Bowie
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bowie clear sky chart from 2005-11-06 to 2026-08-30.

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	15% 6% 2 6% 4 4 4 4 6% 8% 42%	143954
	Night	15% 6% 2 6% 4 4 4 4 5% 7% 43%	138265
Transparency	Day	38% 7% 12% 24% 17% 3	147547
	Night	39% 6% 11% 23% 18% 4	142743
Seeing	Day	19% 13% 29% 24% 12% 3	17369
	Night	17% 13% 30% 28% 11% 1	26788

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	15% 4 2 6% 5% 4 4 3 4 5% 48%	4698
	11th to 20th	Day	16% 8% 3 5% 3 3 3 3 3 4 51%	5280
	21st to end	Day	14% 6% 2 7% 4 4 4 3 4 7% 45%	5780
February	1st to 10th	Day	14% 7% 2 6% 4 5% 5% 4 6% 7% 41%	1890
	11th to 20th	Day	19% 8% 2 6% 3 4 4 2 5% 6% 40%	1932
	21st to end	Day	18% 9% 2 7% 4 4 4 3 4 6% 40%	1730
March	1st to 10th	Day	20% 6% 2 4 3 3 4 3 5% 6% 44%	4879
	11th to 20th	Day	12% 6% 2 5% 4 4 3 3 5% 6% 50%	5090
	21st to end	Day	17% 6% 2 6% 4 4 4 3 5% 7% 42%	5726
April	1st to 10th	Day	14% 7% 2 5% 4 4 4 4 6% 6% 44%	2520
	11th to 20th	Day	13% 5% 2 5% 4 4 4 4 5% 6% 47%	2494
	21st to end	Day	17% 7% 2 4 4 4 4 3 6% 6% 42%	2520
May	1st to 10th	Day	20% 6% 2 7% 3 4 4 4 6% 8% 36%	7373
	11th to 20th	Day	19% 5% 2 6% 4 4 4 4 6% 8% 38%	8121
	21st to end	Day	22% 6% 2 5% 4 4 4 3 5% 7% 37%	9045
June	1st to 10th	Day	11% 4 2 5% 5% 4 5% 5% 7% 9% 43%	2940
	11th to 20th	Day	11% 5% 2 5% 5% 5% 5% 4 6% 8% 43%	2940
	21st to end	Day	11% 5% 1 4 4 5% 6% 4 7% 10% 43%	2940
July	1st to 10th	Day	9% 5% 2 6% 4 5% 5% 5% 7% 10% 42%	8280
	11th to 20th	Day	10% 5% 2 7% 5% 5% 6% 6% 9% 13% 32%	8163
	21st to end	Day	9% 5% 2 6% 5% 6% 6% 5% 8% 10% 39%	8340
August	1st to 10th	Day	16% 6% 2 6% 4 4 5% 5% 7% 10% 33%	4364
	11th to 20th	Day	11% 5% 2 6% 4 5% 6% 4 7% 9% 40%	4072
	21st to end	Day	10% 4 2 4 5% 4 5% 4 7% 9% 46%	4420
September	1st to 10th	Day	14% 5% 2 6% 4 4 4 3 6% 6% 47%	2400
	11th to 20th	Day	12% 5% 2 6% 4 5% 3 3 6% 9% 46%	2400
	21st to end	Day	20% 8% 2 6% 4 4 4 4 5% 7% 36%	2120
October	1st to 10th	Day	16% 5% 2 5% 3 3 3 3 5% 6% 48%	2000
	11th to 20th	Day	17% 5% 2 4 3 3 3 3 4 6% 51%	2000
	21st to end	Day	13% 6% 2 6% 3 3 3 3 5% 6% 50%	2200
November	1st to 10th	Day	12% 5% 2 4 3 3 3 4 5% 7% 53%	1914
	11th to 20th	Day	13% 6% 2 5% 3 3 4 3 6% 6% 50%	1890
	21st to end	Day	14% 6% 2 5% 4 4 4 3 4 6% 48%	1695
December	1st to 10th	Day	13% 5% 3 6% 4 4 3 3 6% 7% 47%	2680
	11th to 20th	Day	18% 9% 2 5% 3 3 4 3 5% 6% 43%	3070
	21st to end	Day	15% 7% 3 6% 4 4 5% 4 5% 7% 39%	4048
January	1st to 10th	Night	12% 7% 2 6% 4 4 5% 4 6% 6% 45%	8191
	11th to 20th	Night	15% 7% 2 5% 3 3 3 3 4 5% 51%	7680
	21st to end	Night	14% 7% 2 5% 4 3 3 3 5% 5% 48%	8401
February	1st to 10th	Night	15% 8% 2 5% 4 4 4 4 6% 6% 42%	2730
	11th to 20th	Night	19% 7% 2 5% 4 4 3 3 4 5% 43%	2572
	21st to end	Night	16% 9% 2 5% 4 4 4 3 5% 6% 43%	2076
March	1st to 10th	Night	16% 6% 2 5% 4 3 3 3 4 5% 49%	5176
