Lyons
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lyons 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	15% 11% 4 9% 6% 5% 5% 4 5% 7% 30%	105248
	Night	17% 12% 4 10% 5% 5% 4 4 5% 6% 28%	104113
Transparency	Day	52% 7% 12% 20% 9% 1	108808
	Night	56% 6% 11% 18% 9% 1	108641
Seeing	Day	22% 17% 30% 20% 9% 3	14781
	Night	23% 16% 28% 23% 10% 1	24163

By Month

Percentage Cloud Cover NE (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	15% 22% 8% 15% 7% 5% 4 3 3 3 15%	2597
	11th to 20th	Day	14% 22% 9% 15% 8% 5% 4 3 4 4 11%	2637
	21st to end	Day	18% 21% 8% 14% 9% 6% 5% 3 4 5% 9%	3133
February	1st to 10th	Day	16% 17% 6% 16% 9% 5% 4 3 4 4 15%	1710
	11th to 20th	Day	14% 17% 8% 16% 8% 5% 5% 4 3 5% 14%	1663
	21st to end	Day	19% 15% 5% 14% 8% 4 5% 3 3 6% 17%	1558
March	1st to 10th	Day	19% 14% 5% 11% 6% 4 3 2 4 5% 27%	3269
	11th to 20th	Day	9% 20% 5% 9% 6% 5% 4 4 5% 5% 28%	3480
	21st to end	Day	16% 12% 5% 10% 5% 5% 4 3 5% 7% 29%	3932
April	1st to 10th	Day	18% 14% 4 8% 4 4 4 2 4 6% 30%	2280
	11th to 20th	Day	20% 10% 3 6% 4 4 4 3 5% 6% 35%	2254
	21st to end	Day	21% 11% 4 7% 4 4 4 4 5% 6% 32%	2364
May	1st to 10th	Day	20% 9% 3 7% 4 5% 4 3 5% 6% 33%	4295
	11th to 20th	Day	15% 9% 3 9% 6% 5% 5% 4 5% 8% 32%	4398
	21st to end	Day	11% 6% 2 6% 5% 5% 5% 4 6% 7% 42%	4837
June	1st to 10th	Day	17% 7% 3 6% 5% 4 6% 3 6% 7% 35%	2660
	11th to 20th	Day	13% 6% 2 6% 5% 4 5% 5% 7% 10% 38%	2660
	21st to end	Day	12% 6% 2 8% 6% 5% 5% 5% 7% 8% 37%	2660
July	1st to 10th	Day	10% 5% 2 6% 5% 5% 5% 5% 7% 11% 39%	4440
	11th to 20th	Day	8% 6% 2 6% 5% 5% 5% 5% 8% 11% 38%	4440
	21st to end	Day	8% 5% 3 8% 6% 6% 6% 5% 8% 8% 38%	4758
August	1st to 10th	Day	17% 6% 3 7% 4 5% 4 4 6% 7% 37%	4104
	11th to 20th	Day	13% 7% 3 8% 6% 6% 6% 5% 6% 9% 33%	3998
	21st to end	Day	13% 7% 2 6% 5% 4 5% 4 6% 8% 40%	4180
September	1st to 10th	Day	13% 7% 2 5% 4 4 5% 5% 7% 8% 40%	2280
	11th to 20th	Day	14% 6% 2 5% 5% 4 4 3 5% 8% 43%	2280
	21st to end	Day	16% 8% 3 7% 5% 6% 5% 4 5% 7% 35%	2002
October	1st to 10th	Day	17% 7% 3 7% 5% 4 5% 4 6% 8% 34%	1900
	11th to 20th	Day	19% 10% 3 8% 6% 5% 4 3 5% 7% 30%	1900
	21st to end	Day	25% 13% 3 8% 4 5% 5% 3 5% 6% 23%	2047
November	1st to 10th	Day	14% 13% 4 9% 6% 5% 5% 4 5% 5% 31%	1761
	11th to 20th	Day	13% 16% 5% 10% 5% 4 5% 3 7% 7% 25%	1625
	21st to end	Day	20% 15% 4 11% 6% 4 5% 3 6% 6% 20%	1600
December	1st to 10th	Day	18% 18% 8% 16% 7% 6% 5% 3 4 5% 11%	2600
	11th to 20th	Day	19% 18% 6% 13% 6% 4 4 3 4 4 18%	2986
	21st to end	Day	21% 17% 6% 14% 8% 5% 4 3 4 6% 11%	3960
January	1st to 10th	Night	17% 20% 7% 19% 7% 5% 4 3 3 4 12%	4569
	11th to 20th	Night	13% 21% 9% 17% 8% 5% 4 3 4 4 14%	4542
	21st to end	Night	21% 21% 7% 16% 8% 5% 4 2 3 4 11%	4546
February	1st to 10th	Night	17% 17% 5% 13% 6% 5% 5% 4 4 4 20%	2470
	11th to 20th	Night	15% 15% 5% 14% 8% 5% 5% 4 5% 6% 18%	2403
