Worthy Garden Club Hopservatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Worthy Garden Club Hopservatory clear sky chart from 2005-11-06 to 2026-03-18.

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	4 6% 2 6% 4 4 4 4 6% 7% 53%	140336
	Night	4 7% 2 6% 4 4 4 4 6% 7% 51%	138510
Transparency	Day	30% 6% 11% 22% 20% 10%	135143
	Night	32% 8% 13% 23% 17% 6%	134698
Seeing	Day	9% 16% 27% 27% 17% 5%	16299
	Night	7% 12% 24% 36% 18% 2	25493

By Month

Percentage Cloud Cover SW (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	6% 13% 4 10% 7% 7% 6% 5% 7% 9% 26%	4722
	11th to 20th	Day	5% 6% 2 5% 4 4 4 3 5% 6% 54%	4740
	21st to end	Day	5% 8% 3 7% 5% 5% 6% 5% 8% 9% 41%	5600
February	1st to 10th	Day	4 10% 3 8% 6% 7% 6% 5% 7% 9% 36%	1890
	11th to 20th	Day	5% 10% 3 7% 5% 6% 5% 4 7% 9% 38%	1856
	21st to end	Day	2 11% 5% 9% 5% 6% 6% 6% 7% 8% 33%	1730
March	1st to 10th	Day	5% 7% 3 7% 5% 6% 6% 5% 8% 12% 37%	4663
	11th to 20th	Day	3 11% 4 9% 6% 5% 6% 4 6% 7% 41%	5078
	21st to end	Day	3 8% 3 9% 7% 7% 8% 6% 8% 10% 31%	5738
April	1st to 10th	Day	6% 12% 4 10% 6% 5% 5% 4 6% 8% 34%	2400
	11th to 20th	Day	6% 10% 3 8% 6% 5% 5% 4 5% 8% 41%	2369
	21st to end	Day	6% 7% 2 7% 5% 4 4 3 6% 8% 47%	2455
May	1st to 10th	Day	8% 7% 2 5% 3 3 4 3 5% 6% 54%	6314
	11th to 20th	Day	5% 5% 3 6% 4 4 5% 4 5% 7% 51%	6277
	21st to end	Day	6% 5% 2 4 4 4 4 4 6% 8% 54%	6902
June	1st to 10th	Day	8% 7% 2 6% 5% 5% 5% 4 5% 7% 47%	2800
	11th to 20th	Day	6% 5% 2 5% 4 3 4 4 5% 7% 55%	2800
	21st to end	Day	3 3 2 3 3 3 3 3 5% 5% 66%	2800
July	1st to 10th	Day	1 1 1 2 2 2 2 2 3 3 81%	6319
	11th to 20th	Day	1 1 1 1 1 2 2 3 3 84%	6320
	21st to end	Day	1 1 2 2 2 2 2 3 6% 79%	6880
August	1st to 10th	Day	2 2 1 3 3 3 4 3 6% 7% 67%	5916
	11th to 20th	Day	2 2 1 3 2 3 3 2 4 5% 73%	5752
	21st to end	Day	4 4 1 3 3 3 3 3 5% 6% 65%	5984
September	1st to 10th	Day	2 2 1 3 2 2 3 2 4 6% 73%	2400
	11th to 20th	Day	3 4 2 5% 3 4 4 4 5% 7% 60%	2400
	21st to end	Day	6% 5% 2 5% 3 3 3 2 4 6% 62%	2141
October	1st to 10th	Day	4 5% 1 4 2 3 3 3 3 5% 66%	3280
	11th to 20th	Day	4 4 2 5% 4 4 5% 5% 6% 9% 52%	3261
	21st to end	Day	7% 7% 2 7% 5% 5% 6% 4 6% 7% 44%	3405
November	1st to 10th	Day	5% 9% 3 8% 5% 6% 6% 4 7% 8% 40%	1854
	11th to 20th	Day	4 7% 3 8% 7% 6% 6% 6% 9% 9% 35%	1710
