Thomas J Boyce Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Thomas J Boyce Park clear sky chart from 2005-11-06 to 2024-02-15.

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% 7% 3 5% 5% 3 5% 4 5% 7% 38%	78214
	Night	17% 7% 3 5% 5% 3 4 4 5% 6% 39%	80857
Transparency	Day	45% 6% 11% 22% 14% 2	77919
	Night	44% 6% 12% 22% 14% 2	80686
Seeing	Day	25% 18% 29% 18% 8% 2	13912
	Night	23% 16% 29% 23% 8% 1	23151

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% 9% 3 5% 5% 3 4 4 5% 5% 45%	2517
	11th to 20th	Day	15% 10% 4 7% 8% 4 4 3 5% 6% 34%	2520
	21st to end	Day	21% 13% 6% 7% 5% 2 4 3 4 5% 30%	2904
February	1st to 10th	Day	17% 8% 3 6% 6% 3 5% 6% 5% 7% 34%	1727
	11th to 20th	Day	15% 7% 3 7% 6% 3 5% 4 5% 7% 38%	1788
	21st to end	Day	19% 9% 4 6% 6% 4 5% 3 4 6% 35%	1480
March	1st to 10th	Day	14% 6% 4 7% 7% 3 5% 4 5% 6% 40%	1797
	11th to 20th	Day	16% 7% 3 6% 6% 3 5% 5% 5% 8% 36%	1863
	21st to end	Day	20% 8% 3 5% 5% 3 4 3 4 6% 38%	2376
April	1st to 10th	Day	18% 9% 3 6% 5% 3 5% 5% 4 6% 36%	2160
	11th to 20th	Day	16% 7% 3 5% 5% 4 4 4 5% 8% 40%	2134
	21st to end	Day	21% 7% 2 5% 4 3 4 4 5% 6% 39%	2227
May	1st to 10th	Day	24% 7% 3 5% 5% 2 4 5% 5% 6% 33%	2340
	11th to 20th	Day	19% 7% 2 4 5% 3 5% 4 5% 7% 39%	2458
	21st to end	Day	14% 6% 3 6% 5% 3 4 5% 6% 8% 40%	2725
June	1st to 10th	Day	18% 5% 2 5% 5% 4 5% 6% 7% 9% 35%	2520
	11th to 20th	Day	16% 7% 3 5% 5% 3 5% 5% 6% 8% 35%	2520
	21st to end	Day	13% 7% 3 6% 6% 3 5% 5% 6% 9% 38%	2520
July	1st to 10th	Day	13% 6% 3 5% 6% 3 5% 5% 6% 8% 40%	2520
	11th to 20th	Day	13% 5% 2 4 5% 4 5% 5% 6% 10% 41%	2520
	21st to end	Day	13% 5% 3 6% 6% 4 5% 6% 6% 8% 39%	2744
August	1st to 10th	Day	11% 6% 3 5% 6% 4 6% 6% 7% 9% 38%	2437
	11th to 20th	Day	13% 6% 3 5% 5% 3 6% 6% 7% 8% 39%	2126
	21st to end	Day	13% 6% 2 5% 5% 4 3 6% 5% 9% 42%	2376
September	1st to 10th	Day	13% 6% 3 5% 5% 4 5% 5% 6% 6% 41%	2160
	11th to 20th	Day	13% 5% 2 5% 4 3 3 3 6% 6% 49%	2065
	21st to end	Day	17% 6% 2 5% 4 3 5% 4 5% 8% 42%	1980
October	1st to 10th	Day	24% 6% 2 5% 4 2 4 3 5% 5% 41%	1906
	11th to 20th	Day	15% 7% 2 5% 5% 3 4 4 5% 7% 44%	1800
	21st to end	Day	24% 6% 2 4 6% 3 4 4 5% 6% 36%	1796
November	1st to 10th	Day	13% 7% 3 4 5% 2 3 4 4 7% 49%	1671
	11th to 20th	Day	18% 7% 2 4 4 2 4 3 6% 7% 43%	1710
	21st to end	Day	18% 6% 3 5% 4 2 4 4 5% 7% 42%	1629
December	1st to 10th	Day	19% 8% 4 7% 6% 3 4 4 5% 6% 35%	1520
	11th to 20th	Day	21% 7% 2 5% 4 2 4 5% 4 6% 41%	1906
	21st to end	Day	20% 11% 4 7% 6% 4 4 4 4 7% 30%	2772
January	1st to 10th	Night	16% 6% 3 5% 4 3 4 4 4 7% 43%	4429
	11th to 20th	Night	16% 8% 3 7% 6% 4 4 5% 4 5% 38%	4440
	21st to end	Night	24% 10% 4 7% 5% 3 3 3 4 5% 31%	4747
February	1st to 10th	Night	16% 10% 4 5% 4 3 6% 4 4 5% 39%	2451
	11th to 20th	Night	15% 8% 3 6% 6% 3 6% 5% 6% 6% 37%	2153
	21st to end	Night	18% 7% 3 5% 6% 3 4 4 5% 6% 38%	1776
