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 2024-01-22.

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	18% 11% 4 8% 6% 3 5% 5% 5% 7% 29%	74794
	Night	18% 12% 5% 8% 6% 3 4 4 5% 6% 28%	75135
Transparency	Day	54% 7% 12% 17% 9% 1	74499
	Night	57% 7% 11% 16% 8% 1	74964
Seeing	Day	24% 18% 29% 18% 8% 3	13544
	Night	23% 17% 27% 23% 8% 1	22905

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	12% 21% 9% 12% 8% 5% 6% 4 4 4 15%	1517
	11th to 20th	Day	17% 19% 8% 15% 11% 4 4 4 4 4 10%	1520
	21st to end	Day	13% 14% 8% 14% 12% 5% 5% 5% 4 5% 14%	1777
February	1st to 10th	Day	17% 17% 8% 15% 11% 4 4 4 4 3 12%	1620
	11th to 20th	Day	16% 15% 8% 17% 9% 4 5% 4 3 4 15%	1595
	21st to end	Day	20% 17% 6% 14% 9% 3 4 3 4 4 17%	1480
March	1st to 10th	Day	15% 14% 8% 14% 8% 4 4 4 5% 4 19%	1842
	11th to 20th	Day	16% 19% 6% 8% 7% 3 4 4 3 4 27%	1980
	21st to end	Day	21% 13% 4 8% 7% 3 3 3 4 6% 29%	2266
April	1st to 10th	Day	18% 14% 6% 7% 5% 3 4 4 4 5% 29%	2160
	11th to 20th	Day	19% 11% 3 5% 4 2 4 5% 4 6% 35%	2134
	21st to end	Day	23% 13% 3 5% 4 2 4 4 5% 6% 32%	2196
May	1st to 10th	Day	20% 9% 4 7% 7% 4 4 4 4 6% 33%	2474
	11th to 20th	Day	16% 8% 2 6% 6% 3 6% 5% 5% 8% 36%	2478
	21st to end	Day	16% 6% 2 4 6% 4 4 4 6% 8% 39%	2725
June	1st to 10th	Day	20% 7% 3 6% 5% 3 4 5% 6% 7% 35%	2520
	11th to 20th	Day	18% 5% 2 5% 6% 3 4 4 7% 9% 37%	2520
	21st to end	Day	15% 6% 2 6% 6% 4 5% 6% 6% 9% 35%	2520
July	1st to 10th	Day	13% 5% 2 5% 4 3 6% 5% 6% 9% 41%	2520
	11th to 20th	Day	13% 5% 2 6% 6% 3 5% 6% 6% 9% 39%	2520
	21st to end	Day	13% 6% 2 6% 6% 4 7% 5% 7% 9% 37%	2744
August	1st to 10th	Day	13% 4 2 6% 6% 4 6% 7% 7% 9% 36%	2338
	11th to 20th	Day	15% 7% 3 6% 7% 4 5% 6% 6% 9% 32%	2252
	21st to end	Day	16% 6% 2 5% 6% 4 5% 6% 5% 9% 35%	2376
September	1st to 10th	Day	17% 5% 2 5% 5% 4 5% 5% 6% 8% 39%	2160
	11th to 20th	Day	18% 5% 2 5% 5% 3 4 4 4 7% 43%	2160
	21st to end	Day	17% 6% 3 6% 6% 3 5% 5% 6% 6% 36%	1915
October	1st to 10th	Day	21% 7% 3 7% 5% 3 5% 5% 5% 7% 33%	1800
	11th to 20th	Day	22% 10% 3 7% 5% 3 4 4 5% 8% 30%	1800
	21st to end	Day	27% 15% 3 6% 5% 3 5% 4 4 6% 22%	1909
November	1st to 10th	Day	15% 13% 3 7% 7% 3 4 5% 4 6% 31%	1671
	11th to 20th	Day	17% 16% 6% 7% 6% 3 4 5% 5% 5% 25%	1587
	21st to end	Day	20% 18% 6% 8% 7% 3 4 3 4 6% 20%	1520
December	1st to 10th	Day	19% 21% 10% 11% 6% 3 4 4 3 6% 14%	1520
	11th to 20th	Day	19% 19% 10% 10% 6% 3 3 4 3 4 19%	1906
	21st to end	Day	27% 20% 7% 8% 7% 4 4 4 3 3 13%	2772
January	1st to 10th	Night	17% 19% 8% 13% 9% 5% 5% 3 4 4 13%	2649
	11th to 20th	Night	16% 18% 9% 14% 11% 3 4 4 4 4 13%	2660
	21st to end	Night	12% 14% 8% 14% 13% 6% 5% 5% 4 4 14%	2609
February	1st to 10th	Night	16% 18% 6% 15% 9% 3 5% 3 4 4 17%	2340
	11th to 20th	Night	14% 15% 7% 14% 10% 4 7% 4 4 4 16%	2251
	21st to end	Night	18% 14% 6% 15% 7% 3 5% 4 4 6% 18%	1776
