McCardell Bicentennial Hall at Middlebury College
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the McCardell Bicentennial Hall at Middlebury College clear sky chart from 2005-11-06 to 2026-06-16.

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% 5% 4 5% 7% 30%	137575
	Night	17% 12% 5% 10% 6% 5% 4 3 5% 6% 27%	134440
Transparency	Day	52% 8% 12% 19% 9% 1	141045
	Night	57% 7% 11% 16% 8% 1	139059
Seeing	Day	26% 20% 29% 17% 6% 2	16736
	Night	25% 17% 28% 22% 7% 1	25750

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	12% 15% 7% 18% 6% 5% 5% 4 5% 4 18%	4661
	11th to 20th	Day	10% 15% 7% 18% 9% 5% 4 3 4 5% 19%	4650
	21st to end	Day	11% 14% 5% 11% 8% 6% 6% 4 5% 6% 24%	5124
February	1st to 10th	Day	13% 13% 5% 12% 8% 6% 4 4 5% 6% 25%	1867
	11th to 20th	Day	12% 15% 6% 13% 6% 5% 5% 2 4 6% 27%	2020
	21st to end	Day	15% 14% 5% 11% 8% 4 3 4 4 6% 26%	1730
March	1st to 10th	Day	21% 14% 6% 12% 4 4 4 3 3 4 25%	4576
	11th to 20th	Day	14% 16% 4 8% 5% 4 4 4 5% 6% 31%	4761
	21st to end	Day	22% 12% 3 9% 4 4 4 3 4 5% 31%	6102
April	1st to 10th	Day	22% 14% 4 6% 4 3 3 3 5% 6% 31%	2520
	11th to 20th	Day	20% 11% 3 7% 5% 4 3 3 4 5% 35%	2494
	21st to end	Day	22% 11% 3 6% 5% 4 4 4 4 6% 32%	2682
May	1st to 10th	Day	29% 10% 3 9% 5% 4 4 3 4 5% 22%	7817
	11th to 20th	Day	18% 9% 3 8% 5% 5% 5% 4 6% 7% 31%	8221
	21st to end	Day	19% 9% 3 7% 5% 5% 4 4 6% 8% 31%	9060
June	1st to 10th	Day	19% 8% 3 8% 5% 5% 5% 4 6% 7% 30%	2940
	11th to 20th	Day	16% 6% 3 7% 5% 5% 4 5% 6% 9% 35%	2870
	21st to end	Day	17% 9% 3 7% 6% 5% 5% 5% 7% 7% 30%	2800
July	1st to 10th	Day	11% 6% 3 7% 5% 6% 6% 5% 8% 10% 33%	6360
	11th to 20th	Day	11% 6% 3 7% 5% 5% 6% 5% 8% 10% 34%	6360
	21st to end	Day	13% 5% 2 6% 4 4 5% 4 7% 9% 40%	6926
August	1st to 10th	Day	15% 7% 3 7% 5% 5% 5% 5% 7% 9% 34%	4563
	11th to 20th	Day	13% 7% 3 9% 6% 5% 5% 5% 7% 8% 33%	3987
	21st to end	Day	12% 6% 2 6% 4 4 5% 5% 7% 8% 41%	4312
September	1st to 10th	Day	13% 5% 2 5% 4 4 4 3 6% 7% 47%	2400
	11th to 20th	Day	13% 6% 2 4 4 3 4 3 5% 7% 49%	2286
	21st to end	Day	16% 6% 2 7% 4 4 4 4 6% 7% 39%	2200
October	1st to 10th	Day	21% 9% 2 7% 5% 4 4 3 4 6% 35%	2115
	11th to 20th	Day	17% 9% 3 7% 6% 4 4 2 6% 7% 35%	1955
	21st to end	Day	25% 11% 3 7% 5% 5% 4 3 4 6% 27%	1980
November	1st to 10th	Day	16% 11% 3 8% 5% 4 4 3 4 7% 33%	1851
	11th to 20th	Day	18% 15% 3 7% 4 5% 4 3 6% 5% 29%	1890
	21st to end	Day	17% 14% 5% 9% 5% 4 5% 4 5% 6% 26%	1701
December	1st to 10th	Day	18% 17% 6% 12% 6% 5% 4 4 5% 5% 17%	2680
	11th to 20th	Day	22% 15% 4 11% 5% 4 4 3 4 5% 23%	3066
	21st to end	Day	21% 16% 5% 11% 6% 5% 5% 4 5% 5% 19%	4048
January	1st to 10th	Night	15% 18% 10% 17% 6% 4 3 2 3 4 20%	8234
	11th to 20th	Night	12% 20% 9% 18% 8% 6% 4 3 4 4 14%	8235
	21st to end	Night	13% 12% 5% 14% 9% 7% 6% 4 5% 5% 18%	9057
February	1st to 10th	Night	14% 14% 5% 13% 7% 6% 4 4 4 5% 23%	2751
