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 2026-10-29.

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% 40%	149580
	Night	15% 7% 2 6% 4 4 4 3 5% 7% 43%	142494
Transparency	Day	40% 5% 12% 24% 16% 3	153173
	Night	40% 5% 11% 24% 17% 3	146973
Seeing	Day	21% 14% 29% 22% 10% 3	17556
	Night	19% 13% 29% 27% 11% 1	26927

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	13% 5% 2 5% 4 4 4 4 5% 6% 47%	4661
	11th to 20th	Day	14% 8% 3 6% 5% 4 3 3 4 4 46%	5201
	21st to end	Day	14% 6% 2 6% 4 4 4 4 6% 6% 42%	5780
February	1st to 10th	Day	13% 8% 3 6% 5% 4 4 4 7% 7% 40%	1890
	11th to 20th	Day	18% 8% 2 6% 4 4 4 3 6% 7% 39%	1929
	21st to end	Day	17% 10% 2 7% 4 4 4 3 4 5% 40%	1730
March	1st to 10th	Day	20% 4 1 4 3 3 4 4 4 7% 45%	4849
	11th to 20th	Day	12% 7% 2 6% 4 3 4 4 5% 6% 47%	5090
	21st to end	Day	16% 7% 2 6% 4 4 5% 3 5% 6% 40%	5762
April	1st to 10th	Day	16% 7% 2 5% 5% 5% 5% 4 6% 7% 40%	2520
	11th to 20th	Day	14% 6% 2 6% 4 3 4 3 6% 7% 44%	2494
	21st to end	Day	18% 5% 2 5% 4 3 4 3 6% 8% 41%	2520
May	1st to 10th	Day	21% 7% 2 6% 4 4 4 4 6% 8% 35%	7396
	11th to 20th	Day	19% 6% 2 6% 4 4 4 4 7% 8% 36%	8221
	21st to end	Day	24% 5% 2 5% 3 4 4 4 5% 7% 36%	9045
June	1st to 10th	Day	12% 6% 2 5% 5% 4 5% 4 7% 10% 40%	2940
	11th to 20th	Day	13% 5% 2 5% 5% 5% 5% 4 6% 9% 40%	2940
	21st to end	Day	11% 4 2 5% 4 5% 5% 5% 6% 10% 44%	2940
July	1st to 10th	Day	10% 6% 2 6% 5% 5% 5% 5% 7% 9% 40%	8280
	11th to 20th	Day	9% 6% 2 7% 5% 6% 6% 6% 9% 12% 33%	8280
	21st to end	Day	9% 6% 2 6% 5% 4 5% 5% 7% 11% 39%	8365
August	1st to 10th	Day	15% 6% 3 8% 6% 6% 7% 5% 8% 9% 28%	6014
	11th to 20th	Day	12% 6% 2 6% 5% 5% 6% 5% 7% 10% 36%	5648
	21st to end	Day	9% 4 2 5% 4 5% 5% 5% 7% 9% 45%	6080
September	1st to 10th	Day	14% 5% 2 6% 4 3 4 3 5% 7% 46%	2520
	11th to 20th	Day	12% 5% 2 5% 4 4 4 3 5% 8% 47%	2520
	21st to end	Day	22% 7% 3 6% 4 4 5% 4 5% 7% 34%	2231
October	1st to 10th	Day	17% 5% 2 5% 3 3 4 3 5% 6% 46%	2100
	11th to 20th	Day	17% 4 2 5% 4 3 4 3 4 6% 49%	2100
	21st to end	Day	14% 6% 2 5% 4 3 4 3 4 5% 50%	2280
November	1st to 10th	Day	13% 5% 1 5% 4 3 3 3 5% 7% 51%	1886
	11th to 20th	Day	14% 6% 2 4 3 4 4 4 5% 5% 49%	1890
	21st to end	Day	15% 6% 2 5% 4 5% 3 3 4 6% 46%	1680
December	1st to 10th	Day	13% 6% 3 7% 4 3 4 4 6% 7% 45%	2680
	11th to 20th	Day	19% 9% 2 5% 4 4 3 3 4 6% 41%	3070
	21st to end	Day	16% 7% 2 6% 4 4 4 4 5% 8% 38%	4048
January	1st to 10th	Night	12% 7% 2 6% 4 4 4 4 6% 7% 44%	8233
	11th to 20th	Night	14% 8% 2 5% 3 3 3 3 4 5% 50%	7744
	21st to end	Night	15% 7% 2 5% 3 3 4 3 5% 6% 47%	8401
February	1st to 10th	Night	15% 8% 2 6% 5% 4 4 3 5% 7% 40%	2730
	11th to 20th	Night	18% 8% 2 6% 4 3 4 3 5% 6% 42%	2575
	21st to end	Night	15% 8% 3 7% 5% 4 4 3 4 5% 43%	2076
March	1st to 10th	Night	17% 7% 2 5% 3 3 3 3 4 6% 48%	5222
