Birmingham
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Birmingham clear sky chart from 2005-11-06 to 2026-10-14.

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	12% 6% 3 7% 5% 5% 5% 4 6% 8% 40%	148656
	Night	12% 7% 2 6% 4 4 4 4 6% 8% 43%	143082
Transparency	Day	41% 4 12% 21% 17% 5%	152436
	Night	39% 4 11% 21% 19% 6%	147377
Seeing	Day	16% 8% 23% 25% 18% 9%	17088
	Night	15% 7% 22% 31% 21% 4	26994

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	18% 11% 5% 6% 3 3 3 3 4 3 41%	5258
	11th to 20th	Day	10% 5% 4 5% 3 2 3 2 3 5% 57%	5538
	21st to end	Day	23% 9% 3 8% 5% 4 3 3 4 5% 35%	6436
February	1st to 10th	Day	17% 11% 2 7% 3 3 4 3 4 6% 39%	2100
	11th to 20th	Day	22% 9% 2 6% 3 3 4 3 4 6% 38%	2048
	21st to end	Day	19% 7% 3 7% 4 4 3 3 4 5% 39%	1730
March	1st to 10th	Day	18% 9% 3 7% 5% 4 4 3 5% 6% 35%	4580
	11th to 20th	Day	11% 7% 3 7% 4 3 4 3 5% 7% 46%	4873
	21st to end	Day	15% 6% 3 7% 4 4 5% 4 5% 7% 41%	5878
April	1st to 10th	Day	11% 6% 3 6% 4 3 4 4 5% 8% 46%	2520
	11th to 20th	Day	11% 5% 2 6% 4 4 4 4 5% 8% 47%	2494
	21st to end	Day	9% 5% 2 6% 5% 4 4 5% 6% 8% 47%	2520
May	1st to 10th	Day	15% 7% 3 7% 5% 5% 6% 4 7% 8% 34%	7492
	11th to 20th	Day	12% 7% 3 7% 5% 5% 6% 5% 7% 8% 36%	7626
	21st to end	Day	14% 9% 3 9% 5% 5% 5% 4 6% 7% 31%	8391
June	1st to 10th	Day	9% 8% 2 7% 4 6% 6% 5% 9% 10% 33%	2730
	11th to 20th	Day	6% 4 2 6% 5% 6% 6% 5% 8% 11% 41%	2730
	21st to end	Day	7% 5% 3 5% 6% 5% 6% 5% 8% 11% 40%	2730
July	1st to 10th	Day	5% 4 2 7% 7% 8% 8% 6% 10% 12% 32%	7680
	11th to 20th	Day	7% 5% 2 7% 6% 7% 8% 7% 11% 13% 28%	7680
	21st to end	Day	7% 6% 3 8% 6% 7% 8% 7% 10% 13% 25%	8129
August	1st to 10th	Day	4 4 2 7% 6% 7% 6% 5% 9% 12% 38%	5545
	11th to 20th	Day	4 3 2 4 4 5% 6% 5% 8% 12% 49%	5486
	21st to end	Day	5% 3 2 6% 5% 4 5% 5% 8% 10% 46%	6080
September	1st to 10th	Day	9% 5% 2 6% 4 6% 6% 5% 6% 9% 42%	2469
	11th to 20th	Day	11% 7% 2 6% 4 4 5% 4 5% 8% 44%	2310
	21st to end	Day	9% 5% 2 6% 4 4 4 4 6% 8% 48%	2310
October	1st to 10th	Day	10% 4 2 5% 4 4 5% 3 5% 6% 52%	2310
	11th to 20th	Day	8% 5% 2 4 3 3 3 3 5% 7% 57%	2233
	21st to end	Day	12% 5% 1 5% 4 4 3 2 4 6% 54%	2070
November	1st to 10th	Day	12% 6% 2 5% 4 4 4 2 4 6% 53%	1852
	11th to 20th	Day	13% 5% 2 4 3 3 4 2 5% 6% 53%	1890
	21st to end	Day	14% 7% 2 5% 5% 4 4 4 5% 7% 45%	1890
December	1st to 10th	Day	19% 8% 2 5% 4 3 3 3 4 6% 42%	3020
	11th to 20th	Day	14% 9% 3 8% 5% 4 4 3 3 5% 42%	3463
	21st to end	Day	18% 10% 4 6% 4 4 3 2 4 6% 39%	4565
January	1st to 10th	Night	17% 10% 3 6% 3 3 4 3 4 5% 42%	7635
	11th to 20th	Night	15% 8% 4 6% 3 3 3 2 4 5% 48%	7403
	21st to end	Night	20% 9% 3 8% 4 3 3 3 3 4 41%	7745
February	1st to 10th	Night	17% 7% 2 7% 4 4 4 3 5% 6% 43%	2520
	11th to 20th	Night	20% 9% 3 6% 5% 4 3 2 4 4 41%	2458
	21st to end	Night	19% 6% 2 6% 4 4 4 4 6% 5% 40%	2076
