Myles Standish State Forest
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Myles Standish State Forest clear sky chart from 2005-11-06 to 2025-12-18.

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% 8% 2 6% 4 4 4 3 5% 7% 39%	126765
	Night	17% 9% 3 6% 4 4 4 3 5% 6% 39%	124255
Transparency	Day	44% 6% 13% 22% 14% 2	130327
	Night	45% 6% 11% 21% 15% 2	128781
Seeing	Day	19% 10% 30% 26% 12% 3	16586
	Night	20% 10% 31% 27% 9% 1	25467

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% 9% 3 7% 3 3 3 3 5% 5% 48%	3597
	11th to 20th	Day	15% 9% 2 5% 3 2 3 3 4 5% 48%	3570
	21st to end	Day	18% 9% 3 7% 4 4 4 3 3 4 41%	4003
February	1st to 10th	Day	19% 9% 4 7% 4 4 4 3 5% 6% 35%	1900
	11th to 20th	Day	15% 7% 3 6% 4 4 4 4 5% 7% 42%	1948
	21st to end	Day	17% 11% 2 6% 4 3 4 3 5% 6% 39%	1650
March	1st to 10th	Day	20% 14% 3 6% 4 3 2 2 4 5% 37%	4476
	11th to 20th	Day	15% 12% 2 7% 4 3 3 3 5% 7% 38%	4842
	21st to end	Day	24% 11% 3 7% 4 4 4 3 4 5% 31%	5648
April	1st to 10th	Day	20% 10% 2 5% 4 3 4 3 5% 6% 38%	2400
	11th to 20th	Day	18% 8% 2 6% 4 4 4 4 4 6% 39%	2412
	21st to end	Day	19% 6% 3 6% 4 4 5% 3 5% 6% 40%	2600
May	1st to 10th	Day	26% 12% 4 7% 4 4 4 3 5% 7% 25%	5886
	11th to 20th	Day	21% 11% 3 7% 5% 4 4 3 5% 7% 32%	5861
	21st to end	Day	20% 8% 3 6% 4 4 4 4 5% 7% 37%	6850
June	1st to 10th	Day	20% 7% 2 5% 4 4 4 4 6% 9% 34%	2800
	11th to 20th	Day	15% 6% 2 6% 4 4 4 5% 6% 8% 38%	2800
	21st to end	Day	14% 7% 3 6% 4 4 5% 4 6% 9% 39%	2800
July	1st to 10th	Day	16% 8% 3 7% 4 4 4 4 7% 10% 33%	6360
	11th to 20th	Day	11% 8% 2 6% 4 4 6% 4 8% 10% 35%	6360
	21st to end	Day	15% 6% 2 6% 4 4 3 3 6% 8% 43%	6836
August	1st to 10th	Day	17% 7% 3 8% 5% 5% 6% 4 6% 8% 33%	4235
	11th to 20th	Day	12% 7% 2 7% 4 5% 5% 5% 6% 8% 39%	4175
	21st to end	Day	8% 4 2 5% 4 5% 5% 4 8% 10% 45%	4316
September	1st to 10th	Day	14% 6% 3 5% 4 4 4 3 5% 6% 47%	2360
	11th to 20th	Day	14% 6% 2 5% 4 3 3 2 4 7% 51%	2200
	21st to end	Day	19% 7% 2 6% 3 4 4 3 5% 6% 41%	2200
October	1st to 10th	Day	21% 6% 2 4 3 3 4 3 5% 6% 44%	2200
	11th to 20th	Day	17% 5% 2 5% 3 4 3 3 5% 7% 46%	1982
	21st to end	Day	18% 7% 2 6% 3 3 3 3 5% 6% 45%	1980
November	1st to 10th	Day	17% 6% 2 5% 3 3 4 3 5% 5% 45%	1851
	11th to 20th	Day	17% 7% 2 4 3 3 3 3 5% 7% 45%	1890
	21st to end	Day	18% 7% 2 5% 3 3 4 3 5% 6% 44%	1890
December	1st to 10th	Day	14% 10% 2 4 3 3 3 2 4 5% 49%	2885
	11th to 20th	Day	18% 8% 2 5% 4 3 3 2 3 5% 46%	3042
	21st to end	Day	19% 11% 3 7% 4 4 4 3 5% 5% 35%	3960
January	1st to 10th	Night	14% 6% 2 5% 3 3 3 3 4 6% 52%	6349
	11th to 20th	Night	15% 11% 4 8% 3 4 3 3 4 5% 41%	6315
	21st to end	Night	17% 11% 4 8% 5% 4 4 3 4 4 37%	6951
February	1st to 10th	Night	17% 10% 3 7% 4 4 3 4 5% 5% 39%	2499
	11th to 20th	Night	18% 9% 3 6% 4 4 4 4 4 5% 40%	2338
	21st to end	Night	17% 8% 2 7% 5% 4 3 3 4 6% 42%	1980
