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 2024-01-13.

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% 10% 4 7% 6% 3 5% 5% 5% 7% 33%	74852
	Night	16% 11% 5% 8% 6% 3 4 4 5% 6% 32%	74914
Transparency	Day	51% 5% 11% 20% 11% 1	74554
	Night	53% 5% 11% 19% 11% 1	74733
Seeing	Day	20% 13% 29% 23% 11% 4	14613
	Night	21% 10% 28% 29% 11% 1	24589

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	16% 15% 6% 14% 10% 4 5% 5% 4 5% 15%	1517
	11th to 20th	Day	15% 20% 9% 13% 9% 4 4 4 4 6% 12%	1461
	21st to end	Day	15% 22% 10% 14% 9% 3 4 4 4 4 12%	1584
February	1st to 10th	Day	15% 16% 7% 15% 11% 5% 6% 4 3 3 16%	1684
	11th to 20th	Day	15% 12% 8% 15% 9% 4 4 4 4 5% 19%	1748
	21st to end	Day	17% 16% 7% 11% 6% 4 5% 4 4 5% 20%	1480
March	1st to 10th	Day	14% 12% 6% 8% 8% 4 4 6% 5% 7% 26%	1800
	11th to 20th	Day	12% 12% 5% 8% 7% 3 4 4 4 7% 34%	1921
	21st to end	Day	19% 13% 4 8% 6% 4 3 4 4 6% 28%	2256
April	1st to 10th	Day	18% 15% 5% 6% 5% 3 4 4 5% 5% 29%	2160
	11th to 20th	Day	18% 12% 3 5% 4 2 4 5% 5% 6% 36%	2176
	21st to end	Day	18% 10% 4 6% 5% 3 4 4 5% 7% 34%	2340
May	1st to 10th	Day	17% 8% 3 6% 6% 3 5% 5% 6% 7% 33%	2340
	11th to 20th	Day	18% 7% 3 6% 5% 3 4 4 5% 7% 37%	2301
	21st to end	Day	12% 6% 3 5% 5% 4 5% 6% 6% 8% 41%	2702
June	1st to 10th	Day	10% 6% 2 6% 6% 3 6% 4 6% 8% 44%	2520
	11th to 20th	Day	10% 6% 2 5% 5% 3 5% 5% 6% 8% 45%	2520
	21st to end	Day	11% 5% 2 6% 6% 3 6% 5% 7% 8% 41%	2520
July	1st to 10th	Day	7% 4 2 5% 4 3 5% 5% 7% 9% 49%	2520
	11th to 20th	Day	10% 5% 2 4 5% 3 5% 5% 6% 9% 45%	2520
	21st to end	Day	7% 4 2 5% 5% 3 5% 5% 8% 9% 45%	2743
August	1st to 10th	Day	9% 4 2 6% 6% 3 6% 5% 7% 9% 42%	2337
	11th to 20th	Day	10% 5% 2 6% 6% 3 5% 5% 6% 7% 43%	2303
	21st to end	Day	12% 4 2 5% 4 3 5% 5% 7% 9% 45%	2392
September	1st to 10th	Day	12% 6% 2 7% 5% 3 5% 5% 5% 9% 40%	2130
	11th to 20th	Day	12% 4 2 5% 4 3 5% 5% 6% 9% 46%	1980
	21st to end	Day	13% 6% 3 6% 5% 3 6% 5% 5% 9% 39%	1980
October	1st to 10th	Day	17% 7% 3 6% 5% 4 5% 4 4 5% 41%	1980
	11th to 20th	Day	24% 9% 3 6% 6% 3 5% 5% 7% 6% 26%	1766
	21st to end	Day	25% 12% 3 8% 6% 4 5% 4 3 6% 24%	1782
November	1st to 10th	Day	15% 12% 4 5% 5% 2 4 5% 5% 6% 36%	1672
	11th to 20th	Day	16% 19% 5% 9% 6% 4 5% 5% 4 5% 23%	1710
	21st to end	Day	21% 16% 8% 9% 5% 3 4 3 4 5% 21%	1710
December	1st to 10th	Day	15% 20% 13% 11% 6% 3 4 4 3 4 16%	1596
	11th to 20th	Day	13% 20% 12% 13% 6% 3 5% 4 4 5% 15%	1918
	21st to end	Day	22% 24% 8% 12% 7% 3 3 3 3 5% 10%	2783
January	1st to 10th	Night	17% 15% 8% 14% 9% 4 4 4 4 4 16%	2648
	11th to 20th	Night	17% 18% 9% 11% 10% 3 4 3 3 4 16%	2561
