Elgin
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Elgin clear sky chart from 2005-11-06 to 2024-11-08.

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	7% 9% 3 7% 5% 4 4 4 5% 6% 45%	105292
	Night	8% 11% 3 8% 5% 5% 5% 4 5% 6% 42%	102476
Transparency	Day	38% 9% 12% 18% 15% 8%	105037
	Night	41% 10% 12% 19% 13% 5%	102320
Seeing	Day	12% 17% 29% 25% 13% 4	14394
	Night	13% 12% 22% 32% 18% 2	23530

By Month

Percentage Cloud Cover SW (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	6% 21% 7% 17% 8% 7% 6% 4 6% 5% 13%	2539
	11th to 20th	Day	9% 17% 6% 13% 7% 6% 6% 5% 6% 6% 19%	2540
	21st to end	Day	11% 14% 4 13% 9% 8% 6% 5% 6% 6% 19%	2794
February	1st to 10th	Day	9% 19% 5% 11% 7% 5% 6% 4 6% 6% 22%	1609
	11th to 20th	Day	9% 19% 5% 12% 7% 5% 6% 4 4 6% 23%	1801
	21st to end	Day	8% 16% 4 13% 9% 6% 7% 4 5% 7% 22%	1570
March	1st to 10th	Day	5% 13% 5% 10% 8% 5% 7% 6% 7% 8% 25%	3138
	11th to 20th	Day	6% 11% 3 8% 5% 5% 4 4 5% 7% 42%	3253
	21st to end	Day	9% 17% 5% 13% 8% 9% 7% 5% 6% 7% 14%	4165
April	1st to 10th	Day	11% 16% 4 11% 7% 5% 5% 4 5% 6% 25%	2280
	11th to 20th	Day	10% 13% 4 8% 6% 6% 4 4 6% 8% 33%	2253
	21st to end	Day	11% 14% 4 9% 6% 5% 5% 4 6% 7% 32%	2470
May	1st to 10th	Day	10% 12% 4 8% 5% 4 5% 3 5% 7% 38%	4256
	11th to 20th	Day	7% 7% 2 5% 4 3 4 3 5% 6% 55%	4377
	21st to end	Day	10% 10% 4 8% 5% 5% 5% 4 6% 9% 35%	4813
June	1st to 10th	Day	14% 9% 3 8% 5% 4 4 3 7% 8% 36%	2660
	11th to 20th	Day	12% 8% 2 6% 5% 4 4 4 5% 7% 43%	2660
	21st to end	Day	5% 3 1 4 3 3 3 3 4 6% 63%	2660
July	1st to 10th	Day	1 1 2 2 2 2 2 3 4 80%	4420
	11th to 20th	Day	2 1 1 2 2 2 2 2 3 5% 78%	4420
	21st to end	Day	1 1 2 2 3 3 2 4 5% 77%	4790
August	1st to 10th	Day	3 3 1 4 2 3 4 3 4 6% 67%	4400
	11th to 20th	Day	2 2 1 3 3 2 2 3 4 6% 72%	4018
	21st to end	Day	3 2 1 3 3 3 4 3 5% 6% 68%	4180
September	1st to 10th	Day	4 2 1 3 2 2 2 2 4 5% 71%	2280
	11th to 20th	Day	7% 5% 2 5% 3 4 3 4 5% 7% 55%	2185
	21st to end	Day	8% 6% 2 6% 4 3 3 3 4 7% 54%	2090
October	1st to 10th	Day	8% 5% 2 4 3 3 2 2 3 5% 63%	3347
	11th to 20th	Day	7% 8% 3 6% 3 4 4 4 7% 9% 45%	3048
	21st to end	Day	11% 12% 4 9% 5% 7% 6% 4 5% 7% 31%	3101
November	1st to 10th	Day	14% 12% 3 10% 6% 6% 5% 4 4 7% 28%	1737
	11th to 20th	Day	10% 17% 4 10% 8% 7% 6% 6% 7% 6% 20%	1676
	21st to end	Day	8% 16% 4 8% 6% 5% 6% 5% 7% 7% 28%	1520
