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 2024-11-28.

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	11% 8% 3 8% 5% 5% 5% 4 6% 8% 37%	105685
	Night	9% 9% 4 9% 6% 5% 5% 4 6% 7% 38%	102446
Transparency	Day	44% 8% 15% 24% 9% 1	105434
	Night	45% 7% 14% 24% 10% 1	102344
Seeing	Day	14% 10% 31% 29% 13% 4	16286
	Night	14% 8% 33% 32% 12% 1	26242

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	5% 17% 5% 12% 7% 8% 5% 4 5% 6% 25%	2219
	11th to 20th	Day	4 8% 4 16% 12% 12% 9% 5% 8% 7% 15%	2326
	21st to end	Day	7% 12% 5% 13% 8% 6% 6% 4 6% 7% 26%	2794
February	1st to 10th	Day	9% 12% 6% 10% 8% 7% 6% 5% 6% 7% 25%	1605
	11th to 20th	Day	6% 10% 3 11% 8% 8% 8% 6% 8% 7% 25%	1664
	21st to end	Day	7% 9% 5% 11% 9% 5% 7% 5% 6% 8% 29%	1543
March	1st to 10th	Day	12% 10% 3 9% 7% 5% 5% 4 5% 8% 32%	3156
	11th to 20th	Day	9% 11% 4 12% 10% 5% 5% 4 6% 7% 27%	3478
	21st to end	Day	9% 12% 5% 14% 7% 6% 5% 3 6% 6% 28%	3814
April	1st to 10th	Day	9% 13% 5% 9% 5% 4 4 4 5% 7% 35%	2313
	11th to 20th	Day	13% 12% 4 10% 5% 4 5% 4 6% 6% 31%	2442
	21st to end	Day	18% 10% 3 9% 5% 4 4 3 5% 6% 33%	2470
May	1st to 10th	Day	19% 10% 3 7% 4 4 4 4 6% 7% 32%	4138
	11th to 20th	Day	18% 9% 2 7% 4 5% 5% 4 6% 7% 33%	4643
	21st to end	Day	18% 9% 3 8% 4 4 4 4 5% 6% 34%	5173
June	1st to 10th	Day	12% 7% 3 6% 5% 4 5% 5% 7% 9% 37%	2850
	11th to 20th	Day	13% 7% 2 6% 5% 5% 5% 5% 7% 8% 37%	2850
	21st to end	Day	11% 5% 2 6% 5% 5% 6% 6% 7% 9% 37%	2850
July	1st to 10th	Day	8% 3 2 5% 5% 5% 6% 6% 8% 10% 43%	4750
	11th to 20th	Day	7% 4 2 5% 3 4 5% 4 6% 9% 52%	4750
	21st to end	Day	5% 4 1 5% 4 4 5% 4 7% 10% 51%	4942
August	1st to 10th	Day	8% 5% 2 7% 4 4 5% 4 6% 8% 45%	4297
	11th to 20th	Day	11% 4 2 5% 3 4 5% 4 6% 8% 48%	4041
	21st to end	Day	9% 4 2 6% 4 4 4 3 6% 8% 49%	4532
September	1st to 10th	Day	10% 5% 2 5% 4 3 4 3 5% 8% 51%	2327
	11th to 20th	Day	15% 6% 2 7% 4 3 4 4 5% 6% 44%	2090
	21st to end	Day	15% 6% 2 6% 4 4 4 3 5% 8% 44%	2090
October	1st to 10th	Day	11% 6% 2 5% 4 3 4 3 5% 6% 50%	3273
	11th to 20th	Day	9% 9% 3 7% 4 4 5% 4 6% 8% 39%	3025
	21st to end	Day	12% 11% 3 8% 4 4 4 4 6% 8% 35%	3091
November	1st to 10th	Day	13% 14% 4 9% 6% 5% 4 4 5% 6% 30%	1659
	11th to 20th	Day	9% 14% 6% 13% 8% 6% 4 4 5% 6% 27%	1600
	21st to end	Day	10% 15% 4 11% 8% 5% 4 4 5% 6% 28%	1439
December	1st to 10th	Day	8% 12% 6% 13% 8% 6% 5% 4 7% 6% 24%	1330
	11th to 20th	Day	8% 14% 5% 15% 8% 6% 5% 5% 5% 6% 22%	1679
	21st to end	Day	9% 10% 4 10% 7% 5% 5% 4 6% 6% 34%	2442
January	1st to 10th	Night	6% 14% 6% 13% 7% 6% 7% 4 5% 6% 27%	4737
	11th to 20th	Night	5% 11% 6% 15% 10% 9% 9% 5% 6% 5% 19%	4578
	21st to end	Night	8% 15% 8% 13% 6% 5% 5% 3 5% 5% 26%	4873
February	1st to 10th	Night	7% 12% 5% 10% 7% 7% 6% 5% 6% 5% 29%	2575
	11th to 20th	Night	5% 9% 4 9% 5% 6% 7% 5% 7% 9% 34%	2403
	21st to end	Night	7% 12% 4 9% 6% 6% 5% 3 7% 7% 35%	1927
