Green Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Green Ridge Observatory clear sky chart from 2005-11-06 to 2024-01-27.

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% 9% 4 7% 6% 4 5% 5% 6% 8% 34%	75059
	Night	15% 9% 4 7% 6% 3 5% 5% 5% 7% 35%	74938
Transparency	Day	48% 7% 13% 20% 11% 1	74772
	Night	49% 6% 12% 21% 12% 1	74745
Seeing	Day	17% 9% 28% 26% 14% 5%	13978
	Night	19% 9% 28% 30% 13% 2	23432

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% 14% 5% 10% 8% 4 6% 4 5% 5% 22%	1548
	11th to 20th	Day	17% 16% 7% 11% 10% 4 5% 4 4 5% 17%	1710
	21st to end	Day	17% 15% 7% 10% 8% 3 5% 5% 6% 5% 18%	1836
February	1st to 10th	Day	16% 14% 6% 10% 8% 4 5% 4 4 6% 21%	1620
	11th to 20th	Day	15% 10% 6% 10% 8% 5% 6% 6% 4 6% 24%	1616
	21st to end	Day	18% 11% 4 10% 9% 4 5% 4 5% 6% 25%	1480
March	1st to 10th	Day	17% 9% 5% 8% 7% 4 5% 5% 6% 6% 28%	1907
	11th to 20th	Day	14% 11% 5% 8% 7% 4 5% 4 4 7% 31%	1980
	21st to end	Day	19% 10% 4 10% 7% 4 4 4 5% 6% 28%	2178
April	1st to 10th	Day	15% 11% 4 7% 5% 4 5% 5% 6% 9% 31%	2026
	11th to 20th	Day	18% 8% 3 6% 5% 4 5% 5% 5% 7% 33%	2312
	21st to end	Day	19% 9% 4 7% 6% 3 4 5% 4 7% 33%	2340
May	1st to 10th	Day	16% 9% 3 7% 6% 4 5% 5% 6% 8% 33%	2340
	11th to 20th	Day	15% 8% 4 6% 6% 3 5% 5% 6% 7% 36%	2301
	21st to end	Day	10% 5% 3 6% 5% 3 5% 5% 6% 10% 43%	2629
June	1st to 10th	Day	10% 7% 2 6% 6% 4 5% 6% 7% 8% 41%	2520
	11th to 20th	Day	9% 5% 2 6% 6% 3 6% 5% 7% 10% 41%	2692
	21st to end	Day	9% 5% 2 4 5% 3 5% 5% 7% 10% 43%	2700
July	1st to 10th	Day	8% 5% 2 5% 4 3 5% 5% 7% 9% 47%	2595
	11th to 20th	Day	10% 5% 2 5% 5% 3 5% 6% 7% 10% 42%	2404
	21st to end	Day	7% 4 3 5% 6% 4 6% 7% 8% 11% 40%	2547
August	1st to 10th	Day	7% 4 3 5% 5% 3 5% 6% 8% 11% 42%	2327
	11th to 20th	Day	8% 5% 3 6% 6% 4 6% 6% 9% 10% 39%	2303
	21st to end	Day	10% 6% 2 5% 6% 3 6% 5% 6% 8% 44%	2562
September	1st to 10th	Day	10% 6% 3 5% 5% 4 6% 5% 6% 8% 42%	2062
	11th to 20th	Day	10% 5% 2 4 5% 3 5% 4 7% 11% 45%	1980
	21st to end	Day	16% 6% 2 5% 5% 3 5% 5% 6% 7% 40%	1980
October	1st to 10th	Day	14% 6% 3 6% 5% 3 5% 4 6% 8% 41%	1867
	11th to 20th	Day	16% 9% 3 7% 6% 5% 6% 6% 6% 7% 32%	1800
	21st to end	Day	21% 10% 3 7% 6% 3 5% 5% 5% 7% 28%	1926
November	1st to 10th	Day	13% 7% 4 6% 7% 3 5% 5% 6% 9% 34%	1672
	11th to 20th	Day	15% 10% 3 8% 6% 3 5% 5% 5% 8% 32%	1639
	21st to end	Day	19% 11% 5% 9% 7% 4 5% 4 6% 7% 23%	1520
December	1st to 10th	Day	17% 13% 6% 9% 8% 3 4 6% 5% 8% 21%	1520
	11th to 20th	Day	19% 13% 7% 8% 7% 3 5% 6% 5% 6% 21%	1910
	21st to end	Day	28% 18% 7% 9% 7% 4 4 4 4 5% 11%	2710
January	1st to 10th	Night	18% 12% 5% 8% 7% 5% 5% 5% 5% 6% 24%	2605
	11th to 20th	Night	19% 17% 6% 9% 7% 4 5% 4 4 5% 20%	2470
	21st to end	Night	15% 14% 7% 10% 8% 5% 5% 4 5% 5% 21%	2664
February	1st to 10th	Night	18% 14% 6% 10% 7% 3 5% 5% 5% 6% 23%	2340
	11th to 20th	Night	17% 11% 6% 8% 6% 4 5% 5% 5% 6% 26%	2228