December	1st to 10th	Day	8% 15% 5% 10% 6% 7% 6% 5% 6% 8% 25%	1520
	11th to 20th	Day	7% 13% 5% 11% 9% 7% 7% 5% 8% 7% 21%	1928
	21st to end	Day	7% 13% 5% 11% 8% 8% 8% 5% 5% 6% 24%	2794
January	1st to 10th	Night	7% 20% 6% 15% 10% 7% 6% 4 5% 6% 14%	4406
	11th to 20th	Night	11% 21% 5% 10% 6% 5% 6% 5% 6% 6% 19%	4420
	21st to end	Night	11% 14% 4 11% 8% 6% 6% 5% 6% 7% 21%	4862
February	1st to 10th	Night	11% 19% 4 11% 7% 5% 4 4 6% 6% 23%	2570
	11th to 20th	Night	8% 18% 5% 11% 6% 5% 5% 4 5% 6% 28%	2266
	21st to end	Night	8% 17% 6% 12% 8% 5% 5% 4 5% 6% 23%	1884
March	1st to 10th	Night	6% 10% 3 9% 7% 6% 6% 5% 7% 8% 32%	3736
	11th to 20th	Night	6% 12% 3 7% 5% 5% 4 4 4 5% 46%	3724
	21st to end	Night	9% 16% 5% 11% 8% 6% 7% 5% 7% 7% 19%	3488
April	1st to 10th	Night	11% 13% 4 10% 5% 6% 5% 4 5% 5% 31%	1900
	11th to 20th	Night	12% 11% 4 7% 5% 5% 4 3 5% 5% 38%	1874
	21st to end	Night	10% 11% 3 7% 4 4 5% 4 7% 6% 40%	1710
May	1st to 10th	Night	12% 10% 2 6% 4 4 4 4 5% 6% 44%	2705
	11th to 20th	Night	7% 6% 2 4 2 3 4 3 5% 6% 59%	2516
	21st to end	Night	14% 9% 3 6% 4 3 4 3 5% 6% 43%	2762
June	1st to 10th	Night	13% 7% 2 6% 4 4 4 4 6% 9% 40%	1520
	11th to 20th	Night	12% 6% 2 5% 4 4 4 4 5% 6% 47%	1520
	21st to end	Night	4 4 1 4 4 3 3 4 5% 6% 61%	1520
July	1st to 10th	Night	1 1 1 1 1 1 2 2 2 4 83%	2540
	11th to 20th	Night	1 1 1 1 2 1 2 3 4 84%	2540
	21st to end	Night	2 2 1 2 2 2 2 2 4 6% 76%	2761
August	1st to 10th	Night	3 2 1 2 2 2 2 3 6% 7% 70%	2529
	11th to 20th	Night	1 2 1 4 2 3 3 2 4 6% 72%	2804
	21st to end	Night	2 2 1 3 2 2 2 2 4 5% 75%	3498
September	1st to 10th	Night	4 2 1 3 2 2 2 2 4 6% 72%	1900
	11th to 20th	Night	6% 4 1 5% 3 4 5% 3 5% 6% 58%	1995
	21st to end	Night	8% 6% 2 6% 2 3 3 2 4 6% 58%	2090
October	1st to 10th	Night	6% 6% 2 4 3 3 2 3 4 4 63%	3631
	11th to 20th	Night	9% 6% 3 6% 4 5% 4 3 5% 7% 48%	3885
	21st to end	Night	8% 13% 4 8% 5% 5% 5% 4 6% 7% 36%	4457
November	1st to 10th	Night	14% 12% 4 8% 7% 4 6% 4 5% 6% 30%	2502
	11th to 20th	Night	13% 14% 4 8% 6% 7% 6% 5% 7% 6% 25%	2503
	21st to end	Night	8% 14% 4 9% 5% 6% 6% 5% 6% 6% 31%	2660
December	1st to 10th	Night	8% 13% 5% 10% 8% 7% 6% 4 7% 8% 25%	2660
	11th to 20th	Night	7% 15% 5% 12% 9% 7% 6% 5% 6% 7% 20%	3276
	21st to end	Night	8% 14% 4 12% 8% 9% 8% 5% 5% 6% 20%	4862

