Effingham
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Effingham clear sky chart from 2005-11-06 to 2025-01-22.

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	13% 8% 3 7% 4 4 4 4 6% 7% 41%	104986
	Night	15% 8% 3 6% 4 4 4 3 5% 6% 41%	104477
Transparency	Day	41% 4 12% 25% 16% 2	108603
	Night	42% 4 10% 24% 17% 2	109001
Seeing	Day	16% 8% 25% 26% 18% 7%	15861
	Night	17% 8% 27% 31% 15% 2	25791

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	13% 11% 7% 11% 5% 5% 3 3 5% 6% 31%	2607
	11th to 20th	Day	15% 9% 3 10% 5% 7% 4 3 7% 6% 30%	2610
	21st to end	Day	25% 20% 4 6% 4 3 2 2 3 5% 25%	3088
February	1st to 10th	Day	17% 11% 4 8% 4 4 4 3 6% 7% 32%	1809
	11th to 20th	Day	16% 10% 3 8% 5% 4 4 4 6% 8% 34%	1848
	21st to end	Day	16% 12% 3 9% 5% 4 3 4 5% 7% 33%	1570
March	1st to 10th	Day	21% 15% 3 7% 4 3 3 2 4 5% 34%	3120
	11th to 20th	Day	12% 8% 2 6% 4 3 4 3 5% 6% 47%	3298
	21st to end	Day	16% 10% 3 7% 5% 4 5% 4 6% 7% 33%	4165
April	1st to 10th	Day	14% 8% 3 7% 4 4 4 4 5% 9% 40%	2280
	11th to 20th	Day	16% 8% 3 6% 5% 4 4 2 5% 5% 42%	2254
	21st to end	Day	19% 6% 3 7% 5% 4 4 3 5% 6% 38%	2285
May	1st to 10th	Day	17% 7% 2 7% 5% 5% 6% 4 7% 10% 32%	4082
	11th to 20th	Day	18% 7% 2 6% 4 4 4 3 5% 7% 39%	4130
	21st to end	Day	9% 5% 2 6% 4 4 5% 4 6% 9% 44%	4824
June	1st to 10th	Day	9% 6% 2 5% 4 4 5% 4 6% 7% 47%	2660
	11th to 20th	Day	8% 4 2 5% 4 5% 5% 5% 5% 8% 50%	2660
	21st to end	Day	7% 5% 2 6% 5% 5% 5% 5% 7% 9% 45%	2660
July	1st to 10th	Day	12% 5% 2 6% 4 4 4 4 7% 10% 41%	4440
	11th to 20th	Day	6% 4 2 5% 4 5% 5% 4 8% 11% 46%	4440
	21st to end	Day	9% 6% 2 7% 5% 6% 6% 6% 7% 10% 38%	4813
August	1st to 10th	Day	8% 4 1 4 3 3 4 3 6% 9% 54%	3972
	11th to 20th	Day	9% 5% 2 7% 5% 5% 5% 4 7% 10% 42%	3729
	21st to end	Day	5% 4 2 5% 4 4 5% 3 6% 9% 53%	4180
September	1st to 10th	Day	13% 5% 2 5% 4 4 4 3 5% 7% 48%	2280
	11th to 20th	Day	8% 4 2 5% 4 5% 5% 4 6% 7% 50%	2166
	21st to end	Day	10% 5% 2 6% 4 4 4 3 5% 7% 51%	2090
October	1st to 10th	Day	11% 4 2 4 3 3 3 3 5% 6% 56%	2043
	11th to 20th	Day	15% 5% 2 5% 3 4 4 3 5% 5% 48%	1900
	21st to end	Day	19% 7% 2 6% 3 3 3 4 4 6% 44%	1943
November	1st to 10th	Day	11% 5% 2 5% 3 3 3 3 5% 5% 53%	1762
	11th to 20th	Day	16% 10% 3 5% 4 4 3 3 4 6% 43%	1800
	21st to end	Day	16% 10% 3 7% 4 5% 4 3 5% 5% 38%	1800
December	1st to 10th	Day	10% 9% 3 7% 3 3 3 3 5% 5% 48%	2688
	11th to 20th	Day	14% 11% 5% 11% 4 4 4 3 4 5% 32%	3008
	21st to end	Day	27% 16% 5% 11% 5% 4 4 3 3 4 19%	3982
January	1st to 10th	Night	16% 13% 5% 10% 4 4 4 3 4 6% 32%	4568
	11th to 20th	Night	15% 14% 6% 11% 5% 5% 7% 3 3 4 27%	4580
	21st to end	Night	25% 15% 7% 8% 4 3 3 2 3 6% 25%	4600
February	1st to 10th	Night	18% 11% 4 9% 5% 3 4 3 5% 7% 32%	2370
	11th to 20th	Night	16% 7% 3 8% 5% 4 4 3 4 6% 39%	2218
	21st to end	Night	20% 10% 3 7% 4 3 3 3 5% 5% 37%	1884