	21st to end	Night	14% 17% 11% 14% 10% 5% 5% 4 4 4 12%	2772
February	1st to 10th	Night	15% 17% 7% 11% 12% 5% 5% 4 4 5% 17%	2271
	11th to 20th	Night	14% 14% 8% 12% 9% 4 4 4 4 5% 22%	2098
	21st to end	Night	18% 14% 6% 10% 6% 3 4 4 4 5% 27%	1776
March	1st to 10th	Night	16% 11% 4 9% 6% 3 3 3 4 6% 33%	2160
	11th to 20th	Night	13% 9% 4 7% 5% 2 4 4 5% 6% 40%	2038
	21st to end	Night	20% 9% 4 7% 4 3 4 4 4 7% 32%	2116
April	1st to 10th	Night	15% 11% 5% 6% 4 3 5% 5% 5% 7% 35%	1800
	11th to 20th	Night	19% 10% 2 5% 5% 3 4 5% 4 6% 37%	1732
	21st to end	Night	18% 8% 3 5% 4 3 4 5% 5% 7% 38%	1620
May	1st to 10th	Night	15% 10% 4 7% 5% 4 5% 3 5% 7% 34%	1620
	11th to 20th	Night	19% 7% 2 4 4 3 3 3 5% 8% 40%	1592
	21st to end	Night	12% 6% 3 5% 6% 3 5% 4 7% 9% 40%	1570
June	1st to 10th	Night	11% 5% 2 3 4 3 4 5% 7% 10% 48%	1440
	11th to 20th	Night	11% 5% 2 4 5% 3 5% 5% 6% 9% 45%	1440
	21st to end	Night	10% 4 2 4 5% 3 6% 5% 5% 10% 45%	1440
July	1st to 10th	Night	7% 4 2 5% 4 2 4 4 7% 9% 52%	1440
	11th to 20th	Night	8% 3 2 5% 5% 3 4 4 5% 8% 53%	1440
	21st to end	Night	6% 4 2 4 6% 3 5% 5% 7% 9% 49%	1575
August	1st to 10th	Night	8% 4 2 3 4 3 4 5% 7% 9% 50%	1601
	11th to 20th	Night	8% 4 2 5% 5% 3 5% 5% 7% 7% 50%	1598
	21st to end	Night	9% 4 2 5% 6% 3 4 4 4 7% 51%	1962
September	1st to 10th	Night	10% 5% 2 4 5% 3 5% 4 5% 8% 48%	1811
	11th to 20th	Night	11% 5% 2 4 4 2 3 4 5% 7% 52%	1980
	21st to end	Night	14% 7% 3 5% 5% 3 4 5% 5% 6% 43%	1980
October	1st to 10th	Night	16% 6% 3 5% 4 3 4 4 4 7% 44%	1980
	11th to 20th	Night	20% 10% 4 8% 5% 3 4 4 3 6% 34%	2189
	21st to end	Night	26% 10% 3 6% 5% 3 4 3 5% 5% 31%	2574
November	1st to 10th	Night	15% 12% 4 6% 5% 3 4 4 5% 6% 37%	2406
	11th to 20th	Night	15% 17% 6% 9% 6% 3 4 5% 4 6% 25%	2470
	21st to end	Night	20% 16% 6% 7% 6% 3 4 5% 4 6% 24%	2470
December	1st to 10th	Night	17% 21% 10% 10% 7% 3 4 4 4 5% 14%	2581
	11th to 20th	Night	15% 20% 10% 13% 7% 3 4 4 4 4 17%	3279
	21st to end	Night	26% 21% 8% 10% 6% 3 4 4 4 5% 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	72% 5% 9% 11% 3	1518
	11th to 20th	Day	74% 5% 12% 6% 2	1461
	21st to end	Day	77% 4 7% 9% 3	1584
February	1st to 10th	Day	74% 4 8% 11% 3	1684
	11th to 20th	Day	68% 4 8% 12% 7%	1758
	21st to end	Day	67% 4 10% 12% 6% 1	1480
March	1st to 10th	Day	57% 5% 12% 18% 8% 1	1800
	11th to 20th	Day	51% 5% 10% 20% 12% 2	1921
	21st to end	Day	59% 3 10% 20% 7% 1	2256
April	1st to 10th	Day	56% 5% 9% 19% 11%	2160
	11th to 20th	Day	47% 5% 9% 21% 14% 3	2176
	21st to end	Day	50% 5% 12% 16% 15% 2	2340
May	1st to 10th	Day	48% 5% 12% 22% 11% 1	2340
	11th to 20th	Day	47% 5% 11% 21% 14% 2	2305
	21st to end	Day	40% 6% 14% 25% 14% 1	2702
