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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 2024-11-06.

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% 9% 3 7% 5% 4 5% 4 6% 7% 38%	101334
	Night	13% 9% 3 7% 4 4 4 3 5% 6% 40%	97813
Transparency	Day	43% 6% 12% 23% 15% 2	104912
	Night	43% 5% 11% 23% 16% 2	102376
Seeing	Day	15% 10% 28% 26% 16% 5%	15732
	Night	17% 10% 31% 30% 12% 1	25554

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	13% 14% 8% 13% 6% 5% 4 3 5% 5% 23%	2527
	11th to 20th	Day	13% 12% 4 13% 8% 6% 9% 5% 8% 5% 17%	2530
	21st to end	Day	19% 20% 9% 12% 5% 5% 3 3 3 5% 17%	3068
February	1st to 10th	Day	15% 13% 6% 12% 5% 6% 3 3 4 5% 29%	1729
	11th to 20th	Day	13% 11% 4 9% 7% 6% 4 3 5% 6% 33%	1848
	21st to end	Day	15% 15% 4 10% 5% 4 4 4 4 5% 30%	1570
March	1st to 10th	Day	18% 16% 4 7% 4 4 3 3 4 5% 33%	3120
	11th to 20th	Day	8% 8% 2 7% 4 4 5% 4 6% 7% 44%	3347
	21st to end	Day	18% 11% 5% 10% 5% 5% 5% 4 5% 7% 26%	4128
April	1st to 10th	Day	15% 11% 3 8% 5% 4 5% 3 5% 6% 36%	2280
	11th to 20th	Day	15% 10% 3 7% 5% 4 4 2 6% 6% 38%	2254
	21st to end	Day	20% 7% 3 7% 4 4 4 4 6% 7% 34%	2285
May	1st to 10th	Day	16% 8% 3 7% 4 5% 5% 5% 7% 9% 32%	4082
	11th to 20th	Day	18% 7% 2 7% 4 4 4 3 5% 8% 37%	4317
	21st to end	Day	10% 6% 2 5% 4 5% 4 4 6% 8% 45%	4824
June	1st to 10th	Day	8% 6% 2 6% 5% 4 4 5% 7% 9% 45%	2660
	11th to 20th	Day	8% 5% 2 5% 5% 4 5% 4 6% 8% 49%	2660
	21st to end	Day	9% 6% 2 6% 5% 5% 5% 4 7% 9% 41%	2660
July	1st to 10th	Day	12% 6% 2 7% 5% 5% 5% 5% 7% 11% 36%	4440
	11th to 20th	Day	7% 4 2 6% 4 4 5% 5% 7% 11% 46%	4440
	21st to end	Day	9% 5% 2 6% 5% 5% 6% 5% 7% 9% 41%	4813
August	1st to 10th	Day	7% 4 2 6% 4 4 5% 4 7% 10% 49%	4139
	11th to 20th	Day	9% 6% 2 6% 5% 4 6% 4 7% 10% 42%	3729
	21st to end	Day	5% 4 1 6% 4 5% 6% 4 7% 9% 48%	4180
September	1st to 10th	Day	11% 5% 2 6% 4 4 4 3 5% 7% 48%	2280
	11th to 20th	Day	10% 4 2 5% 4 4 4 3 5% 7% 52%	2199
	21st to end	Day	10% 6% 2 6% 4 4 3 4 6% 7% 47%	2090
October	1st to 10th	Day	11% 5% 2 6% 4 4 4 4 5% 5% 50%	1984
	11th to 20th	Day	16% 8% 2 6% 4 3 4 3 5% 5% 44%	1900
	21st to end	Day	18% 9% 3 6% 4 4 3 3 5% 6% 38%	1952
November	1st to 10th	Day	12% 7% 2 5% 4 3 3 3 5% 7% 49%	1717
	11th to 20th	Day	16% 11% 3 7% 3 3 4 3 5% 6% 39%	1710
	21st to end	Day	17% 11% 3 9% 4 4 4 3 4 4 37%	1651
December	1st to 10th	Day	14% 13% 5% 9% 6% 4 4 3 6% 6% 29%	1520
	11th to 20th	Day	15% 13% 4 10% 6% 4 4 4 5% 6% 29%	1918
	21st to end	Day	21% 19% 7% 14% 5% 4 4 2 3 5% 16%	2783
January	1st to 10th	Night	14% 15% 5% 11% 4 4 4 3 4 5% 30%	4428
