Sheerness Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sheerness Lake clear sky chart from 2005-11-06 to 2026-02-16.

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	7% 8% 3 8% 5% 5% 5% 4 6% 8% 39%	134687
	Night	6% 8% 3 9% 6% 6% 6% 5% 7% 9% 36%	134877
Transparency	Day	40% 7% 16% 25% 10% 1	134384
	Night	43% 7% 16% 23% 10% 1	134760
Seeing	Day	10% 7% 26% 31% 20% 6%	17068
	Night	10% 6% 30% 37% 15% 2	26378

By Month

Percentage Cloud Cover NW (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	4 13% 6% 14% 8% 6% 7% 4 6% 7% 26%	4125
	11th to 20th	Day	2 7% 4 12% 7% 6% 6% 7% 9% 8% 32%	4119
	21st to end	Day	2 8% 4 10% 6% 5% 5% 5% 7% 9% 38%	4924
February	1st to 10th	Day	6% 12% 5% 12% 8% 8% 4 4 6% 8% 27%	1759
	11th to 20th	Day	4 12% 4 12% 7% 6% 7% 6% 8% 9% 25%	1800
	21st to end	Day	3 13% 4 11% 8% 7% 8% 5% 7% 8% 26%	1501
March	1st to 10th	Day	3 8% 4 11% 8% 6% 5% 3 6% 10% 36%	4639
	11th to 20th	Day	5% 9% 4 10% 6% 5% 5% 4 6% 8% 37%	4999
	21st to end	Day	7% 15% 6% 12% 6% 5% 5% 4 6% 7% 28%	5486
April	1st to 10th	Day	8% 12% 3 8% 7% 6% 6% 4 7% 7% 33%	2470
	11th to 20th	Day	10% 10% 4 9% 6% 5% 5% 4 6% 8% 32%	2570
	21st to end	Day	12% 9% 3 9% 6% 6% 5% 4 7% 9% 32%	2600
May	1st to 10th	Day	13% 9% 3 6% 5% 4 4 3 5% 6% 40%	6244
	11th to 20th	Day	10% 9% 4 9% 7% 6% 6% 5% 7% 8% 27%	6733
	21st to end	Day	9% 7% 3 8% 5% 5% 5% 5% 6% 7% 40%	7405
June	1st to 10th	Day	14% 7% 2 6% 5% 5% 5% 5% 7% 9% 35%	3000
	11th to 20th	Day	16% 9% 3 8% 6% 5% 5% 5% 6% 8% 29%	3000
	21st to end	Day	8% 5% 2 6% 5% 5% 5% 4 8% 10% 43%	3000
July	1st to 10th	Day	6% 5% 2 5% 4 4 5% 4 7% 9% 50%	6780
	11th to 20th	Day	9% 5% 2 6% 4 4 5% 4 7% 10% 45%	6780
	21st to end	Day	6% 4 2 4 4 4 4 4 6% 8% 54%	7376
August	1st to 10th	Day	7% 5% 2 6% 4 5% 5% 4 6% 9% 47%	4560
	11th to 20th	Day	5% 4 2 5% 4 5% 4 4 6% 11% 50%	4158
	21st to end	Day	7% 4 2 4 3 3 3 3 7% 9% 54%	4664
September	1st to 10th	Day	9% 6% 2 5% 4 4 3 4 5% 7% 51%	2510
	11th to 20th	Day	13% 7% 2 6% 3 3 4 3 5% 8% 44%	2210
	21st to end	Day	7% 5% 2 6% 3 4 4 4 6% 9% 49%	2200
October	1st to 10th	Day	5% 5% 3 7% 4 6% 5% 4 6% 8% 47%	3318
	11th to 20th	Day	4 5% 3 7% 4 5% 6% 5% 7% 10% 44%	3161
	21st to end	Day	6% 7% 3 6% 4 5% 5% 4 6% 8% 45%	3141
November	1st to 10th	Day	8% 15% 5% 12% 7% 6% 4 4 6% 7% 27%	1648
	11th to 20th	Day	5% 10% 3 11% 7% 6% 6% 4 7% 8% 33%	1680