March	1st to 10th	Night	25% 10% 2 5% 3 3 4 3 4 5% 36%	5364
	11th to 20th	Night	16% 12% 4 8% 4 4 3 3 4 5% 36%	5117
	21st to end	Night	24% 11% 3 7% 5% 4 4 3 4 4 32%	5268
April	1st to 10th	Night	19% 9% 3 6% 5% 4 5% 3 5% 6% 36%	2000
	11th to 20th	Night	19% 9% 2 5% 5% 4 4 4 5% 6% 37%	1936
	21st to end	Night	18% 8% 3 7% 5% 4 5% 3 5% 5% 38%	1800
May	1st to 10th	Night	27% 11% 3 7% 5% 4 4 3 5% 6% 25%	4054
	11th to 20th	Night	20% 11% 3 8% 5% 5% 4 4 6% 8% 26%	4033
	21st to end	Night	19% 9% 3 8% 5% 5% 5% 4 5% 6% 29%	4066
June	1st to 10th	Night	16% 8% 3 6% 4 4 6% 4 7% 7% 35%	1600
	11th to 20th	Night	18% 8% 2 6% 4 6% 4 3 5% 7% 37%	1600
	21st to end	Night	16% 10% 3 6% 4 3 4 4 6% 9% 37%	1600
July	1st to 10th	Night	16% 9% 3 8% 5% 4 5% 4 6% 9% 31%	3600
	11th to 20th	Night	16% 9% 3 7% 4 4 5% 4 7% 8% 34%	3600
	21st to end	Night	13% 7% 3 7% 5% 5% 5% 4 5% 7% 39%	3969
August	1st to 10th	Night	21% 7% 2 7% 5% 5% 4 4 7% 8% 30%	2915
	11th to 20th	Night	9% 8% 3 8% 4 5% 6% 4 7% 8% 37%	2872
	21st to end	Night	8% 4 1 5% 3 3 4 3 6% 7% 54%	3578
September	1st to 10th	Night	13% 6% 3 6% 4 4 5% 3 6% 6% 46%	2039
	11th to 20th	Night	14% 6% 2 5% 3 3 4 3 4 6% 51%	2200
	21st to end	Night	19% 7% 2 6% 5% 3 5% 4 5% 5% 41%	2200
October	1st to 10th	Night	20% 7% 2 6% 5% 4 3 3 4 6% 42%	2200
	11th to 20th	Night	16% 6% 2 6% 4 3 3 3 4 7% 46%	2411
	21st to end	Night	19% 8% 3 6% 4 4 4 3 5% 6% 39%	2860
November	1st to 10th	Night	16% 6% 2 5% 4 4 3 4 5% 5% 46%	2667
	11th to 20th	Night	17% 7% 2 5% 3 3 3 4 4 6% 46%	2730
	21st to end	Night	16% 7% 2 5% 3 3 4 3 4 7% 45%	2730
December	1st to 10th	Night	18% 8% 2 6% 3 3 3 2 4 4 47%	4511
	11th to 20th	Night	20% 9% 2 5% 3 3 3 3 4 5% 41%	5307
	21st to end	Night	17% 10% 3 7% 4 4 4 3 4 6% 38%	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	38% 4 8% 25% 22% 4	3598
	11th to 20th	Day	38% 6% 10% 22% 16% 8%	3600
	21st to end	Day	47% 5% 10% 19% 17% 2	4003
February	1st to 10th	Day	49% 6% 13% 17% 13% 3	1900
	11th to 20th	Day	43% 6% 13% 21% 15% 2	1957
	21st to end	Day	46% 5% 12% 19% 14% 3	1650
March	1st to 10th	Day	50% 4 11% 13% 11% 10%	4479
	11th to 20th	Day	42% 7% 16% 23% 10% 2	4842
	21st to end	Day	56% 4 7% 14% 13% 6%	5648
April	1st to 10th	Day	46% 5% 10% 19% 16% 3	2400
	11th to 20th	Day	44% 6% 11% 21% 16% 2	2412
	21st to end	Day	43% 7% 12% 19% 16% 4	2600
May	1st to 10th	Day	58% 8% 14% 13% 6% 1	5897
	11th to 20th	Day	52% 6% 15% 16% 10% 1	5865
	21st to end	Day	46% 8% 12% 21% 13% 1	6850
June	1st to 10th	Day	44% 8% 15% 21% 11%	2800
	11th to 20th	Day	41% 8% 15% 22% 14% 1	2800
	21st to end	Day	40% 9% 16% 22% 12% 1	2800
July	1st to 10th	Day	47% 8% 13% 20% 11% 1	6290
	11th to 20th	Day	42% 6% 17% 24% 9% 1	6285
	21st to end	Day	39% 5% 12% 29% 13% 1	6640
August	1st to 10th	Day	47% 7% 18% 20% 8%	4222
	11th to 20th	Day	41% 7% 16% 28% 8% 1	4214
	21st to end	Day	30% 7% 17% 27% 18% 1	4316
