Crawford Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Crawford Observatory clear sky chart from 2005-11-06 to 2024-03-06.

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	12% 6% 3 5% 5% 3 5% 5% 6% 8% 42%	79031
	Night	12% 6% 2 5% 5% 3 4 5% 5% 7% 45%	80494
Transparency	Day	39% 7% 11% 19% 19% 5%	78756
	Night	37% 7% 10% 19% 20% 7%	80288
Seeing	Day	14% 10% 22% 24% 20% 10%	13642
	Night	14% 8% 23% 29% 21% 4	23751

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	16% 11% 3 6% 5% 3 5% 4 6% 5% 37%	2836
	11th to 20th	Day	12% 6% 3 5% 5% 3 3 4 4 5% 50%	2940
	21st to end	Day	22% 10% 2 4 4 2 3 3 4 5% 40%	3476
February	1st to 10th	Day	17% 9% 3 6% 5% 3 4 4 4 5% 40%	1900
	11th to 20th	Day	21% 9% 2 5% 4 2 4 3 4 5% 41%	1848
	21st to end	Day	18% 8% 3 6% 6% 2 4 4 4 6% 38%	1570
March	1st to 10th	Day	15% 7% 2 5% 6% 2 4 3 5% 6% 46%	1850
	11th to 20th	Day	15% 7% 3 6% 6% 3 4 4 6% 6% 38%	1916
	21st to end	Day	15% 6% 3 6% 6% 3 4 4 5% 7% 41%	2247
April	1st to 10th	Day	10% 6% 3 5% 5% 4 5% 5% 5% 6% 47%	2160
	11th to 20th	Day	13% 5% 2 5% 5% 3 4 4 5% 7% 47%	2134
	21st to end	Day	7% 5% 2 5% 4 3 5% 4 5% 9% 51%	2160
May	1st to 10th	Day	8% 4 3 5% 5% 3 4 5% 6% 8% 48%	2320
	11th to 20th	Day	8% 4 2 6% 5% 4 5% 5% 6% 9% 44%	2301
	21st to end	Day	8% 5% 2 6% 6% 4 5% 6% 6% 9% 44%	2531
June	1st to 10th	Day	9% 6% 3 6% 6% 4 6% 7% 8% 10% 34%	2340
	11th to 20th	Day	6% 4 2 5% 6% 3 7% 7% 8% 10% 44%	2340
	21st to end	Day	5% 5% 2 6% 5% 4 6% 6% 8% 12% 39%	2340
July	1st to 10th	Day	9% 5% 3 6% 7% 5% 6% 7% 9% 10% 33%	2340
	11th to 20th	Day	6% 5% 2 7% 7% 5% 9% 8% 9% 12% 31%	2340
	21st to end	Day	5% 4 2 6% 7% 5% 8% 7% 9% 13% 34%	2512
August	1st to 10th	Day	5% 4 1 5% 7% 5% 9% 9% 10% 12% 33%	2148
	11th to 20th	Day	10% 5% 3 7% 6% 4 8% 7% 8% 10% 32%	2125
	21st to end	Day	10% 6% 2 7% 7% 4 6% 6% 8% 9% 34%	2376
September	1st to 10th	Day	9% 6% 3 6% 6% 3 6% 5% 6% 7% 41%	2095
	11th to 20th	Day	11% 8% 3 5% 6% 3 5% 5% 5% 6% 42%	1980
	21st to end	Day	9% 5% 2 5% 5% 3 4 5% 5% 6% 50%	1980
October	1st to 10th	Day	10% 3 1 5% 5% 3 4 5% 5% 6% 53%	1980
	11th to 20th	Day	9% 5% 2 4 4 2 4 3 5% 7% 55%	1980
	21st to end	Day	11% 5% 2 4 4 3 4 3 4 5% 54%	1887
November	1st to 10th	Day	11% 6% 2 5% 5% 2 3 3 4 5% 54%	1672
	11th to 20th	Day	13% 5% 2 4 4 2 4 3 4 5% 53%	1710
	21st to end	Day	13% 7% 3 5% 4 3 4 4 5% 7% 46%	1710
December	1st to 10th	Day	18% 7% 2 5% 5% 3 5% 4 5% 6% 39%	1710
	11th to 20th	Day	16% 9% 2 7% 6% 2 4 4 4 4 43%	2153
	21st to end	Day	18% 8% 4 7% 5% 3 5% 4 5% 6% 36%	3124
January	1st to 10th	Night	17% 11% 3 5% 4 3 4 4 5% 5% 39%	4109
	11th to 20th	Night	14% 8% 3 5% 5% 3 4 3 4 6% 46%	4015
	21st to end	Night	20% 13% 3 5% 4 2 4 3 3 4 40%	4180
February	1st to 10th	Night	16% 6% 3 6% 5% 3 4 4 5% 6% 42%	2280
	11th to 20th	Night	20% 7% 2 6% 4 2 4 3 4 5% 43%	2218
	21st to end	Night	17% 5% 3 6% 5% 3 4 3 6% 7% 41%	1884
