Wharf Road Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wharf Road Observatory clear sky chart from 2005-11-06 to 2026-07-01.

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	18% 12% 4 10% 6% 4 4 3 4 6% 29%	138019
	Night	19% 15% 5% 12% 6% 4 4 3 4 5% 23%	134431
Transparency	Day	57% 4 11% 18% 9% 1	141569
	Night	63% 4 10% 15% 7% 1	138970
Seeing	Day	31% 20% 29% 15% 4 1	18920
	Night	31% 18% 27% 18% 5%	26658

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	15% 24% 9% 17% 11% 6% 2 2 3 2 10%	4093
	11th to 20th	Day	18% 21% 11% 22% 6% 4 3 2 2 3 7%	4882
	21st to end	Day	14% 15% 7% 22% 15% 8% 3 2 2 3 9%	5781
February	1st to 10th	Day	17% 18% 9% 16% 11% 5% 3 3 4 5% 10%	1890
	11th to 20th	Day	17% 14% 5% 16% 12% 5% 3 3 3 5% 17%	1843
	21st to end	Day	12% 15% 7% 11% 8% 6% 3 3 4 5% 25%	1650
March	1st to 10th	Day	23% 16% 5% 13% 8% 5% 3 2 3 4 18%	4943
	11th to 20th	Day	17% 13% 4 10% 5% 4 4 3 5% 6% 29%	5090
	21st to end	Day	26% 15% 5% 10% 4 4 4 3 3 4 22%	5587
April	1st to 10th	Day	22% 14% 3 6% 4 3 3 3 4 6% 30%	2436
	11th to 20th	Day	21% 11% 3 5% 3 3 3 3 4 6% 38%	2676
	21st to end	Day	20% 10% 3 6% 4 4 3 3 5% 6% 35%	2730
May	1st to 10th	Day	24% 12% 4 8% 5% 4 4 3 4 5% 27%	7639
	11th to 20th	Day	15% 9% 3 7% 5% 5% 4 4 5% 8% 35%	8078
	21st to end	Day	16% 11% 4 8% 5% 4 4 3 5% 7% 33%	9059
June	1st to 10th	Day	21% 9% 2 6% 5% 4 5% 4 5% 7% 32%	3063
	11th to 20th	Day	19% 8% 2 6% 4 4 4 4 6% 8% 37%	3150
	21st to end	Day	22% 9% 3 8% 5% 5% 4 3 5% 6% 31%	3150
July	1st to 10th	Day	20% 8% 3 7% 4 4 4 4 6% 8% 31%	6820
	11th to 20th	Day	19% 8% 3 6% 4 3 3 3 6% 9% 35%	6646
	21st to end	Day	13% 7% 3 6% 4 4 4 4 6% 9% 41%	6426
August	1st to 10th	Day	21% 10% 3 7% 4 4 4 4 5% 6% 32%	4235
	11th to 20th	Day	12% 7% 3 7% 5% 4 4 4 5% 9% 40%	4175
	21st to end	Day	10% 6% 2 5% 4 3 3 3 5% 6% 53%	4611
September	1st to 10th	Day	16% 6% 2 5% 3 3 3 3 4 7% 47%	2400
	11th to 20th	Day	14% 7% 3 6% 3 4 4 3 5% 6% 47%	2213
	21st to end	Day	17% 6% 3 5% 3 4 3 3 5% 5% 47%	2200
October	1st to 10th	Day	17% 9% 2 5% 4 3 4 3 5% 7% 42%	2005
	11th to 20th	Day	18% 10% 3 8% 3 4 3 3 5% 7% 35%	2000
	21st to end	Day	22% 12% 3 7% 4 4 4 3 4 6% 32%	2150
November	1st to 10th	Day	20% 13% 3 8% 5% 4 4 3 4 7% 28%	1766
	11th to 20th	Day	20% 20% 7% 8% 5% 4 4 3 4 6% 20%	1680
	21st to end	Day	21% 19% 7% 11% 6% 4 3 3 4 4 17%	1680
December	1st to 10th	Day	20% 20% 9% 18% 5% 3 3 2 3 4 12%	2690
	11th to 20th	Day	23% 17% 6% 16% 7% 4 3 2 3 4 14%	3029
	21st to end	Day	19% 18% 8% 17% 7% 3 3 2 3 4 15%	3553
January	1st to 10th	Night	14% 24% 8% 23% 10% 4 2 2 2 2 8%	8831
	11th to 20th	Night	21% 24% 10% 19% 5% 3 2 2 3 3 8%	7987
	21st to end	Night	13% 15% 6% 23% 15% 6% 3 2 3 4 8%	8400
February	1st to 10th	Night	19% 19% 7% 19% 9% 4 4 3 3 4 10%	2730
	11th to 20th	Night	17% 17% 6% 15% 9% 6% 4 3 3 5% 14%	2663
