Baltimore Woods Nature Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Baltimore Woods Nature Center clear sky chart from 2005-11-06 to 2026-05-17.

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	17% 12% 4 10% 6% 5% 4 4 5% 6% 28%	132283
	Night	17% 13% 5% 11% 6% 5% 4 3 5% 5% 26%	130529
Transparency	Day	54% 7% 12% 18% 9% 1	135813
	Night	58% 7% 11% 16% 8% 1	135086
Seeing	Day	25% 19% 29% 17% 8% 2	16534
	Night	24% 17% 27% 23% 8% 1	25850

By Month

Percentage Cloud Cover NE (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% 20% 9% 23% 8% 4 2 2 3 3 12%	4661
	11th to 20th	Day	12% 20% 9% 18% 10% 7% 4 3 4 4 10%	4650
	21st to end	Day	14% 14% 8% 14% 12% 10% 5% 3 4 4 12%	5753
February	1st to 10th	Day	16% 17% 8% 16% 10% 5% 4 4 4 3 13%	1890
	11th to 20th	Day	15% 18% 7% 18% 8% 5% 4 3 3 4 15%	1869
	21st to end	Day	18% 18% 4 15% 7% 4 3 3 5% 4 18%	1730
March	1st to 10th	Day	18% 16% 6% 14% 7% 4 3 2 3 4 23%	4707
	11th to 20th	Day	11% 20% 6% 8% 5% 3 4 3 4 6% 30%	5090
	21st to end	Day	16% 14% 5% 13% 5% 4 3 3 3 5% 28%	5818
April	1st to 10th	Day	19% 15% 4 9% 5% 4 4 3 4 5% 28%	2520
	11th to 20th	Day	19% 13% 3 6% 4 4 5% 4 4 6% 33%	2494
	21st to end	Day	22% 12% 3 6% 3 4 4 4 5% 6% 32%	2562
May	1st to 10th	Day	30% 10% 3 7% 5% 4 4 3 4 5% 26%	6381
	11th to 20th	Day	17% 9% 3 8% 5% 5% 5% 4 5% 7% 32%	6402
	21st to end	Day	23% 8% 3 6% 4 4 4 4 6% 7% 31%	6949
June	1st to 10th	Day	19% 8% 3 6% 4 4 5% 4 6% 7% 34%	2800
	11th to 20th	Day	18% 6% 2 6% 6% 4 4 4 7% 9% 35%	2800
	21st to end	Day	15% 6% 2 7% 5% 5% 5% 4 7% 9% 35%	2800
July	1st to 10th	Day	12% 5% 2 6% 4 5% 5% 5% 7% 10% 39%	6360
	11th to 20th	Day	10% 6% 2 7% 5% 5% 6% 5% 8% 11% 36%	6360
	21st to end	Day	12% 6% 2 6% 4 4 5% 4 6% 8% 43%	6926
August	1st to 10th	Day	18% 5% 2 6% 4 4 5% 4 6% 8% 36%	4245
	11th to 20th	Day	17% 6% 3 7% 6% 5% 4 4 6% 8% 33%	4078
	21st to end	Day	17% 6% 2 6% 5% 5% 4 4 5% 7% 40%	4312
September	1st to 10th	Day	16% 5% 2 6% 4 5% 5% 3 6% 8% 41%	2400
	11th to 20th	Day	16% 5% 2 6% 4 3 4 3 4 6% 45%	2400
	21st to end	Day	18% 7% 3 7% 5% 4 5% 4 6% 6% 34%	2127
October	1st to 10th	Day	19% 7% 3 7% 4 4 5% 4 5% 7% 36%	2000
	11th to 20th	Day	22% 10% 3 8% 4 4 4 4 5% 7% 31%	2000
	21st to end	Day	25% 16% 2 7% 4 4 5% 3 5% 6% 23%	2121
November	1st to 10th	Day	15% 14% 3 8% 6% 5% 4 3 5% 6% 31%	1851
	11th to 20th	Day	16% 18% 5% 8% 5% 4 4 4 5% 5% 25%	1753
	21st to end	Day	19% 20% 5% 9% 6% 5% 3 3 4 6% 18%	1680
December	1st to 10th	Day	17% 24% 9% 16% 6% 5% 4 3 3 5% 10%	2680
	11th to 20th	Day	18% 19% 8% 14% 5% 4 3 3 3 4 20%	3066
	21st to end	Day	20% 17% 6% 13% 6% 6% 4 3 4 6% 14%	4048
January	1st to 10th	Night	15% 20% 9% 25% 8% 4 3 2 3 3 9%	8234
	11th to 20th	Night	10% 20% 10% 19% 9% 5% 4 3 4 4 11%	8235
	21st to end	Night	13% 13% 6% 16% 11% 9% 6% 4 4 4 15%	8424
February	1st to 10th	Night	15% 17% 6% 16% 8% 5% 5% 2 5% 4 18%	2730