	11th to 20th	Night	11% 6% 2 5% 3 3 4 3 5% 7% 50%	5090
	21st to end	Night	13% 7% 3 6% 4 4 4 3 5% 5% 45%	5434
April	1st to 10th	Night	16% 7% 2 6% 5% 4 5% 4 5% 7% 41%	2100
	11th to 20th	Night	13% 5% 2 6% 4 4 3 4 5% 7% 47%	2075
	21st to end	Night	17% 5% 2 5% 3 4 4 3 6% 7% 44%	2100
May	1st to 10th	Night	19% 8% 3 7% 5% 5% 5% 4 6% 7% 33%	5536
	11th to 20th	Night	20% 7% 2 5% 4 4 4 3 6% 8% 36%	4725
	21st to end	Night	24% 7% 2 7% 4 4 4 3 6% 7% 33%	5108
June	1st to 10th	Night	11% 5% 2 5% 4 4 4 4 7% 10% 44%	1680
	11th to 20th	Night	12% 5% 3 7% 5% 5% 5% 4 6% 10% 40%	1680
	21st to end	Night	10% 5% 2 6% 5% 5% 5% 5% 6% 10% 42%	1680
July	1st to 10th	Night	11% 6% 3 7% 5% 5% 4 5% 7% 9% 40%	4678
	11th to 20th	Night	11% 7% 3 8% 6% 6% 6% 5% 7% 10% 32%	4789
	21st to end	Night	10% 6% 2 7% 5% 5% 5% 5% 7% 9% 40%	5736
August	1st to 10th	Night	17% 5% 3 7% 4 5% 5% 4 6% 9% 34%	3005
	11th to 20th	Night	12% 6% 3 9% 5% 6% 6% 5% 7% 8% 34%	3161
	21st to end	Night	11% 4 2 6% 4 4 4 4 5% 8% 47%	3677
September	1st to 10th	Night	13% 6% 2 5% 4 4 5% 4 4 7% 47%	2000
	11th to 20th	Night	12% 5% 3 6% 3 3 4 4 5% 7% 49%	2000
	21st to end	Night	20% 7% 2 6% 4 4 4 4 5% 7% 37%	2275
October	1st to 10th	Night	18% 6% 2 5% 4 3 4 3 4 6% 46%	2400
	11th to 20th	Night	16% 4 2 4 3 3 3 2 4 7% 51%	2400
	21st to end	Night	15% 4 2 5% 3 3 4 3 5% 7% 50%	2640
November	1st to 10th	Night	11% 6% 2 6% 3 3 3 3 5% 5% 53%	2602
	11th to 20th	Night	15% 6% 2 5% 3 3 3 3 4 6% 50%	2730
	21st to end	Night	13% 4 2 4 4 4 4 4 6% 6% 48%	2923
December	1st to 10th	Night	11% 5% 2 6% 3 3 3 3 5% 7% 52%	4720
	11th to 20th	Night	21% 5% 2 5% 3 4 4 3 5% 6% 41%	5345
	21st to end	Night	17% 7% 2 6% 4 4 5% 4 5% 7% 40%	7150

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	38% 3 8% 27% 20% 4	4699
	11th to 20th	Day	38% 3 6% 22% 22% 8%	5280
	21st to end	Day	39% 5% 10% 32% 12% 3	5780
February	1st to 10th	Day	42% 6% 12% 25% 13% 2	1890
	11th to 20th	Day	45% 4 9% 24% 16% 3	1941
	21st to end	Day	46% 4 12% 21% 14% 4	1730
March	1st to 10th	Day	40% 5% 9% 21% 18% 7%	4879
	11th to 20th	Day	33% 5% 10% 25% 21% 6%	5090
	21st to end	Day	42% 5% 9% 19% 18% 6%	5726
April	1st to 10th	Day	39% 6% 12% 21% 18% 5%	2520
	11th to 20th	Day	36% 6% 10% 22% 20% 6%	2494
	21st to end	Day	40% 6% 11% 22% 17% 4	2520
May	1st to 10th	Day	44% 7% 14% 19% 15% 1	7405
	11th to 20th	Day	41% 8% 12% 26% 13% 1	8125
	21st to end	Day	45% 7% 10% 20% 16% 2	9061
June	1st to 10th	Day	34% 9% 14% 24% 17% 2	2940
	11th to 20th	Day	36% 10% 13% 22% 17% 2	2940
	21st to end	Day	33% 10% 14% 24% 18% 1	2940
July	1st to 10th	Day	36% 10% 18% 20% 14% 3	8210
	11th to 20th	Day	40% 10% 16% 24% 9% 1	8088
	21st to end	Day	37% 8% 13% 22% 20% 1	8156
August	1st to 10th	Day	43% 9% 16% 24% 7%	4351
	11th to 20th	Day	37% 9% 14% 28% 12% 1	4111
	21st to end	Day	32% 8% 14% 28% 16% 2	4420
