Hopewell Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hopewell Observatory clear sky chart from 2005-11-06 to 2024-05-15.

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	15% 6% 2 6% 4 4 4 4 6% 7% 42%	83666
	Night	15% 6% 2 5% 4 4 4 4 5% 7% 44%	85854
Transparency	Day	39% 8% 13% 23% 15% 3	83379
	Night	38% 7% 12% 23% 17% 3	85660
Seeing	Day	18% 12% 26% 24% 15% 6%	14284
	Night	17% 10% 30% 30% 13% 1	23988

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	18% 4 2 5% 4 4 3 4 5% 5% 46%	2659
	11th to 20th	Day	16% 9% 3 8% 4 4 4 3 4 5% 40%	2840
	21st to end	Day	18% 9% 3 7% 5% 4 3 3 4 6% 38%	3124
February	1st to 10th	Day	14% 7% 3 6% 5% 5% 4 4 6% 5% 39%	1710
	11th to 20th	Day	18% 7% 2 5% 4 4 4 4 5% 7% 40%	1688
	21st to end	Day	18% 9% 2 6% 5% 5% 4 3 5% 6% 39%	1570
March	1st to 10th	Day	22% 7% 2 6% 5% 5% 4 3 4 7% 36%	3435
	11th to 20th	Day	10% 5% 2 5% 4 4 4 4 4 7% 50%	3480
	21st to end	Day	20% 7% 2 6% 4 4 3 3 5% 7% 39%	3836
April	1st to 10th	Day	12% 6% 2 6% 5% 4 5% 4 6% 7% 43%	2280
	11th to 20th	Day	14% 6% 2 6% 5% 3 4 3 4 6% 48%	2254
	21st to end	Day	19% 6% 2 6% 4 4 4 4 5% 5% 41%	2280
May	1st to 10th	Day	17% 7% 2 5% 4 4 6% 4 6% 8% 37%	2460
	11th to 20th	Day	19% 6% 2 6% 5% 5% 5% 4 6% 8% 36%	2416
	21st to end	Day	15% 5% 2 5% 4 4 5% 5% 7% 8% 40%	2725
June	1st to 10th	Day	11% 4 2 6% 5% 4 4 5% 7% 8% 43%	2520
	11th to 20th	Day	11% 5% 3 6% 5% 4 5% 5% 8% 9% 40%	2520
	21st to end	Day	8% 4 2 5% 5% 3 6% 5% 7% 11% 44%	2520
July	1st to 10th	Day	9% 5% 2 6% 5% 4 5% 5% 7% 9% 42%	2520
	11th to 20th	Day	5% 4 2 5% 5% 5% 6% 5% 8% 12% 43%	2388
	21st to end	Day	9% 5% 2 7% 6% 6% 6% 6% 8% 10% 36%	2547
August	1st to 10th	Day	9% 6% 3 7% 5% 6% 6% 4 9% 10% 35%	2327
	11th to 20th	Day	12% 5% 2 6% 5% 5% 7% 6% 7% 8% 38%	2232
	21st to end	Day	11% 5% 2 6% 5% 4 5% 4 7% 9% 43%	2376
September	1st to 10th	Day	14% 6% 2 6% 4 4 4 4 4 7% 45%	2160
	11th to 20th	Day	12% 5% 1 6% 4 4 3 3 6% 7% 49%	2156
	21st to end	Day	20% 6% 2 6% 4 4 4 4 5% 5% 40%	1880
October	1st to 10th	Day	17% 5% 2 5% 4 3 4 3 5% 6% 47%	1800
	11th to 20th	Day	17% 5% 1 5% 4 3 4 3 4 5% 48%	1800
	21st to end	Day	15% 6% 1 5% 3 4 2 3 4 6% 49%	1980
November	1st to 10th	Day	13% 5% 2 4 3 3 3 3 5% 7% 52%	1800
	11th to 20th	Day	15% 6% 2 4 4 3 4 3 5% 5% 50%	1661
	21st to end	Day	16% 5% 2 3 4 4 4 4 4 7% 47%	1520
December	1st to 10th	Day	15% 7% 2 6% 4 4 4 4 7% 6% 41%	1520
	11th to 20th	Day	17% 5% 2 6% 4 3 5% 3 5% 7% 45%	1910
	21st to end	Day	19% 6% 2 6% 4 4 5% 5% 6% 7% 36%	2772
January	1st to 10th	Night	14% 7% 2 5% 4 3 4 3 5% 6% 48%	4269
	11th to 20th	Night	18% 8% 2 4 3 3 3 2 4 5% 47%	4120
	21st to end	Night	20% 8% 3 5% 3 3 3 3 4 6% 41%	4532
February	1st to 10th	Night	15% 7% 2 6% 4 4 5% 4 6% 5% 41%	2470
	11th to 20th	Night	19% 7% 2 6% 4 3 3 3 5% 6% 43%	2376
	21st to end	Night	17% 8% 3 6% 4 3 4 3 4 5% 42%	1881