	21st to end	Night	20% 10% 4 7% 7% 3 6% 4 5% 6% 28%	1776
March	1st to 10th	Night	16% 9% 4 7% 7% 4 5% 5% 5% 7% 33%	2052
	11th to 20th	Night	15% 8% 4 6% 5% 3 5% 4 6% 7% 38%	1980
	21st to end	Night	18% 10% 4 6% 6% 2 4 5% 5% 6% 33%	2178
April	1st to 10th	Night	15% 10% 4 6% 6% 3 4 5% 5% 6% 36%	1944
	11th to 20th	Night	17% 7% 3 7% 5% 3 4 4 5% 8% 37%	1600
	21st to end	Night	16% 8% 3 6% 5% 3 5% 4 5% 7% 37%	1620
May	1st to 10th	Night	16% 8% 3 6% 6% 4 5% 6% 7% 8% 32%	1620
	11th to 20th	Night	14% 6% 3 7% 5% 4 5% 5% 5% 7% 38%	1592
	21st to end	Night	10% 5% 2 4 5% 3 5% 5% 6% 8% 48%	1642
June	1st to 10th	Night	10% 5% 2 4 5% 3 4 4 6% 9% 47%	1440
	11th to 20th	Night	10% 4 2 4 5% 4 5% 5% 7% 11% 44%	1262
	21st to end	Night	10% 5% 2 5% 4 3 5% 5% 5% 8% 49%	1260
July	1st to 10th	Night	6% 3 2 5% 5% 3 4 5% 4 8% 55%	1359
	11th to 20th	Night	8% 3 2 4 5% 3 4 4 6% 10% 50%	1552
	21st to end	Night	6% 4 2 4 4 3 5% 7% 7% 10% 48%	1771
August	1st to 10th	Night	6% 4 2 4 4 4 4 6% 7% 9% 50%	1611
	11th to 20th	Night	6% 4 2 5% 6% 3 5% 6% 6% 9% 49%	1598
	21st to end	Night	9% 5% 2 4 5% 3 4 5% 7% 8% 49%	1782
September	1st to 10th	Night	9% 5% 3 6% 5% 4 4 5% 5% 8% 45%	1887
	11th to 20th	Night	9% 4 2 5% 4 3 4 4 4 6% 55%	1980
	21st to end	Night	15% 6% 2 6% 5% 2 4 5% 5% 6% 43%	1980
October	1st to 10th	Night	13% 6% 2 5% 5% 3 4 4 5% 7% 46%	2092
	11th to 20th	Night	17% 7% 3 6% 5% 4 4 5% 5% 7% 37%	2160
	21st to end	Night	22% 9% 3 6% 6% 3 4 4 5% 6% 31%	2425
November	1st to 10th	Night	14% 7% 3 6% 5% 3 4 4 6% 7% 42%	2406
	11th to 20th	Night	16% 9% 3 6% 6% 4 5% 5% 5% 8% 33%	2538
	21st to end	Night	21% 10% 4 7% 6% 3 4 4 5% 6% 30%	2660
December	1st to 10th	Night	18% 14% 5% 9% 7% 3 5% 4 5% 6% 23%	2660
	11th to 20th	Night	16% 14% 5% 8% 6% 4 5% 5% 5% 6% 26%	3285
	21st to end	Night	26% 17% 7% 10% 7% 4 5% 4 4 4 13%	4919

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	64% 6% 11% 13% 6%	1549
	11th to 20th	Day	70% 7% 11% 9% 4	1710
	21st to end	Day	66% 6% 10% 12% 6%	1836
February	1st to 10th	Day	64% 7% 10% 13% 6%	1620
	11th to 20th	Day	60% 6% 10% 15% 8% 1	1625
	21st to end	Day	59% 7% 11% 16% 6% 1	1480
March	1st to 10th	Day	55% 7% 12% 17% 8% 1	1907
	11th to 20th	Day	53% 5% 11% 18% 12% 1	1980
	21st to end	Day	57% 5% 9% 18% 9% 2	2178
April	1st to 10th	Day	50% 7% 13% 18% 11% 1	2026
	11th to 20th	Day	49% 6% 11% 19% 14% 1	2312
	21st to end	Day	52% 5% 12% 18% 11% 2	2340
May	1st to 10th	Day	48% 7% 11% 22% 11% 2	2340
	11th to 20th	Day	46% 6% 14% 18% 13% 2	2305
	21st to end	Day	36% 8% 16% 23% 15% 2	2629
June	1st to 10th	Day	39% 7% 13% 26% 13% 2	2520
	11th to 20th	Day	37% 8% 15% 22% 16% 2	2692
	21st to end	Day	34% 9% 14% 26% 16% 2	2700
July	1st to 10th	Day	32% 8% 10% 27% 19% 3	2526
	11th to 20th	Day	33% 9% 13% 27% 16% 2	2331
	21st to end	Day	34% 9% 17% 22% 15% 2	2405
August	1st to 10th	Day	33% 9% 17% 29% 13% 1	2314
