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 2024-11-11.

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%	100794
	Night	13% 6% 2 5% 4 3 4 3 5% 7% 49%	98422
Transparency	Day	37% 6% 11% 23% 19% 5%	104437
	Night	34% 5% 9% 22% 22% 7%	102920
Seeing	Day	13% 6% 19% 25% 24% 12%	15313
	Night	15% 6% 23% 32% 21% 3	25073

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	12% 7% 2 7% 4 4 4 4 5% 8% 41%	3765
	11th to 20th	Day	11% 5% 2 7% 4 5% 5% 5% 7% 10% 41%	3813
	21st to end	Day	11% 6% 3 7% 5% 6% 6% 5% 7% 8% 36%	4757
June	1st to 10th	Day	7% 6% 2 6% 4 5% 5% 4 6% 9% 44%	2660
	11th to 20th	Day	5% 5% 2 4 4 5% 6% 4 7% 9% 50%	2660
	21st to end	Day	4 3 2 5% 4 4 5% 5% 8% 10% 50%	2660
July	1st to 10th	Day	6% 5% 2 6% 6% 5% 5% 4 8% 11% 40%	4350
	11th to 20th	Day	7% 5% 2 6% 5% 5% 6% 5% 8% 11% 41%	4120
	21st to end	Day	16% 7% 2 8% 5% 5% 5% 5% 7% 8% 32%	4465
August	1st to 10th	Day	3 2 1 3 3 4 4 4 6% 9% 61%	3862
	11th to 20th	Day	5% 4 2 6% 5% 5% 5% 4 6% 11% 47%	3729
	21st to end	Day	5% 4 2 5% 5% 5% 5% 4 6% 8% 50%	4180
September	1st to 10th	Day	9% 6% 2 7% 5% 4 4 4 6% 8% 46%	2280
	11th to 20th	Day	12% 4 2 5% 4 4 5% 4 5% 8% 46%	2256
	21st to end	Day	9% 5% 2 4 3 4 3 4 5% 8% 54%	2090
October	1st to 10th	Day	6% 4 1 5% 3 4 4 4 5% 7% 58%	1910
	11th to 20th	Day	12% 4 2 4 3 3 4 3 3 5% 58%	1900
	21st to end	Day	17% 6% 2 4 3 3 3 2 3 4 53%	2090
November	1st to 10th	Day	14% 5% 1 4 3 2 3 3 4 5% 56%	1894
	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	18% 7% 2 5% 4 4 3 3 5% 9% 40%	3130
	11th to 20th	Night	13% 7% 2 6% 4 3 4 3 4 7% 47%	3076
	21st to end	Night	9% 6% 2 6% 5% 5% 5% 5% 8% 10% 39%	2803
June	1st to 10th	Night	7% 4 2 6% 5% 4 5% 5% 7% 9% 47%	1520
	11th to 20th	Night	2 3 1 3 3 4 5% 4 7% 11% 58%	1520
	21st to end	Night	3 3 2 4 4 4 5% 4 8% 9% 55%	1520
July	1st to 10th	Night	5% 4 2 4 4 4 5% 4 9% 13% 46%	2614
	11th to 20th	Night	6% 4 2 5% 4 4 4 5% 7% 12% 48%	2850
	21st to end	Night	12% 7% 3 7% 5% 4 4 4 6% 8% 39%	3098
August	1st to 10th	Night	2 1 1 2 2 3 3 3 5% 7% 71%	3069
	11th to 20th	Night	4 3 1 5% 3 4 5% 4 8% 10% 53%	3100
	21st to end	Night	4 4 2 4 3 4 4 4 6% 9% 56%	3476
September	1st to 10th	Night	8% 6% 2 5% 4 4 3 3 4 7% 54%	1900
	11th to 20th	Night	11% 5% 2 5% 3 3 4 3 5% 7% 51%	1904
	21st to end	Night	8% 4 2 4 3 3 3 3 5% 6% 58%	2090
October	1st to 10th	Night	7% 2 1 3 2 3 2 3 5% 6% 64%	2266
	11th to 20th	Night	11% 5% 1 4 2 3 3 3 4 6% 59%	2280
	21st to end	Night	15% 5% 2 4 3 3 2 3 3 5% 55%	2508
November	1st to 10th	Night	11% 6% 2 4 4 3 3 3 5% 5% 55%	2400
	11th to 20th	Night	10% 5% 2 5% 3 3 4 3 5% 6% 55%	2477
	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	40% 7% 10% 27% 14% 2	3800
	11th to 20th	Day	36% 10% 15% 24% 14% 1	3817
	21st to end	Day	41% 9% 12% 25% 11% 1	4770
June	1st to 10th	Day	34% 8% 14% 24% 18% 2	2660
	11th to 20th	Day	28% 6% 12% 30% 19% 4	2660
	21st to end	Day	25% 8% 16% 26% 20% 4	2660
July	1st to 10th	Day	33% 9% 18% 26% 12% 1	4283
	11th to 20th	Day	34% 8% 16% 32% 8% 3	4051
	21st to end	Day	47% 7% 14% 23% 7% 1	4325
August	1st to 10th	Day	19% 6% 17% 33% 23% 2	3848
	11th to 20th	Day	31% 7% 18% 30% 13% 2	3765
