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 2025-12-03.

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	12% 6% 2 6% 4 4 4 4 5% 7% 44%	126267
	Night	13% 6% 2 5% 4 3 4 3 5% 7% 48%	124614
Transparency	Day	37% 6% 11% 24% 18% 5%	129871
	Night	35% 5% 9% 23% 21% 7%	129087
Seeing	Day	13% 7% 20% 25% 24% 12%	16734
	Night	15% 6% 23% 32% 21% 3	26480

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% 9% 5% 8% 3 2 2 2 3 4 45%	4031
	11th to 20th	Day	15% 7% 2 5% 4 3 3 2 4 4 50%	4080
	21st to end	Day	21% 8% 2 5% 3 3 3 2 4 4 46%	4488
February	1st to 10th	Day	22% 8% 3 6% 3 4 4 3 3 6% 39%	1902
	11th to 20th	Day	21% 8% 3 5% 4 3 3 3 3 5% 40%	1948
	21st to end	Day	23% 8% 3 6% 3 3 3 3 4 4 39%	1650
March	1st to 10th	Day	18% 12% 4 9% 5% 4 3 2 4 4 35%	4697
	11th to 20th	Day	11% 5% 3 6% 4 3 4 3 4 6% 50%	4980
	21st to end	Day	12% 7% 3 8% 5% 5% 4 3 5% 6% 41%	5707
April	1st to 10th	Day	12% 6% 2 7% 5% 4 4 3 6% 7% 44%	2400
	11th to 20th	Day	14% 6% 2 6% 4 2 4 3 5% 6% 47%	2374
	21st to end	Day	12% 7% 3 7% 4 5% 5% 4 5% 7% 42%	2400
May	1st to 10th	Day	15% 8% 3 8% 4 4 4 4 6% 8% 35%	5405
	11th to 20th	Day	13% 7% 3 7% 4 5% 6% 5% 7% 9% 34%	5467
	21st to end	Day	14% 7% 3 8% 5% 5% 6% 4 7% 8% 34%	6840
June	1st to 10th	Day	7% 6% 2 6% 4 5% 5% 4 7% 9% 44%	2800
	11th to 20th	Day	6% 5% 2 4 5% 5% 6% 4 7% 9% 48%	2800
	21st to end	Day	4 3 2 4 4 4 5% 5% 8% 10% 51%	2800
July	1st to 10th	Day	6% 5% 2 6% 5% 5% 6% 4 8% 11% 41%	6228
	11th to 20th	Day	6% 4 2 6% 5% 5% 6% 5% 8% 12% 43%	5900
	21st to end	Day	11% 5% 2 6% 4 4 5% 5% 7% 11% 40%	6422
August	1st to 10th	Day	2 2 1 3 3 4 4 4 6% 9% 61%	3984
	11th to 20th	Day	5% 4 2 6% 5% 5% 5% 4 6% 11% 47%	3849
	21st to end	Day	6% 4 2 5% 5% 5% 5% 4 6% 8% 50%	4312
September	1st to 10th	Day	9% 6% 2 7% 4 4 4 4 7% 8% 45%	2400
	11th to 20th	Day	12% 4 2 5% 4 5% 5% 4 5% 8% 47%	2375
	21st to end	Day	9% 5% 2 4 3 4 3 4 5% 8% 54%	2200
October	1st to 10th	Day	6% 4 1 5% 3 4 3 3 5% 7% 58%	2010
	11th to 20th	Day	11% 4 2 4 3 3 4 2 3 5% 59%	2000
	21st to end	Day	18% 6% 2 4 3 3 3 2 3 4 52%	2200
November	1st to 10th	Day	13% 5% 1 4 3 2 2 3 3 5% 57%	1991
	11th to 20th	Day	11% 5% 2 6% 3 3 3 3 4 7% 53%	1890
	21st to end	Day	17% 8% 2 6% 3 3 3 3 4 7% 45%	1890
December	1st to 10th	Day	18% 7% 3 5% 4 3 4 3 3 4 45%	2857
	11th to 20th	Day	20% 9% 3 5% 4 3 3 2 4 4 43%	3008
	21st to end	Day	15% 9% 3 7% 4 4 5% 3 4 6% 40%	3982
January	1st to 10th	Night	17% 7% 3 6% 4 3 3 2 3 4 48%	5916
	11th to 20th	Night	16% 6% 2 5% 3 3 2 2 3 4 54%	5900
	21st to end	Night	22% 9% 2 4 3 2 3 2 3 5% 44%	6490
February	1st to 10th	Night	21% 8% 2 6% 4 3 3 2 3 4 43%	2495
	11th to 20th	Night	19% 7% 3 5% 4 4 3 2 4 4 44%	2338
	21st to end	Night	20% 7% 2 6% 4 3 3 3 4 5% 44%	1980
March	1st to 10th	Night	17% 9% 2 6% 5% 3 4 3 4 5% 42%	5199