	11th to 20th	Day	36% 10% 15% 26% 11% 2	2303
	21st to end	Day	36% 8% 13% 24% 16% 2	2562
September	1st to 10th	Day	38% 9% 15% 23% 13% 2	2062
	11th to 20th	Day	33% 6% 15% 31% 14%	1980
	21st to end	Day	42% 7% 14% 25% 12% 1	1980
October	1st to 10th	Day	41% 6% 14% 24% 14% 1	1867
	11th to 20th	Day	49% 7% 15% 20% 9% 1	1800
	21st to end	Day	55% 7% 14% 16% 8%	1926
November	1st to 10th	Day	47% 6% 13% 22% 10% 2	1672
	11th to 20th	Day	50% 6% 17% 16% 10% 1	1639
	21st to end	Day	59% 7% 14% 16% 4	1520
December	1st to 10th	Day	60% 9% 13% 14% 4	1520
	11th to 20th	Day	62% 8% 13% 11% 5%	1906
	21st to end	Day	76% 7% 8% 7% 2	2710
January	1st to 10th	Night	59% 8% 10% 16% 7%	2605
	11th to 20th	Night	67% 6% 12% 11% 4	2470
	21st to end	Night	64% 5% 11% 14% 5%	2664
February	1st to 10th	Night	62% 6% 11% 15% 5% 1	2340
	11th to 20th	Night	57% 6% 10% 17% 10% 1	2230
	21st to end	Night	57% 5% 10% 19% 8% 1	1776
March	1st to 10th	Night	51% 6% 11% 22% 9% 1	2052
	11th to 20th	Night	45% 6% 11% 23% 13% 2	1980
	21st to end	Night	51% 6% 8% 22% 12% 1	2178
April	1st to 10th	Night	49% 5% 11% 20% 14% 2	1944
	11th to 20th	Night	46% 5% 10% 21% 17% 2	1600
	21st to end	Night	46% 5% 10% 20% 15% 3	1620
May	1st to 10th	Night	47% 7% 11% 19% 12% 5%	1620
	11th to 20th	Night	45% 4 12% 19% 17% 3	1593
	21st to end	Night	33% 7% 14% 25% 19% 2	1643
June	1st to 10th	Night	34% 6% 12% 29% 17% 3	1440
	11th to 20th	Night	34% 7% 13% 25% 20% 2	1262
	21st to end	Night	33% 6% 13% 27% 20% 1	1260
July	1st to 10th	Night	29% 6% 9% 29% 23% 5%	1319
	11th to 20th	Night	30% 6% 12% 30% 19% 2	1502
	21st to end	Night	29% 9% 16% 24% 19% 3	1672
August	1st to 10th	Night	28% 9% 15% 32% 15% 2	1600
	11th to 20th	Night	30% 8% 15% 31% 14% 2	1598
	21st to end	Night	30% 6% 13% 30% 18% 2	1782
September	1st to 10th	Night	36% 6% 14% 26% 15% 3	1887
	11th to 20th	Night	30% 6% 12% 32% 19% 1	1980
	21st to end	Night	41% 6% 12% 27% 14% 1	1980
October	1st to 10th	Night	38% 7% 12% 23% 19% 1	2092
	11th to 20th	Night	46% 5% 13% 21% 14%	2160
	21st to end	Night	54% 5% 11% 19% 10% 1	2425
November	1st to 10th	Night	41% 5% 12% 26% 14% 1	2406
	11th to 20th	Night	50% 6% 14% 21% 9% 1	2538
	21st to end	Night	55% 6% 15% 17% 6% 1	2660
December	1st to 10th	Night	61% 7% 13% 15% 4	2660
	11th to 20th	Night	58% 7% 13% 15% 7%	3288
	21st to end	Night	74% 7% 9% 7% 2	4919

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% 17% 7% 1	270
	11th to 20th	Day	26% 15% 41% 12% 4 1	270
	21st to end	Day	28% 12% 34% 21% 5% 1	282
February	1st to 10th	Day	21% 22% 38% 18% 1	240
	11th to 20th	Day	25% 20% 37% 15% 4	240
	21st to end	Day	25% 23% 39% 12% 1	198
March	1st to 10th	Day	21% 17% 33% 23% 5% 1	347
	11th to 20th	Day	20% 13% 36% 24% 7% 1	420
	21st to end	Day	26% 14% 31% 23% 5% 1	462
April	1st to 10th	Day	16% 12% 40% 23% 9% 1	420
	11th to 20th	Day	26% 12% 29% 20% 8% 4	412
	21st to end	Day	23% 11% 31% 24% 9% 2	420
