Godfrey Road Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Godfrey Road Observatory clear sky chart from 2005-11-06 to 2024-11-30.

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	16% 9% 3 8% 5% 5% 5% 4 5% 7% 32%	101611
	Night	17% 10% 3 8% 5% 5% 4 4 5% 6% 32%	98001
Transparency	Day	29% 47% 6% 11% 6%	105123
	Night	30% 47% 6% 10% 6% 1	102578
Seeing	Day	26% 17% 28% 18% 9% 2	14900
	Night	24% 15% 26% 26% 10% 1	23834

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	13% 11% 4 12% 6% 5% 5% 5% 5% 6% 28%	2517
	11th to 20th	Day	14% 13% 6% 13% 7% 6% 5% 4 4 4 23%	2520
	21st to end	Day	14% 15% 7% 12% 6% 6% 4 4 5% 5% 22%	2772
February	1st to 10th	Day	13% 12% 5% 10% 5% 5% 5% 4 5% 7% 28%	1676
	11th to 20th	Day	10% 12% 6% 12% 7% 5% 5% 5% 6% 6% 27%	1848
	21st to end	Day	16% 11% 4 10% 6% 4 4 4 5% 5% 30%	1570
March	1st to 10th	Day	21% 17% 4 9% 6% 4 4 3 3 3 24%	3116
	11th to 20th	Day	14% 14% 6% 9% 6% 4 5% 4 5% 5% 28%	3272
	21st to end	Day	18% 12% 4 10% 5% 4 4 3 4 5% 30%	4129
April	1st to 10th	Day	20% 13% 3 7% 5% 3 4 3 4 6% 33%	2280
	11th to 20th	Day	17% 10% 3 7% 5% 4 5% 4 5% 6% 34%	2254
	21st to end	Day	22% 10% 4 8% 5% 4 4 3 5% 7% 29%	2468
May	1st to 10th	Day	25% 10% 4 8% 5% 5% 4 3 5% 6% 27%	4106
	11th to 20th	Day	17% 8% 3 8% 6% 5% 5% 4 6% 7% 30%	4382
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 4 6% 8% 40%	4837
June	1st to 10th	Day	19% 8% 3 8% 5% 6% 6% 5% 6% 6% 29%	2660
	11th to 20th	Day	17% 7% 2 6% 5% 4 5% 4 5% 8% 36%	2660
	21st to end	Day	19% 8% 2 8% 6% 6% 5% 4 7% 7% 28%	2660
July	1st to 10th	Day	12% 7% 2 6% 5% 5% 6% 4 7% 10% 35%	4440
	11th to 20th	Day	10% 5% 3 6% 6% 6% 6% 6% 9% 10% 34%	4440
	21st to end	Day	16% 7% 2 7% 4 4 6% 4 6% 8% 35%	4814
August	1st to 10th	Day	15% 7% 2 7% 6% 5% 6% 5% 7% 9% 32%	4329
	11th to 20th	Day	15% 8% 4 8% 5% 5% 6% 5% 7% 8% 29%	3959
	21st to end	Day	9% 5% 2 7% 5% 5% 5% 4 7% 10% 40%	4180
September	1st to 10th	Day	12% 5% 2 6% 5% 3 5% 4 6% 8% 44%	2280
	11th to 20th	Day	13% 5% 2 7% 4 4 3 3 5% 6% 47%	2132
	21st to end	Day	16% 7% 2 6% 4 4 4 4 6% 7% 41%	2090
October	1st to 10th	Day	22% 8% 3 7% 4 4 4 3 4 6% 34%	2072
	11th to 20th	Day	15% 8% 3 8% 5% 5% 4 3 5% 6% 37%	1816
	21st to end	Day	23% 11% 4 7% 4 4 4 4 4 6% 28%	1881
November	1st to 10th	Day	13% 9% 4 7% 4 5% 4 4 6% 6% 38%	1761
	11th to 20th	Day	17% 10% 3 7% 4 5% 5% 4 5% 6% 34%	1800
	21st to end	Day	18% 11% 5% 8% 5% 4 4 3 5% 6% 30%	1692
December	1st to 10th	Day	20% 14% 3 10% 7% 5% 5% 3 4 7% 23%	1520
	11th to 20th	Day	22% 13% 3 8% 3 5% 4 3 4 6% 29%	1906
	21st to end	Day	24% 14% 4 12% 6% 5% 4 3 3 4 22%	2772
January	1st to 10th	Night	15% 10% 4 9% 6% 5% 5% 4 6% 7% 30%	4429
	11th to 20th	Night	11% 14% 5% 15% 8% 6% 5% 4 5% 5% 21%	4440