March	1st to 10th	Night	20% 9% 3 7% 4 4 4 3 5% 6% 34%	5493
	11th to 20th	Night	12% 7% 2 5% 3 3 4 4 5% 7% 50%	5292
	21st to end	Night	14% 7% 3 7% 5% 4 4 3 4 5% 44%	5322
April	1st to 10th	Night	11% 4 2 6% 4 4 4 4 6% 8% 46%	2100
	11th to 20th	Night	12% 5% 2 5% 3 3 3 3 5% 7% 51%	2075
	21st to end	Night	10% 6% 2 6% 4 3 4 3 4 6% 51%	2100
May	1st to 10th	Night	14% 8% 3 7% 5% 5% 5% 3 6% 7% 35%	5359
	11th to 20th	Night	12% 8% 3 7% 5% 5% 5% 4 6% 8% 36%	5234
	21st to end	Night	13% 8% 3 8% 5% 5% 5% 5% 7% 9% 32%	5761
June	1st to 10th	Night	6% 5% 2 7% 6% 6% 6% 5% 8% 11% 39%	1890
	11th to 20th	Night	5% 3 2 4 4 4 5% 4 9% 12% 49%	1890
	21st to end	Night	5% 4 2 7% 5% 4 6% 4 7% 12% 43%	1890
July	1st to 10th	Night	4 5% 2 6% 5% 6% 6% 6% 10% 13% 37%	5278
	11th to 20th	Night	6% 6% 2 7% 5% 6% 6% 6% 10% 15% 31%	5277
	21st to end	Night	5% 6% 3 8% 6% 6% 7% 6% 10% 12% 31%	5929
August	1st to 10th	Night	4 4 2 6% 4 5% 6% 5% 8% 11% 45%	4604
	11th to 20th	Night	3 3 2 5% 4 4 5% 5% 8% 13% 48%	4560
	21st to end	Night	4 4 2 5% 4 5% 5% 4 7% 9% 52%	5046
September	1st to 10th	Night	8% 5% 2 7% 6% 5% 5% 4 6% 9% 45%	2127
	11th to 20th	Night	10% 6% 2 6% 4 4 5% 4 6% 7% 47%	2310
	21st to end	Night	6% 5% 2 6% 4 5% 4 3 6% 7% 53%	2310
October	1st to 10th	Night	8% 5% 3 5% 3 3 2 3 4 5% 59%	2310
	11th to 20th	Night	11% 4 2 4 3 3 3 2 4 5% 59%	2234
	21st to end	Night	14% 6% 2 5% 3 2 3 2 3 4 56%	2763
November	1st to 10th	Night	10% 5% 1 5% 3 3 4 3 4 5% 57%	2666
	11th to 20th	Night	11% 6% 2 3 4 3 3 3 5% 5% 56%	2730
	21st to end	Night	13% 6% 2 5% 5% 4 4 3 4 6% 48%	2730
December	1st to 10th	Night	20% 7% 2 5% 3 3 3 2 4 6% 47%	4380
	11th to 20th	Night	15% 8% 3 6% 4 4 3 3 4 5% 45%	4952
	21st to end	Night	19% 8% 3 6% 4 3 3 3 5% 6% 40%	6633

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	48% 2 5% 25% 16% 3	5259
	11th to 20th	Day	32% 3 4 23% 32% 6%	5538
	21st to end	Day	54% 2 4 14% 19% 8%	6436
February	1st to 10th	Day	47% 3 6% 20% 19% 5%	2100
	11th to 20th	Day	49% 3 4 19% 19% 7%	2058
	21st to end	Day	48% 4 5% 14% 22% 8%	1730
March	1st to 10th	Day	49% 3 8% 14% 20% 6%	4580
	11th to 20th	Day	38% 3 6% 17% 21% 15%	4873
	21st to end	Day	44% 4 8% 20% 20% 4	5880
April	1st to 10th	Day	37% 4 11% 21% 19% 8%	2520
	11th to 20th	Day	37% 4 7% 21% 25% 7%	2494
	21st to end	Day	34% 5% 11% 25% 22% 3	2520
May	1st to 10th	Day	46% 6% 11% 22% 13% 2	7528
	11th to 20th	Day	45% 4 16% 22% 12% 1	7630
	21st to end	Day	50% 6% 11% 19% 13% 1	8405
June	1st to 10th	Day	41% 8% 15% 20% 15% 1	2730
	11th to 20th	Day	34% 7% 19% 24% 15% 2	2730
	21st to end	Day	35% 8% 17% 25% 11% 4	2730
July	1st to 10th	Day	40% 6% 25% 21% 7%	7615
	11th to 20th	Day	44% 7% 30% 15% 3	7611
	21st to end	Day	48% 7% 22% 20% 4	7948
August	1st to 10th	Day	35% 6% 16% 28% 14% 1	5533
	11th to 20th	Day	28% 4 22% 31% 13% 2	5522
	21st to end	Day	32% 4 14% 28% 20% 3	6079
