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 2024-10-25.

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% 41%	101123
	Night	15% 6% 2 6% 4 4 4 4 5% 7% 43%	97631
Transparency	Day	39% 7% 12% 23% 15% 3	100921
	Night	40% 6% 11% 23% 16% 3	97503
Seeing	Day	18% 13% 29% 24% 12% 4	14985
	Night	17% 12% 30% 28% 11% 1	24432

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	17% 5% 2 5% 4 3 3 3 4 6% 49%	2526
	11th to 20th	Day	16% 10% 3 6% 4 3 4 4 5% 5% 40%	2840
	21st to end	Day	18% 8% 2 7% 5% 4 4 4 4 6% 38%	3124
February	1st to 10th	Day	15% 7% 2 6% 4 5% 5% 3 6% 7% 40%	1710
	11th to 20th	Day	18% 8% 2 5% 3 4 4 2 6% 7% 42%	1743
	21st to end	Day	19% 9% 2 6% 4 4 4 3 4 6% 39%	1570
March	1st to 10th	Day	23% 7% 2 5% 3 4 4 4 5% 7% 37%	3329
	11th to 20th	Day	10% 4 2 5% 4 4 4 4 5% 7% 51%	3480
	21st to end	Day	21% 7% 2 6% 4 3 4 3 4 6% 41%	3910
April	1st to 10th	Day	13% 7% 2 5% 4 4 4 5% 6% 6% 44%	2280
	11th to 20th	Day	13% 5% 2 5% 4 4 4 4 5% 6% 48%	2254
	21st to end	Day	18% 7% 2 5% 5% 4 4 3 6% 6% 41%	2280
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	14% 6% 2 6% 4 3 3 3 4 6% 49%	2027
November	1st to 10th	Day	12% 6% 2 4 3 3 3 3 5% 6% 53%	1728
	11th to 20th	Day	14% 6% 2 5% 3 3 4 4 6% 6% 50%	1710
	21st to end	Day	14% 6% 2 5% 4 4 4 3 4 6% 48%	1535
December	1st to 10th	Day	17% 5% 2 6% 3 4 3 3 7% 7% 43%	1520
	11th to 20th	Day	16% 7% 2 5% 3 3 4 3 5% 6% 46%	1910
	21st to end	Day	17% 7% 3 7% 4 5% 6% 4 5% 7% 37%	2772
January	1st to 10th	Night	15% 8% 2 6% 3 4 4 3 4 6% 45%	4415
	11th to 20th	Night	19% 8% 2 5% 3 3 3 3 5% 5% 45%	4120
	21st to end	Night	19% 10% 3 6% 3 3 3 3 4 5% 42%	4532
February	1st to 10th	Night	16% 8% 3 4 4 4 3 4 6% 6% 42%	2470
	11th to 20th	Night	19% 8% 2 5% 4 4 3 3 4 5% 43%	2322
	21st to end	Night	17% 9% 2 5% 4 4 3 3 5% 6% 43%	1884
March	1st to 10th	Night	21% 7% 3 6% 4 3 4 3 4 5% 40%	3520
	11th to 20th	Night	12% 5% 2 5% 4 4 4 3 5% 7% 49%	3480
	21st to end	Night	15% 8% 3 6% 4 4 3 2 4 5% 46%	3708
April	1st to 10th	Night	16% 7% 2 6% 5% 4 4 4 5% 7% 41%	1900
	11th to 20th	Night	13% 5% 3 6% 4 3 3 5% 5% 6% 47%	1875
	21st to end	Night	18% 6% 2 5% 3 4 4 3 6% 7% 43%	1900
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	16% 5% 2 5% 3 3 4 3 4 7% 49%	2435
November	1st to 10th	Night	12% 6% 2 5% 3 3 3 3 4 5% 53%	2348
	11th to 20th	Night	15% 6% 2 4 3 3 3 3 4 6% 50%	2470
	21st to end	Night	13% 4 2 4 4 4 4 4 6% 6% 48%	2644
December	1st to 10th	Night	18% 7% 2 6% 4 4 3 4 6% 7% 41%	2660
	11th to 20th	Night	17% 5% 2 5% 4 4 4 4 6% 7% 43%	3285
	21st to end	Night	16% 7% 3 6% 4 5% 5% 4 6% 7% 37%	4884