September	1st to 10th	Day	36% 7% 13% 21% 18% 5%	2400
	11th to 20th	Day	35% 6% 10% 25% 20% 4	2400
	21st to end	Day	47% 6% 9% 19% 16% 3	2120
October	1st to 10th	Day	36% 5% 7% 18% 29% 5%	3260
	11th to 20th	Day	26% 3 7% 28% 26% 9%	3240
	21st to end	Day	23% 3 9% 30% 28% 7%	3538
November	1st to 10th	Day	31% 5% 12% 28% 20% 4	1914
	11th to 20th	Day	34% 5% 10% 24% 22% 4	1890
	21st to end	Day	38% 4 9% 28% 18% 3	1695
December	1st to 10th	Day	36% 5% 14% 27% 14% 4	2680
	11th to 20th	Day	41% 4 12% 30% 10% 2	3066
	21st to end	Day	42% 7% 14% 22% 15% 1	4048
January	1st to 10th	Night	38% 5% 9% 25% 19% 4	8192
	11th to 20th	Night	36% 4 7% 23% 22% 8%	7680
	21st to end	Night	38% 4 7% 30% 19% 3	8401
February	1st to 10th	Night	42% 6% 12% 24% 15% 2	2730
	11th to 20th	Night	44% 3 9% 21% 18% 5%	2574
	21st to end	Night	41% 4 11% 22% 17% 5%	2076
March	1st to 10th	Night	39% 4 7% 25% 15% 9%	5176
	11th to 20th	Night	32% 6% 12% 24% 19% 7%	5090
	21st to end	Night	40% 5% 9% 20% 21% 5%	5434
April	1st to 10th	Night	42% 6% 10% 19% 19% 4	2100
	11th to 20th	Night	36% 7% 12% 21% 20% 5%	2075
	21st to end	Night	38% 6% 10% 24% 17% 5%	2100
May	1st to 10th	Night	49% 7% 11% 19% 12% 2	5566
	11th to 20th	Night	44% 7% 12% 24% 12% 1	4726
	21st to end	Night	49% 7% 11% 17% 15% 2	5115
June	1st to 10th	Night	34% 8% 11% 25% 20% 2	1680
	11th to 20th	Night	39% 8% 14% 23% 14% 3	1680
	21st to end	Night	35% 8% 15% 21% 18% 3	1680
July	1st to 10th	Night	41% 9% 16% 20% 13% 2	4640
	11th to 20th	Night	45% 10% 16% 20% 9% 1	4744
	21st to end	Night	38% 8% 14% 23% 16% 1	5606
August	1st to 10th	Night	45% 8% 17% 21% 8%	2994
	11th to 20th	Night	44% 9% 13% 23% 10% 1	3188
	21st to end	Night	34% 6% 12% 29% 17% 2	3677
September	1st to 10th	Night	38% 7% 10% 22% 18% 6%	2000
	11th to 20th	Night	34% 6% 10% 25% 21% 3	2000
	21st to end	Night	45% 8% 11% 17% 16% 3	2275
October	1st to 10th	Night	40% 5% 10% 19% 20% 5%	3920
	11th to 20th	Night	25% 4 11% 22% 31% 8%	3899
	21st to end	Night	23% 4 10% 31% 25% 8%	4252
November	1st to 10th	Night	33% 5% 10% 24% 22% 6%	2602
	11th to 20th	Night	37% 4 9% 22% 21% 6%	2730
	21st to end	Night	34% 5% 12% 24% 21% 3	2923
December	1st to 10th	Night	33% 3 13% 27% 20% 3	4720
	11th to 20th	Night	44% 4 12% 19% 16% 4	5348
	21st to end	Night	42% 6% 14% 21% 16% 1	7150

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	30% 23% 30% 13% 4	226
	11th to 20th	Day	26% 29% 31% 12% 2	330
	21st to end	Day	20% 28% 36% 14% 1 1	363
February	1st to 10th	Day	26% 25% 34% 13% 3	330
	11th to 20th	Day	35% 22% 33% 8% 1	419
	21st to end	Day	29% 22% 33% 13% 2	446
March	1st to 10th	Day	24% 24% 31% 17% 3 1	540
	11th to 20th	Day	28% 20% 33% 14% 4 1	540
	21st to end	Day	23% 22% 36% 14% 4 1	594
April	1st to 10th	Day	22% 24% 34% 16% 4 1	540
	11th to 20th	Day	17% 20% 34% 19% 7% 2	532
	21st to end	Day	24% 13% 35% 20% 7% 1	540