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	68% 14% 10% 7% 1	2539
	11th to 20th	Day	62% 10% 11% 13% 4 1	2540
	21st to end	Day	63% 14% 13% 8% 3	2794
February	1st to 10th	Day	62% 11% 12% 11% 3	1609
	11th to 20th	Day	60% 12% 10% 11% 6%	1811
	21st to end	Day	60% 12% 10% 11% 5% 1	1570
March	1st to 10th	Day	48% 15% 14% 16% 7%	3138
	11th to 20th	Day	39% 11% 11% 33% 6%	3253
	21st to end	Day	63% 16% 11% 8% 1	4165
April	1st to 10th	Day	58% 10% 14% 14% 3	2280
	11th to 20th	Day	50% 10% 15% 15% 10% 1	2256
	21st to end	Day	51% 10% 11% 18% 9%	2470
May	1st to 10th	Day	42% 12% 14% 23% 9%	4256
	11th to 20th	Day	29% 8% 16% 29% 15% 2	4380
	21st to end	Day	43% 13% 20% 19% 5%	4814
June	1st to 10th	Day	47% 10% 13% 22% 7%	2660
	11th to 20th	Day	40% 9% 15% 21% 13% 2	2660
	21st to end	Day	22% 6% 12% 33% 21% 6%	2660
July	1st to 10th	Day	10% 3 7% 13% 24% 42%	4351
	11th to 20th	Day	10% 3 6% 9% 23% 49%	4345
	21st to end	Day	10% 4 5% 17% 37% 27%	4639
August	1st to 10th	Day	17% 4 8% 13% 37% 21%	4384
	11th to 20th	Day	15% 4 6% 29% 34% 12%	4058
	21st to end	Day	16% 5% 11% 28% 26% 14%	4179
September	1st to 10th	Day	17% 4 11% 24% 29% 15%	2280
	11th to 20th	Day	28% 7% 12% 21% 21% 11%	2185
	21st to end	Day	30% 8% 12% 25% 20% 5%	2090
October	1st to 10th	Day	26% 5% 10% 25% 28% 6%	3347
	11th to 20th	Day	33% 8% 17% 25% 15% 1	3048
	21st to end	Day	51% 9% 10% 22% 8%	3101
November	1st to 10th	Day	56% 10% 12% 17% 6% 1	1737
	11th to 20th	Day	60% 12% 13% 11% 3	1676
	21st to end	Day	53% 12% 13% 13% 8% 1	1520
December	1st to 10th	Day	57% 11% 14% 12% 5% 1	1520
	11th to 20th	Day	57% 15% 15% 11% 2	1928
	21st to end	Day	53% 13% 19% 13% 3	2794
January	1st to 10th	Night	64% 16% 11% 8% 1	4406
	11th to 20th	Night	61% 8% 11% 14% 5%	4420
	21st to end	Night	57% 16% 14% 9% 3	4862
February	1st to 10th	Night	62% 10% 13% 12% 3	2570
	11th to 20th	Night	56% 10% 14% 14% 6%	2267
	21st to end	Night	61% 9% 11% 14% 4 1	1884
March	1st to 10th	Night	43% 11% 16% 23% 7%	3736
	11th to 20th	Night	38% 10% 12% 35% 5%	3724
	21st to end	Night	57% 16% 15% 9% 3	3488
April	1st to 10th	Night	54% 10% 15% 17% 4	1900
	11th to 20th	Night	46% 9% 16% 17% 11% 1	1874
	21st to end	Night	44% 12% 15% 18% 11% 1	1710
May	1st to 10th	Night	37% 12% 16% 22% 12% 1	2705
	11th to 20th	Night	25% 9% 14% 35% 17% 1	2516
	21st to end	Night	39% 14% 19% 22% 6%	2762
June	1st to 10th	Night	39% 12% 13% 26% 10% 1	1520
	11th to 20th	Night	36% 10% 13% 27% 11% 3	1520
	21st to end	Night	23% 7% 14% 29% 21% 6%	1520
July	1st to 10th	Night	8% 4 6% 15% 28% 40%	2500
	11th to 20th	Night	7% 3 7% 13% 20% 50%	2492
	21st to end	Night	11% 3 4 19% 32% 31%	2674
August	1st to 10th	Night	12% 4 8% 16% 44% 16%	2521
	11th to 20th	Night	15% 5% 7% 29% 34% 10%	2830
	21st to end	Night	13% 4 9% 33% 29% 12%	3498
September	1st to 10th	Night	16% 3 10% 27% 28% 16%	1900
	11th to 20th	Night	26% 7% 11% 22% 23% 11%	1995
	21st to end	Night	28% 7% 12% 28% 18% 8%	2090
October	1st to 10th	Night	26% 5% 8% 24% 32% 6%	3631
	11th to 20th	Night	34% 9% 17% 20% 19% 1	3885
	21st to end	Night	43% 10% 10% 25% 12% 1	4457
November	1st to 10th	Night	52% 11% 12% 18% 6% 1	2502
	11th to 20th	Night	56% 10% 14% 15% 4	2503
	21st to end	Night	51% 9% 12% 17% 10% 1	2660
December	1st to 10th	Night	55% 13% 14% 14% 3 1	2660
	11th to 20th	Night	60% 12% 13% 13% 2	3276
	21st to end	Night	55% 11% 20% 10% 4	4862

