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 2024-01-12.

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	13% 6% 2 5% 5% 3 5% 5% 6% 8% 42%	74640
	Night	14% 6% 2 5% 5% 3 4 4 5% 8% 44%	75075
Transparency	Day	40% 6% 12% 22% 17% 4	74357
	Night	39% 6% 12% 22% 18% 4	74877
Seeing	Day	18% 12% 26% 25% 14% 4	14157
	Night	17% 10% 29% 31% 13% 1	23917

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	15% 7% 3 5% 4 2 4 4 4 6% 47%	1668
	11th to 20th	Day	17% 6% 3 4 4 3 4 4 6% 5% 44%	1635
	21st to end	Day	16% 6% 3 4 4 3 4 4 5% 5% 47%	1782
February	1st to 10th	Day	13% 8% 2 6% 4 3 5% 4 6% 7% 41%	1620
	11th to 20th	Day	19% 6% 2 4 4 3 3 4 4 4 46%	1705
	21st to end	Day	18% 7% 3 7% 4 3 4 5% 5% 6% 40%	1480
March	1st to 10th	Day	14% 6% 2 4 4 2 3 3 4 5% 52%	1939
	11th to 20th	Day	17% 6% 3 6% 5% 3 3 3 5% 7% 43%	1980
	21st to end	Day	16% 7% 3 5% 6% 3 5% 4 5% 7% 41%	2222
April	1st to 10th	Day	13% 4 2 4 3 2 3 4 5% 7% 53%	2160
	11th to 20th	Day	10% 5% 2 4 5% 3 4 4 5% 8% 50%	2134
	21st to end	Day	11% 5% 2 6% 5% 4 5% 4 5% 6% 46%	2160
May	1st to 10th	Day	12% 6% 3 4 6% 4 5% 5% 6% 10% 41%	2160
	11th to 20th	Day	16% 6% 3 6% 6% 3 5% 5% 5% 7% 38%	2312
	21st to end	Day	11% 6% 3 6% 6% 4 5% 6% 5% 9% 39%	2725
June	1st to 10th	Day	10% 5% 3 5% 6% 4 6% 6% 6% 10% 38%	2520
	11th to 20th	Day	9% 5% 2 4 6% 5% 6% 6% 8% 10% 39%	2520
	21st to end	Day	8% 5% 3 5% 6% 4 6% 7% 7% 12% 35%	2520
July	1st to 10th	Day	9% 4 2 5% 6% 4 6% 7% 8% 12% 37%	2494
	11th to 20th	Day	7% 5% 2 6% 8% 4 7% 7% 8% 11% 35%	2340
	21st to end	Day	7% 6% 3 7% 7% 4 8% 7% 8% 11% 33%	2547
August	1st to 10th	Day	12% 4 3 7% 6% 5% 7% 8% 7% 10% 30%	2318
	11th to 20th	Day	12% 6% 3 7% 6% 4 6% 7% 7% 10% 31%	2126
	21st to end	Day	11% 6% 3 7% 6% 4 6% 7% 7% 10% 34%	2376
September	1st to 10th	Day	13% 5% 2 6% 6% 4 5% 6% 6% 9% 37%	2160
	11th to 20th	Day	13% 7% 3 6% 6% 4 6% 4 6% 7% 39%	2160
	21st to end	Day	19% 8% 2 7% 6% 3 5% 5% 4 6% 35%	1915
October	1st to 10th	Day	15% 7% 3 6% 4 3 3 4 4 7% 43%	1800
	11th to 20th	Day	14% 7% 2 4 4 3 3 4 5% 6% 49%	1800
	21st to end	Day	12% 5% 3 4 5% 2 4 4 4 5% 52%	1980
November	1st to 10th	Day	15% 5% 2 4 4 2 4 4 4 6% 50%	1817
	11th to 20th	Day	16% 5% 2 4 3 2 3 3 3 7% 51%	1710
	21st to end	Day	14% 4 2 4 4 3 4 3 4 7% 50%	1653
December	1st to 10th	Day	17% 6% 3 5% 5% 3 4 4 5% 7% 41%	1520
	11th to 20th	Day	14% 7% 2 4 3 2 3 3 4 5% 55%	1910
	21st to end	Day	16% 6% 3 5% 5% 2 3 4 5% 7% 44%	2772
January	1st to 10th	Night	15% 7% 3 5% 4 2 4 3 5% 5% 47%	2493
	11th to 20th	Night	15% 7% 3 6% 6% 3 4 4 4 7% 41%	2365
	21st to end	Night	15% 6% 2 5% 5% 2 4 3 4 6% 47%	2574
February	1st to 10th	Night	18% 7% 2 4 4 3 4 4 5% 7% 41%	2340
	11th to 20th	Night	20% 8% 2 4 4 2 3 4 5% 6% 41%	2139
	21st to end	Night	15% 7% 3 5% 4 2 3 3 5% 6% 46%	1776
March	1st to 10th	Night	14% 4 1 5% 4 3 4 3 4 5% 51%	2016