	11th to 20th	Night	10% 7% 2 5% 4 4 4 3 5% 6% 51%	5090
	21st to end	Night	13% 8% 2 6% 5% 4 4 3 4 6% 45%	5411
April	1st to 10th	Night	16% 8% 2 6% 4 4 5% 4 5% 6% 40%	2100
	11th to 20th	Night	13% 7% 2 6% 4 4 4 3 5% 7% 45%	2075
	21st to end	Night	18% 5% 2 4 3 3 4 3 5% 8% 44%	2100
May	1st to 10th	Night	22% 7% 3 6% 5% 4 4 4 5% 7% 34%	5500
	11th to 20th	Night	21% 8% 2 6% 4 3 4 3 6% 8% 34%	4639
	21st to end	Night	25% 7% 2 6% 4 4 4 3 5% 6% 34%	5108
June	1st to 10th	Night	11% 6% 2 5% 5% 4 4 4 6% 9% 45%	1680
	11th to 20th	Night	12% 6% 2 6% 5% 4 5% 4 7% 8% 40%	1680
	21st to end	Night	11% 5% 2 5% 4 5% 4 4 8% 10% 42%	1680
July	1st to 10th	Night	11% 6% 3 8% 5% 5% 5% 4 7% 9% 37%	4678
	11th to 20th	Night	9% 7% 3 8% 6% 6% 5% 5% 7% 10% 34%	4677
	21st to end	Night	9% 6% 2 6% 5% 5% 5% 4 6% 9% 42%	5694
August	1st to 10th	Night	16% 7% 3 8% 5% 5% 5% 5% 7% 10% 29%	4135
	11th to 20th	Night	13% 7% 3 7% 5% 5% 5% 4 6% 8% 36%	4351
	21st to end	Night	12% 5% 3 6% 4 4 4 4 5% 8% 46%	5045
September	1st to 10th	Night	13% 6% 2 5% 4 3 4 3 6% 7% 47%	2100
	11th to 20th	Night	12% 7% 2 5% 3 3 3 3 4 7% 51%	2100
	21st to end	Night	21% 7% 2 7% 5% 4 4 3 5% 6% 37%	2384
October	1st to 10th	Night	19% 6% 2 6% 4 3 3 3 4 5% 45%	2520
	11th to 20th	Night	16% 5% 2 4 3 3 3 2 4 6% 52%	2520
	21st to end	Night	16% 5% 2 4 3 3 4 3 4 6% 51%	2737
November	1st to 10th	Night	11% 5% 2 5% 4 4 3 3 5% 6% 53%	2629
	11th to 20th	Night	14% 7% 2 5% 3 3 3 3 4 6% 49%	2730
	21st to end	Night	13% 5% 2 5% 4 4 4 4 5% 7% 47%	2935
December	1st to 10th	Night	11% 6% 2 5% 4 4 4 3 5% 7% 49%	4720
	11th to 20th	Night	22% 6% 2 5% 3 4 4 3 5% 6% 41%	5345
	21st to end	Night	17% 7% 3 6% 4 4 4 4 6% 7% 37%	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% 4 8% 28% 19% 3	4662
	11th to 20th	Day	42% 3 7% 22% 19% 8%	5201
	21st to end	Day	42% 3 12% 29% 12% 2	5780
February	1st to 10th	Day	43% 4 12% 27% 12% 2	1890
	11th to 20th	Day	45% 3 9% 25% 14% 3	1938
	21st to end	Day	46% 3 10% 23% 13% 4	1730
March	1st to 10th	Day	39% 3 9% 24% 18% 7%	4849
	11th to 20th	Day	37% 5% 9% 26% 18% 6%	5090
	21st to end	Day	44% 4 9% 19% 19% 5%	5762
April	1st to 10th	Day	42% 5% 12% 20% 17% 5%	2520
	11th to 20th	Day	39% 5% 12% 22% 18% 5%	2494
	21st to end	Day	41% 4 10% 22% 18% 3	2520
May	1st to 10th	Day	46% 6% 12% 21% 14% 1	7429
	11th to 20th	Day	44% 6% 12% 25% 12% 1	8225
	21st to end	Day	46% 5% 10% 21% 16% 2	9061
June	1st to 10th	Day	37% 6% 14% 23% 17% 2	2940
	11th to 20th	Day	40% 6% 13% 24% 14% 3	2940
	21st to end	Day	34% 7% 15% 25% 18% 2	2940
July	1st to 10th	Day	38% 10% 14% 21% 15% 3	8210
	11th to 20th	Day	40% 9% 15% 26% 10% 1	8205
	21st to end	Day	36% 7% 11% 24% 20% 1	8180
August	1st to 10th	Day	49% 10% 13% 20% 7%	6001
	11th to 20th	Day	40% 7% 15% 27% 11% 1	5687
	21st to end	Day	33% 7% 15% 28% 16% 1	6080
September	1st to 10th	Day	37% 5% 13% 20% 20% 4	2520
