Orchard Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Orchard Hill 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	17% 10% 3 8% 5% 5% 5% 4 5% 7% 31%	101496
	Night	18% 12% 4 9% 5% 5% 4 3 5% 6% 29%	97589
Transparency	Day	52% 8% 12% 19% 8% 1	104983
	Night	57% 7% 11% 17% 8% 1	102191
Seeing	Day	25% 17% 29% 20% 8% 2	14663
	Night	25% 14% 27% 24% 9% 1	23603

By Month

Percentage Cloud Cover NE (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	17% 17% 5% 13% 6% 5% 5% 4 4 5% 19%	2517
	11th to 20th	Day	15% 17% 7% 16% 7% 5% 4 3 5% 4 17%	2520
	21st to end	Day	16% 16% 5% 11% 6% 7% 6% 4 5% 6% 17%	2772
February	1st to 10th	Day	16% 15% 5% 13% 8% 5% 4 4 4 5% 20%	1667
	11th to 20th	Day	13% 18% 5% 12% 6% 5% 4 4 4 6% 24%	1796
	21st to end	Day	16% 16% 4 8% 7% 5% 4 3 6% 5% 23%	1570
March	1st to 10th	Day	20% 14% 4 9% 5% 4 5% 3 5% 6% 25%	3116
	11th to 20th	Day	15% 18% 4 11% 6% 5% 5% 3 4 6% 23%	3269
	21st to end	Day	17% 11% 4 8% 4 4 4 3 4 5% 37%	4166
April	1st to 10th	Day	22% 13% 3 7% 5% 5% 4 3 4 5% 29%	2280
	11th to 20th	Day	21% 9% 3 7% 4 4 4 3 5% 5% 35%	2254
	21st to end	Day	22% 9% 3 7% 5% 4 5% 3 4 6% 32%	2440
May	1st to 10th	Day	22% 9% 3 7% 5% 4 5% 4 6% 7% 29%	4284
	11th to 20th	Day	16% 8% 3 8% 6% 5% 5% 3 5% 7% 32%	4398
	21st to end	Day	14% 7% 2 6% 6% 5% 5% 4 7% 9% 34%	4837
June	1st to 10th	Day	22% 8% 3 7% 5% 4 5% 4 6% 7% 30%	2660
	11th to 20th	Day	15% 7% 2 6% 4 6% 5% 4 6% 8% 36%	2660
	21st to end	Day	21% 8% 3 7% 6% 4 5% 4 6% 6% 31%	2660
July	1st to 10th	Day	12% 5% 2 7% 6% 5% 6% 5% 7% 9% 36%	4440
	11th to 20th	Day	12% 6% 3 7% 5% 5% 6% 5% 8% 9% 36%	4440
	21st to end	Day	13% 6% 2 6% 4 5% 4 4 6% 9% 41%	4814
August	1st to 10th	Day	15% 7% 3 8% 5% 5% 6% 5% 7% 8% 32%	4423
	11th to 20th	Day	14% 6% 2 8% 5% 4 5% 5% 6% 8% 38%	3937
	21st to end	Day	15% 5% 2 6% 4 4 5% 3 6% 9% 41%	4180
September	1st to 10th	Day	14% 6% 2 5% 4 4 4 4 6% 7% 44%	2280
	11th to 20th	Day	16% 5% 1 5% 4 4 4 3 4 7% 47%	2180
	21st to end	Day	15% 6% 2 6% 5% 5% 4 4 5% 8% 40%	2090
October	1st to 10th	Day	21% 7% 3 7% 6% 5% 5% 4 5% 7% 31%	1995
	11th to 20th	Day	18% 9% 4 7% 5% 5% 6% 5% 5% 6% 31%	1848
	21st to end	Day	24% 12% 3 8% 5% 5% 4 3 4 5% 28%	1881
November	1st to 10th	Day	18% 11% 2 8% 6% 4 4 4 6% 5% 32%	1717
	11th to 20th	Day	19% 12% 4 10% 5% 5% 5% 4 5% 5% 27%	1687
	21st to end	Day	21% 14% 4 8% 6% 5% 5% 5% 5% 5% 21%	1520
December	1st to 10th	Day	23% 17% 5% 11% 6% 5% 4 3 4 5% 18%	1520
	11th to 20th	Day	22% 15% 5% 9% 5% 5% 4 4 4 6% 22%	1906
	21st to end	Day	26% 16% 5% 12% 7% 4 3 3 4 4 16%	2772
January	1st to 10th	Night	17% 19% 7% 13% 5% 4 3 3 4 5% 19%	4429
	11th to 20th	Night	13% 17% 6% 14% 8% 5% 6% 4 5% 4 17%	4440
	21st to end	Night	19% 18% 5% 11% 7% 4 4 3 3 4 22%	4884
February	1st to 10th	Night	16% 16% 7% 13% 7% 6% 4 3 5% 4 18%	2512
	11th to 20th	Night	14% 13% 5% 10% 8% 6% 5% 4 5% 5% 24%	2270
