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 2025-04-26.

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	14% 6% 2 6% 4 4 4 4 6% 7% 43%	113654
	Night	15% 6% 2 6% 4 4 4 4 5% 7% 44%	114955
Transparency	Day	38% 7% 12% 23% 17% 4	117290
	Night	38% 6% 11% 23% 18% 4	119458
Seeing	Day	18% 13% 29% 24% 12% 4	15560
	Night	17% 12% 30% 28% 11% 1	25163

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 4 4 3 3 3 4 6% 52%	3620
	11th to 20th	Day	15% 8% 3 5% 4 3 3 3 4 4 48%	4060
	21st to end	Day	15% 7% 2 7% 4 4 4 3 4 6% 44%	4466
February	1st to 10th	Day	15% 7% 2 6% 4 5% 5% 4 6% 7% 40%	1800
	11th to 20th	Day	19% 8% 2 5% 3 4 4 2 5% 7% 41%	1838
	21st to end	Day	18% 9% 2 6% 4 4 4 3 4 6% 40%	1650
March	1st to 10th	Day	20% 6% 1 4 3 3 4 3 5% 6% 44%	4773
	11th to 20th	Day	12% 6% 2 5% 4 4 3 3 5% 6% 51%	4980
	21st to end	Day	17% 6% 2 6% 4 4 4 3 5% 6% 42%	5602
April	1st to 10th	Day	14% 7% 2 5% 4 4 4 4 6% 6% 43%	2400
	11th to 20th	Day	13% 5% 2 5% 4 4 4 4 5% 6% 47%	2374
	21st to end	Day	17% 6% 2 4 5% 4 4 3 6% 6% 41%	2340
May	1st to 10th	Day	25% 7% 3 7% 4 4 3 4 6% 8% 30%	3951
	11th to 20th	Day	22% 7% 2 7% 4 4 5% 4 6% 7% 31%	4352
	21st to end	Day	11% 5% 2 5% 4 4 5% 4 7% 9% 44%	4823
June	1st to 10th	Day	11% 4 2 5% 5% 4 5% 5% 7% 9% 42%	2660
	11th to 20th	Day	11% 5% 2 5% 5% 5% 5% 4 6% 9% 43%	2660
	21st to end	Day	10% 4 2 4 4 5% 6% 5% 7% 11% 42%	2660
July	1st to 10th	Day	6% 4 2 6% 5% 5% 7% 5% 9% 11% 41%	4440
	11th to 20th	Day	9% 5% 2 6% 5% 5% 5% 5% 8% 12% 38%	4379
	21st to end	Day	11% 6% 2 7% 5% 6% 6% 5% 7% 9% 36%	4466
August	1st to 10th	Day	16% 6% 2 7% 4 4 5% 5% 8% 10% 32%	4104
	11th to 20th	Day	11% 5% 2 6% 4 5% 6% 4 7% 8% 41%	3826
	21st to end	Day	10% 4 2 5% 5% 4 5% 4 7% 9% 46%	4180
September	1st to 10th	Day	14% 5% 2 6% 4 5% 5% 3 6% 6% 46%	2280
	11th to 20th	Day	12% 5% 2 6% 4 5% 4 3 6% 9% 46%	2280
	21st to end	Day	21% 7% 2 6% 4 4 4 4 5% 7% 37%	2014
October	1st to 10th	Day	17% 5% 2 5% 3 3 3 3 5% 6% 47%	1900
	11th to 20th	Day	17% 4 2 4 3 3 3 3 4 6% 51%	1900
	21st to end	Day	13% 6% 2 6% 4 3 3 2 4 6% 50%	2090
November	1st to 10th	Day	12% 5% 2 4 3 3 3 4 5% 6% 53%	1821
	11th to 20th	Day	14% 6% 2 5% 3 3 4 4 6% 6% 50%	1800
	21st to end	Day	14% 6% 2 5% 4 4 4 3 4 6% 48%	1615
December	1st to 10th	Day	12% 4 2 6% 4 4 3 3 6% 7% 48%	2600
	11th to 20th	Day	18% 9% 2 5% 3 3 4 3 5% 6% 43%	2990
	21st to end	Day	16% 7% 3 6% 4 4 5% 4 5% 7% 39%	3960
January	1st to 10th	Night	13% 7% 2 5% 4 4 4 3 4 6% 49%	6321
	11th to 20th	Night	15% 6% 2 5% 3 3 3 3 4 5% 52%	5900
	21st to end	Night	15% 8% 2 5% 4 3 3 3 4 5% 47%	6490
February	1st to 10th	Night	16% 8% 2 4 4 4 4 4 6% 6% 42%	2600
	11th to 20th	Night	19% 7% 2 5% 4 4 3 3 4 5% 43%	2447
	21st to end	Night	16% 8% 2 5% 4 4 4 3 5% 6% 44%	1980
March	1st to 10th	Night	16% 6% 2 5% 4 3 3 3 4 5% 49%	5062
