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 2025-01-22.

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 9% 5% 4 4 4 5% 7% 29%	105256
	Night	18% 13% 5% 10% 5% 4 4 3 5% 5% 28%	104111
Transparency	Day	53% 7% 12% 19% 9% 1	108804
	Night	57% 7% 11% 16% 8% 1	108652
Seeing	Day	24% 18% 29% 18% 8% 3	14825
	Night	23% 17% 27% 23% 8% 1	24164

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% 24% 8% 15% 5% 5% 3 3 3 3 16%	2597
	11th to 20th	Day	15% 21% 8% 16% 9% 5% 3 3 3 3 13%	2600
	21st to end	Day	20% 18% 9% 13% 9% 5% 4 3 4 5% 12%	3106
February	1st to 10th	Day	17% 18% 7% 15% 10% 5% 3 4 4 3 14%	1710
	11th to 20th	Day	15% 17% 7% 19% 8% 5% 4 3 3 4 15%	1686
	21st to end	Day	19% 18% 5% 15% 7% 5% 3 3 4 4 18%	1570
March	1st to 10th	Day	22% 15% 5% 11% 5% 3 3 2 3 4 26%	3203
	11th to 20th	Day	11% 24% 5% 8% 5% 4 4 3 4 5% 27%	3480
	21st to end	Day	17% 14% 4 12% 5% 3 3 3 3 5% 31%	3972
April	1st to 10th	Day	19% 16% 4 8% 4 4 4 3 4 5% 29%	2280
	11th to 20th	Day	20% 12% 3 6% 4 3 4 4 4 6% 34%	2254
	21st to end	Day	22% 13% 3 6% 3 3 4 4 5% 6% 32%	2318
May	1st to 10th	Day	23% 10% 3 6% 5% 4 4 3 4 5% 32%	4352
	11th to 20th	Day	16% 8% 3 9% 6% 5% 5% 4 5% 7% 31%	4398
	21st to end	Day	14% 6% 2 5% 5% 4 4 4 6% 8% 41%	4837
June	1st to 10th	Day	20% 8% 3 6% 4 4 5% 4 6% 7% 33%	2660
	11th to 20th	Day	17% 5% 2 5% 6% 4 4 4 7% 9% 36%	2660
	21st to end	Day	15% 6% 2 7% 5% 5% 5% 4 7% 9% 34%	2660
July	1st to 10th	Day	13% 5% 2 6% 4 4 6% 5% 7% 11% 37%	4440
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 5% 8% 11% 36%	4440
	21st to end	Day	11% 6% 2 7% 5% 5% 5% 5% 7% 9% 37%	4814
August	1st to 10th	Day	19% 5% 2 6% 4 4 5% 5% 6% 8% 34%	4115
	11th to 20th	Day	17% 7% 3 7% 6% 5% 5% 4 6% 8% 32%	3951
	21st to end	Day	17% 6% 2 6% 5% 5% 4 4 5% 8% 39%	4180
September	1st to 10th	Day	16% 5% 2 6% 4 5% 5% 3 6% 8% 40%	2280
	11th to 20th	Day	17% 6% 2 6% 4 4 4 3 4 6% 44%	2280
	21st to end	Day	18% 7% 3 7% 6% 4 5% 4 6% 6% 35%	2021
October	1st to 10th	Day	20% 8% 3 8% 4 4 5% 4 5% 7% 34%	1900
	11th to 20th	Day	21% 9% 3 8% 4 4 4 4 5% 7% 31%	1900
	21st to end	Day	25% 16% 2 7% 4 4 5% 4 5% 6% 23%	2015
November	1st to 10th	Day	15% 14% 3 8% 6% 5% 4 3 5% 6% 31%	1761
	11th to 20th	Day	16% 17% 5% 8% 5% 4 4 4 5% 6% 26%	1670
	21st to end	Day	20% 19% 5% 9% 6% 5% 3 3 5% 7% 19%	1600
December	1st to 10th	Day	17% 24% 10% 16% 6% 5% 4 3 3 4 9%	2600
	11th to 20th	Day	18% 19% 8% 13% 5% 4 3 3 3 4 20%	2986
	21st to end	Day	21% 17% 6% 13% 6% 5% 4 4 4 6% 15%	3960
January	1st to 10th	Night	17% 22% 7% 19% 6% 5% 4 2 3 3 11%	4569
	11th to 20th	Night	13% 21% 10% 15% 8% 5% 4 3 4 4 15%	4580
	21st to end	Night	21% 18% 7% 17% 9% 5% 3 2 3 3 12%	4569
February	1st to 10th	Night	15% 18% 6% 16% 7% 4 5% 2 5% 4 18%	2470
	11th to 20th	Night	13% 16% 7% 17% 8% 7% 5% 2 4 4 16%	2380
	21st to end	Night	18% 14% 5% 16% 6% 5% 4 4 4 5% 19%	1884