	11th to 20th	Night	14% 16% 7% 17% 8% 7% 5% 2 4 4 16%	2637
	21st to end	Night	17% 15% 5% 17% 6% 5% 4 3 4 6% 18%	2076
March	1st to 10th	Night	17% 12% 8% 13% 8% 4 3 3 4 5% 24%	5348
	11th to 20th	Night	16% 17% 6% 8% 4 3 3 3 5% 5% 29%	5089
	21st to end	Night	21% 12% 5% 11% 4 4 4 3 4 4 28%	5355
April	1st to 10th	Night	20% 14% 5% 7% 5% 4 5% 3 5% 5% 27%	2100
	11th to 20th	Night	20% 12% 3 7% 5% 5% 4 3 4 5% 33%	2075
	21st to end	Night	21% 11% 3 6% 3 4 4 4 5% 6% 34%	2076
May	1st to 10th	Night	31% 11% 3 8% 5% 3 4 3 4 5% 23%	3776
	11th to 20th	Night	18% 8% 3 7% 5% 5% 5% 4 6% 7% 35%	3623
	21st to end	Night	24% 7% 2 6% 4 4 4 4 6% 6% 33%	3926
June	1st to 10th	Night	19% 6% 3 7% 5% 3 4 4 6% 7% 36%	1600
	11th to 20th	Night	16% 7% 3 6% 5% 3 5% 4 7% 8% 37%	1600
	21st to end	Night	14% 7% 2 6% 5% 5% 4 4 6% 7% 41%	1600
July	1st to 10th	Night	11% 6% 3 8% 5% 5% 5% 4 7% 9% 38%	3600
	11th to 20th	Night	12% 5% 2 7% 4 4 4 4 6% 8% 43%	3600
	21st to end	Night	11% 6% 3 5% 4 3 5% 3 5% 8% 47%	3926
August	1st to 10th	Night	17% 7% 2 5% 4 4 5% 4 6% 7% 39%	2900
	11th to 20th	Night	14% 6% 2 7% 5% 4 5% 4 6% 7% 40%	2936
	21st to end	Night	13% 6% 2 6% 5% 4 4 4 6% 8% 44%	3586
September	1st to 10th	Night	14% 6% 2 7% 4 4 4 3 5% 7% 45%	2000
	11th to 20th	Night	16% 4 2 5% 3 3 4 3 5% 6% 48%	2000
	21st to end	Night	19% 8% 1 6% 4 4 4 5% 6% 7% 36%	2269
October	1st to 10th	Night	21% 7% 2 7% 5% 5% 4 4 5% 5% 35%	2400
	11th to 20th	Night	22% 9% 3 6% 4 5% 5% 3 5% 7% 32%	2400
	21st to end	Night	27% 13% 3 9% 5% 3 3 3 4 6% 25%	2717
November	1st to 10th	Night	17% 14% 4 8% 5% 5% 3 4 4 5% 33%	2667
	11th to 20th	Night	18% 17% 3 8% 5% 5% 4 3 4 6% 27%	2866
	21st to end	Night	17% 20% 5% 8% 5% 4 5% 4 5% 5% 21%	2940
December	1st to 10th	Night	15% 21% 9% 14% 6% 6% 5% 3 4 4 11%	4720
	11th to 20th	Night	20% 18% 7% 13% 5% 4 4 2 3 4 19%	5348
	21st to end	Night	23% 19% 6% 11% 6% 4 3 2 3 5% 17%	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	77% 5% 9% 7% 2	4662
	11th to 20th	Day	76% 6% 8% 5% 4 1	4680
	21st to end	Day	75% 5% 9% 8% 3	5753
February	1st to 10th	Day	75% 6% 7% 9% 2	1890
	11th to 20th	Day	74% 6% 7% 10% 3	1878
	21st to end	Day	70% 4 10% 11% 4	1730
March	1st to 10th	Day	66% 5% 10% 13% 5%	4710
	11th to 20th	Day	55% 6% 18% 12% 8% 1	5090
	21st to end	Day	58% 5% 8% 17% 11% 1	5818
April	1st to 10th	Day	58% 5% 9% 16% 10% 1	2520
	11th to 20th	Day	51% 7% 11% 18% 12% 1	2494
	21st to end	Day	53% 6% 9% 18% 12% 2	2562
May	1st to 10th	Day	60% 6% 9% 15% 9% 1	6392
	11th to 20th	Day	50% 8% 11% 21% 10% 1	6406
	21st to end	Day	50% 8% 12% 19% 10% 1	6949
June	1st to 10th	Day	47% 9% 12% 18% 13% 1	2800
	11th to 20th	Day	44% 8% 14% 22% 11% 1	2800
	21st to end	Day	45% 9% 15% 20% 11% 1	2800
July	1st to 10th	Day	39% 7% 14% 27% 13% 1	6290
	11th to 20th	Day	38% 9% 16% 24% 11% 1	6285
	21st to end	Day	38% 7% 13% 30% 12%	6728
