Merchants Millpond State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Merchants Millpond State Park clear sky chart from 2005-11-06 to 2025-09-19.

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	12% 6% 2 6% 5% 4 5% 4 6% 8% 41%	125745
	Night	13% 7% 2 6% 4 4 4 3 5% 7% 43%	123285
Transparency	Day	39% 7% 12% 21% 17% 4	129341
	Night	39% 6% 11% 21% 18% 5%	127758
Seeing	Day	18% 13% 27% 24% 14% 4	16453
	Night	17% 10% 29% 31% 13% 1	26093

By Month

Percentage Cloud Cover SE (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	14% 5% 2 4 3 3 3 2 4 4 56%	3964
	11th to 20th	Day	13% 7% 2 4 3 3 3 2 4 5% 54%	4060
	21st to end	Day	11% 8% 3 8% 5% 4 4 3 4 5% 45%	4466
February	1st to 10th	Day	13% 8% 2 7% 4 4 5% 3 6% 7% 42%	1800
	11th to 20th	Day	21% 6% 2 5% 4 3 3 3 4 4 44%	1900
	21st to end	Day	16% 7% 3 6% 4 4 3 4 6% 6% 41%	1650
March	1st to 10th	Day	20% 8% 2 6% 4 3 4 3 5% 6% 40%	4841
	11th to 20th	Day	11% 6% 2 6% 3 3 3 3 4 6% 53%	4980
	21st to end	Day	13% 5% 2 6% 4 4 4 3 5% 6% 48%	5592
April	1st to 10th	Day	13% 5% 2 4 3 3 3 3 5% 7% 51%	2400
	11th to 20th	Day	10% 6% 2 5% 5% 4 4 3 5% 7% 50%	2374
	21st to end	Day	11% 5% 2 7% 4 5% 5% 4 6% 7% 45%	2400
May	1st to 10th	Day	11% 7% 3 7% 6% 6% 5% 5% 7% 10% 35%	5405
	11th to 20th	Day	18% 8% 3 8% 5% 4 5% 4 6% 9% 30%	5914
	21st to end	Day	13% 6% 3 6% 4 4 4 4 6% 8% 42%	6934
June	1st to 10th	Day	10% 6% 3 6% 6% 5% 6% 5% 6% 10% 39%	2800
	11th to 20th	Day	9% 5% 2 5% 6% 6% 5% 5% 8% 10% 40%	2800
	21st to end	Day	8% 6% 3 6% 5% 5% 5% 6% 8% 12% 37%	2800
July	1st to 10th	Day	9% 5% 2 6% 5% 5% 7% 6% 9% 13% 33%	6278
	11th to 20th	Day	9% 7% 3 9% 7% 6% 6% 5% 8% 11% 27%	5900
	21st to end	Day	8% 7% 3 8% 6% 6% 7% 5% 9% 11% 31%	6424
August	1st to 10th	Day	19% 8% 4 11% 6% 6% 6% 5% 6% 9% 20%	4211
	11th to 20th	Day	10% 7% 3 8% 5% 5% 6% 5% 8% 11% 33%	3850
	21st to end	Day	7% 5% 2 7% 5% 6% 6% 5% 7% 11% 40%	4312
September	1st to 10th	Day	14% 6% 2 6% 5% 5% 5% 5% 6% 9% 37%	2400
	11th to 20th	Day	14% 9% 2 7% 5% 5% 5% 4 6% 7% 37%	2376
	21st to end	Day	20% 8% 2 7% 5% 5% 5% 3 5% 6% 35%	2020
October	1st to 10th	Day	15% 8% 3 6% 3 4 3 4 4 8% 43%	1900
	11th to 20th	Day	13% 6% 1 5% 4 4 3 3 4 6% 51%	1900
	21st to end	Day	11% 5% 2 5% 4 3 4 3 4 5% 53%	2090
November	1st to 10th	Day	15% 5% 2 5% 3 3 5% 3 4 6% 49%	1914
	11th to 20th	Day	16% 6% 2 5% 3 3 3 3 4 7% 51%	1800
	21st to end	Day	14% 5% 2 5% 4 4 3 3 4 6% 51%	1740
December	1st to 10th	Day	12% 5% 2 6% 4 4 4 3 4 6% 52%	2600
	11th to 20th	Day	14% 9% 3 7% 4 3 3 3 4 5% 45%	2990
	21st to end	Day	13% 5% 2 6% 4 3 3 3 5% 7% 48%	3960
January	1st to 10th	Night	12% 7% 2 5% 3 3 3 3 4 5% 53%	5963
	11th to 20th	Night	14% 6% 2 5% 4 3 3 3 4 5% 52%	5900
	21st to end	Night	14% 7% 2 6% 4 4 3 3 4 6% 47%	6490
February	1st to 10th	Night	17% 7% 2 5% 4 4 4 3 5% 7% 42%	2600
	11th to 20th	Night	20% 9% 2 5% 4 3 3 3 5% 5% 40%	2384