	21st to end	Night	16% 15% 4 10% 6% 4 4 3 4 5% 29%	1884
March	1st to 10th	Night	21% 12% 5% 8% 5% 5% 4 3 5% 5% 29%	3724
	11th to 20th	Night	19% 18% 5% 8% 6% 4 4 3 3 4 26%	3686
	21st to end	Night	14% 11% 4 11% 6% 4 4 3 4 5% 34%	3466
April	1st to 10th	Night	22% 12% 3 8% 5% 4 5% 3 5% 5% 28%	1900
	11th to 20th	Night	24% 11% 3 7% 5% 4 4 3 3 5% 31%	1875
	21st to end	Night	20% 10% 4 8% 4 4 4 3 4 5% 34%	1739
May	1st to 10th	Night	21% 11% 4 8% 5% 3 5% 4 6% 6% 27%	2686
	11th to 20th	Night	20% 10% 4 7% 4 4 3 3 4 6% 34%	2495
	21st to end	Night	14% 7% 3 7% 5% 6% 4 4 6% 9% 37%	2738
June	1st to 10th	Night	23% 8% 3 5% 5% 4 4 4 6% 7% 30%	1520
	11th to 20th	Night	18% 6% 2 7% 5% 4 4 4 7% 7% 36%	1520
	21st to end	Night	19% 7% 3 7% 4 6% 5% 4 6% 7% 33%	1520
July	1st to 10th	Night	13% 7% 3 7% 6% 6% 5% 5% 6% 8% 35%	2520
	11th to 20th	Night	12% 6% 2 6% 5% 4 5% 4 6% 8% 41%	2520
	21st to end	Night	13% 7% 3 7% 6% 5% 4 5% 6% 7% 38%	2739
August	1st to 10th	Night	17% 8% 3 8% 5% 4 4 4 5% 7% 35%	2506
	11th to 20th	Night	14% 7% 3 8% 5% 5% 5% 4 5% 6% 37%	2855
	21st to end	Night	16% 6% 2 6% 4 4 4 4 6% 7% 42%	3476
September	1st to 10th	Night	14% 4 2 6% 6% 3 4 3 5% 8% 44%	1900
	11th to 20th	Night	14% 5% 2 5% 4 3 3 3 5% 6% 48%	2000
	21st to end	Night	18% 5% 1 6% 4 4 4 4 4 6% 43%	2090
October	1st to 10th	Night	19% 7% 3 8% 5% 4 5% 3 5% 6% 35%	2183
	11th to 20th	Night	20% 9% 3 7% 5% 5% 4 4 5% 5% 32%	2330
	21st to end	Night	24% 10% 3 7% 5% 5% 4 4 5% 5% 27%	2717
November	1st to 10th	Night	20% 10% 3 7% 5% 5% 4 4 5% 6% 30%	2483
	11th to 20th	Night	19% 11% 4 9% 6% 5% 4 3 5% 6% 31%	2490
	21st to end	Night	23% 13% 4 9% 5% 5% 5% 4 5% 5% 23%	2660
December	1st to 10th	Night	21% 19% 6% 11% 6% 5% 5% 3 4 4 16%	2660
	11th to 20th	Night	24% 16% 5% 10% 6% 5% 5% 3 4 4 20%	3288
	21st to end	Night	27% 16% 5% 11% 5% 4 3 2 3 4 19%	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	68% 9% 12% 10% 1	2518
	11th to 20th	Day	69% 9% 9% 8% 3	2520
	21st to end	Day	69% 10% 11% 7% 3	2772
February	1st to 10th	Day	68% 6% 7% 14% 4 1	1667
	11th to 20th	Day	65% 7% 9% 13% 5%	1805
	21st to end	Day	64% 6% 9% 13% 7% 2	1570
March	1st to 10th	Day	62% 8% 10% 14% 5% 1	3119
	11th to 20th	Day	63% 8% 10% 10% 8% 1	3269
	21st to end	Day	53% 6% 7% 18% 15% 2	4166
April	1st to 10th	Day	58% 5% 8% 19% 8% 2	2280
	11th to 20th	Day	53% 6% 7% 19% 13% 2	2254
	21st to end	Day	56% 5% 10% 17% 10% 3	2440
May	1st to 10th	Day	54% 10% 10% 18% 8% 1	4298
	11th to 20th	Day	49% 11% 14% 17% 8% 1	4402
	21st to end	Day	41% 10% 14% 24% 10% 1	4837
June	1st to 10th	Day	53% 7% 13% 17% 10% 1	2660
	11th to 20th	Day	44% 10% 11% 22% 12% 2	2660
	21st to end	Day	52% 8% 12% 20% 8% 1	2660
July	1st to 10th	Day	40% 8% 15% 26% 10%	4370
	11th to 20th	Day	41% 9% 15% 29% 6%	4365
	21st to end	Day	43% 8% 12% 28% 8%	4661
August	1st to 10th	Day	49% 8% 15% 21% 7%	4409