	11th to 20th	Night	16% 7% 2 5% 5% 3 6% 5% 6% 7% 39%	1980
	21st to end	Night	15% 7% 3 5% 5% 3 4 4 4 7% 43%	2134
April	1st to 10th	Night	13% 5% 2 5% 5% 3 4 4 6% 7% 45%	1800
	11th to 20th	Night	13% 6% 2 4 5% 3 3 4 4 7% 50%	1775
	21st to end	Night	14% 5% 3 5% 4 3 4 4 6% 7% 48%	1800
May	1st to 10th	Night	11% 7% 3 5% 5% 2 4 5% 7% 8% 42%	1800
	11th to 20th	Night	14% 6% 3 6% 5% 3 4 5% 6% 9% 40%	1590
	21st to end	Night	12% 5% 2 5% 4 3 5% 6% 5% 11% 42%	1550
June	1st to 10th	Night	10% 4 3 5% 3 4 5% 5% 8% 13% 40%	1440
	11th to 20th	Night	8% 5% 3 6% 6% 3 5% 6% 7% 12% 40%	1440
	21st to end	Night	7% 5% 2 5% 5% 4 6% 6% 8% 10% 42%	1440
July	1st to 10th	Night	6% 6% 2 6% 7% 4 6% 6% 8% 12% 37%	1461
	11th to 20th	Night	8% 3 2 5% 6% 4 6% 6% 8% 12% 40%	1620
	21st to end	Night	7% 5% 3 5% 6% 4 6% 7% 9% 12% 36%	1771
August	1st to 10th	Night	8% 7% 3 7% 7% 3 5% 5% 6% 10% 39%	1611
	11th to 20th	Night	10% 6% 2 7% 6% 4 5% 5% 7% 10% 36%	1765
	21st to end	Night	10% 7% 3 6% 6% 3 5% 5% 6% 10% 38%	1980
September	1st to 10th	Night	12% 5% 3 5% 5% 3 4 5% 6% 9% 44%	1800
	11th to 20th	Night	12% 6% 2 6% 5% 4 5% 4 5% 6% 45%	1800
	21st to end	Night	18% 8% 3 7% 6% 3 5% 4 5% 7% 36%	2039
October	1st to 10th	Night	14% 6% 2 4 4 2 4 4 5% 5% 49%	2160
	11th to 20th	Night	13% 6% 2 5% 5% 2 3 3 5% 6% 50%	2160
	21st to end	Night	12% 5% 2 4 4 3 4 4 4 6% 52%	2376
November	1st to 10th	Night	16% 5% 2 4 4 2 3 3 4 6% 51%	2259
	11th to 20th	Night	15% 7% 2 4 4 2 3 4 5% 6% 49%	2470
	21st to end	Night	13% 4 2 5% 5% 3 4 4 5% 7% 49%	2522
December	1st to 10th	Night	16% 8% 3 7% 5% 3 3 4 4 7% 40%	2660
	11th to 20th	Night	17% 5% 3 4 4 2 4 4 4 7% 46%	3285
	21st to end	Night	15% 7% 2 4 5% 3 4 4 5% 7% 45%	4884

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	40% 4 8% 24% 19% 6%	1669
	11th to 20th	Day	41% 4 10% 20% 20% 4	1635
	21st to end	Day	39% 4 7% 24% 21% 5%	1782
February	1st to 10th	Day	42% 5% 11% 23% 16% 4	1620
	11th to 20th	Day	43% 4 6% 19% 21% 6%	1714
	21st to end	Day	45% 5% 11% 16% 18% 6%	1480
March	1st to 10th	Day	36% 4 9% 24% 22% 5%	1939
	11th to 20th	Day	42% 4 9% 20% 17% 7%	1980
	21st to end	Day	44% 5% 11% 18% 19% 4	2222
April	1st to 10th	Day	32% 4 10% 24% 23% 7%	2160
	11th to 20th	Day	34% 5% 10% 23% 21% 7%	2134
	21st to end	Day	38% 6% 12% 22% 17% 5%	2160
May	1st to 10th	Day	38% 7% 15% 21% 15% 3	2160
	11th to 20th	Day	45% 7% 12% 23% 11% 2	2316
	21st to end	Day	41% 7% 14% 25% 12% 1	2725
June	1st to 10th	Day	40% 8% 13% 21% 16% 2	2520
	11th to 20th	Day	38% 8% 16% 22% 15% 2	2520
	21st to end	Day	40% 8% 15% 21% 13% 2	2520
July	1st to 10th	Day	37% 11% 16% 22% 12% 3	2425
	11th to 20th	Day	38% 10% 18% 23% 8% 2	2271
	21st to end	Day	39% 11% 17% 21% 11% 1	2405
August	1st to 10th	Day	45% 10% 17% 19% 8%	2305
	11th to 20th	Day	44% 10% 16% 19% 10% 1	2126
	21st to end	Day	43% 10% 15% 17% 12% 3	2376
