Mount Pleasant
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mount Pleasant clear sky chart from 2005-11-06 to 2024-11-05.

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	15% 6% 2 6% 4 4 4 4 6% 8% 41%	101253
	Night	15% 7% 2 6% 4 4 4 4 5% 7% 42%	97740
Transparency	Day	40% 6% 12% 23% 16% 3	104890
	Night	40% 6% 12% 24% 17% 3	102242
Seeing	Day	19% 12% 28% 23% 13% 4	14982
	Night	18% 11% 30% 28% 12% 1	24420

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	16% 5% 2 5% 4 3 5% 4 5% 5% 47%	2520
	11th to 20th	Day	14% 11% 3 8% 4 4 4 4 4 5% 38%	2840
	21st to end	Day	19% 9% 3 6% 5% 5% 4 3 5% 5% 36%	3124
February	1st to 10th	Day	14% 8% 2 7% 5% 4 4 4 6% 7% 39%	1710
	11th to 20th	Day	17% 8% 2 5% 6% 4 4 3 5% 6% 41%	1728
	21st to end	Day	18% 9% 3 7% 5% 5% 3 3 4 6% 39%	1570
March	1st to 10th	Day	22% 7% 2 5% 4 4 4 3 5% 8% 36%	3333
	11th to 20th	Day	9% 6% 2 5% 4 4 4 4 6% 7% 48%	3480
	21st to end	Day	20% 7% 2 5% 5% 3 3 3 4 6% 41%	3905
April	1st to 10th	Day	13% 8% 2 6% 5% 3 4 4 8% 7% 40%	2280
	11th to 20th	Day	13% 7% 2 7% 4 5% 3 3 4 6% 46%	2254
	21st to end	Day	19% 6% 2 5% 4 4 4 4 5% 7% 41%	2280
May	1st to 10th	Day	26% 8% 2 7% 4 3 4 4 6% 7% 30%	3988
	11th to 20th	Day	23% 8% 3 7% 4 5% 6% 4 6% 8% 29%	4356
	21st to end	Day	11% 5% 2 6% 4 4 4 4 6% 9% 45%	4823
June	1st to 10th	Day	11% 5% 2 5% 5% 5% 5% 5% 7% 9% 41%	2660
	11th to 20th	Day	11% 5% 3 6% 6% 5% 5% 4 7% 9% 41%	2660
	21st to end	Day	10% 4 2 5% 4 4 5% 5% 7% 11% 45%	2660
July	1st to 10th	Day	6% 4 2 7% 5% 6% 6% 5% 8% 10% 42%	4440
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 5% 8% 11% 40%	4389
	21st to end	Day	11% 7% 3 7% 5% 6% 6% 5% 7% 8% 35%	4466
August	1st to 10th	Day	17% 6% 2 6% 4 6% 6% 6% 7% 9% 32%	4104
	11th to 20th	Day	11% 5% 2 6% 4 6% 5% 5% 7% 9% 39%	3857
	21st to end	Day	11% 5% 2 5% 4 5% 4 4 6% 8% 46%	4180
September	1st to 10th	Day	14% 6% 2 5% 4 4 5% 3 4 7% 46%	2280
	11th to 20th	Day	11% 5% 2 6% 4 4 3 3 6% 8% 47%	2280
	21st to end	Day	20% 8% 3 7% 4 3 4 3 5% 6% 37%	2010
October	1st to 10th	Day	17% 6% 2 5% 4 3 4 3 5% 6% 45%	1900
	11th to 20th	Day	17% 5% 2 3 4 3 4 4 4 6% 49%	1900
	21st to end	Day	14% 5% 2 6% 4 4 4 3 5% 6% 48%	2090
November	1st to 10th	Day	12% 6% 2 4 3 3 4 3 5% 7% 51%	1765
	11th to 20th	Day	14% 6% 2 3 4 3 3 4 5% 5% 50%	1699
	21st to end	Day	15% 6% 1 5% 4 4 4 3 5% 5% 47%	1520
December	1st to 10th	Day	17% 6% 2 5% 3 5% 5% 4 6% 8% 40%	1520
	11th to 20th	Day	16% 6% 2 5% 4 4 4 4 4 8% 43%	1910
	21st to end	Day	17% 7% 2 7% 5% 4 4 4 6% 7% 37%	2772
January	1st to 10th	Night	15% 7% 3 6% 4 4 4 3 5% 6% 43%	4425
	11th to 20th	Night	18% 8% 2 5% 3 3 3 3 5% 6% 45%	4120
	21st to end	Night	20% 10% 3 5% 3 3 3 3 5% 5% 39%	4532
February	1st to 10th	Night	16% 7% 2 5% 5% 4 4 3 6% 7% 41%	2470
	11th to 20th	Night	17% 8% 2 6% 4 4 3 3 5% 6% 43%	2337
	21st to end	Night	16% 8% 3 7% 4 4 4 2 5% 6% 41%	1884