March	1st to 10th	Night	14% 7% 3 4 3 3 4 4 4 6% 48%	2227
	11th to 20th	Night	14% 7% 3 5% 5% 3 5% 5% 6% 7% 42%	2043
	21st to end	Night	12% 6% 2 3 5% 3 4 5% 6% 7% 47%	2123
April	1st to 10th	Night	10% 5% 2 5% 5% 3 5% 5% 6% 7% 47%	1800
	11th to 20th	Night	12% 5% 2 5% 4 2 3 4 5% 7% 51%	1775
	21st to end	Night	8% 4 2 4 6% 3 4 5% 5% 6% 55%	1800
May	1st to 10th	Night	7% 3 2 4 4 3 4 5% 5% 9% 52%	1638
	11th to 20th	Night	7% 4 3 6% 7% 5% 5% 5% 6% 9% 44%	1592
	21st to end	Night	7% 4 2 4 5% 3 5% 6% 7% 11% 47%	1744
June	1st to 10th	Night	5% 5% 3 6% 7% 4 8% 8% 7% 11% 36%	1620
	11th to 20th	Night	3 3 2 4 4 3 5% 6% 8% 13% 50%	1620
	21st to end	Night	5% 3 2 6% 5% 4 5% 7% 8% 13% 42%	1620
July	1st to 10th	Night	6% 4 2 5% 7% 5% 7% 6% 9% 11% 38%	1620
	11th to 20th	Night	4 4 2 7% 7% 4 6% 8% 8% 13% 39%	1620
	21st to end	Night	4 4 3 6% 5% 4 7% 6% 9% 12% 41%	1800
August	1st to 10th	Night	4 4 2 5% 5% 4 5% 7% 9% 14% 40%	1790
	11th to 20th	Night	7% 4 2 6% 6% 5% 6% 5% 8% 11% 41%	1776
	21st to end	Night	10% 7% 3 6% 6% 3 7% 6% 7% 8% 38%	1980
September	1st to 10th	Night	7% 6% 2 5% 7% 4 6% 7% 6% 9% 42%	1845
	11th to 20th	Night	11% 6% 2 4 5% 3 4 5% 6% 8% 47%	1980
	21st to end	Night	7% 4 2 5% 5% 2 4 5% 5% 7% 53%	1980
October	1st to 10th	Night	8% 4 2 3 4 3 3 3 4 6% 59%	1980
	11th to 20th	Night	10% 6% 2 4 4 2 3 4 4 6% 55%	1980
	21st to end	Night	12% 7% 2 5% 5% 2 3 4 3 4 54%	2465
November	1st to 10th	Night	11% 4 2 3 3 2 3 4 4 6% 58%	2406
	11th to 20th	Night	12% 5% 2 4 4 2 3 4 4 6% 54%	2470
	21st to end	Night	12% 5% 2 5% 4 3 4 4 5% 6% 48%	2470
December	1st to 10th	Night	16% 7% 3 5% 4 3 4 4 5% 7% 43%	2470
	11th to 20th	Night	15% 8% 3 5% 4 2 3 3 3 5% 48%	3042
	21st to end	Night	17% 10% 3 5% 5% 3 4 5% 5% 7% 35%	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	48% 4 5% 15% 23% 5%	2837
	11th to 20th	Day	37% 4 6% 26% 21% 6%	2940
	21st to end	Day	47% 3 6% 16% 20% 7%	3476
February	1st to 10th	Day	47% 4 7% 18% 19% 5%	1900
	11th to 20th	Day	47% 4 3 17% 21% 7%	1858
	21st to end	Day	48% 5% 6% 13% 20% 8%	1570
March	1st to 10th	Day	41% 4 8% 17% 20% 10%	1850
	11th to 20th	Day	46% 6% 11% 13% 17% 6%	1916
	21st to end	Day	43% 6% 10% 19% 20% 3	2247
April	1st to 10th	Day	37% 6% 10% 21% 18% 8%	2160
	11th to 20th	Day	36% 6% 7% 20% 23% 8%	2134
	21st to end	Day	30% 6% 10% 23% 28% 3	2160
May	1st to 10th	Day	32% 7% 11% 22% 23% 5%	2320
	11th to 20th	Day	36% 9% 15% 22% 16% 2	2305
	21st to end	Day	36% 8% 12% 22% 18% 3	2531
June	1st to 10th	Day	41% 10% 15% 19% 13% 1	2340
	11th to 20th	Day	32% 11% 19% 24% 13% 2	2340
	21st to end	Day	34% 13% 19% 22% 10% 3	2340
July	1st to 10th	Day	39% 14% 21% 17% 8% 1	2275
	11th to 20th	Day	40% 16% 19% 15% 9% 1	2271
	21st to end	Day	37% 14% 20% 20% 8%	2371
August	1st to 10th	Day	36% 16% 19% 22% 6%	2136
	11th to 20th	Day	44% 10% 18% 15% 9% 3	2125
	21st to end	Day	43% 12% 15% 17% 9% 3	2376