	21st to end	Day	5% 13% 3 9% 7% 6% 6% 4 6% 9% 31%	1480
December	1st to 10th	Day	7% 13% 5% 10% 7% 6% 6% 5% 7% 7% 26%	2360
	11th to 20th	Day	5% 11% 6% 15% 7% 6% 6% 4 6% 9% 24%	2712
	21st to end	Day	3 6% 3 11% 7% 5% 6% 4 6% 8% 41%	3575
January	1st to 10th	Night	4 10% 5% 14% 9% 8% 7% 5% 7% 7% 23%	8768
	11th to 20th	Night	2 6% 3 10% 7% 5% 6% 5% 7% 10% 38%	8779
	21st to end	Night	3 7% 3 10% 6% 6% 7% 5% 7% 9% 36%	9312
February	1st to 10th	Night	6% 10% 4 11% 7% 5% 6% 5% 7% 9% 31%	2860
	11th to 20th	Night	4 12% 4 11% 7% 6% 7% 5% 8% 8% 28%	2597
	21st to end	Night	4 9% 3 10% 8% 5% 7% 5% 8% 9% 32%	2125
March	1st to 10th	Night	2 7% 3 11% 9% 6% 7% 5% 8% 10% 31%	5255
	11th to 20th	Night	5% 8% 3 9% 6% 6% 7% 6% 9% 9% 34%	5000
	21st to end	Night	7% 15% 6% 17% 8% 6% 6% 4 6% 7% 19%	5489
April	1st to 10th	Night	8% 8% 4 11% 7% 6% 5% 4 6% 7% 33%	1927
	11th to 20th	Night	7% 10% 4 11% 6% 5% 6% 4 6% 7% 32%	1781
	21st to end	Night	9% 9% 3 7% 6% 5% 5% 4 7% 10% 36%	1800
May	1st to 10th	Night	15% 10% 3 7% 4 4 5% 4 6% 7% 35%	3720
	11th to 20th	Night	10% 7% 3 8% 7% 6% 7% 6% 9% 9% 29%	3159
	21st to end	Night	10% 7% 3 10% 6% 6% 5% 4 6% 8% 34%	3470
June	1st to 10th	Night	14% 8% 3 7% 6% 6% 5% 4 6% 9% 32%	1400
	11th to 20th	Night	13% 7% 4 7% 6% 5% 6% 6% 7% 9% 30%	1400
	21st to end	Night	10% 5% 2 5% 6% 5% 5% 3 7% 9% 44%	1400
July	1st to 10th	Night	5% 3 2 6% 5% 5% 5% 4 7% 10% 48%	3180
	11th to 20th	Night	7% 4 2 6% 5% 5% 6% 5% 7% 12% 42%	3180
	21st to end	Night	8% 4 2 5% 4 4 4 4 6% 9% 49%	3467
August	1st to 10th	Night	7% 5% 3 6% 4 5% 5% 4 6% 9% 46%	2590
	11th to 20th	Night	4 3 2 6% 5% 5% 5% 5% 7% 12% 45%	2901
	21st to end	Night	7% 3 1 4 3 3 4 3 6% 10% 54%	3245
September	1st to 10th	Night	8% 5% 2 6% 4 4 4 5% 6% 8% 49%	1890
	11th to 20th	Night	12% 7% 2 6% 3 3 4 3 5% 8% 47%	2186
	21st to end	Night	6% 6% 2 5% 4 4 4 3 7% 9% 50%	2200
October	1st to 10th	Night	6% 7% 2 7% 5% 4 5% 4 6% 8% 45%	3873
	11th to 20th	Night	4 5% 2 7% 4 4 5% 4 7% 9% 47%	3986
	21st to end	Night	5% 7% 2 7% 5% 5% 5% 5% 7% 9% 41%	4627
November	1st to 10th	Night	8% 11% 4 9% 6% 6% 5% 5% 6% 8% 32%	2870
	11th to 20th	Night	4 9% 4 9% 7% 6% 6% 6% 7% 9% 34%	2940
	21st to end	Night	5% 11% 3 10% 7% 7% 6% 5% 7% 9% 31%	3137
December	1st to 10th	Night	6% 12% 5% 13% 7% 6% 6% 5% 7% 8% 24%	5040
