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Sugar Grove Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sugar Grove Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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% 8% 3 7% 6% 3 5% 5% 5% 7% 38%	74811
	Night	14% 8% 4 6% 5% 3 4 4 5% 7% 40%	75007
Transparency	Day	45% 6% 12% 22% 13% 2	74512
	Night	44% 5% 11% 22% 15% 2	74827
Seeing	Day	15% 10% 28% 25% 16% 5%	14562
	Night	17% 9% 31% 30% 12% 1	24531

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% 14% 6% 9% 8% 4 5% 4 6% 6% 24%	1517
	11th to 20th	Day	16% 17% 7% 11% 7% 4 5% 4 4 5% 21%	1480
	21st to end	Day	14% 14% 7% 13% 7% 4 4 4 3 5% 25%	1743
February	1st to 10th	Day	16% 13% 6% 11% 6% 3 5% 3 4 5% 28%	1638
	11th to 20th	Day	14% 10% 4 8% 9% 4 5% 4 5% 6% 31%	1748
	21st to end	Day	16% 14% 5% 10% 6% 3 3 5% 4 6% 28%	1480
March	1st to 10th	Day	16% 12% 5% 6% 5% 4 4 5% 4 6% 33%	1800
	11th to 20th	Day	13% 11% 4 8% 6% 3 5% 5% 7% 7% 32%	1903
	21st to end	Day	21% 12% 5% 8% 5% 4 5% 5% 5% 6% 25%	2353
April	1st to 10th	Day	15% 9% 4 7% 6% 2 5% 4 5% 7% 36%	2160
	11th to 20th	Day	16% 9% 3 6% 6% 3 4 3 5% 7% 38%	2134
	21st to end	Day	20% 7% 3 6% 6% 3 4 5% 5% 7% 34%	2164
May	1st to 10th	Day	16% 9% 3 7% 6% 4 5% 6% 6% 7% 32%	2340
	11th to 20th	Day	19% 7% 2 7% 5% 3 5% 5% 6% 7% 35%	2425
	21st to end	Day	12% 6% 3 5% 6% 5% 6% 6% 6% 8% 36%	2725
June	1st to 10th	Day	8% 5% 2 5% 6% 3 4 6% 7% 9% 45%	2520
	11th to 20th	Day	8% 5% 2 5% 6% 3 5% 5% 6% 8% 48%	2520
	21st to end	Day	9% 6% 3 6% 5% 4 5% 6% 6% 10% 41%	2520
July	1st to 10th	Day	8% 4 2 5% 5% 4 5% 6% 7% 10% 45%	2520
	11th to 20th	Day	8% 4 2 5% 5% 3 5% 7% 7% 11% 45%	2520
	21st to end	Day	8% 4 3 4 5% 3 5% 6% 7% 9% 45%	2743
August	1st to 10th	Day	7% 4 2 6% 5% 3 5% 5% 7% 9% 47%	2349
	11th to 20th	Day	7% 6% 2 5% 5% 3 6% 6% 6% 9% 46%	2125
	21st to end	Day	7% 4 1 5% 5% 3 6% 5% 7% 8% 49%	2376
September	1st to 10th	Day	12% 5% 2 5% 5% 4 5% 4 5% 8% 45%	2160
	11th to 20th	Day	10% 4 2 4 4 4 3 4 5% 7% 52%	2084
	21st to end	Day	9% 5% 2 6% 5% 3 4 5% 6% 7% 48%	1980
October	1st to 10th	Day	11% 5% 3 5% 5% 3 4 5% 5% 5% 49%	1880
	11th to 20th	Day	17% 8% 3 5% 4 3 4 4 5% 5% 42%	1800
	21st to end	Day	19% 9% 3 5% 5% 3 3 4 5% 6% 37%	1850
November	1st to 10th	Day	11% 6% 3 5% 4 2 3 4 6% 7% 49%	1672
	11th to 20th	Day	17% 10% 4 6% 4 2 3 4 5% 6% 39%	1710
	21st to end	Day	17% 10% 4 8% 5% 3 4 3 4 4 37%	1651
December	1st to 10th	Day	14% 12% 6% 8% 6% 4 5% 4 6% 6% 29%	1520
	11th to 20th	Day	15% 13% 4 9% 6% 3 4 5% 5% 7% 29%	1918
	21st to end	Day	21% 19% 7% 13% 7% 3 4 3 3 5% 16%	2783
January	1st to 10th	Night	12% 13% 4 8% 7% 4 5% 4 5% 5% 33%	2648
	11th to 20th	Night	15% 13% 6% 8% 7% 4 4 4 4 6% 29%	2591
	21st to end	Night	14% 12% 6% 9% 7% 3 5% 4 5% 5% 30%	2610
February	1st to 10th	Night	17% 12% 7% 8% 7% 3 4 5% 4 6% 29%	2321