	11th to 20th	Night	12% 15% 6% 13% 7% 6% 4 3 5% 5% 23%	2484
	21st to end	Night	15% 15% 4 12% 7% 5% 3 3 4 5% 29%	2076
March	1st to 10th	Night	22% 14% 5% 9% 6% 5% 4 3 4 4 25%	5484
	11th to 20th	Night	15% 15% 4 9% 5% 5% 4 3 4 6% 31%	5389
	21st to end	Night	21% 15% 5% 10% 5% 4 3 3 3 4 28%	5072
April	1st to 10th	Night	22% 12% 4 8% 5% 3 4 3 5% 5% 30%	2100
	11th to 20th	Night	24% 11% 3 8% 5% 3 3 3 3 6% 30%	2075
	21st to end	Night	21% 11% 4 6% 4 4 3 3 4 5% 34%	1937
May	1st to 10th	Night	28% 11% 3 8% 5% 4 4 3 5% 6% 23%	5123
	11th to 20th	Night	19% 10% 3 9% 5% 5% 4 3 5% 7% 29%	4639
	21st to end	Night	20% 8% 3 7% 4 5% 4 4 6% 8% 31%	5114
June	1st to 10th	Night	20% 9% 2 7% 5% 5% 4 3 6% 7% 34%	1680
	11th to 20th	Night	18% 8% 2 6% 4 4 4 3 6% 7% 37%	1640
	21st to end	Night	18% 8% 3 7% 5% 4 4 4 6% 8% 34%	1600
July	1st to 10th	Night	12% 6% 2 8% 5% 5% 5% 5% 8% 9% 34%	3600
	11th to 20th	Night	14% 7% 3 8% 5% 5% 5% 4 7% 8% 34%	3600
	21st to end	Night	10% 6% 3 8% 5% 4 5% 4 6% 8% 40%	3926
August	1st to 10th	Night	17% 8% 3 7% 5% 4 4 3 6% 6% 36%	2586
	11th to 20th	Night	14% 8% 3 7% 4 5% 4 4 6% 8% 36%	3024
	21st to end	Night	11% 6% 3 6% 4 4 5% 4 7% 8% 41%	3586
September	1st to 10th	Night	14% 5% 3 7% 3 4 4 2 5% 6% 47%	2000
	11th to 20th	Night	13% 6% 1 5% 3 3 4 4 5% 6% 51%	2113
	21st to end	Night	16% 6% 2 5% 4 4 4 4 6% 7% 42%	2200
October	1st to 10th	Night	21% 8% 2 8% 5% 4 4 3 5% 6% 33%	2281
	11th to 20th	Night	19% 9% 3 8% 4 4 5% 3 6% 6% 33%	2445
	21st to end	Night	24% 11% 4 8% 5% 5% 4 3 4 5% 27%	2860
November	1st to 10th	Night	19% 11% 4 9% 5% 5% 4 3 4 5% 32%	2667
	11th to 20th	Night	19% 13% 3 8% 5% 4 3 2 4 6% 31%	2730
	21st to end	Night	19% 14% 5% 9% 6% 5% 4 3 5% 5% 25%	2914
December	1st to 10th	Night	18% 22% 9% 15% 6% 5% 4 3 3 4 12%	4720
	11th to 20th	Night	25% 15% 4 9% 5% 4 3 3 3 6% 22%	5348
	21st to end	Night	22% 17% 6% 10% 7% 6% 5% 3 4 5% 17%	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% 7% 11% 13% 3	4662
	11th to 20th	Day	68% 6% 7% 11% 7% 1	4680
	21st to end	Day	60% 7% 10% 13% 9% 1	5124
February	1st to 10th	Day	62% 6% 10% 15% 6% 2	1867
	11th to 20th	Day	60% 8% 9% 16% 7% 1	2029
	21st to end	Day	59% 8% 10% 12% 10% 1	1730
March	1st to 10th	Day	64% 6% 9% 10% 8% 4	4579
	11th to 20th	Day	53% 7% 15% 14% 8% 2	4761
	21st to end	Day	55% 7% 7% 12% 16% 2	6102
April	1st to 10th	Day	57% 5% 9% 18% 10% 2	2520
	11th to 20th	Day	52% 7% 9% 17% 14% 1	2494
	21st to end	Day	55% 6% 9% 17% 11% 2	2682
May	1st to 10th	Day	63% 8% 7% 14% 7%	7829
	11th to 20th	Day	51% 8% 14% 18% 8% 1	8225
	21st to end	Day	50% 9% 11% 23% 7%	9061
June	1st to 10th	Day	52% 8% 13% 17% 9% 1	2940
	11th to 20th	Day	47% 8% 12% 19% 12% 1	2870
	21st to end	Day	52% 8% 11% 19% 9% 1	2800
July	1st to 10th	Day	43% 8% 17% 23% 9%	6290
	11th to 20th	Day	42% 9% 15% 24% 9%	6285
	21st to end	Day	40% 8% 14% 31% 7%	6728
