Sycamore Stars Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sycamore Stars Observatory clear sky chart from 2005-11-06 to 2024-11-11.

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	14% 11% 4 8% 5% 5% 4 4 5% 7% 34%	101262
	Night	15% 12% 5% 9% 5% 4 4 3 5% 6% 32%	97956
Transparency	Day	49% 5% 11% 21% 13% 1	104847
	Night	52% 5% 10% 20% 12% 1	102512
Seeing	Day	20% 13% 30% 22% 11% 4	15807
	Night	20% 10% 28% 29% 11% 1	25653

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% 22% 7% 14% 7% 5% 5% 3 4 5% 13%	2527
	11th to 20th	Day	13% 20% 9% 16% 10% 13% 3 2 3 4 7%	2530
	21st to end	Day	23% 26% 9% 13% 6% 3 3 2 3 4 9%	2783
February	1st to 10th	Day	14% 18% 6% 16% 9% 6% 5% 3 3 3 18%	1777
	11th to 20th	Day	14% 15% 7% 16% 8% 5% 4 3 4 5% 20%	1848
	21st to end	Day	16% 18% 5% 12% 5% 5% 5% 3 4 5% 21%	1570
March	1st to 10th	Day	17% 14% 5% 8% 5% 4 4 4 5% 7% 28%	3120
	11th to 20th	Day	11% 11% 6% 10% 5% 5% 5% 4 5% 7% 31%	3379
	21st to end	Day	20% 13% 7% 9% 6% 4 4 3 4 4 25%	3961
April	1st to 10th	Day	17% 16% 4 6% 5% 5% 4 3 5% 5% 29%	2280
	11th to 20th	Day	18% 12% 3 5% 4 3 3 4 5% 5% 37%	2299
	21st to end	Day	18% 10% 3 7% 4 5% 4 3 5% 7% 35%	2470
May	1st to 10th	Day	17% 8% 3 7% 4 4 5% 4 6% 7% 36%	4082
	11th to 20th	Day	15% 8% 3 7% 5% 4 5% 4 6% 7% 37%	4081
	21st to end	Day	11% 6% 2 6% 4 4 4 4 6% 8% 44%	4787
June	1st to 10th	Day	10% 6% 2 7% 5% 4 5% 3 7% 8% 43%	2660
	11th to 20th	Day	10% 6% 2 5% 5% 4 4 4 6% 9% 45%	2660
	21st to end	Day	11% 5% 2 7% 5% 5% 5% 4 6% 8% 40%	2660
July	1st to 10th	Day	12% 7% 2 7% 5% 5% 5% 4 7% 9% 38%	4440
	11th to 20th	Day	8% 4 2 5% 4 4 4 4 7% 9% 49%	4440
	21st to end	Day	7% 5% 2 7% 4 5% 5% 5% 7% 9% 44%	4813
August	1st to 10th	Day	11% 5% 2 6% 5% 4 5% 4 6% 8% 43%	4114
	11th to 20th	Day	11% 6% 2 6% 4 4 4 4 6% 7% 46%	4044
	21st to end	Day	9% 5% 2 6% 4 4 5% 3 7% 9% 46%	4196
September	1st to 10th	Day	12% 6% 2 7% 4 4 5% 4 6% 9% 42%	2248
	11th to 20th	Day	11% 4 2 5% 3 4 4 4 6% 8% 48%	2090
	21st to end	Day	14% 7% 2 7% 4 4 5% 4 5% 8% 38%	2090
October	1st to 10th	Day	16% 7% 2 7% 4 4 5% 3 4 5% 43%	2090
	11th to 20th	Day	22% 10% 3 7% 5% 4 5% 4 7% 6% 28%	1863
	21st to end	Day	23% 12% 3 9% 5% 5% 4 4 4 6% 24%	1881
November	1st to 10th	Day	15% 12% 4 6% 4 3 5% 4 5% 6% 36%	1762
	11th to 20th	Day	16% 21% 4 10% 5% 4 5% 4 4 5% 23%	1710
	21st to end	Day	21% 17% 8% 10% 4 4 3 2 4 5% 21%	1710
December	1st to 10th	Day	15% 23% 10% 12% 7% 4 4 3 3 4 16%	1596
	11th to 20th	Day	13% 23% 10% 14% 5% 4 4 3 4 5% 15%	1918
	21st to end	Day	22% 25% 7% 14% 6% 3 3 2 3 5% 10%	2783
January	1st to 10th	Night	17% 20% 11% 14% 6% 5% 4 3 3 4 14%	4428
	11th to 20th	Night	14% 20% 10% 16% 8% 10% 3 2 3 3 9%	4440
	21st to end	Night	24% 20% 9% 16% 6% 5% 3 2 3 3 9%	4884
February	1st to 10th	Night	14% 18% 5% 13% 11% 5% 4 3 4 4 19%	2398
	11th to 20th	Night	13% 16% 7% 14% 7% 5% 3 3 4 5% 23%	2218
