Conway Summit
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Conway Summit clear sky chart from 2005-11-06 to 2025-12-18.

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	1 3 1 4 2 3 3 3 4 7% 69%	135604
	Night	1 2 1 3 2 2 3 3 5% 7% 71%	132853
Transparency	Day	14% 7% 10% 19% 27% 23%	130621
	Night	13% 7% 11% 22% 28% 19%	128814
Seeing	Day	4 13% 28% 29% 19% 7%	16564
	Night	2 6% 27% 37% 23% 5%	26045

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	2 1 2 2 2 2 2 5% 10% 72%	3639
	11th to 20th	Day	1 1 2 3 3 3 3 6% 9% 69%	3747
	21st to end	Day	4 3 6% 3 3 4 4 6% 9% 57%	4510
February	1st to 10th	Day	3 1 4 2 2 3 4 5% 7% 67%	1894
	11th to 20th	Day	3 1 4 4 3 3 3 8% 9% 60%	1950
	21st to end	Day	2 2 4 3 3 4 3 6% 8% 66%	1650
March	1st to 10th	Day	4 3 7% 4 5% 5% 4 7% 9% 52%	4518
	11th to 20th	Day	3 2 6% 2 3 3 3 5% 10% 62%	4814
	21st to end	Day	1 3 3 5% 3 3 3 3 5% 8% 62%	5916
April	1st to 10th	Day	1 3 2 5% 3 3 4 4 7% 9% 59%	2400
	11th to 20th	Day	1 3 1 3 3 3 4 3 7% 8% 64%	2369
	21st to end	Day	1 4 1 4 3 2 3 4 6% 7% 65%	2400
May	1st to 10th	Day	2 5% 1 3 2 2 3 2 4 5% 70%	5738
	11th to 20th	Day	1 3 1 3 2 2 3 3 4 5% 72%	5901
	21st to end	Day	2 4 2 4 3 2 3 2 4 6% 69%	6902
June	1st to 10th	Day	3 4 2 3 4 3 4 4 6% 6% 62%	2800
	11th to 20th	Day	1 1 1 3 2 2 3 2 4 4 78%	2800
	21st to end	Day	2 3 1 3 2 3 2 3 4 4 73%	2800
July	1st to 10th	Day	2 2 1 2 1 2 2 2 2 3 81%	6319
	11th to 20th	Day	3 5% 2 5% 3 4 3 3 4 5% 62%	6320
	21st to end	Day	3 3 1 4 3 3 4 3 4 6% 65%	6751
August	1st to 10th	Day	3 3 1 3 2 2 3 2 3 4 74%	5520
	11th to 20th	Day	2 2 1 3 2 2 2 2 2 3 80%	5364
	21st to end	Day	4 4 2 4 3 3 2 2 3 4 70%	5984
September	1st to 10th	Day	2 3 1 3 2 2 3 2 3 3 75%	2400
	11th to 20th	Day	2 3 1 3 2 2 3 2 4 5% 72%	2327
	21st to end	Day	1 2 1 2 2 2 3 2 3 5% 76%	2200
October	1st to 10th	Day	2 3 1 3 2 2 2 2 4 5% 72%	3449
	11th to 20th	Day	2 2 1 2 1 1 2 1 2 4 81%	3261
	21st to end	Day	2 1 2 2 2 2 2 4 6% 78%	3437
November	1st to 10th	Day	1 1 3 2 4 3 2 5% 8% 70%	1854
	11th to 20th	Day	1 3 1 2 1 2 2 3 5% 9% 70%	1890
	21st to end	Day	1 3 1 2 2 2 3 3 6% 8% 71%	1890
December	1st to 10th	Day	2 1 2 2 2 3 3 5% 9% 72%	2802
	11th to 20th	Day	3 1 4 3 3 3 3 6% 9% 64%	3084
	21st to end	Day	5% 2 4 3 3 4 4 7% 14% 55%	4004
January	1st to 10th	Night	2 2 4 2 2 2 2 5% 10% 69%	6306
	11th to 20th	Night	1 1 3 2 3 3 3 7% 8% 69%	6215
	21st to end	Night	1 4 3 7% 3 3 3 3 6% 8% 60%	6468
February	1st to 10th	Night	3 1 5% 2 4 3 3 6% 9% 62%	2504
	11th to 20th	Night	1 3 1 4 3 3 4 3 6% 10% 63%	2338
	21st to end	Night	3 1 4 3 2 4 3 7% 9% 66%	1980
March	1st to 10th	Night	3 2 6% 4 4 5% 4 7% 9% 56%	5376
	11th to 20th	Night	4 2 5% 2 2 3 3 5% 9% 64%	5182
	21st to end	Night	1 3 1 5% 3 3 4 4 6% 9% 61%	5057