May	1st to 10th	Day	23% 11% 28% 26% 10% 3	423
	11th to 20th	Day	17% 8% 28% 28% 16% 3	447
	21st to end	Day	12% 5% 24% 31% 23% 6%	485
June	1st to 10th	Day	12% 6% 27% 36% 15% 3	450
	11th to 20th	Day	12% 6% 29% 34% 17% 2	622
	21st to end	Day	12% 5% 28% 36% 16% 3	630
July	1st to 10th	Day	9% 3 21% 33% 25% 9%	621
	11th to 20th	Day	12% 3 22% 31% 21% 10%	504
	21st to end	Day	9% 2 22% 32% 26% 10%	488
August	1st to 10th	Day	9% 4 17% 31% 26% 13%	446
	11th to 20th	Day	12% 5% 14% 33% 22% 14%	439
	21st to end	Day	10% 4 19% 31% 26% 11%	495
September	1st to 10th	Day	13% 3 20% 30% 23% 11%	450
	11th to 20th	Day	8% 4 19% 26% 30% 12%	450
	21st to end	Day	18% 6% 22% 29% 16% 8%	450
October	1st to 10th	Day	18% 7% 26% 25% 18% 6%	450
	11th to 20th	Day	17% 15% 33% 24% 9% 2	450
	21st to end	Day	27% 11% 35% 20% 5% 1	441
November	1st to 10th	Day	14% 19% 33% 23% 8% 3	270
	11th to 20th	Day	22% 18% 31% 19% 8% 2	237
	21st to end	Day	23% 11% 41% 21% 4 1	180
December	1st to 10th	Day	22% 18% 32% 17% 9% 1	180
	11th to 20th	Day	29% 15% 35% 18% 3	180
	21st to end	Day	29% 20% 31% 17% 4	209
January	1st to 10th	Night	25% 14% 35% 18% 6% 1	907
	11th to 20th	Night	29% 13% 33% 23% 3	760
	21st to end	Night	22% 10% 35% 27% 7%	820
February	1st to 10th	Night	25% 11% 37% 24% 3	720
	11th to 20th	Night	23% 14% 32% 25% 6%	703
	21st to end	Night	26% 11% 39% 22% 2	592
March	1st to 10th	Night	20% 11% 34% 29% 6%	720
	11th to 20th	Night	19% 10% 36% 26% 9% 1	720
	21st to end	Night	21% 10% 33% 26% 9% 1	792
April	1st to 10th	Night	21% 10% 33% 30% 5% 1	720
	11th to 20th	Night	19% 9% 33% 28% 10% 1	536
	21st to end	Night	20% 7% 34% 31% 9% 1	540
May	1st to 10th	Night	18% 5% 29% 33% 14% 1	540
	11th to 20th	Night	14% 5% 26% 38% 15% 2	531
	21st to end	Night	11% 3 22% 40% 23% 1	482
June	1st to 10th	Night	11% 5% 27% 42% 15%	360
	11th to 20th	Night	11% 4 21% 47% 16% 1	360
	21st to end	Night	11% 3 23% 43% 19% 1	360
July	1st to 10th	Night	7% 2 14% 42% 33% 3	444
	11th to 20th	Night	11% 3 16% 39% 29% 3	522
	21st to end	Night	9% 3 14% 45% 27% 2	591
August	1st to 10th	Night	8% 1 12% 41% 33% 5%	537
	11th to 20th	Night	7% 3 12% 37% 35% 6%	534
	21st to end	Night	11% 2 16% 37% 29% 5%	594
September	1st to 10th	Night	12% 4 17% 35% 27% 6%	712
	11th to 20th	Night	10% 4 16% 35% 29% 6%	720
	21st to end	Night	18% 4 21% 31% 20% 7%	720
October	1st to 10th	Night	15% 5% 25% 33% 19% 3	720
	11th to 20th	Night	20% 11% 29% 27% 12% 2	720
	21st to end	Night	26% 10% 30% 28% 5% 1	792
November	1st to 10th	Night	16% 12% 28% 28% 13% 2	740
	11th to 20th	Night	21% 14% 34% 22% 7% 1	760
	21st to end	Night	27% 13% 30% 23% 7%	760
December	1st to 10th	Night	25% 15% 33% 20% 6% 1	760
	11th to 20th	Night	22% 16% 36% 23% 4	760
	21st to end	Night	29% 14% 32% 23% 2	883

Page generated at 2024-01-24 09:37:30. Version ac07

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