March	1st to 10th	Night	16% 17% 7% 12% 7% 3 3 4 4 4 22%	2101
	11th to 20th	Night	17% 15% 7% 9% 6% 3 4 4 5% 4 27%	1979
	21st to end	Night	19% 14% 4 8% 6% 3 4 4 4 5% 30%	2089
April	1st to 10th	Night	20% 13% 6% 6% 5% 3 5% 4 5% 6% 28%	1800
	11th to 20th	Night	19% 11% 3 7% 5% 4 4 4 4 6% 33%	1775
	21st to end	Night	21% 11% 3 5% 4 3 4 4 5% 6% 33%	1780
May	1st to 10th	Night	21% 10% 2 6% 5% 3 4 5% 5% 6% 32%	1484
	11th to 20th	Night	13% 7% 3 5% 5% 4 5% 5% 7% 8% 39%	1415
	21st to end	Night	13% 6% 2 5% 5% 2 5% 4 7% 8% 43%	1550
June	1st to 10th	Night	19% 5% 3 6% 5% 2 4 5% 6% 8% 36%	1440
	11th to 20th	Night	16% 7% 3 5% 6% 2 5% 5% 5% 9% 39%	1440
	21st to end	Night	14% 6% 3 5% 5% 3 5% 4 6% 7% 42%	1440
July	1st to 10th	Night	9% 5% 3 4 6% 2 6% 6% 6% 8% 45%	1440
	11th to 20th	Night	11% 4 2 6% 4 3 6% 5% 6% 8% 47%	1440
	21st to end	Night	13% 6% 2 4 5% 2 5% 4 6% 8% 44%	1574
August	1st to 10th	Night	11% 4 2 5% 5% 4 6% 5% 7% 7% 45%	1597
	11th to 20th	Night	13% 6% 3 5% 7% 3 5% 5% 6% 7% 39%	1629
	21st to end	Night	15% 5% 2 4 5% 2 4 5% 6% 8% 44%	1980
September	1st to 10th	Night	15% 5% 2 5% 5% 3 4 4 5% 7% 43%	1800
	11th to 20th	Night	18% 4 2 5% 4 2 4 4 4 7% 47%	1800
	21st to end	Night	18% 6% 1 5% 5% 3 4 6% 6% 8% 38%	2041
October	1st to 10th	Night	22% 7% 2 6% 6% 3 5% 5% 5% 5% 33%	2160
	11th to 20th	Night	23% 8% 3 5% 5% 3 5% 4 5% 7% 31%	2160
	21st to end	Night	30% 13% 3 7% 6% 2 3 3 4 5% 23%	2445
November	1st to 10th	Night	16% 14% 4 7% 6% 3 4 4 4 5% 33%	2407
	11th to 20th	Night	19% 15% 4 8% 5% 3 5% 4 4 6% 27%	2592
	21st to end	Night	17% 18% 6% 7% 6% 3 5% 5% 5% 6% 23%	2660
December	1st to 10th	Night	20% 20% 9% 10% 5% 4 5% 5% 4 5% 15%	2660
	11th to 20th	Night	21% 16% 7% 12% 7% 3 5% 4 4 4 18%	3288
	21st to end	Night	29% 18% 7% 8% 5% 3 3 3 3 5% 14%	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	72% 5% 10% 9% 3	1518
	11th to 20th	Day	77% 7% 6% 6% 3	1520
	21st to end	Day	72% 5% 11% 7% 4	1777
February	1st to 10th	Day	76% 6% 7% 8% 2	1620
	11th to 20th	Day	74% 6% 7% 10% 3	1604
	21st to end	Day	73% 4 10% 10% 4	1480
March	1st to 10th	Day	68% 7% 10% 11% 4 1	1845
	11th to 20th	Day	62% 5% 9% 14% 10% 1	1980
	21st to end	Day	59% 4 8% 16% 12% 2	2266
April	1st to 10th	Day	57% 5% 9% 17% 10% 2	2160
	11th to 20th	Day	49% 6% 12% 19% 13% 1	2134
	21st to end	Day	53% 6% 9% 18% 11% 2	2196
May	1st to 10th	Day	53% 6% 10% 18% 11% 2	2474
	11th to 20th	Day	45% 7% 12% 21% 12% 2	2482
	21st to end	Day	42% 8% 16% 20% 12% 1	2725
June	1st to 10th	Day	47% 8% 12% 18% 13% 1	2520
	11th to 20th	Day	43% 8% 13% 23% 12% 1	2520
	21st to end	Day	45% 9% 15% 20% 11% 1	2520
July	1st to 10th	Day	39% 8% 12% 26% 13% 1	2450
	11th to 20th	Day	39% 10% 16% 26% 8% 1	2445
	21st to end	Day	42% 9% 14% 22% 12% 1	2591
August	1st to 10th	Day	41% 10% 15% 22% 11% 1	2324
