Dulaney Springs Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dulaney Springs Park clear sky chart from 2005-11-06 to 2025-06-10.

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 5% 4 6% 8% 41%	119620
	Night	15% 7% 2 6% 4 4 4 3 5% 7% 43%	118615
Transparency	Day	40% 5% 11% 24% 16% 3	123254
	Night	40% 4 11% 24% 18% 4	123119
Seeing	Day	21% 14% 29% 22% 11% 3	15690
	Night	20% 13% 29% 27% 11% 1	25186

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	14% 5% 2 4 3 3 4 4 5% 6% 50%	3597
	11th to 20th	Day	13% 8% 3 8% 5% 4 4 3 4 5% 43%	3995
	21st to end	Day	16% 8% 2 6% 4 4 4 3 5% 6% 43%	4466
February	1st to 10th	Day	14% 8% 3 6% 5% 4 4 4 7% 6% 39%	1800
	11th to 20th	Day	18% 7% 2 5% 4 4 4 3 6% 7% 39%	1835
	21st to end	Day	18% 10% 2 6% 4 4 4 3 4 5% 41%	1650
March	1st to 10th	Day	19% 4 1 4 3 3 4 4 5% 7% 46%	4744
	11th to 20th	Day	11% 7% 2 6% 4 3 4 3 5% 6% 47%	4980
	21st to end	Day	16% 7% 2 6% 4 4 5% 3 5% 6% 40%	5638
April	1st to 10th	Day	16% 7% 2 5% 5% 6% 5% 4 6% 7% 39%	2400
	11th to 20th	Day	14% 6% 2 6% 4 3 4 3 6% 6% 44%	2374
	21st to end	Day	18% 5% 2 5% 4 4 4 3 6% 8% 41%	2400
May	1st to 10th	Day	24% 7% 2 6% 4 4 4 4 6% 8% 31%	5698
	11th to 20th	Day	24% 6% 2 6% 4 4 4 4 7% 8% 31%	6318
	21st to end	Day	17% 5% 2 6% 4 5% 5% 4 7% 8% 38%	6934
June	1st to 10th	Day	13% 6% 2 5% 5% 4 5% 5% 7% 10% 39%	2786
	11th to 20th	Day	12% 5% 2 5% 5% 5% 5% 4 6% 9% 40%	2660
	21st to end	Day	10% 4 2 5% 4 5% 5% 5% 7% 10% 44%	2660
July	1st to 10th	Day	6% 5% 2 5% 5% 5% 7% 6% 8% 11% 41%	4440
	11th to 20th	Day	9% 5% 2 6% 5% 5% 5% 6% 8% 11% 38%	4440
	21st to end	Day	11% 7% 3 7% 6% 5% 6% 5% 7% 9% 34%	4477
August	1st to 10th	Day	18% 5% 2 6% 5% 5% 6% 5% 7% 8% 32%	4104
	11th to 20th	Day	11% 5% 2 6% 5% 5% 6% 5% 6% 9% 39%	3831
	21st to end	Day	11% 5% 2 5% 4 5% 5% 4 6% 9% 46%	4180
September	1st to 10th	Day	15% 5% 2 6% 4 3 4 3 5% 7% 45%	2280
	11th to 20th	Day	12% 5% 2 5% 4 4 4 3 5% 9% 47%	2280
	21st to end	Day	21% 7% 2 6% 4 4 4 4 5% 7% 35%	2019
October	1st to 10th	Day	18% 5% 2 5% 3 3 4 3 5% 6% 45%	1900
	11th to 20th	Day	17% 4 2 4 4 3 4 3 4 6% 48%	1900
	21st to end	Day	15% 6% 2 6% 4 3 4 3 4 5% 48%	2090
November	1st to 10th	Day	13% 5% 1 5% 4 3 3 3 5% 7% 51%	1794
	11th to 20th	Day	14% 6% 2 4 3 4 4 4 5% 6% 49%	1800
	21st to end	Day	15% 6% 2 5% 4 5% 3 3 4 6% 46%	1600
December	1st to 10th	Day	13% 6% 3 6% 4 3 4 3 6% 7% 45%	2600
	11th to 20th	Day	19% 9% 2 5% 4 4 3 3 4 6% 41%	2990
	21st to end	Day	16% 7% 2 6% 4 4 4 4 5% 8% 38%	3960
January	1st to 10th	Night	13% 6% 2 6% 3 4 3 3 5% 7% 48%	6349
	11th to 20th	Night	14% 7% 2 5% 3 3 3 3 4 6% 50%	5950
	21st to end	Night	17% 7% 2 6% 3 3 4 3 4 5% 46%	6490
February	1st to 10th	Night	16% 8% 2 6% 4 4 4 3 5% 7% 40%	2600
	11th to 20th	Night	18% 8% 2 6% 4 3 4 3 5% 6% 42%	2449
	21st to end	Night	15% 8% 3 7% 5% 4 4 3 4 5% 42%	1980