March	1st to 10th	Night	21% 6% 2 6% 4 3 5% 3 5% 6% 38%	3418
	11th to 20th	Night	11% 6% 2 4 4 3 4 3 5% 8% 50%	3480
	21st to end	Night	14% 8% 2 6% 4 3 3 3 4 6% 47%	3795
April	1st to 10th	Night	15% 7% 3 6% 5% 4 4 4 5% 6% 41%	1900
	11th to 20th	Night	13% 6% 2 5% 5% 3 4 4 5% 8% 46%	1875
	21st to end	Night	17% 5% 1 5% 3 4 4 4 6% 7% 43%	1900
May	1st to 10th	Night	17% 5% 3 6% 4 4 5% 5% 6% 8% 37%	1734
	11th to 20th	Night	18% 7% 2 6% 5% 4 4 4 6% 8% 37%	1562
	21st to end	Night	13% 6% 2 6% 4 4 4 3 6% 10% 41%	1550
June	1st to 10th	Night	10% 5% 2 5% 4 4 4 4 7% 9% 44%	1440
	11th to 20th	Night	13% 5% 3 5% 4 5% 6% 4 5% 8% 42%	1440
	21st to end	Night	9% 4 2 6% 4 5% 5% 4 7% 10% 44%	1440
July	1st to 10th	Night	11% 6% 2 7% 4 4 5% 5% 6% 10% 41%	1440
	11th to 20th	Night	5% 5% 2 7% 5% 5% 5% 5% 6% 11% 45%	1567
	21st to end	Night	9% 4 2 5% 5% 5% 5% 5% 8% 10% 42%	1771
August	1st to 10th	Night	9% 5% 2 6% 6% 7% 7% 5% 8% 9% 38%	1611
	11th to 20th	Night	10% 6% 2 7% 5% 7% 5% 4 7% 9% 38%	1648
	21st to end	Night	9% 6% 3 6% 4 5% 5% 4 6% 10% 40%	1980
September	1st to 10th	Night	15% 6% 2 5% 4 4 4 4 6% 6% 44%	1800
	11th to 20th	Night	10% 6% 2 5% 4 4 4 3 5% 7% 50%	1800
	21st to end	Night	19% 7% 2 6% 4 3 4 3 5% 5% 41%	2079
October	1st to 10th	Night	20% 5% 2 5% 3 3 3 3 4 5% 47%	2160
	11th to 20th	Night	16% 6% 1 5% 3 3 3 3 4 5% 51%	2160
	21st to end	Night	15% 5% 2 5% 3 4 3 3 5% 6% 50%	2376
November	1st to 10th	Night	12% 6% 2 5% 4 3 3 2 4 6% 53%	2274
	11th to 20th	Night	14% 6% 2 4 3 3 3 4 5% 7% 50%	2517
	21st to end	Night	14% 5% 1 5% 4 4 4 4 5% 6% 49%	2660
December	1st to 10th	Night	17% 7% 3 6% 4 4 4 3 5% 5% 42%	2660
	11th to 20th	Night	17% 6% 2 6% 4 4 4 3 4 7% 44%	3285
	21st to end	Night	18% 6% 2 6% 4 4 5% 4 6% 8% 37%	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	37% 5% 9% 30% 14% 4	2660
	11th to 20th	Day	44% 6% 10% 19% 15% 6%	2840
	21st to end	Day	47% 6% 10% 22% 12% 2	3124
February	1st to 10th	Day	43% 7% 13% 23% 12% 2	1710
	11th to 20th	Day	43% 4 11% 22% 17% 3	1697
	21st to end	Day	45% 5% 13% 18% 15% 3	1570
March	1st to 10th	Day	47% 6% 11% 20% 13% 4	3435
	11th to 20th	Day	31% 7% 11% 26% 21% 4	3480
	21st to end	Day	44% 7% 11% 19% 15% 3	3836
April	1st to 10th	Day	38% 6% 12% 20% 18% 5%	2280
	11th to 20th	Day	37% 6% 11% 21% 20% 6%	2254
	21st to end	Day	42% 8% 11% 21% 14% 4	2280
May	1st to 10th	Day	42% 8% 14% 19% 14% 2	2460
	11th to 20th	Day	44% 9% 13% 20% 12% 2	2420
	21st to end	Day	38% 9% 15% 25% 11% 1	2725
June	1st to 10th	Day	35% 9% 15% 24% 15% 1	2520
	11th to 20th	Day	38% 11% 14% 22% 13% 2	2520
	21st to end	Day	31% 11% 17% 24% 16% 1	2520
July	1st to 10th	Day	35% 11% 14% 21% 16% 2	2450
	11th to 20th	Day	29% 11% 17% 26% 15% 2	2316
	21st to end	Day	37% 11% 14% 20% 16% 1	2405
August	1st to 10th	Day	38% 10% 18% 22% 10% 1	2314
	11th to 20th	Day	38% 12% 14% 21% 14% 1	2232
	21st to end	Day	35% 9% 16% 24% 13% 3	2376