March	1st to 10th	Night	20% 15% 2 6% 4 4 3 3 4 5% 35%	3733
	11th to 20th	Night	13% 6% 3 5% 4 3 3 2 5% 6% 51%	3691
	21st to end	Night	18% 8% 3 7% 5% 4 4 4 5% 6% 36%	3466
April	1st to 10th	Night	13% 7% 3 7% 4 4 4 3 4 5% 45%	1900
	11th to 20th	Night	16% 7% 2 5% 4 3 4 3 4 7% 44%	1875
	21st to end	Night	18% 9% 3 5% 4 4 3 4 5% 6% 39%	1892
May	1st to 10th	Night	17% 8% 3 6% 5% 4 5% 4 6% 7% 36%	2813
	11th to 20th	Night	16% 6% 2 6% 4 4 4 4 6% 7% 41%	2763
	21st to end	Night	10% 6% 3 7% 4 5% 5% 5% 6% 10% 41%	2743
June	1st to 10th	Night	8% 6% 2 5% 5% 3 4 3 6% 8% 51%	1520
	11th to 20th	Night	6% 4 1 5% 4 5% 3 4 6% 9% 52%	1520
	21st to end	Night	7% 5% 1 5% 4 5% 5% 4 7% 11% 46%	1520
July	1st to 10th	Night	12% 5% 2 5% 3 4 4 3 5% 9% 47%	2530
	11th to 20th	Night	5% 3 2 4 4 4 5% 4 6% 7% 55%	2530
	21st to end	Night	9% 7% 3 8% 5% 4 5% 5% 8% 9% 39%	2750
August	1st to 10th	Night	5% 4 2 4 4 3 4 4 6% 9% 57%	2956
	11th to 20th	Night	8% 4 2 6% 3 5% 5% 4 6% 9% 49%	3100
	21st to end	Night	5% 3 1 4 3 3 4 4 6% 9% 58%	3476
September	1st to 10th	Night	11% 5% 2 5% 3 3 3 3 5% 7% 54%	1900
	11th to 20th	Night	6% 4 2 6% 4 3 4 3 5% 8% 53%	1994
	21st to end	Night	11% 5% 1 5% 4 4 4 3 5% 6% 52%	2090
October	1st to 10th	Night	9% 4 1 5% 3 3 3 3 5% 6% 58%	2133
	11th to 20th	Night	15% 5% 2 5% 3 3 3 3 4 6% 54%	2280
	21st to end	Night	18% 8% 2 5% 4 3 3 3 4 6% 44%	2653
November	1st to 10th	Night	11% 7% 2 5% 3 3 3 3 4 5% 53%	2536
	11th to 20th	Night	14% 7% 2 6% 4 4 3 3 4 6% 47%	2600
	21st to end	Night	20% 9% 4 6% 4 3 3 2 4 6% 40%	2600
December	1st to 10th	Night	14% 9% 3 7% 4 4 3 3 4 5% 46%	4498
	11th to 20th	Night	18% 8% 3 7% 4 3 4 3 5% 7% 38%	5199
	21st to end	Night	30% 15% 5% 7% 4 4 3 3 4 4 20%	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	54% 3 7% 25% 9% 1	2608
	11th to 20th	Day	55% 4 11% 18% 11% 1	2610
	21st to end	Day	64% 2 7% 18% 8% 1	3088
February	1st to 10th	Day	51% 4 11% 23% 10% 2	1809
	11th to 20th	Day	49% 4 10% 23% 12% 2	1858
	21st to end	Day	51% 4 8% 22% 12% 3	1570
March	1st to 10th	Day	55% 3 6% 20% 13% 3	3120
	11th to 20th	Day	38% 4 13% 26% 17% 2	3298
	21st to end	Day	49% 5% 14% 24% 8% 1	4165
April	1st to 10th	Day	42% 5% 12% 25% 15% 1	2280
	11th to 20th	Day	45% 3 10% 26% 14% 3	2254
	21st to end	Day	47% 3 11% 25% 12% 3	2285
May	1st to 10th	Day	47% 6% 15% 25% 7%	4120
	11th to 20th	Day	46% 4 11% 28% 10%	4134
	21st to end	Day	36% 6% 13% 22% 21% 2	4837
June	1st to 10th	Day	34% 5% 14% 27% 16% 4	2660
	11th to 20th	Day	32% 5% 12% 26% 22% 4	2660
	21st to end	Day	34% 5% 16% 24% 16% 4	2660
July	1st to 10th	Day	37% 5% 11% 29% 15% 2	4371
	11th to 20th	Day	30% 7% 13% 31% 17% 2	4365
	21st to end	Day	38% 8% 17% 23% 11% 2	4662
August	1st to 10th	Day	26% 5% 15% 37% 16% 1	3957
	11th to 20th	Day	35% 6% 15% 27% 16% 1	3765
	21st to end	Day	27% 5% 16% 34% 14% 4	4179