March	1st to 10th	Night	17% 6% 2 5% 4 3 3 3 4 6% 48%	5108
	11th to 20th	Night	10% 7% 2 4 4 4 4 3 5% 6% 51%	4980
	21st to end	Night	13% 8% 2 6% 5% 4 4 3 4 6% 45%	5294
April	1st to 10th	Night	17% 8% 2 6% 4 4 5% 4 6% 6% 39%	2000
	11th to 20th	Night	14% 7% 2 6% 4 4 4 3 5% 7% 44%	1975
	21st to end	Night	18% 5% 2 4 3 3 4 3 5% 7% 44%	2000
May	1st to 10th	Night	25% 8% 3 5% 5% 4 4 4 6% 7% 30%	4226
	11th to 20th	Night	24% 9% 3 6% 4 4 4 3 6% 7% 30%	3575
	21st to end	Night	20% 6% 2 6% 4 4 4 4 6% 8% 37%	3920
June	1st to 10th	Night	11% 6% 2 5% 5% 4 4 4 6% 9% 45%	1598
	11th to 20th	Night	11% 6% 2 6% 5% 4 4 5% 7% 8% 41%	1520
	21st to end	Night	10% 5% 2 5% 4 5% 4 5% 8% 10% 43%	1520
July	1st to 10th	Night	6% 5% 3 8% 5% 5% 6% 6% 8% 10% 38%	2520
	11th to 20th	Night	9% 6% 2 6% 6% 5% 5% 5% 7% 10% 39%	2520
	21st to end	Night	12% 7% 3 7% 5% 5% 5% 4 5% 8% 39%	3073
August	1st to 10th	Night	19% 5% 2 6% 4 4 5% 5% 7% 10% 33%	2825
	11th to 20th	Night	12% 8% 3 7% 5% 5% 5% 4 6% 7% 37%	2965
	21st to end	Night	13% 5% 2 5% 3 4 4 3 6% 8% 48%	3476
September	1st to 10th	Night	14% 6% 2 6% 4 3 3 3 5% 7% 47%	1900
	11th to 20th	Night	11% 7% 2 5% 3 4 3 3 4 7% 52%	1900
	21st to end	Night	20% 7% 2 6% 4 4 4 2 5% 6% 40%	2157
October	1st to 10th	Night	20% 6% 2 6% 4 3 3 3 4 5% 43%	2280
	11th to 20th	Night	15% 4 2 4 3 3 3 2 4 7% 52%	2280
	21st to end	Night	17% 5% 2 4 3 3 4 3 4 6% 49%	2508
November	1st to 10th	Night	11% 5% 2 5% 4 4 3 3 4 5% 54%	2501
	11th to 20th	Night	14% 8% 2 5% 3 3 3 3 4 6% 49%	2600
	21st to end	Night	13% 5% 2 5% 4 4 4 4 5% 7% 48%	2795
December	1st to 10th	Night	11% 6% 2 5% 4 4 4 3 5% 7% 49%	4580
	11th to 20th	Night	22% 6% 2 5% 3 4 4 3 5% 6% 40%	5205
	21st to end	Night	17% 7% 3 6% 4 4 4 4 6% 7% 37%	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	34% 4 7% 28% 23% 4	3598
	11th to 20th	Day	45% 3 7% 21% 17% 7%	3995
	21st to end	Day	43% 3 12% 26% 13% 2	4466
February	1st to 10th	Day	44% 4 12% 27% 11% 2	1800
	11th to 20th	Day	45% 3 9% 26% 15% 3	1844
	21st to end	Day	46% 3 10% 23% 14% 4	1650
March	1st to 10th	Day	39% 3 9% 24% 18% 7%	4744
	11th to 20th	Day	36% 4 9% 26% 18% 6%	4980
	21st to end	Day	45% 4 8% 19% 19% 6%	5638
April	1st to 10th	Day	43% 5% 11% 20% 17% 5%	2400
	11th to 20th	Day	39% 5% 11% 22% 18% 6%	2374
	21st to end	Day	41% 4 10% 22% 19% 3	2400
May	1st to 10th	Day	50% 6% 13% 18% 11% 2	5731
	11th to 20th	Day	50% 6% 11% 21% 10% 1	6322
	21st to end	Day	41% 7% 12% 23% 16% 2	6949
June	1st to 10th	Day	38% 7% 14% 23% 16% 2	2786
	11th to 20th	Day	39% 7% 13% 24% 14% 3	2660
	21st to end	Day	33% 7% 15% 25% 18% 2	2660
July	1st to 10th	Day	34% 11% 17% 21% 13% 5%	4370
	11th to 20th	Day	36% 8% 17% 27% 10% 1	4365
	21st to end	Day	43% 8% 12% 19% 17% 1	4334
August	1st to 10th	Day	47% 8% 12% 24% 8%	4091
	11th to 20th	Day	38% 7% 11% 29% 14% 1	3870
	21st to end	Day	34% 6% 12% 28% 17% 2	4180
