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 2025-02-21.

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% 10% 4 9% 5% 5% 5% 4 5% 7% 31%	108487
	Night	18% 12% 5% 10% 5% 5% 4 3 5% 6% 28%	110056
Transparency	Day	52% 8% 12% 19% 9% 1	112003
	Night	57% 7% 11% 16% 8% 1	114704
Seeing	Day	25% 20% 29% 18% 7% 2	15004
	Night	24% 17% 28% 23% 8% 1	24132

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% 16% 8% 19% 5% 4 4 3 4 4 19%	3597
	11th to 20th	Day	11% 14% 7% 18% 8% 4 4 3 4 6% 22%	3570
	21st to end	Day	13% 15% 5% 10% 6% 5% 6% 4 5% 6% 26%	3960
February	1st to 10th	Day	14% 13% 5% 12% 7% 5% 4 4 5% 6% 24%	1778
	11th to 20th	Day	12% 15% 6% 13% 6% 5% 5% 2 4 6% 26%	1921
	21st to end	Day	16% 13% 5% 10% 8% 4 3 4 4 6% 26%	1570
March	1st to 10th	Day	23% 15% 5% 10% 5% 4 4 3 4 4 22%	3116
	11th to 20th	Day	15% 20% 4 9% 5% 4 4 3 4 4 26%	3256
	21st to end	Day	18% 12% 3 10% 4 4 4 3 4 4 34%	4166
April	1st to 10th	Day	22% 13% 4 6% 4 3 3 3 5% 6% 32%	2280
	11th to 20th	Day	20% 10% 3 7% 5% 4 3 3 4 5% 36%	2254
	21st to end	Day	23% 11% 3 6% 5% 4 4 4 4 6% 31%	2426
May	1st to 10th	Day	26% 9% 3 8% 5% 4 4 3 5% 5% 28%	4202
	11th to 20th	Day	17% 8% 3 8% 5% 5% 5% 4 6% 8% 31%	4398
	21st to end	Day	12% 6% 3 6% 5% 5% 5% 4 6% 9% 38%	4837
June	1st to 10th	Day	20% 8% 3 8% 5% 5% 5% 4 6% 7% 30%	2660
	11th to 20th	Day	17% 6% 3 6% 5% 5% 4 5% 6% 9% 35%	2660
	21st to end	Day	17% 9% 3 7% 5% 5% 5% 5% 7% 7% 29%	2660
July	1st to 10th	Day	11% 6% 2 7% 5% 5% 5% 5% 7% 10% 36%	4440
	11th to 20th	Day	11% 6% 2 6% 5% 6% 6% 5% 8% 11% 33%	4440
	21st to end	Day	13% 6% 2 7% 5% 5% 5% 4 7% 9% 37%	4814
August	1st to 10th	Day	15% 7% 3 7% 5% 5% 5% 5% 7% 9% 33%	4423
	11th to 20th	Day	13% 8% 3 9% 6% 5% 5% 5% 7% 8% 33%	3863
	21st to end	Day	12% 6% 2 6% 4 4 5% 5% 6% 9% 41%	4180
September	1st to 10th	Day	13% 5% 2 5% 4 4 4 4 6% 7% 46%	2280
	11th to 20th	Day	13% 6% 2 4 4 3 3 3 5% 7% 48%	2172
	21st to end	Day	16% 6% 2 7% 4 4 4 4 6% 7% 39%	2090
October	1st to 10th	Day	22% 9% 2 7% 5% 4 5% 3 4 6% 32%	2009
	11th to 20th	Day	17% 9% 3 7% 6% 4 4 2 6% 7% 35%	1857
	21st to end	Day	25% 11% 3 7% 5% 4 4 3 4 6% 27%	1881
November	1st to 10th	Day	15% 11% 3 8% 5% 4 4 3 4 7% 34%	1761
	11th to 20th	Day	18% 14% 3 7% 4 5% 4 3 6% 5% 29%	1800
	21st to end	Day	18% 13% 5% 9% 5% 4 6% 4 5% 6% 27%	1620
December	1st to 10th	Day	18% 17% 7% 12% 6% 5% 4 4 5% 5% 17%	2600
	11th to 20th	Day	22% 15% 4 11% 5% 4 4 3 4 5% 23%	2986
	21st to end	Day	21% 17% 5% 10% 6% 5% 5% 4 5% 5% 19%	3960
January	1st to 10th	Night	14% 18% 10% 17% 5% 4 3 2 3 3 20%	6349
	11th to 20th	Night	11% 18% 8% 19% 7% 6% 4 3 4 4 15%	6315
	21st to end	Night	16% 14% 6% 14% 7% 5% 5% 4 5% 5% 19%	6996
February	1st to 10th	Night	15% 15% 5% 13% 7% 5% 4 3 4 5% 22%	2620
	11th to 20th	Night	13% 15% 6% 13% 7% 6% 4 3 5% 5% 23%	2363