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	36% 4 8% 31% 16% 4	2527
	11th to 20th	Day	45% 5% 10% 20% 16% 4	2840
	21st to end	Day	46% 7% 11% 23% 11% 2	3124
February	1st to 10th	Day	43% 6% 12% 24% 13% 2	1710
	11th to 20th	Day	43% 4 9% 25% 16% 3	1752
	21st to end	Day	47% 4 12% 19% 14% 4	1570
March	1st to 10th	Day	45% 6% 10% 22% 13% 4	3329
	11th to 20th	Day	30% 6% 9% 28% 23% 4	3480
	21st to end	Day	45% 5% 9% 20% 18% 3	3910
April	1st to 10th	Day	38% 7% 12% 21% 18% 5%	2280
	11th to 20th	Day	36% 7% 9% 22% 20% 6%	2254
	21st to end	Day	41% 6% 10% 21% 17% 4	2280
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	38% 6% 10% 23% 20% 3	1900
	11th to 20th	Day	35% 4 10% 25% 22% 4	1900
	21st to end	Day	36% 4 8% 26% 23% 3	2027
November	1st to 10th	Day	32% 5% 11% 28% 19% 4	1728
	11th to 20th	Day	34% 5% 10% 24% 22% 4	1710
	21st to end	Day	38% 4 9% 28% 18% 3	1535
December	1st to 10th	Day	40% 6% 15% 24% 12% 3	1520
	11th to 20th	Day	39% 5% 10% 32% 12% 3	1906
	21st to end	Day	44% 7% 13% 24% 12% 1	2772
January	1st to 10th	Night	39% 6% 8% 26% 16% 4	4415
	11th to 20th	Night	40% 5% 9% 25% 18% 3	4120
	21st to end	Night	45% 4 7% 26% 16% 1	4532
February	1st to 10th	Night	41% 6% 12% 25% 14% 2	2470
	11th to 20th	Night	44% 3 9% 21% 18% 5%	2324
	21st to end	Night	42% 4 11% 22% 17% 5%	1884
March	1st to 10th	Night	46% 5% 8% 25% 14% 2	3520
	11th to 20th	Night	31% 7% 11% 27% 20% 4	3480
	21st to end	Night	41% 5% 8% 20% 20% 6%	3708
April	1st to 10th	Night	42% 6% 9% 19% 20% 4	1900
	11th to 20th	Night	36% 7% 12% 21% 19% 5%	1875
	21st to end	Night	39% 6% 9% 24% 16% 5%	1900
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% 21% 18% 4	2280
	11th to 20th	Night	34% 4 10% 27% 21% 4	2280
	21st to end	Night	35% 6% 8% 25% 22% 5%	2435
November	1st to 10th	Night	34% 5% 10% 25% 21% 6%	2348
	11th to 20th	Night	36% 4 10% 22% 22% 6%	2470
	21st to end	Night	34% 5% 12% 25% 21% 3	2644
December	1st to 10th	Night	43% 5% 12% 24% 15% 3	2660
	11th to 20th	Night	40% 4 11% 23% 19% 3	3288
	21st to end	Night	43% 7% 14% 23% 11% 1	4884

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	26% 24% 31% 14% 4 1	184
	11th to 20th	Day	24% 28% 33% 13% 2	270
	21st to end	Day	20% 25% 36% 16% 1 1	297
February	1st to 10th	Day	23% 24% 36% 13% 3	270
	11th to 20th	Day	32% 23% 36% 7% 2	350
	21st to end	Day	30% 21% 32% 14% 2	382
March	1st to 10th	Day	22% 25% 32% 18% 3 1	460
	11th to 20th	Day	26% 21% 34% 13% 4 1	460
	21st to end	Day	24% 20% 35% 16% 5% 1	506
April	1st to 10th	Day	20% 24% 36% 15% 4 1	460
	11th to 20th	Day	16% 20% 34% 20% 8% 2	452
	21st to end	Day	24% 13% 36% 19% 6% 1	460
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	17% 13% 35% 24% 9% 3	514
November	1st to 10th	Day	16% 13% 35% 22% 10% 4	393
	11th to 20th	Day	17% 19% 33% 21% 8% 2	370
	21st to end	Day	22% 19% 29% 20% 11%	195
December	1st to 10th	Day	19% 26% 36% 14% 5% 1	180
	11th to 20th	Day	22% 23% 31% 19% 5%	180
	21st to end	Day	23% 17% 33% 21% 6%	198
January	1st to 10th	Night	19% 20% 39% 19% 3	760
	11th to 20th	Night	23% 17% 34% 22% 5%	760
	21st to end	Night	19% 20% 38% 22% 2	836
February	1st to 10th	Night	19% 18% 35% 25% 3	760
	11th to 20th	Night	24% 24% 35% 16% 1	743
	21st to end	Night	24% 20% 37% 17% 2	628
March	1st to 10th	Night	19% 18% 37% 23% 3	760
	11th to 20th	Night	21% 19% 36% 19% 4 1	760
	21st to end	Night	19% 16% 40% 21% 4	836
April	1st to 10th	Night	20% 22% 36% 18% 4	760
	11th to 20th	Night	14% 16% 36% 28% 7%	751
	21st to end	Night	21% 12% 32% 28% 8%	760
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% 25% 12% 1	812
November	1st to 10th	Night	15% 10% 35% 27% 11% 2	740
	11th to 20th	Night	18% 18% 30% 25% 9%	760
	21st to end	Night	16% 17% 33% 26% 8% 1	760
December	1st to 10th	Night	21% 18% 33% 19% 8% 1	760
	11th to 20th	Night	18% 15% 39% 22% 6%	760
	21st to end	Night	19% 17% 33% 29% 3	836

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