September	1st to 10th	Day	37% 8% 12% 20% 17% 5%	2469
	11th to 20th	Day	39% 6% 10% 22% 19% 4	2310
	21st to end	Day	34% 5% 9% 22% 23% 7%	2310
October	1st to 10th	Day	25% 3 5% 14% 32% 22%	3700
	11th to 20th	Day	19% 2 4 15% 32% 28%	3601
	21st to end	Day	26% 2 5% 20% 35% 12%	3320
November	1st to 10th	Day	34% 3 7% 18% 27% 12%	1852
	11th to 20th	Day	33% 3 6% 20% 27% 11%	1890
	21st to end	Day	39% 4 7% 18% 25% 8%	1890
December	1st to 10th	Day	44% 2 5% 18% 27% 4	3020
	11th to 20th	Day	47% 2 8% 19% 18% 6%	3460
	21st to end	Day	47% 3 5% 24% 20% 1	4565
January	1st to 10th	Night	46% 2 6% 25% 19% 2	7636
	11th to 20th	Night	41% 2 4 18% 26% 9%	7403
	21st to end	Night	49% 2 3 16% 23% 7%	7745
February	1st to 10th	Night	44% 3 5% 19% 22% 8%	2520
	11th to 20th	Night	48% 2 5% 18% 17% 9%	2459
	21st to end	Night	44% 5% 6% 14% 21% 10%	2076
March	1st to 10th	Night	51% 3 5% 15% 18% 7%	5493
	11th to 20th	Night	35% 3 7% 16% 22% 17%	5292
	21st to end	Night	43% 3 6% 23% 18% 7%	5322
April	1st to 10th	Night	35% 4 13% 21% 20% 7%	2100
	11th to 20th	Night	33% 4 7% 22% 23% 11%	2075
	21st to end	Night	34% 4 11% 25% 22% 5%	2100
May	1st to 10th	Night	46% 6% 12% 17% 16% 3	5387
	11th to 20th	Night	45% 5% 13% 23% 12% 2	5235
	21st to end	Night	46% 8% 12% 20% 13% 1	5771
June	1st to 10th	Night	35% 8% 15% 21% 18% 2	1890
	11th to 20th	Night	27% 7% 21% 27% 16% 2	1890
	21st to end	Night	32% 8% 16% 24% 16% 4	1890
July	1st to 10th	Night	36% 6% 29% 22% 7% 1	5235
	11th to 20th	Night	40% 8% 33% 15% 3 1	5226
	21st to end	Night	43% 7% 27% 18% 5%	5796
August	1st to 10th	Night	31% 5% 20% 30% 13% 1	4592
	11th to 20th	Night	26% 5% 24% 31% 12% 2	4590
	21st to end	Night	28% 4 15% 28% 22% 3	5046
September	1st to 10th	Night	36% 6% 16% 20% 17% 6%	2127
	11th to 20th	Night	35% 8% 10% 22% 21% 5%	2310
	21st to end	Night	31% 3 11% 23% 24% 8%	2310
October	1st to 10th	Night	24% 2 5% 16% 29% 23%	3700
	11th to 20th	Night	18% 2 3 18% 29% 29%	3605
	21st to end	Night	24% 2 3 23% 32% 16%	4463
November	1st to 10th	Night	30% 3 9% 18% 26% 13%	2666
	11th to 20th	Night	32% 2 6% 19% 28% 13%	2730
	21st to end	Night	37% 4 6% 19% 24% 9%	2730
December	1st to 10th	Night	41% 3 5% 21% 26% 5%	4380
	11th to 20th	Night	44% 2 9% 16% 24% 5%	4954
	21st to end	Night	45% 4 6% 25% 19% 2	6633

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	29% 19% 31% 18% 3	330
	11th to 20th	Day	25% 24% 31% 15% 6%	330
	21st to end	Day	28% 22% 36% 12% 2 1	363
February	1st to 10th	Day	24% 22% 40% 11% 3	330
	11th to 20th	Day	37% 18% 33% 11% 2	330
	21st to end	Day	29% 20% 38% 10% 3	273
March	1st to 10th	Day	26% 17% 36% 17% 4 1	330
	11th to 20th	Day	22% 19% 36% 17% 6% 1	440
	21st to end	Day	22% 14% 35% 23% 6% 1	594
April	1st to 10th	Day	20% 11% 34% 24% 9% 1	540
	11th to 20th	Day	17% 11% 36% 23% 12% 1	532
	21st to end	Day	14% 10% 30% 31% 13% 2	540