September	1st to 10th	Day	40% 9% 13% 16% 17% 5%	2095
	11th to 20th	Day	41% 7% 11% 17% 19% 4	1980
	21st to end	Day	34% 5% 11% 20% 22% 8%	1980
October	1st to 10th	Day	31% 7% 10% 18% 25% 10%	1980
	11th to 20th	Day	30% 4 7% 23% 28% 8%	1980
	21st to end	Day	33% 4 6% 16% 30% 11%	1887
November	1st to 10th	Day	34% 3 6% 16% 29% 11%	1672
	11th to 20th	Day	35% 3 6% 18% 27% 11%	1710
	21st to end	Day	38% 5% 8% 17% 24% 8%	1710
December	1st to 10th	Day	45% 5% 8% 16% 20% 6%	1710
	11th to 20th	Day	46% 3 5% 17% 22% 6%	2150
	21st to end	Day	49% 4 7% 17% 20% 3	3124
January	1st to 10th	Night	47% 3 6% 15% 25% 5%	4109
	11th to 20th	Night	41% 4 5% 21% 20% 9%	4015
	21st to end	Night	50% 3 3 14% 25% 5%	4180
February	1st to 10th	Night	44% 4 6% 18% 20% 8%	2280
	11th to 20th	Night	46% 4 4 16% 20% 10%	2219
	21st to end	Night	43% 6% 8% 15% 18% 9%	1884
March	1st to 10th	Night	38% 5% 8% 17% 21% 13%	2227
	11th to 20th	Night	40% 7% 10% 16% 20% 7%	2043
	21st to end	Night	35% 6% 9% 24% 21% 5%	2123
April	1st to 10th	Night	36% 6% 10% 20% 20% 8%	1800
	11th to 20th	Night	33% 5% 8% 20% 24% 10%	1775
	21st to end	Night	30% 6% 10% 25% 22% 7%	1800
May	1st to 10th	Night	28% 7% 11% 23% 25% 5%	1638
	11th to 20th	Night	36% 9% 15% 21% 17% 3	1593
	21st to end	Night	29% 11% 13% 25% 18% 5%	1745
June	1st to 10th	Night	36% 14% 16% 17% 16% 1	1620
	11th to 20th	Night	24% 10% 22% 27% 14% 3	1620
	21st to end	Night	30% 11% 18% 22% 15% 4	1620
July	1st to 10th	Night	34% 15% 20% 19% 10% 2	1575
	11th to 20th	Night	32% 14% 23% 19% 10% 2	1566
	21st to end	Night	31% 12% 26% 20% 10% 1	1700
August	1st to 10th	Night	29% 13% 21% 27% 9%	1778
	11th to 20th	Night	35% 13% 21% 16% 11% 4	1776
	21st to end	Night	41% 12% 12% 20% 11% 4	1980
September	1st to 10th	Night	35% 12% 13% 18% 16% 6%	1845
	11th to 20th	Night	34% 10% 11% 20% 21% 5%	1980
	21st to end	Night	29% 7% 10% 22% 23% 8%	1980
October	1st to 10th	Night	26% 4 10% 21% 26% 13%	1980
	11th to 20th	Night	30% 5% 8% 20% 26% 11%	1980
	21st to end	Night	35% 4 5% 14% 30% 13%	2465
November	1st to 10th	Night	28% 4 9% 18% 27% 14%	2406
	11th to 20th	Night	32% 4 6% 18% 26% 14%	2470
	21st to end	Night	37% 5% 7% 17% 24% 10%	2470
December	1st to 10th	Night	42% 5% 9% 18% 21% 5%	2470
	11th to 20th	Night	42% 3 6% 14% 30% 6%	3044
	21st to end	Night	47% 4 8% 19% 19% 3	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	20% 25% 36% 15% 4	270
	11th to 20th	Day	20% 24% 32% 17% 6% 1	270
	21st to end	Day	24% 26% 35% 12% 3 1	297
February	1st to 10th	Day	24% 23% 33% 16% 3	270
	11th to 20th	Day	34% 22% 30% 12% 1	270
	21st to end	Day	24% 26% 42% 8%	225
March	1st to 10th	Day	22% 22% 35% 16% 4 1	255
	11th to 20th	Day	20% 21% 33% 17% 8% 1	356
	21st to end	Day	21% 18% 31% 20% 9%	462
April	1st to 10th	Day	19% 14% 32% 23% 12% 1	420
	11th to 20th	Day	16% 15% 30% 24% 13% 2	412
	21st to end	Day	11% 13% 29% 31% 13% 2	420