March	1st to 10th	Night	20% 8% 2 5% 4 4 4 4 4 6% 39%	3515
	11th to 20th	Night	11% 5% 2 5% 4 3 4 4 6% 7% 50%	3480
	21st to end	Night	14% 10% 3 6% 4 3 3 3 4 4 47%	3726
April	1st to 10th	Night	15% 8% 2 5% 5% 5% 4 4 6% 6% 40%	1900
	11th to 20th	Night	13% 6% 2 6% 5% 4 4 4 5% 6% 45%	1875
	21st to end	Night	17% 6% 2 5% 3 3 4 3 6% 7% 43%	1900
May	1st to 10th	Night	25% 8% 3 6% 4 4 4 3 5% 8% 31%	2922
	11th to 20th	Night	24% 9% 2 7% 4 4 3 4 5% 7% 30%	2536
	21st to end	Night	11% 4 2 5% 4 4 5% 5% 7% 10% 42%	2732
June	1st to 10th	Night	11% 4 2 5% 4 5% 4 4 8% 10% 44%	1520
	11th to 20th	Night	11% 5% 3 7% 5% 4 5% 5% 6% 10% 41%	1520
	21st to end	Night	10% 5% 2 5% 4 6% 5% 3 8% 11% 43%	1520
July	1st to 10th	Night	7% 5% 3 7% 6% 6% 7% 4 7% 10% 39%	2520
	11th to 20th	Night	8% 6% 3 7% 5% 6% 5% 5% 8% 10% 39%	2567
	21st to end	Night	11% 8% 2 7% 5% 5% 5% 4 6% 10% 38%	3087
August	1st to 10th	Night	18% 6% 2 7% 4 4 5% 5% 7% 10% 32%	2825
	11th to 20th	Night	10% 9% 3 7% 6% 5% 6% 5% 6% 7% 36%	2939
	21st to end	Night	11% 5% 2 5% 3 4 4 3 5% 9% 47%	3476
September	1st to 10th	Night	14% 7% 2 5% 4 3 4 3 5% 7% 46%	1900
	11th to 20th	Night	9% 8% 2 5% 4 3 3 2 3 8% 51%	1900
	21st to end	Night	20% 6% 2 7% 5% 3 5% 3 5% 6% 39%	2166
October	1st to 10th	Night	19% 6% 2 5% 3 3 3 3 4 5% 45%	2280
	11th to 20th	Night	15% 5% 2 4 3 3 3 3 4 6% 52%	2280
	21st to end	Night	15% 6% 2 4 3 2 4 3 5% 6% 49%	2508
November	1st to 10th	Night	12% 6% 2 6% 3 3 3 3 4 6% 53%	2410
	11th to 20th	Night	14% 7% 2 5% 4 3 3 3 4 5% 50%	2479
	21st to end	Night	13% 4 2 5% 5% 4 4 3 6% 7% 47%	2660
December	1st to 10th	Night	17% 7% 2 6% 4 4 4 4 5% 6% 41%	2660
	11th to 20th	Night	17% 6% 2 6% 4 4 4 3 5% 6% 43%	3285
	21st to end	Night	16% 7% 2 6% 5% 5% 5% 5% 7% 8% 36%	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	38% 4 10% 31% 14% 4	2521
	11th to 20th	Day	47% 5% 11% 20% 14% 4	2840
	21st to end	Day	48% 6% 12% 21% 11% 2	3124
February	1st to 10th	Day	43% 6% 13% 24% 12% 2	1710
	11th to 20th	Day	44% 4 10% 25% 14% 3	1737
	21st to end	Day	47% 4 11% 20% 14% 4	1570
March	1st to 10th	Day	46% 5% 11% 23% 12% 3	3333
	11th to 20th	Day	32% 6% 10% 28% 20% 4	3480
	21st to end	Day	45% 5% 9% 20% 17% 3	3905
April	1st to 10th	Day	40% 7% 12% 19% 17% 5%	2280
	11th to 20th	Day	39% 5% 11% 22% 18% 6%	2254
	21st to end	Day	43% 5% 10% 20% 18% 3	2280
May	1st to 10th	Day	52% 7% 10% 19% 10% 1	4024
	11th to 20th	Day	50% 9% 14% 17% 8% 1	4360
	21st to end	Day	34% 8% 14% 25% 17% 2	4837
June	1st to 10th	Day	37% 8% 13% 24% 15% 2	2660
	11th to 20th	Day	38% 10% 11% 24% 14% 2	2660
	21st to end	Day	33% 8% 15% 24% 18% 2	2660
July	1st to 10th	Day	36% 8% 17% 21% 13% 5%	4370
	11th to 20th	Day	36% 8% 16% 28% 11% 2	4314
	21st to end	Day	44% 7% 13% 18% 17% 1	4324
August	1st to 10th	Day	46% 7% 14% 24% 9%	4091
	11th to 20th	Day	38% 7% 12% 27% 16% 1	3896
	21st to end	Day	36% 5% 13% 27% 18% 2	4180