	21st to end	Night	15% 14% 4 11% 7% 5% 3 3 4 5% 29%	1885
March	1st to 10th	Night	24% 13% 4 8% 6% 4 4 3 4 5% 26%	3724
	11th to 20th	Night	16% 18% 4 9% 5% 4 3 3 3 5% 29%	3674
	21st to end	Night	17% 14% 4 10% 5% 3 3 3 3 4 34%	3466
April	1st to 10th	Night	21% 12% 4 7% 5% 3 4 3 5% 6% 30%	1900
	11th to 20th	Night	24% 11% 3 7% 5% 3 3 3 3 7% 31%	1875
	21st to end	Night	22% 11% 4 6% 5% 4 3 4 4 5% 33%	1753
May	1st to 10th	Night	27% 10% 3 7% 4 4 4 3 5% 7% 25%	2753
	11th to 20th	Night	21% 10% 3 8% 6% 5% 4 3 4 6% 31%	2495
	21st to end	Night	16% 7% 2 7% 4 5% 4 4 7% 9% 38%	2738
June	1st to 10th	Night	19% 9% 2 7% 5% 5% 4 3 6% 7% 32%	1520
	11th to 20th	Night	18% 7% 2 6% 4 3 4 4 6% 8% 39%	1520
	21st to end	Night	19% 7% 3 7% 5% 4 4 4 6% 8% 33%	1520
July	1st to 10th	Night	13% 6% 3 8% 6% 5% 5% 5% 7% 7% 35%	2520
	11th to 20th	Night	15% 6% 2 6% 4 4 5% 4 7% 9% 37%	2520
	21st to end	Night	12% 7% 4 9% 4 4 5% 5% 6% 8% 36%	2739
August	1st to 10th	Night	17% 8% 3 7% 5% 4 4 3 6% 6% 35%	2506
	11th to 20th	Night	14% 8% 3 8% 5% 5% 4 4 6% 8% 35%	2929
	21st to end	Night	11% 6% 3 6% 4 4 5% 4 7% 8% 41%	3476
September	1st to 10th	Night	14% 5% 3 7% 3 4 4 2 5% 6% 46%	1900
	11th to 20th	Night	14% 6% 1 5% 3 3 3 3 5% 6% 51%	2007
	21st to end	Night	16% 6% 2 6% 4 4 4 4 6% 7% 42%	2090
October	1st to 10th	Night	22% 9% 3 8% 5% 5% 4 3 5% 6% 31%	2167
	11th to 20th	Night	19% 9% 3 8% 5% 4 5% 3 6% 6% 33%	2323
	21st to end	Night	24% 11% 4 9% 5% 5% 4 3 4 5% 27%	2717
November	1st to 10th	Night	18% 11% 3 9% 5% 5% 4 3 4 5% 33%	2537
	11th to 20th	Night	20% 12% 3 8% 5% 4 3 3 4 6% 32%	2600
	21st to end	Night	19% 14% 4 9% 6% 5% 4 3 6% 5% 25%	2775
December	1st to 10th	Night	18% 22% 9% 15% 6% 5% 4 3 3 4 12%	4580
	11th to 20th	Night	25% 15% 4 9% 5% 4 3 3 3 6% 23%	5208
	21st to end	Night	22% 17% 6% 10% 7% 6% 5% 3 4 5% 17%	6996

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	68% 6% 10% 13% 3	3598
	11th to 20th	Day	65% 7% 8% 12% 7% 2	3600
	21st to end	Day	60% 6% 10% 12% 10% 1	3960
February	1st to 10th	Day	62% 6% 10% 14% 6% 2	1778
	11th to 20th	Day	61% 7% 9% 15% 7% 1	1930
	21st to end	Day	59% 8% 10% 12% 11% 2	1570
March	1st to 10th	Day	65% 7% 9% 11% 7% 1	3119
	11th to 20th	Day	59% 9% 12% 11% 8% 1	3256
	21st to end	Day	52% 8% 7% 14% 17% 2	4166
April	1st to 10th	Day	56% 5% 9% 19% 9% 2	2280
	11th to 20th	Day	51% 7% 10% 17% 14% 1	2254
	21st to end	Day	56% 6% 9% 15% 11% 2	2426
May	1st to 10th	Day	58% 8% 9% 18% 7% 1	4216
	11th to 20th	Day	49% 10% 14% 17% 9% 1	4402
	21st to end	Day	40% 10% 13% 25% 11% 1	4837
June	1st to 10th	Day	53% 8% 14% 16% 9% 1	2660
	11th to 20th	Day	47% 8% 12% 19% 12% 2	2660
	21st to end	Day	53% 8% 11% 18% 8% 1	2660
July	1st to 10th	Day	40% 8% 15% 25% 10%	4370
	11th to 20th	Day	41% 10% 17% 26% 6%	4365
	21st to end	Day	43% 10% 14% 25% 8%	4661
August	1st to 10th	Day	47% 8% 16% 20% 8%	4409