May	1st to 10th	Day	11% 12% 25% 30% 17% 5%	423
	11th to 20th	Day	9% 4 24% 32% 20% 11%	447
	21st to end	Day	11% 5% 19% 30% 21% 15%	485
June	1st to 10th	Day	11% 3 16% 31% 25% 14%	450
	11th to 20th	Day	7% 3 15% 24% 31% 20%	450
	21st to end	Day	7% 5% 13% 23% 34% 18%	450
July	1st to 10th	Day	8% 2 7% 24% 33% 26%	445
	11th to 20th	Day	4 2 6% 21% 34% 32%	444
	21st to end	Day	5% 1 7% 21% 40% 26%	488
August	1st to 10th	Day	7% 2 9% 23% 31% 28%	446
	11th to 20th	Day	8% 2 8% 26% 36% 19%	439
	21st to end	Day	14% 3 7% 25% 33% 19%	495
September	1st to 10th	Day	7% 5% 10% 29% 34% 15%	450
	11th to 20th	Day	11% 5% 13% 26% 34% 11%	450
	21st to end	Day	8% 4 17% 28% 33% 10%	450
October	1st to 10th	Day	12% 5% 22% 29% 24% 7%	450
	11th to 20th	Day	12% 8% 21% 34% 22% 2	450
	21st to end	Day	16% 12% 24% 30% 14% 4	356
November	1st to 10th	Day	18% 9% 29% 28% 10% 6%	270
	11th to 20th	Day	15% 17% 34% 24% 9%	270
	21st to end	Day	13% 19% 34% 23% 10% 1	270
December	1st to 10th	Day	24% 19% 33% 19% 5%	270
	11th to 20th	Day	26% 20% 29% 18% 6% 1	270
	21st to end	Day	24% 23% 29% 20% 5%	297
January	1st to 10th	Night	22% 16% 32% 25% 5%	760
	11th to 20th	Night	20% 18% 29% 25% 7%	760
	21st to end	Night	21% 14% 37% 24% 4	836
February	1st to 10th	Night	20% 14% 32% 30% 4	760
	11th to 20th	Night	26% 13% 32% 25% 4	743
	21st to end	Night	20% 17% 36% 24% 3	628
March	1st to 10th	Night	18% 15% 31% 31% 5%	743
	11th to 20th	Night	17% 14% 35% 23% 10% 1	720
	21st to end	Night	16% 13% 33% 27% 10%	737
April	1st to 10th	Night	12% 11% 34% 28% 14% 1	540
	11th to 20th	Night	14% 12% 30% 28% 15% 1	533
	21st to end	Night	9% 10% 28% 35% 16% 2	540
May	1st to 10th	Night	8% 6% 28% 31% 24% 2	540
	11th to 20th	Night	8% 4 22% 36% 25% 5%	531
	21st to end	Night	8% 1 13% 36% 34% 9%	584
June	1st to 10th	Night	6% 2 10% 40% 37% 6%	540
	11th to 20th	Night	4 1 9% 29% 41% 15%	540
	21st to end	Night	6% 2 7% 29% 45% 11%	540
July	1st to 10th	Night	6% 1 6% 26% 44% 16%	525
	11th to 20th	Night	4 1 7% 21% 44% 23%	522
	21st to end	Night	5% 1 7% 26% 46% 16%	591
August	1st to 10th	Night	5% 1 5% 24% 49% 17%	537
	11th to 20th	Night	9% 1 7% 29% 45% 9%	534
	21st to end	Night	13% 2 7% 26% 39% 14%	594
September	1st to 10th	Night	8% 2 9% 27% 44% 10%	585
	11th to 20th	Night	13% 4 12% 30% 36% 6%	720
	21st to end	Night	10% 2 15% 34% 37% 4	720
October	1st to 10th	Night	9% 3 20% 34% 27% 5%	720
	11th to 20th	Night	12% 5% 24% 33% 23% 3	720
	21st to end	Night	16% 8% 21% 33% 19% 2	792
November	1st to 10th	Night	13% 8% 20% 36% 22% 3	740
	11th to 20th	Night	13% 11% 26% 34% 14% 1	760
	21st to end	Night	15% 12% 29% 32% 12% 1	760
December	1st to 10th	Night	20% 11% 30% 29% 9% 1	760
	11th to 20th	Night	21% 12% 30% 26% 10%	760
	21st to end	Night	24% 13% 28% 29% 6%	836

Page generated at 2024-03-03 05:28:55. Version ac07

Copyright © 2024 Attilla Danko.