Keswick Observing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Keswick Observing Site clear sky chart from 2005-11-06 to 2025-02-06.

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	13% 10% 4 9% 6% 5% 5% 4 6% 7% 31%	109115
	Night	14% 11% 4 10% 6% 5% 5% 4 5% 7% 30%	109091
Transparency	Day	51% 5% 12% 21% 10% 1	112751
	Night	52% 5% 12% 20% 10% 1	113620
Seeing	Day	17% 9% 28% 26% 15% 5%	14987
	Night	19% 8% 29% 30% 12% 1	24119

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	12% 12% 4 15% 6% 6% 5% 4 5% 6% 24%	3597
	11th to 20th	Day	7% 15% 7% 19% 10% 9% 6% 4 6% 5% 12%	3858
	21st to end	Day	13% 16% 6% 14% 8% 7% 5% 5% 6% 6% 14%	4466
February	1st to 10th	Day	12% 15% 6% 13% 8% 7% 6% 5% 5% 5% 18%	1755
	11th to 20th	Day	11% 13% 6% 13% 8% 6% 5% 4 5% 6% 24%	1663
	21st to end	Day	15% 13% 5% 11% 6% 6% 4 4 6% 6% 23%	1451
March	1st to 10th	Day	16% 12% 5% 9% 6% 4 4 3 5% 5% 31%	3432
	11th to 20th	Day	9% 14% 6% 11% 5% 7% 6% 4 5% 5% 27%	3480
	21st to end	Day	14% 8% 3 10% 6% 5% 4 4 4 5% 36%	3815
April	1st to 10th	Day	16% 13% 3 9% 6% 5% 4 4 5% 5% 29%	2247
	11th to 20th	Day	19% 10% 2 6% 5% 4 4 3 5% 6% 36%	2337
	21st to end	Day	19% 9% 3 8% 6% 4 3 3 5% 6% 35%	2470
May	1st to 10th	Day	14% 8% 3 8% 5% 4 4 4 5% 7% 36%	4126
	11th to 20th	Day	15% 9% 3 8% 4 5% 4 4 6% 8% 35%	4398
	21st to end	Day	11% 6% 2 6% 4 4 4 3 6% 8% 45%	4837
June	1st to 10th	Day	16% 7% 3 6% 5% 4 5% 4 7% 7% 37%	2660
	11th to 20th	Day	11% 5% 2 7% 4 4 5% 5% 7% 9% 41%	2723
	21st to end	Day	14% 7% 2 6% 5% 5% 4 4 6% 8% 39%	2850
July	1st to 10th	Day	11% 5% 2 6% 6% 5% 6% 5% 7% 9% 37%	4646
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 5% 7% 9% 42%	4440
	21st to end	Day	8% 6% 2 7% 5% 5% 5% 4 6% 9% 43%	4547
August	1st to 10th	Day	13% 8% 3 6% 4 5% 5% 4 6% 8% 38%	4104
	11th to 20th	Day	12% 7% 2 8% 4 4 5% 4 7% 10% 37%	4044
	21st to end	Day	9% 6% 2 6% 4 4 5% 4 7% 8% 44%	4374
September	1st to 10th	Day	14% 6% 2 6% 4 5% 5% 4 5% 8% 41%	2280
	11th to 20th	Day	12% 6% 2 6% 4 5% 4 4 6% 8% 43%	2171
	21st to end	Day	14% 7% 2 7% 5% 6% 5% 4 6% 7% 36%	2049
October	1st to 10th	Day	18% 9% 2 8% 5% 4 4 4 5% 7% 34%	1900
	11th to 20th	Day	19% 10% 4 10% 6% 5% 4 5% 6% 6% 27%	1900
	21st to end	Day	24% 13% 4 10% 6% 4 5% 3 5% 5% 21%	2090
November	1st to 10th	Day	14% 13% 4 9% 7% 5% 4 4 7% 7% 28%	1659
	11th to 20th	Day	13% 16% 4 10% 7% 6% 5% 4 6% 6% 22%	1600
	21st to end	Day	17% 18% 5% 11% 7% 6% 5% 4 5% 5% 16%	1600
December	1st to 10th	Day	15% 22% 7% 17% 8% 6% 4 4 4 4 9%	2600
	11th to 20th	Day	15% 18% 5% 10% 6% 6% 5% 4 4 5% 19%	2986
	21st to end	Day	22% 15% 7% 16% 6% 6% 5% 3 4 5% 11%	3960
January	1st to 10th	Night	12% 14% 6% 17% 7% 5% 5% 4 5% 7% 18%	6349
	11th to 20th	Night	11% 12% 6% 16% 10% 8% 7% 4 5% 5% 14%	6025
	21st to end	Night	13% 13% 6% 13% 8% 6% 6% 5% 6% 6% 18%	6490
February	1st to 10th	Night	12% 16% 5% 12% 8% 7% 5% 4 6% 6% 19%	2536
