Boyertown Planetarium
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Boyertown Planetarium clear sky chart from 2005-11-06 to 2024-04-03.

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	16% 6% 3 5% 5% 3 5% 5% 5% 7% 40%	78799
	Night	17% 6% 2 5% 5% 3 4 4 5% 7% 42%	81305
Transparency	Day	42% 6% 11% 23% 15% 2	78508
	Night	42% 6% 11% 23% 16% 3	81130
Seeing	Day	23% 15% 28% 20% 11% 4	14094
	Night	20% 13% 29% 27% 10% 1	23541

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	15% 8% 3 5% 5% 3 4 4 4 5% 44%	2517
	11th to 20th	Day	15% 10% 4 8% 7% 3 5% 5% 4 6% 34%	2598
	21st to end	Day	21% 9% 3 7% 5% 3 4 3 4 6% 34%	3124
February	1st to 10th	Day	16% 7% 3 6% 5% 3 5% 4 5% 7% 38%	1710
	11th to 20th	Day	16% 7% 4 6% 5% 3 4 4 5% 7% 39%	1778
	21st to end	Day	20% 10% 3 6% 5% 3 4 3 4 5% 37%	1570
March	1st to 10th	Day	15% 7% 3 5% 5% 3 5% 4 4 6% 44%	1918
	11th to 20th	Day	16% 7% 2 7% 6% 3 4 5% 5% 6% 39%	2090
	21st to end	Day	21% 7% 3 4 5% 3 4 3 4 7% 39%	2418
April	1st to 10th	Day	17% 6% 3 6% 5% 3 4 4 5% 7% 40%	2184
	11th to 20th	Day	16% 6% 3 5% 5% 2 4 4 5% 8% 42%	2134
	21st to end	Day	17% 5% 3 6% 5% 3 4 6% 6% 7% 39%	2160
May	1st to 10th	Day	19% 6% 3 6% 5% 3 6% 5% 6% 6% 35%	2326
	11th to 20th	Day	21% 6% 2 5% 5% 3 5% 5% 5% 6% 36%	2478
	21st to end	Day	15% 7% 2 5% 5% 3 5% 5% 5% 7% 39%	2725
June	1st to 10th	Day	14% 5% 2 5% 5% 3 5% 5% 7% 10% 38%	2520
	11th to 20th	Day	14% 5% 3 5% 6% 4 5% 6% 6% 9% 37%	2520
	21st to end	Day	12% 4 2 4 5% 3 5% 7% 6% 10% 40%	2520
July	1st to 10th	Day	11% 4 3 5% 6% 4 6% 6% 7% 10% 39%	2520
	11th to 20th	Day	8% 4 2 5% 5% 3 6% 6% 8% 10% 43%	2520
	21st to end	Day	10% 6% 3 6% 7% 4 6% 7% 6% 9% 37%	2687
August	1st to 10th	Day	10% 5% 3 5% 7% 3 5% 6% 7% 9% 39%	2327
	11th to 20th	Day	11% 6% 2 5% 6% 3 5% 5% 6% 10% 40%	2152
	21st to end	Day	14% 6% 2 5% 5% 3 4 5% 7% 10% 40%	2376
September	1st to 10th	Day	16% 6% 2 4 4 3 5% 4 5% 6% 43%	2160
	11th to 20th	Day	14% 4 2 3 4 2 4 4 5% 8% 50%	2147
	21st to end	Day	18% 6% 3 5% 5% 3 4 4 5% 6% 40%	1957
October	1st to 10th	Day	19% 5% 2 4 4 3 3 5% 6% 8% 41%	1800
	11th to 20th	Day	17% 5% 2 5% 4 3 5% 4 5% 7% 45%	1800
	21st to end	Day	20% 6% 2 4 5% 3 3 4 4 5% 42%	1930
November	1st to 10th	Day	14% 6% 3 3 4 1 3 4 3 6% 52%	1671
	11th to 20th	Day	17% 5% 2 4 4 3 4 4 6% 6% 46%	1710
	21st to end	Day	15% 6% 2 4 5% 3 4 5% 6% 8% 43%	1554
December	1st to 10th	Day	19% 8% 2 5% 5% 3 4 4 5% 7% 36%	1520
	11th to 20th	Day	20% 7% 3 4 4 3 3 4 5% 6% 40%	1906
	21st to end	Day	18% 7% 3 6% 6% 5% 4 5% 6% 7% 33%	2772
January	1st to 10th	Night	16% 6% 2 5% 5% 3 4 4 5% 6% 44%	4429
	11th to 20th	Night	18% 7% 3 5% 5% 3 4 3 5% 6% 41%	4344
	21st to end	Night	24% 8% 2 5% 5% 3 3 4 4 5% 36%	4532
February	1st to 10th	Night	17% 8% 3 5% 5% 3 4 4 4 7% 40%	2470
	11th to 20th	Night	17% 7% 3 5% 5% 3 5% 5% 4 5% 40%	2286
	21st to end	Night	19% 7% 2 5% 4 2 4 5% 5% 6% 41%	1884
