Meetinghouse Hill
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Meetinghouse Hill clear sky chart from 2005-11-06 to 2025-11-18.

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	17% 7% 2 6% 4 4 4 4 6% 7% 38%	126664
	Night	17% 8% 2 6% 4 4 4 3 5% 6% 40%	123716
Transparency	Day	28% 39% 7% 14% 10% 2	130184
	Night	28% 38% 7% 14% 11% 2	128283
Seeing	Day	24% 18% 31% 18% 7% 2	16292
	Night	22% 16% 33% 23% 6%	25188

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	11% 6% 3 9% 6% 5% 5% 4 6% 7% 38%	3597
	11th to 20th	Day	12% 7% 4 7% 4 4 4 4 5% 6% 44%	3570
	21st to end	Day	15% 10% 3 6% 4 4 3 3 5% 6% 43%	3960
February	1st to 10th	Day	16% 7% 3 7% 5% 5% 6% 4 5% 5% 35%	1836
	11th to 20th	Day	13% 7% 2 8% 6% 4 5% 5% 5% 7% 38%	1948
	21st to end	Day	17% 11% 3 7% 5% 4 4 3 5% 5% 37%	1650
March	1st to 10th	Day	19% 11% 3 7% 4 4 4 3 4 5% 35%	4476
	11th to 20th	Day	15% 9% 2 5% 5% 4 4 4 5% 7% 40%	4722
	21st to end	Day	24% 10% 2 6% 3 3 3 4 5% 7% 33%	5849
April	1st to 10th	Day	17% 10% 3 7% 5% 5% 4 4 4 5% 37%	2400
	11th to 20th	Day	17% 6% 2 7% 4 4 4 4 6% 8% 38%	2374
	21st to end	Day	20% 7% 2 7% 5% 4 4 4 5% 6% 36%	2600
May	1st to 10th	Day	31% 10% 2 7% 4 4 4 3 5% 6% 24%	5886
	11th to 20th	Day	20% 8% 3 9% 5% 5% 5% 4 6% 7% 30%	6085
	21st to end	Day	19% 6% 3 6% 5% 5% 5% 3 6% 8% 34%	6949
June	1st to 10th	Day	19% 6% 2 6% 5% 5% 4 5% 7% 8% 34%	2800
	11th to 20th	Day	17% 5% 3 6% 5% 4 5% 4 6% 9% 36%	2800
	21st to end	Day	18% 7% 2 6% 5% 5% 5% 4 5% 8% 34%	2800
July	1st to 10th	Day	15% 6% 2 7% 5% 6% 5% 5% 7% 9% 34%	6360
	11th to 20th	Day	9% 5% 2 6% 5% 5% 6% 5% 8% 11% 38%	6360
	21st to end	Day	15% 6% 2 6% 4 3 4 4 6% 8% 42%	6926
August	1st to 10th	Day	14% 6% 2 7% 5% 6% 5% 5% 6% 9% 35%	4349
	11th to 20th	Day	14% 7% 2 7% 5% 5% 5% 4 7% 7% 37%	4084
	21st to end	Day	8% 4 2 6% 5% 5% 6% 5% 8% 10% 42%	4312
September	1st to 10th	Day	13% 5% 2 6% 4 4 4 4 6% 7% 46%	2400
	11th to 20th	Day	14% 5% 2 5% 3 3 4 3 4 6% 51%	2218
	21st to end	Day	16% 6% 2 6% 4 4 4 3 5% 7% 44%	2200
October	1st to 10th	Day	22% 5% 2 5% 5% 4 4 3 4 5% 41%	2200
	11th to 20th	Day	16% 5% 2 5% 3 4 4 4 5% 8% 45%	1933
	21st to end	Day	21% 6% 2 6% 4 4 5% 3 4 6% 39%	1980
November	1st to 10th	Day	13% 6% 2 7% 4 4 3 3 4 5% 48%	1851
	11th to 20th	Day	17% 6% 1 4 3 4 3 3 5% 5% 47%	1863
	21st to end	Day	18% 7% 2 5% 5% 4 5% 2 5% 5% 42%	1780
December	1st to 10th	Day	15% 7% 2 5% 4 4 4 3 6% 6% 43%	2600
	11th to 20th	Day	21% 6% 2 4 4 3 3 4 5% 6% 43%	2986
	21st to end	Day	17% 12% 3 6% 4 3 4 3 4 6% 38%	3960
January	1st to 10th	Night	13% 7% 2 6% 4 4 4 4 6% 7% 45%	6349
	11th to 20th	Night	11% 8% 3 8% 5% 5% 4 4 5% 7% 39%	6315
	21st to end	Night	14% 10% 4 7% 4 4 4 4 4 6% 38%	6996
February	1st to 10th	Night	15% 9% 3 6% 4 4 5% 4 6% 6% 38%	2560
	11th to 20th	Night	12% 8% 3 6% 5% 6% 5% 4 5% 6% 40%	2338