	21st to end	Day	4 8% 4 7% 5% 4 5% 6% 8% 9% 39%	1680
December	1st to 10th	Day	3 6% 3 5% 4 3 3 4 6% 7% 56%	2700
	11th to 20th	Day	6% 13% 4 10% 6% 6% 5% 6% 7% 8% 28%	3108
	21st to end	Day	5% 11% 4 11% 7% 6% 5% 5% 8% 9% 28%	4092
January	1st to 10th	Night	5% 10% 4 10% 7% 7% 7% 6% 8% 9% 27%	8172
	11th to 20th	Night	3 6% 3 7% 4 4 4 4 5% 7% 54%	8220
	21st to end	Night	6% 11% 4 9% 5% 5% 4 4 5% 7% 40%	8599
February	1st to 10th	Night	4 11% 4 9% 6% 4 5% 5% 7% 8% 38%	2730
	11th to 20th	Night	4 10% 3 9% 5% 5% 5% 5% 7% 8% 39%	2651
	21st to end	Night	3 9% 4 8% 5% 6% 6% 5% 6% 10% 37%	2076
March	1st to 10th	Night	5% 8% 2 5% 4 5% 7% 6% 9% 11% 38%	5438
	11th to 20th	Night	2 5% 2 6% 4 5% 5% 5% 7% 9% 49%	5077
	21st to end	Night	4 8% 3 9% 6% 6% 7% 6% 8% 10% 33%	5236
April	1st to 10th	Night	6% 11% 3 7% 5% 5% 5% 4 6% 7% 40%	2000
	11th to 20th	Night	5% 9% 3 6% 5% 4 5% 5% 8% 7% 42%	1979
	21st to end	Night	6% 8% 3 5% 4 4 5% 4 7% 9% 45%	1943
May	1st to 10th	Night	7% 7% 2 5% 3 3 3 3 4 6% 56%	3645
	11th to 20th	Night	4 5% 2 5% 4 5% 5% 4 5% 5% 55%	3616
	21st to end	Night	6% 5% 2 4 4 3 4 3 5% 6% 58%	3972
June	1st to 10th	Night	10% 6% 3 5% 5% 3 4 4 4 7% 50%	1600
	11th to 20th	Night	6% 5% 2 5% 3 2 3 3 5% 7% 60%	1600
	21st to end	Night	3 3 1 2 3 2 3 3 3 7% 69%	1600
July	1st to 10th	Night	2 1 1 2 1 3 3 2 3 3 79%	3640
	11th to 20th	Night	1 1 1 1 1 1 1 2 2 87%	3640
	21st to end	Night	2 2 1 2 2 3 2 2 3 5% 77%	3970
August	1st to 10th	Night	2 2 2 4 3 3 3 3 5% 6% 66%	3888
	11th to 20th	Night	1 2 1 2 2 2 3 2 4 5% 76%	4096
	21st to end	Night	3 3 1 3 2 2 3 2 4 5% 71%	5015
September	1st to 10th	Night	2 1 1 2 1 2 3 3 3 5% 77%	2000
	11th to 20th	Night	3 3 1 5% 3 3 4 2 6% 6% 64%	2000
	21st to end	Night	6% 4 1 4 3 2 2 2 5% 6% 64%	2254
October	1st to 10th	Night	4 4 2 4 2 2 3 2 3 4 70%	3920
	11th to 20th	Night	4 4 2 5% 4 4 4 4 5% 8% 55%	3897
	21st to end	Night	4 6% 3 8% 6% 5% 5% 5% 6% 8% 45%	4400
November	1st to 10th	Night	6% 9% 3 7% 6% 4 5% 5% 7% 8% 40%	2665
	11th to 20th	Night	6% 8% 3 9% 6% 5% 5% 5% 8% 8% 37%	2909
	21st to end	Night	3 9% 2 6% 4 4 5% 5% 7% 8% 45%	2940
December	1st to 10th	Night	3 6% 2 5% 3 3 3 3 5% 7% 59%	4700
	11th to 20th	Night	7% 10% 4 10% 6% 7% 7% 5% 8% 9% 28%	5316
	21st to end	Night	4 11% 4 9% 6% 6% 6% 5% 7% 8% 35%	7106