	11th to 20th	Night	12% 15% 5% 11% 7% 6% 5% 5% 6% 6% 23%	2403
	21st to end	Night	14% 11% 4 13% 7% 6% 5% 4 6% 6% 25%	1996
March	1st to 10th	Night	16% 11% 4 9% 6% 5% 4 3 5% 6% 31%	3408
	11th to 20th	Night	12% 11% 4 10% 5% 4 5% 4 5% 7% 33%	3479
	21st to end	Night	14% 7% 4 10% 6% 6% 5% 4 5% 6% 33%	3817
April	1st to 10th	Night	18% 12% 3 8% 5% 5% 5% 4 5% 6% 30%	1933
	11th to 20th	Night	17% 8% 3 6% 5% 4 4 4 5% 8% 36%	1806
	21st to end	Night	16% 9% 4 9% 5% 4 4 3 4 6% 35%	1710
May	1st to 10th	Night	16% 7% 2 6% 5% 4 4 3 5% 8% 39%	2815
	11th to 20th	Night	14% 8% 2 6% 4 4 5% 4 7% 8% 38%	2495
	21st to end	Night	9% 5% 2 6% 3 3 4 4 6% 8% 50%	2738
June	1st to 10th	Night	13% 7% 2 6% 5% 5% 5% 4 6% 8% 39%	1520
	11th to 20th	Night	9% 4 2 6% 5% 6% 5% 4 7% 8% 43%	1449
	21st to end	Night	10% 6% 3 7% 5% 5% 4 4 5% 9% 42%	1330
July	1st to 10th	Night	5% 5% 3 6% 5% 5% 5% 4 6% 7% 50%	2303
	11th to 20th	Night	12% 5% 2 4 4 3 4 4 5% 8% 50%	2520
	21st to end	Night	7% 5% 2 5% 3 4 5% 4 7% 9% 48%	2989
August	1st to 10th	Night	10% 6% 3 5% 4 5% 4 4 6% 9% 46%	2825
	11th to 20th	Night	13% 5% 2 6% 3 4 4 3 6% 8% 46%	2785
	21st to end	Night	9% 6% 2 6% 4 4 5% 4 6% 8% 45%	3248
September	1st to 10th	Night	10% 6% 2 6% 4 4 4 4 6% 8% 45%	1900
	11th to 20th	Night	11% 5% 2 6% 3 3 3 3 5% 8% 50%	2005
	21st to end	Night	16% 7% 3 6% 5% 4 3 3 6% 5% 42%	2130
October	1st to 10th	Night	16% 8% 3 7% 4 5% 5% 4 5% 7% 36%	2280
	11th to 20th	Night	17% 10% 4 8% 6% 5% 5% 3 5% 6% 31%	2280
	21st to end	Night	21% 11% 4 8% 6% 5% 4 4 6% 6% 24%	2508
November	1st to 10th	Night	17% 9% 4 9% 5% 4 5% 4 5% 7% 32%	2635
	11th to 20th	Night	15% 16% 5% 10% 6% 5% 4 4 5% 7% 24%	2800
	21st to end	Night	18% 16% 5% 10% 6% 6% 5% 4 6% 6% 20%	2800
December	1st to 10th	Night	14% 19% 7% 15% 8% 6% 6% 4 5% 5% 13%	4580
	11th to 20th	Night	14% 15% 6% 14% 7% 6% 6% 5% 6% 5% 16%	5208
	21st to end	Night	21% 18% 6% 16% 6% 5% 5% 3 4 5% 11%	6996

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	59% 4 13% 15% 8%	3598
	11th to 20th	Day	71% 6% 10% 9% 4	3892
	21st to end	Day	68% 5% 10% 10% 7%	4466
February	1st to 10th	Day	67% 5% 9% 15% 4	1755
	11th to 20th	Day	61% 4 10% 17% 7% 1	1672
	21st to end	Day	61% 4 10% 17% 7%	1451
March	1st to 10th	Day	56% 3 13% 18% 10%	3435
	11th to 20th	Day	59% 4 10% 18% 8% 1	3480
	21st to end	Day	50% 4 9% 20% 15% 2	3815
April	1st to 10th	Day	56% 4 9% 19% 10% 1	2247
	11th to 20th	Day	49% 4 10% 22% 14% 1	2337
	21st to end	Day	51% 4 11% 19% 13% 3	2470
May	1st to 10th	Day	48% 3 11% 23% 13% 2	4138
	11th to 20th	Day	48% 4 14% 23% 10% 1	4402
	21st to end	Day	38% 3 14% 24% 17% 3	4837
June	1st to 10th	Day	45% 5% 12% 23% 14% 1	2660
	11th to 20th	Day	39% 5% 13% 26% 16% 1	2723
	21st to end	Day	43% 5% 13% 24% 14% 1	2850
July	1st to 10th	Day	41% 6% 16% 22% 14% 1	4575
	11th to 20th	Day	35% 7% 14% 34% 10% 1	4365
	21st to end	Day	37% 6% 12% 28% 16% 1	4402