	11th to 20th	Day	36% 5% 9% 28% 20% 3	2520
	21st to end	Day	49% 5% 7% 19% 17% 2	2231
October	1st to 10th	Day	37% 4 7% 19% 28% 5%	3360
	11th to 20th	Day	27% 3 10% 26% 24% 9%	3340
	21st to end	Day	25% 2 10% 29% 28% 5%	3618
November	1st to 10th	Day	32% 3 13% 25% 22% 4	1886
	11th to 20th	Day	36% 3 10% 24% 23% 3	1890
	21st to end	Day	40% 3 11% 30% 14% 2	1680
December	1st to 10th	Day	39% 3 15% 27% 12% 3	2680
	11th to 20th	Day	45% 3 11% 29% 10% 2	3066
	21st to end	Day	44% 5% 15% 19% 15% 2	4048
January	1st to 10th	Night	39% 4 10% 26% 17% 3	8234
	11th to 20th	Night	38% 3 8% 23% 22% 7%	7744
	21st to end	Night	38% 3 7% 29% 20% 3	8401
February	1st to 10th	Night	45% 4 12% 23% 14% 2	2730
	11th to 20th	Night	44% 3 9% 21% 18% 4	2577
	21st to end	Night	44% 2 11% 21% 16% 5%	2076
March	1st to 10th	Night	40% 3 9% 26% 12% 10%	5222
	11th to 20th	Night	34% 4 11% 30% 15% 6%	5090
	21st to end	Night	41% 4 8% 19% 24% 4	5411
April	1st to 10th	Night	43% 4 10% 20% 19% 4	2100
	11th to 20th	Night	40% 4 11% 21% 19% 5%	2075
	21st to end	Night	39% 5% 10% 22% 18% 5%	2100
May	1st to 10th	Night	50% 5% 11% 19% 13% 3	5530
	11th to 20th	Night	47% 5% 12% 24% 10% 1	4640
	21st to end	Night	50% 6% 10% 19% 13% 2	5115
June	1st to 10th	Night	36% 6% 11% 25% 20% 2	1680
	11th to 20th	Night	40% 6% 14% 23% 16% 2	1680
	21st to end	Night	35% 7% 12% 27% 17% 2	1680
July	1st to 10th	Night	42% 8% 15% 18% 13% 3	4640
	11th to 20th	Night	44% 9% 14% 22% 11% 1	4632
	21st to end	Night	37% 7% 14% 24% 18% 1	5565
August	1st to 10th	Night	48% 9% 17% 17% 8% 1	4124
	11th to 20th	Night	43% 7% 13% 24% 11% 1	4378
	21st to end	Night	37% 5% 11% 30% 16% 2	5045
September	1st to 10th	Night	36% 5% 11% 23% 20% 5%	2100
	11th to 20th	Night	35% 4 9% 26% 24% 4	2100
	21st to end	Night	48% 5% 8% 18% 18% 3	2384
October	1st to 10th	Night	42% 4 9% 20% 21% 4	4040
	11th to 20th	Night	26% 3 10% 25% 29% 7%	4019
	21st to end	Night	25% 3 10% 31% 25% 6%	4349
November	1st to 10th	Night	32% 5% 8% 26% 22% 6%	2629
	11th to 20th	Night	38% 3 9% 24% 21% 5%	2730
	21st to end	Night	37% 4 12% 25% 20% 2	2935
December	1st to 10th	Night	36% 3 13% 30% 16% 2	4720
	11th to 20th	Night	45% 3 12% 18% 18% 4	5348
	21st to end	Night	44% 5% 13% 20% 17% 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	33% 23% 30% 10% 4 1	220
	11th to 20th	Day	35% 26% 28% 10% 1	316
	21st to end	Day	25% 30% 31% 11% 3	363
February	1st to 10th	Day	29% 25% 33% 10% 2	330
	11th to 20th	Day	37% 21% 35% 6% 1	416
	21st to end	Day	28% 24% 32% 13% 3	446
March	1st to 10th	Day	29% 24% 29% 16% 3	540
	11th to 20th	Day	30% 21% 31% 13% 4 1	540
	21st to end	Day	26% 21% 33% 14% 4 1	594
April	1st to 10th	Day	25% 22% 34% 13% 4 2	540
	11th to 20th	Day	24% 19% 32% 15% 7% 2	532
	21st to end	Day	27% 16% 35% 15% 6% 1	540
May	1st to 10th	Day	29% 16% 31% 15% 6% 2	543