August	1st to 10th	Day	46% 8% 16% 21% 8%	4549
	11th to 20th	Day	47% 8% 17% 22% 5%	4026
	21st to end	Day	38% 9% 19% 23% 11% 1	4312
September	1st to 10th	Day	37% 7% 14% 30% 12% 1	2400
	11th to 20th	Day	36% 5% 11% 30% 17% 1	2286
	21st to end	Day	42% 8% 15% 23% 11% 2	2200
October	1st to 10th	Day	47% 7% 9% 25% 12% 1	3440
	11th to 20th	Day	46% 5% 15% 21% 12%	3158
	21st to end	Day	45% 7% 12% 27% 8% 1	3180
November	1st to 10th	Day	51% 7% 13% 19% 9%	1851
	11th to 20th	Day	57% 6% 12% 13% 11% 2	1890
	21st to end	Day	59% 9% 14% 14% 4	1701
December	1st to 10th	Day	67% 9% 11% 10% 3	2680
	11th to 20th	Day	63% 6% 9% 15% 6%	3066
	21st to end	Day	65% 6% 8% 13% 7% 1	4048
January	1st to 10th	Night	69% 5% 12% 10% 3	8234
	11th to 20th	Night	74% 7% 7% 7% 4 1	8280
	21st to end	Night	66% 6% 8% 11% 7% 1	9057
February	1st to 10th	Night	64% 6% 10% 13% 7% 1	2751
	11th to 20th	Night	62% 7% 9% 14% 8% 1	2486
	21st to end	Night	59% 7% 11% 16% 7% 2	2076
March	1st to 10th	Night	62% 6% 8% 12% 10% 1	5494
	11th to 20th	Night	54% 7% 16% 14% 7% 2	5390
	21st to end	Night	59% 7% 6% 13% 13% 2	5072
April	1st to 10th	Night	57% 6% 8% 16% 11% 1	2100
	11th to 20th	Night	56% 6% 9% 17% 11% 1	2075
	21st to end	Night	52% 7% 8% 18% 12% 3	1937
May	1st to 10th	Night	61% 7% 10% 14% 8% 1	5129
	11th to 20th	Night	54% 8% 10% 19% 8% 1	4640
	21st to end	Night	50% 8% 11% 21% 10% 1	5115
June	1st to 10th	Night	49% 8% 12% 18% 12% 1	1680
	11th to 20th	Night	46% 8% 14% 19% 11% 2	1640
	21st to end	Night	49% 8% 13% 21% 9% 1	1600
July	1st to 10th	Night	43% 8% 19% 20% 9%	3560
	11th to 20th	Night	46% 9% 12% 22% 10%	3552
	21st to end	Night	40% 8% 15% 30% 8%	3809
August	1st to 10th	Night	49% 7% 13% 22% 9% 1	2576
	11th to 20th	Night	45% 7% 17% 22% 8%	3051
	21st to end	Night	36% 9% 18% 25% 11% 1	3586
September	1st to 10th	Night	38% 8% 15% 27% 12% 1	2000
	11th to 20th	Night	35% 5% 14% 30% 15% 1	2113
	21st to end	Night	41% 7% 13% 23% 13% 2	2200
October	1st to 10th	Night	53% 7% 10% 21% 8% 1	3736
	11th to 20th	Night	49% 5% 12% 20% 14% 1	3981
	21st to end	Night	51% 6% 13% 23% 6%	4610
November	1st to 10th	Night	55% 7% 11% 17% 8% 2	2667
	11th to 20th	Night	55% 6% 12% 15% 9% 2	2730
	21st to end	Night	60% 7% 14% 14% 5%	2914
December	1st to 10th	Night	76% 6% 8% 8% 1	4720
	11th to 20th	Night	64% 7% 8% 11% 9%	5348
	21st to end	Night	69% 5% 7% 13% 5% 2	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	26% 29% 28% 15% 2	220
	11th to 20th	Day	30% 28% 30% 10% 1 1	220
	21st to end	Day	26% 30% 31% 10% 2	242
February	1st to 10th	Day	31% 34% 28% 7% 1	319
	11th to 20th	Day	28% 31% 30% 10% 2	508
	21st to end	Day	31% 26% 32% 9% 2	446
March	1st to 10th	Day	30% 21% 34% 13% 2	540
	11th to 20th	Day	31% 30% 26% 11% 2 1	540
	21st to end	Day	35% 25% 25% 10% 4 1	594
April	1st to 10th	Day	39% 20% 24% 12% 4 1	540
	11th to 20th	Day	38% 21% 24% 10% 5% 1	532
