Morden
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Morden clear sky chart from 2005-11-06 to 2026-02-01.

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	10% 8% 3 8% 5% 5% 5% 4 6% 8% 37%	131536
	Night	8% 9% 4 9% 6% 5% 5% 4 6% 7% 37%	129241
Transparency	Day	44% 8% 15% 24% 9% 1	131243
	Night	45% 7% 14% 23% 10% 1	129116
Seeing	Day	14% 10% 31% 29% 13% 4	17887
	Night	14% 9% 33% 32% 11% 1	27946

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% 15% 7% 8% 6% 5% 8% 7% 21%	3249
	11th to 20th	Day	4 7% 3 13% 10% 9% 8% 10% 9% 8% 17%	3416
	21st to end	Day	5% 10% 5% 12% 7% 7% 7% 4 6% 7% 29%	4092
February	1st to 10th	Day	9% 12% 6% 9% 8% 7% 6% 4 7% 7% 26%	1690
	11th to 20th	Day	6% 9% 3 11% 7% 8% 8% 6% 8% 8% 26%	1754
	21st to end	Day	6% 9% 4 11% 9% 6% 7% 5% 7% 8% 28%	1622
March	1st to 10th	Day	9% 10% 4 8% 6% 5% 5% 4 6% 10% 34%	4539
	11th to 20th	Day	9% 11% 4 12% 9% 5% 5% 4 6% 8% 26%	4978
	21st to end	Day	9% 13% 5% 14% 7% 6% 5% 3 6% 6% 26%	5464
April	1st to 10th	Day	9% 13% 5% 9% 5% 4 4 4 5% 7% 35%	2435
	11th to 20th	Day	12% 12% 4 10% 5% 4 5% 4 6% 6% 31%	2572
	21st to end	Day	18% 10% 3 9% 5% 4 4 3 5% 6% 33%	2600
May	1st to 10th	Day	13% 7% 2 5% 3 3 3 3 6% 8% 45%	5918
	11th to 20th	Day	20% 9% 2 7% 4 4 5% 4 6% 8% 31%	6667
	21st to end	Day	13% 7% 3 7% 4 4 4 3 5% 6% 44%	7428
June	1st to 10th	Day	13% 7% 3 6% 5% 4 5% 5% 7% 9% 38%	3000
	11th to 20th	Day	13% 6% 2 6% 5% 5% 5% 5% 8% 8% 37%	3000
	21st to end	Day	11% 5% 2 6% 5% 5% 6% 5% 7% 9% 37%	3000
July	1st to 10th	Day	8% 4 2 5% 4 5% 5% 5% 8% 10% 44%	6800
	11th to 20th	Day	10% 5% 2 6% 4 4 5% 4 6% 8% 46%	6800
	21st to end	Day	7% 5% 2 6% 4 4 5% 4 7% 10% 45%	7094
August	1st to 10th	Day	8% 5% 2 7% 4 4 5% 4 6% 9% 45%	4433
	11th to 20th	Day	11% 4 2 5% 3 4 4 4 6% 8% 48%	4171
	21st to end	Day	9% 5% 2 6% 4 4 4 3 6% 8% 49%	4675
September	1st to 10th	Day	10% 5% 2 5% 4 4 4 3 5% 8% 50%	2450
	11th to 20th	Day	16% 7% 2 7% 4 3 4 4 5% 6% 42%	2200
	21st to end	Day	14% 6% 2 5% 4 4 4 3 5% 8% 46%	2200
October	1st to 10th	Day	11% 6% 2 5% 4 3 4 3 5% 6% 50%	3377
	11th to 20th	Day	10% 9% 3 7% 4 4 5% 4 6% 8% 39%	3121
	21st to end	Day	12% 11% 3 8% 4 4 4 4 6% 8% 35%	3190
November	1st to 10th	Day	13% 14% 4 10% 6% 5% 4 4 5% 6% 30%	1744
	11th to 20th	Day	9% 13% 5% 13% 8% 5% 4 4 4 6% 29%	1680
	21st to end	Day	10% 15% 4 12% 8% 5% 4 3 5% 6% 27%	1533
December	1st to 10th	Day	9% 12% 6% 15% 10% 9% 6% 4 6% 6% 18%	2360
	11th to 20th	Day	8% 13% 4 13% 8% 6% 5% 5% 5% 6% 27%	2709
	21st to end	Day	7% 10% 4 14% 9% 6% 5% 3 5% 6% 31%	3575
January	1st to 10th	Night	4 11% 5% 16% 9% 7% 7% 5% 7% 6% 24%	6937
	11th to 20th	Night	4 11% 5% 12% 8% 8% 10% 8% 7% 6% 22%	6704
	21st to end	Night	7% 15% 7% 13% 6% 5% 6% 4 5% 6% 27%	7128
February	1st to 10th	Night	7% 12% 5% 10% 7% 7% 6% 5% 6% 5% 29%	2711
	11th to 20th	Night	5% 9% 4 9% 5% 6% 7% 5% 7% 9% 35%	2533
