Hazard
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hazard clear sky chart from 2005-11-06 to 2024-12-09.

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% 9% 3 7% 5% 4 5% 4 6% 7% 36%	101414
	Night	15% 9% 3 7% 4 4 4 4 5% 7% 38%	98326
Transparency	Day	45% 4 10% 23% 15% 2	105182
	Night	45% 4 10% 22% 16% 3	102697
Seeing	Day	21% 13% 24% 22% 15% 6%	15004
	Night	20% 11% 21% 29% 17% 2	25081

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	15% 15% 7% 12% 5% 3 3 3 5% 7% 24%	2836
	11th to 20th	Day	18% 15% 8% 11% 7% 5% 3 3 3 3 25%	2840
	21st to end	Day	22% 18% 5% 7% 4 3 3 3 4 5% 27%	3124
February	1st to 10th	Day	18% 14% 4 9% 4 3 4 3 5% 6% 30%	1786
	11th to 20th	Day	21% 11% 4 9% 4 4 4 3 5% 5% 29%	1848
	21st to end	Day	20% 12% 4 9% 5% 4 4 3 4 5% 30%	1570
March	1st to 10th	Day	22% 14% 4 6% 4 4 3 3 4 5% 31%	3275
	11th to 20th	Day	15% 8% 3 7% 4 4 3 3 4 7% 43%	3480
	21st to end	Day	17% 9% 3 6% 4 4 4 3 6% 7% 37%	3815
April	1st to 10th	Day	15% 7% 3 7% 5% 4 4 4 6% 7% 37%	2106
	11th to 20th	Day	17% 8% 2 7% 4 4 3 3 5% 6% 42%	2340
	21st to end	Day	17% 7% 2 7% 5% 5% 4 4 6% 7% 37%	2470
May	1st to 10th	Day	17% 10% 3 9% 6% 6% 5% 4 5% 7% 27%	4082
	11th to 20th	Day	16% 9% 3 9% 5% 5% 5% 4 5% 6% 33%	4081
	21st to end	Day	11% 6% 2 6% 5% 5% 6% 4 8% 11% 35%	4476
June	1st to 10th	Day	11% 6% 2 6% 5% 5% 6% 5% 6% 10% 37%	2470
	11th to 20th	Day	8% 6% 2 7% 5% 5% 6% 5% 8% 9% 40%	2470
	21st to end	Day	9% 6% 3 6% 7% 5% 5% 4 8% 9% 38%	2470
July	1st to 10th	Day	8% 4 2 7% 6% 5% 7% 5% 7% 10% 38%	4120
	11th to 20th	Day	10% 6% 2 6% 4 5% 6% 4 7% 10% 39%	4120
	21st to end	Day	18% 10% 4 10% 7% 6% 6% 4 6% 8% 21%	4466
August	1st to 10th	Day	9% 6% 3 8% 5% 6% 5% 5% 8% 10% 36%	4104
	11th to 20th	Day	11% 5% 2 7% 5% 5% 7% 5% 7% 10% 36%	4044
	21st to end	Day	6% 3 1 4 3 4 5% 3 6% 8% 56%	4264
September	1st to 10th	Day	13% 6% 2 5% 5% 5% 5% 4 6% 6% 43%	2090
	11th to 20th	Day	14% 5% 2 7% 4 4 5% 3 5% 7% 43%	2090
	21st to end	Day	17% 7% 2 6% 4 3 4 3 6% 6% 42%	2090
October	1st to 10th	Day	13% 4 3 5% 4 3 3 3 5% 6% 50%	2076
	11th to 20th	Day	14% 5% 3 6% 4 3 3 3 5% 6% 49%	1900
	21st to end	Day	19% 8% 2 4 4 3 3 3 5% 7% 44%	2090
November	1st to 10th	Day	13% 6% 2 5% 3 3 3 3 5% 5% 50%	1762
	11th to 20th	Day	14% 11% 2 6% 4 3 4 4 4 6% 42%	1800
	21st to end	Day	15% 12% 4 6% 3 3 4 3 4 6% 40%	1800
December	1st to 10th	Day	20% 12% 4 8% 4 5% 4 3 4 5% 30%	1782
	11th to 20th	Day	17% 13% 4 8% 4 3 4 4 6% 6% 32%	2153
	21st to end	Day	15% 18% 4 7% 4 5% 6% 3 6% 6% 24%	3124
January	1st to 10th	Night	16% 20% 7% 9% 5% 4 4 3 3 4 25%	4109
	11th to 20th	Night	20% 13% 4 10% 5% 4 3 3 3 5% 31%	4120
	21st to end	Night	23% 13% 4 9% 4 4 4 3 4 5% 29%	4532
February	1st to 10th	Night	18% 11% 4 9% 5% 4 3 3 5% 6% 31%	2390
	11th to 20th	Night	24% 11% 4 8% 4 4 4 3 4 4 29%	2218
	21st to end	Night	22% 14% 4 8% 4 4 4 4 5% 6% 27%	1884