	11th to 20th	Night	5% 12% 5% 13% 8% 6% 6% 5% 8% 8% 23%	5700
	21st to end	Night	3 6% 2 9% 7% 6% 6% 5% 6% 7% 42%	7623

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	57% 5% 10% 18% 9%	4125
	11th to 20th	Day	45% 7% 15% 13% 18% 2	4140
	21st to end	Day	39% 7% 20% 26% 7%	4925
February	1st to 10th	Day	54% 6% 13% 17% 9% 1	1759
	11th to 20th	Day	51% 10% 14% 16% 10%	1809
	21st to end	Day	52% 8% 11% 19% 10%	1501
March	1st to 10th	Day	43% 6% 17% 24% 10%	4639
	11th to 20th	Day	43% 6% 16% 22% 13%	5000
	21st to end	Day	53% 8% 13% 19% 7%	5486
April	1st to 10th	Day	46% 8% 16% 21% 9%	2470
	11th to 20th	Day	47% 7% 14% 22% 8% 1	2570
	21st to end	Day	46% 8% 15% 23% 7% 1	2600
May	1st to 10th	Day	43% 6% 10% 22% 14% 5%	6244
	11th to 20th	Day	48% 10% 13% 22% 7%	6737
	21st to end	Day	39% 9% 15% 27% 10% 1	7406
June	1st to 10th	Day	42% 9% 17% 21% 10% 1	3000
	11th to 20th	Day	50% 8% 15% 20% 7% 1	3000
	21st to end	Day	33% 10% 23% 26% 8% 1	3000
July	1st to 10th	Day	28% 7% 18% 31% 15% 1	6706
	11th to 20th	Day	33% 7% 19% 28% 12% 1	6699
	21st to end	Day	26% 6% 18% 30% 17% 4	7169
August	1st to 10th	Day	32% 7% 18% 32% 10% 1	4542
	11th to 20th	Day	27% 8% 23% 35% 8% 1	4197
	21st to end	Day	25% 6% 22% 35% 12% 1	4663
September	1st to 10th	Day	32% 6% 15% 28% 13% 5%	2510
	11th to 20th	Day	38% 5% 16% 30% 10% 1	2210
	21st to end	Day	31% 8% 15% 31% 12% 3	2200
October	1st to 10th	Day	34% 6% 20% 30% 10%	3318
	11th to 20th	Day	34% 6% 18% 31% 10% 1	3161
	21st to end	Day	36% 5% 13% 34% 11% 1	3141
November	1st to 10th	Day	56% 6% 13% 17% 7% 1	1648
	11th to 20th	Day	49% 7% 17% 20% 7% 1	1680
	21st to end	Day	49% 7% 16% 21% 7%	1480
December	1st to 10th	Day	54% 7% 18% 17% 3 1	2360
	11th to 20th	Day	56% 7% 15% 18% 3 1	2714
	21st to end	Day	40% 5% 11% 26% 15% 3	3575
January	1st to 10th	Night	56% 8% 12% 14% 9% 1	8769
	11th to 20th	Night	40% 5% 18% 20% 14% 2	8820
	21st to end	Night	42% 7% 18% 24% 8%	9312
February	1st to 10th	Night	48% 7% 14% 19% 12%	2860
	11th to 20th	Night	50% 9% 13% 17% 12% 1	2598
	21st to end	Night	44% 8% 14% 21% 11% 1	2125
March	1st to 10th	Night	42% 7% 21% 21% 9%	5255
	11th to 20th	Night	41% 8% 17% 26% 8% 1	5000
	21st to end	Night	61% 9% 10% 12% 6% 1	5489
April	1st to 10th	Night	47% 7% 15% 19% 12%	1927
	11th to 20th	Night	48% 6% 12% 22% 11% 1	1781
