Southport
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Southport clear sky chart from 2005-11-06 to 2025-11-18.

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% 6% 2 6% 4 4 5% 4 6% 8% 43%	126228
	Night	11% 6% 2 6% 4 4 4 4 6% 8% 44%	124112
Transparency	Day	38% 8% 14% 19% 16% 5%	129828
	Night	37% 7% 13% 19% 18% 6%	128581
Seeing	Day	13% 10% 26% 28% 17% 6%	17118
	Night	14% 9% 24% 31% 19% 3	27324

By Month

Percentage Cloud Cover SE (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% 5% 2 4 3 3 3 3 5% 6% 55%	4056
	11th to 20th	Day	11% 5% 2 5% 4 3 4 3 4 6% 52%	4060
	21st to end	Day	14% 9% 4 7% 4 4 4 3 4 5% 43%	4466
February	1st to 10th	Day	15% 6% 3 6% 5% 5% 4 3 6% 6% 42%	1800
	11th to 20th	Day	18% 7% 3 5% 4 3 4 3 4 5% 45%	1866
	21st to end	Day	13% 6% 2 5% 4 3 5% 4 5% 6% 45%	1770
March	1st to 10th	Day	20% 8% 3 7% 4 3 3 3 5% 5% 38%	4935
	11th to 20th	Day	8% 4 2 4 3 4 5% 4 5% 7% 54%	4980
	21st to end	Day	12% 5% 2 6% 4 4 4 3 4 5% 51%	5465
April	1st to 10th	Day	10% 4 1 4 4 3 4 4 6% 8% 52%	2356
	11th to 20th	Day	9% 4 2 4 3 4 4 3 6% 7% 54%	2374
	21st to end	Day	8% 3 2 4 3 3 4 4 5% 9% 55%	2400
May	1st to 10th	Day	7% 5% 2 7% 5% 5% 5% 5% 7% 9% 41%	5405
	11th to 20th	Day	16% 6% 3 7% 5% 5% 5% 4 6% 10% 34%	5859
	21st to end	Day	9% 4 2 6% 4 5% 5% 5% 7% 9% 44%	6433
June	1st to 10th	Day	10% 7% 2 6% 6% 5% 5% 5% 7% 10% 37%	2600
	11th to 20th	Day	8% 5% 2 6% 5% 4 4 6% 8% 12% 42%	2600
	21st to end	Day	7% 4 2 6% 5% 5% 6% 5% 8% 12% 38%	2600
July	1st to 10th	Day	9% 6% 3 8% 5% 6% 6% 5% 8% 13% 31%	5900
	11th to 20th	Day	5% 5% 2 7% 5% 6% 6% 5% 8% 13% 36%	5900
	21st to end	Day	7% 7% 3 8% 6% 5% 6% 6% 9% 12% 32%	6424
August	1st to 10th	Day	19% 11% 4 9% 5% 5% 5% 4 6% 10% 22%	4234
	11th to 20th	Day	7% 5% 2 7% 5% 5% 6% 5% 8% 11% 38%	3859
	21st to end	Day	7% 6% 3 7% 5% 4 5% 3 7% 10% 43%	4312
September	1st to 10th	Day	10% 5% 2 6% 5% 5% 5% 4 7% 9% 42%	2400
	11th to 20th	Day	15% 8% 3 6% 5% 4 4 3 6% 8% 37%	2343
	21st to end	Day	16% 7% 4 7% 5% 5% 4 3 5% 7% 37%	2113
October	1st to 10th	Day	13% 6% 2 7% 5% 4 4 4 5% 6% 44%	2000
	11th to 20th	Day	10% 4 2 5% 4 3 3 3 5% 5% 57%	2000
	21st to end	Day	10% 5% 2 6% 3 3 3 3 4 6% 56%	2200
November	1st to 10th	Day	11% 5% 2 4 4 4 2 3 4 7% 54%	2057
	11th to 20th	Day	12% 5% 2 5% 4 3 4 3 4 6% 51%	2070