	21st to end	Night	17% 13% 5% 14% 6% 5% 5% 3 5% 5% 21%	1895
March	1st to 10th	Night	19% 11% 4 9% 5% 4 4 4 4 6% 29%	3569
	11th to 20th	Night	16% 19% 5% 9% 5% 4 4 3 5% 7% 23%	3479
	21st to end	Night	19% 9% 4 11% 5% 4 4 3 4 6% 31%	3700
April	1st to 10th	Night	19% 12% 4 7% 6% 5% 4 4 5% 6% 29%	1900
	11th to 20th	Night	19% 9% 2 7% 5% 4 4 4 4 6% 34%	1875
	21st to end	Night	18% 9% 4 7% 4 4 5% 3 6% 7% 34%	1833
May	1st to 10th	Night	23% 9% 3 9% 5% 4 4 3 5% 5% 29%	2646
	11th to 20th	Night	18% 7% 3 6% 4 4 4 4 6% 8% 35%	2495
	21st to end	Night	10% 6% 3 6% 4 4 5% 4 6% 9% 42%	2738
June	1st to 10th	Night	13% 9% 2 6% 4 5% 5% 4 5% 9% 37%	1520
	11th to 20th	Night	11% 7% 2 6% 5% 4 5% 4 7% 9% 40%	1520
	21st to end	Night	10% 7% 2 7% 5% 5% 5% 4 6% 8% 40%	1520
July	1st to 10th	Night	11% 7% 3 7% 4 4 4 4 7% 9% 41%	2520
	11th to 20th	Night	10% 5% 2 7% 4 4 5% 4 6% 9% 45%	2520
	21st to end	Night	11% 6% 3 7% 4 4 4 4 7% 9% 41%	2791
August	1st to 10th	Night	13% 7% 2 7% 4 4 4 4 7% 9% 40%	2825
	11th to 20th	Night	14% 7% 3 7% 4 4 5% 4 5% 7% 39%	2785
	21st to end	Night	7% 5% 2 6% 5% 5% 5% 4 7% 10% 45%	3476
September	1st to 10th	Night	14% 6% 2 6% 4 4 3 4 6% 7% 45%	1900
	11th to 20th	Night	13% 7% 2 6% 4 3 3 4 6% 7% 45%	1900
	21st to end	Night	16% 7% 2 7% 5% 5% 5% 4 6% 8% 37%	2174
October	1st to 10th	Night	20% 8% 2 8% 5% 5% 4 4 5% 6% 34%	2280
	11th to 20th	Night	21% 9% 2 7% 5% 4 4 4 5% 7% 32%	2280
	21st to end	Night	26% 12% 3 7% 5% 5% 4 3 4 6% 25%	2549
November	1st to 10th	Night	17% 12% 4 7% 5% 4 4 4 5% 6% 33%	2537
	11th to 20th	Night	16% 14% 3 9% 5% 5% 4 5% 5% 6% 27%	2772
	21st to end	Night	19% 17% 5% 8% 5% 4 4 4 5% 6% 22%	2800
December	1st to 10th	Night	18% 18% 7% 14% 7% 5% 5% 4 4 5% 13%	4580
	11th to 20th	Night	21% 16% 7% 12% 5% 4 4 3 4 4 20%	5208
	21st to end	Night	25% 17% 5% 12% 6% 4 4 3 5% 5% 13%	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	74% 5% 10% 9% 2	2598
	11th to 20th	Day	77% 5% 10% 6% 2	2637
	21st to end	Day	77% 7% 10% 5% 1	3133
February	1st to 10th	Day	72% 5% 9% 11% 2	1710
	11th to 20th	Day	73% 6% 7% 12% 3	1672
	21st to end	Day	70% 4 10% 12% 4	1558
March	1st to 10th	Day	61% 5% 9% 21% 4	3272
	11th to 20th	Day	56% 7% 15% 13% 9% 1	3480
	21st to end	Day	53% 6% 9% 22% 9% 1	3932
April	1st to 10th	Day	56% 5% 9% 17% 12% 2	2280
	11th to 20th	Day	49% 6% 9% 20% 14% 2	2254
	21st to end	Day	53% 5% 8% 19% 14% 2	2364
May	1st to 10th	Day	51% 6% 9% 19% 13% 2	4307
	11th to 20th	Day	48% 8% 11% 22% 8% 1	4402
	21st to end	Day	37% 9% 12% 25% 15% 2	4837
June	1st to 10th	Day	45% 7% 11% 20% 16% 1	2660
	11th to 20th	Day	39% 8% 13% 25% 14% 1	2660
	21st to end	Day	42% 8% 13% 22% 14% 1	2660
July	1st to 10th	Day	36% 8% 14% 28% 13% 1	4370
	11th to 20th	Day	35% 9% 16% 26% 13% 1	4365
	21st to end	Day	39% 9% 15% 24% 13% 1	4606
August	1st to 10th	Day	44% 7% 13% 21% 14% 1	4091