	21st to end	Night	20% 13% 5% 11% 7% 6% 4 3 5% 4 22%	4884
February	1st to 10th	Night	12% 12% 4 10% 7% 6% 5% 5% 7% 7% 26%	2501
	11th to 20th	Night	10% 9% 5% 11% 7% 7% 5% 4 6% 6% 28%	2218
	21st to end	Night	13% 10% 4 10% 7% 6% 4 4 5% 6% 31%	1884
March	1st to 10th	Night	23% 13% 3 8% 6% 4 4 4 4 5% 26%	3724
	11th to 20th	Night	14% 14% 4 10% 7% 5% 5% 4 4 5% 30%	3685
	21st to end	Night	19% 13% 3 9% 4 3 4 3 4 5% 32%	3498
April	1st to 10th	Night	19% 10% 2 8% 5% 5% 4 3 5% 6% 32%	1900
	11th to 20th	Night	19% 11% 3 7% 4 4 4 3 5% 5% 34%	1875
	21st to end	Night	21% 10% 3 6% 4 4 4 3 5% 7% 33%	1710
May	1st to 10th	Night	26% 11% 3 8% 4 4 4 3 4 6% 26%	2834
	11th to 20th	Night	19% 10% 4 10% 5% 6% 5% 4 5% 5% 28%	2540
	21st to end	Night	15% 5% 2 6% 4 4 5% 4 6% 9% 39%	2738
June	1st to 10th	Night	20% 5% 2 7% 7% 5% 5% 4 6% 8% 32%	1520
	11th to 20th	Night	19% 7% 3 5% 4 4 5% 5% 5% 7% 38%	1520
	21st to end	Night	17% 7% 3 8% 4 5% 5% 4 6% 7% 35%	1520
July	1st to 10th	Night	12% 5% 2 6% 6% 6% 6% 5% 7% 8% 37%	2520
	11th to 20th	Night	14% 6% 2 6% 4 5% 4 4 6% 8% 41%	2520
	21st to end	Night	15% 7% 3 5% 4 4 4 4 6% 7% 40%	2739
August	1st to 10th	Night	19% 9% 3 9% 5% 4 4 4 4 6% 34%	2569
	11th to 20th	Night	15% 8% 3 6% 5% 4 5% 4 6% 9% 37%	2865
	21st to end	Night	9% 5% 2 5% 4 3 5% 4 7% 10% 45%	3476
September	1st to 10th	Night	13% 6% 2 5% 3 3 5% 4 5% 7% 48%	1900
	11th to 20th	Night	13% 5% 2 6% 3 3 3 3 5% 7% 49%	2047
	21st to end	Night	15% 6% 2 5% 5% 4 4 3 6% 6% 44%	2090
October	1st to 10th	Night	21% 7% 3 7% 5% 4 3 4 6% 6% 34%	2104
	11th to 20th	Night	16% 9% 3 7% 5% 5% 5% 4 5% 7% 35%	2362
	21st to end	Night	22% 10% 3 7% 5% 4 4 3 6% 6% 30%	2717
November	1st to 10th	Night	14% 8% 3 8% 5% 4 5% 3 6% 6% 37%	2537
	11th to 20th	Night	16% 9% 3 6% 5% 5% 5% 4 6% 7% 35%	2600
	21st to end	Night	17% 11% 4 8% 6% 5% 4 3 6% 7% 31%	2703
December	1st to 10th	Night	18% 14% 5% 11% 6% 5% 5% 4 5% 6% 21%	2660
	11th to 20th	Night	20% 11% 4 9% 6% 4 4 3 4 7% 27%	3288
	21st to end	Night	24% 13% 6% 12% 5% 4 4 3 4 4 21%	4884

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	35% 42% 6% 13% 3	2518
	11th to 20th	Day	44% 40% 4 10% 2 1	2520
	21st to end	Day	43% 41% 5% 7% 3	2772
February	1st to 10th	Day	20% 66% 5% 6% 3	1676
	11th to 20th	Day	21% 64% 3 6% 5%	1857
	21st to end	Day	17% 66% 5% 6% 6% 1	1570
March	1st to 10th	Day	43% 41% 4 5% 7% 1	3119
	11th to 20th	Day	35% 43% 6% 7% 7% 2	3272
	21st to end	Day	37% 39% 3 7% 12% 1	4129
April	1st to 10th	Day	21% 64% 2 7% 3 1	2280
	11th to 20th	Day	18% 66% 3 7% 5% 1	2254
	21st to end	Day	20% 66% 3 6% 5%	2468
May	1st to 10th	Day	38% 43% 6% 11% 3	4120
	11th to 20th	Day	33% 44% 11% 8% 3	4386
	21st to end	Day	24% 43% 8% 18% 8%	4837