	11th to 20th	Night	13% 10% 4 9% 6% 3 5% 4 5% 7% 35%	2098
	21st to end	Night	17% 12% 5% 7% 5% 2 4 3 4 6% 34%	1776
March	1st to 10th	Night	15% 10% 4 7% 6% 3 4 4 4 6% 36%	2160
	11th to 20th	Night	16% 9% 3 6% 5% 2 4 5% 5% 7% 38%	2072
	21st to end	Night	20% 9% 4 6% 6% 4 5% 4 5% 6% 31%	2002
April	1st to 10th	Night	13% 8% 3 6% 5% 4 4 4 6% 7% 41%	1800
	11th to 20th	Night	16% 8% 2 5% 5% 4 4 4 5% 6% 42%	1775
	21st to end	Night	20% 7% 3 6% 6% 3 4 4 4 6% 36%	1795
May	1st to 10th	Night	15% 7% 3 6% 6% 3 5% 4 6% 9% 37%	1620
	11th to 20th	Night	16% 6% 3 7% 5% 3 3 4 5% 8% 42%	1466
	21st to end	Night	9% 6% 3 7% 7% 3 5% 5% 8% 9% 38%	1551
June	1st to 10th	Night	9% 4 2 4 4 3 4 5% 6% 9% 51%	1440
	11th to 20th	Night	7% 5% 2 6% 5% 3 4 4 7% 7% 50%	1440
	21st to end	Night	8% 4 2 5% 6% 4 6% 5% 7% 8% 44%	1440
July	1st to 10th	Night	7% 5% 2 4 4 3 4 5% 6% 11% 49%	1440
	11th to 20th	Night	5% 3 2 3 3 4 4 3 6% 8% 58%	1440
	21st to end	Night	3 4 2 5% 5% 3 6% 3 6% 10% 54%	1575
August	1st to 10th	Night	6% 3 1 4 4 3 3 5% 6% 9% 53%	1583
	11th to 20th	Night	6% 4 2 5% 4 4 4 5% 5% 8% 53%	1776
	21st to end	Night	6% 3 1 4 4 3 4 4 5% 7% 57%	1980
September	1st to 10th	Night	12% 3 2 5% 4 3 3 4 4 7% 53%	1800
	11th to 20th	Night	9% 3 2 4 4 2 3 4 5% 8% 56%	1858
	21st to end	Night	7% 5% 2 5% 5% 3 5% 5% 5% 7% 52%	1980
October	1st to 10th	Night	11% 4 2 4 4 3 4 4 4 6% 53%	2078
	11th to 20th	Night	16% 5% 2 4 3 3 3 3 5% 6% 50%	2160
	21st to end	Night	19% 9% 2 5% 5% 3 3 4 4 6% 39%	2506
November	1st to 10th	Night	10% 6% 2 5% 5% 3 4 4 4 5% 52%	2406
	11th to 20th	Night	13% 7% 4 7% 4 3 4 5% 4 7% 43%	2470
	21st to end	Night	18% 9% 4 6% 5% 3 3 4 5% 6% 38%	2527
December	1st to 10th	Night	16% 11% 5% 8% 5% 3 5% 4 5% 6% 33%	2660
	11th to 20th	Night	16% 11% 5% 9% 5% 3 3 4 4 5% 36%	3279
	21st to end	Night	23% 19% 8% 10% 7% 3 3 3 3 4 17%	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	61% 4 9% 16% 10% 1	1518
	11th to 20th	Day	66% 4 11% 13% 6%	1480
	21st to end	Day	63% 4 11% 15% 7%	1743
February	1st to 10th	Day	60% 4 10% 17% 7% 2	1638
	11th to 20th	Day	55% 5% 11% 20% 9% 1	1758
	21st to end	Day	58% 6% 8% 19% 8% 1	1480
March	1st to 10th	Day	52% 6% 11% 20% 10% 1	1800
	11th to 20th	Day	50% 5% 14% 21% 8% 1	1903
	21st to end	Day	59% 6% 10% 18% 5% 1	2353
April	1st to 10th	Day	48% 5% 12% 23% 12%	2160
	11th to 20th	Day	47% 5% 9% 24% 12% 3	2134
	21st to end	Day	49% 6% 13% 19% 12% 2	2164
May	1st to 10th	Day	49% 8% 13% 22% 8%	2340
	11th to 20th	Day	47% 7% 12% 20% 12% 1	2429
	21st to end	Day	43% 8% 13% 19% 15% 2	2725
June	1st to 10th	Day	34% 9% 12% 27% 15% 3	2520
	11th to 20th	Day	33% 7% 11% 24% 22% 4	2520
	21st to end	Day	38% 8% 14% 22% 16% 3	2520
July	1st to 10th	Day	34% 7% 14% 28% 13% 4	2451
	11th to 20th	Day	32% 9% 15% 28% 14% 2	2445
	21st to end	Day	31% 9% 14% 28% 16% 1	2591
August	1st to 10th	Day	31% 9% 17% 30% 11% 2	2334