	21st to end	Night	17% 14% 5% 11% 5% 4 4 4 5% 5% 27%	1884
March	1st to 10th	Night	17% 11% 4 9% 5% 4 4 3 4 6% 35%	3733
	11th to 20th	Night	10% 8% 4 7% 5% 3 4 3 5% 7% 43%	3580
	21st to end	Night	18% 12% 6% 10% 5% 4 4 3 5% 6% 27%	3700
April	1st to 10th	Night	14% 13% 3 6% 4 4 5% 4 5% 6% 35%	1900
	11th to 20th	Night	19% 11% 2 6% 4 4 4 3 4 5% 36%	1829
	21st to end	Night	17% 9% 2 6% 4 4 4 3 5% 6% 38%	1710
May	1st to 10th	Night	14% 10% 3 8% 4 5% 4 3 6% 8% 36%	2813
	11th to 20th	Night	18% 8% 2 6% 4 4 3 2 5% 7% 42%	2812
	21st to end	Night	13% 7% 2 6% 5% 4 4 4 6% 7% 42%	2775
June	1st to 10th	Night	11% 5% 2 4 4 4 4 4 7% 9% 47%	1520
	11th to 20th	Night	11% 6% 2 5% 5% 4 5% 4 7% 8% 44%	1520
	21st to end	Night	10% 4 2 5% 5% 5% 5% 5% 5% 10% 45%	1520
July	1st to 10th	Night	9% 5% 2 6% 5% 5% 5% 4 8% 9% 42%	2530
	11th to 20th	Night	7% 4 1 5% 4 3 3 3 5% 7% 56%	2530
	21st to end	Night	7% 6% 2 6% 5% 4 5% 4 7% 10% 46%	2750
August	1st to 10th	Night	10% 5% 2 5% 4 4 4 3 7% 9% 47%	2815
	11th to 20th	Night	11% 6% 2 6% 3 4 4 3 6% 7% 48%	2785
	21st to end	Night	9% 6% 3 7% 5% 5% 5% 4 5% 7% 46%	3444
September	1st to 10th	Night	10% 5% 2 5% 4 4 4 3 5% 8% 49%	1912
	11th to 20th	Night	10% 5% 2 5% 3 3 3 3 5% 7% 54%	2090
	21st to end	Night	14% 8% 3 6% 4 4 4 4 5% 6% 42%	2090
October	1st to 10th	Night	16% 6% 2 6% 3 4 4 3 4 7% 46%	2090
	11th to 20th	Night	19% 10% 3 8% 4 4 4 3 3 6% 36%	2312
	21st to end	Night	25% 10% 3 7% 4 4 4 3 5% 6% 31%	2717
November	1st to 10th	Night	15% 13% 3 7% 4 4 4 3 5% 6% 37%	2536
	11th to 20th	Night	15% 18% 5% 10% 5% 5% 4 4 4 6% 25%	2477
	21st to end	Night	19% 17% 5% 8% 5% 4 4 3 5% 6% 24%	2470
December	1st to 10th	Night	17% 24% 8% 11% 6% 4 4 3 4 5% 14%	2581
	11th to 20th	Night	14% 22% 9% 14% 6% 4 4 3 4 4 16%	3279
	21st to end	Night	26% 22% 7% 10% 5% 4 4 3 4 4 11%	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	74% 5% 10% 9% 2	2528
	11th to 20th	Day	83% 4 7% 4 1	2530
	21st to end	Day	81% 3 7% 7% 2	2783
February	1st to 10th	Day	72% 4 8% 11% 5% 1	1777
	11th to 20th	Day	67% 4 8% 13% 7%	1858
	21st to end	Day	66% 4 11% 13% 5% 1	1570
March	1st to 10th	Day	56% 5% 11% 20% 8%	3120
	11th to 20th	Day	51% 6% 13% 22% 8% 1	3379
	21st to end	Day	63% 4 9% 18% 6% 1	3961
April	1st to 10th	Day	56% 5% 9% 18% 12%	2280
	11th to 20th	Day	47% 5% 9% 22% 14% 2	2299
	21st to end	Day	50% 4 12% 17% 15% 2	2470
May	1st to 10th	Day	45% 6% 10% 23% 15% 1	4120
	11th to 20th	Day	43% 6% 13% 23% 13% 1	4085
	21st to end	Day	36% 7% 11% 22% 23% 2	4800
June	1st to 10th	Day	37% 6% 11% 27% 18% 2	2660
	11th to 20th	Day	35% 5% 13% 25% 20% 2	2660
	21st to end	Day	40% 6% 13% 22% 17% 3	2660
July	1st to 10th	Day	43% 5% 13% 20% 16% 3	4371
	11th to 20th	Day	29% 5% 14% 32% 17% 2	4365
	21st to end	Day	34% 7% 16% 21% 21% 2	4662
August	1st to 10th	Day	36% 7% 12% 27% 16% 1	4100