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	16% 28% 28% 16% 9% 3	180
	11th to 20th	Day	16% 22% 36% 14% 8% 4	180
	21st to end	Day	17% 19% 35% 21% 8% 1	198
February	1st to 10th	Day	19% 28% 35% 14% 5%	269
	11th to 20th	Day	20% 28% 30% 18% 5%	432
	21st to end	Day	21% 24% 29% 20% 5% 1	382
March	1st to 10th	Day	18% 25% 34% 17% 5%	460
	11th to 20th	Day	15% 22% 30% 22% 10% 1	460
	21st to end	Day	20% 25% 32% 17% 5%	506
April	1st to 10th	Day	20% 24% 27% 18% 8% 3	460
	11th to 20th	Day	18% 24% 30% 17% 8% 3	452
	21st to end	Day	15% 20% 30% 24% 10% 1	460
May	1st to 10th	Day	14% 17% 33% 25% 9% 2	463
	11th to 20th	Day	18% 14% 28% 23% 12% 4	488
	21st to end	Day	13% 15% 24% 29% 15% 5%	529
June	1st to 10th	Day	16% 14% 22% 27% 14% 6%	490
	11th to 20th	Day	13% 19% 31% 25% 10% 3	490
	21st to end	Day	4 10% 32% 32% 17% 5%	490
July	1st to 10th	Day	2 8% 31% 35% 20% 4	486
	11th to 20th	Day	2 11% 33% 32% 18% 4	484
	21st to end	Day	1 9% 31% 30% 20% 8%	531
August	1st to 10th	Day	4 8% 29% 32% 20% 8%	487
	11th to 20th	Day	3 8% 23% 35% 22% 10%	477
	21st to end	Day	6% 13% 27% 30% 17% 8%	539
September	1st to 10th	Day	4 12% 24% 28% 22% 10%	490
	11th to 20th	Day	9% 11% 26% 30% 18% 6%	490
	21st to end	Day	10% 11% 27% 31% 17% 4	490
October	1st to 10th	Day	11% 13% 30% 24% 19% 3	490
	11th to 20th	Day	11% 18% 26% 24% 16% 5%	428
	21st to end	Day	15% 20% 24% 28% 8% 4	330
November	1st to 10th	Day	21% 18% 29% 24% 8%	291
	11th to 20th	Day	15% 22% 26% 26% 10% 1	254
	21st to end	Day	17% 13% 33% 27% 9%	180
December	1st to 10th	Day	15% 20% 32% 18% 11% 4	180
	11th to 20th	Day	19% 32% 31% 15% 2 1	180
	21st to end	Day	13% 29% 26% 24% 6% 2	198
January	1st to 10th	Night	18% 18% 30% 20% 12% 1	760
	11th to 20th	Night	19% 17% 25% 26% 12% 1	760
	21st to end	Night	15% 15% 25% 30% 14% 1	836
February	1st to 10th	Night	19% 18% 26% 29% 6% 2	760
	11th to 20th	Night	16% 16% 23% 32% 12% 1	744
	21st to end	Night	18% 20% 26% 23% 11% 2	628
March	1st to 10th	Night	16% 18% 24% 30% 11% 1	760
	11th to 20th	Night	13% 16% 25% 30% 15% 1	760
	21st to end	Night	17% 15% 29% 28% 10% 1	836
April	1st to 10th	Night	15% 14% 26% 28% 15% 2	760
	11th to 20th	Night	13% 15% 28% 27% 15% 2	746
	21st to end	Night	10% 14% 24% 35% 16% 1	570
May	1st to 10th	Night	9% 11% 24% 36% 18% 2	480
	11th to 20th	Night	13% 7% 13% 31% 33% 4	374
	21st to end	Night	14% 9% 15% 34% 27% 2	411
June	1st to 10th	Night	12% 9% 15% 36% 25% 3	380
	11th to 20th	Night	13% 7% 21% 37% 21% 1	380
	21st to end	Night	5% 4 16% 44% 30% 2	380
July	1st to 10th	Night	2 3 13% 44% 35% 2	370
	11th to 20th	Night	1 2 12% 54% 29% 1	368
	21st to end	Night	3 2 10% 49% 33% 3	416
August	1st to 10th	Night	3 2 11% 43% 39% 3	378
	11th to 20th	Night	2 2 12% 41% 39% 5%	555
	21st to end	Night	4 3 18% 39% 32% 3	836
September	1st to 10th	Night	5% 3 13% 42% 32% 5%	760
	11th to 20th	Night	5% 4 14% 36% 34% 7%	760
	21st to end	Night	10% 4 18% 37% 26% 5%	760
October	1st to 10th	Night	12% 6% 16% 40% 24% 3	760
	11th to 20th	Night	13% 10% 18% 34% 21% 4	760
	21st to end	Night	15% 11% 22% 34% 15% 3	836
November	1st to 10th	Night	19% 15% 27% 31% 9% 1	770
	11th to 20th	Night	21% 13% 28% 26% 11% 1	760
	21st to end	Night	13% 17% 27% 27% 13% 3	760
December	1st to 10th	Night	15% 16% 27% 29% 11% 2	760
	11th to 20th	Night	17% 19% 31% 24% 9% 1	760
	21st to end	Night	19% 23% 28% 24% 5% 1	836

Page generated at 2024-11-05 05:15:50. Version ac07

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