	11th to 20th	Night	11% 7% 2 5% 3 3 4 3 5% 7% 50%	4980
	21st to end	Night	13% 7% 3 6% 4 4 4 3 5% 6% 45%	5316
April	1st to 10th	Night	16% 7% 2 6% 5% 4 5% 4 5% 7% 40%	2000
	11th to 20th	Night	14% 5% 3 6% 4 3 3 5% 5% 6% 46%	1975
	21st to end	Night	17% 6% 2 5% 3 4 4 3 6% 8% 43%	1957
May	1st to 10th	Night	22% 9% 3 6% 5% 4 4 4 6% 7% 31%	2972
	11th to 20th	Night	23% 9% 3 7% 4 4 4 4 5% 7% 32%	2541
	21st to end	Night	11% 5% 1 6% 4 5% 4 4 7% 11% 43%	2732
June	1st to 10th	Night	11% 4 2 5% 4 4 4 4 7% 10% 43%	1520
	11th to 20th	Night	11% 4 3 6% 5% 5% 5% 4 6% 10% 41%	1520
	21st to end	Night	9% 5% 2 5% 5% 5% 5% 5% 7% 10% 43%	1520
July	1st to 10th	Night	7% 5% 2 7% 5% 5% 5% 5% 8% 10% 41%	2520
	11th to 20th	Night	9% 6% 2 7% 5% 5% 5% 5% 7% 10% 39%	2576
	21st to end	Night	11% 7% 3 7% 5% 5% 5% 5% 7% 8% 37%	3087
August	1st to 10th	Night	17% 5% 3 7% 4 5% 5% 4 7% 9% 34%	2825
	11th to 20th	Night	12% 6% 3 9% 5% 5% 6% 5% 7% 8% 34%	2969
	21st to end	Night	11% 4 2 6% 4 4 4 4 5% 8% 48%	3476
September	1st to 10th	Night	14% 6% 2 5% 4 4 5% 4 4 7% 46%	1900
	11th to 20th	Night	11% 5% 2 6% 3 3 4 3 5% 8% 49%	1900
	21st to end	Night	20% 7% 2 6% 4 4 4 4 5% 7% 38%	2161
October	1st to 10th	Night	18% 6% 2 5% 4 3 4 3 4 6% 45%	2280
	11th to 20th	Night	15% 4 2 4 3 3 3 3 4 7% 51%	2280
	21st to end	Night	15% 4 2 5% 3 3 4 3 5% 7% 50%	2508
November	1st to 10th	Night	11% 6% 2 6% 3 3 3 3 5% 6% 53%	2475
	11th to 20th	Night	15% 6% 2 4 3 3 3 3 4 6% 49%	2600
	21st to end	Night	13% 4 2 4 4 3 4 4 7% 6% 48%	2784
December	1st to 10th	Night	11% 5% 2 6% 3 3 3 3 5% 7% 52%	4580
	11th to 20th	Night	21% 5% 2 5% 3 4 4 3 5% 6% 40%	5205
	21st to end	Night	17% 7% 2 6% 4 4 5% 4 5% 7% 40%	6996

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	33% 4 7% 28% 24% 5%	3621
	11th to 20th	Day	40% 4 8% 21% 20% 7%	4060
	21st to end	Day	41% 5% 10% 28% 13% 3	4466
February	1st to 10th	Day	43% 6% 12% 25% 12% 2	1800
	11th to 20th	Day	44% 4 9% 24% 16% 3	1847
	21st to end	Day	46% 4 12% 20% 15% 4	1650
March	1st to 10th	Day	40% 5% 9% 21% 18% 7%	4773
	11th to 20th	Day	33% 5% 10% 25% 21% 6%	4980
	21st to end	Day	42% 5% 9% 18% 19% 6%	5602
April	1st to 10th	Day	39% 7% 11% 21% 17% 5%	2400
	11th to 20th	Day	36% 6% 10% 22% 20% 6%	2374
	21st to end	Day	41% 6% 11% 22% 17% 4	2340
May	1st to 10th	Day	50% 8% 11% 19% 10% 1	3986
	11th to 20th	Day	47% 10% 14% 19% 9% 1	4356
	21st to end	Day	33% 9% 14% 25% 17% 3	4837
June	1st to 10th	Day	35% 10% 14% 25% 15% 1	2660
	11th to 20th	Day	36% 10% 13% 23% 17% 2	2660
	21st to end	Day	33% 10% 15% 23% 17% 2	2660
July	1st to 10th	Day	33% 11% 20% 19% 12% 5%	4370
	11th to 20th	Day	36% 9% 18% 26% 9% 2	4304
	21st to end	Day	42% 9% 14% 19% 16% 1	4324
August	1st to 10th	Day	43% 9% 16% 24% 7%	4091
	11th to 20th	Day	36% 9% 13% 28% 13% 1	3865
	21st to end	Day	32% 8% 14% 28% 16% 2	4180