	21st to end	Night	14% 9% 3 7% 4 4 4 3 6% 5% 40%	1980
March	1st to 10th	Night	21% 9% 2 4 4 4 4 4 4 6% 38%	5364
	11th to 20th	Night	15% 9% 3 7% 5% 4 4 4 5% 6% 38%	5237
	21st to end	Night	24% 8% 2 5% 3 4 4 3 6% 6% 34%	5068
April	1st to 10th	Night	18% 8% 3 7% 5% 4 4 4 5% 6% 35%	2000
	11th to 20th	Night	20% 6% 2 5% 5% 3 4 3 6% 6% 39%	1975
	21st to end	Night	21% 7% 3 6% 4 3 4 3 4 6% 40%	1800
May	1st to 10th	Night	33% 10% 2 6% 3 3 3 3 5% 7% 24%	4054
	11th to 20th	Night	16% 9% 3 9% 6% 5% 5% 4 6% 7% 30%	3851
	21st to end	Night	21% 8% 3 7% 4 4 4 4 5% 7% 33%	3926
June	1st to 10th	Night	18% 8% 2 7% 4 5% 4 3 4 7% 39%	1600
	11th to 20th	Night	18% 7% 2 6% 4 4 4 4 6% 9% 37%	1600
	21st to end	Night	17% 6% 2 6% 4 3 5% 4 5% 7% 41%	1600
July	1st to 10th	Night	13% 5% 2 6% 5% 5% 4 4 5% 9% 41%	3600
	11th to 20th	Night	11% 7% 2 7% 4 4 5% 4 6% 9% 41%	3600
	21st to end	Night	12% 6% 2 5% 4 4 4 3 5% 6% 49%	3926
August	1st to 10th	Night	19% 7% 3 7% 4 5% 5% 4 5% 6% 36%	2767
	11th to 20th	Night	13% 8% 3 7% 5% 6% 5% 4 6% 7% 37%	2960
	21st to end	Night	9% 4 1 4 2 3 3 3 5% 8% 58%	3586
September	1st to 10th	Night	13% 5% 2 5% 4 3 3 3 4 7% 50%	2000
	11th to 20th	Night	13% 5% 1 4 3 2 3 3 5% 6% 54%	2181
	21st to end	Night	16% 4 2 6% 4 4 4 3 5% 6% 46%	2200
October	1st to 10th	Night	20% 6% 3 5% 3 4 4 2 5% 6% 43%	2200
	11th to 20th	Night	16% 5% 1 4 3 4 5% 4 6% 7% 46%	2464
	21st to end	Night	21% 7% 2 5% 3 4 4 3 5% 6% 39%	2860
November	1st to 10th	Night	14% 6% 2 5% 3 4 4 3 5% 6% 47%	2667
	11th to 20th	Night	16% 6% 2 5% 4 4 4 3 4 5% 46%	2692
	21st to end	Night	15% 7% 1 5% 4 4 4 3 5% 7% 44%	2616
December	1st to 10th	Night	16% 10% 3 6% 4 3 4 4 5% 6% 40%	4580
	11th to 20th	Night	21% 8% 2 6% 3 3 3 3 4 5% 41%	5208
	21st to end	Night	18% 10% 3 6% 4 4 4 3 5% 5% 39%	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	34% 27% 5% 19% 13% 1	3598
	11th to 20th	Day	28% 28% 7% 18% 15% 4	3600
	21st to end	Day	33% 29% 4 14% 16% 3	3960
February	1st to 10th	Day	17% 62% 6% 8% 5% 1	1836
	11th to 20th	Day	19% 61% 3 7% 9% 2	1957
	21st to end	Day	16% 62% 4 9% 7% 1	1650
March	1st to 10th	Day	40% 29% 6% 8% 8% 9%	4479
	11th to 20th	Day	30% 31% 10% 20% 9% 1	4722
	21st to end	Day	40% 28% 4 10% 12% 5%	5849
April	1st to 10th	Day	22% 62% 2 7% 5% 2	2400
	11th to 20th	Day	16% 63% 4 8% 8% 1	2374
	21st to end	Day	20% 61% 3 7% 8% 1	2600
May	1st to 10th	Day	47% 30% 10% 9% 5%	5897
	11th to 20th	Day	41% 31% 11% 11% 5%	6089
	21st to end	Day	37% 30% 8% 16% 9%	6949
June	1st to 10th	Day	16% 63% 5% 10% 7%	2800
	11th to 20th	Day	15% 63% 5% 9% 7% 1	2800
	21st to end	Day	16% 62% 4 9% 7% 1	2800
July	1st to 10th	Day	35% 28% 10% 15% 12%	6290
	11th to 20th	Day	28% 29% 13% 19% 10% 1	6285
	21st to end	Day	30% 26% 8% 21% 14% 1	6728
August	1st to 10th	Day	30% 38% 10% 15% 6%	4335
	11th to 20th	Day	28% 38% 11% 17% 6%	4123