September	1st to 10th	Day	38% 7% 12% 20% 19% 4	2280
	11th to 20th	Day	35% 5% 10% 24% 21% 4	2280
	21st to end	Day	46% 6% 8% 19% 19% 2	2010
October	1st to 10th	Day	39% 4 6% 17% 28% 5%	3160
	11th to 20th	Day	27% 4 9% 26% 24% 10%	3140
	21st to end	Day	24% 3 10% 29% 29% 5%	3428
November	1st to 10th	Day	32% 5% 13% 25% 21% 4	1765
	11th to 20th	Day	35% 5% 10% 23% 23% 3	1699
	21st to end	Day	39% 5% 11% 28% 16% 2	1520
December	1st to 10th	Day	42% 6% 14% 24% 12% 2	1520
	11th to 20th	Day	40% 5% 12% 30% 12% 2	1906
	21st to end	Day	45% 6% 15% 21% 12% 1	2772
January	1st to 10th	Night	41% 5% 10% 26% 15% 3	4425
	11th to 20th	Night	41% 4 12% 25% 16% 2	4120
	21st to end	Night	46% 5% 7% 27% 14% 2	4532
February	1st to 10th	Night	43% 5% 13% 24% 13% 2	2470
	11th to 20th	Night	43% 4 10% 22% 17% 4	2339
	21st to end	Night	44% 4 10% 22% 15% 5%	1884
March	1st to 10th	Night	46% 6% 9% 26% 12% 2	3515
	11th to 20th	Night	32% 6% 10% 32% 17% 3	3480
	21st to end	Night	40% 5% 9% 20% 21% 5%	3726
April	1st to 10th	Night	42% 6% 10% 19% 19% 4	1900
	11th to 20th	Night	38% 5% 12% 20% 19% 5%	1875
	21st to end	Night	39% 6% 11% 22% 16% 5%	1900
May	1st to 10th	Night	52% 6% 9% 19% 11% 2	2951
	11th to 20th	Night	52% 9% 11% 16% 10% 1	2537
	21st to end	Night	34% 9% 17% 24% 12% 3	2739
June	1st to 10th	Night	34% 8% 11% 27% 18% 2	1520
	11th to 20th	Night	37% 9% 13% 24% 15% 2	1520
	21st to end	Night	35% 8% 13% 24% 18% 3	1520
July	1st to 10th	Night	40% 8% 20% 16% 12% 4	2480
	11th to 20th	Night	38% 7% 18% 24% 11% 2	2519
	21st to end	Night	42% 6% 14% 20% 17% 1	2988
August	1st to 10th	Night	45% 8% 18% 20% 9% 1	2814
	11th to 20th	Night	44% 6% 10% 25% 13% 1	2966
	21st to end	Night	34% 5% 11% 31% 16% 2	3476
September	1st to 10th	Night	37% 6% 11% 20% 20% 5%	1900
	11th to 20th	Night	34% 4 9% 26% 23% 3	1900
	21st to end	Night	46% 6% 9% 18% 19% 3	2166
October	1st to 10th	Night	42% 4 10% 20% 20% 4	3800
	11th to 20th	Night	25% 3 10% 24% 30% 7%	3779
	21st to end	Night	24% 3 11% 31% 25% 6%	4120
November	1st to 10th	Night	33% 5% 10% 25% 22% 5%	2410
	11th to 20th	Night	37% 6% 8% 23% 21% 5%	2479
	21st to end	Night	36% 6% 11% 25% 19% 3	2660
December	1st to 10th	Night	43% 6% 12% 24% 13% 2	2660
	11th to 20th	Night	41% 5% 10% 21% 18% 3	3288
	21st to end	Night	42% 7% 16% 22% 11% 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	27% 24% 32% 14% 2 1	182
	11th to 20th	Day	29% 24% 31% 13% 3	270
	21st to end	Day	24% 25% 34% 14% 3 1	297
February	1st to 10th	Day	25% 21% 40% 11% 3	270
	11th to 20th	Day	33% 21% 38% 7% 1	335
	21st to end	Day	31% 20% 31% 16% 2	382
March	1st to 10th	Day	23% 24% 30% 20% 3	460
	11th to 20th	Day	27% 21% 32% 15% 4 1	460
	21st to end	Day	24% 20% 33% 17% 5% 1	506
April	1st to 10th	Day	22% 21% 36% 15% 4 2	460
	11th to 20th	Day	18% 17% 33% 18% 11% 3	452
	21st to end	Day	26% 14% 34% 17% 7% 2	460
