Phillips Community College
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Phillips Community College clear sky chart from 2005-11-06 to 2024-05-30.

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	12% 7% 2 6% 4 4 4 4 5% 7% 44%	83994
	Night	13% 6% 2 5% 4 3 4 3 5% 7% 49%	85924
Transparency	Day	38% 6% 11% 22% 19% 4	83715
	Night	35% 5% 9% 22% 22% 6%	85724
Seeing	Day	13% 7% 19% 25% 24% 12%	14630
	Night	15% 6% 23% 32% 21% 3	24523

By Month

Percentage Cloud Cover SE (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	17% 12% 4 7% 3 2 2 2 3 4 44%	2815
	11th to 20th	Day	19% 8% 3 5% 3 3 3 2 4 4 45%	2850
	21st to end	Day	23% 9% 2 5% 3 3 3 2 4 4 42%	3135
February	1st to 10th	Day	21% 8% 3 6% 3 4 4 3 3 6% 40%	1806
	11th to 20th	Day	21% 9% 3 5% 4 3 3 3 3 5% 41%	1848
	21st to end	Day	24% 8% 3 6% 3 3 3 3 4 4 37%	1570
March	1st to 10th	Day	18% 13% 4 9% 5% 3 3 2 4 4 34%	3267
	11th to 20th	Day	13% 6% 3 7% 5% 4 4 4 5% 7% 43%	3480
	21st to end	Day	13% 7% 3 8% 5% 5% 4 3 5% 5% 41%	3989
April	1st to 10th	Day	12% 6% 2 7% 5% 4 4 3 6% 7% 44%	2280
	11th to 20th	Day	15% 6% 2 6% 4 3 4 3 5% 6% 46%	2254
	21st to end	Day	12% 7% 3 7% 4 5% 5% 4 5% 6% 43%	2280
May	1st to 10th	Day	13% 7% 3 7% 4 4 4 4 5% 7% 42%	2280
	11th to 20th	Day	10% 5% 2 7% 4 5% 5% 5% 6% 9% 41%	2267
	21st to end	Day	7% 6% 2 7% 6% 6% 6% 6% 8% 8% 39%	2811
June	1st to 10th	Day	7% 6% 2 7% 5% 5% 5% 4 7% 9% 43%	2520
	11th to 20th	Day	5% 4 1 4 4 5% 5% 4 7% 9% 50%	2520
	21st to end	Day	4 4 2 4 4 4 5% 4 7% 9% 51%	2520
July	1st to 10th	Day	6% 6% 2 6% 6% 5% 6% 5% 9% 11% 36%	2472
	11th to 20th	Day	6% 5% 2 6% 5% 6% 6% 5% 8% 9% 42%	2340
	21st to end	Day	7% 4 1 5% 5% 6% 6% 6% 8% 10% 41%	2546
August	1st to 10th	Day	5% 4 2 6% 6% 6% 6% 6% 8% 11% 41%	2198
	11th to 20th	Day	8% 5% 2 7% 5% 5% 5% 4 5% 11% 42%	2125
	21st to end	Day	8% 5% 2 5% 6% 5% 5% 4 7% 9% 43%	2376
September	1st to 10th	Day	8% 5% 2 7% 5% 4 4 4 6% 8% 45%	2160
	11th to 20th	Day	11% 4 2 5% 4 4 5% 4 5% 8% 47%	2138
	21st to end	Day	9% 5% 2 4 3 3 3 3 5% 8% 55%	1980
October	1st to 10th	Day	6% 4 1 5% 3 4 4 4 5% 7% 56%	1810
	11th to 20th	Day	13% 4 2 5% 3 3 4 3 4 5% 56%	1800
	21st to end	Day	18% 6% 2 4 3 3 3 2 3 4 52%	1980
November	1st to 10th	Day	12% 5% 1 4 3 2 3 3 4 5% 59%	1798
	11th to 20th	Day	12% 5% 2 6% 3 3 3 3 4 7% 52%	1710
	21st to end	Day	18% 8% 2 6% 3 3 3 3 4 7% 44%	1710
December	1st to 10th	Day	20% 8% 3 5% 5% 3 4 3 4 5% 40%	1658
	11th to 20th	Day	15% 8% 3 6% 5% 3 4 3 5% 4 43%	1918
	21st to end	Day	14% 9% 3 8% 5% 5% 5% 4 5% 6% 37%	2783
January	1st to 10th	Night	18% 7% 2 6% 4 3 3 3 3 5% 45%	4136
	11th to 20th	Night	19% 6% 2 6% 3 3 3 2 3 4 49%	4120
	21st to end	Night	23% 8% 2 4 3 2 3 2 3 4 46%	4532
February	1st to 10th	Night	20% 8% 2 6% 4 3 3 2 4 4 43%	2371
	11th to 20th	Night	18% 7% 3 5% 4 4 3 2 4 4 45%	2218
	21st to end	Night	21% 7% 2 6% 3 3 3 3 4 5% 42%	1884