March	1st to 10th	Night	16% 5% 2 4 4 3 4 4 5% 6% 45%	2246
	11th to 20th	Night	17% 7% 2 4 5% 3 4 4 4 5% 44%	2089
	21st to end	Night	18% 7% 3 5% 4 3 3 3 4 7% 43%	2180
April	1st to 10th	Night	18% 7% 2 5% 5% 3 5% 5% 5% 7% 39%	1821
	11th to 20th	Night	14% 6% 3 6% 5% 2 5% 5% 5% 8% 42%	1775
	21st to end	Night	21% 4 2 5% 4 2 3 4 5% 7% 43%	1800
May	1st to 10th	Night	19% 10% 2 5% 5% 4 5% 4 5% 6% 36%	1648
	11th to 20th	Night	17% 6% 2 6% 6% 3 4 5% 5% 7% 38%	1415
	21st to end	Night	15% 6% 2 5% 6% 3 4 4 6% 9% 41%	1550
June	1st to 10th	Night	16% 6% 2 4 5% 4 5% 5% 5% 8% 42%	1440
	11th to 20th	Night	13% 5% 2 5% 5% 3 5% 5% 6% 10% 40%	1440
	21st to end	Night	12% 3 2 3 6% 3 5% 6% 6% 9% 45%	1440
July	1st to 10th	Night	10% 5% 2 6% 7% 4 6% 6% 6% 8% 39%	1440
	11th to 20th	Night	8% 3 3 5% 5% 3 6% 6% 6% 11% 43%	1440
	21st to end	Night	10% 5% 2 4 6% 3 4 6% 8% 10% 42%	1628
August	1st to 10th	Night	9% 5% 3 4 5% 3 5% 6% 7% 10% 42%	1611
	11th to 20th	Night	12% 6% 3 6% 7% 4 5% 5% 6% 8% 39%	1728
	21st to end	Night	14% 4 2 5% 5% 3 4 6% 6% 8% 42%	1980
September	1st to 10th	Night	16% 5% 3 5% 5% 3 4 4 4 7% 46%	1800
	11th to 20th	Night	13% 5% 2 4 3 2 4 3 5% 8% 52%	1813
	21st to end	Night	17% 6% 2 4 4 3 4 5% 5% 6% 44%	2000
October	1st to 10th	Night	19% 7% 2 5% 4 3 4 4 3 5% 44%	2160
	11th to 20th	Night	17% 5% 2 4 3 3 4 3 4 7% 48%	2160
	21st to end	Night	19% 7% 2 4 4 2 3 4 3 6% 47%	2425
November	1st to 10th	Night	12% 5% 2 4 3 2 4 4 5% 6% 52%	2407
	11th to 20th	Night	17% 7% 2 4 4 2 4 3 4 5% 47%	2470
	21st to end	Night	14% 5% 2 4 5% 3 4 4 6% 8% 45%	2622
December	1st to 10th	Night	20% 6% 3 5% 4 3 5% 5% 5% 6% 38%	2660
	11th to 20th	Night	18% 5% 2 5% 5% 3 4 5% 5% 7% 40%	3288
	21st to end	Night	19% 7% 3 6% 5% 3 4 5% 4 7% 37%	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	42% 3 13% 26% 12% 3	2518
	11th to 20th	Day	50% 6% 10% 19% 13% 2	2598
	21st to end	Day	51% 6% 11% 21% 9% 1	3124
February	1st to 10th	Day	45% 6% 13% 22% 12% 2	1710
	11th to 20th	Day	46% 4 9% 24% 14% 2	1787
	21st to end	Day	49% 4 9% 22% 12% 4	1570
March	1st to 10th	Day	42% 5% 10% 27% 14% 3	1921
	11th to 20th	Day	44% 6% 10% 21% 15% 4	2090
	21st to end	Day	47% 4 8% 20% 18% 3	2418
April	1st to 10th	Day	43% 5% 9% 22% 15% 5%	2184
	11th to 20th	Day	41% 5% 11% 22% 17% 4	2134
	21st to end	Day	42% 6% 10% 21% 16% 5%	2160
May	1st to 10th	Day	47% 6% 9% 19% 15% 4	2326
	11th to 20th	Day	47% 7% 9% 21% 14% 2	2482
	21st to end	Day	42% 7% 13% 21% 14% 2	2725
June	1st to 10th	Day	40% 8% 13% 24% 14% 1	2520
	11th to 20th	Day	42% 8% 14% 24% 10% 2	2520
	21st to end	Day	37% 9% 14% 26% 14% 1	2520
July	1st to 10th	Day	39% 8% 12% 24% 15% 2	2450
	11th to 20th	Day	32% 9% 15% 26% 16% 2	2445
	21st to end	Day	41% 9% 10% 22% 16% 2	2537
August	1st to 10th	Day	39% 9% 13% 23% 16% 1	2314
	11th to 20th	Day	38% 9% 15% 22% 16% 1	2152