	21st to end	Night	7% 11% 4 9% 6% 6% 5% 3 7% 7% 35%	2025
March	1st to 10th	Night	7% 11% 3 8% 6% 5% 5% 4 6% 7% 38%	5333
	11th to 20th	Night	8% 9% 4 9% 7% 6% 6% 4 6% 7% 34%	4980
	21st to end	Night	9% 13% 6% 14% 6% 5% 4 3 5% 5% 31%	5467
April	1st to 10th	Night	8% 9% 3 7% 5% 4 5% 4 6% 8% 41%	1961
	11th to 20th	Night	12% 12% 5% 8% 4 4 6% 4 5% 5% 35%	1779
	21st to end	Night	14% 10% 2 7% 5% 5% 5% 4 5% 7% 37%	1800
May	1st to 10th	Night	16% 6% 2 5% 5% 4 4 3 5% 7% 42%	4062
	11th to 20th	Night	16% 9% 2 7% 5% 4 5% 5% 6% 7% 36%	3234
	21st to end	Night	13% 6% 2 5% 3 3 3 3 5% 6% 51%	3470
June	1st to 10th	Night	10% 5% 2 5% 6% 5% 4 5% 7% 8% 45%	1400
	11th to 20th	Night	12% 5% 2 6% 5% 3 4 4 7% 9% 45%	1400
	21st to end	Night	10% 5% 2 5% 4 4 4 4 8% 8% 46%	1400
July	1st to 10th	Night	6% 4 2 4 3 4 3 4 6% 9% 54%	3180
	11th to 20th	Night	6% 4 2 5% 3 3 4 3 6% 9% 54%	3180
	21st to end	Night	5% 4 1 5% 4 4 5% 5% 7% 10% 49%	3756
August	1st to 10th	Night	5% 4 2 5% 4 4 4 4 7% 8% 53%	2725
	11th to 20th	Night	8% 3 2 5% 3 4 4 4 6% 10% 50%	2888
	21st to end	Night	9% 4 2 5% 3 4 4 4 5% 7% 53%	3234
September	1st to 10th	Night	9% 4 2 5% 3 3 3 3 5% 7% 55%	1948
	11th to 20th	Night	13% 5% 1 5% 3 3 4 3 6% 8% 49%	2200
	21st to end	Night	14% 5% 3 6% 3 4 4 3 5% 7% 46%	2200
October	1st to 10th	Night	11% 6% 2 5% 4 4 4 4 4 7% 50%	3770
	11th to 20th	Night	10% 8% 3 6% 5% 4 5% 3 5% 8% 43%	4019
	21st to end	Night	8% 10% 3 7% 6% 5% 4 3 6% 7% 41%	4610
November	1st to 10th	Night	12% 10% 4 9% 6% 4 5% 5% 6% 7% 32%	2772
	11th to 20th	Night	9% 15% 5% 10% 6% 4 4 4 6% 6% 31%	2940
	21st to end	Night	10% 13% 4 12% 7% 5% 4 4 5% 7% 30%	3082
December	1st to 10th	Night	7% 13% 5% 16% 11% 7% 6% 4 5% 6% 21%	5050
	11th to 20th	Night	7% 14% 5% 15% 7% 7% 6% 4 5% 5% 24%	5718
	21st to end	Night	8% 10% 4 14% 10% 6% 5% 3 5% 6% 30%	7645

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	58% 8% 10% 20% 4	3249
	11th to 20th	Day	56% 9% 10% 17% 8%	3438
	21st to end	Day	54% 7% 16% 20% 4	4092
February	1st to 10th	Day	56% 7% 11% 17% 9% 1	1690
	11th to 20th	Day	51% 7% 13% 18% 10%	1763
	21st to end	Day	52% 7% 13% 19% 8% 1	1622
March	1st to 10th	Day	44% 7% 19% 19% 11%	4539
	11th to 20th	Day	53% 8% 15% 18% 6%	4980
	21st to end	Day	56% 7% 11% 20% 6%	5464
April	1st to 10th	Day	48% 7% 12% 22% 9% 1	2435
	11th to 20th	Day	51% 7% 12% 19% 11% 1	2572
	21st to end	Day	52% 7% 14% 17% 8% 2	2600
May	1st to 10th	Day	36% 5% 13% 25% 18% 2	5918
	11th to 20th	Day	48% 7% 11% 22% 12% 1	6671
	21st to end	Day	39% 6% 9% 23% 21% 3	7428
June	1st to 10th	Day	40% 9% 17% 23% 10% 1	3000
	11th to 20th	Day	42% 9% 16% 24% 9% 1	3000
	21st to end	Day	40% 11% 18% 25% 7% 1	3000
July	1st to 10th	Day	31% 10% 26% 27% 5%	6726
	11th to 20th	Day	34% 7% 21% 33% 6%	6719
	21st to end	Day	32% 10% 22% 27% 9%	6896
August	1st to 10th	Day	33% 9% 18% 27% 13% 1	4417
	11th to 20th	Day	33% 8% 18% 35% 6%	4210