	11th to 20th	Night	12% 6% 2 5% 3 4 4 3 4 7% 51%	4980
	21st to end	Night	14% 7% 3 6% 4 4 4 3 5% 7% 44%	5220
April	1st to 10th	Night	11% 6% 2 5% 4 4 3 4 6% 7% 48%	2000
	11th to 20th	Night	12% 5% 2 4 4 3 5% 3 4 7% 51%	1975
	21st to end	Night	12% 7% 3 6% 3 3 3 3 5% 7% 49%	2000
May	1st to 10th	Night	18% 8% 3 6% 4 4 4 3 5% 8% 37%	4490
	11th to 20th	Night	19% 9% 3 8% 4 3 4 3 4 6% 36%	4408
	21st to end	Night	11% 7% 3 7% 5% 5% 4 4 7% 9% 39%	4028
June	1st to 10th	Night	7% 4 2 5% 5% 4 5% 5% 7% 10% 47%	1600
	11th to 20th	Night	3 3 1 3 3 4 5% 4 8% 10% 56%	1600
	21st to end	Night	3 3 1 5% 4 4 5% 4 8% 9% 56%	1600
July	1st to 10th	Night	5% 4 2 5% 5% 4 5% 5% 8% 12% 46%	3744
	11th to 20th	Night	5% 3 1 5% 4 4 4 5% 7% 14% 48%	4077
	21st to end	Night	9% 5% 2 6% 4 4 4 4 7% 11% 44%	4449
August	1st to 10th	Night	2 1 1 2 2 3 3 3 5% 7% 71%	3166
	11th to 20th	Night	4 3 1 5% 3 4 5% 4 8% 10% 54%	3200
	21st to end	Night	4 4 2 4 4 4 4 4 6% 9% 56%	3586
September	1st to 10th	Night	8% 6% 2 5% 4 4 3 4 4 7% 54%	2000
	11th to 20th	Night	11% 4 2 4 3 3 4 4 5% 7% 52%	2004
	21st to end	Night	8% 4 2 4 3 3 3 3 5% 6% 57%	2200
October	1st to 10th	Night	7% 3 1 3 2 3 2 3 5% 6% 64%	2385
	11th to 20th	Night	10% 5% 1 4 2 3 3 3 4 6% 60%	2400
	21st to end	Night	16% 5% 2 4 3 3 2 3 3 5% 54%	2640
November	1st to 10th	Night	10% 6% 2 4 3 3 3 3 5% 5% 56%	2523
	11th to 20th	Night	10% 5% 2 5% 3 3 3 3 4 6% 57%	2730
	21st to end	Night	13% 6% 3 5% 4 3 3 3 4 4 50%	2730
December	1st to 10th	Night	17% 7% 2 5% 3 3 3 3 4 5% 49%	4366
	11th to 20th	Night	19% 7% 2 6% 4 3 3 3 4 4 45%	5199
	21st to end	Night	18% 7% 2 5% 4 4 4 3 5% 5% 41%	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	45% 3 8% 26% 17% 2	4032
	11th to 20th	Day	38% 4 7% 25% 24% 3	4080
	21st to end	Day	43% 3 5% 18% 24% 7%	4488
February	1st to 10th	Day	48% 4 8% 20% 16% 4	1902
	11th to 20th	Day	48% 4 5% 19% 18% 5%	1958
	21st to end	Day	48% 3 8% 16% 18% 7%	1650
March	1st to 10th	Day	54% 4 5% 15% 14% 9%	4697
	11th to 20th	Day	36% 5% 6% 20% 23% 11%	4980
	21st to end	Day	43% 4 8% 23% 20% 2	5709
April	1st to 10th	Day	38% 6% 10% 22% 20% 4	2400
	11th to 20th	Day	37% 6% 7% 23% 20% 6%	2374
	21st to end	Day	39% 6% 11% 22% 21% 1	2400
May	1st to 10th	Day	45% 7% 10% 26% 11% 1	5440
	11th to 20th	Day	42% 9% 16% 21% 11% 1	5471
	21st to end	Day	44% 8% 12% 21% 13% 1	6854
June	1st to 10th	Day	34% 7% 14% 24% 19% 2	2800
	11th to 20th	Day	30% 6% 12% 30% 18% 4	2800
	21st to end	Day	24% 9% 17% 27% 19% 4	2800
July	1st to 10th	Day	33% 8% 16% 26% 15% 1	6161
	11th to 20th	Day	30% 8% 22% 32% 6% 2	5831
	21st to end	Day	36% 7% 18% 32% 6%	6240
August	1st to 10th	Day	18% 6% 17% 34% 23% 2	3970
	11th to 20th	Day	30% 7% 18% 31% 12% 1	3885
	21st to end	Day	30% 6% 12% 25% 24% 3	4311
September	1st to 10th	Day	34% 8% 10% 23% 18% 6%	2400
	11th to 20th	Day	35% 7% 10% 19% 23% 7%	2375