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	51% 9% 16% 17% 6%	4723
	11th to 20th	Day	30% 7% 8% 21% 26% 7%	4740
	21st to end	Day	37% 8% 12% 16% 21% 6%	5600
February	1st to 10th	Day	43% 11% 15% 19% 10% 1	1890
	11th to 20th	Day	42% 11% 17% 19% 10% 2	1865
	21st to end	Day	45% 13% 16% 15% 9% 2	1730
March	1st to 10th	Day	37% 8% 13% 26% 12% 4	4663
	11th to 20th	Day	40% 7% 12% 26% 14%	5078
	21st to end	Day	44% 11% 17% 20% 8%	5738
April	1st to 10th	Day	46% 10% 15% 18% 10% 2	2400
	11th to 20th	Day	42% 8% 14% 19% 14% 3	2372
	21st to end	Day	35% 9% 16% 24% 14% 2	2455
May	1st to 10th	Day	30% 6% 9% 26% 25% 3	6314
	11th to 20th	Day	31% 4 11% 28% 24% 3	6280
	21st to end	Day	27% 7% 16% 35% 15%	6904
June	1st to 10th	Day	37% 7% 12% 29% 14% 1	2800
	11th to 20th	Day	28% 6% 11% 30% 21% 3	2800
	21st to end	Day	19% 5% 11% 29% 26% 10%	2800
July	1st to 10th	Day	10% 3 4 16% 28% 39%	6251
	11th to 20th	Day	8% 2 4 8% 22% 56%	6245
	21st to end	Day	10% 1 3 28% 36% 21%	6681
August	1st to 10th	Day	17% 4 5% 16% 35% 23%	4309
	11th to 20th	Day	15% 2 5% 27% 34% 15%	4163
	21st to end	Day	17% 2 6% 26% 27% 21%	4311
September	1st to 10th	Day	14% 3 6% 24% 33% 20%	2400
	11th to 20th	Day	24% 6% 10% 25% 24% 12%	2400
	21st to end	Day	24% 6% 11% 25% 23% 12%	2141
October	1st to 10th	Day	23% 4 10% 20% 26% 17%	3280
	11th to 20th	Day	29% 5% 15% 26% 21% 3	3261
	21st to end	Day	39% 6% 8% 26% 19% 2	3405
November	1st to 10th	Day	41% 9% 16% 22% 12% 1	1854
	11th to 20th	Day	42% 14% 20% 15% 9% 1	1710
	21st to end	Day	40% 12% 16% 17% 14% 1	1680
December	1st to 10th	Day	28% 8% 13% 24% 25% 3	2700
	11th to 20th	Day	51% 8% 18% 15% 6% 1	3108
	21st to end	Day	50% 9% 14% 20% 6% 1	4092
January	1st to 10th	Night	50% 10% 18% 16% 5%	8172
	11th to 20th	Night	30% 7% 10% 21% 24% 8%	8220
	21st to end	Night	44% 6% 10% 14% 20% 6%	8599
February	1st to 10th	Night	43% 13% 18% 16% 10% 1	2730
	11th to 20th	Night	41% 11% 17% 20% 9% 2	2653
	21st to end	Night	42% 14% 16% 18% 9% 1	2076
March	1st to 10th	Night	35% 10% 13% 28% 11% 3	5438
	11th to 20th	Night	30% 8% 17% 29% 16%	5077
	21st to end	Night	42% 14% 18% 20% 6%	5236
April	1st to 10th	Night	43% 11% 19% 19% 8% 1	2000
	11th to 20th	Night	39% 10% 16% 21% 12% 2	1979
	21st to end	Night	36% 11% 17% 24% 11% 1	1943
May	1st to 10th	Night	27% 9% 12% 26% 25% 1	3642
	11th to 20th	Night	29% 6% 17% 30% 16% 1	3616
	21st to end	Night	25% 9% 26% 32% 7%	3972
June	1st to 10th	Night	35% 8% 13% 31% 13% 1	1600
	11th to 20th	Night	25% 7% 14% 35% 17% 3	1600
	21st to end	Night	17% 5% 13% 33% 25% 7%	1600
July	1st to 10th	Night	13% 2 6% 21% 26% 33%	3600
	11th to 20th	Night	7% 2 4 14% 26% 47%	3592
	21st to end	Night	14% 2 3 31% 31% 19%	3857
August	1st to 10th	Night	16% 3 6% 19% 39% 17%	2821
	11th to 20th	Night	13% 3 6% 37% 32% 9%	2960
	21st to end	Night	14% 2 8% 30% 30% 16%	3608
September	1st to 10th	Night	12% 3 7% 26% 35% 17%	2000
	11th to 20th	Night	21% 6% 11% 25% 26% 11%	2000
	21st to end	Night	22% 6% 10% 24% 25% 13%	2254
October	1st to 10th	Night	21% 4 8% 23% 32% 13%	3920
	11th to 20th	Night	28% 5% 20% 26% 17% 3	3897
	21st to end	Night	36% 7% 11% 29% 15% 2	4400
November	1st to 10th	Night	42% 10% 16% 17% 13% 3	2665
	11th to 20th	Night	42% 12% 17% 19% 9% 1	2909
	21st to end	Night	35% 11% 16% 18% 16% 2	2940
December	1st to 10th	Night	26% 8% 12% 25% 27% 3	4700
	11th to 20th	Night	51% 10% 16% 16% 7% 1	5316
	21st to end	Night	45% 10% 17% 20% 7% 1	7106

