Sheridan
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sheridan clear sky chart from 2005-11-06 to 2024-11-02.

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 8% 5% 5% 5% 4 5% 6% 39%	101779
	Night	15% 8% 3 8% 5% 4 4 3 5% 6% 39%	97301
Transparency	Day	46% 3 13% 20% 13% 4	101524
	Night	47% 3 14% 21% 12% 4	97145
Seeing	Day	16% 7% 20% 26% 21% 10%	14924
	Night	18% 4 18% 36% 22% 2	23598

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	25% 16% 7% 13% 7% 7% 6% 3 4 5% 7%	2539
	11th to 20th	Day	29% 11% 4 11% 6% 6% 5% 4 4 4 16%	2540
	21st to end	Day	28% 13% 4 12% 7% 6% 5% 4 4 3 13%	3144
February	1st to 10th	Day	22% 14% 5% 12% 6% 5% 5% 5% 5% 6% 15%	1710
	11th to 20th	Day	21% 13% 4 11% 7% 6% 4 5% 5% 5% 18%	1665
	21st to end	Day	19% 15% 4 11% 7% 6% 5% 3 5% 5% 18%	1464
March	1st to 10th	Day	14% 13% 5% 12% 9% 7% 8% 4 6% 6% 18%	3350
	11th to 20th	Day	16% 10% 3 8% 5% 5% 5% 3 3 5% 37%	3490
	21st to end	Day	18% 13% 4 12% 8% 7% 7% 5% 5% 6% 16%	3855
April	1st to 10th	Day	19% 13% 4 11% 7% 6% 5% 4 6% 6% 19%	2280
	11th to 20th	Day	18% 12% 4 9% 6% 5% 6% 4 5% 4 25%	2272
	21st to end	Day	16% 10% 3 9% 7% 6% 6% 5% 7% 7% 24%	2470
May	1st to 10th	Day	15% 9% 3 7% 5% 5% 5% 4 6% 6% 35%	4282
	11th to 20th	Day	8% 6% 2 5% 3 3 4 4 5% 8% 53%	4377
	21st to end	Day	13% 7% 2 8% 6% 6% 7% 6% 9% 8% 28%	4813
June	1st to 10th	Day	15% 9% 4 8% 5% 4 5% 4 6% 7% 32%	2660
	11th to 20th	Day	11% 8% 3 8% 7% 6% 6% 6% 7% 8% 30%	2660
	21st to end	Day	6% 4 2 6% 4 4 4 3 5% 7% 54%	2841
July	1st to 10th	Day	3 2 1 3 2 2 3 2 3 4 74%	4490
	11th to 20th	Day	3 2 1 2 2 2 2 3 3 4 76%	4420
	21st to end	Day	4 2 1 2 2 2 2 2 3 5% 75%	4734
August	1st to 10th	Day	1 3 1 3 3 3 3 3 4 6% 70%	4091
	11th to 20th	Day	5% 3 2 5% 4 4 4 4 7% 8% 55%	4026
	21st to end	Day	5% 6% 2 4 3 4 3 3 5% 8% 57%	4340
September	1st to 10th	Day	4 3 1 4 2 3 4 3 5% 7% 64%	2280
	11th to 20th	Day	9% 6% 2 6% 5% 5% 5% 4 6% 8% 45%	2242
	21st to end	Day	13% 5% 2 6% 4 5% 4 3 4 6% 47%	2020
October	1st to 10th	Day	13% 8% 3 7% 6% 5% 4 3 5% 6% 40%	1900
	11th to 20th	Day	15% 8% 4 9% 4 5% 6% 4 7% 7% 32%	1900
	21st to end	Day	19% 10% 4 10% 5% 5% 5% 2 4 6% 30%	2085
November	1st to 10th	Day	20% 14% 5% 11% 7% 5% 5% 4 5% 6% 17%	1557
	11th to 20th	Day	21% 13% 5% 10% 7% 5% 5% 4 5% 6% 19%	1520
	21st to end	Day	19% 12% 4 11% 7% 5% 6% 4 5% 6% 22%	1520
December	1st to 10th	Day	20% 11% 4 12% 5% 5% 5% 4 5% 5% 23%	1520
	11th to 20th	Day	21% 12% 5% 13% 7% 6% 6% 5% 5% 6% 14%	1928
	21st to end	Day	25% 16% 7% 14% 6% 6% 6% 4 4 4 8%	2794
January	1st to 10th	Night	25% 14% 6% 12% 7% 6% 5% 4 5% 5% 11%	4406
	11th to 20th	Night	25% 14% 6% 11% 6% 5% 4 3 4 4 18%	4420
	21st to end	Night	31% 13% 5% 11% 6% 5% 4 3 4 4 16%	4521
February	1st to 10th	Night	18% 13% 4 11% 7% 5% 5% 4 5% 6% 20%	2470
	11th to 20th	Night	19% 11% 3 9% 5% 5% 5% 5% 5% 6% 26%	2402