	21st to end	Night	14% 16% 6% 13% 7% 4 5% 3 4 6% 22%	2154
March	1st to 10th	Night	22% 18% 7% 14% 9% 4 2 2 2 4 16%	5116
	11th to 20th	Night	17% 15% 5% 11% 6% 5% 4 3 5% 5% 24%	5089
	21st to end	Night	28% 13% 5% 8% 5% 4 3 2 3 4 25%	5587
April	1st to 10th	Night	24% 15% 4 7% 4 4 3 2 5% 5% 27%	2184
	11th to 20th	Night	22% 12% 3 6% 4 3 4 3 6% 7% 28%	1890
	21st to end	Night	23% 11% 3 7% 4 4 4 3 4 7% 31%	1890
May	1st to 10th	Night	26% 14% 4 8% 4 4 3 3 4 5% 23%	5259
	11th to 20th	Night	21% 11% 3 7% 4 4 4 3 6% 7% 30%	4791
	21st to end	Night	17% 12% 4 9% 5% 5% 4 4 5% 6% 30%	5147
June	1st to 10th	Night	24% 8% 3 7% 4 4 4 4 7% 9% 27%	1573
	11th to 20th	Night	19% 8% 2 6% 4 3 5% 4 7% 8% 33%	1470
	21st to end	Night	20% 9% 4 10% 5% 6% 5% 4 6% 7% 25%	1470
July	1st to 10th	Night	24% 10% 3 8% 5% 4 5% 4 6% 7% 24%	3160
	11th to 20th	Night	21% 9% 2 7% 4 4 5% 4 6% 7% 31%	3285
	21st to end	Night	15% 7% 2 7% 4 4 5% 4 6% 8% 38%	4423
August	1st to 10th	Night	23% 10% 3 7% 4 3 4 3 5% 7% 31%	2915
	11th to 20th	Night	16% 9% 3 7% 6% 5% 5% 4 6% 8% 31%	2872
	21st to end	Night	11% 7% 3 7% 4 4 4 3 6% 8% 44%	3285
September	1st to 10th	Night	15% 6% 3 6% 3 4 4 4 6% 7% 44%	2000
	11th to 20th	Night	16% 8% 3 5% 3 3 4 3 5% 7% 43%	2185
	21st to end	Night	16% 8% 3 6% 5% 5% 4 3 6% 6% 39%	2200
October	1st to 10th	Night	18% 7% 2 6% 4 4 4 3 5% 7% 40%	2395
	11th to 20th	Night	18% 10% 3 7% 4 4 4 3 5% 6% 36%	2400
	21st to end	Night	24% 13% 3 7% 4 3 4 3 4 5% 30%	2685
November	1st to 10th	Night	23% 13% 3 7% 5% 4 4 3 5% 6% 29%	2751
	11th to 20th	Night	20% 22% 6% 9% 4 4 4 3 4 5% 19%	2940
	21st to end	Night	22% 19% 6% 11% 4 4 3 3 4 5% 19%	2940
December	1st to 10th	Night	17% 22% 10% 17% 6% 4 3 3 4 5% 9%	4720
	11th to 20th	Night	17% 19% 7% 18% 6% 4 3 2 3 4 17%	5377
	21st to end	Night	22% 21% 7% 14% 6% 2 2 2 3 4 17%	7667

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	84% 2 9% 4 1	4094
	11th to 20th	Day	87% 3 4 5% 1	4915
	21st to end	Day	81% 5% 6% 5% 2 1	5781
February	1st to 10th	Day	78% 4 8% 6% 3	1890
	11th to 20th	Day	73% 4 8% 11% 4	1851
	21st to end	Day	62% 5% 11% 15% 7% 1	1650
March	1st to 10th	Day	73% 3 6% 11% 5% 1	4947
	11th to 20th	Day	57% 4 13% 19% 7% 1	5090
	21st to end	Day	70% 2 5% 14% 8% 1	5587
April	1st to 10th	Day	59% 3 8% 15% 13% 2	2436
	11th to 20th	Day	50% 3 9% 24% 13% 1	2676
	21st to end	Day	51% 3 10% 20% 13% 3	2730
May	1st to 10th	Day	61% 4 10% 18% 7% 1	7651
	11th to 20th	Day	49% 5% 15% 21% 9% 1	8082
	21st to end	Day	53% 4 13% 16% 13% 1	9060
June	1st to 10th	Day	52% 4 11% 22% 10%	3063
	11th to 20th	Day	46% 4 13% 22% 13% 1	3150
	21st to end	Day	55% 5% 11% 18% 10% 1	3150
July	1st to 10th	Day	50% 5% 15% 19% 10% 1	6745
	11th to 20th	Day	45% 5% 13% 26% 11% 1	6565
	21st to end	Day	39% 7% 17% 25% 12%	6242