May	1st to 10th	Day	26% 15% 30% 18% 8% 3	463
	11th to 20th	Day	22% 11% 29% 24% 11% 3	487
	21st to end	Day	17% 6% 24% 28% 22% 4	529
June	1st to 10th	Day	15% 10% 29% 22% 19% 6%	490
	11th to 20th	Day	15% 7% 27% 29% 18% 4	490
	21st to end	Day	11% 6% 30% 32% 16% 5%	490
July	1st to 10th	Day	12% 4 21% 31% 22% 11%	485
	11th to 20th	Day	6% 3 21% 34% 28% 9%	484
	21st to end	Day	13% 3 23% 30% 25% 6%	532
August	1st to 10th	Day	13% 3 20% 31% 24% 9%	486
	11th to 20th	Day	13% 4 22% 30% 22% 10%	479
	21st to end	Day	11% 3 22% 31% 22% 11%	539
September	1st to 10th	Day	16% 7% 19% 26% 21% 12%	490
	11th to 20th	Day	13% 3 22% 31% 20% 10%	490
	21st to end	Day	26% 10% 21% 27% 12% 4	490
October	1st to 10th	Day	22% 8% 24% 23% 17% 7%	490
	11th to 20th	Day	16% 15% 26% 27% 13% 3	490
	21st to end	Day	15% 14% 35% 26% 9% 2	539
November	1st to 10th	Day	17% 13% 32% 25% 11% 2	408
	11th to 20th	Day	19% 16% 34% 20% 10% 1	359
	21st to end	Day	23% 17% 34% 21% 6%	180
December	1st to 10th	Day	23% 21% 36% 15% 3 2	180
	11th to 20th	Day	28% 19% 29% 17% 7%	180
	21st to end	Day	26% 15% 34% 19% 6%	198
January	1st to 10th	Night	19% 18% 40% 20% 3	760
	11th to 20th	Night	22% 17% 35% 22% 4	760
	21st to end	Night	20% 19% 39% 20% 1	836
February	1st to 10th	Night	21% 16% 36% 25% 2	760
	11th to 20th	Night	26% 21% 36% 15% 1	743
	21st to end	Night	25% 18% 38% 16% 3	628
March	1st to 10th	Night	19% 16% 39% 22% 3	760
	11th to 20th	Night	21% 17% 36% 20% 5% 1	760
	21st to end	Night	20% 15% 41% 19% 4 1	836
April	1st to 10th	Night	20% 18% 38% 20% 4	760
	11th to 20th	Night	15% 14% 36% 28% 7% 1	751
	21st to end	Night	21% 11% 35% 26% 8%	760
May	1st to 10th	Night	22% 8% 31% 29% 9% 1	642
	11th to 20th	Night	22% 7% 28% 31% 10%	402
	21st to end	Night	16% 5% 21% 36% 20% 3	411
June	1st to 10th	Night	13% 2 28% 36% 21%	380
	11th to 20th	Night	13% 3 23% 40% 20% 1	380
	21st to end	Night	11% 2 26% 46% 16%	380
July	1st to 10th	Night	10% 2 18% 39% 26% 4	370
	11th to 20th	Night	8% 1 16% 39% 34% 2	389
	21st to end	Night	9% 2 15% 44% 26% 3	624
August	1st to 10th	Night	13% 2 12% 41% 28% 3	567
	11th to 20th	Night	13% 4 17% 39% 25% 3	653
	21st to end	Night	12% 3 16% 38% 27% 4	836
September	1st to 10th	Night	16% 3 19% 34% 25% 4	760
	11th to 20th	Night	13% 3 16% 38% 26% 4	760
	21st to end	Night	23% 4 21% 33% 16% 2	760
October	1st to 10th	Night	21% 7% 22% 28% 18% 4	760
	11th to 20th	Night	18% 8% 29% 32% 13% 1	760
	21st to end	Night	20% 10% 31% 28% 12%	836
November	1st to 10th	Night	15% 9% 32% 32% 10% 2	760
	11th to 20th	Night	17% 17% 30% 28% 6% 1	760
	21st to end	Night	17% 16% 33% 27% 8% 1	760
December	1st to 10th	Night	23% 13% 37% 19% 7% 1	760
	11th to 20th	Night	18% 12% 43% 22% 5%	760
	21st to end	Night	20% 13% 36% 28% 2	836

Page generated at 2024-11-03 02:11:08. Version ac07

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