	21st to end	Night	17% 12% 4 10% 7% 5% 5% 4 5% 6% 24%	1989
March	1st to 10th	Night	12% 10% 5% 12% 9% 8% 7% 5% 4 6% 23%	3520
	11th to 20th	Night	14% 8% 2 7% 5% 4 4 3 4 5% 43%	3490
	21st to end	Night	19% 13% 4 11% 8% 6% 5% 4 5% 6% 20%	3785
April	1st to 10th	Night	18% 11% 4 9% 7% 6% 5% 4 4 6% 27%	1900
	11th to 20th	Night	14% 9% 4 9% 7% 5% 4 4 6% 7% 32%	1852
	21st to end	Night	13% 9% 3 8% 4 4 5% 5% 7% 7% 34%	1710
May	1st to 10th	Night	17% 7% 2 6% 4 3 3 3 4 5% 46%	2680
	11th to 20th	Night	6% 4 1 5% 3 3 3 3 6% 7% 59%	2516
	21st to end	Night	6% 5% 2 6% 5% 5% 6% 6% 8% 9% 41%	2762
June	1st to 10th	Night	13% 6% 3 7% 5% 5% 5% 3 5% 6% 42%	1520
	11th to 20th	Night	7% 6% 3 6% 5% 4 4 4 6% 8% 47%	1516
	21st to end	Night	5% 5% 2 5% 4 3 3 2 4 6% 62%	1330
July	1st to 10th	Night	2 1 2 1 1 1 1 2 5% 84%	2444
	11th to 20th	Night	3 2 1 2 1 2 1 2 2 4 80%	2540
	21st to end	Night	2 1 2 1 1 2 1 4 4 82%	2815
August	1st to 10th	Night	1 2 1 2 1 1 2 2 4 5% 79%	2848
	11th to 20th	Night	5% 3 1 4 3 2 3 3 5% 7% 65%	2812
	21st to end	Night	6% 3 1 4 3 3 2 2 4 6% 66%	3333
September	1st to 10th	Night	4 2 1 2 2 3 3 2 5% 6% 70%	1900
	11th to 20th	Night	7% 5% 2 5% 4 5% 3 4 5% 6% 54%	1933
	21st to end	Night	8% 5% 1 5% 4 4 4 3 5% 7% 55%	2159
October	1st to 10th	Night	11% 5% 2 6% 3 4 4 3 5% 5% 52%	2280
	11th to 20th	Night	14% 6% 3 6% 4 4 4 4 6% 8% 43%	2280
	21st to end	Night	17% 8% 3 7% 3 4 4 4 5% 6% 38%	2511
November	1st to 10th	Night	22% 8% 4 9% 6% 6% 5% 4 5% 5% 26%	2539
	11th to 20th	Night	22% 12% 4 10% 6% 5% 5% 4 5% 5% 22%	2660
	21st to end	Night	17% 10% 4 8% 6% 6% 5% 4 5% 5% 29%	2660
December	1st to 10th	Night	19% 11% 4 10% 6% 5% 5% 4 6% 5% 25%	2660
	11th to 20th	Night	22% 13% 4 11% 7% 5% 5% 4 5% 6% 19%	3276
	21st to end	Night	22% 14% 5% 11% 7% 6% 5% 3 5% 4 18%	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	81% 2 6% 8% 2 1	2539
	11th to 20th	Day	71% 2 11% 11% 3 2	2540
	21st to end	Day	75% 3 8% 9% 4	3144
February	1st to 10th	Day	69% 4 11% 12% 4	1710
	11th to 20th	Day	68% 4 11% 11% 5% 1	1674
	21st to end	Day	67% 3 12% 11% 6% 1	1464
March	1st to 10th	Day	65% 2 15% 15% 4	3350
	11th to 20th	Day	51% 3 9% 26% 11%	3490
	21st to end	Day	68% 2 15% 11% 4	3855
April	1st to 10th	Day	64% 4 13% 14% 4	2280
	11th to 20th	Day	59% 4 11% 15% 9% 2	2275
	21st to end	Day	56% 5% 15% 15% 7% 1	2470
May	1st to 10th	Day	49% 2 11% 24% 13%	4282
	11th to 20th	Day	30% 2 18% 33% 15% 1	4380
	21st to end	Day	51% 5% 24% 18% 2	4814
June	1st to 10th	Day	50% 3 17% 22% 7% 1	2660
	11th to 20th	Day	49% 4 20% 21% 6%	2660
	21st to end	Day	29% 3 20% 31% 12% 4	2841
July	1st to 10th	Day	16% 2 9% 19% 24% 30%	4421
	11th to 20th	Day	13% 1 7% 22% 42% 14%	4345
	21st to end	Day	15% 2 11% 30% 37% 5%	4584
August	1st to 10th	Day	17% 1 11% 33% 26% 12%	4076
	11th to 20th	Day	27% 1 21% 33% 13% 4	4065