August	1st to 10th	Day	54% 4 10% 20% 11%	4222
	11th to 20th	Day	41% 6% 17% 25% 11%	4214
	21st to end	Day	32% 4 15% 28% 20% 1	4611
September	1st to 10th	Day	39% 3 12% 29% 16% 2	2400
	11th to 20th	Day	39% 4 12% 26% 18% 2	2213
	21st to end	Day	42% 3 9% 27% 17% 2	2200
October	1st to 10th	Day	44% 5% 11% 28% 12%	3265
	11th to 20th	Day	47% 4 9% 28% 12%	3240
	21st to end	Day	47% 3 13% 23% 14% 1	3452
November	1st to 10th	Day	59% 4 11% 19% 7% 1	1766
	11th to 20th	Day	67% 4 9% 14% 4 1	1680
	21st to end	Day	73% 4 10% 11% 2	1680
December	1st to 10th	Day	79% 4 6% 10% 1	2690
	11th to 20th	Day	75% 5% 7% 9% 3 1	3028
	21st to end	Day	75% 4 9% 6% 6%	3553
January	1st to 10th	Night	84% 3 6% 6% 1	8831
	11th to 20th	Night	83% 4 5% 6% 2	8029
	21st to end	Night	81% 4 6% 7% 2	8400
February	1st to 10th	Night	80% 4 5% 7% 4	2730
	11th to 20th	Night	76% 3 7% 11% 3	2666
	21st to end	Night	64% 4 10% 15% 6% 1	2154
March	1st to 10th	Night	73% 5% 5% 9% 7% 1	5125
	11th to 20th	Night	61% 5% 13% 16% 6%	5090
	21st to end	Night	65% 3 6% 17% 8% 1	5587
April	1st to 10th	Night	61% 3 8% 13% 12% 2	2184
	11th to 20th	Night	54% 5% 8% 20% 12% 1	1890
	21st to end	Night	56% 3 9% 18% 12% 1	1890
May	1st to 10th	Night	65% 3 9% 17% 6%	5265
	11th to 20th	Night	53% 5% 14% 19% 7% 2	4792
	21st to end	Night	53% 6% 14% 17% 9% 1	5148
June	1st to 10th	Night	51% 5% 13% 22% 8% 1	1573
	11th to 20th	Night	45% 5% 14% 24% 10% 1	1470
	21st to end	Night	54% 8% 12% 15% 9% 2	1470
July	1st to 10th	Night	57% 6% 12% 16% 9%	3125
	11th to 20th	Night	48% 7% 15% 18% 11% 1	3243
	21st to end	Night	42% 6% 15% 24% 13%	4293
August	1st to 10th	Night	53% 4 12% 23% 8%	2903
	11th to 20th	Night	46% 7% 18% 22% 7%	2899
	21st to end	Night	35% 7% 15% 26% 16% 1	3284
September	1st to 10th	Night	39% 5% 11% 29% 15% 1	2000
	11th to 20th	Night	40% 4 10% 28% 16% 1	2185
	21st to end	Night	45% 4 9% 25% 15% 2	2200
October	1st to 10th	Night	46% 4 13% 25% 12% 1	3915
	11th to 20th	Night	44% 3 12% 25% 15%	3899
	21st to end	Night	49% 3 9% 25% 13%	4333
November	1st to 10th	Night	56% 6% 12% 18% 9%	2751
	11th to 20th	Night	68% 5% 9% 13% 5%	2940
	21st to end	Night	68% 5% 13% 11% 3	2940
December	1st to 10th	Night	78% 5% 8% 9% 1	4720
	11th to 20th	Night	72% 5% 9% 12% 2	5379
	21st to end	Night	74% 3 7% 11% 4	7667

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	46% 25% 20% 8%	220
	11th to 20th	Day	42% 25% 22% 8% 2	327
	21st to end	Day	31% 27% 32% 9% 1	473
February	1st to 10th	Day	35% 26% 27% 10% 2	430
	11th to 20th	Day	39% 28% 22% 8% 2	426
	21st to end	Day	34% 27% 26% 11% 1	405
March	1st to 10th	Day	38% 24% 30% 6% 1	540
	11th to 20th	Day	37% 26% 25% 8% 2	540
	21st to end	Day	40% 26% 22% 9% 3 1	594
April	1st to 10th	Day	45% 26% 21% 7% 1 1	540
	11th to 20th	Day	38% 26% 24% 10% 2	532
	21st to end	Day	34% 19% 29% 12% 5%	540