	11th to 20th	Day	33% 8% 12% 30% 15% 2	2125
	21st to end	Day	29% 8% 13% 24% 20% 6%	2376
September	1st to 10th	Day	36% 6% 11% 23% 19% 5%	2160
	11th to 20th	Day	32% 6% 9% 26% 22% 5%	2084
	21st to end	Day	34% 5% 8% 28% 22% 3	1980
October	1st to 10th	Day	37% 5% 10% 24% 20% 4	1880
	11th to 20th	Day	44% 4 9% 22% 20% 2	1800
	21st to end	Day	48% 4 11% 22% 12% 2	1850
November	1st to 10th	Day	35% 5% 15% 25% 17% 4	1672
	11th to 20th	Day	46% 3 10% 25% 13% 2	1710
	21st to end	Day	51% 4 10% 23% 11%	1651
December	1st to 10th	Day	55% 6% 12% 19% 8% 1	1520
	11th to 20th	Day	55% 5% 9% 23% 7% 1	1915
	21st to end	Day	73% 4 8% 10% 4	2783
January	1st to 10th	Night	53% 4 10% 19% 14%	2648
	11th to 20th	Night	58% 4 12% 17% 9%	2591
	21st to end	Night	56% 4 12% 17% 9% 1	2610
February	1st to 10th	Night	58% 4 10% 17% 10% 2	2321
	11th to 20th	Night	50% 4 12% 21% 11% 2	2099
	21st to end	Night	52% 3 10% 22% 11% 3	1776
March	1st to 10th	Night	50% 4 10% 22% 13% 1	2160
	11th to 20th	Night	45% 5% 12% 21% 13% 3	2072
	21st to end	Night	54% 5% 11% 19% 9% 1	2002
April	1st to 10th	Night	42% 5% 12% 24% 15% 3	1800
	11th to 20th	Night	43% 5% 9% 23% 15% 5%	1775
	21st to end	Night	49% 5% 11% 20% 12% 4	1795
May	1st to 10th	Night	44% 6% 13% 24% 12% 1	1620
	11th to 20th	Night	42% 6% 12% 22% 17% 1	1467
	21st to end	Night	41% 7% 14% 18% 17% 3	1552
June	1st to 10th	Night	31% 6% 13% 28% 17% 5%	1440
	11th to 20th	Night	31% 6% 12% 23% 23% 5%	1440
	21st to end	Night	35% 8% 15% 22% 17% 3	1440
July	1st to 10th	Night	30% 7% 14% 29% 16% 3	1400
	11th to 20th	Night	24% 6% 13% 31% 22% 3	1392
	21st to end	Night	25% 8% 14% 31% 19% 3	1487
August	1st to 10th	Night	26% 8% 16% 32% 17% 2	1574
	11th to 20th	Night	29% 7% 11% 31% 20% 2	1776
	21st to end	Night	26% 8% 12% 27% 21% 6%	1980
September	1st to 10th	Night	32% 5% 9% 26% 21% 7%	1800
	11th to 20th	Night	27% 5% 9% 27% 27% 5%	1858
	21st to end	Night	31% 6% 9% 27% 23% 4	1980
October	1st to 10th	Night	32% 6% 9% 24% 23% 5%	2078
	11th to 20th	Night	36% 3 8% 28% 21% 4	2160
	21st to end	Night	46% 4 9% 22% 17% 2	2506
November	1st to 10th	Night	35% 4 10% 26% 19% 5%	2406
	11th to 20th	Night	42% 3 12% 23% 17% 2	2470
	21st to end	Night	48% 4 10% 24% 14% 1	2527
December	1st to 10th	Night	52% 4 12% 21% 10% 1	2660
	11th to 20th	Night	52% 4 11% 22% 10% 1	3281
	21st to end	Night	73% 4 6% 11% 6%	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	24% 16% 34% 21% 5%	270
	11th to 20th	Day	25% 22% 39% 13% 2	255
	21st to end	Day	17% 19% 38% 22% 4	264
February	1st to 10th	Day	27% 16% 38% 17% 2	240
	11th to 20th	Day	25% 18% 36% 17% 5%	240
	21st to end	Day	28% 16% 40% 15% 1	198
March	1st to 10th	Day	22% 24% 32% 19% 4	240
	11th to 20th	Day	23% 20% 36% 15% 6%	240
	21st to end	Day	30% 15% 32% 16% 6% 1	439
April	1st to 10th	Day	20% 13% 36% 25% 6%	420
	11th to 20th	Day	18% 17% 31% 20% 12% 2	412