	11th to 20th	Day	47% 8% 18% 22% 5%	3902
	21st to end	Day	38% 9% 19% 23% 11% 1	4180
September	1st to 10th	Day	37% 7% 14% 29% 12%	2280
	11th to 20th	Day	37% 6% 12% 29% 16% 1	2172
	21st to end	Day	42% 8% 15% 23% 10% 2	2090
October	1st to 10th	Day	48% 7% 9% 25% 11% 1	3334
	11th to 20th	Day	46% 5% 15% 21% 12%	3060
	21st to end	Day	45% 7% 12% 27% 8% 1	3081
November	1st to 10th	Day	51% 7% 14% 19% 9%	1761
	11th to 20th	Day	56% 6% 12% 13% 11% 2	1800
	21st to end	Day	58% 9% 15% 15% 4	1620
December	1st to 10th	Day	68% 9% 11% 9% 2	2600
	11th to 20th	Day	63% 6% 9% 15% 6%	2986
	21st to end	Day	65% 6% 8% 13% 7% 1	3960
January	1st to 10th	Night	70% 6% 13% 10% 3	6349
	11th to 20th	Night	71% 7% 9% 8% 4 1	6360
	21st to end	Night	66% 5% 8% 10% 8% 1	6996
February	1st to 10th	Night	65% 6% 10% 12% 6% 1	2620
	11th to 20th	Night	62% 6% 9% 14% 8% 1	2365
	21st to end	Night	58% 6% 11% 16% 7% 2	1885
March	1st to 10th	Night	61% 7% 9% 15% 8% 1	3734
	11th to 20th	Night	56% 8% 12% 15% 8% 1	3675
	21st to end	Night	53% 8% 7% 14% 15% 3	3466
April	1st to 10th	Night	57% 5% 8% 17% 11% 2	1900
	11th to 20th	Night	55% 6% 9% 17% 11% 1	1875
	21st to end	Night	53% 7% 8% 17% 11% 3	1753
May	1st to 10th	Night	57% 9% 9% 16% 8% 1	2759
	11th to 20th	Night	55% 7% 11% 17% 9% 1	2496
	21st to end	Night	41% 10% 14% 19% 14% 2	2739
June	1st to 10th	Night	49% 9% 13% 17% 11% 1	1520
	11th to 20th	Night	45% 8% 14% 20% 11% 2	1520
	21st to end	Night	49% 8% 13% 21% 8% 1	1520
July	1st to 10th	Night	45% 9% 16% 18% 12% 1	2480
	11th to 20th	Night	43% 10% 14% 24% 9%	2472
	21st to end	Night	45% 8% 12% 26% 9%	2651
August	1st to 10th	Night	50% 7% 12% 21% 9%	2496
	11th to 20th	Night	46% 7% 17% 22% 8%	2956
	21st to end	Night	36% 9% 18% 25% 11% 1	3476
September	1st to 10th	Night	38% 8% 15% 27% 11% 1	1900
	11th to 20th	Night	35% 5% 15% 30% 14% 1	2007
	21st to end	Night	41% 7% 14% 23% 13% 2	2090
October	1st to 10th	Night	54% 7% 10% 21% 7% 1	3622
	11th to 20th	Night	49% 5% 12% 20% 14% 1	3859
	21st to end	Night	51% 6% 13% 23% 6%	4467
November	1st to 10th	Night	55% 7% 12% 17% 8% 2	2537
	11th to 20th	Night	54% 7% 12% 16% 10% 2	2600
	21st to end	Night	59% 7% 15% 14% 5%	2775
December	1st to 10th	Night	77% 6% 8% 8% 1	4580
	11th to 20th	Night	64% 7% 8% 11% 9%	5208
	21st to end	Night	69% 5% 7% 13% 5% 2	6996

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% 31% 27% 14% 2	200
	11th to 20th	Day	28% 28% 32% 11% 1 1	200
	21st to end	Day	25% 30% 32% 10% 3	220
February	1st to 10th	Day	32% 36% 26% 4 1	290
	11th to 20th	Day	29% 32% 28% 10% 2	469
	21st to end	Day	32% 24% 32% 10% 2	382
March	1st to 10th	Day	28% 21% 34% 15% 2	460
	11th to 20th	Day	28% 30% 26% 13% 2 1	460
	21st to end	Day	32% 24% 26% 11% 5% 2	506
April	1st to 10th	Day	36% 20% 25% 14% 5% 1	460
	11th to 20th	Day	35% 23% 24% 12% 6% 1	452
