Mill Pond Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mill Pond Observatory clear sky chart from 2005-11-06 to 2026-07-16.

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% 10% 4 9% 5% 5% 4 4 5% 6% 31%	138352
	Night	17% 12% 4 9% 5% 5% 4 3 5% 6% 29%	134314
Transparency	Day	51% 6% 12% 21% 9% 1	141795
	Night	54% 6% 11% 19% 10% 1	138960
Seeing	Day	24% 18% 30% 18% 8% 2	16640
	Night	24% 15% 30% 23% 8% 1	25644

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% 19% 6% 15% 5% 5% 4 3 5% 5% 20%	4661
	11th to 20th	Day	11% 18% 7% 14% 6% 6% 5% 3 5% 4 19%	4650
	21st to end	Day	10% 16% 7% 14% 9% 8% 5% 4 5% 5% 19%	5166
February	1st to 10th	Day	15% 16% 4 12% 7% 4 4 4 5% 5% 25%	1890
	11th to 20th	Day	14% 14% 4 11% 7% 5% 4 4 6% 5% 26%	1911
	21st to end	Day	19% 15% 6% 10% 5% 5% 4 3 5% 5% 24%	1730
March	1st to 10th	Day	18% 13% 5% 12% 5% 5% 4 3 5% 5% 24%	4576
	11th to 20th	Day	12% 14% 4 10% 6% 4 4 4 5% 6% 29%	4935
	21st to end	Day	19% 10% 3 9% 6% 4 4 3 4 4 34%	6008
April	1st to 10th	Day	21% 13% 3 8% 5% 3 3 3 3 5% 32%	2520
	11th to 20th	Day	22% 11% 3 7% 5% 4 3 3 4 6% 33%	2494
	21st to end	Day	22% 10% 3 8% 5% 4 3 4 4 5% 32%	2646
May	1st to 10th	Day	23% 10% 3 9% 5% 5% 5% 4 6% 6% 23%	8237
	11th to 20th	Day	18% 9% 4 8% 5% 5% 4 4 5% 7% 32%	8221
	21st to end	Day	21% 9% 3 6% 4 4 4 3 5% 7% 33%	9060
June	1st to 10th	Day	22% 7% 3 7% 5% 4 4 4 5% 7% 30%	2940
	11th to 20th	Day	15% 6% 2 7% 6% 5% 5% 4 6% 8% 37%	2940
	21st to end	Day	18% 8% 3 7% 5% 4 5% 4 6% 9% 31%	2940
July	1st to 10th	Day	12% 6% 3 8% 6% 6% 6% 4 7% 8% 33%	6500
	11th to 20th	Day	11% 5% 2 7% 5% 5% 5% 4 7% 8% 41%	6430
	21st to end	Day	11% 5% 2 5% 4 4 4 4 7% 10% 45%	6926
August	1st to 10th	Day	14% 7% 3 7% 5% 5% 5% 4 6% 9% 35%	4563
	11th to 20th	Day	13% 7% 2 7% 4 4 5% 4 6% 8% 39%	4066
	21st to end	Day	15% 5% 2 6% 4 5% 5% 4 6% 9% 38%	4312
September	1st to 10th	Day	13% 6% 2 6% 4 4 4 4 6% 8% 44%	2400
	11th to 20th	Day	12% 4 2 5% 4 4 4 3 5% 7% 49%	2352
	21st to end	Day	17% 7% 3 6% 4 4 4 3 6% 7% 41%	2200
October	1st to 10th	Day	19% 8% 2 7% 4 3 4 4 5% 6% 37%	2010
	11th to 20th	Day	19% 10% 3 9% 6% 4 5% 3 4 6% 31%	2000
	21st to end	Day	24% 12% 4 7% 4 4 5% 3 4 5% 28%	1983
November	1st to 10th	Day	16% 10% 3 8% 6% 5% 5% 4 4 6% 32%	1851
	11th to 20th	Day	17% 11% 4 9% 6% 6% 5% 3 4 7% 29%	1760
	21st to end	Day	21% 15% 4 9% 6% 6% 4 4 5% 5% 20%	1680
December	1st to 10th	Day	20% 20% 6% 11% 5% 5% 5% 4 5% 5% 15%	2680
	11th to 20th	Day	19% 16% 5% 12% 5% 4 5% 3 4 5% 23%	3066
	21st to end	Day	23% 16% 4 10% 6% 4 4 3 5% 4 22%	4048
January	1st to 10th	Night	14% 21% 8% 14% 6% 4 4 3 4 4 20%	8234
	11th to 20th	Night	12% 17% 8% 18% 7% 6% 5% 3 4 4 15%	8235
	21st to end	Night	12% 15% 6% 11% 7% 7% 5% 4 4 6% 23%	9001
February	1st to 10th	Night	14% 14% 5% 12% 7% 6% 5% 4 6% 5% 22%	2730
	11th to 20th	Night	13% 14% 4 11% 6% 6% 5% 4 5% 4 28%	2595