	21st to end	Night	15% 8% 2 5% 4 3 3 3 5% 6% 48%	1980
March	1st to 10th	Night	20% 7% 2 6% 4 4 4 3 4 5% 41%	5007
	11th to 20th	Night	13% 5% 2 6% 3 4 4 3 5% 5% 50%	4980
	21st to end	Night	15% 6% 2 5% 4 4 4 2 4 6% 49%	5340
April	1st to 10th	Night	13% 6% 2 6% 5% 4 4 4 6% 7% 45%	2000
	11th to 20th	Night	12% 6% 2 5% 4 3 3 3 4 7% 50%	1975
	21st to end	Night	13% 5% 3 5% 4 3 4 3 7% 7% 48%	2000
May	1st to 10th	Night	11% 8% 3 9% 6% 4 5% 4 6% 9% 33%	4490
	11th to 20th	Night	19% 8% 3 8% 5% 4 4 4 5% 7% 33%	4002
	21st to end	Night	14% 8% 2 7% 4 4 5% 3 5% 9% 38%	3920
June	1st to 10th	Night	9% 5% 2 5% 4 5% 5% 5% 8% 12% 39%	1600
	11th to 20th	Night	9% 6% 2 6% 5% 4 5% 5% 7% 11% 39%	1600
	21st to end	Night	7% 6% 2 6% 4 5% 6% 5% 8% 9% 44%	1600
July	1st to 10th	Night	7% 5% 2 7% 5% 6% 6% 6% 9% 14% 32%	3661
	11th to 20th	Night	9% 8% 3 9% 6% 6% 7% 5% 8% 12% 27%	4057
	21st to end	Night	12% 7% 3 7% 5% 5% 5% 5% 8% 10% 34%	4427
August	1st to 10th	Night	19% 9% 3 8% 5% 5% 5% 4 5% 9% 28%	2915
	11th to 20th	Night	10% 8% 3 8% 6% 5% 5% 4 6% 9% 36%	3188
	21st to end	Night	8% 6% 2 5% 4 4 5% 5% 7% 10% 44%	3586
September	1st to 10th	Night	12% 5% 3 6% 4 3 5% 4 6% 9% 44%	2000
	11th to 20th	Night	15% 7% 2 7% 4 5% 4 3 5% 6% 42%	1981
	21st to end	Night	18% 8% 3 8% 5% 3 5% 3 5% 7% 35%	2154
October	1st to 10th	Night	14% 6% 2 5% 3 4 4 3 5% 5% 49%	2280
	11th to 20th	Night	12% 6% 2 5% 4 3 3 3 5% 5% 52%	2280
	21st to end	Night	11% 5% 2 5% 3 3 3 3 4 6% 53%	2508
November	1st to 10th	Night	15% 5% 3 4 3 3 4 3 4 6% 50%	2381
	11th to 20th	Night	15% 7% 2 5% 4 3 3 4 5% 6% 49%	2600
	21st to end	Night	12% 4 2 5% 4 4 4 4 5% 6% 49%	2655
December	1st to 10th	Night	10% 6% 2 6% 4 4 3 3 4 6% 52%	4580
	11th to 20th	Night	17% 7% 3 8% 5% 5% 5% 4 4 6% 37%	5205
	21st to end	Night	12% 6% 2 5% 4 4 4 3 5% 7% 50%	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	33% 3 5% 23% 23% 14%	3965
	11th to 20th	Day	34% 3 5% 17% 33% 7%	4060
	21st to end	Day	41% 5% 7% 24% 19% 4	4466
February	1st to 10th	Day	41% 5% 11% 24% 16% 4	1800
	11th to 20th	Day	44% 4 7% 19% 20% 6%	1909
	21st to end	Day	43% 5% 11% 16% 20% 5%	1650
March	1st to 10th	Day	46% 4 7% 18% 17% 8%	4841
	11th to 20th	Day	33% 4 7% 19% 26% 11%	4980
	21st to end	Day	37% 4 13% 18% 22% 5%	5592
April	1st to 10th	Day	33% 5% 10% 23% 23% 6%	2400
	11th to 20th	Day	33% 5% 11% 24% 21% 6%	2374
	21st to end	Day	37% 6% 13% 23% 17% 5%	2400
May	1st to 10th	Day	42% 10% 17% 19% 11% 1	5437
	11th to 20th	Day	49% 8% 13% 19% 10% 1	5918
	21st to end	Day	39% 7% 12% 26% 14% 2	6949
June	1st to 10th	Day	39% 8% 13% 22% 16% 2	2800
	11th to 20th	Day	37% 8% 16% 23% 15% 1	2800
	21st to end	Day	37% 8% 16% 24% 14% 2	2800
July	1st to 10th	Day	37% 11% 19% 21% 9% 2	6209
	11th to 20th	Day	47% 13% 23% 13% 3 1	5831
	21st to end	Day	41% 12% 15% 22% 10% 1	6240
August	1st to 10th	Day	58% 9% 16% 13% 5%	4198
	11th to 20th	Day	41% 10% 15% 23% 12% 1	3886