	11th to 20th	Day	44% 9% 15% 24% 7%	4037
	21st to end	Day	39% 8% 11% 34% 8% 1	4180
September	1st to 10th	Day	39% 8% 11% 28% 12% 1	2280
	11th to 20th	Day	38% 6% 13% 26% 15% 1	2280
	21st to end	Day	48% 6% 11% 24% 11%	2002
October	1st to 10th	Day	41% 7% 16% 25% 11%	3160
	11th to 20th	Day	47% 6% 15% 21% 11%	3140
	21st to end	Day	48% 8% 14% 23% 7%	3349
November	1st to 10th	Day	54% 7% 12% 17% 9% 1	1761
	11th to 20th	Day	57% 6% 13% 15% 7% 1	1625
	21st to end	Day	65% 6% 14% 14% 2	1600
December	1st to 10th	Day	77% 7% 9% 7% 1	2600
	11th to 20th	Day	69% 5% 12% 8% 6%	2986
	21st to end	Day	73% 6% 13% 6% 2	3960
January	1st to 10th	Night	77% 6% 9% 6% 2	4569
	11th to 20th	Night	73% 5% 9% 9% 4	4542
	21st to end	Night	79% 4 8% 7% 2	4546
February	1st to 10th	Night	68% 5% 10% 12% 5%	2470
	11th to 20th	Night	67% 5% 10% 13% 4	2405
	21st to end	Night	65% 5% 12% 12% 6%	1895
March	1st to 10th	Night	56% 6% 11% 20% 6%	3579
	11th to 20th	Night	61% 5% 12% 15% 6%	3480
	21st to end	Night	54% 5% 7% 22% 10% 1	3700
April	1st to 10th	Night	57% 5% 10% 19% 8% 2	1900
	11th to 20th	Night	51% 6% 10% 17% 15% 1	1875
	21st to end	Night	48% 6% 10% 19% 14% 3	1833
May	1st to 10th	Night	56% 6% 10% 15% 10% 3	2653
	11th to 20th	Night	45% 9% 13% 22% 9% 1	2496
	21st to end	Night	36% 9% 13% 21% 20% 2	2739
June	1st to 10th	Night	43% 8% 11% 22% 16% 1	1520
	11th to 20th	Night	39% 7% 12% 22% 17% 2	1520
	21st to end	Night	40% 8% 11% 24% 16% 1	1520
July	1st to 10th	Night	39% 7% 13% 23% 16% 2	2480
	11th to 20th	Night	35% 8% 13% 29% 14% 1	2472
	21st to end	Night	38% 8% 12% 24% 16% 1	2702
August	1st to 10th	Night	40% 7% 14% 26% 12% 1	2814
	11th to 20th	Night	44% 7% 14% 27% 9%	2812
	21st to end	Night	32% 8% 13% 34% 12% 1	3476
September	1st to 10th	Night	38% 7% 13% 27% 13% 2	1900
	11th to 20th	Night	38% 5% 12% 28% 17% 1	1900
	21st to end	Night	45% 7% 12% 24% 12% 1	2174
October	1st to 10th	Night	47% 6% 10% 26% 10%	3800
	11th to 20th	Night	49% 5% 12% 20% 13% 1	3779
	21st to end	Night	48% 6% 13% 26% 7% 1	4197
November	1st to 10th	Night	53% 6% 11% 20% 8% 2	2537
	11th to 20th	Night	56% 6% 13% 16% 8% 1	2772
	21st to end	Night	62% 6% 14% 14% 3	2800
December	1st to 10th	Night	75% 6% 11% 7% 1	4580
	11th to 20th	Night	68% 5% 8% 11% 7% 1	5208
	21st to end	Night	72% 7% 9% 8% 3	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	29% 28% 32% 8% 5%	200
	11th to 20th	Day	30% 28% 31% 10% 1	213
	21st to end	Day	28% 26% 33% 11% 2	300
February	1st to 10th	Day	28% 33% 31% 7% 1	270
	11th to 20th	Day	32% 29% 35% 4	270
	21st to end	Day	35% 23% 29% 12% 1	370
March	1st to 10th	Day	22% 26% 34% 14% 3 1	460
	11th to 20th	Day	29% 24% 30% 14% 3	460
	21st to end	Day	33% 21% 29% 13% 4 1	506
April	1st to 10th	Day	28% 22% 33% 12% 5% 1	460
	11th to 20th	Day	30% 21% 26% 13% 8% 2	452
	21st to end	Day	29% 20% 28% 16% 6% 1	460