	21st to end	Day	32% 7% 21% 31% 9%	4674
September	1st to 10th	Day	32% 7% 17% 31% 12% 1	2450
	11th to 20th	Day	42% 8% 17% 23% 9% 1	2200
	21st to end	Day	37% 7% 14% 31% 10%	2200
October	1st to 10th	Day	36% 5% 12% 34% 13% 1	3377
	11th to 20th	Day	40% 7% 11% 28% 13%	3121
	21st to end	Day	47% 6% 13% 25% 9%	3190
November	1st to 10th	Day	54% 8% 11% 19% 8% 1	1744
	11th to 20th	Day	56% 9% 13% 14% 7% 1	1680
	21st to end	Day	57% 9% 12% 16% 5%	1533
December	1st to 10th	Day	65% 7% 12% 12% 4	2360
	11th to 20th	Day	57% 7% 12% 14% 9% 1	2710
	21st to end	Day	55% 6% 9% 21% 8%	3575
January	1st to 10th	Night	58% 7% 12% 18% 5%	6937
	11th to 20th	Night	58% 8% 9% 19% 5%	6744
	21st to end	Night	57% 6% 12% 19% 6%	7128
February	1st to 10th	Night	53% 8% 11% 17% 11%	2711
	11th to 20th	Night	43% 8% 15% 21% 13%	2534
	21st to end	Night	47% 7% 11% 22% 11% 1	2025
March	1st to 10th	Night	43% 7% 17% 21% 11% 2	5333
	11th to 20th	Night	46% 7% 13% 21% 13% 1	4980
	21st to end	Night	55% 6% 10% 21% 8% 1	5467
April	1st to 10th	Night	39% 7% 13% 25% 14% 3	1961
	11th to 20th	Night	49% 6% 10% 20% 13% 2	1779
	21st to end	Night	46% 7% 13% 21% 11% 2	1800
May	1st to 10th	Night	40% 5% 10% 27% 17% 1	4062
	11th to 20th	Night	45% 8% 11% 21% 14% 2	3234
	21st to end	Night	33% 6% 10% 25% 22% 4	3470
June	1st to 10th	Night	34% 9% 19% 26% 10% 2	1400
	11th to 20th	Night	36% 7% 17% 25% 13% 2	1400
	21st to end	Night	32% 11% 18% 31% 7% 1	1400
July	1st to 10th	Night	25% 10% 26% 31% 7% 1	3145
	11th to 20th	Night	25% 7% 19% 40% 8% 1	3138
	21st to end	Night	27% 9% 26% 29% 8% 1	3650
August	1st to 10th	Night	26% 8% 17% 31% 16% 1	2717
	11th to 20th	Night	29% 7% 21% 33% 9% 1	2915
	21st to end	Night	30% 7% 17% 34% 11% 1	3234
September	1st to 10th	Night	28% 6% 16% 33% 16% 1	1948
	11th to 20th	Night	33% 8% 19% 26% 13% 1	2200
	21st to end	Night	37% 6% 11% 31% 13% 1	2200
October	1st to 10th	Night	35% 6% 12% 31% 14% 2	3770
	11th to 20th	Night	38% 6% 11% 29% 15%	4019
	21st to end	Night	41% 7% 13% 30% 8%	4610
November	1st to 10th	Night	49% 8% 14% 18% 9% 2	2772
	11th to 20th	Night	54% 7% 15% 15% 8% 1	2940
	21st to end	Night	55% 7% 14% 17% 6%	3082
December	1st to 10th	Night	64% 7% 12% 12% 4	5050
	11th to 20th	Night	61% 6% 11% 14% 7%	5716
	21st to end	Night	55% 7% 12% 18% 7%	7645

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	9% 9% 37% 31% 12% 3	330
	11th to 20th	Day	9% 12% 38% 31% 9% 1	330
	21st to end	Day	13% 11% 36% 28% 10% 2	363
February	1st to 10th	Day	16% 13% 35% 30% 4 2	300
	11th to 20th	Day	7% 13% 38% 31% 9% 2	300
	21st to end	Day	8% 8% 47% 27% 8% 2	249
March	1st to 10th	Day	13% 9% 35% 32% 9% 2	300
	11th to 20th	Day	15% 11% 34% 25% 11% 4	300
	21st to end	Day	13% 15% 33% 28% 9% 2	330
April	1st to 10th	Day	13% 18% 31% 27% 9% 2	535
	11th to 20th	Day	19% 14% 30% 26% 11% 1	690
	21st to end	Day	21% 12% 28% 26% 10% 2	700
May	1st to 10th	Day	16% 11% 32% 27% 12% 2	703