September	1st to 10th	Day	39% 5% 12% 19% 21% 4	2280
	11th to 20th	Day	35% 5% 9% 27% 21% 4	2280
	21st to end	Day	48% 4 7% 20% 19% 2	2019
October	1st to 10th	Day	38% 4 7% 19% 28% 5%	3160
	11th to 20th	Day	26% 3 10% 26% 24% 9%	3140
	21st to end	Day	25% 2 10% 30% 28% 5%	3428
November	1st to 10th	Day	33% 4 13% 25% 22% 4	1794
	11th to 20th	Day	36% 3 10% 25% 23% 3	1800
	21st to end	Day	40% 3 11% 30% 14% 2	1600
December	1st to 10th	Day	38% 3 16% 27% 12% 4	2600
	11th to 20th	Day	46% 3 11% 29% 10% 1	2986
	21st to end	Day	44% 5% 15% 19% 15% 2	3960
January	1st to 10th	Night	37% 3 8% 26% 22% 4	6349
	11th to 20th	Night	36% 3 9% 26% 20% 7%	5950
	21st to end	Night	41% 2 8% 28% 18% 2	6490
February	1st to 10th	Night	45% 4 13% 24% 13% 1	2600
	11th to 20th	Night	44% 3 9% 22% 18% 4	2451
	21st to end	Night	45% 2 11% 21% 16% 5%	1980
March	1st to 10th	Night	39% 3 9% 27% 12% 10%	5108
	11th to 20th	Night	34% 4 11% 29% 15% 6%	4980
	21st to end	Night	41% 4 8% 19% 24% 4	5294
April	1st to 10th	Night	44% 5% 10% 20% 19% 4	2000
	11th to 20th	Night	40% 4 10% 21% 20% 5%	1975
	21st to end	Night	39% 5% 10% 22% 19% 5%	2000
May	1st to 10th	Night	53% 5% 11% 17% 11% 3	4256
	11th to 20th	Night	52% 6% 11% 19% 10% 1	3576
	21st to end	Night	44% 7% 13% 22% 12% 2	3927
June	1st to 10th	Night	36% 6% 12% 25% 19% 2	1598
	11th to 20th	Night	38% 7% 14% 24% 16% 2	1520
	21st to end	Night	34% 7% 13% 27% 17% 3	1520
July	1st to 10th	Night	39% 9% 20% 16% 12% 4	2480
	11th to 20th	Night	38% 9% 17% 25% 11% 2	2472
	21st to end	Night	42% 7% 13% 21% 16% 1	2975
August	1st to 10th	Night	44% 8% 18% 21% 8% 1	2814
	11th to 20th	Night	44% 6% 10% 26% 13% 1	2992
	21st to end	Night	35% 5% 11% 31% 17% 2	3476
September	1st to 10th	Night	37% 5% 11% 22% 20% 5%	1900
	11th to 20th	Night	34% 3 9% 26% 24% 4	1900
	21st to end	Night	46% 4 8% 19% 19% 3	2157
October	1st to 10th	Night	43% 4 10% 19% 21% 4	3800
	11th to 20th	Night	25% 3 10% 26% 30% 7%	3779
	21st to end	Night	25% 3 11% 31% 25% 5%	4120
November	1st to 10th	Night	33% 5% 8% 26% 22% 6%	2501
	11th to 20th	Night	38% 3 9% 25% 20% 5%	2600
	21st to end	Night	37% 4 12% 25% 20% 2	2795
December	1st to 10th	Night	36% 3 13% 30% 16% 2	4580
	11th to 20th	Night	46% 3 13% 18% 17% 4	5208
	21st to end	Night	44% 5% 13% 20% 17% 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	34% 24% 29% 10% 4 1	200
	11th to 20th	Day	35% 24% 30% 11% 1	287
	21st to end	Day	25% 28% 32% 12% 3	330
February	1st to 10th	Day	30% 25% 33% 10% 2	300
	11th to 20th	Day	37% 22% 35% 5% 1	382
	21st to end	Day	29% 24% 31% 14% 3	414
March	1st to 10th	Day	27% 24% 30% 17% 3	500
	11th to 20th	Day	29% 21% 31% 13% 4 1	500
	21st to end	Day	27% 21% 33% 15% 4 1	550
April	1st to 10th	Day	26% 22% 34% 13% 3 1	500
	11th to 20th	Day	25% 19% 31% 15% 7% 2	492
	21st to end	Day	27% 16% 35% 14% 6% 1	500
