Page generated at 2026-03-15 00:23:57. Version ac07

Copyright © 2026 Attilla Danko.