March	1st to 10th	Night	16% 6% 3 4 5% 3 5% 5% 5% 7% 40%	2150
	11th to 20th	Night	17% 7% 2 6% 6% 3 4 5% 5% 6% 38%	2093
	21st to end	Night	18% 7% 3 5% 4 3 5% 4 6% 6% 39%	1980
April	1st to 10th	Night	17% 9% 4 6% 6% 4 5% 4 6% 6% 35%	1800
	11th to 20th	Night	18% 6% 3 6% 6% 3 5% 4 4 6% 39%	1775
	21st to end	Night	21% 7% 3 5% 4 3 3 4 5% 6% 38%	1731
May	1st to 10th	Night	22% 8% 3 6% 6% 5% 4 4 4 7% 32%	1620
	11th to 20th	Night	18% 8% 4 5% 5% 4 4 4 4 6% 38%	1450
	21st to end	Night	16% 6% 2 5% 5% 2 6% 5% 5% 7% 40%	1550
June	1st to 10th	Night	17% 6% 2 6% 4 3 4 5% 4 7% 41%	1440
	11th to 20th	Night	15% 6% 3 6% 4 3 5% 5% 6% 8% 39%	1440
	21st to end	Night	13% 5% 3 4 4 3 4 5% 6% 10% 44%	1440
July	1st to 10th	Night	13% 6% 3 4 5% 3 5% 5% 7% 6% 42%	1440
	11th to 20th	Night	13% 5% 3 4 6% 3 5% 6% 6% 9% 39%	1440
	21st to end	Night	10% 6% 2 4 6% 3 6% 6% 7% 8% 42%	1574
August	1st to 10th	Night	8% 6% 2 5% 6% 3 6% 5% 7% 8% 44%	1481
	11th to 20th	Night	12% 6% 2 7% 6% 4 5% 6% 7% 8% 37%	1774
	21st to end	Night	16% 5% 2 4 4 2 4 4 5% 7% 46%	1980
September	1st to 10th	Night	16% 6% 3 5% 5% 3 3 4 4 6% 46%	1800
	11th to 20th	Night	13% 6% 2 3 3 2 3 3 3 6% 54%	1894
	21st to end	Night	17% 7% 3 4 4 3 4 4 4 7% 45%	1980
October	1st to 10th	Night	20% 7% 3 6% 4 2 3 3 4 6% 42%	2052
	11th to 20th	Night	15% 6% 2 5% 4 3 4 5% 5% 7% 45%	2160
	21st to end	Night	22% 7% 2 5% 5% 3 4 4 5% 5% 37%	2558
November	1st to 10th	Night	14% 6% 2 4 5% 3 4 5% 5% 6% 46%	2407
	11th to 20th	Night	18% 6% 3 4 5% 2 4 4 5% 6% 43%	2470
	21st to end	Night	14% 6% 3 5% 5% 3 5% 5% 5% 7% 42%	2550
December	1st to 10th	Night	19% 7% 3 6% 5% 3 4 4 5% 6% 37%	2660
	11th to 20th	Night	20% 7% 3 5% 5% 4 4 5% 6% 5% 36%	3288
	21st to end	Night	22% 11% 4 7% 4 3 4 4 4 6% 31%	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	41% 5% 10% 34% 8% 2	2518
	11th to 20th	Day	51% 5% 12% 22% 8% 1	2520
	21st to end	Day	57% 5% 8% 19% 9% 1	2904
February	1st to 10th	Day	49% 6% 12% 19% 13% 1	1727
	11th to 20th	Day	45% 6% 10% 22% 15% 3	1797
	21st to end	Day	52% 4 9% 20% 12% 2	1480
March	1st to 10th	Day	45% 5% 13% 21% 14% 3	1800
	11th to 20th	Day	46% 5% 11% 22% 14% 2	1863
	21st to end	Day	49% 4 9% 17% 17% 5%	2376
April	1st to 10th	Day	48% 6% 9% 20% 14% 3	2160
	11th to 20th	Day	44% 6% 10% 22% 16% 2	2134
	21st to end	Day	47% 5% 10% 20% 15% 4	2227
May	1st to 10th	Day	53% 6% 8% 18% 13% 2	2340
	11th to 20th	Day	43% 7% 10% 21% 17% 2	2462
	21st to end	Day	42% 8% 15% 21% 12% 2	2725
June	1st to 10th	Day	46% 8% 13% 22% 11% 1	2520
	11th to 20th	Day	45% 8% 13% 22% 11% 1	2520
	21st to end	Day	43% 9% 12% 23% 12% 1	2520
July	1st to 10th	Day	42% 8% 12% 20% 16% 1	2450
	11th to 20th	Day	38% 8% 13% 26% 13% 1	2445
	21st to end	Day	42% 8% 13% 19% 16% 2	2591
August	1st to 10th	Day	42% 9% 12% 24% 12% 1	2423
	11th to 20th	Day	40% 9% 16% 23% 12% 1	2126