March	1st to 10th	Night	18% 9% 2 6% 4 4 4 3 5% 6% 40%	3615
	11th to 20th	Night	14% 7% 2 5% 4 3 3 3 4 7% 48%	3480
	21st to end	Night	13% 7% 3 6% 4 4 4 4 5% 7% 44%	3640
April	1st to 10th	Night	10% 6% 2 5% 4 4 3 4 7% 7% 49%	1900
	11th to 20th	Night	13% 5% 2 4 4 3 4 3 5% 7% 50%	1875
	21st to end	Night	11% 6% 3 6% 3 3 3 2 5% 7% 50%	1900
May	1st to 10th	Night	12% 6% 2 5% 4 4 3 3 5% 8% 48%	1900
	11th to 20th	Night	11% 6% 2 5% 4 4 5% 3 5% 8% 47%	1842
	21st to end	Night	5% 5% 2 5% 4 4 4 5% 9% 12% 44%	1659
June	1st to 10th	Night	7% 4 2 5% 5% 4 5% 5% 8% 9% 47%	1440
	11th to 20th	Night	2 3 1 2 3 4 4 4 7% 11% 59%	1440
	21st to end	Night	3 3 1 4 4 4 5% 4 8% 9% 56%	1440
July	1st to 10th	Night	3 4 2 4 5% 4 5% 5% 10% 11% 47%	1482
	11th to 20th	Night	5% 3 1 5% 5% 4 4 5% 8% 12% 47%	1620
	21st to end	Night	4 3 2 4 4 3 5% 5% 8% 11% 52%	1772
August	1st to 10th	Night	4 2 1 4 4 4 4 5% 7% 10% 55%	1740
	11th to 20th	Night	5% 4 2 6% 4 5% 5% 5% 9% 10% 45%	1776
	21st to end	Night	6% 4 2 4 4 4 4 3 6% 10% 51%	1980
September	1st to 10th	Night	8% 5% 2 5% 4 4 4 3 4 8% 55%	1800
	11th to 20th	Night	10% 5% 2 4 3 3 4 3 5% 7% 52%	1803
	21st to end	Night	8% 4 2 4 3 2 3 3 5% 6% 59%	1980
October	1st to 10th	Night	7% 2 1 3 2 3 2 3 5% 6% 63%	2146
	11th to 20th	Night	11% 5% 1 4 2 3 3 3 4 6% 57%	2160
	21st to end	Night	16% 5% 2 4 3 3 3 3 3 5% 53%	2376
November	1st to 10th	Night	9% 5% 2 4 3 2 3 3 5% 5% 58%	2277
	11th to 20th	Night	10% 5% 2 5% 3 3 4 3 5% 6% 55%	2470
	21st to end	Night	13% 6% 3 5% 5% 4 3 3 4 4 50%	2470
December	1st to 10th	Night	17% 8% 3 5% 4 3 3 3 4 5% 45%	2517
	11th to 20th	Night	16% 6% 2 5% 4 3 3 3 4 5% 49%	3279
	21st to end	Night	16% 7% 2 6% 5% 4 5% 4 5% 6% 40%	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	46% 3 5% 21% 21% 3	2816
	11th to 20th	Day	42% 5% 8% 24% 19% 2	2850
	21st to end	Day	46% 4 6% 19% 22% 3	3135
February	1st to 10th	Day	47% 4 9% 20% 17% 4	1806
	11th to 20th	Day	48% 4 5% 20% 19% 5%	1858
	21st to end	Day	50% 3 8% 16% 16% 7%	1570
March	1st to 10th	Day	54% 4 7% 11% 15% 8%	3267
	11th to 20th	Day	41% 6% 8% 24% 17% 5%	3480
	21st to end	Day	44% 5% 7% 22% 20% 2	3989
April	1st to 10th	Day	38% 6% 10% 22% 20% 4	2280
	11th to 20th	Day	38% 6% 7% 23% 20% 6%	2254
	21st to end	Day	39% 6% 11% 22% 22% 1	2280
May	1st to 10th	Day	42% 6% 11% 22% 17% 3	2280
	11th to 20th	Day	36% 9% 15% 23% 15% 2	2271
	21st to end	Day	37% 10% 15% 25% 12% 1	2811
June	1st to 10th	Day	35% 8% 14% 24% 18% 2	2520
	11th to 20th	Day	27% 6% 13% 31% 18% 4	2520
	21st to end	Day	25% 8% 16% 26% 20% 4	2520
July	1st to 10th	Day	33% 12% 18% 21% 13% 3	2405
	11th to 20th	Day	32% 9% 20% 24% 10% 5%	2271
	21st to end	Day	32% 9% 19% 28% 12% 1	2405
August	1st to 10th	Day	32% 9% 19% 28% 11% 1	2184
	11th to 20th	Day	37% 8% 14% 24% 15% 3	2125
	21st to end	Day	34% 7% 15% 23% 16% 4	2376