March	1st to 10th	Night	9% 12% 3 9% 7% 5% 5% 3 5% 6% 36%	3707
	11th to 20th	Night	7% 8% 4 9% 7% 5% 5% 4 6% 7% 39%	3480
	21st to end	Night	8% 11% 6% 15% 6% 5% 4 3 6% 5% 31%	3817
April	1st to 10th	Night	8% 8% 3 7% 5% 4 5% 4 6% 9% 41%	1863
	11th to 20th	Night	12% 12% 5% 8% 4 4 6% 3 5% 5% 35%	1689
	21st to end	Night	14% 10% 2 6% 5% 5% 5% 4 5% 7% 37%	1710
May	1st to 10th	Night	22% 6% 3 5% 4 4 4 3 5% 7% 36%	2832
	11th to 20th	Night	14% 8% 2 6% 4 3 5% 4 6% 6% 41%	2248
	21st to end	Night	18% 7% 2 5% 3 3 3 3 5% 6% 44%	2414
June	1st to 10th	Night	10% 5% 2 5% 6% 4 4 5% 7% 8% 44%	1330
	11th to 20th	Night	12% 5% 2 5% 5% 3 4 4 7% 9% 45%	1330
	21st to end	Night	10% 4 2 5% 4 5% 4 4 8% 8% 46%	1330
July	1st to 10th	Night	8% 3 1 4 3 4 3 4 6% 10% 55%	2220
	11th to 20th	Night	5% 3 1 4 3 3 4 4 6% 9% 59%	2220
	21st to end	Night	5% 4 1 4 4 4 5% 5% 8% 10% 51%	2620
August	1st to 10th	Night	5% 4 2 5% 4 4 4 4 7% 8% 53%	2641
	11th to 20th	Night	8% 4 2 5% 3 4 4 4 6% 9% 50%	2798
	21st to end	Night	10% 4 2 5% 3 4 4 4 5% 7% 53%	3135
September	1st to 10th	Night	9% 4 2 5% 3 3 3 3 5% 7% 56%	1851
	11th to 20th	Night	12% 5% 1 5% 3 3 4 3 5% 8% 50%	2090
	21st to end	Night	15% 5% 3 7% 3 4 4 3 5% 7% 44%	2090
October	1st to 10th	Night	11% 6% 2 5% 4 4 4 4 4 7% 50%	3655
	11th to 20th	Night	9% 8% 3 6% 4 4 5% 3 6% 9% 44%	3895
	21st to end	Night	7% 9% 3 7% 5% 5% 4 4 6% 7% 42%	4467
November	1st to 10th	Night	12% 10% 4 9% 6% 4 5% 5% 6% 7% 32%	2637
	11th to 20th	Night	9% 16% 5% 10% 6% 4 4 4 6% 6% 30%	2800
	21st to end	Night	10% 14% 4 11% 7% 5% 4 4 5% 7% 29%	2891
December	1st to 10th	Night	7% 13% 4 13% 8% 6% 6% 4 5% 7% 28%	2850
	11th to 20th	Night	9% 15% 6% 14% 7% 6% 6% 4 5% 6% 22%	3518
	21st to end	Night	10% 11% 4 11% 7% 5% 4 3 5% 5% 33%	5225

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% 13% 17% 4	2219
	11th to 20th	Day	64% 9% 9% 14% 4	2348
	21st to end	Day	57% 7% 9% 22% 5%	2794
February	1st to 10th	Day	56% 7% 11% 17% 8%	1605
	11th to 20th	Day	53% 8% 13% 16% 9%	1673
	21st to end	Day	53% 7% 12% 19% 9% 1	1543
March	1st to 10th	Day	49% 7% 16% 21% 7%	3156
	11th to 20th	Day	53% 8% 13% 18% 7%	3480
	21st to end	Day	55% 8% 11% 19% 7%	3814
April	1st to 10th	Day	48% 7% 12% 23% 9% 1	2313
	11th to 20th	Day	51% 7% 12% 18% 11% 1	2442
	21st to end	Day	51% 7% 15% 18% 8% 2	2470
May	1st to 10th	Day	49% 6% 14% 20% 11% 1	4138
	11th to 20th	Day	46% 8% 12% 22% 10% 1	4647
	21st to end	Day	49% 7% 12% 23% 9% 1	5173
June	1st to 10th	Day	40% 9% 18% 22% 10% 1	2850
	11th to 20th	Day	42% 9% 15% 24% 10% 1	2850
	21st to end	Day	40% 10% 17% 25% 7% 1	2850
July	1st to 10th	Day	31% 12% 24% 28% 5%	4676
	11th to 20th	Day	27% 7% 22% 36% 8%	4669
	21st to end	Day	27% 8% 23% 32% 9%	4786
August	1st to 10th	Day	33% 8% 18% 28% 12% 1	4281
	11th to 20th	Day	33% 8% 18% 35% 6%	4080