	11th to 20th	Night	13% 18% 6% 10% 5% 6% 6% 4 5% 4 21%	4440
	21st to end	Night	22% 17% 7% 9% 4 4 3 3 4 5% 22%	4596
February	1st to 10th	Night	16% 12% 6% 9% 5% 4 4 4 4 6% 31%	2450
	11th to 20th	Night	13% 10% 4 8% 6% 4 4 3 5% 6% 36%	2218
	21st to end	Night	16% 12% 4 8% 4 3 4 3 5% 6% 36%	1884
March	1st to 10th	Night	18% 14% 3 6% 3 3 3 3 5% 5% 37%	3733
	11th to 20th	Night	12% 7% 3 5% 4 3 3 4 5% 6% 48%	3642
	21st to end	Night	20% 9% 4 9% 5% 5% 4 4 5% 6% 29%	3502
April	1st to 10th	Night	13% 9% 2 6% 5% 4 4 3 6% 7% 41%	1900
	11th to 20th	Night	16% 8% 2 5% 4 4 4 3 5% 6% 42%	1875
	21st to end	Night	20% 7% 2 7% 5% 4 4 3 4 6% 37%	1894
May	1st to 10th	Night	17% 9% 3 7% 5% 5% 4 3 6% 8% 33%	2813
	11th to 20th	Night	14% 6% 2 7% 4 4 4 3 6% 8% 41%	2582
	21st to end	Night	9% 6% 2 6% 4 5% 4 4 6% 9% 45%	2743
June	1st to 10th	Night	9% 5% 2 4 4 4 4 4 6% 9% 50%	1520
	11th to 20th	Night	7% 5% 1 7% 4 4 4 4 7% 7% 50%	1520
	21st to end	Night	8% 5% 2 6% 6% 6% 5% 5% 7% 8% 44%	1520
July	1st to 10th	Night	12% 6% 2 6% 4 5% 4 4 6% 10% 42%	2530
	11th to 20th	Night	4 4 2 4 4 4 4 3 7% 7% 58%	2530
	21st to end	Night	6% 7% 2 6% 5% 4 5% 3 6% 9% 47%	2750
August	1st to 10th	Night	6% 3 1 5% 4 4 3 4 7% 9% 54%	2792
	11th to 20th	Night	7% 4 2 5% 4 4 4 4 6% 8% 51%	3100
	21st to end	Night	6% 4 1 5% 4 4 4 4 6% 9% 54%	3476
September	1st to 10th	Night	11% 4 2 5% 3 3 3 3 4 7% 54%	1900
	11th to 20th	Night	8% 4 1 5% 3 3 4 3 6% 8% 55%	1962
	21st to end	Night	8% 6% 2 6% 4 4 5% 4 5% 6% 50%	2090
October	1st to 10th	Night	11% 4 2 5% 4 4 4 3 4 6% 55%	2194
	11th to 20th	Night	15% 6% 2 4 3 3 3 2 5% 6% 52%	2280
	21st to end	Night	18% 9% 2 6% 4 4 4 3 5% 6% 40%	2646
November	1st to 10th	Night	11% 6% 2 6% 4 4 4 3 5% 5% 51%	2483
	11th to 20th	Night	13% 8% 3 7% 4 4 4 4 5% 7% 42%	2470
	21st to end	Night	17% 10% 4 6% 4 4 4 3 5% 6% 38%	2527
December	1st to 10th	Night	15% 12% 4 9% 4 4 4 3 5% 6% 33%	2660
	11th to 20th	Night	16% 12% 5% 9% 4 4 3 3 4 5% 36%	3279
	21st to end	Night	23% 20% 7% 11% 5% 4 3 2 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	63% 4 9% 18% 6%	2528
	11th to 20th	Day	65% 7% 10% 11% 7%	2530
	21st to end	Day	72% 3 8% 13% 5%	3068
February	1st to 10th	Day	58% 4 10% 18% 9% 2	1729
	11th to 20th	Day	53% 5% 11% 21% 11% 1	1858
	21st to end	Day	55% 6% 8% 21% 8% 2	1570
March	1st to 10th	Day	55% 5% 8% 17% 14% 2	3120
	11th to 20th	Day	37% 7% 13% 26% 16% 1	3347
	21st to end	Day	56% 7% 15% 18% 3 1	4128
April	1st to 10th	Day	48% 5% 11% 23% 12%	2280
	11th to 20th	Day	46% 5% 9% 24% 13% 3	2254
	21st to end	Day	48% 6% 13% 19% 12% 2	2285
May	1st to 10th	Day	46% 9% 12% 25% 8%	4120
	11th to 20th	Day	45% 7% 10% 28% 9% 1	4321