	11th to 20th	Day	46% 8% 18% 23% 5%	3977
	21st to end	Day	40% 7% 17% 21% 14% 1	4180
September	1st to 10th	Day	39% 8% 12% 29% 12% 1	2280
	11th to 20th	Day	38% 6% 11% 31% 13% 1	2180
	21st to end	Day	43% 8% 16% 23% 9% 1	2090
October	1st to 10th	Day	46% 6% 12% 27% 8%	3320
	11th to 20th	Day	49% 6% 14% 21% 9%	3051
	21st to end	Day	50% 6% 14% 24% 5% 1	3081
November	1st to 10th	Day	57% 7% 12% 17% 7%	1717
	11th to 20th	Day	62% 7% 11% 12% 7% 1	1687
	21st to end	Day	65% 8% 13% 11% 3	1520
December	1st to 10th	Day	73% 6% 10% 9% 3	1520
	11th to 20th	Day	65% 8% 10% 12% 4	1906
	21st to end	Day	71% 10% 10% 7% 2	2772
January	1st to 10th	Night	71% 8% 12% 8% 1	4429
	11th to 20th	Night	69% 10% 11% 8% 3	4440
	21st to end	Night	71% 6% 11% 9% 4 1	4884
February	1st to 10th	Night	69% 7% 9% 10% 5%	2512
	11th to 20th	Night	66% 7% 8% 13% 6%	2272
	21st to end	Night	62% 5% 10% 14% 8% 1	1884
March	1st to 10th	Night	58% 8% 10% 15% 8% 1	3734
	11th to 20th	Night	61% 7% 8% 15% 8% 1	3687
	21st to end	Night	56% 6% 7% 17% 12% 1	3466
April	1st to 10th	Night	59% 4 10% 16% 9% 1	1900
	11th to 20th	Night	57% 5% 9% 16% 12% 1	1875
	21st to end	Night	54% 7% 8% 15% 13% 3	1739
May	1st to 10th	Night	56% 9% 8% 17% 9% 2	2692
	11th to 20th	Night	51% 8% 11% 20% 9% 1	2496
	21st to end	Night	42% 10% 13% 19% 15% 1	2739
June	1st to 10th	Night	52% 7% 11% 19% 9% 1	1520
	11th to 20th	Night	45% 7% 14% 21% 11% 2	1520
	21st to end	Night	50% 9% 13% 18% 10%	1520
July	1st to 10th	Night	46% 7% 14% 21% 12% 1	2480
	11th to 20th	Night	43% 8% 13% 27% 8%	2472
	21st to end	Night	46% 8% 12% 22% 11%	2651
August	1st to 10th	Night	50% 7% 13% 22% 7%	2496
	11th to 20th	Night	48% 7% 16% 20% 8%	2881
	21st to end	Night	41% 7% 14% 23% 14% 1	3476
September	1st to 10th	Night	40% 8% 13% 27% 11% 1	1900
	11th to 20th	Night	37% 6% 15% 30% 11% 1	2000
	21st to end	Night	41% 8% 12% 24% 13% 1	2090
October	1st to 10th	Night	54% 5% 10% 23% 7%	3638
	11th to 20th	Night	52% 5% 11% 22% 11%	3866
	21st to end	Night	52% 6% 13% 20% 9%	4467
November	1st to 10th	Night	56% 6% 12% 17% 8% 1	2483
	11th to 20th	Night	58% 7% 11% 15% 7% 2	2490
	21st to end	Night	65% 7% 11% 13% 3	2660
December	1st to 10th	Night	75% 6% 9% 8% 1	2660
	11th to 20th	Night	71% 7% 9% 10% 3	3288
	21st to end	Night	73% 6% 8% 10% 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	29% 22% 26% 17% 6% 1	180
	11th to 20th	Day	31% 27% 29% 9% 3 1	180
	21st to end	Day	25% 20% 35% 16% 5%	198
February	1st to 10th	Day	32% 30% 28% 8% 2	249
	11th to 20th	Day	26% 29% 33% 10% 2	404
	21st to end	Day	29% 22% 33% 15% 2	382
March	1st to 10th	Day	33% 18% 28% 19% 2	460
	11th to 20th	Day	26% 26% 28% 16% 3 1	460
	21st to end	Day	34% 21% 24% 14% 6% 1	506
April	1st to 10th	Day	32% 19% 25% 19% 4 1	460
	11th to 20th	Day	31% 22% 23% 15% 7% 2	452
	21st to end	Day	32% 19% 29% 15% 5% 2	460