	21st to end	Day	10% 6% 1 6% 4 4 4 3 5% 6% 52%	1924
December	1st to 10th	Day	10% 5% 2 6% 4 4 4 3 6% 5% 52%	2628
	11th to 20th	Day	13% 6% 2 8% 4 4 4 4 4 5% 46%	3373
	21st to end	Day	14% 7% 2 5% 4 4 4 4 6% 7% 45%	4466
January	1st to 10th	Night	10% 5% 2 5% 3 3 3 3 4 6% 55%	5889
	11th to 20th	Night	13% 6% 2 5% 3 4 4 4 6% 7% 46%	5900
	21st to end	Night	12% 7% 3 7% 4 4 4 3 4 6% 47%	6490
February	1st to 10th	Night	16% 7% 2 6% 4 4 4 4 5% 6% 43%	2600
	11th to 20th	Night	18% 8% 3 6% 4 3 3 3 5% 6% 41%	2417
	21st to end	Night	15% 6% 2 7% 5% 4 4 3 5% 6% 43%	1855
March	1st to 10th	Night	17% 8% 3 7% 5% 4 4 3 4 5% 39%	4918
	11th to 20th	Night	12% 4 2 5% 4 3 4 4 6% 8% 49%	4980
	21st to end	Night	13% 4 2 5% 3 3 4 3 4 6% 53%	5467
April	1st to 10th	Night	10% 6% 2 5% 4 3 4 3 7% 7% 48%	2042
	11th to 20th	Night	10% 5% 2 5% 4 4 5% 3 5% 6% 51%	1975
	21st to end	Night	7% 4 2 4 4 4 4 4 6% 7% 55%	2000
May	1st to 10th	Night	8% 6% 2 6% 5% 4 4 5% 6% 10% 43%	4490
	11th to 20th	Night	14% 7% 2 7% 5% 4 5% 4 7% 9% 36%	4062
	21st to end	Night	12% 5% 2 6% 4 4 5% 4 7% 9% 41%	4421
June	1st to 10th	Night	10% 6% 3 6% 6% 5% 5% 4 8% 11% 35%	1800
	11th to 20th	Night	9% 4 2 5% 4 5% 5% 4 9% 10% 42%	1800
	21st to end	Night	8% 5% 2 6% 5% 6% 6% 6% 9% 12% 37%	1800
July	1st to 10th	Night	7% 5% 3 7% 6% 7% 6% 6% 8% 13% 33%	4058
	11th to 20th	Night	6% 5% 2 8% 5% 5% 6% 5% 10% 17% 31%	4057
	21st to end	Night	6% 5% 3 7% 6% 6% 7% 6% 10% 13% 31%	4427
August	1st to 10th	Night	18% 10% 3 7% 5% 4 4 5% 8% 10% 26%	2915
	11th to 20th	Night	7% 5% 2 6% 5% 6% 6% 5% 8% 12% 38%	3157
	21st to end	Night	7% 5% 3 7% 5% 5% 5% 4 7% 10% 44%	3586
September	1st to 10th	Night	11% 5% 2 6% 5% 6% 6% 5% 6% 9% 40%	2000
	11th to 20th	Night	13% 7% 2 9% 5% 4 6% 5% 7% 10% 33%	2052
	21st to end	Night	17% 7% 2 7% 4 4 4 3 5% 7% 39%	2285
October	1st to 10th	Night	13% 6% 2 7% 4 5% 4 4 4 7% 44%	2400
	11th to 20th	Night	10% 4 1 4 3 3 4 3 5% 8% 53%	2400
	21st to end	Night	10% 5% 2 4 3 4 4 3 5% 6% 55%	2640
November	1st to 10th	Night	12% 4 2 5% 3 4 3 3 4 6% 53%	2461
	11th to 20th	Night	12% 6% 3 6% 4 4 4 3 5% 7% 48%	2485
	21st to end	Night	10% 5% 2 5% 4 4 3 3 7% 7% 49%	2452
December	1st to 10th	Night	10% 5% 2 5% 4 3 3 3 5% 6% 54%	4519
	11th to 20th	Night	13% 8% 3 7% 5% 3 4 3 5% 6% 43%	4822
	21st to end	Night	13% 6% 2 6% 4 3 4 4 6% 7% 46%	6490