	21st to end	Day	34% 8% 10% 22% 23% 3	4837
June	1st to 10th	Day	34% 9% 12% 27% 15% 3	2660
	11th to 20th	Day	32% 7% 11% 25% 22% 4	2660
	21st to end	Day	38% 7% 14% 22% 16% 3	2660
July	1st to 10th	Day	40% 7% 13% 27% 11% 2	4371
	11th to 20th	Day	30% 9% 16% 27% 18% 1	4365
	21st to end	Day	35% 10% 17% 20% 16% 2	4662
August	1st to 10th	Day	28% 8% 19% 31% 13% 1	4124
	11th to 20th	Day	35% 8% 14% 27% 16% 1	3765
	21st to end	Day	30% 7% 14% 29% 16% 4	4179
September	1st to 10th	Day	35% 6% 10% 24% 21% 5%	2280
	11th to 20th	Day	31% 6% 9% 26% 22% 5%	2199
	21st to end	Day	36% 5% 8% 27% 21% 3	2090
October	1st to 10th	Day	25% 4 7% 23% 38% 3	3296
	11th to 20th	Day	30% 3 9% 22% 34% 3	3140
	21st to end	Day	40% 4 9% 24% 21% 2	3190
November	1st to 10th	Day	35% 5% 14% 25% 17% 4	1717
	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	57% 4 11% 19% 9%	4428
	11th to 20th	Night	65% 4 9% 14% 7% 1	4440
	21st to end	Night	66% 4 9% 15% 6%	4596
February	1st to 10th	Night	55% 4 10% 18% 11% 2	2450
	11th to 20th	Night	49% 4 12% 21% 12% 2	2219
	21st to end	Night	51% 3 9% 22% 12% 2	1884
March	1st to 10th	Night	49% 5% 10% 23% 12% 1	3733
	11th to 20th	Night	36% 6% 9% 27% 20% 3	3642
	21st to end	Night	53% 7% 11% 21% 7% 1	3502
April	1st to 10th	Night	43% 5% 11% 24% 15% 3	1900
	11th to 20th	Night	43% 5% 9% 24% 15% 5%	1875
	21st to end	Night	48% 5% 11% 20% 13% 3	1894
May	1st to 10th	Night	47% 7% 13% 22% 11% 1	2840
	11th to 20th	Night	40% 7% 13% 28% 11%	2583
	21st to end	Night	35% 7% 12% 20% 23% 4	2751
June	1st to 10th	Night	31% 6% 13% 28% 17% 5%	1520
	11th to 20th	Night	32% 6% 12% 23% 23% 5%	1520
	21st to end	Night	35% 8% 14% 22% 16% 4	1520
July	1st to 10th	Night	38% 6% 12% 27% 14% 3	2490
	11th to 20th	Night	23% 7% 13% 30% 25% 2	2482
	21st to end	Night	33% 9% 15% 22% 17% 5%	2662
August	1st to 10th	Night	25% 8% 17% 31% 18% 2	2783
	11th to 20th	Night	29% 8% 13% 32% 18% 1	3130
	21st to end	Night	26% 7% 13% 32% 17% 4	3476
September	1st to 10th	Night	31% 5% 9% 25% 23% 7%	1900
	11th to 20th	Night	27% 5% 9% 26% 27% 6%	1962
	21st to end	Night	32% 6% 9% 26% 22% 4	2090
October	1st to 10th	Night	21% 4 6% 26% 39% 4	3662
	11th to 20th	Night	24% 2 8% 25% 35% 5%	3779
	21st to end	Night	36% 4 9% 23% 23% 4	4358
November	1st to 10th	Night	35% 5% 10% 26% 19% 5%	2483
	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	24% 21% 40% 13% 2	270
	21st to end	Day	20% 18% 35% 24% 4	297
February	1st to 10th	Day	25% 15% 39% 19% 3	270
	11th to 20th	Day	23% 17% 37% 18% 6%	270
	21st to end	Day	26% 17% 40% 16% 2	225
March	1st to 10th	Day	21% 24% 33% 18% 3	270