	21st to end	Night	41% 9% 13% 26% 11% 2	1800
May	1st to 10th	Night	46% 6% 8% 24% 13% 3	3718
	11th to 20th	Night	43% 10% 17% 22% 7% 1	3159
	21st to end	Night	44% 10% 14% 24% 7% 1	3470
June	1st to 10th	Night	46% 9% 13% 21% 10% 1	1400
	11th to 20th	Night	46% 10% 16% 18% 8% 1	1400
	21st to end	Night	35% 8% 20% 28% 9% 1	1400
July	1st to 10th	Night	30% 7% 22% 22% 17% 1	3145
	11th to 20th	Night	33% 8% 18% 31% 9% 1	3138
	21st to end	Night	31% 6% 17% 28% 16% 2	3369
August	1st to 10th	Night	34% 7% 18% 29% 11% 1	2583
	11th to 20th	Night	29% 7% 17% 38% 8% 1	2928
	21st to end	Night	25% 5% 18% 36% 14% 2	3245
September	1st to 10th	Night	31% 9% 16% 23% 15% 7%	1890
	11th to 20th	Night	35% 6% 15% 28% 13% 3	2186
	21st to end	Night	30% 7% 17% 29% 16% 2	2200
October	1st to 10th	Night	35% 5% 19% 27% 13% 1	3873
	11th to 20th	Night	31% 5% 17% 33% 13% 2	3986
	21st to end	Night	37% 6% 15% 33% 8% 1	4627
November	1st to 10th	Night	48% 8% 13% 20% 10% 1	2870
	11th to 20th	Night	44% 9% 17% 19% 10%	2940
	21st to end	Night	48% 9% 17% 19% 6% 1	3137
December	1st to 10th	Night	56% 8% 16% 15% 4 1	5040
	11th to 20th	Night	56% 9% 18% 14% 4	5697
	21st to end	Night	39% 6% 11% 24% 17% 3	7623

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	7% 6% 33% 29% 19% 6%	220
	11th to 20th	Day	6% 11% 28% 34% 17% 4	220
	21st to end	Day	6% 9% 34% 28% 18% 5%	242
February	1st to 10th	Day	10% 9% 33% 31% 12% 4	261
	11th to 20th	Day	10% 8% 27% 37% 15% 3	315
	21st to end	Day	6% 8% 30% 30% 21% 6%	265
March	1st to 10th	Day	8% 11% 32% 29% 15% 4	500
	11th to 20th	Day	10% 6% 33% 31% 15% 5%	500
	21st to end	Day	9% 9% 34% 29% 15% 4	550
April	1st to 10th	Day	10% 13% 33% 28% 12% 5%	500
	11th to 20th	Day	12% 12% 30% 30% 13% 3	492
	21st to end	Day	12% 10% 29% 32% 14% 4	500
May	1st to 10th	Day	14% 8% 22% 31% 20% 5%	659
	11th to 20th	Day	10% 6% 23% 34% 21% 6%	725
	21st to end	Day	13% 6% 21% 28% 23% 8%	789
June	1st to 10th	Day	14% 10% 22% 33% 17% 5%	730
	11th to 20th	Day	16% 7% 29% 27% 18% 4	730
	21st to end	Day	10% 4 22% 32% 24% 8%	730
July	1st to 10th	Day	7% 3 19% 35% 27% 9%	721
	11th to 20th	Day	10% 5% 21% 34% 24% 7%	718
	21st to end	Day	4 4 18% 31% 32% 10%	794
August	1st to 10th	Day	10% 5% 14% 36% 24% 10%	592
	11th to 20th	Day	8% 3 20% 32% 29% 8%	517
	21st to end	Day	8% 7% 18% 28% 30% 10%	583