	11th to 20th	Day	25% 12% 32% 21% 8% 2	567
	21st to end	Day	24% 7% 27% 26% 14% 2	617
June	1st to 10th	Day	15% 11% 31% 26% 12% 4	570
	11th to 20th	Day	18% 9% 29% 30% 12% 2	570
	21st to end	Day	13% 11% 29% 29% 15% 4	570
July	1st to 10th	Day	13% 4 22% 33% 21% 7%	565
	11th to 20th	Day	6% 4 24% 37% 22% 7%	564
	21st to end	Day	12% 5% 29% 32% 19% 4	620
August	1st to 10th	Day	11% 6% 24% 33% 18% 7%	566
	11th to 20th	Day	13% 4 22% 35% 18% 8%	559
	21st to end	Day	10% 5% 30% 30% 17% 8%	627
September	1st to 10th	Day	15% 8% 22% 30% 16% 9%	570
	11th to 20th	Day	14% 6% 21% 35% 16% 7%	570
	21st to end	Day	29% 10% 22% 25% 11% 3	570
October	1st to 10th	Day	24% 8% 26% 23% 14% 5%	570
	11th to 20th	Day	20% 16% 29% 22% 12% 2	570
	21st to end	Day	17% 17% 33% 22% 8% 2	615
November	1st to 10th	Day	18% 14% 36% 22% 9% 2	444
	11th to 20th	Day	21% 19% 33% 19% 8%	430
	21st to end	Day	29% 19% 30% 18% 5%	220
December	1st to 10th	Day	26% 20% 39% 12% 2 1	220
	11th to 20th	Day	30% 21% 33% 13% 3	220
	21st to end	Day	29% 19% 30% 17% 5%	242
January	1st to 10th	Night	22% 19% 36% 21% 3	840
	11th to 20th	Night	25% 18% 32% 21% 4	840
	21st to end	Night	21% 20% 38% 20% 1	924
February	1st to 10th	Night	23% 17% 35% 24% 3	840
	11th to 20th	Night	29% 20% 34% 16% 1	823
	21st to end	Night	25% 18% 36% 18% 3	692
March	1st to 10th	Night	23% 19% 34% 22% 3	840
	11th to 20th	Night	23% 20% 32% 20% 5%	840
	21st to end	Night	21% 18% 39% 18% 4	924
April	1st to 10th	Night	23% 21% 34% 19% 4	840
	11th to 20th	Night	17% 17% 35% 24% 7%	831
	21st to end	Night	22% 15% 30% 26% 7%	840
May	1st to 10th	Night	23% 12% 29% 28% 7% 1	727
	11th to 20th	Night	22% 11% 27% 31% 8%	414
	21st to end	Night	19% 8% 22% 34% 15% 2	455
June	1st to 10th	Night	12% 5% 26% 37% 19% 1	420
	11th to 20th	Night	13% 7% 23% 40% 16% 1	420
	21st to end	Night	12% 3 25% 42% 16%	420
July	1st to 10th	Night	11% 5% 15% 40% 25% 3	410
	11th to 20th	Night	8% 4 16% 41% 29% 2	408
	21st to end	Night	9% 3 18% 42% 24% 3	674
August	1st to 10th	Night	13% 3 14% 40% 27% 3	627
	11th to 20th	Night	15% 4 15% 38% 26% 2	737
	21st to end	Night	14% 4 19% 35% 25% 3	924
September	1st to 10th	Night	15% 5% 21% 34% 23% 3	840
	11th to 20th	Night	13% 5% 17% 35% 26% 4	840
	21st to end	Night	24% 6% 21% 30% 17% 1	840
October	1st to 10th	Night	22% 7% 20% 27% 19% 4	840
	11th to 20th	Night	20% 12% 25% 30% 13% 1	840
	21st to end	Night	19% 14% 28% 27% 12% 1	913
November	1st to 10th	Night	16% 12% 32% 30% 10% 1	820
	11th to 20th	Night	20% 17% 29% 26% 6% 1	840
	21st to end	Night	18% 17% 32% 27% 6%	840
December	1st to 10th	Night	24% 15% 35% 19% 7% 1	840
	11th to 20th	Night	20% 15% 38% 21% 5%	840
	21st to end	Night	23% 15% 34% 25% 3	924

Page generated at 2026-10-26 04:37:53. Version ac07

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