March	1st to 10th	Night	20% 13% 5% 10% 5% 4 3 3 4 5% 29%	3633
	11th to 20th	Night	17% 22% 7% 10% 5% 4 3 3 4 4 23%	3479
	21st to end	Night	20% 13% 4 10% 4 4 4 3 4 4 31%	3659
April	1st to 10th	Night	20% 14% 5% 6% 5% 4 5% 3 5% 6% 28%	1900
	11th to 20th	Night	19% 11% 3 7% 5% 5% 4 3 4 6% 33%	1875
	21st to end	Night	21% 11% 3 6% 3 4 4 4 5% 6% 33%	1878
May	1st to 10th	Night	24% 10% 2 8% 5% 4 4 4 5% 6% 29%	2586
	11th to 20th	Night	17% 8% 3 7% 5% 5% 5% 3 6% 7% 35%	2495
	21st to end	Night	14% 6% 2 6% 4 4 4 4 7% 8% 41%	2738
June	1st to 10th	Night	19% 6% 3 7% 5% 3 4 4 6% 8% 36%	1520
	11th to 20th	Night	16% 7% 3 6% 5% 3 5% 4 7% 8% 38%	1520
	21st to end	Night	14% 7% 2 6% 5% 5% 4 4 6% 7% 40%	1520
July	1st to 10th	Night	12% 6% 3 8% 5% 5% 5% 4 7% 8% 39%	2520
	11th to 20th	Night	11% 5% 2 6% 4 5% 4 4 7% 8% 44%	2520
	21st to end	Night	13% 7% 3 6% 5% 3 5% 4 6% 8% 42%	2739
August	1st to 10th	Night	17% 7% 2 5% 4 4 5% 4 5% 7% 39%	2811
	11th to 20th	Night	15% 6% 3 7% 5% 4 5% 4 6% 7% 39%	2844
	21st to end	Night	13% 6% 2 5% 5% 4 4 4 6% 8% 44%	3476
September	1st to 10th	Night	15% 6% 2 7% 4 4 4 3 5% 7% 44%	1900
	11th to 20th	Night	17% 5% 2 5% 3 3 3 3 5% 6% 48%	1900
	21st to end	Night	19% 7% 1 6% 4 4 4 5% 6% 7% 36%	2155
October	1st to 10th	Night	21% 7% 2 7% 5% 5% 5% 4 5% 5% 33%	2280
	11th to 20th	Night	23% 9% 3 6% 4 4 5% 3 5% 7% 32%	2280
	21st to end	Night	28% 13% 3 8% 5% 3 3 3 4 6% 24%	2581
November	1st to 10th	Night	16% 14% 4 8% 5% 4 3 4 4 5% 33%	2537
	11th to 20th	Night	18% 16% 3 8% 5% 5% 4 3 4 6% 27%	2729
	21st to end	Night	17% 20% 5% 8% 5% 4 5% 4 5% 6% 22%	2800
December	1st to 10th	Night	15% 21% 9% 14% 6% 6% 5% 4 4 4 11%	4580
	11th to 20th	Night	21% 18% 7% 12% 5% 4 4 3 3 3 19%	5208
	21st to end	Night	23% 19% 6% 11% 6% 4 3 3 3 5% 17%	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	73% 5% 11% 9% 2	2598
	11th to 20th	Day	75% 8% 8% 6% 2	2600
	21st to end	Day	76% 6% 10% 5% 2	3106
February	1st to 10th	Day	74% 6% 8% 10% 2	1710
	11th to 20th	Day	73% 7% 7% 10% 3	1695
	21st to end	Day	70% 4 10% 11% 4	1570
March	1st to 10th	Day	63% 6% 9% 17% 5%	3206
	11th to 20th	Day	58% 8% 15% 10% 8% 1	3480
	21st to end	Day	55% 6% 9% 21% 9% 1	3972
April	1st to 10th	Day	58% 5% 9% 17% 10% 2	2280
	11th to 20th	Day	50% 7% 11% 19% 12% 1	2254
	21st to end	Day	53% 6% 9% 18% 12% 2	2318
May	1st to 10th	Day	53% 6% 10% 18% 11% 1	4366
	11th to 20th	Day	49% 9% 13% 20% 7% 1	4402
	21st to end	Day	38% 9% 14% 24% 14% 1	4837
June	1st to 10th	Day	48% 9% 12% 18% 13% 1	2660
	11th to 20th	Day	43% 8% 14% 23% 12% 1	2660
	21st to end	Day	45% 9% 15% 20% 11% 1	2660
July	1st to 10th	Day	39% 7% 15% 26% 12% 1	4370
	11th to 20th	Day	37% 10% 17% 26% 10%	4365
	21st to end	Day	41% 9% 16% 24% 10%	4661
August	1st to 10th	Day	45% 8% 14% 19% 12% 1	4101
	11th to 20th	Day	47% 8% 16% 22% 6%	3990