	21st to end	Day	38% 8% 11% 22% 17% 3	2376
September	1st to 10th	Day	41% 7% 11% 20% 19% 3	2160
	11th to 20th	Day	32% 5% 10% 25% 23% 4	2147
	21st to end	Day	45% 5% 8% 19% 21% 2	1957
October	1st to 10th	Day	41% 7% 11% 23% 17% 1	1800
	11th to 20th	Day	39% 5% 11% 24% 20% 2	1800
	21st to end	Day	43% 5% 9% 24% 17% 2	1930
November	1st to 10th	Day	35% 5% 13% 25% 19% 4	1671
	11th to 20th	Day	38% 6% 9% 25% 20% 2	1710
	21st to end	Day	38% 6% 13% 30% 11% 2	1554
December	1st to 10th	Day	47% 6% 15% 19% 12% 1	1520
	11th to 20th	Day	44% 4 16% 24% 10% 1	1906
	21st to end	Day	48% 7% 12% 21% 10% 1	2772
January	1st to 10th	Night	41% 5% 10% 28% 12% 3	4429
	11th to 20th	Night	45% 4 12% 25% 12% 2	4344
	21st to end	Night	51% 4 8% 26% 10% 2	4532
February	1st to 10th	Night	45% 5% 12% 26% 11% 2	2470
	11th to 20th	Night	46% 4 9% 20% 18% 3	2288
	21st to end	Night	44% 5% 8% 23% 17% 4	1884
March	1st to 10th	Night	39% 5% 11% 25% 16% 3	2256
	11th to 20th	Night	42% 6% 8% 23% 17% 3	2090
	21st to end	Night	43% 4 9% 19% 19% 5%	2180
April	1st to 10th	Night	44% 5% 11% 20% 16% 4	1821
	11th to 20th	Night	41% 6% 10% 21% 20% 3	1775
	21st to end	Night	41% 5% 10% 22% 17% 5%	1800
May	1st to 10th	Night	48% 6% 9% 17% 16% 3	1648
	11th to 20th	Night	45% 8% 10% 16% 18% 3	1416
	21st to end	Night	40% 9% 15% 18% 15% 2	1551
June	1st to 10th	Night	40% 6% 11% 22% 19% 2	1440
	11th to 20th	Night	38% 9% 14% 23% 14% 1	1440
	21st to end	Night	34% 8% 14% 29% 14% 2	1440
July	1st to 10th	Night	40% 10% 14% 19% 14% 3	1400
	11th to 20th	Night	32% 10% 15% 26% 14% 3	1392
	21st to end	Night	34% 11% 15% 22% 17% 2	1537
August	1st to 10th	Night	35% 10% 15% 23% 16% 1	1600
	11th to 20th	Night	43% 7% 13% 19% 16% 2	1728
	21st to end	Night	38% 8% 13% 19% 19% 2	1980
September	1st to 10th	Night	40% 6% 10% 21% 20% 3	1800
	11th to 20th	Night	32% 6% 10% 22% 26% 4	1813
	21st to end	Night	40% 6% 8% 22% 22% 2	2000
October	1st to 10th	Night	44% 5% 11% 24% 15% 2	2160
	11th to 20th	Night	36% 5% 11% 28% 17% 2	2160
	21st to end	Night	40% 4 9% 27% 18% 2	2425
November	1st to 10th	Night	33% 6% 12% 26% 19% 5%	2407
	11th to 20th	Night	40% 4 9% 23% 19% 4	2470
	21st to end	Night	38% 4 13% 28% 15% 2	2622
December	1st to 10th	Night	47% 6% 12% 21% 14% 1	2660
	11th to 20th	Night	43% 5% 12% 22% 15% 3	3288
	21st to end	Night	47% 6% 13% 23% 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	33% 22% 26% 14% 4 1	180
	11th to 20th	Day	38% 26% 26% 8% 1	204
	21st to end	Day	29% 29% 26% 12% 3 1	297
February	1st to 10th	Day	30% 25% 32% 9% 3 1	270
	11th to 20th	Day	32% 25% 32% 10% 1	386
	21st to end	Day	37% 18% 27% 14% 3	382
March	1st to 10th	Day	33% 17% 29% 17% 5%	460
	11th to 20th	Day	30% 25% 28% 12% 3 1	460
	21st to end	Day	31% 23% 30% 10% 5% 1	506
April	1st to 10th	Day	27% 24% 30% 14% 5% 1	428
	11th to 20th	Day	24% 23% 27% 16% 7% 3	412
	21st to end	Day	30% 17% 33% 13% 4 2	420