	21st to end	Day	32% 7% 21% 30% 9%	4531
September	1st to 10th	Day	32% 7% 17% 31% 13% 1	2327
	11th to 20th	Day	40% 8% 17% 25% 9% 1	2090
	21st to end	Day	39% 7% 14% 31% 9%	2090
October	1st to 10th	Day	36% 5% 12% 34% 12% 1	3273
	11th to 20th	Day	40% 7% 11% 28% 13%	3025
	21st to end	Day	47% 6% 13% 25% 9%	3091
November	1st to 10th	Day	54% 8% 11% 19% 7% 1	1659
	11th to 20th	Day	58% 9% 12% 14% 7%	1600
	21st to end	Day	57% 10% 13% 16% 5%	1439
December	1st to 10th	Day	59% 8% 13% 15% 5%	1330
	11th to 20th	Day	61% 7% 11% 13% 6% 1	1680
	21st to end	Day	50% 7% 11% 22% 9%	2442
January	1st to 10th	Night	56% 8% 14% 17% 5%	4737
	11th to 20th	Night	64% 7% 9% 15% 5%	4618
	21st to end	Night	59% 7% 10% 18% 6%	4873
February	1st to 10th	Night	53% 8% 11% 17% 10% 1	2575
	11th to 20th	Night	45% 8% 15% 19% 13%	2404
	21st to end	Night	48% 7% 12% 21% 11% 1	1927
March	1st to 10th	Night	47% 7% 13% 23% 9%	3707
	11th to 20th	Night	41% 7% 15% 24% 12% 1	3480
	21st to end	Night	54% 7% 11% 19% 9% 1	3817
April	1st to 10th	Night	38% 8% 13% 25% 14% 3	1863
	11th to 20th	Night	49% 5% 10% 20% 13% 2	1689
	21st to end	Night	45% 7% 14% 21% 11% 2	1710
May	1st to 10th	Night	46% 5% 11% 27% 10% 1	2832
	11th to 20th	Night	41% 8% 12% 25% 11% 3	2248
	21st to end	Night	40% 6% 13% 29% 12%	2414
June	1st to 10th	Night	34% 9% 19% 26% 10% 2	1330
	11th to 20th	Night	36% 7% 16% 26% 14% 2	1330
	21st to end	Night	32% 11% 17% 32% 7% 1	1330
July	1st to 10th	Night	24% 10% 26% 31% 8% 1	2185
	11th to 20th	Night	20% 7% 18% 43% 11% 1	2178
	21st to end	Night	26% 8% 24% 32% 10% 1	2537
August	1st to 10th	Night	26% 8% 17% 32% 16% 1	2633
	11th to 20th	Night	29% 8% 21% 33% 9% 1	2825
	21st to end	Night	30% 7% 17% 34% 11% 1	3135
September	1st to 10th	Night	28% 6% 15% 33% 16% 1	1851
	11th to 20th	Night	32% 7% 19% 27% 13% 1	2090
	21st to end	Night	39% 6% 12% 30% 13% 1	2090
October	1st to 10th	Night	35% 6% 12% 31% 14% 2	3655
	11th to 20th	Night	37% 6% 11% 30% 15%	3895
	21st to end	Night	41% 7% 13% 30% 9%	4467
November	1st to 10th	Night	49% 8% 14% 18% 8% 2	2637
	11th to 20th	Night	56% 7% 14% 15% 7% 1	2800
	21st to end	Night	55% 8% 14% 17% 6%	2891
December	1st to 10th	Night	57% 7% 15% 16% 6%	2850
	11th to 20th	Night	62% 8% 14% 12% 5%	3516
	21st to end	Night	53% 7% 12% 18% 10% 1	5225

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	10% 8% 35% 32% 12% 3	270
	11th to 20th	Day	9% 10% 37% 33% 10% 1	270
	21st to end	Day	13% 9% 33% 31% 12% 2	297
February	1st to 10th	Day	16% 11% 37% 30% 5% 2	270
	11th to 20th	Day	8% 13% 39% 30% 9% 2	270
	21st to end	Day	8% 6% 48% 27% 9% 2	225
March	1st to 10th	Day	13% 8% 34% 34% 10% 1	270
	11th to 20th	Day	14% 11% 33% 26% 12% 4	270
	21st to end	Day	13% 14% 31% 29% 10% 3	297
April	1st to 10th	Day	13% 18% 31% 27% 9% 2	493
	11th to 20th	Day	20% 12% 30% 26% 11% 1	640
	21st to end	Day	21% 12% 29% 26% 10% 2	650