August	1st to 10th	Day	43% 5% 15% 24% 12% 1	4091
	11th to 20th	Day	41% 6% 18% 26% 9%	4083
	21st to end	Day	35% 6% 14% 32% 12% 1	4374
September	1st to 10th	Day	41% 6% 12% 29% 11% 2	2280
	11th to 20th	Day	38% 5% 13% 30% 13% 1	2171
	21st to end	Day	46% 5% 13% 26% 9%	2049
October	1st to 10th	Day	43% 6% 13% 26% 12% 1	3160
	11th to 20th	Day	46% 6% 14% 22% 12%	3140
	21st to end	Day	57% 6% 15% 18% 4	3428
November	1st to 10th	Day	54% 5% 14% 19% 7% 1	1659
	11th to 20th	Day	60% 5% 13% 13% 8% 1	1600
	21st to end	Day	69% 6% 10% 13% 2	1600
December	1st to 10th	Day	78% 6% 8% 7% 1	2600
	11th to 20th	Day	66% 7% 9% 10% 7%	2986
	21st to end	Day	76% 5% 8% 8% 4	3960
January	1st to 10th	Night	65% 4 11% 15% 4	6349
	11th to 20th	Night	69% 5% 11% 10% 5%	6066
	21st to end	Night	63% 7% 11% 11% 8% 1	6490
February	1st to 10th	Night	64% 5% 10% 17% 4	2536
	11th to 20th	Night	60% 5% 10% 18% 7%	2405
	21st to end	Night	59% 3 12% 18% 8% 1	1996
March	1st to 10th	Night	55% 2 11% 22% 8% 1	3418
	11th to 20th	Night	50% 4 14% 22% 9% 1	3480
	21st to end	Night	49% 5% 9% 21% 14% 1	3817
April	1st to 10th	Night	55% 4 9% 20% 12% 1	1933
	11th to 20th	Night	47% 5% 8% 22% 16% 2	1806
	21st to end	Night	50% 4 9% 18% 16% 2	1710
May	1st to 10th	Night	45% 3 13% 19% 17% 3	2822
	11th to 20th	Night	44% 4 14% 25% 12% 2	2496
	21st to end	Night	34% 3 14% 27% 19% 2	2739
June	1st to 10th	Night	42% 4 11% 26% 15% 2	1520
	11th to 20th	Night	37% 6% 11% 24% 21% 2	1449
	21st to end	Night	40% 5% 13% 26% 15% 1	1330
July	1st to 10th	Night	32% 5% 16% 27% 18% 2	2265
	11th to 20th	Night	33% 5% 13% 35% 14% 1	2472
	21st to end	Night	31% 7% 13% 32% 15% 1	2894
August	1st to 10th	Night	35% 4 15% 28% 16% 1	2814
	11th to 20th	Night	35% 5% 19% 28% 12% 1	2812
	21st to end	Night	35% 6% 15% 32% 12% 1	3248
September	1st to 10th	Night	37% 5% 15% 29% 13% 1	1900
	11th to 20th	Night	32% 5% 13% 32% 17%	2005
	21st to end	Night	44% 4 13% 28% 11%	2130
October	1st to 10th	Night	35% 6% 12% 26% 21% 1	3800
	11th to 20th	Night	48% 4 15% 22% 11%	3779
	21st to end	Night	47% 7% 16% 24% 7%	4120
November	1st to 10th	Night	51% 5% 12% 22% 9% 1	2635
	11th to 20th	Night	59% 5% 12% 15% 7% 1	2800
	21st to end	Night	64% 5% 15% 14% 2	2800
December	1st to 10th	Night	72% 6% 11% 9% 2	4580
	11th to 20th	Night	66% 7% 10% 11% 5%	5208
	21st to end	Night	76% 5% 9% 8% 3	6996

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	15% 14% 40% 21% 10% 1	200
	11th to 20th	Day	18% 12% 42% 20% 6% 2	263
	21st to end	Day	20% 13% 35% 25% 6% 1	330
February	1st to 10th	Day	18% 14% 44% 17% 6% 1	285
	11th to 20th	Day	16% 18% 40% 24% 2	270
	21st to end	Day	24% 19% 32% 23% 2	235
March	1st to 10th	Day	19% 10% 38% 25% 8%	460
	11th to 20th	Day	17% 14% 36% 25% 8% 1	460
	21st to end	Day	25% 8% 33% 23% 10% 1	506
April	1st to 10th	Day	20% 13% 32% 23% 10% 2	460
	11th to 20th	Day	27% 10% 28% 19% 12% 5%	452