	21st to end	Day	29% 5% 11% 22% 23% 10%	2200
October	1st to 10th	Day	16% 3 5% 15% 30% 31%	3270
	11th to 20th	Day	18% 2 4 20% 39% 17%	3240
	21st to end	Day	28% 3 4 25% 31% 9%	3538
November	1st to 10th	Day	31% 3 7% 23% 27% 8%	1991
	11th to 20th	Day	32% 4 7% 21% 27% 9%	1890
	21st to end	Day	41% 3 6% 20% 24% 5%	1890
December	1st to 10th	Day	44% 3 6% 24% 20% 3	2857
	11th to 20th	Day	47% 3 5% 21% 19% 5%	3005
	21st to end	Day	45% 4 9% 26% 14% 2	3982
January	1st to 10th	Night	42% 3 6% 25% 21% 2	5916
	11th to 20th	Night	36% 4 5% 21% 28% 7%	5900
	21st to end	Night	45% 2 6% 20% 22% 5%	6490
February	1st to 10th	Night	47% 3 6% 19% 21% 4	2495
	11th to 20th	Night	44% 4 6% 21% 18% 7%	2339
	21st to end	Night	44% 4 7% 15% 22% 8%	1980
March	1st to 10th	Night	44% 4 6% 14% 20% 12%	5199
	11th to 20th	Night	34% 4 6% 21% 19% 16%	4980
	21st to end	Night	39% 5% 7% 23% 22% 4	5220
April	1st to 10th	Night	34% 5% 11% 23% 20% 7%	2000
	11th to 20th	Night	34% 4 7% 23% 23% 9%	1975
	21st to end	Night	35% 5% 10% 24% 22% 4	2000
May	1st to 10th	Night	45% 6% 12% 21% 13% 2	4520
	11th to 20th	Night	49% 6% 11% 22% 11% 1	4409
	21st to end	Night	39% 9% 12% 21% 15% 4	4036
June	1st to 10th	Night	29% 9% 13% 25% 23% 2	1600
	11th to 20th	Night	20% 7% 15% 29% 25% 4	1600
	21st to end	Night	22% 8% 14% 29% 22% 5%	1600
July	1st to 10th	Night	27% 9% 19% 25% 18% 1	3704
	11th to 20th	Night	24% 8% 21% 35% 10% 2	4026
	21st to end	Night	34% 7% 17% 32% 10%	4320
August	1st to 10th	Night	13% 5% 12% 38% 28% 4	3156
	11th to 20th	Night	23% 7% 21% 29% 17% 2	3230
	21st to end	Night	25% 7% 11% 24% 29% 5%	3586
September	1st to 10th	Night	31% 6% 9% 25% 21% 8%	2000
	11th to 20th	Night	30% 6% 11% 20% 26% 7%	2004
	21st to end	Night	27% 5% 9% 21% 27% 11%	2200
October	1st to 10th	Night	14% 3 6% 18% 27% 32%	3905
	11th to 20th	Night	17% 3 4 16% 33% 27%	3899
	21st to end	Night	25% 3 5% 22% 30% 15%	4252
November	1st to 10th	Night	31% 4 6% 21% 28% 10%	2523
	11th to 20th	Night	30% 4 7% 22% 27% 11%	2730
	21st to end	Night	37% 4 7% 20% 25% 7%	2730
December	1st to 10th	Night	39% 3 6% 28% 21% 4	4366
	11th to 20th	Night	44% 3 6% 21% 22% 5%	5201
	21st to end	Night	43% 5% 9% 23% 17% 3	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	26% 11% 37% 19% 6% 1	300
	11th to 20th	Day	25% 14% 37% 20% 3 1	300
	21st to end	Day	18% 15% 43% 18% 5% 1	330
February	1st to 10th	Day	25% 12% 31% 21% 10% 1	300
	11th to 20th	Day	28% 17% 33% 17% 4	300
	21st to end	Day	31% 12% 33% 14% 9%	249
March	1st to 10th	Day	22% 13% 33% 21% 9% 1	300
	11th to 20th	Day	18% 18% 36% 22% 6%	300
	21st to end	Day	17% 14% 37% 22% 9%	433
April	1st to 10th	Day	16% 14% 32% 26% 10% 2	500
	11th to 20th	Day	19% 11% 30% 26% 11% 3	492
	21st to end	Day	15% 9% 29% 27% 17% 3	500
May	1st to 10th	Day	13% 12% 26% 32% 14% 2	503