	21st to end	Day	30% 7% 12% 24% 24% 3	4179
September	1st to 10th	Day	34% 8% 10% 22% 18% 7%	2280
	11th to 20th	Day	36% 7% 11% 16% 24% 7%	2256
	21st to end	Day	29% 4 11% 23% 23% 10%	2090
October	1st to 10th	Day	16% 3 5% 15% 29% 31%	3170
	11th to 20th	Day	18% 2 4 20% 39% 17%	3140
	21st to end	Day	28% 3 4 25% 31% 10%	3428
November	1st to 10th	Day	32% 3 7% 23% 26% 9%	1894
	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	41% 6% 11% 22% 16% 3	3160
	11th to 20th	Night	38% 6% 13% 26% 15% 1	3077
	21st to end	Night	35% 10% 14% 25% 15% 2	2811
June	1st to 10th	Night	30% 8% 13% 25% 22% 2	1520
	11th to 20th	Night	19% 7% 15% 29% 25% 5%	1520
	21st to end	Night	23% 8% 13% 29% 23% 5%	1520
July	1st to 10th	Night	27% 9% 22% 25% 16% 2	2572
	11th to 20th	Night	26% 7% 15% 36% 13% 3	2796
	21st to end	Night	43% 6% 13% 26% 12% 1	2999
August	1st to 10th	Night	12% 5% 12% 38% 28% 5%	3059
	11th to 20th	Night	24% 7% 21% 29% 17% 2	3130
	21st to end	Night	24% 7% 11% 23% 30% 5%	3476
September	1st to 10th	Night	31% 6% 9% 24% 21% 9%	1900
	11th to 20th	Night	31% 6% 10% 19% 26% 7%	1904
	21st to end	Night	27% 5% 9% 22% 27% 10%	2090
October	1st to 10th	Night	14% 3 6% 18% 27% 32%	3786
	11th to 20th	Night	17% 3 4 16% 33% 28%	3779
	21st to end	Night	24% 3 5% 22% 30% 15%	4120
November	1st to 10th	Night	31% 4 6% 21% 28% 10%	2400
	11th to 20th	Night	31% 4 7% 21% 28% 11%	2477
	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%	693
June	1st to 10th	Day	9% 3 12% 28% 31% 17%	680
	11th to 20th	Day	6% 3 8% 32% 36% 16%	680
	21st to end	Day	6% 1 9% 34% 31% 19%	680
July	1st to 10th	Day	5% 2 7% 25% 38% 24%	671
	11th to 20th	Day	7% 2 6% 22% 36% 27%	668
	21st to end	Day	8% 2 4 22% 37% 27%	739
August	1st to 10th	Day	5% 1 5% 27% 38% 23%	538
	11th to 20th	Day	10% 2 5% 22% 41% 19%	479
	21st to end	Day	11% 2 4 14% 36% 33%	539
September	1st to 10th	Day	9% 1 8% 23% 41% 17%	490
	11th to 20th	Day	11% 2 7% 22% 32% 26%	490
	21st to end	Day	15% 2 9% 26% 31% 16%	490
October	1st to 10th	Day	7% 3 19% 25% 30% 16%	310
	11th to 20th	Day	8% 5% 32% 29% 19% 6%	300
	21st to end	Day	21% 7% 26% 28% 14% 4	330
November	1st to 10th	Day	17% 8% 23% 26% 21% 4	300
	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% 37% 30% 6%	617
June	1st to 10th	Night	7% 3 8% 41% 35% 6%	570
	11th to 20th	Night	2 2 7% 37% 48% 4	570
	21st to end	Night	4 1 8% 36% 43% 9%	570
July	1st to 10th	Night	4 2 6% 30% 49% 10%	555
	11th to 20th	Night	6% 1 5% 26% 49% 12%	552
	21st to end	Night	5% 1 4 29% 47% 13%	624
August	1st to 10th	Night	4 1 4 29% 52% 11%	567
	11th to 20th	Night	7% 1 4 34% 43% 10%	564
	21st to end	Night	7% 1 4 24% 51% 12%	627
September	1st to 10th	Night	9% 1 6% 34% 44% 6%	570
	11th to 20th	Night	11% 2 9% 30% 38% 9%	574
	21st to end	Night	11% 3 14% 33% 35% 5%	760
October	1st to 10th	Night	8% 3 13% 35% 36% 5%	760
	11th to 20th	Night	13% 3 23% 40% 17% 3	760
	21st to end	Night	17% 7% 21% 36% 18% 1	836
November	1st to 10th	Night	14% 5% 23% 37% 20% 2	780
	11th to 20th	Night	12% 7% 29% 39% 12% 1	763
	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 2024-11-08 05:44:50. Version ac07

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