April	1st to 10th	Night	1 3 1 4 3 4 3 3 5% 8% 65%	2000
	11th to 20th	Night	3 1 3 4 3 3 4 5% 6% 69%	1979
	21st to end	Night	2 4 2 3 3 2 2 2 4 6% 71%	2000
May	1st to 10th	Night	2 4 2 3 2 2 2 2 3 5% 76%	4246
	11th to 20th	Night	1 2 1 2 2 2 3 2 3 5% 77%	3992
	21st to end	Night	2 3 1 2 2 2 2 2 3 4 78%	3972
June	1st to 10th	Night	3 3 1 3 2 2 3 4 5% 6% 68%	1600
	11th to 20th	Night	2 1 1 2 1 1 2 1 3 5% 82%	1600
	21st to end	Night	1 2 1 2 2 2 2 1 2 4 81%	1600
July	1st to 10th	Night	1 1 1 1 1 1 2 3 89%	3640
	11th to 20th	Night	3 4 1 4 3 2 3 2 4 4 70%	3640
	21st to end	Night	1 2 1 2 2 2 2 2 3 4 80%	4100
August	1st to 10th	Night	2 1 1 2 1 1 2 1 3 4 83%	4304
	11th to 20th	Night	1 1 1 1 1 1 1 2 2 4 84%	4506
	21st to end	Night	3 2 1 2 1 2 2 2 3 4 79%	5015
September	1st to 10th	Night	1 1 1 1 1 2 1 2 3 86%	2000
	11th to 20th	Night	2 2 1 2 2 2 2 2 4 5% 77%	2071
	21st to end	Night	1 2 1 2 1 1 1 2 3 5% 80%	2200
October	1st to 10th	Night	3 3 1 3 2 1 1 2 2 5% 78%	3748
	11th to 20th	Night	1 1 1 2 1 1 1 2 3 4 82%	3897
	21st to end	Night	1 1 2 1 2 2 1 3 6% 79%	4368
November	1st to 10th	Night	1 1 2 2 2 2 3 4 7% 75%	2665
	11th to 20th	Night	1 2 1 2 2 3 3 2 5% 6% 73%	2730
	21st to end	Night	1 3 1 2 2 2 2 3 4 9% 71%	2730
December	1st to 10th	Night	2 1 2 2 2 3 3 5% 7% 74%	4598
	11th to 20th	Night	2 1 3 2 2 3 4 7% 13% 62%	5274
	21st to end	Night	5% 2 5% 3 4 5% 5% 8% 14% 48%	6952

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	10% 8% 25% 27% 26% 5%	3639
	11th to 20th	Day	13% 11% 12% 17% 27% 20%	3747
	21st to end	Day	21% 9% 15% 18% 26% 11%	4510
February	1st to 10th	Day	17% 8% 15% 23% 24% 13%	1894
	11th to 20th	Day	17% 8% 14% 27% 24% 9%	1960
	21st to end	Day	15% 10% 18% 28% 21% 8%	1650
March	1st to 10th	Day	21% 12% 15% 17% 25% 9%	4518
	11th to 20th	Day	12% 12% 19% 33% 18% 6%	4814
	21st to end	Day	16% 11% 19% 27% 23% 5%	5916
April	1st to 10th	Day	19% 11% 17% 27% 19% 8%	2400
	11th to 20th	Day	17% 9% 15% 28% 22% 9%	2372
	21st to end	Day	16% 9% 18% 30% 23% 5%	2400
May	1st to 10th	Day	14% 9% 9% 26% 34% 9%	5738
	11th to 20th	Day	13% 7% 8% 22% 36% 14%	5904
	21st to end	Day	15% 6% 8% 16% 43% 12%	6904
June	1st to 10th	Day	19% 8% 11% 22% 29% 10%	2800
	11th to 20th	Day	10% 4 7% 18% 34% 27%	2800
	21st to end	Day	13% 5% 4 10% 33% 35%	2800
July	1st to 10th	Day	9% 3 2 5% 12% 70%	6251
	11th to 20th	Day	18% 7% 4 7% 14% 49%	6245
	21st to end	Day	16% 7% 6% 11% 22% 38%	6555
August	1st to 10th	Day	18% 5% 5% 8% 23% 41%	4015
	11th to 20th	Day	9% 3 2 6% 18% 62%	3880
	21st to end	Day	10% 2 3 8% 30% 48%	4311
September	1st to 10th	Day	14% 3 5% 9% 30% 39%	2400
	11th to 20th	Day	14% 4 5% 19% 30% 27%	2327
	21st to end	Day	11% 3 5% 19% 34% 28%	2200
October	1st to 10th	Day	13% 4 6% 12% 35% 30%	3449