September	1st to 10th	Day	37% 8% 13% 18% 19% 4	2160
	11th to 20th	Day	34% 6% 9% 28% 20% 4	2156
	21st to end	Day	43% 8% 10% 20% 17% 2	1880
October	1st to 10th	Day	38% 6% 11% 25% 16% 3	1800
	11th to 20th	Day	37% 5% 10% 25% 20% 3	1800
	21st to end	Day	35% 5% 9% 26% 22% 3	1980
November	1st to 10th	Day	33% 5% 13% 25% 20% 5%	1800
	11th to 20th	Day	34% 6% 10% 23% 21% 6%	1661
	21st to end	Day	36% 6% 11% 27% 18% 2	1520
December	1st to 10th	Day	40% 7% 13% 24% 12% 3	1520
	11th to 20th	Day	38% 5% 11% 31% 11% 4	1906
	21st to end	Day	41% 9% 15% 25% 10% 1	2772
January	1st to 10th	Night	35% 6% 10% 27% 18% 4	4269
	11th to 20th	Night	39% 5% 10% 23% 19% 4	4120
	21st to end	Night	44% 5% 10% 25% 15% 1	4532
February	1st to 10th	Night	42% 7% 13% 23% 14% 2	2470
	11th to 20th	Night	42% 4 10% 21% 17% 5%	2378
	21st to end	Night	43% 5% 11% 21% 15% 5%	1881
March	1st to 10th	Night	44% 7% 11% 24% 12% 2	3418
	11th to 20th	Night	30% 7% 12% 25% 23% 4	3480
	21st to end	Night	39% 5% 9% 22% 19% 5%	3795
April	1st to 10th	Night	41% 7% 9% 19% 19% 4	1900
	11th to 20th	Night	35% 7% 13% 20% 19% 6%	1875
	21st to end	Night	37% 9% 11% 24% 13% 5%	1900
May	1st to 10th	Night	41% 9% 13% 20% 13% 4	1734
	11th to 20th	Night	44% 8% 13% 20% 14% 2	1563
	21st to end	Night	37% 9% 18% 22% 13% 1	1551
June	1st to 10th	Night	33% 9% 14% 25% 17% 2	1440
	11th to 20th	Night	38% 10% 15% 21% 14% 2	1440
	21st to end	Night	33% 8% 17% 22% 18% 3	1440
July	1st to 10th	Night	37% 11% 17% 19% 13% 4	1400
	11th to 20th	Night	30% 11% 18% 22% 17% 2	1516
	21st to end	Night	32% 10% 19% 24% 15% 1	1672
August	1st to 10th	Night	38% 12% 16% 20% 13% 1	1600
	11th to 20th	Night	40% 10% 15% 21% 13% 2	1648
	21st to end	Night	37% 9% 16% 22% 14% 3	1980
September	1st to 10th	Night	39% 8% 11% 20% 18% 5%	1800
	11th to 20th	Night	34% 6% 10% 26% 22% 3	1800
	21st to end	Night	44% 6% 10% 19% 17% 3	2079
October	1st to 10th	Night	40% 5% 13% 22% 18% 3	2160
	11th to 20th	Night	35% 5% 9% 26% 22% 3	2160
	21st to end	Night	35% 6% 9% 24% 22% 4	2376
November	1st to 10th	Night	33% 4 10% 26% 21% 6%	2274
	11th to 20th	Night	35% 5% 8% 23% 22% 6%	2517
	21st to end	Night	35% 5% 12% 25% 20% 4	2660
December	1st to 10th	Night	43% 5% 11% 23% 14% 3	2660
	11th to 20th	Night	40% 6% 10% 23% 17% 4	3288
	21st to end	Night	41% 10% 16% 20% 12% 1	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	22% 29% 30% 17% 2	222
	11th to 20th	Day	30% 24% 29% 16% 2	270
	21st to end	Day	22% 26% 35% 12% 4 1	297
February	1st to 10th	Day	21% 24% 37% 14% 4	270
	11th to 20th	Day	34% 23% 34% 7% 2	295
	21st to end	Day	27% 20% 32% 19% 2	382
March	1st to 10th	Day	22% 22% 30% 22% 3	460
	11th to 20th	Day	23% 23% 32% 17% 5% 2	460
	21st to end	Day	21% 19% 33% 20% 6% 1	506
April	1st to 10th	Day	21% 22% 29% 21% 7% 1	460
	11th to 20th	Day	15% 18% 28% 22% 13% 3	452
	21st to end	Day	23% 13% 33% 19% 10% 2	460