	21st to end	Night	14% 15% 4 10% 6% 5% 4 4 4 5% 29%	2076
March	1st to 10th	Night	20% 13% 4 9% 6% 4 4 3 4 4 29%	5484
	11th to 20th	Night	15% 13% 4 8% 6% 5% 5% 4 5% 8% 29%	5241
	21st to end	Night	17% 12% 4 9% 5% 5% 4 3 5% 5% 32%	5166
April	1st to 10th	Night	23% 11% 3 7% 5% 4 4 3 5% 6% 31%	2100
	11th to 20th	Night	22% 10% 3 8% 5% 4 3 4 4 5% 33%	2075
	21st to end	Night	21% 9% 3 7% 5% 3 4 2 5% 6% 34%	1982
May	1st to 10th	Night	20% 10% 3 9% 6% 5% 5% 4 6% 7% 23%	4668
	11th to 20th	Night	18% 9% 3 8% 5% 4 4 4 5% 7% 32%	4639
	21st to end	Night	18% 9% 3 7% 4 5% 4 4 6% 7% 32%	5114
June	1st to 10th	Night	19% 6% 3 7% 6% 4 5% 5% 6% 9% 30%	1680
	11th to 20th	Night	17% 7% 2 6% 4 4 4 3 5% 8% 40%	1680
	21st to end	Night	18% 6% 4 7% 5% 5% 5% 3 6% 7% 34%	1680
July	1st to 10th	Night	12% 7% 3 7% 5% 6% 5% 5% 7% 9% 34%	3680
	11th to 20th	Night	12% 7% 3 7% 5% 4 4 3 6% 7% 42%	3640
	21st to end	Night	10% 6% 2 6% 4 4 5% 5% 5% 8% 45%	3926
August	1st to 10th	Night	14% 8% 3 6% 5% 4 4 3 7% 8% 39%	2586
	11th to 20th	Night	14% 7% 3 7% 4 5% 5% 3 5% 7% 41%	2944
	21st to end	Night	13% 7% 2 7% 5% 4 6% 3 5% 8% 40%	3586
September	1st to 10th	Night	10% 6% 3 8% 5% 4 5% 3 5% 7% 44%	2000
	11th to 20th	Night	14% 6% 2 5% 4 3 3 2 5% 7% 49%	2047
	21st to end	Night	17% 5% 2 5% 5% 4 4 4 5% 7% 42%	2200
October	1st to 10th	Night	19% 6% 3 6% 4 4 4 4 5% 5% 39%	2389
	11th to 20th	Night	18% 9% 3 8% 5% 4 5% 4 5% 7% 33%	2400
	21st to end	Night	23% 9% 3 8% 5% 4 4 4 4 6% 29%	2855
November	1st to 10th	Night	20% 10% 4 7% 4 4 3 3 4 6% 33%	2667
	11th to 20th	Night	17% 10% 3 9% 5% 5% 5% 4 5% 5% 32%	2856
	21st to end	Night	20% 13% 4 10% 6% 5% 4 3 5% 5% 24%	2940
December	1st to 10th	Night	17% 18% 6% 12% 7% 6% 5% 4 4 5% 17%	4720
	11th to 20th	Night	23% 16% 5% 10% 5% 4 4 3 3 4 23%	5348
	21st to end	Night	26% 17% 4 10% 4 4 3 3 4 5% 20%	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	66% 6% 11% 13% 4	4662
	11th to 20th	Day	66% 5% 8% 11% 8% 1	4680
	21st to end	Day	65% 6% 10% 9% 9% 1	5166
February	1st to 10th	Day	62% 4 8% 20% 5% 2	1890
	11th to 20th	Day	59% 5% 11% 17% 7% 1	1920
	21st to end	Day	63% 4 10% 13% 9% 1	1730
March	1st to 10th	Day	60% 5% 9% 14% 9% 3	4579
	11th to 20th	Day	54% 5% 16% 14% 9% 1	4935
	21st to end	Day	53% 4 6% 16% 18% 2	6008
April	1st to 10th	Day	55% 4 8% 19% 12% 3	2520
	11th to 20th	Day	53% 4 6% 20% 16% 2	2494
	21st to end	Day	54% 5% 8% 17% 13% 4	2646
May	1st to 10th	Day	57% 7% 9% 17% 9% 1	8249
	11th to 20th	Day	51% 7% 12% 21% 8% 1	8225
	21st to end	Day	49% 6% 11% 24% 10% 1	9061
June	1st to 10th	Day	52% 6% 10% 19% 12% 1	2940
	11th to 20th	Day	44% 6% 11% 24% 13% 2	2940
	21st to end	Day	49% 7% 13% 21% 10% 1	2940
July	1st to 10th	Day	44% 8% 14% 25% 9%	6430
	11th to 20th	Day	37% 8% 14% 29% 13%	6355
	21st to end	Day	33% 7% 15% 37% 9%	6728
August	1st to 10th	Day	44% 7% 17% 24% 8%	4549