August	1st to 10th	Day	44% 8% 14% 20% 13% 1	4231
	11th to 20th	Day	47% 8% 16% 22% 6%	4117
	21st to end	Day	43% 6% 12% 32% 7% 1	4312
September	1st to 10th	Day	40% 8% 12% 28% 11% 1	2400
	11th to 20th	Day	40% 6% 11% 26% 16% 1	2400
	21st to end	Day	48% 7% 11% 23% 10% 1	2127
October	1st to 10th	Day	42% 7% 14% 25% 11% 1	3260
	11th to 20th	Day	47% 5% 15% 19% 13%	3240
	21st to end	Day	47% 7% 15% 22% 8% 1	3411
November	1st to 10th	Day	53% 8% 11% 17% 10% 1	1851
	11th to 20th	Day	59% 6% 12% 14% 7% 2	1753
	21st to end	Day	67% 7% 13% 12% 2	1680
December	1st to 10th	Day	79% 5% 8% 6% 1	2680
	11th to 20th	Day	69% 5% 12% 9% 5%	3066
	21st to end	Day	69% 7% 11% 9% 3	4048
January	1st to 10th	Night	81% 5% 6% 5% 2	8234
	11th to 20th	Night	74% 6% 8% 7% 5%	8280
	21st to end	Night	71% 5% 9% 8% 7%	8424
February	1st to 10th	Night	69% 6% 8% 11% 5%	2730
	11th to 20th	Night	72% 6% 9% 10% 4	2639
	21st to end	Night	67% 6% 10% 10% 6%	2076
March	1st to 10th	Night	62% 6% 12% 14% 7%	5358
	11th to 20th	Night	55% 6% 17% 14% 5% 3	5090
	21st to end	Night	59% 5% 7% 19% 9% 1	5355
April	1st to 10th	Night	59% 6% 11% 16% 7% 2	2100
	11th to 20th	Night	54% 6% 10% 16% 13% 1	2075
	21st to end	Night	49% 6% 11% 18% 13% 3	2076
May	1st to 10th	Night	63% 6% 8% 11% 8% 3	3782
	11th to 20th	Night	46% 8% 14% 20% 11% 1	3624
	21st to end	Night	49% 8% 13% 17% 12% 1	3927
June	1st to 10th	Night	45% 7% 13% 20% 14% 1	1600
	11th to 20th	Night	42% 9% 13% 20% 14% 1	1600
	21st to end	Night	40% 9% 11% 25% 14% 1	1600
July	1st to 10th	Night	41% 7% 15% 21% 15% 1	3560
	11th to 20th	Night	37% 7% 15% 25% 15% 1	3552
	21st to end	Night	35% 6% 12% 29% 17% 1	3809
August	1st to 10th	Night	42% 9% 14% 24% 10% 1	2890
	11th to 20th	Night	43% 7% 16% 25% 9%	2963
	21st to end	Night	36% 8% 14% 32% 10% 1	3586
September	1st to 10th	Night	39% 8% 13% 25% 14% 2	2000
	11th to 20th	Night	37% 5% 12% 29% 16% 1	2000
	21st to end	Night	44% 9% 13% 22% 11% 1	2269
October	1st to 10th	Night	50% 7% 10% 21% 12%	3920
	11th to 20th	Night	49% 5% 13% 17% 13% 2	3899
	21st to end	Night	50% 6% 12% 24% 7% 1	4377
November	1st to 10th	Night	53% 7% 10% 18% 10% 2	2667
	11th to 20th	Night	58% 7% 10% 16% 6% 2	2866
	21st to end	Night	63% 8% 13% 13% 3	2940
December	1st to 10th	Night	76% 6% 10% 7% 1	4720
	11th to 20th	Night	68% 6% 8% 10% 7%	5348
	21st to end	Night	71% 7% 8% 10% 4 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	34% 27% 29% 8% 3	220
	11th to 20th	Day	32% 33% 26% 7% 1	220
	21st to end	Day	31% 27% 31% 8% 2	357
February	1st to 10th	Day	32% 32% 29% 7% 1	330
	11th to 20th	Day	32% 33% 30% 4	356
	21st to end	Day	36% 25% 29% 9% 1	446
March	1st to 10th	Day	29% 24% 31% 14% 2	540
	11th to 20th	Day	34% 23% 29% 11% 3	540
	21st to end	Day	35% 24% 24% 12% 3 1	594
April	1st to 10th	Day	35% 23% 26% 11% 5%	540
	11th to 20th	Day	31% 27% 24% 10% 7% 2	532
	21st to end	Day	33% 18% 28% 15% 5% 2	540