March	1st to 10th	Night	22% 13% 2 6% 4 4 4 2 3 6% 32%	3577
	11th to 20th	Night	14% 8% 3 4 4 3 4 3 5% 7% 46%	3480
	21st to end	Night	13% 8% 2 7% 5% 4 5% 4 5% 7% 40%	3817
April	1st to 10th	Night	13% 8% 2 7% 4 4 4 4 5% 6% 43%	2089
	11th to 20th	Night	15% 7% 2 5% 5% 4 4 4 5% 7% 42%	1787
	21st to end	Night	15% 8% 2 5% 5% 4 5% 3 6% 7% 40%	1710
May	1st to 10th	Night	17% 8% 3 8% 6% 5% 6% 4 6% 8% 29%	2813
	11th to 20th	Night	20% 7% 3 5% 4 3 4 3 6% 8% 37%	2812
	21st to end	Night	10% 5% 3 7% 5% 5% 5% 4 8% 9% 39%	3079
June	1st to 10th	Night	9% 5% 2 6% 4 4 4 5% 8% 9% 43%	1710
	11th to 20th	Night	5% 4 2 6% 5% 5% 5% 6% 7% 10% 46%	1710
	21st to end	Night	9% 5% 2 7% 4 4 5% 5% 7% 11% 41%	1710
July	1st to 10th	Night	9% 5% 2 6% 4 5% 6% 6% 8% 11% 38%	2840
	11th to 20th	Night	9% 5% 2 5% 3 4 5% 4 7% 10% 46%	2840
	21st to end	Night	15% 9% 3 10% 6% 5% 6% 4 5% 9% 28%	3087
August	1st to 10th	Night	10% 6% 2 7% 5% 4 5% 4 6% 10% 41%	2825
	11th to 20th	Night	11% 6% 2 7% 4 4 4 4 8% 9% 40%	2785
	21st to end	Night	5% 2 1 3 3 3 3 3 6% 8% 61%	3362
September	1st to 10th	Night	11% 5% 3 6% 3 4 4 3 7% 7% 46%	2082
	11th to 20th	Night	13% 6% 2 7% 5% 3 4 3 5% 8% 45%	2090
	21st to end	Night	13% 5% 2 5% 4 3 4 4 5% 6% 48%	2090
October	1st to 10th	Night	12% 4 2 5% 3 3 3 3 5% 7% 52%	2104
	11th to 20th	Night	17% 7% 2 5% 3 2 3 2 4 5% 48%	2280
	21st to end	Night	16% 7% 2 4 4 4 4 3 4 6% 46%	2508
November	1st to 10th	Night	14% 8% 2 5% 3 3 2 3 5% 6% 49%	2531
	11th to 20th	Night	15% 8% 3 5% 4 3 4 3 4 7% 43%	2600
	21st to end	Night	15% 11% 3 6% 3 3 4 3 5% 5% 43%	2600
December	1st to 10th	Night	20% 14% 5% 9% 4 4 3 4 5% 5% 29%	2581
	11th to 20th	Night	18% 13% 5% 9% 4 3 3 3 4 5% 32%	3042
	21st to end	Night	18% 15% 4 8% 5% 5% 6% 3 5% 8% 21%	4532

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	61% 2 6% 19% 11% 1	2837
	11th to 20th	Day	67% 2 6% 15% 9% 1	2840
	21st to end	Day	62% 2 6% 19% 11% 1	3124
February	1st to 10th	Day	56% 4 7% 18% 15% 1	1786
	11th to 20th	Day	58% 3 6% 18% 12% 2	1858
	21st to end	Day	58% 3 7% 16% 12% 4	1570
March	1st to 10th	Day	57% 2 7% 17% 14% 4	3275
	11th to 20th	Day	43% 3 7% 24% 19% 3	3480
	21st to end	Day	47% 3 7% 29% 13% 1	3815
April	1st to 10th	Day	44% 3 11% 23% 15% 3	2106
	11th to 20th	Day	43% 3 8% 22% 19% 5%	2340
	21st to end	Day	46% 4 10% 25% 12% 2	2470
May	1st to 10th	Day	57% 4 11% 18% 10% 1	4120
	11th to 20th	Day	52% 5% 9% 23% 10% 1	4085
	21st to end	Day	40% 6% 14% 21% 16% 3	4489
June	1st to 10th	Day	42% 7% 12% 24% 14% 1	2470
	11th to 20th	Day	39% 7% 14% 19% 18% 2	2470
	21st to end	Day	40% 7% 13% 20% 17% 3	2470
July	1st to 10th	Day	38% 8% 20% 20% 12% 1	4055
	11th to 20th	Day	37% 7% 14% 32% 9% 2	4051
	21st to end	Day	60% 6% 10% 15% 8% 1	4324
August	1st to 10th	Day	40% 8% 16% 25% 11%	4091
	11th to 20th	Day	39% 7% 15% 26% 11% 1	4083
	21st to end	Day	27% 5% 14% 38% 15% 1	4264