	11th to 20th	Day	40% 7% 16% 29% 7%	4106
	21st to end	Day	41% 8% 16% 23% 11%	4312
September	1st to 10th	Day	37% 6% 14% 30% 12%	2400
	11th to 20th	Day	35% 5% 12% 32% 15% 1	2352
	21st to end	Day	43% 6% 14% 26% 11% 1	2200
October	1st to 10th	Day	44% 6% 13% 29% 9%	3270
	11th to 20th	Day	46% 5% 15% 26% 7% 1	3240
	21st to end	Day	47% 5% 18% 23% 7%	3183
November	1st to 10th	Day	52% 6% 12% 21% 8% 1	1851
	11th to 20th	Day	56% 6% 11% 16% 10% 1	1760
	21st to end	Day	65% 6% 12% 11% 5%	1680
December	1st to 10th	Day	70% 7% 11% 11% 2	2680
	11th to 20th	Day	64% 6% 9% 15% 6%	3066
	21st to end	Day	65% 5% 8% 16% 6%	4048
January	1st to 10th	Night	68% 5% 10% 12% 5%	8234
	11th to 20th	Night	71% 5% 8% 9% 6%	8280
	21st to end	Night	62% 5% 9% 13% 10% 1	9001
February	1st to 10th	Night	63% 5% 9% 16% 6% 1	2730
	11th to 20th	Night	58% 5% 10% 20% 7%	2597
	21st to end	Night	57% 4 8% 18% 11% 1	2076
March	1st to 10th	Night	58% 4 7% 15% 12% 3	5494
	11th to 20th	Night	52% 6% 14% 16% 8% 3	5242
	21st to end	Night	54% 4 6% 22% 13% 2	5166
April	1st to 10th	Night	55% 4 7% 18% 13% 2	2100
	11th to 20th	Night	53% 5% 8% 19% 14% 1	2075
	21st to end	Night	51% 4 8% 18% 16% 4	1982
May	1st to 10th	Night	57% 7% 11% 17% 7% 1	4674
	11th to 20th	Night	49% 8% 10% 21% 11% 1	4640
	21st to end	Night	49% 7% 10% 20% 14% 1	5115
June	1st to 10th	Night	48% 7% 12% 19% 12% 1	1680
	11th to 20th	Night	42% 6% 11% 22% 17% 2	1680
	21st to end	Night	48% 6% 13% 20% 13%	1680
July	1st to 10th	Night	43% 8% 17% 21% 11%	3640
	11th to 20th	Night	38% 7% 15% 29% 11%	3592
	21st to end	Night	35% 8% 14% 28% 15%	3809
August	1st to 10th	Night	42% 6% 16% 26% 9%	2576
	11th to 20th	Night	42% 6% 16% 27% 8%	2970
	21st to end	Night	40% 8% 15% 24% 12% 1	3586
September	1st to 10th	Night	40% 6% 10% 29% 15% 1	2000
	11th to 20th	Night	34% 5% 12% 35% 13% 1	2047
	21st to end	Night	42% 5% 12% 27% 14% 1	2200
October	1st to 10th	Night	41% 6% 15% 27% 10% 1	3909
	11th to 20th	Night	43% 6% 14% 27% 9%	3899
	21st to end	Night	47% 6% 17% 20% 10%	4605
November	1st to 10th	Night	52% 5% 13% 21% 8% 1	2667
	11th to 20th	Night	53% 6% 12% 19% 9% 1	2856
	21st to end	Night	62% 5% 12% 16% 5%	2940
December	1st to 10th	Night	69% 5% 12% 11% 3	4720
	11th to 20th	Night	66% 4 6% 15% 9% 1	5348
	21st to end	Night	66% 4 7% 13% 9%	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	28% 20% 35% 15% 3	220
	11th to 20th	Day	31% 30% 28% 7% 4	220
	21st to end	Day	18% 27% 36% 16% 4	250
February	1st to 10th	Day	30% 29% 27% 12% 2	330
	11th to 20th	Day	29% 28% 35% 8%	398
	21st to end	Day	30% 21% 34% 13% 1	446
March	1st to 10th	Day	30% 23% 30% 14% 4	540
	11th to 20th	Day	29% 24% 31% 12% 2 1	540
	21st to end	Day	32% 25% 25% 12% 5% 1	594
April	1st to 10th	Day	33% 22% 29% 13% 4	540
	11th to 20th	Day	36% 20% 25% 13% 6% 1	532
	21st to end	Day	32% 19% 29% 12% 7% 1	540