	21st to end	Day	39% 7% 11% 24% 18% 1	2376
September	1st to 10th	Day	42% 7% 10% 23% 16% 2	2160
	11th to 20th	Day	35% 6% 9% 24% 24% 2	2065
	21st to end	Day	42% 6% 11% 21% 18% 3	1980
October	1st to 10th	Day	47% 5% 8% 23% 14% 3	1906
	11th to 20th	Day	40% 6% 13% 27% 13% 2	1800
	21st to end	Day	50% 5% 10% 19% 13% 3	1796
November	1st to 10th	Day	37% 4 13% 26% 17% 3	1671
	11th to 20th	Day	40% 5% 12% 23% 16% 3	1710
	21st to end	Day	43% 4 13% 26% 12% 2	1629
December	1st to 10th	Day	50% 5% 14% 17% 13% 1	1520
	11th to 20th	Day	45% 5% 15% 21% 12% 2	1906
	21st to end	Day	55% 5% 10% 20% 8% 1	2772
January	1st to 10th	Night	41% 5% 12% 29% 11% 3	4429
	11th to 20th	Night	47% 5% 13% 22% 11% 2	4440
	21st to end	Night	56% 4 9% 19% 11% 1	4747
February	1st to 10th	Night	47% 6% 12% 22% 11% 2	2451
	11th to 20th	Night	46% 6% 11% 17% 17% 4	2155
	21st to end	Night	46% 5% 9% 23% 13% 4	1776
March	1st to 10th	Night	42% 6% 13% 22% 14% 3	2160
	11th to 20th	Night	45% 6% 11% 21% 15% 3	2094
	21st to end	Night	45% 5% 9% 18% 18% 4	1980
April	1st to 10th	Night	47% 6% 12% 19% 14% 2	1800
	11th to 20th	Night	45% 6% 10% 20% 18% 1	1775
	21st to end	Night	46% 5% 10% 21% 14% 4	1731
May	1st to 10th	Night	53% 6% 10% 16% 13% 2	1620
	11th to 20th	Night	47% 5% 10% 19% 16% 3	1451
	21st to end	Night	43% 7% 14% 21% 12% 1	1551
June	1st to 10th	Night	45% 5% 11% 23% 15% 1	1440
	11th to 20th	Night	42% 8% 16% 24% 10% 1	1440
	21st to end	Night	36% 9% 14% 26% 14%	1440
July	1st to 10th	Night	39% 8% 13% 24% 15% 2	1400
	11th to 20th	Night	39% 8% 15% 29% 9% 1	1392
	21st to end	Night	38% 7% 15% 22% 16% 2	1486
August	1st to 10th	Night	35% 10% 16% 25% 14% 1	1471
	11th to 20th	Night	42% 10% 14% 23% 10% 1	1774
	21st to end	Night	37% 7% 12% 25% 18% 1	1980
September	1st to 10th	Night	41% 6% 9% 27% 16% 1	1800
	11th to 20th	Night	32% 5% 11% 24% 26% 1	1894
	21st to end	Night	41% 5% 9% 22% 22% 2	1980
October	1st to 10th	Night	45% 6% 11% 22% 14% 2	2052
	11th to 20th	Night	39% 5% 12% 29% 13% 1	2160
	21st to end	Night	46% 6% 12% 20% 13% 1	2558
November	1st to 10th	Night	38% 6% 11% 21% 20% 4	2407
	11th to 20th	Night	42% 4 11% 21% 17% 3	2470
	21st to end	Night	41% 4 15% 28% 11% 1	2550
December	1st to 10th	Night	47% 6% 13% 21% 13% 1	2660
	11th to 20th	Night	46% 6% 15% 17% 13% 2	3288
	21st to end	Night	52% 5% 11% 20% 11%	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	34% 25% 26% 13% 2	180
	11th to 20th	Day	38% 25% 25% 11% 1	180
	21st to end	Day	28% 29% 31% 9% 2 1	236
February	1st to 10th	Day	39% 29% 24% 7% 1	287
	11th to 20th	Day	33% 27% 30% 9% 1	432
	21st to end	Day	37% 23% 29% 9% 2	346
March	1st to 10th	Day	29% 24% 34% 12% 2	420
	11th to 20th	Day	30% 27% 30% 11% 2 1	420
	21st to end	Day	34% 21% 30% 9% 5%	462
April	1st to 10th	Day	34% 24% 25% 9% 6% 1	420
	11th to 20th	Day	30% 25% 26% 12% 6% 1	412
	21st to end	Day	30% 19% 35% 11% 4 1	420