	21st to end	Day	20% 38% 8% 20% 12% 1	4312
September	1st to 10th	Day	15% 57% 6% 13% 8% 1	2400
	11th to 20th	Day	17% 57% 4 10% 12% 2	2218
	21st to end	Day	18% 57% 4 11% 8% 1	2200
October	1st to 10th	Day	27% 37% 4 15% 14% 2	3590
	11th to 20th	Day	19% 36% 4 19% 19% 3	3123
	21st to end	Day	19% 36% 5% 24% 14% 2	3180
November	1st to 10th	Day	19% 54% 7% 11% 8% 1	1851
	11th to 20th	Day	17% 55% 3 8% 14% 2	1863
	21st to end	Day	17% 57% 6% 11% 7% 1	1780
December	1st to 10th	Day	25% 37% 10% 23% 7%	2600
	11th to 20th	Day	29% 32% 8% 13% 15% 3	2986
	21st to end	Day	36% 27% 5% 15% 12% 5%	3960
January	1st to 10th	Night	28% 27% 7% 25% 11% 2	6349
	11th to 20th	Night	33% 28% 9% 15% 12% 3	6360
	21st to end	Night	38% 28% 6% 11% 12% 4	6996
February	1st to 10th	Night	18% 62% 5% 8% 6% 1	2560
	11th to 20th	Night	17% 61% 5% 7% 9% 2	2340
	21st to end	Night	17% 62% 3 9% 6% 3	1980
March	1st to 10th	Night	37% 29% 6% 10% 11% 7%	5374
	11th to 20th	Night	33% 30% 13% 14% 9% 1	5238
	21st to end	Night	39% 29% 3 8% 17% 5%	5068
April	1st to 10th	Night	22% 62% 2 6% 6% 2	2000
	11th to 20th	Night	18% 63% 4 7% 8% 1	1975
	21st to end	Night	18% 62% 4 7% 9% 1	1800
May	1st to 10th	Night	46% 30% 10% 9% 5%	4060
	11th to 20th	Night	39% 33% 11% 12% 6%	3852
	21st to end	Night	39% 30% 10% 12% 7% 1	3927
June	1st to 10th	Night	17% 62% 3 11% 8%	1600
	11th to 20th	Night	15% 64% 6% 10% 6%	1600
	21st to end	Night	15% 61% 5% 12% 7% 1	1600
July	1st to 10th	Night	30% 27% 10% 20% 12%	3560
	11th to 20th	Night	30% 29% 13% 13% 14% 1	3552
	21st to end	Night	27% 26% 8% 25% 13%	3809
August	1st to 10th	Night	34% 38% 8% 12% 7% 1	2757
	11th to 20th	Night	29% 39% 10% 16% 6%	2987
	21st to end	Night	13% 37% 11% 23% 15% 1	3586
September	1st to 10th	Night	14% 57% 5% 13% 10%	2000
	11th to 20th	Night	15% 57% 3 11% 13% 1	2181
	21st to end	Night	19% 57% 4 12% 7% 1	2200
October	1st to 10th	Night	23% 37% 10% 17% 11% 1	3590
	11th to 20th	Night	14% 36% 7% 18% 23% 3	4013
	21st to end	Night	20% 36% 7% 26% 10% 2	4610
November	1st to 10th	Night	18% 55% 4 12% 9% 2	2667
	11th to 20th	Night	17% 55% 4 9% 13% 2	2692
	21st to end	Night	16% 57% 7% 12% 8% 1	2616
December	1st to 10th	Night	29% 37% 6% 19% 8%	4580
	11th to 20th	Night	34% 32% 8% 8% 17% 1	5208
	21st to end	Night	35% 27% 6% 15% 14% 3	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	33% 26% 27% 13% 3	200
	11th to 20th	Day	33% 23% 31% 12% 2 1	200
	21st to end	Day	28% 28% 31% 10% 4	220
February	1st to 10th	Day	32% 29% 27% 11% 1	368
	11th to 20th	Day	31% 31% 27% 10% 1	496
	21st to end	Day	29% 25% 31% 13% 2	414
March	1st to 10th	Day	31% 24% 32% 10% 2	500
	11th to 20th	Day	31% 27% 29% 9% 3 1	500
	21st to end	Day	33% 23% 29% 10% 4 1	550
April	1st to 10th	Day	34% 22% 28% 11% 5%	500
	11th to 20th	Day	32% 23% 30% 10% 4 1	492
	21st to end	Day	29% 21% 31% 13% 5% 1	500