May	1st to 10th	Day	22% 15% 29% 19% 12% 5%	463
	11th to 20th	Day	20% 8% 32% 22% 14% 4	463
	21st to end	Day	19% 4 22% 27% 20% 8%	485
June	1st to 10th	Day	12% 5% 26% 29% 22% 7%	450
	11th to 20th	Day	13% 8% 24% 30% 17% 8%	450
	21st to end	Day	9% 5% 25% 34% 20% 8%	450
July	1st to 10th	Day	11% 3 15% 30% 27% 14%	445
	11th to 20th	Day	4 2 16% 34% 32% 12%	444
	21st to end	Day	12% 2 18% 31% 28% 9%	488
August	1st to 10th	Day	12% 4 16% 26% 30% 13%	446
	11th to 20th	Day	13% 3 13% 31% 26% 13%	439
	21st to end	Day	9% 2 17% 32% 24% 16%	495
September	1st to 10th	Day	17% 4 20% 24% 19% 16%	450
	11th to 20th	Day	13% 5% 17% 30% 23% 12%	450
	21st to end	Day	23% 9% 21% 25% 17% 4	450
October	1st to 10th	Day	20% 6% 19% 27% 20% 8%	450
	11th to 20th	Day	15% 13% 25% 28% 16% 3	450
	21st to end	Day	17% 11% 34% 25% 10% 3	495
November	1st to 10th	Day	16% 11% 31% 28% 12% 3	428
	11th to 20th	Day	18% 12% 33% 24% 11% 2	321
	21st to end	Day	18% 19% 32% 21% 8% 1	180
December	1st to 10th	Day	18% 18% 37% 21% 4 2	180
	11th to 20th	Day	23% 18% 31% 21% 7%	180
	21st to end	Day	23% 17% 33% 20% 7% 1	198
January	1st to 10th	Night	20% 17% 41% 20% 3	760
	11th to 20th	Night	22% 14% 35% 26% 4	760
	21st to end	Night	19% 15% 42% 21% 2	836
February	1st to 10th	Night	19% 13% 40% 25% 3	760
	11th to 20th	Night	24% 18% 40% 16% 2	743
	21st to end	Night	24% 17% 37% 19% 3	628
March	1st to 10th	Night	19% 16% 40% 23% 3	760
	11th to 20th	Night	23% 16% 35% 22% 5% 1	760
	21st to end	Night	18% 15% 40% 21% 5%	836
April	1st to 10th	Night	18% 18% 38% 22% 4	760
	11th to 20th	Night	15% 12% 35% 29% 8% 1	751
	21st to end	Night	19% 9% 32% 32% 8%	760
May	1st to 10th	Night	21% 8% 27% 32% 12% 1	594
	11th to 20th	Night	20% 4 27% 37% 11% 1	477
	21st to end	Night	15% 2 20% 41% 20% 1	389
June	1st to 10th	Night	9% 4 23% 43% 21% 1	360
	11th to 20th	Night	13% 3 21% 41% 20% 1	360
	21st to end	Night	7% 3 20% 51% 17% 1	360
July	1st to 10th	Night	11% 2 20% 37% 26% 4	350
	11th to 20th	Night	7% 1 14% 36% 38% 4	472
	21st to end	Night	9% 2 15% 41% 29% 4	591
August	1st to 10th	Night	9% 2 12% 43% 32% 2	537
	11th to 20th	Night	10% 3 11% 43% 30% 3	584
	21st to end	Night	10% 3 14% 41% 27% 4	792
September	1st to 10th	Night	17% 2 16% 32% 29% 4	720
	11th to 20th	Night	11% 3 16% 36% 30% 3	720
	21st to end	Night	21% 4 22% 33% 20% 1	720
October	1st to 10th	Night	21% 4 21% 30% 19% 5%	720
	11th to 20th	Night	17% 8% 28% 33% 14%	720
	21st to end	Night	17% 10% 32% 28% 12%	792
November	1st to 10th	Night	14% 8% 34% 32% 11% 1	740
	11th to 20th	Night	17% 11% 34% 30% 7% 1	760
	21st to end	Night	15% 13% 34% 30% 8% 1	760
December	1st to 10th	Night	21% 11% 37% 24% 7%	760
	11th to 20th	Night	18% 9% 41% 27% 5%	760
	21st to end	Night	20% 12% 34% 31% 3	836

Page generated at 2024-05-12 00:20:42. Version ac07

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