	21st to end	Day	35% 9% 13% 27% 14% 2	4312
September	1st to 10th	Day	41% 9% 14% 17% 16% 3	2400
	11th to 20th	Day	46% 5% 10% 21% 16% 2	2376
	21st to end	Day	50% 4 10% 19% 14% 3	2020
October	1st to 10th	Day	33% 5% 9% 23% 27% 4	3160
	11th to 20th	Day	25% 3 5% 20% 36% 11%	3140
	21st to end	Day	23% 3 6% 27% 30% 10%	3428
November	1st to 10th	Day	37% 4 9% 24% 23% 4	1914
	11th to 20th	Day	35% 3 10% 22% 23% 7%	1800
	21st to end	Day	35% 4 7% 25% 23% 5%	1740
December	1st to 10th	Day	34% 4 8% 25% 23% 5%	2600
	11th to 20th	Day	42% 4 10% 21% 16% 6%	2986
	21st to end	Day	36% 4 11% 27% 20% 1	3960
January	1st to 10th	Night	33% 3 5% 21% 26% 11%	5963
	11th to 20th	Night	36% 3 5% 19% 31% 6%	5900
	21st to end	Night	40% 4 7% 23% 21% 6%	6490
February	1st to 10th	Night	42% 4 11% 22% 17% 5%	2600
	11th to 20th	Night	46% 4 8% 19% 18% 6%	2386
	21st to end	Night	40% 4 7% 23% 19% 8%	1980
March	1st to 10th	Night	46% 4 8% 16% 17% 9%	5007
	11th to 20th	Night	36% 5% 8% 15% 23% 13%	4980
	21st to end	Night	38% 4 10% 24% 17% 6%	5340
April	1st to 10th	Night	38% 6% 12% 17% 22% 6%	2000
	11th to 20th	Night	35% 4 10% 26% 20% 6%	1975
	21st to end	Night	36% 5% 13% 25% 18% 4	2000
May	1st to 10th	Night	44% 10% 16% 19% 10% 1	4520
	11th to 20th	Night	49% 8% 10% 21% 9% 1	4003
	21st to end	Night	42% 8% 15% 23% 11% 1	3927
June	1st to 10th	Night	35% 10% 15% 25% 14% 1	1600
	11th to 20th	Night	37% 10% 17% 22% 14% 1	1600
	21st to end	Night	33% 10% 15% 25% 13% 3	1600
July	1st to 10th	Night	38% 13% 20% 19% 9% 1	3622
	11th to 20th	Night	47% 13% 23% 13% 3 1	4006
	21st to end	Night	42% 10% 15% 20% 13%	4297
August	1st to 10th	Night	52% 8% 19% 17% 4	2904
	11th to 20th	Night	42% 9% 16% 22% 10%	3218
	21st to end	Night	34% 7% 13% 26% 17% 2	3586
September	1st to 10th	Night	34% 9% 18% 19% 16% 4	2000
	11th to 20th	Night	42% 7% 10% 19% 20% 2	1981
	21st to end	Night	47% 5% 12% 17% 16% 2	2154
October	1st to 10th	Night	38% 5% 9% 23% 23% 3	3800
	11th to 20th	Night	25% 3 6% 20% 31% 14%	3779
	21st to end	Night	21% 3 7% 29% 25% 14%	4120
November	1st to 10th	Night	36% 4 9% 21% 25% 5%	2381
	11th to 20th	Night	37% 5% 9% 18% 22% 9%	2600
	21st to end	Night	35% 4 8% 25% 23% 5%	2655
December	1st to 10th	Night	35% 3 7% 22% 25% 7%	4580
	11th to 20th	Night	48% 5% 9% 16% 15% 6%	5208
	21st to end	Night	34% 5% 14% 27% 18% 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	24% 31% 31% 12% 2	280
	11th to 20th	Day	22% 29% 35% 12% 1	300
	21st to end	Day	25% 25% 41% 9% 1 1	330
February	1st to 10th	Day	23% 27% 36% 10% 4	300
	11th to 20th	Day	32% 26% 28% 11% 2	448
	21st to end	Day	24% 22% 33% 17% 4	414
March	1st to 10th	Day	23% 25% 34% 13% 5%	500
	11th to 20th	Day	24% 22% 32% 15% 6% 1	500
	21st to end	Day	22% 21% 38% 14% 4 1	550
April	1st to 10th	Day	23% 19% 38% 14% 5% 1	500
	11th to 20th	Day	16% 19% 35% 19% 9% 2	492
	21st to end	Day	16% 17% 33% 24% 9% 1	500