May	1st to 10th	Day	26% 20% 33% 15% 5% 1	543
	11th to 20th	Day	19% 21% 31% 18% 10% 1	567
	21st to end	Day	22% 19% 31% 20% 7% 1	617
June	1st to 10th	Day	27% 13% 32% 20% 7% 2	570
	11th to 20th	Day	18% 19% 30% 24% 7% 2	570
	21st to end	Day	24% 12% 34% 18% 9% 2	570
July	1st to 10th	Day	15% 11% 33% 27% 12% 2	565
	11th to 20th	Day	13% 13% 33% 27% 10% 3	544
	21st to end	Day	15% 11% 35% 27% 10% 2	576
August	1st to 10th	Day	15% 9% 28% 32% 14% 3	526
	11th to 20th	Day	15% 8% 29% 29% 14% 7%	519
	21st to end	Day	16% 12% 31% 23% 14% 5%	583
September	1st to 10th	Day	17% 12% 29% 21% 15% 6%	530
	11th to 20th	Day	12% 10% 25% 24% 19% 10%	530
	21st to end	Day	19% 13% 31% 18% 14% 4	530
October	1st to 10th	Day	21% 16% 27% 20% 13% 3	530
	11th to 20th	Day	24% 23% 28% 19% 6% 1	530
	21st to end	Day	32% 16% 30% 17% 5%	463
November	1st to 10th	Day	29% 20% 26% 17% 5% 1	425
	11th to 20th	Day	25% 23% 31% 16% 4 1	300
	21st to end	Day	32% 25% 27% 13% 4	220
December	1st to 10th	Day	30% 19% 33% 15% 3	220
	11th to 20th	Day	31% 28% 31% 9% 1	220
	21st to end	Day	31% 26% 27% 14% 2	242
January	1st to 10th	Night	27% 20% 36% 14% 3	840
	11th to 20th	Night	30% 20% 27% 19% 4	840
	21st to end	Night	22% 18% 35% 21% 4	924
February	1st to 10th	Night	22% 20% 34% 21% 3	840
	11th to 20th	Night	23% 22% 35% 17% 3	823
	21st to end	Night	25% 17% 33% 23% 2	692
March	1st to 10th	Night	25% 20% 31% 20% 4	840
	11th to 20th	Night	27% 19% 32% 18% 3	840
	21st to end	Night	27% 17% 27% 24% 5%	924
April	1st to 10th	Night	31% 16% 29% 20% 4	840
	11th to 20th	Night	26% 19% 30% 20% 5%	831
	21st to end	Night	29% 15% 29% 20% 7%	722
May	1st to 10th	Night	27% 11% 30% 23% 7% 2	428
	11th to 20th	Night	23% 13% 30% 24% 9% 1	414
	21st to end	Night	17% 11% 39% 25% 8%	455
June	1st to 10th	Night	20% 10% 29% 32% 9%	420
	11th to 20th	Night	20% 11% 27% 30% 10% 1	420
	21st to end	Night	19% 9% 31% 27% 14% 1	420
July	1st to 10th	Night	11% 9% 31% 35% 14% 1	410
	11th to 20th	Night	13% 6% 29% 36% 16%	398
	21st to end	Night	14% 5% 30% 37% 13% 1	438
August	1st to 10th	Night	14% 4 25% 38% 19% 1	398
	11th to 20th	Night	15% 4 23% 35% 21% 2	623
	21st to end	Night	16% 7% 28% 31% 16% 2	880
September	1st to 10th	Night	14% 8% 31% 32% 15% 1	800
	11th to 20th	Night	17% 7% 21% 31% 21% 4	800
	21st to end	Night	19% 10% 28% 23% 18% 2	800
October	1st to 10th	Night	23% 9% 29% 26% 13% 1	800
	11th to 20th	Night	24% 13% 31% 23% 9%	800
	21st to end	Night	28% 16% 28% 24% 4	880
November	1st to 10th	Night	29% 17% 25% 22% 7% 1	820
	11th to 20th	Night	24% 18% 34% 16% 8%	840
	21st to end	Night	28% 20% 26% 20% 7%	840
December	1st to 10th	Night	30% 18% 29% 19% 4	840
	11th to 20th	Night	32% 22% 26% 15% 4 1	840
	21st to end	Night	37% 19% 26% 15% 3	924

Page generated at 2026-07-13 03:14:53. Version ac07

Copyright © 2026 Attilla Danko.