September	1st to 10th	Day	36% 5% 10% 25% 20% 4	2280
	11th to 20th	Day	32% 5% 10% 26% 25% 3	2166
	21st to end	Day	33% 4 7% 28% 24% 4	2090
October	1st to 10th	Day	19% 2 8% 25% 41% 5%	3394
	11th to 20th	Day	26% 4 8% 23% 36% 4	3140
	21st to end	Day	35% 3 7% 25% 28% 2	3181
November	1st to 10th	Day	33% 4 11% 28% 19% 5%	1762
	11th to 20th	Day	43% 2 9% 24% 17% 5%	1800
	21st to end	Day	49% 2 9% 24% 14% 1	1800
December	1st to 10th	Day	39% 4 14% 29% 14%	2688
	11th to 20th	Day	54% 3 9% 24% 8% 1	3005
	21st to end	Day	70% 3 10% 12% 4 1	3982
January	1st to 10th	Night	54% 4 11% 22% 9%	4568
	11th to 20th	Night	62% 3 8% 17% 9% 1	4580
	21st to end	Night	63% 3 8% 17% 8%	4600
February	1st to 10th	Night	54% 3 11% 21% 10% 2	2370
	11th to 20th	Night	47% 2 10% 22% 16% 2	2219
	21st to end	Night	49% 3 10% 23% 13% 2	1884
March	1st to 10th	Night	54% 3 7% 22% 13% 1	3733
	11th to 20th	Night	36% 3 12% 25% 22% 2	3691
	21st to end	Night	48% 5% 10% 29% 7% 1	3466
April	1st to 10th	Night	42% 3 9% 26% 17% 3	1900
	11th to 20th	Night	40% 3 8% 25% 20% 3	1875
	21st to end	Night	46% 4 10% 23% 14% 3	1892
May	1st to 10th	Night	47% 6% 17% 21% 8% 1	2840
	11th to 20th	Night	41% 6% 13% 27% 12% 1	2764
	21st to end	Night	38% 6% 12% 22% 19% 3	2751
June	1st to 10th	Night	32% 4 12% 27% 22% 3	1520
	11th to 20th	Night	28% 5% 11% 26% 23% 6%	1520
	21st to end	Night	31% 6% 14% 23% 18% 7%	1520
July	1st to 10th	Night	35% 5% 11% 26% 19% 4	2490
	11th to 20th	Night	25% 6% 12% 32% 23% 3	2482
	21st to end	Night	38% 8% 16% 21% 16% 2	2662
August	1st to 10th	Night	24% 6% 15% 37% 17% 1	2947
	11th to 20th	Night	31% 6% 12% 30% 20% 1	3130
	21st to end	Night	22% 6% 15% 34% 20% 4	3476
September	1st to 10th	Night	30% 3 8% 30% 21% 6%	1900
	11th to 20th	Night	29% 4 6% 30% 26% 5%	1994
	21st to end	Night	33% 4 8% 24% 26% 5%	2090
October	1st to 10th	Night	18% 2 7% 23% 45% 5%	3562
	11th to 20th	Night	24% 2 7% 26% 37% 5%	3779
	21st to end	Night	33% 3 8% 26% 25% 5%	4365
November	1st to 10th	Night	34% 3 9% 25% 23% 6%	2536
	11th to 20th	Night	39% 3 7% 25% 23% 3	2600
	21st to end	Night	47% 2 9% 24% 16% 1	2600
December	1st to 10th	Night	42% 3 11% 28% 16%	4498
	11th to 20th	Night	46% 4 13% 23% 13%	5201
	21st to end	Night	68% 3 10% 13% 5% 1	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	23% 14% 37% 18% 7%	300
	11th to 20th	Day	26% 19% 34% 18% 3	300
	21st to end	Day	23% 16% 37% 20% 4	300
February	1st to 10th	Day	26% 15% 39% 17% 2	270
	11th to 20th	Day	26% 21% 30% 20% 3	270
	21st to end	Day	26% 16% 36% 20% 2	225
March	1st to 10th	Day	23% 19% 38% 17% 4	270
	11th to 20th	Day	26% 18% 37% 15% 4 1	275
	21st to end	Day	31% 11% 35% 15% 7% 1	506
April	1st to 10th	Day	22% 12% 33% 25% 7% 2	460
	11th to 20th	Day	21% 14% 27% 22% 14% 2	452
	21st to end	Day	24% 8% 36% 21% 9% 2	460
May	1st to 10th	Day	21% 12% 27% 25% 11% 3	463