May	1st to 10th	Day	30% 19% 30% 13% 6% 2	543
	11th to 20th	Day	22% 16% 32% 19% 8% 3	551
	21st to end	Day	20% 14% 30% 22% 12% 2	573
June	1st to 10th	Day	22% 18% 29% 21% 8% 1	530
	11th to 20th	Day	17% 15% 31% 24% 10% 2	530
	21st to end	Day	18% 16% 34% 23% 7% 2	530
July	1st to 10th	Day	12% 12% 31% 29% 13% 3	525
	11th to 20th	Day	13% 9% 31% 30% 15% 2	524
	21st to end	Day	13% 8% 40% 26% 11% 3	576
August	1st to 10th	Day	12% 10% 29% 28% 16% 6%	526
	11th to 20th	Day	16% 10% 28% 26% 15% 6%	519
	21st to end	Day	14% 13% 31% 23% 13% 7%	583
September	1st to 10th	Day	17% 14% 24% 24% 14% 8%	530
	11th to 20th	Day	14% 8% 26% 23% 19% 10%	530
	21st to end	Day	19% 15% 29% 20% 13% 4	530
October	1st to 10th	Day	22% 15% 27% 18% 13% 5%	530
	11th to 20th	Day	29% 20% 25% 18% 7% 1	530
	21st to end	Day	35% 19% 28% 15% 3	539
November	1st to 10th	Day	28% 22% 27% 16% 6% 1	425
	11th to 20th	Day	34% 24% 24% 15% 2 1	293
	21st to end	Day	42% 20% 30% 7%	220
December	1st to 10th	Day	36% 25% 29% 6% 4	220
	11th to 20th	Day	35% 29% 25% 10% 1	220
	21st to end	Day	32% 28% 29% 10% 2	242
January	1st to 10th	Night	28% 30% 29% 12% 2	840
	11th to 20th	Night	28% 27% 28% 15% 3	840
	21st to end	Night	22% 25% 33% 16% 4	924
February	1st to 10th	Night	28% 23% 32% 17% 1	840
	11th to 20th	Night	27% 25% 32% 15% 1	823
	21st to end	Night	28% 25% 30% 14% 3	692
March	1st to 10th	Night	27% 21% 31% 18% 3	840
	11th to 20th	Night	28% 24% 27% 19% 3	840
	21st to end	Night	28% 21% 28% 18% 5%	924
April	1st to 10th	Night	27% 19% 31% 21% 2	840
	11th to 20th	Night	27% 18% 27% 21% 6% 1	831
	21st to end	Night	26% 13% 28% 26% 6%	816
May	1st to 10th	Night	27% 12% 23% 30% 8% 1	470
	11th to 20th	Night	15% 10% 33% 32% 8% 1	406
	21st to end	Night	15% 8% 32% 33% 12%	433
June	1st to 10th	Night	20% 7% 25% 34% 13% 1	400
	11th to 20th	Night	17% 10% 21% 39% 13% 1	400
	21st to end	Night	14% 7% 30% 41% 8% 1	400
July	1st to 10th	Night	11% 4 22% 45% 16% 2	390
	11th to 20th	Night	12% 3 22% 45% 18% 1	388
	21st to end	Night	13% 5% 26% 43% 12% 1	438
August	1st to 10th	Night	12% 5% 25% 37% 20% 1	582
	11th to 20th	Night	13% 6% 21% 34% 24% 3	629
	21st to end	Night	14% 7% 24% 33% 21% 1	880
September	1st to 10th	Night	16% 8% 25% 31% 19% 2	800
	11th to 20th	Night	16% 7% 18% 32% 24% 4	800
	21st to end	Night	20% 13% 21% 27% 17% 2	800
October	1st to 10th	Night	24% 13% 25% 20% 18% 1	800
	11th to 20th	Night	26% 16% 30% 21% 7%	800
	21st to end	Night	35% 14% 27% 20% 3	880
November	1st to 10th	Night	27% 19% 27% 19% 7%	820
	11th to 20th	Night	30% 22% 25% 16% 5% 1	840
	21st to end	Night	28% 25% 28% 15% 4	840
December	1st to 10th	Night	32% 25% 26% 15% 2	840
	11th to 20th	Night	28% 27% 29% 14% 2	840
	21st to end	Night	31% 26% 28% 13% 2	924

Page generated at 2026-05-14 01:58:54. Version ac07

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