	21st to end	Day	27% 2 15% 28% 23% 5%	4339
September	1st to 10th	Day	20% 3 14% 31% 21% 11%	2280
	11th to 20th	Day	37% 3 16% 23% 16% 5%	2242
	21st to end	Day	39% 3 14% 24% 15% 5%	2020
October	1st to 10th	Day	44% 3 10% 22% 18% 3	1900
	11th to 20th	Day	50% 3 14% 19% 12% 1	1900
	21st to end	Day	57% 2 9% 16% 14% 1	2085
November	1st to 10th	Day	67% 4 10% 15% 5%	1557
	11th to 20th	Day	65% 3 12% 12% 7% 1	1520
	21st to end	Day	63% 3 9% 13% 11% 1	1520
December	1st to 10th	Day	62% 4 12% 13% 9% 1	1520
	11th to 20th	Day	70% 3 13% 13% 2	1928
	21st to end	Day	81% 2 7% 6% 4	2794
January	1st to 10th	Night	76% 2 8% 9% 4 1	4406
	11th to 20th	Night	71% 2 9% 12% 4 2	4420
	21st to end	Night	74% 2 9% 10% 6% 1	4521
February	1st to 10th	Night	64% 6% 12% 14% 5%	2470
	11th to 20th	Night	57% 3 15% 15% 7% 2	2404
	21st to end	Night	60% 4 14% 13% 7% 1	1989
March	1st to 10th	Night	60% 2 12% 21% 5%	3520
	11th to 20th	Night	43% 3 15% 29% 9% 1	3490
	21st to end	Night	65% 3 13% 18% 2	3785
April	1st to 10th	Night	58% 4 16% 15% 7%	1900
	11th to 20th	Night	50% 4 17% 17% 8% 3	1852
	21st to end	Night	48% 5% 16% 22% 7% 2	1710
May	1st to 10th	Night	43% 1 13% 31% 10% 1	2680
	11th to 20th	Night	26% 2 16% 37% 16% 2	2516
	21st to end	Night	38% 4 36% 19% 3	2762
June	1st to 10th	Night	43% 3 18% 29% 7% 1	1520
	11th to 20th	Night	35% 3 23% 31% 8%	1516
	21st to end	Night	25% 2 21% 35% 12% 4	1330
July	1st to 10th	Night	9% 1 10% 22% 26% 32%	2404
	11th to 20th	Night	12% 1 9% 20% 35% 24%	2492
	21st to end	Night	9% 1 12% 30% 40% 8%	2727
August	1st to 10th	Night	10% 1 9% 37% 36% 7%	2839
	11th to 20th	Night	22% 1 24% 36% 12% 5%	2839
	21st to end	Night	22% 2 18% 28% 25% 6%	3333
September	1st to 10th	Night	16% 3 14% 32% 24% 11%	1900
	11th to 20th	Night	32% 3 16% 26% 15% 9%	1933
	21st to end	Night	30% 3 17% 24% 19% 7%	2159
October	1st to 10th	Night	35% 3 11% 29% 18% 4	2280
	11th to 20th	Night	40% 4 15% 23% 16% 2	2280
	21st to end	Night	47% 3 12% 20% 15% 3	2511
November	1st to 10th	Night	58% 5% 12% 19% 7%	2539
	11th to 20th	Night	62% 4 12% 13% 7% 2	2660
	21st to end	Night	55% 4 12% 13% 13% 2	2660
December	1st to 10th	Night	58% 4 11% 14% 11%	2660
	11th to 20th	Night	67% 4 10% 13% 6%	3276
	21st to end	Night	69% 2 13% 13% 3	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	33% 11% 22% 19% 9% 5%	180
	11th to 20th	Day	29% 7% 19% 24% 12% 8%	180
	21st to end	Day	27% 6% 17% 25% 19% 6%	405
February	1st to 10th	Day	27% 9% 21% 22% 14% 7%	370
	11th to 20th	Day	31% 8% 22% 22% 13% 4	365
	21st to end	Day	23% 17% 24% 20% 11% 4	332
March	1st to 10th	Day	26% 7% 27% 24% 13% 3	460
	11th to 20th	Day	25% 10% 21% 25% 16% 4	460
	21st to end	Day	27% 12% 22% 24% 14% 2	506
April	1st to 10th	Day	24% 14% 20% 20% 16% 5%	460
	11th to 20th	Day	24% 10% 25% 22% 12% 6%	452
	21st to end	Day	20% 10% 27% 24% 14% 5%	460