June	1st to 10th	Day	37% 6% 11% 27% 17% 2	2520
	11th to 20th	Day	36% 5% 13% 24% 20% 2	2520
	21st to end	Day	40% 6% 13% 22% 16% 3	2520
July	1st to 10th	Day	30% 6% 12% 28% 19% 5%	2451
	11th to 20th	Day	34% 6% 11% 28% 17% 3	2445
	21st to end	Day	32% 7% 14% 27% 18% 3	2591
August	1st to 10th	Day	34% 9% 12% 29% 14% 2	2323
	11th to 20th	Day	37% 6% 15% 27% 13% 2	2303
	21st to end	Day	34% 6% 12% 27% 17% 4	2392
September	1st to 10th	Day	40% 6% 13% 24% 15% 3	2130
	11th to 20th	Day	34% 5% 12% 31% 16% 1	1980
	21st to end	Day	42% 6% 11% 24% 17% 1	1980
October	1st to 10th	Day	46% 5% 8% 26% 14% 1	1980
	11th to 20th	Day	56% 6% 10% 20% 8%	1766
	21st to end	Day	63% 4 11% 15% 7% 1	1782
November	1st to 10th	Day	48% 5% 11% 22% 13% 1	1672
	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	71% 5% 9% 12% 3	2648
	11th to 20th	Night	73% 4 10% 8% 4	2561
	21st to end	Night	76% 4 8% 7% 3	2772
February	1st to 10th	Night	72% 4 8% 11% 5%	2271
	11th to 20th	Night	65% 4 7% 16% 7%	2099
	21st to end	Night	60% 3 12% 15% 7% 2	1776
March	1st to 10th	Night	54% 3 13% 21% 8% 1	2160
	11th to 20th	Night	45% 4 12% 22% 14% 3	2038
	21st to end	Night	53% 4 10% 22% 10% 2	2116
April	1st to 10th	Night	48% 5% 12% 22% 13% 1	1800
	11th to 20th	Night	49% 4 8% 19% 17% 3	1732
	21st to end	Night	46% 5% 11% 19% 16% 2	1620
May	1st to 10th	Night	50% 4 12% 21% 11% 2	1620
	11th to 20th	Night	43% 6% 11% 21% 16% 3	1593
	21st to end	Night	39% 7% 14% 25% 13% 2	1571
June	1st to 10th	Night	32% 5% 12% 30% 18% 3	1440
	11th to 20th	Night	34% 8% 13% 23% 20% 2	1440
	21st to end	Night	34% 6% 16% 25% 16% 3	1440
July	1st to 10th	Night	28% 5% 15% 27% 20% 5%	1400
	11th to 20th	Night	29% 6% 13% 29% 21% 2	1392
	21st to end	Night	30% 7% 14% 24% 21% 4	1487
August	1st to 10th	Night	29% 6% 15% 30% 18% 2	1591
	11th to 20th	Night	32% 6% 15% 29% 17% 2	1598
	21st to end	Night	33% 7% 9% 26% 22% 4	1962
September	1st to 10th	Night	34% 6% 12% 27% 18% 3	1811
	11th to 20th	Night	33% 5% 8% 33% 20% 1	1980
	21st to end	Night	41% 5% 12% 25% 16% 1	1980
October	1st to 10th	Night	41% 5% 9% 27% 17% 1	1980
	11th to 20th	Night	52% 4 10% 21% 12% 1	2189
	21st to end	Night	56% 4 11% 19% 10% 1	2574
November	1st to 10th	Night	48% 5% 9% 23% 13% 1	2406
	11th to 20th	Night	61% 4 12% 16% 7% 1	2470
	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% 16% 38% 15% 3 1	248
	21st to end	Day	26% 20% 33% 17% 4	264
February	1st to 10th	Day	28% 21% 33% 15% 3	240
	11th to 20th	Day	29% 24% 35% 10% 3	240
	21st to end	Day	29% 32% 28% 10% 1 1	198
March	1st to 10th	Day	23% 29% 32% 13% 3	240
	11th to 20th	Day	24% 17% 29% 23% 6% 1	361