September	1st to 10th	Day	37% 7% 13% 20% 19% 5%	2280
	11th to 20th	Day	35% 6% 10% 24% 21% 4	2280
	21st to end	Day	46% 6% 8% 19% 17% 3	2014
October	1st to 10th	Day	37% 5% 7% 17% 28% 5%	3160
	11th to 20th	Day	25% 3 7% 28% 26% 9%	3140
	21st to end	Day	23% 3 9% 30% 28% 7%	3428
November	1st to 10th	Day	32% 5% 12% 28% 20% 4	1821
	11th to 20th	Day	34% 5% 10% 24% 22% 4	1800
	21st to end	Day	38% 4 9% 28% 18% 3	1615
December	1st to 10th	Day	35% 5% 14% 27% 14% 4	2600
	11th to 20th	Day	42% 4 13% 30% 10% 2	2986
	21st to end	Day	42% 7% 14% 22% 15% 1	3960
January	1st to 10th	Night	36% 5% 6% 25% 24% 5%	6321
	11th to 20th	Night	34% 4 8% 25% 21% 7%	5900
	21st to end	Night	40% 4 7% 27% 19% 2	6490
February	1st to 10th	Night	42% 6% 12% 25% 14% 2	2600
	11th to 20th	Night	44% 3 9% 21% 18% 5%	2449
	21st to end	Night	42% 4 11% 22% 17% 5%	1980
March	1st to 10th	Night	39% 4 7% 25% 15% 9%	5062
	11th to 20th	Night	32% 6% 12% 24% 19% 7%	4980
	21st to end	Night	40% 5% 9% 20% 21% 6%	5316
April	1st to 10th	Night	43% 6% 9% 18% 19% 4	2000
	11th to 20th	Night	36% 7% 12% 21% 20% 5%	1975
	21st to end	Night	39% 6% 10% 23% 17% 5%	1957
May	1st to 10th	Night	51% 8% 11% 18% 10% 2	3002
	11th to 20th	Night	50% 9% 11% 19% 10% 1	2542
	21st to end	Night	32% 10% 17% 22% 16% 3	2739
June	1st to 10th	Night	34% 8% 12% 26% 18% 2	1520
	11th to 20th	Night	37% 9% 14% 24% 14% 3	1520
	21st to end	Night	34% 8% 15% 22% 18% 3	1520
July	1st to 10th	Night	37% 9% 22% 18% 11% 3	2480
	11th to 20th	Night	38% 9% 19% 23% 9% 1	2528
	21st to end	Night	42% 8% 13% 22% 14% 1	2988
August	1st to 10th	Night	45% 8% 17% 21% 8%	2814
	11th to 20th	Night	44% 9% 12% 23% 10% 1	2996
	21st to end	Night	33% 6% 12% 29% 17% 2	3476
September	1st to 10th	Night	39% 7% 10% 21% 18% 5%	1900
	11th to 20th	Night	33% 6% 10% 25% 22% 4	1900
	21st to end	Night	44% 8% 10% 17% 17% 3	2161
October	1st to 10th	Night	41% 5% 10% 19% 19% 5%	3800
	11th to 20th	Night	24% 4 11% 22% 32% 8%	3779
	21st to end	Night	22% 4 10% 31% 25% 8%	4120
November	1st to 10th	Night	33% 5% 10% 24% 22% 6%	2475
	11th to 20th	Night	37% 4 10% 22% 21% 6%	2600
	21st to end	Night	34% 5% 12% 24% 21% 3	2784
December	1st to 10th	Night	33% 4 13% 27% 21% 3	4580
	11th to 20th	Night	44% 4 13% 19% 16% 4	5208
	21st to end	Night	42% 6% 14% 21% 16% 1	6996

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	205
	11th to 20th	Day	25% 28% 33% 12% 2	300
	21st to end	Day	20% 26% 37% 15% 2 1	330
February	1st to 10th	Day	25% 25% 35% 11% 3	300
	11th to 20th	Day	35% 23% 34% 7% 2	385
	21st to end	Day	29% 21% 34% 14% 2	414
March	1st to 10th	Day	23% 24% 32% 18% 2 1	500
	11th to 20th	Day	27% 20% 34% 13% 5% 1	500
	21st to end	Day	23% 21% 35% 15% 4 1	550
April	1st to 10th	Day	22% 24% 35% 14% 4 1	500
	11th to 20th	Day	17% 21% 34% 19% 7% 2	492
	21st to end	Day	24% 13% 36% 20% 6% 1	480