May	1st to 10th	Day	30% 15% 31% 15% 7% 2	503
	11th to 20th	Day	26% 12% 32% 20% 8% 2	527
	21st to end	Day	21% 7% 28% 27% 15% 3	573
June	1st to 10th	Day	17% 12% 29% 25% 13% 4	526
	11th to 20th	Day	17% 7% 28% 31% 14% 3	490
	21st to end	Day	12% 11% 31% 29% 14% 3	490
July	1st to 10th	Day	13% 4 22% 33% 21% 8%	485
	11th to 20th	Day	6% 4 23% 38% 22% 7%	484
	21st to end	Day	13% 5% 29% 30% 19% 4	532
August	1st to 10th	Day	11% 6% 23% 34% 19% 7%	486
	11th to 20th	Day	12% 3 22% 35% 18% 9%	479
	21st to end	Day	10% 5% 27% 31% 18% 9%	539
September	1st to 10th	Day	16% 9% 19% 29% 17% 10%	490
	11th to 20th	Day	13% 6% 21% 34% 17% 8%	490
	21st to end	Day	29% 10% 21% 25% 12% 3	490
October	1st to 10th	Day	26% 8% 26% 22% 14% 5%	490
	11th to 20th	Day	18% 16% 28% 22% 14% 2	490
	21st to end	Day	18% 16% 35% 21% 8% 2	539
November	1st to 10th	Day	17% 13% 36% 22% 10% 2	412
	11th to 20th	Day	20% 19% 33% 20% 9% 1	400
	21st to end	Day	29% 18% 29% 19% 6%	200
December	1st to 10th	Day	25% 20% 39% 13% 3 1	200
	11th to 20th	Day	30% 21% 32% 14% 4	200
	21st to end	Day	28% 18% 30% 18% 5%	220
January	1st to 10th	Night	23% 19% 35% 20% 3	800
	11th to 20th	Night	25% 18% 32% 21% 4	800
	21st to end	Night	21% 19% 38% 20% 1	880
February	1st to 10th	Night	23% 16% 35% 24% 3	800
	11th to 20th	Night	30% 20% 34% 15% 1	783
	21st to end	Night	25% 18% 36% 18% 3	660
March	1st to 10th	Night	23% 19% 34% 21% 3	800
	11th to 20th	Night	23% 20% 32% 20% 5% 1	800
	21st to end	Night	21% 18% 38% 18% 4	880
April	1st to 10th	Night	23% 21% 34% 18% 4	800
	11th to 20th	Night	18% 17% 34% 24% 7%	791
	21st to end	Night	22% 15% 31% 25% 7%	800
May	1st to 10th	Night	23% 11% 29% 29% 8% 1	692
	11th to 20th	Night	23% 11% 27% 31% 8% 1	394
	21st to end	Night	18% 8% 22% 35% 16% 2	433
June	1st to 10th	Night	13% 4 26% 38% 19% 1	400
	11th to 20th	Night	12% 6% 23% 41% 18% 1	380
	21st to end	Night	11% 3 27% 43% 16%	380
July	1st to 10th	Night	10% 5% 16% 41% 25% 3	370
	11th to 20th	Night	8% 4 16% 40% 29% 2	368
	21st to end	Night	10% 3 18% 42% 24% 3	610
August	1st to 10th	Night	13% 2 14% 41% 26% 3	567
	11th to 20th	Night	15% 4 15% 37% 26% 3	666
	21st to end	Night	14% 4 17% 34% 26% 4	836
September	1st to 10th	Night	16% 4 21% 32% 23% 3	760
	11th to 20th	Night	13% 5% 17% 34% 27% 4	760
	21st to end	Night	24% 5% 22% 30% 18% 1	760
October	1st to 10th	Night	24% 8% 20% 27% 18% 4	760
	11th to 20th	Night	19% 11% 25% 31% 13% 1	760
	21st to end	Night	20% 14% 28% 26% 12% 1	836
November	1st to 10th	Night	15% 11% 32% 30% 10% 2	780
	11th to 20th	Night	20% 17% 29% 27% 7% 1	800
	21st to end	Night	18% 17% 32% 27% 6% 1	800
December	1st to 10th	Night	24% 15% 34% 19% 7% 1	800
	11th to 20th	Night	20% 15% 39% 21% 6%	800
	21st to end	Night	23% 15% 34% 26% 3	880

Page generated at 2025-06-07 10:28:15. Version ac07

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