	21st to end	Day	31% 24% 25% 13% 5% 2	460
May	1st to 10th	Day	30% 21% 25% 14% 8% 1	463
	11th to 20th	Day	23% 16% 35% 19% 5% 1	487
	21st to end	Day	19% 19% 33% 22% 6% 1	529
June	1st to 10th	Day	23% 17% 36% 17% 7%	490
	11th to 20th	Day	19% 18% 34% 20% 8% 1	490
	21st to end	Day	26% 17% 31% 19% 7% 1	490
July	1st to 10th	Day	17% 13% 33% 25% 11% 1	485
	11th to 20th	Day	17% 11% 34% 26% 10% 1	484
	21st to end	Day	17% 12% 39% 24% 7% 2	532
August	1st to 10th	Day	16% 12% 30% 29% 11% 2	486
	11th to 20th	Day	20% 11% 28% 23% 13% 5%	479
	21st to end	Day	15% 15% 28% 26% 11% 4	539
September	1st to 10th	Day	17% 12% 29% 25% 11% 6%	490
	11th to 20th	Day	17% 14% 22% 22% 19% 7%	490
	21st to end	Day	18% 17% 29% 19% 13% 5%	490
October	1st to 10th	Day	28% 15% 25% 16% 12% 4	490
	11th to 20th	Day	26% 18% 28% 21% 7%	467
	21st to end	Day	34% 20% 28% 16% 3	429
November	1st to 10th	Day	28% 22% 27% 17% 6%	395
	11th to 20th	Day	30% 25% 24% 17% 4 1	400
	21st to end	Day	32% 23% 29% 15% 1	220
December	1st to 10th	Day	29% 26% 29% 15% 3	200
	11th to 20th	Day	35% 28% 29% 8% 1	200
	21st to end	Day	32% 25% 33% 8% 3	220
January	1st to 10th	Night	24% 25% 34% 15% 2	800
	11th to 20th	Night	27% 23% 30% 16% 3	800
	21st to end	Night	19% 23% 34% 21% 3	880
February	1st to 10th	Night	24% 23% 35% 17% 1	800
	11th to 20th	Night	22% 26% 34% 16% 2	783
	21st to end	Night	25% 22% 32% 19% 2	629
March	1st to 10th	Night	26% 20% 32% 21% 2	760
	11th to 20th	Night	25% 24% 28% 18% 4	760
	21st to end	Night	26% 22% 26% 19% 6%	836
April	1st to 10th	Night	30% 18% 27% 21% 4	760
	11th to 20th	Night	29% 21% 25% 18% 7% 1	751
	21st to end	Night	28% 18% 28% 21% 5%	613
May	1st to 10th	Night	30% 14% 28% 20% 8%	528
	11th to 20th	Night	22% 10% 36% 25% 6% 1	374
	21st to end	Night	20% 9% 31% 30% 9% 1	411
June	1st to 10th	Night	23% 9% 30% 27% 11%	380
	11th to 20th	Night	22% 7% 27% 32% 12% 1	380
	21st to end	Night	22% 5% 27% 37% 8% 1	380
July	1st to 10th	Night	15% 4 27% 37% 16% 1	370
	11th to 20th	Night	15% 5% 23% 39% 16% 2	368
	21st to end	Night	13% 6% 21% 46% 13%	416
August	1st to 10th	Night	17% 5% 18% 42% 17% 1	378
	11th to 20th	Night	18% 5% 22% 34% 19% 2	643
	21st to end	Night	17% 8% 22% 34% 18% 1	836
September	1st to 10th	Night	19% 8% 26% 31% 14% 2	760
	11th to 20th	Night	18% 8% 22% 29% 20% 4	760
	21st to end	Night	19% 11% 26% 25% 17% 2	760
October	1st to 10th	Night	30% 11% 21% 22% 15% 1	760
	11th to 20th	Night	26% 16% 24% 25% 9% 1	760
	21st to end	Night	33% 16% 28% 19% 5%	836
November	1st to 10th	Night	27% 18% 30% 18% 7%	780
	11th to 20th	Night	26% 21% 29% 17% 6% 1	800
	21st to end	Night	27% 25% 28% 16% 5% 1	800
December	1st to 10th	Night	31% 24% 27% 15% 3	800
	11th to 20th	Night	27% 22% 28% 20% 3	800
	21st to end	Night	33% 19% 31% 15% 2	880

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