September	1st to 10th	Day	40% 6% 11% 21% 17% 6%	2090
	11th to 20th	Day	40% 5% 11% 25% 17% 1	2090
	21st to end	Day	42% 3 9% 23% 20% 2	2090
October	1st to 10th	Day	28% 4 8% 21% 36% 3	3453
	11th to 20th	Day	27% 2 10% 26% 29% 6%	3140
	21st to end	Day	31% 2 8% 30% 19% 9%	3428
November	1st to 10th	Day	36% 3 8% 24% 25% 4	1762
	11th to 20th	Day	44% 3 5% 23% 20% 5%	1800
	21st to end	Day	46% 3 8% 22% 18% 3	1800
December	1st to 10th	Day	57% 3 8% 20% 11% 1	1782
	11th to 20th	Day	53% 3 10% 17% 16% 2	2150
	21st to end	Day	60% 3 8% 22% 7%	3124
January	1st to 10th	Night	66% 2 5% 14% 11% 1	4109
	11th to 20th	Night	59% 2 5% 15% 16% 3	4120
	21st to end	Night	60% 2 7% 17% 13% 1	4532
February	1st to 10th	Night	55% 4 10% 18% 12% 2	2390
	11th to 20th	Night	59% 3 6% 17% 11% 3	2219
	21st to end	Night	59% 3 8% 15% 11% 3	1884
March	1st to 10th	Night	56% 2 6% 17% 16% 2	3577
	11th to 20th	Night	40% 2 8% 31% 12% 6%	3480
	21st to end	Night	45% 3 9% 25% 16% 1	3817
April	1st to 10th	Night	42% 5% 9% 23% 17% 3	2089
	11th to 20th	Night	42% 3 9% 22% 17% 7%	1787
	21st to end	Night	43% 4 12% 26% 13% 1	1710
May	1st to 10th	Night	52% 6% 13% 20% 8% 1	2840
	11th to 20th	Night	46% 6% 12% 26% 8% 1	2813
	21st to end	Night	39% 7% 13% 24% 16% 2	3087
June	1st to 10th	Night	35% 8% 17% 23% 15% 3	1710
	11th to 20th	Night	30% 8% 19% 24% 17% 2	1710
	21st to end	Night	36% 8% 15% 22% 15% 4	1710
July	1st to 10th	Night	36% 9% 19% 23% 10% 2	2795
	11th to 20th	Night	31% 6% 18% 32% 10% 2	2786
	21st to end	Night	52% 7% 12% 19% 10% 1	2988
August	1st to 10th	Night	37% 7% 17% 26% 12% 1	2814
	11th to 20th	Night	39% 6% 14% 27% 13% 1	2812
	21st to end	Night	21% 5% 14% 39% 20% 2	3362
September	1st to 10th	Night	35% 5% 14% 22% 18% 6%	2082
	11th to 20th	Night	38% 6% 9% 23% 22% 2	2090
	21st to end	Night	36% 6% 8% 25% 23% 3	2090
October	1st to 10th	Night	30% 5% 7% 21% 33% 4	3507
	11th to 20th	Night	30% 2 6% 24% 28% 10%	3779
	21st to end	Night	27% 2 6% 27% 27% 11%	4120
November	1st to 10th	Night	38% 3 7% 21% 24% 6%	2531
	11th to 20th	Night	42% 3 7% 20% 22% 6%	2600
	21st to end	Night	44% 3 7% 26% 17% 3	2600
December	1st to 10th	Night	58% 3 9% 17% 11% 2	2581
	11th to 20th	Night	56% 2 7% 19% 14% 2	3044
	21st to end	Night	62% 3 9% 15% 11% 1	4532

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	26% 29% 27% 14% 4 1	270
	11th to 20th	Day	38% 28% 20% 12% 2	270
	21st to end	Day	32% 28% 28% 9% 4	297
February	1st to 10th	Day	31% 24% 26% 14% 3 1	270
	11th to 20th	Day	41% 29% 19% 8% 2	270
	21st to end	Day	38% 25% 29% 6% 1	225
March	1st to 10th	Day	31% 20% 29% 14% 4 1	360
	11th to 20th	Day	26% 25% 29% 17% 3 1	460
	21st to end	Day	31% 18% 28% 16% 7%	506
April	1st to 10th	Day	29% 17% 27% 18% 8% 1	460
	11th to 20th	Day	23% 17% 31% 18% 8% 2	452
	21st to end	Day	24% 17% 28% 18% 9% 3	460