	11th to 20th	Day	18% 6% 24% 29% 17% 6%	510
	21st to end	Day	10% 5% 26% 31% 19% 8%	734
June	1st to 10th	Day	11% 4 19% 32% 26% 8%	680
	11th to 20th	Day	9% 3 22% 34% 26% 7%	680
	21st to end	Day	7% 5% 27% 32% 21% 9%	680
July	1st to 10th	Day	11% 2 13% 29% 26% 18%	671
	11th to 20th	Day	7% 2 14% 35% 28% 13%	668
	21st to end	Day	10% 2 12% 33% 32% 11%	739
August	1st to 10th	Day	10% 2 12% 30% 33% 13%	557
	11th to 20th	Day	10% 3 15% 32% 25% 15%	479
	21st to end	Day	7% 2 12% 28% 35% 17%	539
September	1st to 10th	Day	13% 3 14% 27% 32% 11%	490
	11th to 20th	Day	9% 1 10% 32% 31% 17%	490
	21st to end	Day	13% 7% 22% 24% 22% 11%	490
October	1st to 10th	Day	10% 4 23% 33% 24% 5%	443
	11th to 20th	Day	15% 12% 34% 24% 11% 4	300
	21st to end	Day	28% 12% 32% 25% 4 1	330
November	1st to 10th	Day	14% 10% 34% 23% 15% 4	300
	11th to 20th	Day	20% 15% 34% 22% 8% 2	300
	21st to end	Day	25% 11% 31% 23% 9%	300
December	1st to 10th	Day	19% 15% 39% 17% 6% 3	300
	11th to 20th	Day	23% 11% 38% 22% 6%	300
	21st to end	Day	33% 14% 32% 16% 5%	330
January	1st to 10th	Night	19% 15% 37% 24% 4	1000
	11th to 20th	Night	23% 15% 36% 23% 4	1000
	21st to end	Night	22% 12% 36% 27% 2	1051
February	1st to 10th	Night	24% 13% 34% 27% 2	850
	11th to 20th	Night	20% 15% 36% 27% 2	743
	21st to end	Night	27% 12% 37% 22% 2	628
March	1st to 10th	Night	23% 12% 37% 23% 4	760
	11th to 20th	Night	20% 12% 35% 28% 6% 1	708
	21st to end	Night	26% 6% 32% 29% 6%	627
April	1st to 10th	Night	17% 12% 34% 31% 6%	570
	11th to 20th	Night	19% 11% 28% 30% 11% 1	563
	21st to end	Night	24% 6% 32% 29% 8% 1	570
May	1st to 10th	Night	17% 5% 34% 34% 10% 1	570
	11th to 20th	Night	16% 3 24% 36% 18% 3	561
	21st to end	Night	9% 2 24% 38% 24% 3	617
June	1st to 10th	Night	11% 2 20% 42% 24% 1	570
	11th to 20th	Night	8% 2 19% 45% 26% 1	570
	21st to end	Night	8% 2 22% 39% 28% 1	570
July	1st to 10th	Night	11% 2 8% 34% 37% 8%	555
	11th to 20th	Night	4 4 13% 40% 34% 5%	552
	21st to end	Night	8% 2 11% 41% 34% 4	624
August	1st to 10th	Night	7% 3 9% 40% 37% 5%	567
	11th to 20th	Night	7% 2 10% 43% 34% 4	564
	21st to end	Night	7% 2 11% 33% 42% 6%	627
September	1st to 10th	Night	13% 2 11% 37% 33% 5%	570
	11th to 20th	Night	7% 2 13% 37% 36% 5%	664
	21st to end	Night	12% 4 21% 30% 28% 5%	760
October	1st to 10th	Night	10% 4 22% 38% 22% 4	760
	11th to 20th	Night	16% 10% 29% 27% 17% 1	760
	21st to end	Night	20% 11% 32% 30% 6%	836
November	1st to 10th	Night	15% 7% 35% 33% 10% 1	780
	11th to 20th	Night	17% 11% 32% 30% 9% 1	800
	21st to end	Night	24% 12% 30% 26% 8%	800
December	1st to 10th	Night	23% 10% 36% 26% 5%	944
	11th to 20th	Night	24% 8% 31% 30% 5% 1	1000
	21st to end	Night	32% 11% 32% 21% 3	1100

Page generated at 2025-01-19 02:06:44. Version ac07

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