September	1st to 10th	Day	34% 9% 11% 22% 18% 6%	2160
	11th to 20th	Day	35% 7% 11% 16% 24% 7%	2138
	21st to end	Day	27% 4 11% 23% 24% 10%	1980
October	1st to 10th	Day	27% 6% 9% 25% 24% 10%	1810
	11th to 20th	Day	32% 4 6% 20% 28% 10%	1800
	21st to end	Day	38% 4 4 21% 25% 9%	1980
November	1st to 10th	Day	29% 3 7% 24% 27% 9%	1798
	11th to 20th	Day	34% 5% 6% 20% 26% 9%	1710
	21st to end	Day	42% 3 7% 20% 23% 5%	1710
December	1st to 10th	Day	47% 4 9% 19% 17% 5%	1658
	11th to 20th	Day	44% 4 6% 19% 23% 4	1915
	21st to end	Day	46% 5% 10% 20% 16% 2	2783
January	1st to 10th	Night	43% 4 5% 19% 26% 3	4136
	11th to 20th	Night	41% 4 6% 21% 22% 5%	4120
	21st to end	Night	44% 3 6% 21% 21% 4	4532
February	1st to 10th	Night	47% 3 6% 18% 21% 5%	2371
	11th to 20th	Night	43% 4 6% 21% 19% 7%	2219
	21st to end	Night	45% 4 8% 15% 21% 8%	1884
March	1st to 10th	Night	45% 6% 8% 14% 17% 11%	3615
	11th to 20th	Night	37% 5% 8% 22% 20% 8%	3480
	21st to end	Night	39% 6% 8% 21% 24% 2	3640
April	1st to 10th	Night	33% 5% 11% 23% 20% 7%	1900
	11th to 20th	Night	34% 4 7% 22% 23% 9%	1875
	21st to end	Night	35% 5% 9% 25% 23% 4	1900
May	1st to 10th	Night	34% 5% 12% 23% 20% 5%	1900
	11th to 20th	Night	36% 7% 12% 24% 20% 2	1843
	21st to end	Night	28% 10% 15% 27% 18% 2	1660
June	1st to 10th	Night	29% 9% 13% 25% 22% 2	1440
	11th to 20th	Night	18% 7% 15% 31% 25% 4	1440
	21st to end	Night	23% 8% 13% 28% 23% 5%	1440
July	1st to 10th	Night	24% 12% 20% 26% 15% 3	1440
	11th to 20th	Night	25% 9% 19% 28% 13% 6%	1566
	21st to end	Night	23% 8% 18% 35% 16% 1	1673
August	1st to 10th	Night	21% 8% 19% 35% 16% 1	1730
	11th to 20th	Night	31% 10% 17% 24% 16% 3	1776
	21st to end	Night	27% 8% 16% 25% 19% 5%	1980
September	1st to 10th	Night	30% 6% 9% 25% 22% 8%	1800
	11th to 20th	Night	30% 7% 11% 19% 27% 7%	1803
	21st to end	Night	26% 5% 9% 22% 28% 11%	1980
October	1st to 10th	Night	22% 5% 8% 27% 26% 12%	2146
	11th to 20th	Night	28% 5% 6% 20% 29% 12%	2160
	21st to end	Night	35% 4 5% 18% 28% 9%	2376
November	1st to 10th	Night	28% 4 6% 22% 29% 10%	2277
	11th to 20th	Night	30% 4 7% 21% 28% 11%	2470
	21st to end	Night	37% 4 7% 20% 25% 7%	2470
December	1st to 10th	Night	42% 4 7% 22% 19% 6%	2517
	11th to 20th	Night	39% 4 6% 21% 26% 5%	3281
	21st to end	Night	43% 6% 9% 19% 19% 4	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	27% 10% 37% 19% 7% 1	270
	11th to 20th	Day	27% 14% 36% 19% 3 1	270
	21st to end	Day	19% 14% 42% 19% 6% 1	297
February	1st to 10th	Day	25% 12% 31% 21% 10% 1	270
	11th to 20th	Day	28% 17% 32% 19% 4	270
	21st to end	Day	35% 14% 32% 12% 8%	225
March	1st to 10th	Day	22% 13% 33% 23% 9% 1	270
	11th to 20th	Day	17% 19% 35% 23% 6%	270
	21st to end	Day	17% 14% 37% 22% 10% 1	395
April	1st to 10th	Day	16% 13% 32% 27% 10% 2	460
	11th to 20th	Day	20% 11% 29% 27% 11% 3	452
	21st to end	Day	16% 10% 30% 25% 16% 3	460