June	1st to 10th	Day	18% 66% 4 6% 6%	2660
	11th to 20th	Day	17% 65% 3 8% 6% 1	2660
	21st to end	Day	19% 64% 4 8% 5% 1	2660
July	1st to 10th	Day	27% 36% 10% 16% 10%	4370
	11th to 20th	Day	29% 36% 11% 19% 5%	4365
	21st to end	Day	32% 36% 8% 15% 9%	4661
August	1st to 10th	Day	34% 37% 9% 14% 6%	4315
	11th to 20th	Day	36% 37% 10% 15% 2	3998
	21st to end	Day	25% 36% 11% 17% 9% 1	4180
September	1st to 10th	Day	13% 61% 5% 14% 6% 1	2280
	11th to 20th	Day	16% 59% 4 11% 8% 1	2132
	21st to end	Day	16% 61% 4 13% 5% 1	2090
October	1st to 10th	Day	33% 36% 4 16% 10% 1	3449
	11th to 20th	Day	28% 36% 8% 16% 12%	2993
	21st to end	Day	26% 36% 6% 23% 8% 1	3081
November	1st to 10th	Day	22% 57% 7% 9% 5%	1761
	11th to 20th	Day	23% 57% 5% 6% 10%	1800
	21st to end	Day	24% 57% 9% 6% 3	1692
December	1st to 10th	Day	26% 60% 6% 6% 2	1520
	11th to 20th	Day	32% 49% 5% 9% 6% 1	1906
	21st to end	Day	44% 38% 4 8% 6%	2772
January	1st to 10th	Night	34% 39% 12% 11% 4	4429
	11th to 20th	Night	42% 40% 7% 7% 4 1	4440
	21st to end	Night	45% 41% 5% 6% 2	4884
February	1st to 10th	Night	21% 65% 4 6% 3 1	2501
	11th to 20th	Night	20% 65% 4 6% 6%	2220
	21st to end	Night	17% 65% 5% 7% 4 1	1884
March	1st to 10th	Night	38% 41% 6% 7% 6% 1	3734
	11th to 20th	Night	35% 43% 4 8% 8% 1	3686
	21st to end	Night	38% 40% 3 6% 11% 2	3498
April	1st to 10th	Night	20% 65% 3 6% 6%	1900
	11th to 20th	Night	19% 65% 3 7% 5%	1875
	21st to end	Night	19% 66% 2 5% 6% 1	1710
May	1st to 10th	Night	37% 44% 7% 8% 3	2840
	11th to 20th	Night	37% 43% 8% 8% 3	2541
	21st to end	Night	24% 43% 11% 12% 9% 1	2739
June	1st to 10th	Night	16% 66% 3 8% 6%	1520
	11th to 20th	Night	16% 65% 6% 7% 6%	1520
	21st to end	Night	17% 64% 4 11% 4 1	1520
July	1st to 10th	Night	30% 36% 10% 14% 9%	2480
	11th to 20th	Night	31% 36% 7% 18% 7%	2472
	21st to end	Night	32% 36% 6% 19% 7%	2651
August	1st to 10th	Night	38% 37% 6% 13% 6%	2559
	11th to 20th	Night	34% 39% 11% 11% 5%	2892
	21st to end	Night	22% 36% 14% 19% 9%	3476
September	1st to 10th	Night	13% 60% 6% 14% 7%	1900
	11th to 20th	Night	14% 61% 5% 11% 7% 1	2047
	21st to end	Night	15% 60% 5% 12% 7% 1	2090
October	1st to 10th	Night	34% 36% 7% 16% 5% 1	3507
	11th to 20th	Night	28% 37% 7% 14% 13% 1	3924
	21st to end	Night	29% 37% 7% 20% 7%	4467
November	1st to 10th	Night	22% 57% 6% 11% 4 1	2537
	11th to 20th	Night	22% 57% 5% 8% 8%	2600
	21st to end	Night	24% 58% 6% 8% 4	2703
December	1st to 10th	Night	26% 61% 5% 6% 2	2660
	11th to 20th	Night	33% 49% 7% 5% 5%	3288
	21st to end	Night	45% 39% 4 10% 3	4884

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	31% 18% 33% 13% 4 1	180
	11th to 20th	Day	37% 26% 24% 9% 3 1	180
	21st to end	Day	23% 28% 29% 13% 6% 1	198