	21st to end	Day	22% 10% 27% 26% 11% 4	460
May	1st to 10th	Day	17% 6% 26% 30% 15% 5%	463
	11th to 20th	Day	17% 5% 22% 30% 19% 7%	487
	21st to end	Day	14% 5% 22% 30% 21% 7%	529
June	1st to 10th	Day	16% 6% 25% 29% 20% 3	490
	11th to 20th	Day	13% 7% 23% 31% 21% 5%	553
	21st to end	Day	16% 7% 25% 31% 16% 4	680
July	1st to 10th	Day	10% 4 21% 31% 27% 7%	612
	11th to 20th	Day	12% 3 21% 28% 26% 10%	484
	21st to end	Day	10% 4 17% 37% 23% 10%	532
August	1st to 10th	Day	12% 4 17% 28% 28% 12%	486
	11th to 20th	Day	10% 4 16% 28% 28% 14%	479
	21st to end	Day	12% 4 22% 28% 23% 10%	539
September	1st to 10th	Day	13% 7% 20% 24% 24% 11%	490
	11th to 20th	Day	10% 4 17% 26% 25% 19%	490
	21st to end	Day	14% 7% 26% 24% 20% 9%	490
October	1st to 10th	Day	20% 7% 28% 22% 15% 8%	490
	11th to 20th	Day	22% 10% 35% 23% 8% 2	490
	21st to end	Day	29% 10% 32% 22% 7% 1	539
November	1st to 10th	Day	21% 17% 30% 20% 11% 2	263
	11th to 20th	Day	21% 20% 33% 20% 5% 2	200
	21st to end	Day	25% 16% 37% 19% 4	200
December	1st to 10th	Day	20% 17% 39% 20% 5% 1	200
	11th to 20th	Day	21% 21% 36% 16% 6% 1	200
	21st to end	Day	26% 9% 40% 19% 5%	220
January	1st to 10th	Night	20% 13% 40% 19% 7% 1	800
	11th to 20th	Night	23% 10% 34% 25% 7% 1	800
	21st to end	Night	19% 8% 33% 31% 8% 1	880
February	1st to 10th	Night	19% 10% 41% 25% 4	781
	11th to 20th	Night	20% 10% 37% 28% 4	743
	21st to end	Night	19% 10% 37% 28% 5%	628
March	1st to 10th	Night	18% 9% 36% 30% 6%	760
	11th to 20th	Night	18% 11% 37% 27% 7% 1	760
	21st to end	Night	20% 8% 32% 29% 11%	836
April	1st to 10th	Night	23% 9% 33% 29% 6%	760
	11th to 20th	Night	20% 7% 32% 29% 10% 2	682
	21st to end	Night	21% 7% 29% 30% 13%	570
May	1st to 10th	Night	18% 3 24% 37% 16% 2	565
	11th to 20th	Night	16% 4 25% 40% 14% 1	374
	21st to end	Night	11% 4 22% 40% 21% 1	411
June	1st to 10th	Night	14% 6% 27% 38% 14% 1	380
	11th to 20th	Night	8% 7% 23% 45% 16% 1	380
	21st to end	Night	14% 3 22% 41% 19% 1	380
July	1st to 10th	Night	8% 3 16% 48% 24% 1	370
	11th to 20th	Night	12% 3 20% 41% 22% 2	368
	21st to end	Night	9% 3 17% 44% 25% 1	565
August	1st to 10th	Night	11% 2 14% 42% 29% 2	567
	11th to 20th	Night	7% 3 15% 37% 34% 4	564
	21st to end	Night	12% 4 20% 35% 27% 3	699
September	1st to 10th	Night	12% 5% 22% 34% 21% 6%	760
	11th to 20th	Night	14% 3 19% 31% 25% 8%	760
	21st to end	Night	19% 6% 20% 31% 19% 5%	760
October	1st to 10th	Night	18% 6% 28% 28% 18% 2	760
	11th to 20th	Night	23% 11% 29% 28% 9% 1	760
	21st to end	Night	26% 11% 31% 25% 6%	836
November	1st to 10th	Night	23% 11% 28% 26% 11% 1	780
	11th to 20th	Night	23% 14% 33% 21% 8% 1	800
	21st to end	Night	27% 13% 33% 23% 4	800
December	1st to 10th	Night	26% 13% 38% 18% 4 1	800
	11th to 20th	Night	22% 14% 38% 21% 5% 1	800
	21st to end	Night	28% 11% 35% 22% 4	880

Page generated at 2025-02-03 03:05:53. Version ac07

Copyright © 2025 Attilla Danko.