May	1st to 10th	Day	13% 12% 25% 32% 16% 3	463
	11th to 20th	Day	10% 5% 24% 29% 23% 9%	487
	21st to end	Day	10% 4 19% 30% 25% 12%	684
June	1st to 10th	Day	10% 2 12% 27% 32% 18%	630
	11th to 20th	Day	5% 2 8% 33% 36% 16%	630
	21st to end	Day	6% 2 9% 35% 31% 18%	630
July	1st to 10th	Day	5% 2 7% 25% 37% 24%	621
	11th to 20th	Day	7% 2 6% 21% 36% 28%	618
	21st to end	Day	7% 2 4 21% 38% 29%	684
August	1st to 10th	Day	5% 1 5% 26% 39% 24%	496
	11th to 20th	Day	11% 2 4 21% 42% 20%	439
	21st to end	Day	12% 2 4 14% 36% 32%	495
September	1st to 10th	Day	9% 1 7% 22% 43% 19%	450
	11th to 20th	Day	9% 2 8% 22% 33% 26%	450
	21st to end	Day	15% 2 8% 26% 32% 17%	450
October	1st to 10th	Day	8% 3 21% 23% 30% 15%	280
	11th to 20th	Day	9% 5% 34% 30% 16% 6%	270
	21st to end	Day	23% 6% 29% 27% 12% 3	297
November	1st to 10th	Day	14% 7% 22% 28% 23% 5%	270
	11th to 20th	Day	10% 8% 32% 35% 13% 2	270
	21st to end	Day	22% 10% 30% 20% 15% 3	270
December	1st to 10th	Day	23% 12% 33% 20% 11% 1	270
	11th to 20th	Day	20% 13% 31% 21% 13% 2	270
	21st to end	Day	25% 15% 30% 24% 5% 1	297
January	1st to 10th	Night	21% 10% 36% 28% 6%	950
	11th to 20th	Night	24% 10% 32% 29% 5% 1	950
	21st to end	Night	21% 9% 37% 30% 3	1045
February	1st to 10th	Night	25% 11% 31% 28% 5%	851
	11th to 20th	Night	22% 11% 38% 26% 3	743
	21st to end	Night	24% 14% 36% 24% 3	628
March	1st to 10th	Night	19% 9% 32% 33% 7%	694
	11th to 20th	Night	19% 10% 32% 32% 6% 1	570
	21st to end	Night	18% 8% 33% 30% 11%	627
April	1st to 10th	Night	13% 10% 35% 31% 9% 1	570
	11th to 20th	Night	17% 9% 29% 33% 11% 1	563
	21st to end	Night	14% 8% 31% 34% 12% 1	570
May	1st to 10th	Night	13% 9% 23% 38% 15% 1	570
	11th to 20th	Night	14% 2 23% 37% 21% 3	561
	21st to end	Night	6% 3 18% 36% 30% 6%	611
June	1st to 10th	Night	6% 2 8% 41% 36% 7%	540
	11th to 20th	Night	2 1 7% 37% 48% 4	540
	21st to end	Night	4 1 7% 37% 42% 9%	540
July	1st to 10th	Night	3 2 6% 30% 49% 10%	525
	11th to 20th	Night	6% 1 5% 25% 49% 13%	522
	21st to end	Night	4 1 4 29% 48% 14%	591
August	1st to 10th	Night	4 1 4 28% 53% 10%	537
	11th to 20th	Night	7% 1 4 34% 43% 10%	534
	21st to end	Night	7% 1 4 24% 52% 12%	594
September	1st to 10th	Night	9% 1 5% 33% 45% 6%	540
	11th to 20th	Night	10% 2 9% 30% 40% 9%	543
	21st to end	Night	11% 3 13% 33% 35% 5%	720
October	1st to 10th	Night	8% 3 14% 33% 36% 5%	720
	11th to 20th	Night	14% 3 24% 39% 17% 3	720
	21st to end	Night	17% 7% 21% 35% 18% 1	792
November	1st to 10th	Night	12% 5% 22% 38% 21% 3	740
	11th to 20th	Night	12% 8% 29% 39% 12% 1	760
	21st to end	Night	16% 9% 29% 31% 14% 1	760
December	1st to 10th	Night	20% 8% 31% 32% 9%	807
	11th to 20th	Night	22% 9% 27% 33% 9%	950
	21st to end	Night	24% 10% 31% 29% 7%	1045

Page generated at 2024-05-26 23:31:46. Version ac07

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