May	1st to 10th	Day	16% 11% 24% 24% 17% 8%	463
	11th to 20th	Day	17% 10% 20% 24% 17% 11%	488
	21st to end	Day	11% 9% 20% 25% 22% 13%	529
June	1st to 10th	Day	16% 8% 20% 26% 18% 12%	490
	11th to 20th	Day	13% 9% 24% 30% 19% 5%	490
	21st to end	Day	5% 7% 26% 28% 24% 10%	671
July	1st to 10th	Day	5% 3 16% 33% 30% 12%	530
	11th to 20th	Day	3 4 17% 28% 32% 16%	484
	21st to end	Day	2 2 14% 29% 34% 18%	531
August	1st to 10th	Day	3 3 11% 32% 30% 22%	487
	11th to 20th	Day	4 2 10% 26% 33% 25%	477
	21st to end	Day	6% 3 16% 31% 28% 16%	539
September	1st to 10th	Day	6% 3 18% 28% 28% 18%	490
	11th to 20th	Day	10% 5% 15% 28% 29% 12%	490
	21st to end	Day	14% 5% 16% 30% 26% 9%	490
October	1st to 10th	Day	14% 7% 19% 24% 22% 13%	490
	11th to 20th	Day	19% 6% 17% 23% 24% 11%	490
	21st to end	Day	24% 8% 22% 26% 13% 7%	534
November	1st to 10th	Day	24% 7% 25% 27% 12% 5%	213
	11th to 20th	Day	20% 9% 24% 21% 19% 7%	180
	21st to end	Day	23% 8% 19% 24% 15% 11%	180
December	1st to 10th	Day	27% 4 18% 28% 14% 9%	180
	11th to 20th	Day	34% 3 22% 26% 11% 3	180
	21st to end	Day	31% 6% 24% 23% 13% 3	198
January	1st to 10th	Night	29% 7% 21% 26% 15% 3	760
	11th to 20th	Night	28% 6% 17% 27% 19% 3	760
	21st to end	Night	26% 4 15% 35% 18% 3	836
February	1st to 10th	Night	24% 4 21% 31% 18% 2	760
	11th to 20th	Night	23% 6% 22% 30% 19% 1	744
	21st to end	Night	24% 8% 22% 34% 12%	628
March	1st to 10th	Night	21% 6% 22% 34% 15% 2	760
	11th to 20th	Night	21% 3 21% 34% 18% 1	760
	21st to end	Night	25% 5% 22% 31% 16% 1	836
April	1st to 10th	Night	23% 6% 20% 31% 18% 1	760
	11th to 20th	Night	18% 6% 24% 35% 15% 2	724
	21st to end	Night	17% 3 19% 42% 19% 1	570
May	1st to 10th	Night	13% 3 21% 46% 17% 1	468
	11th to 20th	Night	12% 4 18% 42% 24% 2	374
	21st to end	Night	12% 3 18% 43% 21% 2	411
June	1st to 10th	Night	16% 3 16% 43% 22% 1	380
	11th to 20th	Night	9% 3 23% 45% 20% 1	380
	21st to end	Night	7% 2 16% 49% 25%	380
July	1st to 10th	Night	4 1 11% 55% 28% 1	370
	11th to 20th	Night	4 1 18% 50% 27%	368
	21st to end	Night	3 13% 49% 33% 2	446
August	1st to 10th	Night	2 1 10% 43% 40% 4	567
	11th to 20th	Night	5% 7% 41% 44% 3	564
	21st to end	Night	5% 1 14% 44% 32% 3	736
September	1st to 10th	Night	5% 1 15% 38% 39% 2	760
	11th to 20th	Night	8% 3 10% 39% 32% 7%	760
	21st to end	Night	11% 3 14% 37% 31% 5%	760
October	1st to 10th	Night	13% 2 17% 39% 26% 4	760
	11th to 20th	Night	17% 3 14% 35% 27% 5%	760
	21st to end	Night	21% 2 23% 30% 19% 5%	836
November	1st to 10th	Night	25% 3 17% 38% 17%	744
	11th to 20th	Night	27% 7% 20% 28% 16% 2	760
	21st to end	Night	22% 4 19% 34% 18% 3	760
December	1st to 10th	Night	22% 4 17% 35% 18% 4	760
	11th to 20th	Night	29% 6% 22% 28% 14% 1	760
	21st to end	Night	30% 6% 23% 27% 12% 1	836

Page generated at 2024-10-29 22:22:59. Version ac07

Copyright © 2024 Attilla Danko.