	11th to 20th	Day	11% 6% 26% 28% 21% 8%	527
	21st to end	Day	10% 4 20% 31% 24% 11%	746
June	1st to 10th	Day	9% 2 14% 29% 30% 16%	730
	11th to 20th	Day	7% 3 10% 31% 35% 15%	730
	21st to end	Day	5% 1 8% 32% 32% 21%	730
July	1st to 10th	Day	5% 2 6% 25% 38% 24%	721
	11th to 20th	Day	7% 2 6% 21% 37% 28%	718
	21st to end	Day	8% 2 4 21% 38% 28%	794
August	1st to 10th	Day	5% 1 5% 26% 39% 23%	580
	11th to 20th	Day	9% 2 5% 20% 41% 23%	519
	21st to end	Day	11% 2 5% 16% 35% 31%	583
September	1st to 10th	Day	9% 2 8% 23% 41% 16%	530
	11th to 20th	Day	11% 2 7% 21% 33% 26%	530
	21st to end	Day	15% 3 10% 26% 31% 15%	530
October	1st to 10th	Day	8% 2 19% 25% 31% 15%	340
	11th to 20th	Day	8% 5% 32% 30% 20% 6%	330
	21st to end	Day	22% 7% 25% 28% 13% 4	363
November	1st to 10th	Day	16% 9% 24% 26% 20% 5%	330
	11th to 20th	Day	9% 8% 33% 34% 13% 2	330
	21st to end	Day	21% 10% 32% 21% 13% 3	330
December	1st to 10th	Day	23% 12% 33% 21% 10% 1	306
	11th to 20th	Day	21% 14% 31% 21% 12% 2	300
	21st to end	Day	25% 15% 29% 24% 5% 1	330
January	1st to 10th	Night	21% 10% 36% 28% 6%	1000
	11th to 20th	Night	23% 10% 33% 29% 4 1	1000
	21st to end	Night	21% 9% 37% 30% 3	1100
February	1st to 10th	Night	25% 11% 32% 28% 5%	895
	11th to 20th	Night	23% 11% 38% 25% 3	783
	21st to end	Night	22% 14% 35% 26% 3	660
March	1st to 10th	Night	19% 9% 33% 32% 7%	730
	11th to 20th	Night	18% 11% 33% 31% 6% 1	600
	21st to end	Night	18% 8% 33% 30% 10%	660
April	1st to 10th	Night	15% 10% 35% 31% 9% 1	600
	11th to 20th	Night	16% 9% 30% 33% 11% 1	593
	21st to end	Night	14% 8% 31% 34% 13% 1	600
May	1st to 10th	Night	14% 9% 23% 39% 14% 1	600
	11th to 20th	Night	15% 3 24% 35% 20% 3	591
	21st to end	Night	7% 3 18% 37% 29% 6%	650
June	1st to 10th	Night	7% 3 9% 41% 34% 6%	600
	11th to 20th	Night	3 2 8% 38% 46% 4	600
	21st to end	Night	3 1 7% 35% 44% 9%	600
July	1st to 10th	Night	4 2 6% 30% 50% 10%	585
	11th to 20th	Night	6% 1 4 26% 50% 12%	582
	21st to end	Night	5% 1 4 28% 48% 13%	657
August	1st to 10th	Night	4 1 4 30% 52% 10%	597
	11th to 20th	Night	7% 1 4 33% 43% 11%	594
	21st to end	Night	7% 1 4 26% 50% 11%	660
September	1st to 10th	Night	9% 1 6% 34% 43% 6%	600
	11th to 20th	Night	11% 2 8% 30% 40% 9%	604
	21st to end	Night	11% 3 14% 33% 34% 5%	800
October	1st to 10th	Night	8% 3 13% 35% 36% 5%	800
	11th to 20th	Night	13% 3 22% 41% 19% 2	800
	21st to end	Night	17% 7% 22% 36% 17% 1	880
November	1st to 10th	Night	13% 5% 23% 38% 19% 2	820
	11th to 20th	Night	11% 7% 30% 39% 12%	840
	21st to end	Night	16% 8% 29% 31% 13% 1	840
December	1st to 10th	Night	20% 8% 32% 32% 8%	859
	11th to 20th	Night	22% 9% 28% 33% 9%	1000
	21st to end	Night	24% 10% 31% 29% 7%	1100

Page generated at 2025-11-30 00:00:56. Version ac07

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