	11th to 20th	Day	36% 6% 12% 29% 16% 1	4083
	21st to end	Day	34% 5% 13% 28% 18% 2	4195
September	1st to 10th	Day	38% 6% 13% 25% 16% 3	2248
	11th to 20th	Day	33% 5% 12% 31% 18% 2	2090
	21st to end	Day	43% 6% 11% 23% 17% 1	2090
October	1st to 10th	Day	30% 3 7% 39% 19% 1	3480
	11th to 20th	Day	41% 5% 12% 25% 18%	3066
	21st to end	Day	51% 3 11% 24% 10% 1	3081
November	1st to 10th	Day	49% 5% 11% 22% 12% 1	1762
	11th to 20th	Day	64% 5% 9% 16% 6% 1	1710
	21st to end	Day	66% 4 12% 14% 4	1710
December	1st to 10th	Day	73% 5% 8% 11% 3	1596
	11th to 20th	Day	72% 5% 11% 9% 2	1915
	21st to end	Day	78% 4 8% 8% 2	2783
January	1st to 10th	Night	75% 5% 8% 8% 4	4428
	11th to 20th	Night	81% 4 6% 5% 3	4440
	21st to end	Night	81% 4 7% 6% 2	4884
February	1st to 10th	Night	69% 4 9% 12% 6%	2398
	11th to 20th	Night	64% 4 7% 17% 7%	2219
	21st to end	Night	60% 4 12% 15% 7% 2	1884
March	1st to 10th	Night	51% 4 13% 25% 7% 1	3733
	11th to 20th	Night	40% 6% 13% 24% 15% 2	3580
	21st to end	Night	58% 5% 11% 17% 8% 1	3700
April	1st to 10th	Night	48% 5% 11% 22% 13% 1	1900
	11th to 20th	Night	50% 4 7% 19% 17% 3	1829
	21st to end	Night	46% 6% 11% 19% 16% 2	1710
May	1st to 10th	Night	46% 5% 11% 23% 13% 1	2840
	11th to 20th	Night	42% 5% 9% 22% 18% 3	2813
	21st to end	Night	40% 6% 10% 20% 20% 2	2783
June	1st to 10th	Night	32% 6% 13% 30% 17% 3	1520
	11th to 20th	Night	35% 8% 13% 23% 20% 2	1520
	21st to end	Night	35% 6% 16% 24% 16% 2	1520
July	1st to 10th	Night	37% 5% 13% 25% 13% 7%	2490
	11th to 20th	Night	27% 5% 14% 28% 25% 1	2482
	21st to end	Night	33% 6% 16% 17% 26% 2	2662
August	1st to 10th	Night	34% 5% 14% 30% 16% 1	2805
	11th to 20th	Night	35% 5% 11% 32% 17% 1	2812
	21st to end	Night	37% 6% 9% 28% 18% 2	3444
September	1st to 10th	Night	32% 5% 13% 27% 20% 3	1912
	11th to 20th	Night	31% 5% 8% 32% 22% 2	2090
	21st to end	Night	42% 5% 11% 25% 16% 1	2090
October	1st to 10th	Night	28% 4 9% 35% 23% 1	3480
	11th to 20th	Night	42% 3 11% 23% 21%	3848
	21st to end	Night	44% 3 9% 28% 16%	4467
November	1st to 10th	Night	49% 5% 9% 23% 13% 1	2536
	11th to 20th	Night	61% 4 12% 16% 7% 1	2477
	21st to end	Night	62% 4 13% 17% 3	2470
December	1st to 10th	Night	73% 4 8% 10% 4	2581
	11th to 20th	Night	72% 4 10% 10% 4	3281
	21st to end	Night	76% 5% 10% 7% 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% 17% 34% 20% 6%	270
	11th to 20th	Day	27% 17% 37% 15% 3 1	270
	21st to end	Day	28% 18% 32% 18% 4	297
February	1st to 10th	Day	27% 20% 32% 16% 3 1	270
	11th to 20th	Day	28% 23% 34% 12% 3	270
	21st to end	Day	28% 31% 28% 10% 2	225
March	1st to 10th	Day	23% 28% 34% 13% 3	270
	11th to 20th	Day	26% 17% 30% 21% 6% 1	398
	21st to end	Day	32% 17% 29% 18% 4 1	506
April	1st to 10th	Day	28% 14% 34% 18% 5%	460
	11th to 20th	Day	28% 20% 27% 15% 6% 3	452
	21st to end	Day	27% 16% 30% 19% 7% 1	460