	21st to end	Day	43% 6% 12% 31% 7% 1	4180
September	1st to 10th	Day	41% 8% 12% 27% 11% 1	2280
	11th to 20th	Day	41% 6% 11% 24% 16% 1	2280
	21st to end	Day	48% 7% 11% 23% 10% 1	2021
October	1st to 10th	Day	43% 7% 14% 25% 10% 1	3160
	11th to 20th	Day	47% 5% 15% 20% 13%	3140
	21st to end	Day	47% 7% 16% 22% 8% 1	3305
November	1st to 10th	Day	52% 8% 11% 17% 10% 1	1761
	11th to 20th	Day	59% 7% 12% 14% 7% 2	1670
	21st to end	Day	66% 7% 13% 13% 2	1600
December	1st to 10th	Day	80% 5% 8% 6% 1	2600
	11th to 20th	Day	69% 5% 12% 9% 5%	2986
	21st to end	Day	69% 7% 11% 9% 3	3960
January	1st to 10th	Night	77% 7% 8% 5% 2	4569
	11th to 20th	Night	72% 8% 8% 8% 4	4580
	21st to end	Night	79% 5% 7% 6% 2	4569
February	1st to 10th	Night	69% 6% 9% 11% 4	2470
	11th to 20th	Night	71% 6% 8% 10% 4	2382
	21st to end	Night	66% 7% 11% 10% 6%	1884
March	1st to 10th	Night	57% 7% 12% 17% 7%	3643
	11th to 20th	Night	62% 7% 13% 13% 5%	3480
	21st to end	Night	56% 6% 8% 21% 9% 1	3659
April	1st to 10th	Night	57% 6% 11% 17% 7% 2	1900
	11th to 20th	Night	53% 6% 10% 16% 14% 1	1875
	21st to end	Night	50% 6% 11% 17% 13% 3	1878
May	1st to 10th	Night	53% 9% 11% 15% 9% 3	2592
	11th to 20th	Night	46% 10% 15% 20% 8% 1	2496
	21st to end	Night	37% 10% 15% 19% 17% 2	2739
June	1st to 10th	Night	44% 8% 13% 20% 14% 1	1520
	11th to 20th	Night	41% 9% 13% 21% 14% 2	1520
	21st to end	Night	41% 9% 10% 25% 14% 1	1520
July	1st to 10th	Night	42% 8% 14% 20% 14% 2	2480
	11th to 20th	Night	35% 8% 16% 28% 13%	2472
	21st to end	Night	40% 7% 12% 25% 15% 1	2651
August	1st to 10th	Night	43% 9% 14% 24% 9% 1	2801
	11th to 20th	Night	43% 7% 16% 25% 9%	2871
	21st to end	Night	36% 8% 14% 32% 10% 1	3476
September	1st to 10th	Night	39% 8% 13% 24% 13% 2	1900
	11th to 20th	Night	38% 5% 12% 28% 16% 1	1900
	21st to end	Night	44% 9% 13% 23% 10% 1	2155
October	1st to 10th	Night	51% 7% 10% 20% 11%	3800
	11th to 20th	Night	49% 6% 13% 16% 13% 2	3779
	21st to end	Night	50% 6% 13% 25% 6% 1	4241
November	1st to 10th	Night	53% 7% 10% 18% 10% 2	2537
	11th to 20th	Night	57% 7% 11% 17% 6% 2	2729
	21st to end	Night	62% 8% 13% 13% 3	2800
December	1st to 10th	Night	76% 6% 10% 7% 1	4580
	11th to 20th	Night	68% 7% 8% 10% 7%	5208
	21st to end	Night	71% 7% 7% 10% 4 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	32% 27% 30% 9% 3	200
	11th to 20th	Day	31% 32% 29% 8% 1 1	200
	21st to end	Day	26% 29% 33% 9% 2	294
February	1st to 10th	Day	31% 33% 30% 6%	270
	11th to 20th	Day	31% 34% 31% 4	293
	21st to end	Day	37% 23% 29% 10% 1	382
March	1st to 10th	Day	28% 24% 30% 15% 3	460
	11th to 20th	Day	30% 24% 30% 12% 3	460
	21st to end	Day	34% 23% 25% 13% 4 1	506
April	1st to 10th	Day	32% 23% 27% 11% 6%	460
	11th to 20th	Day	29% 25% 24% 11% 8% 2	452
	21st to end	Day	34% 16% 27% 16% 5% 2	460