May	1st to 10th	Day	29% 18% 27% 18% 7% 2	463
	11th to 20th	Day	22% 16% 32% 21% 9% 1	487
	21st to end	Day	19% 17% 32% 24% 9% 1	529
June	1st to 10th	Day	27% 13% 33% 20% 6% 1	490
	11th to 20th	Day	19% 17% 29% 23% 10% 2	490
	21st to end	Day	25% 13% 33% 19% 9% 1	490
July	1st to 10th	Day	16% 9% 33% 29% 12% 2	485
	11th to 20th	Day	16% 9% 35% 27% 12% 2	484
	21st to end	Day	18% 7% 34% 32% 9% 1	532
August	1st to 10th	Day	15% 11% 30% 30% 12% 2	486
	11th to 20th	Day	16% 9% 27% 30% 14% 4	479
	21st to end	Day	16% 12% 31% 25% 12% 6%	539
September	1st to 10th	Day	17% 13% 30% 21% 13% 6%	490
	11th to 20th	Day	17% 13% 20% 24% 19% 8%	490
	21st to end	Day	14% 13% 30% 24% 13% 5%	490
October	1st to 10th	Day	25% 15% 26% 16% 15% 3	490
	11th to 20th	Day	29% 19% 23% 20% 8% 2	463
	21st to end	Day	38% 15% 27% 17% 4	429
November	1st to 10th	Day	31% 20% 29% 14% 6% 1	381
	11th to 20th	Day	29% 29% 23% 13% 6% 1	347
	21st to end	Day	35% 22% 26% 16% 2	180
December	1st to 10th	Day	28% 24% 29% 16% 2	180
	11th to 20th	Day	27% 28% 34% 10% 1	180
	21st to end	Day	30% 28% 28% 12% 2 1	198
January	1st to 10th	Night	29% 22% 30% 16% 3	760
	11th to 20th	Night	29% 21% 28% 18% 4	760
	21st to end	Night	23% 16% 32% 25% 4 1	836
February	1st to 10th	Night	24% 18% 33% 23% 2	760
	11th to 20th	Night	23% 19% 34% 21% 3	743
	21st to end	Night	24% 19% 30% 22% 4	628
March	1st to 10th	Night	28% 17% 28% 24% 3 1	760
	11th to 20th	Night	30% 19% 25% 21% 6%	760
	21st to end	Night	28% 18% 24% 21% 8%	836
April	1st to 10th	Night	31% 13% 27% 24% 4	760
	11th to 20th	Night	30% 17% 23% 22% 8%	751
	21st to end	Night	30% 14% 28% 21% 6%	599
May	1st to 10th	Night	28% 10% 28% 25% 8%	487
	11th to 20th	Night	23% 11% 30% 26% 9% 1	374
	21st to end	Night	18% 9% 29% 33% 9% 1	411
June	1st to 10th	Night	27% 9% 24% 30% 9% 1	380
	11th to 20th	Night	18% 9% 29% 30% 14% 1	380
	21st to end	Night	21% 7% 26% 36% 9% 1	380
July	1st to 10th	Night	14% 5% 29% 37% 15%	370
	11th to 20th	Night	11% 4 24% 44% 16% 1	368
	21st to end	Night	18% 3 21% 44% 15%	416
August	1st to 10th	Night	16% 3 19% 43% 18% 1	378
	11th to 20th	Night	14% 5% 22% 36% 20% 3	594
	21st to end	Night	16% 7% 23% 33% 19% 1	836
September	1st to 10th	Night	17% 7% 26% 32% 16% 2	760
	11th to 20th	Night	18% 7% 19% 29% 23% 4	760
	21st to end	Night	20% 10% 27% 24% 18% 2	760
October	1st to 10th	Night	28% 11% 24% 22% 14% 1	760
	11th to 20th	Night	28% 12% 26% 24% 9% 1	760
	21st to end	Night	32% 14% 29% 21% 4	836
November	1st to 10th	Night	29% 17% 29% 19% 6% 1	764
	11th to 20th	Night	29% 18% 27% 18% 7% 1	760
	21st to end	Night	33% 20% 25% 16% 5% 1	760
December	1st to 10th	Night	34% 20% 27% 15% 4	760
	11th to 20th	Night	29% 21% 28% 17% 5% 1	760
	21st to end	Night	32% 21% 28% 17% 3	836

Page generated at 2024-11-03 13:19:00. Version ac07

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