May	1st to 10th	Day	32% 19% 26% 15% 6% 3	423
	11th to 20th	Day	25% 15% 31% 18% 9% 2	447
	21st to end	Day	20% 9% 27% 24% 16% 4	485
June	1st to 10th	Day	16% 12% 32% 23% 12% 4	450
	11th to 20th	Day	18% 12% 30% 24% 13% 3	450
	21st to end	Day	13% 10% 32% 27% 14% 4	450
July	1st to 10th	Day	12% 4 24% 30% 22% 7%	445
	11th to 20th	Day	11% 3 25% 34% 23% 5%	444
	21st to end	Day	12% 6% 30% 30% 18% 4	488
August	1st to 10th	Day	11% 6% 24% 30% 22% 8%	446
	11th to 20th	Day	13% 6% 20% 34% 19% 8%	439
	21st to end	Day	13% 7% 24% 28% 16% 12%	495
September	1st to 10th	Day	20% 9% 21% 26% 16% 9%	450
	11th to 20th	Day	16% 5% 28% 24% 16% 10%	450
	21st to end	Day	21% 14% 24% 23% 13% 4	450
October	1st to 10th	Day	26% 8% 24% 21% 15% 6%	450
	11th to 20th	Day	21% 17% 25% 24% 12% 2	450
	21st to end	Day	24% 16% 34% 14% 9% 2	470
November	1st to 10th	Day	22% 13% 29% 22% 11% 3	365
	11th to 20th	Day	25% 20% 30% 19% 6% 1	370
	21st to end	Day	24% 19% 33% 19% 4 1	214
December	1st to 10th	Day	35% 22% 28% 9% 5% 1	180
	11th to 20th	Day	37% 23% 24% 12% 3	180
	21st to end	Day	31% 19% 31% 13% 6% 1	198
January	1st to 10th	Night	21% 22% 36% 17% 3	760
	11th to 20th	Night	27% 17% 30% 22% 3	760
	21st to end	Night	20% 21% 35% 22% 2	836
February	1st to 10th	Night	23% 18% 35% 23% 1	760
	11th to 20th	Night	27% 24% 34% 14% 1	743
	21st to end	Night	28% 18% 35% 16% 3	628
March	1st to 10th	Night	24% 20% 29% 22% 4	760
	11th to 20th	Night	24% 22% 31% 17% 5%	760
	21st to end	Night	22% 17% 36% 19% 5%	836
April	1st to 10th	Night	23% 21% 33% 17% 4	729
	11th to 20th	Night	18% 15% 37% 23% 7%	711
	21st to end	Night	24% 13% 30% 26% 6%	720
May	1st to 10th	Night	26% 11% 30% 25% 7% 1	568
	11th to 20th	Night	21% 6% 32% 32% 8%	354
	21st to end	Night	17% 7% 21% 40% 13% 1	389
June	1st to 10th	Night	16% 5% 26% 36% 16%	360
	11th to 20th	Night	12% 5% 29% 40% 12% 1	360
	21st to end	Night	11% 3 24% 47% 14%	360
July	1st to 10th	Night	13% 3 20% 43% 21% 2	350
	11th to 20th	Night	9% 3 20% 41% 26% 2	348
	21st to end	Night	12% 3 19% 40% 23% 2	448
August	1st to 10th	Night	11% 3 15% 43% 27% 2	537
	11th to 20th	Night	14% 4 17% 35% 28% 3	664
	21st to end	Night	15% 3 17% 39% 23% 3	792
September	1st to 10th	Night	19% 4 23% 32% 20% 3	720
	11th to 20th	Night	15% 5% 19% 35% 23% 4	720
	21st to end	Night	20% 5% 23% 31% 19% 2	720
October	1st to 10th	Night	23% 7% 23% 26% 17% 4	720
	11th to 20th	Night	19% 11% 28% 29% 13%	720
	21st to end	Night	24% 13% 29% 25% 9%	792
November	1st to 10th	Night	17% 11% 31% 27% 13% 1	740
	11th to 20th	Night	22% 16% 27% 27% 7% 1	760
	21st to end	Night	18% 17% 32% 25% 7%	760
December	1st to 10th	Night	27% 16% 31% 20% 5% 1	760
	11th to 20th	Night	21% 17% 35% 21% 6%	760
	21st to end	Night	23% 17% 31% 26% 3	836

Page generated at 2024-03-31 06:08:50. Version ac07

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