	11th to 20th	Day	21% 10% 30% 24% 12% 3	725
	21st to end	Day	18% 8% 25% 30% 15% 4	789
June	1st to 10th	Day	14% 12% 29% 25% 15% 6%	730
	11th to 20th	Day	15% 10% 36% 25% 12% 2	730
	21st to end	Day	12% 9% 30% 31% 15% 3	730
July	1st to 10th	Day	7% 6% 26% 33% 18% 10%	721
	11th to 20th	Day	11% 6% 30% 27% 20% 6%	718
	21st to end	Day	4 6% 26% 37% 20% 7%	794
August	1st to 10th	Day	7% 6% 27% 33% 21% 6%	726
	11th to 20th	Day	11% 5% 24% 32% 19% 9%	715
	21st to end	Day	10% 8% 28% 31% 18% 5%	803
September	1st to 10th	Day	12% 10% 30% 32% 13% 3	580
	11th to 20th	Day	21% 11% 28% 27% 10% 3	330
	21st to end	Day	18% 10% 32% 28% 11% 2	330
October	1st to 10th	Day	19% 11% 29% 28% 11% 1	330
	11th to 20th	Day	15% 13% 39% 25% 6% 2	330
	21st to end	Day	22% 12% 34% 21% 8% 2	363
November	1st to 10th	Day	22% 12% 29% 25% 9% 2	330
	11th to 20th	Day	16% 18% 35% 23% 7% 1	330
	21st to end	Day	16% 12% 37% 27% 7%	330
December	1st to 10th	Day	14% 10% 35% 29% 9% 2	330
	11th to 20th	Day	15% 17% 36% 26% 6%	330
	21st to end	Day	14% 10% 35% 27% 10% 5%	363
January	1st to 10th	Night	11% 11% 37% 30% 11% 1	1050
	11th to 20th	Night	15% 10% 36% 32% 6%	1050
	21st to end	Night	13% 12% 38% 29% 7% 1	1155
February	1st to 10th	Night	13% 11% 35% 32% 9% 1	1001
	11th to 20th	Night	10% 9% 37% 32% 11% 2	979
	21st to end	Night	13% 7% 35% 32% 10% 2	705
March	1st to 10th	Night	14% 11% 33% 28% 12% 2	785
	11th to 20th	Night	10% 8% 39% 31% 10% 2	600
	21st to end	Night	17% 8% 30% 30% 12% 3	660
April	1st to 10th	Night	12% 9% 36% 32% 10% 1	600
	11th to 20th	Night	16% 8% 34% 30% 11% 1	593
	21st to end	Night	19% 7% 26% 36% 11% 1	600
May	1st to 10th	Night	18% 5% 34% 31% 12% 1	600
	11th to 20th	Night	16% 8% 30% 31% 14%	591
	21st to end	Night	19% 8% 28% 34% 11% 1	650
June	1st to 10th	Night	12% 8% 30% 35% 14% 1	600
	11th to 20th	Night	14% 6% 32% 33% 15%	600
	21st to end	Night	10% 6% 28% 38% 17% 1	600
July	1st to 10th	Night	5% 4 26% 39% 23% 2	585
	11th to 20th	Night	7% 5% 29% 36% 21% 1	582
	21st to end	Night	6% 3 25% 43% 20% 2	657
August	1st to 10th	Night	8% 4 21% 46% 20% 1	597
	11th to 20th	Night	10% 4 24% 37% 23% 3	594
	21st to end	Night	10% 5% 28% 39% 18% 1	660
September	1st to 10th	Night	11% 4 30% 35% 18% 2	600
	11th to 20th	Night	13% 7% 30% 39% 12% 1	600
	21st to end	Night	16% 7% 32% 31% 14%	600
October	1st to 10th	Night	18% 9% 35% 29% 8% 1	702
	11th to 20th	Night	19% 10% 32% 29% 9%	870
	21st to end	Night	17% 12% 37% 25% 9% 1	1100
November	1st to 10th	Night	16% 13% 34% 28% 8% 1	1025
	11th to 20th	Night	15% 12% 38% 26% 7% 2	1050
	21st to end	Night	17% 13% 39% 24% 5% 2	1050
December	1st to 10th	Night	12% 12% 35% 31% 9% 1	1050
	11th to 20th	Night	15% 12% 35% 29% 8% 1	1050
	21st to end	Night	19% 8% 34% 29% 10% 1	1155

Page generated at 2026-01-29 00:21:45. Version ac07

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