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	31% 4 6% 17% 35% 8%	4057
	11th to 20th	Day	33% 4 5% 16% 32% 10%	4060
	21st to end	Day	42% 7% 6% 16% 20% 9%	4466
February	1st to 10th	Day	42% 5% 9% 21% 19% 5%	1800
	11th to 20th	Day	44% 5% 7% 15% 21% 8%	1875
	21st to end	Day	38% 6% 11% 18% 17% 9%	1770
March	1st to 10th	Day	48% 5% 8% 14% 19% 7%	4935
	11th to 20th	Day	28% 6% 9% 15% 25% 16%	4980
	21st to end	Day	36% 5% 10% 22% 19% 8%	5465
April	1st to 10th	Day	29% 7% 13% 22% 22% 7%	2356
	11th to 20th	Day	29% 5% 13% 25% 19% 9%	2374
	21st to end	Day	27% 7% 15% 24% 23% 4	2400
May	1st to 10th	Day	36% 11% 21% 23% 8% 1	5437
	11th to 20th	Day	46% 9% 15% 19% 10% 1	5863
	21st to end	Day	35% 11% 15% 22% 16% 2	6447
June	1st to 10th	Day	43% 10% 15% 22% 10%	2600
	11th to 20th	Day	34% 12% 20% 22% 10% 1	2600
	21st to end	Day	37% 13% 20% 22% 7%	2600
July	1st to 10th	Day	42% 14% 26% 14% 3 1	5835
	11th to 20th	Day	40% 16% 32% 9% 2	5831
	21st to end	Day	44% 14% 19% 17% 5%	6240
August	1st to 10th	Day	59% 10% 18% 10% 2	4221
	11th to 20th	Day	39% 14% 18% 21% 8%	3895
	21st to end	Day	37% 9% 19% 29% 5% 1	4312
September	1st to 10th	Day	39% 12% 15% 17% 13% 3	2400
	11th to 20th	Day	46% 8% 12% 17% 14% 3	2343
	21st to end	Day	47% 8% 11% 17% 14% 3	2113
October	1st to 10th	Day	40% 6% 7% 21% 22% 4	3260
	11th to 20th	Day	21% 4 6% 17% 28% 24%	3240
	21st to end	Day	28% 5% 6% 23% 29% 9%	3538
November	1st to 10th	Day	31% 5% 9% 20% 25% 10%	2057
	11th to 20th	Day	36% 4 7% 18% 25% 10%	2070
	21st to end	Day	33% 5% 10% 20% 24% 8%	1924
December	1st to 10th	Day	32% 6% 9% 16% 23% 14%	2628
	11th to 20th	Day	40% 6% 10% 18% 20% 7%	3370
	21st to end	Day	37% 6% 13% 24% 18% 3	4466
January	1st to 10th	Night	31% 4 6% 17% 35% 7%	5889
	11th to 20th	Night	36% 5% 6% 15% 32% 6%	5900
	21st to end	Night	39% 6% 6% 15% 25% 10%	6490
February	1st to 10th	Night	42% 4 9% 19% 19% 7%	2600
	11th to 20th	Night	44% 5% 8% 15% 20% 8%	2419
	21st to end	Night	40% 5% 11% 17% 17% 10%	1855
March	1st to 10th	Night	47% 5% 8% 14% 20% 6%	4918
	11th to 20th	Night	33% 5% 9% 12% 23% 17%	4980
	21st to end	Night	34% 5% 11% 24% 19% 7%	5467
April	1st to 10th	Night	33% 5% 15% 17% 22% 8%	2042
	11th to 20th	Night	34% 6% 12% 22% 18% 9%	1975
	21st to end	Night	28% 7% 15% 27% 19% 4	2000
May	1st to 10th	Night	35% 10% 19% 26% 9% 1	4520
	11th to 20th	Night	44% 8% 17% 20% 10%	4063
	21st to end	Night	37% 10% 16% 20% 16%	4429
June	1st to 10th	Night	41% 9% 20% 21% 9% 1	1800
	11th to 20th	Night	33% 13% 21% 24% 9% 1	1800
	21st to end	Night	36% 13% 22% 23% 7% 1	1800
July	1st to 10th	Night	40% 13% 29% 15% 3	4015
	11th to 20th	Night	40% 15% 34% 9% 2	4006
	21st to end	Night	41% 15% 19% 21% 4	4297
August	1st to 10th	Night	52% 10% 23% 12% 2	2904
	11th to 20th	Night	35% 14% 21% 23% 7%	3187
	21st to end	Night	33% 10% 19% 32% 6% 1	3586
September	1st to 10th	Night	37% 11% 20% 17% 12% 3	2000
	11th to 20th	Night	40% 11% 14% 21% 12% 2	2052
	21st to end	Night	45% 7% 13% 21% 12% 2	2285
October	1st to 10th	Night	39% 6% 9% 19% 22% 6%	3920
	11th to 20th	Night	20% 4 6% 16% 22% 32%	3899
	21st to end	Night	24% 4 8% 25% 27% 11%	4252
November	1st to 10th	Night	32% 5% 11% 18% 24% 10%	2461
	11th to 20th	Night	37% 4 9% 16% 24% 10%	2485
	21st to end	Night	32% 6% 10% 22% 23% 6%	2452
December	1st to 10th	Night	32% 5% 7% 14% 28% 14%	4519
	11th to 20th	Night	41% 5% 12% 17% 18% 7%	4824
	21st to end	Night	37% 5% 12% 24% 20% 2	6490