September	1st to 10th	Day	41% 9% 15% 16% 16% 3	2160
	11th to 20th	Day	43% 5% 10% 22% 17% 2	2160
	21st to end	Day	50% 4 10% 20% 14% 2	1915
October	1st to 10th	Day	41% 5% 8% 22% 21% 4	1800
	11th to 20th	Day	36% 4 6% 26% 23% 5%	1800
	21st to end	Day	35% 4 6% 21% 27% 6%	1980
November	1st to 10th	Day	37% 4 9% 23% 23% 4	1817
	11th to 20th	Day	35% 3 10% 22% 23% 7%	1710
	21st to end	Day	36% 4 7% 26% 22% 5%	1653
December	1st to 10th	Day	42% 4 12% 20% 16% 4	1520
	11th to 20th	Day	34% 3 8% 29% 18% 8%	1906
	21st to end	Day	41% 4 9% 27% 18% 2	2772
January	1st to 10th	Night	40% 3 8% 22% 20% 7%	2493
	11th to 20th	Night	45% 5% 9% 21% 16% 5%	2365
	21st to end	Night	39% 4 7% 23% 21% 6%	2574
February	1st to 10th	Night	42% 4 10% 21% 18% 5%	2340
	11th to 20th	Night	45% 4 7% 19% 18% 6%	2141
	21st to end	Night	41% 4 7% 22% 19% 8%	1776
March	1st to 10th	Night	36% 4 11% 23% 21% 6%	2016
	11th to 20th	Night	44% 5% 10% 20% 17% 4	1980
	21st to end	Night	42% 5% 11% 21% 17% 4	2134
April	1st to 10th	Night	37% 6% 11% 17% 22% 6%	1800
	11th to 20th	Night	36% 4 9% 24% 20% 6%	1775
	21st to end	Night	36% 5% 13% 24% 18% 4	1800
May	1st to 10th	Night	38% 7% 15% 24% 14% 3	1800
	11th to 20th	Night	40% 9% 13% 21% 14% 3	1591
	21st to end	Night	36% 9% 17% 25% 11% 2	1551
June	1st to 10th	Night	34% 9% 16% 26% 13% 1	1440
	11th to 20th	Night	37% 10% 17% 21% 14% 1	1440
	21st to end	Night	35% 11% 16% 22% 13% 3	1440
July	1st to 10th	Night	37% 11% 18% 19% 12% 3	1420
	11th to 20th	Night	33% 9% 23% 25% 8% 2	1566
	21st to end	Night	35% 12% 17% 26% 9% 1	1672
August	1st to 10th	Night	40% 9% 23% 21% 7%	1600
	11th to 20th	Night	40% 9% 19% 21% 10% 1	1765
	21st to end	Night	41% 8% 17% 21% 10% 3	1980
September	1st to 10th	Night	34% 10% 19% 18% 15% 4	1800
	11th to 20th	Night	39% 7% 10% 21% 20% 3	1800
	21st to end	Night	47% 5% 12% 17% 16% 2	2039
October	1st to 10th	Night	36% 5% 9% 23% 23% 4	2160
	11th to 20th	Night	36% 4 8% 24% 23% 5%	2160
	21st to end	Night	34% 4 7% 21% 26% 7%	2376
November	1st to 10th	Night	37% 4 9% 21% 25% 5%	2259
	11th to 20th	Night	37% 4 9% 18% 23% 9%	2470
	21st to end	Night	36% 4 8% 24% 23% 6%	2522
December	1st to 10th	Night	46% 4 10% 19% 18% 4	2660
	11th to 20th	Night	39% 4 9% 21% 20% 6%	3288
	21st to end	Night	38% 5% 11% 24% 19% 2	4884

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% 30% 32% 13% 2	252
	11th to 20th	Day	21% 28% 36% 13% 2	245
	21st to end	Day	26% 24% 39% 10% 1 1	264
February	1st to 10th	Day	23% 27% 37% 9% 4	240
	11th to 20th	Day	30% 27% 28% 12% 3	373
	21st to end	Day	25% 24% 32% 15% 4	346
March	1st to 10th	Day	20% 25% 36% 13% 6%	420
	11th to 20th	Day	25% 20% 34% 14% 5% 1	420
	21st to end	Day	22% 20% 36% 15% 5% 2	462
April	1st to 10th	Day	23% 17% 37% 15% 5% 1	420
	11th to 20th	Day	15% 19% 34% 19% 10% 3	412
	21st to end	Day	17% 16% 34% 23% 8% 1	420