May	1st to 10th	Day	27% 16% 27% 18% 8% 5%	463
	11th to 20th	Day	19% 13% 26% 24% 14% 5%	487
	21st to end	Day	14% 8% 24% 24% 19% 11%	529
June	1st to 10th	Day	13% 7% 26% 26% 18% 10%	490
	11th to 20th	Day	9% 7% 23% 26% 25% 10%	490
	21st to end	Day	9% 6% 31% 25% 20% 9%	490
July	1st to 10th	Day	14% 5% 18% 27% 20% 16%	485
	11th to 20th	Day	9% 6% 17% 32% 22% 15%	484
	21st to end	Day	15% 6% 16% 30% 23% 11%	532
August	1st to 10th	Day	14% 5% 18% 27% 24% 12%	486
	11th to 20th	Day	15% 5% 20% 26% 25% 10%	479
	21st to end	Day	11% 2 12% 29% 30% 15%	539
September	1st to 10th	Day	14% 4 14% 24% 32% 11%	490
	11th to 20th	Day	16% 3 12% 29% 28% 13%	490
	21st to end	Day	20% 8% 18% 27% 19% 7%	490
October	1st to 10th	Day	16% 8% 19% 27% 22% 9%	490
	11th to 20th	Day	18% 12% 26% 24% 16% 4	490
	21st to end	Day	25% 10% 25% 24% 12% 3	539
November	1st to 10th	Day	21% 14% 29% 22% 10% 4	300
	11th to 20th	Day	26% 14% 33% 16% 10% 1	300
	21st to end	Day	27% 18% 29% 19% 7% 1	300
December	1st to 10th	Day	32% 20% 30% 14% 3 1	294
	11th to 20th	Day	28% 17% 29% 19% 7% 1	270
	21st to end	Day	33% 20% 29% 13% 5%	297
January	1st to 10th	Night	28% 21% 28% 20% 4	760
	11th to 20th	Night	33% 20% 24% 20% 4	760
	21st to end	Night	25% 18% 33% 22% 2	836
February	1st to 10th	Night	25% 18% 30% 25% 2	760
	11th to 20th	Night	34% 19% 31% 15% 2	743
	21st to end	Night	35% 17% 30% 16% 2	628
March	1st to 10th	Night	27% 16% 29% 23% 5%	760
	11th to 20th	Night	25% 18% 29% 21% 6% 1	760
	21st to end	Night	22% 16% 29% 25% 8%	836
April	1st to 10th	Night	22% 16% 26% 27% 9%	759
	11th to 20th	Night	21% 12% 28% 27% 11% 1	563
	21st to end	Night	19% 8% 33% 31% 9% 1	570
May	1st to 10th	Night	18% 9% 27% 30% 14% 2	570
	11th to 20th	Night	18% 6% 20% 35% 20% 1	561
	21st to end	Night	10% 3 19% 34% 26% 7%	617
June	1st to 10th	Night	12% 4 14% 39% 28% 3	570
	11th to 20th	Night	5% 2 16% 38% 32% 6%	570
	21st to end	Night	10% 2 17% 37% 29% 5%	570
July	1st to 10th	Night	14% 2 10% 29% 36% 8%	555
	11th to 20th	Night	7% 2 11% 31% 43% 6%	552
	21st to end	Night	14% 2 8% 33% 36% 6%	624
August	1st to 10th	Night	12% 3 7% 31% 40% 6%	567
	11th to 20th	Night	13% 1 8% 36% 34% 7%	564
	21st to end	Night	10% 1 9% 30% 41% 9%	627
September	1st to 10th	Night	13% 3 10% 31% 37% 6%	752
	11th to 20th	Night	15% 2 12% 31% 34% 5%	760
	21st to end	Night	15% 4 16% 35% 26% 4	760
October	1st to 10th	Night	14% 6% 16% 31% 29% 4	760
	11th to 20th	Night	21% 8% 19% 33% 17% 2	760
	21st to end	Night	21% 9% 23% 32% 14% 1	836
November	1st to 10th	Night	17% 11% 22% 32% 16% 3	780
	11th to 20th	Night	20% 15% 25% 31% 9% 1	800
	21st to end	Night	24% 12% 22% 31% 10%	800
December	1st to 10th	Night	29% 16% 25% 24% 5%	795
	11th to 20th	Night	24% 18% 25% 27% 6% 1	760
	21st to end	Night	29% 17% 24% 27% 4	836

Page generated at 2024-12-06 03:54:53. Version ac07

Copyright © 2024 Attilla Danko.