May	1st to 10th	Day	15% 8% 30% 29% 14% 4	543
	11th to 20th	Day	11% 4 31% 29% 17% 7%	567
	21st to end	Day	16% 4 21% 28% 18% 13%	617
June	1st to 10th	Day	14% 4 16% 31% 23% 12%	570
	11th to 20th	Day	9% 3 14% 27% 29% 18%	570
	21st to end	Day	10% 4 8% 28% 31% 19%	570
July	1st to 10th	Day	6% 2 7% 28% 34% 24%	565
	11th to 20th	Day	8% 1 7% 22% 34% 27%	564
	21st to end	Day	8% 3 8% 25% 35% 21%	620
August	1st to 10th	Day	9% 1 10% 26% 31% 22%	566
	11th to 20th	Day	8% 3 6% 28% 36% 18%	559
	21st to end	Day	12% 2 11% 28% 30% 18%	627
September	1st to 10th	Day	9% 2 11% 35% 29% 14%	570
	11th to 20th	Day	13% 3 12% 29% 34% 11%	570
	21st to end	Day	11% 3 15% 32% 29% 8%	570
October	1st to 10th	Day	13% 5% 24% 34% 19% 5%	570
	11th to 20th	Day	11% 6% 26% 36% 19% 1	542
	21st to end	Day	19% 11% 27% 31% 12% 1	383
November	1st to 10th	Day	21% 8% 34% 27% 8% 2	330
	11th to 20th	Day	17% 12% 42% 22% 6%	330
	21st to end	Day	16% 19% 36% 20% 7% 1	330
December	1st to 10th	Day	29% 15% 33% 20% 3	330
	11th to 20th	Day	24% 15% 39% 15% 6% 1	330
	21st to end	Day	29% 15% 31% 19% 5%	363
January	1st to 10th	Night	21% 13% 35% 26% 4	840
	11th to 20th	Night	24% 14% 30% 25% 7%	840
	21st to end	Night	22% 13% 35% 27% 3	924
February	1st to 10th	Night	22% 11% 33% 30% 5%	840
	11th to 20th	Night	26% 13% 34% 24% 3	823
	21st to end	Night	23% 14% 35% 25% 2	692
March	1st to 10th	Night	20% 11% 32% 31% 6%	840
	11th to 20th	Night	17% 10% 37% 27% 9% 1	840
	21st to end	Night	17% 11% 34% 29% 8%	813
April	1st to 10th	Night	13% 10% 34% 30% 12%	630
	11th to 20th	Night	16% 7% 32% 30% 14% 1	623
	21st to end	Night	14% 8% 26% 34% 17% 2	630
May	1st to 10th	Night	12% 5% 27% 34% 19% 3	630
	11th to 20th	Night	11% 3 24% 34% 24% 4	621
	21st to end	Night	9% 2 14% 35% 33% 6%	683
June	1st to 10th	Night	10% 2 10% 41% 33% 5%	630
	11th to 20th	Night	7% 1 9% 30% 40% 12%	630
	21st to end	Night	7% 2 8% 29% 42% 12%	630
July	1st to 10th	Night	6% 1 5% 28% 44% 15%	615
	11th to 20th	Night	7% 1 4 24% 44% 20%	612
	21st to end	Night	7% 2 6% 25% 47% 14%	690
August	1st to 10th	Night	6% 1 3 27% 48% 15%	627
	11th to 20th	Night	9% 1 6% 27% 45% 11%	624
	21st to end	Night	11% 1 7% 29% 42% 10%	693
September	1st to 10th	Night	9% 3 9% 32% 39% 9%	657
	11th to 20th	Night	13% 3 8% 32% 39% 6%	840
	21st to end	Night	8% 2 14% 33% 39% 4	840
October	1st to 10th	Night	11% 3 20% 36% 25% 5%	840
	11th to 20th	Night	12% 5% 22% 39% 20% 3	813
	21st to end	Night	16% 7% 20% 37% 18% 2	880
November	1st to 10th	Night	14% 5% 20% 38% 19% 3	820
	11th to 20th	Night	15% 6% 30% 35% 12% 1	840
	21st to end	Night	17% 7% 29% 34% 11% 1	840
December	1st to 10th	Night	23% 10% 27% 32% 8% 1	840
	11th to 20th	Night	23% 9% 28% 31% 8%	840
	21st to end	Night	26% 10% 30% 27% 7%	924

Page generated at 2026-10-11 04:06:30. Version ac07

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