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	17% 23% 32% 18% 9% 1	220
	11th to 20th	Day	16% 11% 30% 26% 12% 5%	220
	21st to end	Day	10% 21% 26% 28% 12% 2	386
February	1st to 10th	Day	14% 24% 26% 26% 10% 1	430
	11th to 20th	Day	11% 26% 32% 20% 9% 1	431
	21st to end	Day	13% 26% 30% 24% 8%	446
March	1st to 10th	Day	12% 24% 33% 25% 6%	540
	11th to 20th	Day	12% 27% 26% 24% 11% 1	529
	21st to end	Day	13% 27% 29% 23% 7% 1	550
April	1st to 10th	Day	13% 22% 29% 21% 12% 3	500
	11th to 20th	Day	13% 23% 30% 23% 8% 4	492
	21st to end	Day	9% 23% 29% 23% 13% 4	500
May	1st to 10th	Day	10% 19% 28% 26% 13% 3	503
	11th to 20th	Day	16% 16% 27% 20% 16% 5%	528
	21st to end	Day	11% 12% 25% 27% 18% 6%	573
June	1st to 10th	Day	8% 14% 28% 25% 19% 6%	530
	11th to 20th	Day	7% 18% 31% 24% 16% 3	530
	21st to end	Day	4 7% 26% 31% 24% 8%	530
July	1st to 10th	Day	2 6% 27% 36% 21% 7%	526
	11th to 20th	Day	1 4 32% 31% 23% 8%	524
	21st to end	Day	1 5% 27% 35% 22% 9%	575
August	1st to 10th	Day	2 5% 24% 35% 24% 11%	527
	11th to 20th	Day	2 5% 23% 32% 26% 13%	517
	21st to end	Day	4 8% 22% 32% 24% 10%	583
September	1st to 10th	Day	3 5% 21% 34% 28% 9%	530
	11th to 20th	Day	5% 9% 21% 33% 25% 7%	530
	21st to end	Day	8% 13% 20% 32% 23% 5%	530
October	1st to 10th	Day	8% 15% 24% 28% 21% 4	530
	11th to 20th	Day	10% 16% 23% 25% 22% 4	530
	21st to end	Day	11% 17% 29% 22% 16% 4	492
November	1st to 10th	Day	11% 17% 29% 28% 13% 2	330
	11th to 20th	Day	9% 26% 26% 23% 14% 3	235
	21st to end	Day	12% 22% 21% 29% 14% 2	220
December	1st to 10th	Day	10% 21% 24% 24% 14% 8%	220
	11th to 20th	Day	16% 25% 33% 21% 5%	220
	21st to end	Day	16% 23% 27% 24% 7% 3	242
January	1st to 10th	Night	10% 20% 33% 25% 11% 2	840
	11th to 20th	Night	7% 18% 30% 26% 17% 2	840
	21st to end	Night	10% 14% 26% 34% 14% 2	924
February	1st to 10th	Night	8% 18% 31% 31% 11% 1	840
	11th to 20th	Night	8% 14% 32% 34% 12% 1	824
	21st to end	Night	9% 18% 32% 33% 8%	692
March	1st to 10th	Night	10% 19% 28% 32% 10% 1	840
	11th to 20th	Night	7% 17% 28% 34% 14% 1	828
	21st to end	Night	7% 19% 31% 30% 12% 1	880
April	1st to 10th	Night	11% 15% 28% 32% 15% 1	800
	11th to 20th	Night	9% 13% 30% 31% 15% 2	791
	21st to end	Night	9% 11% 27% 36% 16% 1	743
May	1st to 10th	Night	9% 8% 23% 40% 19% 1	405
	11th to 20th	Night	8% 7% 19% 43% 21% 1	394
	21st to end	Night	9% 7% 21% 36% 24% 2	433
June	1st to 10th	Night	9% 7% 21% 43% 20% 1	400
	11th to 20th	Night	7% 5% 22% 46% 20% 1	400
	21st to end	Night	4 2 14% 59% 22%	400
July	1st to 10th	Night	2 1 9% 59% 27% 1	390
	11th to 20th	Night	2 11% 65% 21% 1	388
	21st to end	Night	1 1 10% 57% 30% 1	438
August	1st to 10th	Night	2 1 6% 52% 36% 3	527
	11th to 20th	Night	1 1 8% 43% 41% 6%	612
	21st to end	Night	2 2 17% 47% 30% 2	880
September	1st to 10th	Night	2 2 15% 47% 31% 3	800
	11th to 20th	Night	4 3 14% 43% 31% 5%	800
	21st to end	Night	7% 5% 18% 38% 27% 5%	800
October	1st to 10th	Night	8% 5% 22% 38% 23% 3	800
	11th to 20th	Night	7% 10% 22% 35% 22% 4	800
	21st to end	Night	8% 13% 26% 33% 15% 6%	880
November	1st to 10th	Night	9% 14% 30% 32% 13% 1	820
	11th to 20th	Night	10% 20% 28% 26% 14% 2	840
	21st to end	Night	7% 18% 25% 33% 14% 3	840
December	1st to 10th	Night	9% 14% 26% 31% 17% 2	840
	11th to 20th	Night	9% 20% 30% 29% 12% 1	840
	21st to end	Night	10% 24% 32% 24% 10% 1	924

Page generated at 2026-03-14 23:23:52. Version ac07

Copyright © 2026 Attilla Danko.