	11th to 20th	Day	47% 10% 15% 21% 8%	2252
	21st to end	Day	45% 7% 14% 22% 10% 1	2376
September	1st to 10th	Day	42% 8% 12% 26% 11% 1	2160
	11th to 20th	Day	43% 6% 11% 23% 16% 1	2160
	21st to end	Day	47% 7% 11% 24% 10% 1	1915
October	1st to 10th	Day	49% 8% 13% 18% 11% 1	1800
	11th to 20th	Day	52% 8% 15% 18% 7%	1800
	21st to end	Day	63% 7% 11% 12% 6% 1	1909
November	1st to 10th	Day	52% 8% 11% 17% 10% 1	1671
	11th to 20th	Day	59% 7% 12% 14% 6% 2	1587
	21st to end	Day	66% 7% 13% 12% 2	1520
December	1st to 10th	Day	73% 6% 10% 9% 2	1520
	11th to 20th	Day	70% 6% 13% 8% 3	1906
	21st to end	Day	75% 7% 8% 9% 1	2772
January	1st to 10th	Night	75% 7% 7% 8% 4	2649
	11th to 20th	Night	73% 8% 9% 7% 3	2660
	21st to end	Night	73% 6% 8% 9% 3 1	2609
February	1st to 10th	Night	71% 6% 8% 10% 4	2340
	11th to 20th	Night	72% 5% 8% 10% 4	2253
	21st to end	Night	67% 6% 10% 10% 6%	1776
March	1st to 10th	Night	66% 5% 11% 14% 4	2111
	11th to 20th	Night	60% 6% 9% 16% 8%	1980
	21st to end	Night	58% 4 8% 17% 11% 2	2089
April	1st to 10th	Night	57% 6% 11% 17% 7% 2	1800
	11th to 20th	Night	53% 6% 10% 17% 14% 1	1775
	21st to end	Night	51% 6% 11% 17% 12% 3	1780
May	1st to 10th	Night	51% 7% 10% 16% 13% 3	1484
	11th to 20th	Night	40% 8% 13% 24% 13% 2	1416
	21st to end	Night	37% 10% 17% 21% 12% 2	1551
June	1st to 10th	Night	44% 7% 14% 20% 14% 1	1440
	11th to 20th	Night	42% 9% 13% 20% 15% 2	1440
	21st to end	Night	39% 9% 10% 26% 14% 1	1440
July	1st to 10th	Night	34% 10% 15% 22% 16% 3	1400
	11th to 20th	Night	34% 8% 15% 29% 14%	1392
	21st to end	Night	37% 8% 15% 24% 15% 2	1486
August	1st to 10th	Night	35% 11% 15% 28% 11% 1	1587
	11th to 20th	Night	44% 7% 16% 25% 8%	1629
	21st to end	Night	36% 9% 15% 26% 12% 1	1980
September	1st to 10th	Night	40% 8% 13% 24% 12% 2	1800
	11th to 20th	Night	39% 5% 12% 27% 16% 1	1800
	21st to end	Night	42% 9% 13% 24% 11% 1	2041
October	1st to 10th	Night	52% 8% 12% 17% 12%	2160
	11th to 20th	Night	52% 8% 14% 16% 9% 1	2160
	21st to end	Night	64% 6% 11% 12% 6% 1	2445
November	1st to 10th	Night	53% 8% 10% 17% 10% 2	2407
	11th to 20th	Night	58% 7% 11% 16% 6% 2	2592
	21st to end	Night	62% 8% 14% 13% 3	2660
December	1st to 10th	Night	72% 7% 11% 8% 2	2660
	11th to 20th	Night	69% 8% 9% 10% 3	3288
	21st to end	Night	73% 7% 9% 10% 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	32% 23% 32% 9% 3	180
	11th to 20th	Day	29% 32% 29% 8% 1 1	180
	21st to end	Day	23% 31% 34% 8% 3	261
February	1st to 10th	Day	33% 35% 29% 4	240
	11th to 20th	Day	31% 34% 31% 4	262
	21st to end	Day	38% 24% 27% 10% 1	346
March	1st to 10th	Day	26% 25% 31% 15% 2	420
	11th to 20th	Day	29% 25% 29% 13% 4	420
	21st to end	Day	34% 22% 24% 14% 4 2	462
April	1st to 10th	Day	30% 23% 29% 12% 6%	420
	11th to 20th	Day	27% 25% 25% 12% 9% 3	412
	21st to end	Day	35% 16% 28% 15% 5% 2	420