May	1st to 10th	Day	25% 16% 30% 21% 6% 2	463
	11th to 20th	Day	21% 10% 31% 24% 10% 5%	487
	21st to end	Day	15% 10% 30% 27% 13% 5%	710
June	1st to 10th	Day	15% 10% 35% 25% 11% 4	680
	11th to 20th	Day	14% 11% 32% 28% 13% 2	680
	21st to end	Day	15% 11% 34% 25% 12% 4	680
July	1st to 10th	Day	9% 6% 29% 30% 16% 10%	671
	11th to 20th	Day	12% 6% 32% 27% 16% 7%	668
	21st to end	Day	9% 6% 30% 29% 20% 7%	739
August	1st to 10th	Day	11% 4 22% 27% 22% 13%	496
	11th to 20th	Day	11% 5% 24% 29% 22% 9%	479
	21st to end	Day	13% 5% 21% 29% 25% 7%	539
September	1st to 10th	Day	15% 8% 22% 27% 21% 8%	490
	11th to 20th	Day	9% 4 21% 29% 27% 9%	490
	21st to end	Day	20% 12% 21% 26% 15% 7%	490
October	1st to 10th	Day	19% 11% 26% 26% 15% 3	490
	11th to 20th	Day	27% 17% 29% 22% 5%	400
	21st to end	Day	33% 18% 32% 13% 2 1	330
November	1st to 10th	Day	25% 17% 32% 19% 5% 1	300
	11th to 20th	Day	28% 24% 30% 16% 3	270
	21st to end	Day	32% 17% 38% 10% 3	270
December	1st to 10th	Day	30% 25% 27% 13% 4	270
	11th to 20th	Day	23% 24% 37% 14% 2	270
	21st to end	Day	26% 24% 35% 12% 2	297
January	1st to 10th	Night	25% 15% 33% 19% 7%	950
	11th to 20th	Night	27% 14% 33% 21% 4 1	950
	21st to end	Night	23% 12% 32% 30% 3	1045
February	1st to 10th	Night	23% 14% 35% 24% 4	770
	11th to 20th	Night	21% 17% 33% 25% 4	743
	21st to end	Night	25% 17% 37% 18% 4	628
March	1st to 10th	Night	22% 14% 31% 25% 7% 1	760
	11th to 20th	Night	18% 14% 36% 26% 6% 1	760
	21st to end	Night	24% 12% 31% 25% 8%	770
April	1st to 10th	Night	18% 14% 33% 28% 6% 1	570
	11th to 20th	Night	26% 10% 34% 23% 6% 1	563
	21st to end	Night	23% 9% 33% 28% 7% 1	570
May	1st to 10th	Night	19% 8% 36% 28% 8% 1	570
	11th to 20th	Night	21% 7% 26% 36% 10%	561
	21st to end	Night	15% 5% 28% 33% 17% 1	617
June	1st to 10th	Night	12% 5% 28% 40% 14% 1	570
	11th to 20th	Night	14% 4 26% 40% 16%	570
	21st to end	Night	12% 3 24% 38% 22% 2	570
July	1st to 10th	Night	10% 2 19% 40% 26% 3	555
	11th to 20th	Night	10% 2 17% 44% 23% 4	552
	21st to end	Night	8% 3 16% 45% 27% 1	624
August	1st to 10th	Night	11% 1 13% 44% 26% 4	567
	11th to 20th	Night	11% 1 15% 42% 28% 4	564
	21st to end	Night	11% 3 17% 36% 31% 3	627
September	1st to 10th	Night	12% 4 15% 40% 26% 3	582
	11th to 20th	Night	11% 5% 17% 38% 26% 3	760
	21st to end	Night	17% 7% 23% 30% 18% 4	760
October	1st to 10th	Night	19% 7% 22% 33% 18% 1	760
	11th to 20th	Night	25% 12% 26% 27% 8% 1	760
	21st to end	Night	30% 13% 29% 21% 6%	836
November	1st to 10th	Night	22% 14% 29% 25% 9% 1	780
	11th to 20th	Night	25% 15% 33% 22% 5% 1	763
	21st to end	Night	27% 11% 33% 24% 4	760
December	1st to 10th	Night	27% 15% 32% 21% 5%	871
	11th to 20th	Night	26% 15% 34% 22% 3	950
	21st to end	Night	34% 14% 32% 18% 2	1045

Page generated at 2024-11-08 06:44:51. Version ac07

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