May	1st to 10th	Day	24% 16% 31% 19% 8% 2	463
	11th to 20th	Day	20% 11% 33% 24% 9% 1	487
	21st to end	Day	19% 7% 24% 30% 16% 4	529
June	1st to 10th	Day	13% 8% 30% 26% 18% 5%	490
	11th to 20th	Day	13% 8% 28% 32% 15% 4	490
	21st to end	Day	11% 6% 28% 34% 16% 5%	490
July	1st to 10th	Day	9% 3 20% 37% 24% 8%	485
	11th to 20th	Day	4 1 19% 42% 27% 7%	484
	21st to end	Day	12% 2 22% 36% 23% 4	532
August	1st to 10th	Day	11% 5% 21% 33% 23% 7%	486
	11th to 20th	Day	12% 3 18% 35% 22% 9%	479
	21st to end	Day	9% 4 22% 32% 23% 10%	539
September	1st to 10th	Day	17% 5% 20% 28% 20% 11%	490
	11th to 20th	Day	13% 4 26% 31% 20% 7%	490
	21st to end	Day	26% 10% 26% 26% 10% 3	490
October	1st to 10th	Day	22% 8% 22% 25% 17% 5%	490
	11th to 20th	Day	17% 13% 29% 24% 13% 3	490
	21st to end	Day	16% 12% 35% 24% 10% 3	539
November	1st to 10th	Day	15% 14% 35% 23% 9% 4	426
	11th to 20th	Day	17% 19% 34% 21% 8% 2	400
	21st to end	Day	24% 20% 28% 19% 10%	215
December	1st to 10th	Day	19% 25% 38% 14% 5% 1	200
	11th to 20th	Day	22% 22% 33% 19% 5%	200
	21st to end	Day	22% 18% 34% 21% 5%	220
January	1st to 10th	Night	20% 21% 38% 18% 3	800
	11th to 20th	Night	22% 18% 34% 22% 4	800
	21st to end	Night	19% 20% 38% 22% 2	880
February	1st to 10th	Night	20% 17% 36% 24% 3	800
	11th to 20th	Night	25% 24% 34% 15% 1	783
	21st to end	Night	23% 19% 38% 17% 2	660
March	1st to 10th	Night	19% 19% 37% 22% 3	800
	11th to 20th	Night	21% 19% 36% 19% 5% 1	800
	21st to end	Night	19% 16% 40% 20% 4	880
April	1st to 10th	Night	21% 21% 36% 18% 4	800
	11th to 20th	Night	15% 17% 35% 27% 6%	791
	21st to end	Night	20% 12% 32% 28% 8%	783
May	1st to 10th	Night	21% 10% 33% 26% 10% 1	667
	11th to 20th	Night	16% 10% 33% 30% 11%	407
	21st to end	Night	15% 4 24% 36% 18% 1	411
June	1st to 10th	Night	12% 3 27% 39% 19% 1	380
	11th to 20th	Night	9% 6% 28% 40% 16% 1	380
	21st to end	Night	10% 3 27% 46% 14% 1	380
July	1st to 10th	Night	8% 2 23% 39% 26% 2	370
	11th to 20th	Night	7% 1 16% 45% 29% 3	398
	21st to end	Night	8% 2 22% 40% 24% 4	624
August	1st to 10th	Night	10% 3 15% 45% 25% 2	567
	11th to 20th	Night	11% 3 18% 41% 25% 2	670
	21st to end	Night	12% 3 16% 38% 26% 5%	836
September	1st to 10th	Night	16% 3 20% 34% 24% 4	760
	11th to 20th	Night	13% 4 16% 38% 25% 4	760
	21st to end	Night	23% 6% 24% 30% 16% 1	760
October	1st to 10th	Night	19% 8% 23% 28% 18% 5%	760
	11th to 20th	Night	16% 11% 27% 31% 13% 1	760
	21st to end	Night	18% 12% 32% 26% 12% 1	836
November	1st to 10th	Night	14% 10% 35% 27% 11% 2	780
	11th to 20th	Night	18% 18% 30% 25% 8%	800
	21st to end	Night	16% 17% 33% 26% 8% 1	800
December	1st to 10th	Night	21% 17% 34% 19% 8% 1	800
	11th to 20th	Night	19% 15% 38% 23% 6%	800
	21st to end	Night	19% 16% 32% 29% 3	880

Page generated at 2025-04-23 09:25:03. Version ac07

Copyright © 2025 Attilla Danko.