May	1st to 10th	Day	23% 17% 33% 18% 7% 1	543
	11th to 20th	Day	20% 12% 34% 24% 9% 1	567
	21st to end	Day	22% 9% 24% 28% 14% 4	617
June	1st to 10th	Day	12% 8% 31% 26% 18% 5%	570
	11th to 20th	Day	14% 10% 27% 31% 14% 4	570
	21st to end	Day	12% 6% 27% 32% 17% 6%	570
July	1st to 10th	Day	10% 3 20% 35% 25% 7%	565
	11th to 20th	Day	4 2 20% 42% 26% 7%	564
	21st to end	Day	11% 2 23% 36% 23% 5%	620
August	1st to 10th	Day	12% 4 21% 34% 21% 7%	566
	11th to 20th	Day	13% 4 19% 36% 20% 8%	559
	21st to end	Day	9% 5% 24% 32% 21% 10%	619
September	1st to 10th	Day	16% 5% 22% 28% 19% 10%	530
	11th to 20th	Day	13% 4 25% 31% 20% 7%	530
	21st to end	Day	26% 10% 26% 25% 9% 3	530
October	1st to 10th	Day	21% 8% 22% 26% 17% 6%	530
	11th to 20th	Day	19% 14% 29% 23% 13% 2	530
	21st to end	Day	16% 15% 34% 23% 9% 3	583
November	1st to 10th	Day	16% 14% 36% 22% 8% 3	459
	11th to 20th	Day	18% 19% 33% 20% 7% 1	430
	21st to end	Day	26% 19% 29% 18% 9%	235
December	1st to 10th	Day	21% 23% 38% 14% 4	220
	11th to 20th	Day	22% 21% 34% 18% 5%	220
	21st to end	Day	24% 19% 33% 19% 5%	242
January	1st to 10th	Night	19% 21% 39% 18% 3	840
	11th to 20th	Night	23% 18% 34% 21% 4	840
	21st to end	Night	19% 20% 38% 21% 2	924
February	1st to 10th	Night	20% 17% 36% 24% 3	840
	11th to 20th	Night	25% 24% 34% 16% 1	823
	21st to end	Night	23% 20% 37% 18% 2	692
March	1st to 10th	Night	20% 19% 37% 22% 3	840
	11th to 20th	Night	21% 19% 35% 19% 5% 1	840
	21st to end	Night	19% 17% 40% 20% 4	924
April	1st to 10th	Night	20% 22% 36% 18% 4	840
	11th to 20th	Night	14% 17% 35% 28% 6%	831
	21st to end	Night	20% 11% 33% 28% 7%	840
May	1st to 10th	Night	20% 11% 34% 25% 9% 1	737
	11th to 20th	Night	16% 10% 34% 30% 10%	450
	21st to end	Night	17% 5% 24% 35% 17% 1	455
June	1st to 10th	Night	11% 3 28% 38% 19%	420
	11th to 20th	Night	11% 7% 27% 39% 15% 1	420
	21st to end	Night	10% 3 27% 45% 14% 1	420
July	1st to 10th	Night	8% 3 22% 40% 26% 2	410
	11th to 20th	Night	7% 1 16% 45% 29% 2	442
	21st to end	Night	8% 2 22% 40% 24% 3	690
August	1st to 10th	Night	10% 3 16% 44% 25% 2	627
	11th to 20th	Night	11% 3 17% 41% 25% 2	742
	21st to end	Night	12% 4 16% 38% 25% 4	917
September	1st to 10th	Night	16% 3 21% 34% 23% 4	800
	11th to 20th	Night	14% 4 16% 38% 25% 4	800
	21st to end	Night	24% 6% 23% 31% 16% 1	800
October	1st to 10th	Night	18% 8% 23% 28% 18% 5%	800
	11th to 20th	Night	17% 11% 28% 30% 13% 1	800
	21st to end	Night	18% 12% 32% 26% 11% 1	880
November	1st to 10th	Night	15% 11% 35% 28% 10% 1	820
	11th to 20th	Night	18% 18% 31% 24% 8%	840
	21st to end	Night	17% 17% 33% 26% 7% 1	840
December	1st to 10th	Night	21% 18% 34% 19% 8% 1	840
	11th to 20th	Night	20% 15% 37% 23% 5%	840
	21st to end	Night	20% 16% 33% 28% 3	924

Page generated at 2026-08-27 04:07:13. Version ac07

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