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	17% 23% 41% 16% 2	300
	11th to 20th	Day	12% 22% 39% 24% 4	300
	21st to end	Day	18% 22% 42% 16% 2	330
February	1st to 10th	Day	16% 20% 42% 21% 2	300
	11th to 20th	Day	27% 19% 34% 18% 2	414
	21st to end	Day	15% 18% 41% 21% 4	414
March	1st to 10th	Day	14% 21% 35% 22% 7%	500
	11th to 20th	Day	17% 18% 40% 18% 5% 1	500
	21st to end	Day	14% 20% 38% 19% 7% 1	550
April	1st to 10th	Day	14% 21% 31% 24% 9% 1	500
	11th to 20th	Day	11% 15% 31% 25% 14% 4	492
	21st to end	Day	9% 12% 30% 27% 18% 4	500
May	1st to 10th	Day	7% 14% 38% 25% 11% 5%	503
	11th to 20th	Day	15% 8% 24% 32% 17% 4	527
	21st to end	Day	13% 6% 19% 31% 21% 10%	573
June	1st to 10th	Day	13% 5% 23% 32% 20% 6%	530
	11th to 20th	Day	9% 3 19% 34% 24% 12%	530
	21st to end	Day	7% 3 16% 38% 27% 9%	530
July	1st to 10th	Day	9% 3 10% 35% 32% 11%	525
	11th to 20th	Day	10% 2 9% 34% 34% 11%	524
	21st to end	Day	7% 4 14% 36% 31% 9%	576
August	1st to 10th	Day	16% 5% 13% 29% 27% 10%	526
	11th to 20th	Day	11% 3 13% 28% 31% 14%	519
	21st to end	Day	11% 5% 11% 31% 28% 14%	583
September	1st to 10th	Day	9% 2 19% 32% 25% 14%	530
	11th to 20th	Day	19% 4 17% 32% 20% 8%	530
	21st to end	Day	20% 4 21% 26% 21% 9%	530
October	1st to 10th	Day	17% 7% 22% 30% 17% 7%	530
	11th to 20th	Day	11% 6% 26% 36% 18% 4	530
	21st to end	Day	11% 8% 29% 33% 16% 4	583
November	1st to 10th	Day	15% 9% 29% 28% 15% 3	535
	11th to 20th	Day	15% 16% 36% 24% 8% 1	528
	21st to end	Day	11% 12% 36% 27% 12% 2	439
December	1st to 10th	Day	18% 13% 39% 23% 7% 1	207
	11th to 20th	Day	18% 18% 33% 22% 9% 1	300
	21st to end	Day	19% 17% 38% 18% 7% 2	330
January	1st to 10th	Night	14% 19% 37% 25% 6%	800
	11th to 20th	Night	14% 17% 29% 32% 8%	800
	21st to end	Night	17% 16% 37% 27% 3	880
February	1st to 10th	Night	20% 11% 36% 28% 6%	800
	11th to 20th	Night	22% 17% 34% 25% 2	783
	21st to end	Night	19% 15% 31% 28% 7%	660
March	1st to 10th	Night	14% 15% 36% 27% 7%	800
	11th to 20th	Night	15% 14% 35% 28% 8% 1	800
	21st to end	Night	16% 12% 35% 27% 9%	880
April	1st to 10th	Night	14% 14% 35% 29% 8% 1	800
	11th to 20th	Night	13% 11% 28% 31% 14% 2	791
	21st to end	Night	8% 9% 32% 36% 15% 1	800
May	1st to 10th	Night	8% 10% 33% 35% 14% 1	800
	11th to 20th	Night	16% 6% 25% 31% 20% 2	608
	21st to end	Night	13% 3 13% 32% 31% 8%	650
June	1st to 10th	Night	11% 4 17% 39% 26% 4	600
	11th to 20th	Night	10% 3 13% 37% 30% 8%	600
	21st to end	Night	9% 4 11% 41% 31% 5%	600
July	1st to 10th	Night	6% 3 10% 36% 39% 6%	585
	11th to 20th	Night	7% 2 8% 34% 41% 8%	582
	21st to end	Night	7% 2 10% 39% 35% 6%	657
August	1st to 10th	Night	13% 3 9% 35% 33% 7%	597
	11th to 20th	Night	10% 2 10% 30% 39% 9%	762
	21st to end	Night	12% 3 10% 31% 35% 10%	880
September	1st to 10th	Night	13% 3 12% 29% 36% 8%	800
	11th to 20th	Night	16% 3 13% 35% 27% 7%	800
	21st to end	Night	21% 5% 14% 28% 27% 6%	800
October	1st to 10th	Night	13% 5% 22% 32% 22% 6%	800
	11th to 20th	Night	13% 7% 22% 34% 20% 3	800
	21st to end	Night	12% 9% 22% 32% 21% 4	880
November	1st to 10th	Night	13% 7% 28% 32% 16% 3	820
	11th to 20th	Night	16% 11% 29% 29% 14% 1	829
	21st to end	Night	11% 12% 30% 30% 16% 2	800
December	1st to 10th	Night	18% 12% 30% 30% 9% 1	800
	11th to 20th	Night	16% 12% 29% 30% 12% 1	800
	21st to end	Night	18% 13% 31% 28% 10%	880

Page generated at 2025-11-15 00:55:54. Version ac07

Copyright © 2025 Attilla Danko.