	11th to 20th	Day	22% 21% 36% 15% 5%	270
	21st to end	Day	29% 15% 33% 16% 5% 1	482
April	1st to 10th	Day	21% 14% 36% 23% 5%	460
	11th to 20th	Day	18% 20% 30% 20% 11% 2	452
	21st to end	Day	21% 17% 34% 20% 7% 1	460
May	1st to 10th	Day	19% 14% 32% 24% 8% 2	463
	11th to 20th	Day	21% 11% 26% 27% 13% 3	619
	21st to end	Day	14% 7% 32% 26% 15% 7%	734
June	1st to 10th	Day	9% 6% 27% 30% 21% 6%	680
	11th to 20th	Day	8% 6% 25% 34% 21% 5%	680
	21st to end	Day	9% 8% 34% 29% 17% 4	680
July	1st to 10th	Day	9% 3 20% 28% 24% 16%	671
	11th to 20th	Day	8% 3 21% 32% 25% 10%	668
	21st to end	Day	8% 3 17% 35% 30% 7%	739
August	1st to 10th	Day	7% 2 18% 35% 28% 10%	638
	11th to 20th	Day	9% 5% 20% 27% 27% 12%	479
	21st to end	Day	8% 2 16% 30% 35% 9%	539
September	1st to 10th	Day	11% 5% 20% 29% 30% 5%	490
	11th to 20th	Day	8% 4 15% 31% 31% 12%	490
	21st to end	Day	12% 11% 24% 23% 22% 8%	490
October	1st to 10th	Day	13% 5% 28% 31% 18% 5%	384
	11th to 20th	Day	17% 20% 30% 24% 8% 2	300
	21st to end	Day	28% 16% 35% 17% 4 1	330
November	1st to 10th	Day	12% 16% 31% 25% 12% 4	285
	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	21% 15% 38% 21% 5%	950
	21st to end	Night	21% 15% 36% 25% 3	1045
February	1st to 10th	Night	22% 12% 39% 23% 4	930
	11th to 20th	Night	20% 13% 37% 27% 3	743
	21st to end	Night	24% 16% 37% 20% 2	628
March	1st to 10th	Night	20% 13% 39% 24% 4	760
	11th to 20th	Night	19% 13% 34% 27% 6% 1	667
	21st to end	Night	24% 11% 37% 23% 5%	627
April	1st to 10th	Night	17% 15% 36% 27% 4	570
	11th to 20th	Night	18% 13% 34% 26% 9%	563
	21st to end	Night	24% 10% 33% 26% 6% 1	570
May	1st to 10th	Night	18% 9% 35% 31% 6% 1	570
	11th to 20th	Night	17% 6% 27% 37% 12% 1	561
	21st to end	Night	11% 4 32% 31% 20% 2	617
June	1st to 10th	Night	10% 4 25% 46% 15%	570
	11th to 20th	Night	9% 4 25% 45% 16% 1	570
	21st to end	Night	9% 3 29% 38% 21% 1	570
July	1st to 10th	Night	11% 3 14% 35% 32% 5%	555
	11th to 20th	Night	7% 2 16% 44% 29% 2	552
	21st to end	Night	5% 1 14% 45% 33% 1	624
August	1st to 10th	Night	8% 2 12% 44% 31% 4	567
	11th to 20th	Night	6% 3 15% 42% 29% 5%	564
	21st to end	Night	6% 2 15% 39% 36% 2	627
September	1st to 10th	Night	12% 4 15% 38% 28% 3	570
	11th to 20th	Night	9% 2 17% 38% 29% 4	632
	21st to end	Night	11% 7% 23% 34% 23% 2	760
October	1st to 10th	Night	12% 4 28% 35% 18% 2	760
	11th to 20th	Night	17% 12% 30% 30% 11% 1	760
	21st to end	Night	24% 12% 34% 22% 7%	836
November	1st to 10th	Night	14% 11% 38% 27% 9% 1	764
	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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