September	1st to 10th	Day	38% 6% 11% 24% 20% 1	2360
	11th to 20th	Day	34% 5% 10% 26% 21% 3	2200
	21st to end	Day	43% 6% 9% 21% 18% 2	2200
October	1st to 10th	Day	38% 5% 11% 28% 16% 3	3590
	11th to 20th	Day	32% 4 8% 29% 24% 2	3211
	21st to end	Day	30% 4 15% 32% 17% 3	3180
November	1st to 10th	Day	41% 6% 13% 21% 17% 2	1851
	11th to 20th	Day	39% 6% 12% 22% 18% 3	1890
	21st to end	Day	42% 6% 13% 25% 13% 2	1890
December	1st to 10th	Day	39% 3 14% 27% 16% 1	2885
	11th to 20th	Day	42% 4 15% 16% 18% 5%	3042
	21st to end	Day	51% 5% 11% 20% 9% 4	3960
January	1st to 10th	Night	34% 3 10% 33% 17% 2	6349
	11th to 20th	Night	46% 4 11% 21% 14% 4	6360
	21st to end	Night	50% 5% 9% 17% 15% 4	6951
February	1st to 10th	Night	47% 6% 12% 21% 11% 2	2499
	11th to 20th	Night	47% 5% 9% 21% 15% 3	2340
	21st to end	Night	45% 5% 11% 22% 14% 3	1980
March	1st to 10th	Night	50% 5% 9% 15% 14% 7%	5374
	11th to 20th	Night	48% 7% 15% 17% 12% 2	5118
	21st to end	Night	56% 4 5% 11% 18% 5%	5268
April	1st to 10th	Night	48% 6% 10% 18% 15% 4	2000
	11th to 20th	Night	47% 6% 10% 18% 17% 3	1936
	21st to end	Night	47% 6% 11% 18% 15% 4	1800
May	1st to 10th	Night	59% 8% 14% 11% 6% 2	4060
	11th to 20th	Night	55% 8% 14% 13% 7% 2	4034
	21st to end	Night	53% 8% 13% 16% 10%	4067
June	1st to 10th	Night	47% 9% 12% 20% 12% 1	1600
	11th to 20th	Night	45% 6% 11% 23% 14% 1	1600
	21st to end	Night	44% 7% 14% 22% 12% 1	1600
July	1st to 10th	Night	52% 7% 9% 18% 14%	3560
	11th to 20th	Night	48% 6% 16% 20% 9% 1	3552
	21st to end	Night	44% 6% 12% 24% 13% 1	3852
August	1st to 10th	Night	51% 8% 13% 18% 9% 1	2903
	11th to 20th	Night	41% 8% 15% 28% 8%	2899
	21st to end	Night	29% 6% 15% 28% 22% 1	3578
September	1st to 10th	Night	38% 7% 12% 24% 19% 1	2039
	11th to 20th	Night	35% 5% 11% 24% 23% 2	2200
	21st to end	Night	45% 6% 9% 19% 18% 3	2200
October	1st to 10th	Night	41% 4 11% 27% 15% 3	3590
	11th to 20th	Night	27% 4 9% 25% 31% 3	3921
	21st to end	Night	34% 4 11% 27% 21% 2	4610
November	1st to 10th	Night	40% 6% 11% 24% 16% 3	2667
	11th to 20th	Night	41% 5% 11% 22% 18% 4	2730
	21st to end	Night	39% 5% 15% 27% 12% 2	2730
December	1st to 10th	Night	42% 4 12% 25% 16% 1	4511
	11th to 20th	Night	46% 4 14% 15% 18% 2	5307
	21st to end	Night	48% 6% 11% 19% 14% 1	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	23% 21% 36% 16% 6%	200
	11th to 20th	Day	22% 21% 37% 17% 4	200
	21st to end	Day	19% 16% 44% 16% 5% 1	237
February	1st to 10th	Day	25% 14% 39% 19% 2	450
	11th to 20th	Day	24% 20% 41% 14% 2	496
	21st to end	Day	22% 17% 38% 18% 4	414
March	1st to 10th	Day	24% 17% 35% 19% 5%	500
	11th to 20th	Day	19% 17% 41% 19% 4	500
	21st to end	Day	24% 16% 35% 17% 7% 2	550
April	1st to 10th	Day	27% 15% 32% 18% 7% 1	500
	11th to 20th	Day	23% 14% 36% 21% 5%	492
	21st to end	Day	21% 12% 35% 23% 7% 2	500