May	1st to 10th	Day	34% 19% 28% 13% 4 1	503
	11th to 20th	Day	22% 18% 38% 16% 4 2	527
	21st to end	Day	18% 15% 36% 23% 6% 1	573
June	1st to 10th	Day	19% 15% 37% 18% 8% 2	530
	11th to 20th	Day	18% 16% 37% 21% 7% 1	530
	21st to end	Day	20% 15% 34% 21% 8% 3	530
July	1st to 10th	Day	18% 10% 30% 28% 12% 2	525
	11th to 20th	Day	12% 9% 35% 30% 12% 3	524
	21st to end	Day	13% 9% 37% 31% 8% 2	576
August	1st to 10th	Day	13% 9% 30% 32% 13% 3	526
	11th to 20th	Day	17% 8% 29% 27% 15% 4	519
	21st to end	Day	12% 11% 33% 27% 13% 4	583
September	1st to 10th	Day	18% 9% 30% 22% 15% 5%	530
	11th to 20th	Day	18% 11% 26% 19% 17% 9%	530
	21st to end	Day	19% 13% 30% 23% 9% 5%	530
October	1st to 10th	Day	27% 13% 23% 20% 13% 4	530
	11th to 20th	Day	22% 17% 30% 21% 8% 2	478
	21st to end	Day	29% 16% 30% 19% 6% 1	462
November	1st to 10th	Day	23% 21% 29% 19% 8% 1	425
	11th to 20th	Day	31% 18% 30% 16% 3 1	421
	21st to end	Day	31% 20% 29% 15% 5%	380
December	1st to 10th	Day	26% 30% 26% 15% 4	200
	11th to 20th	Day	40% 21% 30% 8% 2	200
	21st to end	Day	28% 25% 29% 13% 4 1	220
January	1st to 10th	Night	22% 25% 38% 14% 2	800
	11th to 20th	Night	27% 22% 33% 16% 2	800
	21st to end	Night	20% 22% 39% 16% 3	880
February	1st to 10th	Night	23% 21% 38% 17% 1	800
	11th to 20th	Night	23% 25% 38% 13% 1	783
	21st to end	Night	23% 25% 34% 15% 2	660
March	1st to 10th	Night	26% 23% 33% 17% 2	800
	11th to 20th	Night	23% 23% 34% 16% 3	800
	21st to end	Night	26% 21% 33% 16% 4	880
April	1st to 10th	Night	27% 19% 34% 17% 3	800
	11th to 20th	Night	25% 22% 32% 17% 4	791
	21st to end	Night	24% 20% 34% 19% 2	600
May	1st to 10th	Night	27% 14% 36% 20% 4	600
	11th to 20th	Night	21% 14% 39% 22% 4	514
	21st to end	Night	20% 7% 39% 28% 6%	433
June	1st to 10th	Night	20% 12% 34% 27% 7%	400
	11th to 20th	Night	21% 7% 32% 33% 6% 1	400
	21st to end	Night	17% 5% 37% 35% 5%	400
July	1st to 10th	Night	17% 6% 31% 38% 8% 1	390
	11th to 20th	Night	14% 4 29% 41% 11% 1	388
	21st to end	Night	13% 5% 32% 41% 10%	438
August	1st to 10th	Night	14% 5% 29% 40% 12%	501
	11th to 20th	Night	14% 6% 29% 36% 14% 1	641
	21st to end	Night	15% 5% 25% 38% 15% 1	880
September	1st to 10th	Night	16% 6% 32% 32% 12% 1	800
	11th to 20th	Night	15% 7% 29% 29% 19% 2	800
	21st to end	Night	19% 9% 29% 29% 13% 2	800
October	1st to 10th	Night	25% 11% 25% 25% 12% 1	800
	11th to 20th	Night	20% 14% 33% 23% 10% 1	800
	21st to end	Night	26% 16% 31% 22% 5%	880
November	1st to 10th	Night	20% 16% 33% 24% 7% 1	820
	11th to 20th	Night	22% 20% 34% 18% 6% 1	829
	21st to end	Night	25% 20% 33% 18% 4	800
December	1st to 10th	Night	26% 20% 36% 14% 4	800
	11th to 20th	Night	26% 22% 32% 17% 3	800
	21st to end	Night	26% 21% 33% 18% 2	880

Page generated at 2025-11-15 00:55:59. Version ac07

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