May	1st to 10th	Day	27% 19% 29% 15% 7% 2	463
	11th to 20th	Day	20% 15% 33% 20% 9% 3	487
	21st to end	Day	17% 15% 30% 23% 12% 2	529
June	1st to 10th	Day	22% 17% 30% 21% 9% 1	490
	11th to 20th	Day	16% 15% 31% 25% 11% 2	490
	21st to end	Day	18% 17% 34% 22% 7% 2	490
July	1st to 10th	Day	12% 11% 30% 29% 14% 4	485
	11th to 20th	Day	13% 9% 30% 30% 15% 3	484
	21st to end	Day	12% 8% 39% 26% 12% 3	532
August	1st to 10th	Day	13% 10% 29% 27% 14% 6%	486
	11th to 20th	Day	16% 10% 28% 26% 14% 6%	479
	21st to end	Day	14% 13% 30% 23% 13% 7%	539
September	1st to 10th	Day	18% 13% 24% 23% 13% 8%	490
	11th to 20th	Day	14% 9% 25% 22% 19% 10%	490
	21st to end	Day	19% 16% 28% 21% 13% 4	490
October	1st to 10th	Day	23% 16% 27% 16% 13% 4	490
	11th to 20th	Day	28% 20% 25% 19% 7% 1	490
	21st to end	Day	35% 19% 27% 15% 3	499
November	1st to 10th	Day	26% 22% 28% 17% 6% 1	395
	11th to 20th	Day	33% 25% 24% 15% 2 1	270
	21st to end	Day	41% 20% 32% 8% 1	200
December	1st to 10th	Day	37% 23% 29% 7% 4 1	200
	11th to 20th	Day	33% 30% 26% 11% 1	200
	21st to end	Day	30% 28% 30% 11% 2	220
January	1st to 10th	Night	27% 30% 29% 13% 2	800
	11th to 20th	Night	27% 27% 29% 15% 3 1	800
	21st to end	Night	20% 25% 34% 17% 4	841
February	1st to 10th	Night	28% 23% 32% 16% 1	760
	11th to 20th	Night	26% 27% 32% 14% 1	743
	21st to end	Night	28% 25% 30% 14% 3	628
March	1st to 10th	Night	26% 22% 30% 19% 3	760
	11th to 20th	Night	26% 24% 26% 20% 3	760
	21st to end	Night	27% 20% 28% 19% 6%	836
April	1st to 10th	Night	26% 18% 31% 22% 2	760
	11th to 20th	Night	26% 18% 27% 21% 7% 1	751
	21st to end	Night	26% 13% 27% 27% 6%	738
May	1st to 10th	Night	25% 12% 22% 32% 8% 1	426
	11th to 20th	Night	14% 10% 33% 33% 9% 1	374
	21st to end	Night	14% 8% 32% 33% 13%	411
June	1st to 10th	Night	19% 7% 25% 35% 13% 1	380
	11th to 20th	Night	17% 9% 20% 40% 14% 1	380
	21st to end	Night	14% 6% 30% 41% 8% 1	380
July	1st to 10th	Night	11% 3 22% 46% 17% 2	370
	11th to 20th	Night	12% 3 22% 44% 18% 1	368
	21st to end	Night	13% 5% 26% 42% 13% 1	416
August	1st to 10th	Night	12% 5% 25% 36% 20% 1	553
	11th to 20th	Night	13% 6% 22% 32% 23% 3	597
	21st to end	Night	13% 7% 24% 34% 21% 1	836
September	1st to 10th	Night	17% 8% 25% 31% 18% 2	760
	11th to 20th	Night	17% 7% 18% 31% 23% 4	760
	21st to end	Night	19% 13% 21% 26% 17% 3	760
October	1st to 10th	Night	24% 13% 25% 19% 17% 1	760
	11th to 20th	Night	26% 16% 29% 21% 8%	760
	21st to end	Night	36% 14% 27% 19% 3	836
November	1st to 10th	Night	26% 19% 28% 20% 7%	780
	11th to 20th	Night	29% 23% 26% 16% 5% 1	800
	21st to end	Night	27% 25% 28% 16% 5%	800
December	1st to 10th	Night	32% 25% 26% 14% 2	800
	11th to 20th	Night	28% 26% 28% 15% 3	800
	21st to end	Night	30% 26% 28% 13% 3	880

Page generated at 2025-01-19 03:06:47. Version ac07

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