May	1st to 10th	Day	23% 18% 32% 17% 8% 2	463
	11th to 20th	Day	18% 14% 33% 25% 9% 1	487
	21st to end	Day	14% 13% 33% 24% 12% 3	529
June	1st to 10th	Day	20% 15% 28% 27% 7% 2	490
	11th to 20th	Day	15% 11% 32% 28% 11% 2	490
	21st to end	Day	15% 14% 34% 26% 9% 2	490
July	1st to 10th	Day	12% 8% 27% 33% 16% 4	485
	11th to 20th	Day	13% 7% 29% 32% 17% 3	484
	21st to end	Day	11% 8% 36% 30% 12% 3	532
August	1st to 10th	Day	13% 6% 30% 27% 18% 6%	486
	11th to 20th	Day	13% 6% 32% 27% 14% 8%	479
	21st to end	Day	15% 9% 27% 27% 14% 7%	539
September	1st to 10th	Day	14% 13% 24% 27% 14% 8%	490
	11th to 20th	Day	13% 9% 22% 26% 20% 11%	490
	21st to end	Day	18% 14% 27% 24% 13% 5%	490
October	1st to 10th	Day	21% 15% 29% 19% 12% 3	490
	11th to 20th	Day	25% 17% 32% 16% 8% 2	490
	21st to end	Day	33% 18% 31% 15% 4	516
November	1st to 10th	Day	25% 20% 29% 18% 7% 1	395
	11th to 20th	Day	25% 28% 28% 14% 4	225
	21st to end	Day	34% 26% 28% 11% 2	200
December	1st to 10th	Day	34% 19% 31% 12% 4 1	200
	11th to 20th	Day	34% 25% 29% 12% 2	200
	21st to end	Day	30% 26% 30% 12% 1	220
January	1st to 10th	Night	28% 28% 29% 13% 3	800
	11th to 20th	Night	29% 23% 30% 16% 2	800
	21st to end	Night	20% 26% 33% 17% 3	841
February	1st to 10th	Night	28% 24% 31% 16% 1	760
	11th to 20th	Night	25% 26% 33% 13% 2	743
	21st to end	Night	26% 25% 31% 15% 2	628
March	1st to 10th	Night	27% 20% 32% 18% 4	760
	11th to 20th	Night	28% 21% 27% 19% 4	760
	21st to end	Night	25% 18% 31% 19% 6% 1	836
April	1st to 10th	Night	25% 16% 33% 22% 4	760
	11th to 20th	Night	25% 16% 28% 23% 6% 1	751
	21st to end	Night	24% 13% 27% 26% 9%	693
May	1st to 10th	Night	26% 10% 21% 31% 11% 1	461
	11th to 20th	Night	15% 8% 32% 34% 10% 1	374
	21st to end	Night	10% 7% 34% 30% 18%	411
June	1st to 10th	Night	16% 8% 26% 34% 16% 1	380
	11th to 20th	Night	14% 9% 24% 36% 16% 1	380
	21st to end	Night	13% 7% 27% 41% 11% 1	380
July	1st to 10th	Night	9% 4 22% 42% 22% 2	370
	11th to 20th	Night	11% 3 21% 41% 23% 1	368
	21st to end	Night	13% 3 24% 40% 18% 2	444
August	1st to 10th	Night	11% 4 23% 38% 21% 3	567
	11th to 20th	Night	12% 5% 20% 34% 25% 3	564
	21st to end	Night	11% 7% 23% 34% 24% 2	836
September	1st to 10th	Night	16% 7% 23% 31% 21% 3	760
	11th to 20th	Night	17% 7% 17% 30% 25% 4	760
	21st to end	Night	19% 10% 22% 27% 20% 3	760
October	1st to 10th	Night	23% 12% 25% 21% 17% 2	760
	11th to 20th	Night	25% 15% 30% 21% 8% 1	760
	21st to end	Night	32% 13% 31% 20% 3	836
November	1st to 10th	Night	26% 15% 30% 22% 7%	780
	11th to 20th	Night	24% 22% 30% 16% 6% 1	800
	21st to end	Night	29% 21% 28% 16% 5%	800
December	1st to 10th	Night	32% 24% 28% 13% 3	800
	11th to 20th	Night	28% 25% 29% 16% 3	800
	21st to end	Night	34% 21% 29% 14% 1	880

Page generated at 2025-01-19 03:06:46. Version ac07

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