May	1st to 10th	Day	28% 11% 33% 22% 6% 1	503
	11th to 20th	Day	20% 7% 34% 27% 9% 2	527
	21st to end	Day	19% 6% 29% 29% 15% 3	573
June	1st to 10th	Day	19% 4 28% 34% 13% 2	530
	11th to 20th	Day	15% 8% 30% 33% 12% 2	530
	21st to end	Day	16% 5% 25% 35% 16% 3	530
July	1st to 10th	Day	16% 3 19% 38% 20% 4	525
	11th to 20th	Day	13% 4 20% 33% 25% 5%	524
	21st to end	Day	13% 4 24% 39% 17% 3	576
August	1st to 10th	Day	13% 4 20% 38% 21% 3	526
	11th to 20th	Day	14% 5% 19% 35% 22% 5%	519
	21st to end	Day	12% 4 23% 31% 21% 8%	583
September	1st to 10th	Day	18% 3 24% 30% 18% 7%	530
	11th to 20th	Day	15% 6% 26% 26% 18% 9%	530
	21st to end	Day	23% 6% 26% 28% 12% 5%	530
October	1st to 10th	Day	24% 7% 23% 25% 15% 6%	530
	11th to 20th	Day	20% 8% 30% 24% 15% 3	453
	21st to end	Day	23% 10% 33% 21% 11% 3	462
November	1st to 10th	Day	15% 16% 31% 24% 12% 2	425
	11th to 20th	Day	19% 17% 38% 19% 6%	430
	21st to end	Day	19% 20% 31% 21% 8% 1	430
December	1st to 10th	Day	19% 15% 40% 19% 7%	347
	11th to 20th	Day	27% 20% 32% 19% 2	214
	21st to end	Day	22% 19% 36% 15% 6% 2	220
January	1st to 10th	Night	21% 15% 43% 18% 3	800
	11th to 20th	Night	25% 19% 36% 17% 3	800
	21st to end	Night	19% 17% 40% 20% 4	880
February	1st to 10th	Night	22% 16% 37% 24% 2	800
	11th to 20th	Night	24% 17% 43% 15% 1	783
	21st to end	Night	21% 15% 39% 21% 4	660
March	1st to 10th	Night	22% 17% 35% 23% 3	800
	11th to 20th	Night	21% 12% 39% 24% 4 1	800
	21st to end	Night	23% 12% 36% 22% 7%	880
April	1st to 10th	Night	23% 11% 36% 25% 5%	800
	11th to 20th	Night	23% 11% 35% 27% 5%	752
	21st to end	Night	21% 8% 36% 27% 8%	600
May	1st to 10th	Night	28% 6% 31% 27% 9% 1	600
	11th to 20th	Night	22% 7% 36% 27% 8% 1	592
	21st to end	Night	22% 5% 21% 40% 11% 1	495
June	1st to 10th	Night	17% 5% 28% 35% 15% 1	400
	11th to 20th	Night	23% 3 21% 43% 10% 1	400
	21st to end	Night	20% 4 19% 43% 14%	400
July	1st to 10th	Night	14% 4 19% 46% 15% 2	390
	11th to 20th	Night	15% 4 19% 41% 19% 2	388
	21st to end	Night	15% 2 19% 50% 14% 1	456
August	1st to 10th	Night	11% 4 20% 46% 19% 1	598
	11th to 20th	Night	15% 2 18% 45% 19% 2	592
	21st to end	Night	15% 3 17% 40% 22% 4	872
September	1st to 10th	Night	15% 3 23% 37% 21% 2	800
	11th to 20th	Night	16% 4 21% 32% 22% 5%	800
	21st to end	Night	22% 4 23% 31% 17% 3	800
October	1st to 10th	Night	23% 7% 23% 26% 16% 4	800
	11th to 20th	Night	19% 9% 31% 26% 13% 2	800
	21st to end	Night	22% 10% 35% 24% 8% 1	880
November	1st to 10th	Night	19% 9% 33% 27% 11% 1	820
	11th to 20th	Night	20% 17% 34% 21% 7% 1	840
	21st to end	Night	19% 18% 33% 23% 6% 1	840
December	1st to 10th	Night	24% 15% 37% 19% 5%	840
	11th to 20th	Night	23% 17% 37% 20% 3	829
	21st to end	Night	23% 15% 39% 20% 3	880

Page generated at 2025-12-15 01:13:56. Version ac07

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