	11th to 20th	Day	10% 2 4 13% 47% 23%	3261
	21st to end	Day	8% 4 5% 22% 43% 17%	3437
November	1st to 10th	Day	13% 6% 14% 25% 29% 14%	1854
	11th to 20th	Day	10% 8% 14% 27% 31% 11%	1890
	21st to end	Day	12% 6% 12% 29% 29% 12%	1890
December	1st to 10th	Day	10% 7% 11% 28% 31% 13%	2802
	11th to 20th	Day	15% 12% 20% 25% 20% 9%	3084
	21st to end	Day	18% 10% 22% 25% 20% 6%	4004
January	1st to 10th	Night	13% 8% 19% 28% 26% 6%	6306
	11th to 20th	Night	12% 10% 15% 20% 29% 14%	6215
	21st to end	Night	21% 10% 13% 19% 26% 12%	6468
February	1st to 10th	Night	18% 9% 14% 24% 21% 13%	2504
	11th to 20th	Night	15% 7% 15% 27% 27% 9%	2339
	21st to end	Night	15% 9% 15% 30% 23% 9%	1980
March	1st to 10th	Night	19% 10% 15% 19% 27% 10%	5376
	11th to 20th	Night	13% 10% 15% 37% 21% 4	5182
	21st to end	Night	16% 9% 20% 32% 19% 4	5057
April	1st to 10th	Night	17% 9% 17% 30% 19% 7%	2000
	11th to 20th	Night	16% 8% 16% 27% 24% 10%	1979
	21st to end	Night	16% 7% 17% 35% 22% 4	2000
May	1st to 10th	Night	13% 5% 8% 34% 35% 5%	4243
	11th to 20th	Night	10% 5% 10% 27% 37% 11%	3993
	21st to end	Night	10% 5% 8% 22% 48% 7%	3972
June	1st to 10th	Night	15% 7% 11% 28% 32% 7%	1600
	11th to 20th	Night	8% 4 7% 19% 36% 26%	1600
	21st to end	Night	10% 3 4 14% 35% 35%	1600
July	1st to 10th	Night	3 2 3 5% 14% 73%	3600
	11th to 20th	Night	15% 5% 4 8% 18% 50%	3592
	21st to end	Night	8% 4 3 17% 28% 40%	3985
August	1st to 10th	Night	11% 3 5% 12% 29% 40%	3126
	11th to 20th	Night	6% 3 3 9% 19% 60%	3256
	21st to end	Night	5% 2 3 12% 33% 45%	3608
September	1st to 10th	Night	6% 3 4 13% 36% 38%	2000
	11th to 20th	Night	10% 4 7% 18% 37% 24%	2071
	21st to end	Night	9% 3 6% 19% 38% 25%	2200
October	1st to 10th	Night	11% 4 5% 15% 41% 25%	3748
	11th to 20th	Night	7% 3 5% 15% 45% 25%	3897
	21st to end	Night	7% 5% 6% 21% 39% 22%	4368
November	1st to 10th	Night	9% 7% 12% 28% 30% 13%	2665
	11th to 20th	Night	12% 7% 14% 28% 29% 11%	2730
	21st to end	Night	12% 6% 15% 25% 30% 11%	2730
December	1st to 10th	Night	10% 7% 12% 26% 29% 15%	4598
	11th to 20th	Night	13% 11% 21% 24% 24% 6%	5274
	21st to end	Night	21% 13% 20% 18% 19% 9%	6952

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	4 17% 37% 26% 14% 3	200
	11th to 20th	Day	1 15% 30% 29% 18% 7%	242
	21st to end	Day	3 13% 24% 35% 19% 6%	440
February	1st to 10th	Day	7% 15% 30% 26% 16% 6%	447
	11th to 20th	Day	4 16% 31% 29% 17% 3	495
	21st to end	Day	4 15% 33% 31% 15% 2	414
March	1st to 10th	Day	3 18% 35% 30% 12% 3	500
	11th to 20th	Day	5% 22% 29% 23% 16% 5%	500
	21st to end	Day	5% 21% 35% 26% 13% 1	550
April	1st to 10th	Day	6% 19% 32% 24% 17% 2	500
	11th to 20th	Day	6% 21% 31% 26% 13% 4	492
	21st to end	Day	4 18% 28% 27% 16% 6%	500
May	1st to 10th	Day	7% 16% 33% 27% 13% 5%	503