	21st to end	Day	32% 16% 27% 19% 4 1	462
April	1st to 10th	Day	29% 14% 33% 19% 6%	420
	11th to 20th	Day	28% 20% 26% 16% 7% 3	412
	21st to end	Day	28% 16% 30% 18% 8% 1	420
May	1st to 10th	Day	26% 16% 28% 20% 7% 2	423
	11th to 20th	Day	22% 11% 30% 22% 11% 4	447
	21st to end	Day	15% 10% 30% 27% 13% 5%	656
June	1st to 10th	Day	14% 9% 36% 26% 11% 4	630
	11th to 20th	Day	15% 11% 29% 29% 13% 3	630
	21st to end	Day	14% 9% 35% 26% 13% 4	630
July	1st to 10th	Day	8% 5% 28% 31% 18% 11%	621
	11th to 20th	Day	13% 6% 31% 27% 17% 6%	618
	21st to end	Day	9% 6% 30% 29% 19% 7%	684
August	1st to 10th	Day	11% 3 20% 28% 23% 14%	456
	11th to 20th	Day	11% 4 23% 29% 23% 9%	439
	21st to end	Day	14% 5% 21% 29% 24% 7%	495
September	1st to 10th	Day	16% 7% 21% 28% 21% 8%	450
	11th to 20th	Day	10% 4 22% 30% 25% 9%	450
	21st to end	Day	18% 12% 20% 26% 15% 8%	450
October	1st to 10th	Day	20% 10% 26% 25% 16% 4	450
	11th to 20th	Day	29% 18% 27% 22% 4	365
	21st to end	Day	35% 18% 32% 12% 3 1	297
November	1st to 10th	Day	24% 17% 33% 19% 6% 1	270
	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% 13% 33% 21% 5% 1	915
	21st to end	Night	22% 12% 32% 30% 4	990
February	1st to 10th	Night	24% 15% 35% 23% 4	729
	11th to 20th	Night	22% 17% 32% 25% 4	703
	21st to end	Night	25% 17% 36% 18% 4	592
March	1st to 10th	Night	22% 15% 30% 25% 8% 1	720
	11th to 20th	Night	18% 13% 36% 26% 6% 1	720
	21st to end	Night	24% 12% 31% 26% 8%	730
April	1st to 10th	Night	18% 14% 33% 29% 6% 1	540
	11th to 20th	Night	25% 9% 34% 24% 6% 1	533
	21st to end	Night	23% 9% 32% 28% 7% 1	540
May	1st to 10th	Night	20% 8% 35% 28% 8% 1	540
	11th to 20th	Night	22% 7% 26% 35% 10%	531
	21st to end	Night	15% 5% 28% 33% 18% 1	584
June	1st to 10th	Night	12% 5% 28% 40% 15% 1	540
	11th to 20th	Night	14% 4 24% 41% 16%	540
	21st to end	Night	12% 2 23% 39% 22% 2	540
July	1st to 10th	Night	10% 2 18% 40% 27% 3	525
	11th to 20th	Night	10% 2 17% 45% 22% 4	522
	21st to end	Night	8% 3 17% 45% 26% 1	591
August	1st to 10th	Night	11% 1 12% 45% 27% 4	537
	11th to 20th	Night	10% 1 13% 42% 30% 4	534
	21st to end	Night	11% 3 17% 36% 30% 3	594
September	1st to 10th	Night	13% 4 15% 39% 26% 4	551
	11th to 20th	Night	12% 5% 17% 37% 26% 4	720
	21st to end	Night	17% 7% 23% 29% 19% 4	720
October	1st to 10th	Night	20% 6% 21% 33% 19% 2	720
	11th to 20th	Night	25% 13% 27% 27% 8% 1	720
	21st to end	Night	32% 12% 29% 21% 6%	792
November	1st to 10th	Night	21% 14% 29% 25% 10% 1	740
	11th to 20th	Night	24% 15% 33% 22% 5% 1	760
	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 2024-01-10 19:35:26. Version ac07

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