May	1st to 10th	Day	35% 22% 30% 10% 3	543
	11th to 20th	Day	28% 22% 29% 17% 5%	721
	21st to end	Day	31% 19% 29% 17% 3 1	845
June	1st to 10th	Day	34% 16% 26% 19% 4	780
	11th to 20th	Day	25% 17% 34% 18% 6% 1	780
	21st to end	Day	30% 14% 33% 16% 5% 1	780
July	1st to 10th	Day	23% 12% 38% 20% 7% 1	720
	11th to 20th	Day	22% 10% 37% 21% 8% 1	718
	21st to end	Day	21% 11% 43% 22% 3	577
August	1st to 10th	Day	17% 12% 42% 23% 4 1	526
	11th to 20th	Day	20% 11% 35% 23% 10% 1	519
	21st to end	Day	18% 15% 32% 26% 7% 2	583
September	1st to 10th	Day	19% 14% 39% 21% 6% 1	530
	11th to 20th	Day	23% 16% 31% 20% 7% 3	530
	21st to end	Day	23% 18% 30% 20% 7% 2	530
October	1st to 10th	Day	27% 16% 25% 20% 9% 2	423
	11th to 20th	Day	30% 18% 30% 15% 5% 2	420
	21st to end	Day	34% 21% 28% 12% 4 1	462
November	1st to 10th	Day	36% 22% 27% 11% 3 1	425
	11th to 20th	Day	44% 21% 20% 10% 3	430
	21st to end	Day	41% 25% 23% 7% 3 1	430
December	1st to 10th	Day	40% 27% 23% 10% 1	430
	11th to 20th	Day	49% 26% 18% 5% 1	409
	21st to end	Day	42% 26% 25% 6% 1	242
January	1st to 10th	Night	37% 26% 23% 12% 1	950
	11th to 20th	Night	40% 23% 23% 11% 3	855
	21st to end	Night	31% 27% 27% 11% 2	924
February	1st to 10th	Night	36% 25% 27% 11% 2	840
	11th to 20th	Night	39% 23% 25% 11% 2	823
	21st to end	Night	27% 26% 27% 16% 3	692
March	1st to 10th	Night	34% 24% 28% 12% 1	840
	11th to 20th	Night	32% 22% 25% 17% 3	840
	21st to end	Night	32% 22% 26% 16% 4	924
April	1st to 10th	Night	40% 18% 25% 15% 2	714
	11th to 20th	Night	31% 21% 29% 17% 2	624
	21st to end	Night	33% 16% 26% 18% 6%	630
May	1st to 10th	Night	30% 16% 32% 18% 4 1	630
	11th to 20th	Night	29% 15% 28% 23% 4	622
	21st to end	Night	22% 16% 38% 20% 4 1	682
June	1st to 10th	Night	29% 11% 30% 24% 5%	523
	11th to 20th	Night	24% 13% 33% 25% 5% 1	420
	21st to end	Night	23% 9% 38% 20% 8% 1	420
July	1st to 10th	Night	19% 9% 40% 25% 6%	390
	11th to 20th	Night	23% 7% 33% 24% 11%	435
	21st to end	Night	19% 9% 35% 32% 5%	656
August	1st to 10th	Night	19% 8% 34% 31% 8% 1	598
	11th to 20th	Night	20% 9% 29% 30% 11% 1	592
	21st to end	Night	18% 8% 33% 30% 10%	660
September	1st to 10th	Night	18% 10% 34% 28% 10% 1	600
	11th to 20th	Night	21% 10% 26% 29% 12% 1	785
	21st to end	Night	23% 12% 30% 24% 10% 1	800
October	1st to 10th	Night	23% 11% 27% 28% 10% 1	800
	11th to 20th	Night	25% 19% 28% 19% 8% 1	800
	21st to end	Night	37% 20% 22% 16% 5%	880
November	1st to 10th	Night	35% 18% 25% 17% 5% 1	864
	11th to 20th	Night	36% 23% 21% 15% 5%	950
	21st to end	Night	38% 21% 23% 14% 3	950
December	1st to 10th	Night	40% 21% 25% 12% 2	950
	11th to 20th	Night	40% 27% 23% 9% 2	950
	21st to end	Night	41% 24% 22% 12% 2	1045

Page generated at 2026-06-28 03:10:48. Version ac07

Copyright © 2026 Attilla Danko.