May	1st to 10th	Day	36% 21% 24% 12% 5% 2	423
	11th to 20th	Day	24% 22% 31% 19% 3 1	447
	21st to end	Day	23% 11% 29% 24% 11% 2	485
June	1st to 10th	Day	22% 14% 32% 20% 11% 2	450
	11th to 20th	Day	20% 16% 32% 21% 9% 2	450
	21st to end	Day	16% 17% 28% 25% 11% 2	450
July	1st to 10th	Day	17% 10% 31% 25% 13% 3	445
	11th to 20th	Day	14% 7% 31% 31% 14% 3	444
	21st to end	Day	14% 10% 36% 26% 11% 2	488
August	1st to 10th	Day	14% 8% 32% 28% 13% 6%	446
	11th to 20th	Day	18% 8% 30% 26% 13% 6%	439
	21st to end	Day	14% 12% 29% 24% 14% 6%	495
September	1st to 10th	Day	21% 12% 24% 20% 16% 6%	450
	11th to 20th	Day	16% 11% 29% 23% 12% 8%	450
	21st to end	Day	21% 14% 30% 21% 9% 5%	450
October	1st to 10th	Day	33% 8% 27% 16% 12% 4	450
	11th to 20th	Day	20% 21% 29% 21% 8% 1	450
	21st to end	Day	33% 16% 24% 21% 7%	403
November	1st to 10th	Day	24% 18% 25% 21% 10% 1	365
	11th to 20th	Day	32% 23% 25% 15% 5% 1	370
	21st to end	Day	26% 26% 28% 16% 4	289
December	1st to 10th	Day	32% 27% 27% 11% 4	180
	11th to 20th	Day	42% 20% 27% 10% 1	180
	21st to end	Day	32% 27% 25% 13% 3	198
January	1st to 10th	Night	24% 22% 38% 14% 3	760
	11th to 20th	Night	29% 22% 30% 17% 3	760
	21st to end	Night	24% 24% 33% 16% 3	836
February	1st to 10th	Night	26% 22% 31% 19% 2	760
	11th to 20th	Night	26% 25% 36% 12% 1	722
	21st to end	Night	32% 21% 30% 15% 2	592
March	1st to 10th	Night	26% 22% 34% 15% 3	720
	11th to 20th	Night	23% 27% 29% 17% 3	720
	21st to end	Night	26% 23% 30% 16% 4 1	792
April	1st to 10th	Night	28% 22% 29% 19% 3	720
	11th to 20th	Night	24% 20% 31% 19% 5%	711
	21st to end	Night	25% 20% 31% 18% 5%	651
May	1st to 10th	Night	29% 16% 29% 19% 6% 1	540
	11th to 20th	Night	23% 16% 36% 21% 4	389
	21st to end	Night	20% 8% 28% 33% 10% 1	389
June	1st to 10th	Night	21% 7% 31% 31% 10% 1	360
	11th to 20th	Night	21% 8% 28% 28% 15%	360
	21st to end	Night	16% 5% 27% 39% 13%	360
July	1st to 10th	Night	16% 5% 20% 40% 18% 1	350
	11th to 20th	Night	17% 3 23% 39% 17% 1	348
	21st to end	Night	12% 5% 27% 38% 17%	394
August	1st to 10th	Night	13% 4 24% 42% 15% 2	407
	11th to 20th	Night	15% 4 21% 38% 19% 2	710
	21st to end	Night	19% 5% 21% 35% 19% 2	792
September	1st to 10th	Night	19% 7% 27% 31% 13% 3	720
	11th to 20th	Night	17% 9% 25% 29% 18% 3	720
	21st to end	Night	22% 8% 25% 27% 14% 3	720
October	1st to 10th	Night	26% 12% 24% 25% 11% 2	720
	11th to 20th	Night	20% 14% 32% 25% 9% 1	720
	21st to end	Night	29% 15% 29% 20% 6%	792
November	1st to 10th	Night	21% 16% 31% 22% 9% 1	740
	11th to 20th	Night	26% 18% 31% 18% 7% 1	760
	21st to end	Night	22% 21% 30% 21% 6% 1	760
December	1st to 10th	Night	29% 21% 28% 18% 4 1	760
	11th to 20th	Night	27% 23% 28% 19% 3	760
	21st to end	Night	30% 19% 33% 16% 2	836

Page generated at 2024-02-12 06:35:32. Version ac07

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