May	1st to 10th	Day	16% 19% 34% 20% 9% 1	503
	11th to 20th	Day	20% 9% 33% 25% 10% 3	527
	21st to end	Day	18% 9% 24% 29% 16% 5%	573
June	1st to 10th	Day	12% 7% 29% 32% 17% 2	530
	11th to 20th	Day	12% 9% 21% 32% 21% 5%	530
	21st to end	Day	8% 6% 21% 35% 23% 6%	530
July	1st to 10th	Day	12% 3 16% 35% 26% 8%	525
	11th to 20th	Day	8% 3 14% 39% 29% 8%	524
	21st to end	Day	8% 3 21% 38% 22% 9%	576
August	1st to 10th	Day	16% 5% 18% 34% 20% 6%	526
	11th to 20th	Day	11% 3 18% 30% 28% 11%	519
	21st to end	Day	11% 4 18% 33% 25% 10%	583
September	1st to 10th	Day	15% 5% 21% 26% 20% 13%	530
	11th to 20th	Day	18% 6% 20% 28% 20% 8%	522
	21st to end	Day	25% 8% 21% 23% 16% 6%	490
October	1st to 10th	Day	20% 7% 18% 27% 18% 8%	490
	11th to 20th	Day	15% 11% 30% 25% 16% 3	490
	21st to end	Day	16% 10% 30% 24% 14% 6%	539
November	1st to 10th	Day	19% 11% 31% 24% 11% 4	472
	11th to 20th	Day	19% 18% 30% 23% 11% 1	400
	21st to end	Day	19% 17% 26% 24% 13% 1	340
December	1st to 10th	Day	24% 18% 38% 16% 4 1	200
	11th to 20th	Day	21% 23% 32% 20% 6% 1	200
	21st to end	Day	25% 19% 28% 16% 10% 2	220
January	1st to 10th	Night	20% 20% 34% 22% 4 1	800
	11th to 20th	Night	20% 16% 35% 24% 6%	800
	21st to end	Night	18% 16% 41% 24% 2	880
February	1st to 10th	Night	22% 15% 39% 21% 4	800
	11th to 20th	Night	27% 19% 36% 17% 1	783
	21st to end	Night	20% 19% 37% 22% 2	660
March	1st to 10th	Night	19% 16% 36% 25% 4	800
	11th to 20th	Night	21% 16% 37% 21% 4	800
	21st to end	Night	19% 16% 38% 22% 5%	880
April	1st to 10th	Night	18% 18% 41% 21% 3	800
	11th to 20th	Night	15% 14% 40% 25% 6%	791
	21st to end	Night	15% 10% 38% 30% 7%	800
May	1st to 10th	Night	15% 13% 37% 29% 6%	800
	11th to 20th	Night	14% 8% 31% 36% 10% 1	587
	21st to end	Night	12% 3 24% 45% 16%	433
June	1st to 10th	Night	10% 4 25% 44% 17%	400
	11th to 20th	Night	9% 4 21% 44% 21% 2	400
	21st to end	Night	7% 3 20% 51% 18% 1	400
July	1st to 10th	Night	8% 2 16% 50% 22% 1	413
	11th to 20th	Night	10% 1 11% 43% 30% 5%	582
	21st to end	Night	10% 3 16% 44% 26% 2	657
August	1st to 10th	Night	13% 3 13% 43% 24% 4	597
	11th to 20th	Night	13% 2 12% 44% 25% 4	781
	21st to end	Night	12% 3 13% 37% 31% 4	880
September	1st to 10th	Night	13% 2 18% 37% 26% 5%	800
	11th to 20th	Night	16% 6% 18% 33% 24% 4	793
	21st to end	Night	22% 5% 18% 32% 21% 1	760
October	1st to 10th	Night	16% 5% 19% 32% 23% 4	760
	11th to 20th	Night	16% 8% 29% 29% 15% 2	760
	21st to end	Night	15% 7% 28% 32% 16% 2	836
November	1st to 10th	Night	18% 7% 28% 31% 13% 3	780
	11th to 20th	Night	19% 10% 31% 30% 10% 1	800
	21st to end	Night	15% 12% 30% 31% 12% 1	800
December	1st to 10th	Night	21% 13% 32% 27% 7% 1	800
	11th to 20th	Night	17% 11% 35% 29% 7%	800
	21st to end	Night	19% 13% 32% 29% 7%	880

Page generated at 2025-09-16 01:49:14. Version ac07

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