September	1st to 10th	Day	11% 8% 22% 28% 25% 6%	530
	11th to 20th	Day	16% 6% 19% 28% 25% 5%	530
	21st to end	Day	10% 11% 29% 30% 16% 4	530
October	1st to 10th	Day	16% 4 26% 30% 19% 5%	365
	11th to 20th	Day	10% 7% 35% 28% 17% 4	330
	21st to end	Day	9% 11% 36% 31% 11% 2	363
November	1st to 10th	Day	15% 9% 31% 30% 14% 2	330
	11th to 20th	Day	12% 10% 36% 29% 12% 2	330
	21st to end	Day	7% 6% 33% 33% 13% 8%	225
December	1st to 10th	Day	10% 6% 32% 32% 16% 3	220
	11th to 20th	Day	9% 12% 30% 35% 11% 2	220
	21st to end	Day	7% 7% 24% 36% 21% 5%	242
January	1st to 10th	Night	9% 6% 33% 36% 15% 1	1050
	11th to 20th	Night	9% 9% 33% 37% 12% 1	1050
	21st to end	Night	8% 10% 33% 35% 12% 2	1035
February	1st to 10th	Night	9% 8% 27% 37% 16% 3	840
	11th to 20th	Night	9% 6% 30% 38% 15% 1	804
	21st to end	Night	6% 4 25% 40% 21% 4	660
March	1st to 10th	Night	7% 5% 30% 40% 15% 3	800
	11th to 20th	Night	8% 5% 31% 40% 14% 3	800
	21st to end	Night	12% 7% 28% 35% 16% 2	880
April	1st to 10th	Night	10% 7% 31% 33% 16% 3	662
	11th to 20th	Night	12% 7% 33% 36% 11% 1	593
	21st to end	Night	13% 7% 27% 39% 14% 1	600
May	1st to 10th	Night	16% 7% 25% 36% 16% 2	599
	11th to 20th	Night	10% 4 28% 39% 19% 1	394
	21st to end	Night	17% 4 26% 29% 22% 2	433
June	1st to 10th	Night	16% 7% 29% 32% 14% 3	400
	11th to 20th	Night	14% 5% 31% 33% 18% 1	400
	21st to end	Night	12% 5% 22% 38% 22% 2	400
July	1st to 10th	Night	7% 2 21% 48% 21% 1	390
	11th to 20th	Night	9% 4 22% 44% 21% 1	388
	21st to end	Night	5% 3 24% 40% 26% 3	438
August	1st to 10th	Night	6% 4 23% 38% 24% 4	447
	11th to 20th	Night	7% 5% 19% 45% 23% 1	594
	21st to end	Night	9% 5% 21% 39% 25% 1	660
September	1st to 10th	Night	10% 4 23% 42% 20% 2	600
	11th to 20th	Night	16% 3 23% 37% 20% 1	786
	21st to end	Night	7% 6% 32% 38% 16% 2	800
October	1st to 10th	Night	13% 5% 28% 37% 17% 1	800
	11th to 20th	Night	9% 6% 32% 37% 14% 2	800
	21st to end	Night	10% 10% 33% 36% 12%	895
November	1st to 10th	Night	13% 7% 35% 35% 9% 1	1025
	11th to 20th	Night	8% 8% 38% 35% 8% 3	1050
	21st to end	Night	9% 6% 35% 38% 12% 2	1050
December	1st to 10th	Night	11% 8% 29% 35% 15% 2	1050
	11th to 20th	Night	9% 7% 37% 34% 11% 2	1050
	21st to end	Night	9% 4 33% 38% 13% 3	1155

Page generated at 2026-02-12 23:42:11. Version ac07

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