May	1st to 10th	Day	27% 19% 30% 15% 7% 2	423
	11th to 20th	Day	20% 16% 33% 20% 9% 2	447
	21st to end	Day	18% 14% 30% 23% 13% 3	485
June	1st to 10th	Day	22% 16% 31% 22% 8% 1	450
	11th to 20th	Day	17% 14% 32% 24% 11% 2	450
	21st to end	Day	17% 16% 35% 23% 8% 2	450
July	1st to 10th	Day	13% 10% 29% 30% 15% 4	445
	11th to 20th	Day	14% 8% 30% 31% 15% 3	444
	21st to end	Day	12% 8% 40% 26% 11% 3	488
August	1st to 10th	Day	11% 10% 30% 28% 15% 6%	446
	11th to 20th	Day	16% 8% 29% 26% 14% 6%	439
	21st to end	Day	13% 13% 31% 22% 14% 7%	495
September	1st to 10th	Day	18% 13% 25% 23% 13% 8%	450
	11th to 20th	Day	16% 10% 27% 22% 17% 9%	450
	21st to end	Day	18% 16% 28% 20% 14% 4	450
October	1st to 10th	Day	23% 15% 27% 15% 14% 5%	450
	11th to 20th	Day	28% 20% 26% 19% 6% 1	450
	21st to end	Day	37% 19% 26% 15% 3	459
November	1st to 10th	Day	25% 21% 28% 18% 7% 1	365
	11th to 20th	Day	33% 24% 25% 15% 1 1	247
	21st to end	Day	38% 19% 34% 8% 1	180
December	1st to 10th	Day	36% 23% 29% 7% 4 1	180
	11th to 20th	Day	31% 31% 27% 11% 1	180
	21st to end	Day	31% 29% 30% 9% 1	198
January	1st to 10th	Night	27% 29% 29% 13% 2	760
	11th to 20th	Night	26% 26% 28% 16% 3 1	760
	21st to end	Night	19% 26% 35% 17% 4	800
February	1st to 10th	Night	28% 23% 33% 15% 1	720
	11th to 20th	Night	26% 27% 32% 14% 2	703
	21st to end	Night	28% 25% 30% 14% 3	592
March	1st to 10th	Night	26% 22% 30% 19% 3	720
	11th to 20th	Night	26% 24% 27% 20% 3	720
	21st to end	Night	27% 20% 28% 19% 6% 1	792
April	1st to 10th	Night	25% 19% 31% 22% 2	720
	11th to 20th	Night	25% 18% 27% 22% 7% 1	711
	21st to end	Night	27% 13% 27% 27% 6%	700
May	1st to 10th	Night	26% 11% 22% 32% 8% 1	404
	11th to 20th	Night	14% 11% 33% 33% 8% 1	354
	21st to end	Night	14% 7% 33% 33% 13% 1	389
June	1st to 10th	Night	20% 6% 23% 36% 13% 1	360
	11th to 20th	Night	17% 9% 20% 39% 14% 1	360
	21st to end	Night	14% 5% 31% 43% 8% 1	360
July	1st to 10th	Night	11% 3 21% 47% 17% 2	350
	11th to 20th	Night	12% 3 22% 44% 18% 1	348
	21st to end	Night	13% 4 27% 41% 13% 2	394
August	1st to 10th	Night	12% 5% 25% 36% 21% 1	523
	11th to 20th	Night	13% 6% 21% 33% 24% 3	565
	21st to end	Night	14% 7% 24% 33% 21% 1	792
September	1st to 10th	Night	17% 7% 24% 32% 18% 2	720
	11th to 20th	Night	18% 7% 19% 31% 21% 4	720
	21st to end	Night	18% 13% 22% 26% 18% 3	720
October	1st to 10th	Night	24% 13% 26% 18% 17% 1	720
	11th to 20th	Night	26% 16% 30% 21% 7%	720
	21st to end	Night	37% 15% 27% 19% 3	792
November	1st to 10th	Night	26% 19% 27% 20% 8%	740
	11th to 20th	Night	28% 24% 26% 16% 5% 1	760
	21st to end	Night	26% 25% 28% 16% 5%	760
December	1st to 10th	Night	33% 24% 26% 14% 3	760
	11th to 20th	Night	27% 26% 29% 15% 3	760
	21st to end	Night	31% 26% 29% 12% 2	836

Page generated at 2024-01-19 09:28:34. Version ac07

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