	21st to end	Day	31% 24% 25% 13% 5% 2	540
May	1st to 10th	Day	34% 21% 25% 13% 7% 1	543
	11th to 20th	Day	26% 16% 34% 18% 4 1	567
	21st to end	Day	21% 20% 33% 20% 6% 1	617
June	1st to 10th	Day	24% 16% 35% 18% 6%	570
	11th to 20th	Day	21% 19% 34% 18% 7% 1	550
	21st to end	Day	25% 17% 32% 20% 6% 1	530
July	1st to 10th	Day	17% 13% 35% 24% 10% 1	525
	11th to 20th	Day	17% 12% 34% 26% 10% 1	524
	21st to end	Day	17% 12% 40% 23% 7% 1	576
August	1st to 10th	Day	15% 11% 30% 30% 12% 2	526
	11th to 20th	Day	19% 11% 28% 23% 14% 5%	519
	21st to end	Day	15% 15% 30% 25% 11% 4	583
September	1st to 10th	Day	17% 12% 28% 26% 10% 6%	530
	11th to 20th	Day	16% 13% 23% 23% 19% 7%	530
	21st to end	Day	18% 16% 30% 19% 12% 5%	530
October	1st to 10th	Day	27% 15% 25% 18% 12% 4	530
	11th to 20th	Day	27% 18% 28% 20% 7%	505
	21st to end	Day	33% 21% 28% 16% 2	462
November	1st to 10th	Day	31% 22% 26% 16% 5%	425
	11th to 20th	Day	29% 25% 24% 17% 4 1	430
	21st to end	Day	33% 24% 28% 14% 1	241
December	1st to 10th	Day	30% 25% 28% 14% 2	220
	11th to 20th	Day	36% 27% 29% 7% 1	220
	21st to end	Day	32% 24% 33% 8% 2	242
January	1st to 10th	Night	24% 25% 34% 15% 2	840
	11th to 20th	Night	28% 24% 29% 16% 3	840
	21st to end	Night	19% 23% 34% 20% 3	924
February	1st to 10th	Night	23% 22% 36% 18% 1	840
	11th to 20th	Night	22% 25% 35% 16% 2	823
	21st to end	Night	25% 22% 33% 18% 2	692
March	1st to 10th	Night	27% 21% 31% 19% 2	840
	11th to 20th	Night	26% 24% 28% 17% 4	840
	21st to end	Night	28% 21% 27% 18% 5%	924
April	1st to 10th	Night	31% 19% 27% 19% 4	840
	11th to 20th	Night	31% 21% 25% 17% 6%	831
	21st to end	Night	28% 18% 28% 21% 5%	677
May	1st to 10th	Night	30% 15% 28% 20% 7%	584
	11th to 20th	Night	22% 11% 37% 24% 6% 1	414
	21st to end	Night	21% 10% 32% 29% 8% 1	455
June	1st to 10th	Night	23% 9% 30% 27% 10%	420
	11th to 20th	Night	23% 8% 27% 31% 11%	410
	21st to end	Night	21% 6% 26% 37% 8% 1	400
July	1st to 10th	Night	15% 4 27% 38% 15% 1	390
	11th to 20th	Night	16% 5% 23% 38% 15% 2	388
	21st to end	Night	13% 6% 24% 44% 13%	438
August	1st to 10th	Night	16% 5% 19% 42% 18% 1	398
	11th to 20th	Night	18% 5% 21% 34% 19% 2	678
	21st to end	Night	16% 8% 22% 35% 18% 1	880
September	1st to 10th	Night	19% 8% 26% 31% 14% 2	800
	11th to 20th	Night	17% 8% 22% 30% 20% 3	800
	21st to end	Night	20% 11% 26% 25% 16% 2	800
October	1st to 10th	Night	29% 11% 21% 23% 15% 1	800
	11th to 20th	Night	26% 16% 24% 24% 9% 1	800
	21st to end	Night	33% 16% 28% 19% 4	880
November	1st to 10th	Night	28% 17% 30% 17% 6%	820
	11th to 20th	Night	26% 21% 29% 16% 6% 1	840
	21st to end	Night	27% 24% 28% 16% 4	840
December	1st to 10th	Night	32% 24% 27% 15% 3	840
	11th to 20th	Night	27% 22% 28% 20% 3	840
	21st to end	Night	33% 20% 30% 15% 2	924

Page generated at 2026-06-13 02:31:45. Version ac07

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