May	1st to 10th	Day	17% 19% 34% 20% 8% 1	423
	11th to 20th	Day	19% 8% 31% 28% 11% 3	447
	21st to end	Day	19% 6% 22% 31% 17% 5%	485
June	1st to 10th	Day	14% 6% 26% 33% 19% 2	450
	11th to 20th	Day	14% 9% 21% 32% 20% 5%	450
	21st to end	Day	10% 6% 22% 35% 21% 5%	450
July	1st to 10th	Day	12% 3 16% 35% 26% 8%	445
	11th to 20th	Day	9% 1 13% 39% 30% 7%	444
	21st to end	Day	8% 3 21% 39% 22% 7%	488
August	1st to 10th	Day	13% 4 17% 35% 22% 8%	446
	11th to 20th	Day	12% 2 15% 30% 30% 11%	439
	21st to end	Day	12% 3 15% 32% 26% 10%	495
September	1st to 10th	Day	14% 4 20% 26% 22% 14%	450
	11th to 20th	Day	16% 5% 19% 30% 21% 10%	450
	21st to end	Day	25% 8% 21% 23% 17% 6%	450
October	1st to 10th	Day	21% 7% 19% 27% 17% 9%	450
	11th to 20th	Day	16% 10% 30% 24% 17% 3	450
	21st to end	Day	17% 11% 30% 24% 13% 5%	495
November	1st to 10th	Day	19% 11% 29% 24% 12% 4	435
	11th to 20th	Day	19% 18% 29% 23% 11% 1	370
	21st to end	Day	19% 15% 26% 25% 13% 2	313
December	1st to 10th	Day	24% 18% 38% 16% 4 1	180
	11th to 20th	Day	19% 22% 32% 20% 6% 1	180
	21st to end	Day	27% 19% 24% 17% 11% 2	198
January	1st to 10th	Night	19% 19% 34% 23% 4 1	760
	11th to 20th	Night	20% 14% 34% 25% 6%	728
	21st to end	Night	18% 16% 41% 23% 2	792
February	1st to 10th	Night	23% 14% 39% 21% 4	720
	11th to 20th	Night	26% 19% 36% 18% 1	703
	21st to end	Night	20% 19% 37% 21% 3	592
March	1st to 10th	Night	18% 15% 37% 25% 5%	720
	11th to 20th	Night	21% 14% 38% 21% 5%	720
	21st to end	Night	20% 15% 36% 24% 5%	792
April	1st to 10th	Night	18% 17% 41% 21% 3	720
	11th to 20th	Night	15% 14% 39% 26% 6%	711
	21st to end	Night	16% 10% 38% 29% 7%	720
May	1st to 10th	Night	15% 13% 37% 29% 5%	720
	11th to 20th	Night	14% 7% 30% 37% 11% 1	529
	21st to end	Night	12% 2 21% 48% 17%	389
June	1st to 10th	Night	10% 4 24% 45% 17%	360
	11th to 20th	Night	9% 2 21% 45% 21% 2	360
	21st to end	Night	8% 3 21% 51% 16% 1	360
July	1st to 10th	Night	8% 2 17% 51% 22% 1	370
	11th to 20th	Night	9% 1 11% 44% 31% 4	522
	21st to end	Night	9% 2 17% 46% 25% 1	591
August	1st to 10th	Night	11% 2 13% 44% 26% 4	537
	11th to 20th	Night	13% 2 11% 44% 26% 4	701
	21st to end	Night	13% 3 13% 35% 32% 4	792
September	1st to 10th	Night	12% 2 16% 37% 28% 6%	720
	11th to 20th	Night	14% 4 18% 35% 25% 4	720
	21st to end	Night	22% 5% 18% 32% 21% 1	720
October	1st to 10th	Night	16% 4 20% 32% 23% 4	720
	11th to 20th	Night	17% 8% 29% 29% 16% 2	720
	21st to end	Night	16% 7% 29% 31% 15% 2	792
November	1st to 10th	Night	19% 7% 27% 30% 14% 3	740
	11th to 20th	Night	19% 10% 31% 30% 10% 1	760
	21st to end	Night	15% 11% 29% 31% 13% 1	760
December	1st to 10th	Night	21% 13% 31% 27% 7% 1	760
	11th to 20th	Night	17% 11% 34% 30% 7%	760
	21st to end	Night	19% 14% 31% 29% 7%	836

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