	21st to end	Day	22% 15% 34% 20% 7% 1	420
May	1st to 10th	Day	21% 13% 31% 24% 8% 3	423
	11th to 20th	Day	22% 11% 26% 27% 12% 3	571
	21st to end	Day	14% 6% 32% 25% 15% 7%	679
June	1st to 10th	Day	9% 5% 26% 30% 23% 7%	630
	11th to 20th	Day	9% 6% 25% 33% 22% 5%	630
	21st to end	Day	9% 8% 32% 29% 17% 4	630
July	1st to 10th	Day	9% 3 17% 29% 25% 17%	621
	11th to 20th	Day	8% 3 20% 33% 26% 10%	618
	21st to end	Day	8% 2 17% 35% 30% 7%	684
August	1st to 10th	Day	7% 2 16% 35% 28% 11%	590
	11th to 20th	Day	8% 5% 18% 26% 29% 13%	439
	21st to end	Day	8% 2 17% 30% 33% 10%	495
September	1st to 10th	Day	12% 6% 20% 27% 31% 5%	450
	11th to 20th	Day	8% 4 16% 31% 29% 13%	450
	21st to end	Day	10% 10% 24% 24% 22% 9%	450
October	1st to 10th	Day	13% 5% 28% 31% 17% 5%	350
	11th to 20th	Day	18% 21% 30% 24% 6% 1	270
	21st to end	Day	30% 15% 35% 16% 3 1	297
November	1st to 10th	Day	11% 16% 33% 26% 12% 4	270
	11th to 20th	Day	20% 18% 34% 19% 9% 1	270
	21st to end	Day	25% 10% 36% 24% 4	270
December	1st to 10th	Day	13% 20% 42% 16% 6% 3	270
	11th to 20th	Day	19% 18% 36% 24% 4	270
	21st to end	Day	23% 23% 36% 15% 3	297
January	1st to 10th	Night	18% 15% 41% 22% 5%	950
	11th to 20th	Night	20% 15% 38% 21% 5%	926
	21st to end	Night	20% 15% 37% 25% 3	990
February	1st to 10th	Night	23% 12% 39% 22% 4	881
	11th to 20th	Night	21% 13% 37% 26% 3	703
	21st to end	Night	25% 16% 37% 20% 2	592
March	1st to 10th	Night	21% 12% 38% 24% 4	720
	11th to 20th	Night	20% 12% 34% 28% 6% 1	632
	21st to end	Night	24% 10% 37% 23% 6%	594
April	1st to 10th	Night	16% 15% 37% 28% 4	540
	11th to 20th	Night	17% 13% 33% 27% 10%	533
	21st to end	Night	25% 10% 32% 26% 6% 1	540
May	1st to 10th	Night	18% 8% 35% 31% 7% 1	540
	11th to 20th	Night	18% 6% 27% 35% 13% 1	531
	21st to end	Night	11% 4 30% 31% 21% 2	584
June	1st to 10th	Night	10% 3 24% 46% 16%	540
	11th to 20th	Night	9% 3 25% 46% 16% 1	540
	21st to end	Night	9% 3 28% 38% 21% 1	540
July	1st to 10th	Night	10% 2 14% 35% 33% 6%	525
	11th to 20th	Night	7% 2 17% 44% 28% 2	522
	21st to end	Night	5% 1 14% 45% 33% 1	591
August	1st to 10th	Night	7% 2 12% 45% 31% 4	537
	11th to 20th	Night	6% 3 15% 41% 30% 5%	534
	21st to end	Night	6% 2 15% 39% 36% 2	594
September	1st to 10th	Night	13% 4 15% 38% 28% 3	540
	11th to 20th	Night	10% 2 18% 37% 29% 4	598
	21st to end	Night	10% 6% 23% 35% 24% 2	720
October	1st to 10th	Night	12% 4 29% 35% 18% 2	720
	11th to 20th	Night	18% 12% 30% 30% 9% 1	720
	21st to end	Night	25% 12% 34% 22% 7%	792
November	1st to 10th	Night	13% 10% 39% 27% 9% 1	740
	11th to 20th	Night	16% 15% 35% 27% 6%	760
	21st to end	Night	21% 12% 37% 25% 5%	817
December	1st to 10th	Night	21% 11% 40% 22% 5%	950
	11th to 20th	Night	22% 11% 34% 27% 5%	950
	21st to end	Night	29% 16% 33% 20% 2	1045

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