	11th to 20th	Day	8% 20% 28% 23% 14% 8%	528
	21st to end	Day	7% 14% 24% 28% 19% 8%	573
June	1st to 10th	Day	6% 15% 25% 25% 22% 8%	530
	11th to 20th	Day	4 16% 29% 27% 16% 7%	530
	21st to end	Day	3 10% 26% 35% 18% 8%	530
July	1st to 10th	Day	2 7% 29% 33% 20% 9%	526
	11th to 20th	Day	4 4 22% 34% 26% 11%	524
	21st to end	Day	6% 5% 22% 35% 22% 11%	575
August	1st to 10th	Day	4 8% 26% 31% 21% 11%	527
	11th to 20th	Day	3 7% 27% 30% 23% 10%	517
	21st to end	Day	2 7% 25% 34% 22% 10%	583
September	1st to 10th	Day	3 7% 23% 35% 24% 8%	530
	11th to 20th	Day	5% 13% 27% 29% 22% 4	530
	21st to end	Day	3 9% 24% 36% 23% 5%	530
October	1st to 10th	Day	5% 14% 26% 28% 21% 7%	530
	11th to 20th	Day	3 11% 27% 28% 24% 7%	530
	21st to end	Day	4 11% 26% 28% 24% 7%	511
November	1st to 10th	Day	5% 8% 27% 27% 21% 12%	330
	11th to 20th	Day	7% 11% 24% 27% 22% 9%	330
	21st to end	Day	2 10% 27% 28% 25% 7%	330
December	1st to 10th	Day	6% 7% 27% 28% 20% 13%	253
	11th to 20th	Day	4 12% 23% 31% 20% 10%	214
	21st to end	Day	5% 19% 29% 26% 15% 5%	220
January	1st to 10th	Night	3 7% 36% 29% 17% 8%	800
	11th to 20th	Night	1 6% 33% 39% 15% 6%	800
	21st to end	Night	2 6% 33% 35% 19% 6%	880
February	1st to 10th	Night	2 8% 33% 34% 19% 4	800
	11th to 20th	Night	1 9% 34% 32% 18% 5%	784
	21st to end	Night	1 10% 36% 36% 13% 4	660
March	1st to 10th	Night	2 9% 39% 32% 13% 4	800
	11th to 20th	Night	2 10% 34% 29% 18% 7%	800
	21st to end	Night	2 11% 38% 33% 15% 2	880
April	1st to 10th	Night	3 8% 34% 35% 18% 3	800
	11th to 20th	Night	2 9% 34% 34% 17% 5%	791
	21st to end	Night	3 8% 29% 36% 19% 6%	800
May	1st to 10th	Night	4 7% 30% 37% 18% 4	668
	11th to 20th	Night	4 6% 25% 38% 24% 2	562
	21st to end	Night	5% 5% 25% 33% 28% 4	433
June	1st to 10th	Night	3 3 21% 40% 32% 3	400
	11th to 20th	Night	2 2 26% 40% 27% 3	400
	21st to end	Night	1 1 21% 49% 25% 3	400
July	1st to 10th	Night	1 11% 52% 34% 3	390
	11th to 20th	Night	2 1 11% 47% 37% 2	388
	21st to end	Night	2 8% 47% 38% 6%	493
August	1st to 10th	Night	3 1 13% 41% 36% 6%	716
	11th to 20th	Night	3 1 14% 43% 34% 5%	792
	21st to end	Night	2 1 12% 44% 36% 5%	880
September	1st to 10th	Night	1 2 14% 41% 36% 6%	800
	11th to 20th	Night	3 3 19% 40% 30% 6%	800
	21st to end	Night	2 3 19% 39% 30% 8%	800
October	1st to 10th	Night	3 4 21% 38% 27% 6%	800
	11th to 20th	Night	3 5% 19% 40% 27% 7%	800
	21st to end	Night	2 4 23% 34% 25% 11%	880
November	1st to 10th	Night	1 5% 26% 34% 26% 8%	820
	11th to 20th	Night	3 7% 28% 37% 20% 5%	840
	21st to end	Night	3 6% 30% 33% 23% 5%	840
December	1st to 10th	Night	2 6% 34% 37% 15% 6%	840
	11th to 20th	Night	1 7% 36% 36% 16% 4	828
	21st to end	Night	1 11% 39% 32% 13% 3	880

Page generated at 2025-12-14 22:13:54. Version ac07

Copyright © 2025 Attilla Danko.