May	1st to 10th	Day	17% 10% 31% 27% 12% 2	653
	11th to 20th	Day	20% 10% 30% 24% 13% 3	675
	21st to end	Day	19% 9% 25% 29% 15% 2	734
June	1st to 10th	Day	14% 11% 29% 25% 15% 6%	680
	11th to 20th	Day	16% 10% 36% 23% 12% 3	680
	21st to end	Day	11% 8% 29% 32% 16% 4	680
July	1st to 10th	Day	8% 6% 26% 31% 18% 10%	671
	11th to 20th	Day	10% 6% 29% 28% 20% 6%	668
	21st to end	Day	4 6% 27% 37% 20% 7%	739
August	1st to 10th	Day	7% 5% 28% 33% 20% 7%	676
	11th to 20th	Day	11% 5% 23% 32% 20% 9%	665
	21st to end	Day	10% 9% 28% 31% 18% 5%	748
September	1st to 10th	Day	12% 9% 30% 32% 13% 3	537
	11th to 20th	Day	18% 12% 29% 28% 11% 3	300
	21st to end	Day	20% 10% 32% 26% 11%	300
October	1st to 10th	Day	20% 11% 28% 28% 11% 1	300
	11th to 20th	Day	12% 12% 40% 27% 6% 2	300
	21st to end	Day	22% 12% 35% 22% 8% 2	330
November	1st to 10th	Day	23% 10% 28% 27% 10% 2	300
	11th to 20th	Day	17% 15% 37% 23% 6% 1	300
	21st to end	Day	17% 13% 36% 26% 7%	291
December	1st to 10th	Day	13% 9% 34% 31% 11% 3	270
	11th to 20th	Day	14% 14% 38% 28% 6%	270
	21st to end	Day	13% 9% 34% 28% 10% 4	297
January	1st to 10th	Night	11% 11% 36% 29% 11% 1	950
	11th to 20th	Night	15% 9% 36% 33% 7%	950
	21st to end	Night	13% 11% 37% 30% 7% 1	1045
February	1st to 10th	Night	13% 10% 35% 32% 9% 1	950
	11th to 20th	Night	10% 9% 36% 32% 11% 2	929
	21st to end	Night	13% 7% 35% 33% 10% 2	671
March	1st to 10th	Night	15% 10% 32% 29% 13% 2	746
	11th to 20th	Night	9% 8% 39% 32% 11% 2	570
	21st to end	Night	17% 8% 29% 31% 12% 3	627
April	1st to 10th	Night	12% 9% 37% 32% 10% 1	570
	11th to 20th	Night	17% 8% 34% 30% 11% 1	563
	21st to end	Night	19% 6% 25% 37% 11% 1	570
May	1st to 10th	Night	19% 5% 32% 32% 11% 1	570
	11th to 20th	Night	16% 8% 29% 33% 14%	561
	21st to end	Night	19% 8% 29% 34% 10% 1	617
June	1st to 10th	Night	12% 8% 28% 36% 14% 1	570
	11th to 20th	Night	15% 6% 33% 31% 16%	570
	21st to end	Night	10% 5% 28% 38% 18% 1	570
July	1st to 10th	Night	5% 4 26% 39% 23% 2	555
	11th to 20th	Night	7% 6% 28% 37% 22% 1	552
	21st to end	Night	6% 3 25% 43% 21% 2	624
August	1st to 10th	Night	8% 4 21% 47% 20% 1	567
	11th to 20th	Night	10% 4 24% 36% 23% 3	564
	21st to end	Night	11% 4 27% 39% 18% 1	627
September	1st to 10th	Night	12% 4 30% 35% 18% 2	570
	11th to 20th	Night	12% 6% 29% 40% 12% 1	570
	21st to end	Night	16% 7% 33% 31% 13%	570
October	1st to 10th	Night	18% 9% 34% 30% 8% 1	667
	11th to 20th	Night	18% 10% 33% 30% 9%	826
	21st to end	Night	16% 12% 37% 25% 9% 1	1045
November	1st to 10th	Night	16% 12% 34% 28% 8% 1	975
	11th to 20th	Night	16% 11% 37% 27% 7% 2	1000
	21st to end	Night	18% 13% 39% 24% 5% 2	986
December	1st to 10th	Night	12% 11% 35% 32% 9% 1	950
	11th to 20th	Night	15% 11% 34% 30% 9% 1	950
	21st to end	Night	20% 7% 35% 29% 9% 1	1045

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