February	1st to 10th	Day	34% 31% 26% 6% 3	271
	11th to 20th	Day	31% 26% 30% 12% 2	456
	21st to end	Day	31% 24% 25% 15% 4	382
March	1st to 10th	Day	28% 20% 34% 14% 4	460
	11th to 20th	Day	33% 24% 27% 11% 4 1	460
	21st to end	Day	32% 22% 24% 12% 7% 3	506
April	1st to 10th	Day	37% 20% 23% 12% 6% 2	460
	11th to 20th	Day	35% 24% 21% 13% 7% 1	452
	21st to end	Day	34% 21% 25% 11% 6% 2	460
May	1st to 10th	Day	33% 22% 24% 13% 6% 2	463
	11th to 20th	Day	23% 18% 31% 18% 7% 2	487
	21st to end	Day	20% 16% 31% 22% 9% 2	529
June	1st to 10th	Day	22% 15% 34% 20% 8% 1	490
	11th to 20th	Day	20% 16% 32% 19% 10% 2	490
	21st to end	Day	23% 17% 30% 19% 10% 2	490
July	1st to 10th	Day	18% 11% 33% 24% 12% 3	485
	11th to 20th	Day	14% 9% 37% 25% 13% 2	484
	21st to end	Day	15% 11% 34% 26% 12% 2	532
August	1st to 10th	Day	14% 13% 29% 25% 17% 2	486
	11th to 20th	Day	19% 11% 25% 24% 15% 7%	479
	21st to end	Day	14% 12% 28% 25% 15% 6%	539
September	1st to 10th	Day	16% 11% 27% 23% 15% 7%	490
	11th to 20th	Day	18% 11% 25% 18% 18% 9%	490
	21st to end	Day	19% 12% 29% 22% 12% 7%	490
October	1st to 10th	Day	26% 13% 24% 20% 13% 4	490
	11th to 20th	Day	26% 15% 25% 20% 12% 2	445
	21st to end	Day	39% 15% 24% 15% 7%	429
November	1st to 10th	Day	27% 17% 23% 21% 12% 1	395
	11th to 20th	Day	30% 21% 24% 18% 7% 1	400
	21st to end	Day	36% 17% 26% 16% 5%	294
December	1st to 10th	Day	32% 21% 29% 12% 6% 1	180
	11th to 20th	Day	36% 22% 28% 11% 3	180
	21st to end	Day	35% 19% 30% 13% 3 1	198
January	1st to 10th	Night	23% 21% 31% 22% 4	760
	11th to 20th	Night	26% 20% 28% 22% 3	760
	21st to end	Night	20% 20% 35% 20% 4	836
February	1st to 10th	Night	24% 18% 33% 22% 3	760
	11th to 20th	Night	24% 22% 31% 20% 3	743
	21st to end	Night	25% 19% 30% 23% 4	628
March	1st to 10th	Night	28% 15% 30% 23% 3	760
	11th to 20th	Night	26% 21% 25% 22% 6%	760
	21st to end	Night	28% 18% 27% 19% 8% 1	836
April	1st to 10th	Night	28% 19% 25% 23% 4	760
	11th to 20th	Night	25% 21% 25% 21% 7% 1	751
	21st to end	Night	26% 19% 27% 23% 5%	570
May	1st to 10th	Night	30% 14% 26% 23% 7%	570
	11th to 20th	Night	19% 13% 30% 29% 8%	406
	21st to end	Night	19% 9% 28% 32% 12% 1	411
June	1st to 10th	Night	22% 8% 24% 35% 10% 1	380
	11th to 20th	Night	20% 9% 21% 36% 14%	380
	21st to end	Night	21% 6% 22% 39% 12%	380
July	1st to 10th	Night	17% 4 19% 43% 16% 1	370
	11th to 20th	Night	17% 3 21% 37% 20% 2	368
	21st to end	Night	14% 5% 18% 43% 19% 1	416
August	1st to 10th	Night	19% 3 13% 43% 22%	415
	11th to 20th	Night	17% 6% 22% 34% 19% 2	606
	21st to end	Night	18% 6% 16% 35% 22% 2	836
September	1st to 10th	Night	17% 7% 24% 31% 20% 2	760
	11th to 20th	Night	17% 9% 20% 27% 24% 4	760
	21st to end	Night	19% 10% 22% 29% 17% 2	760
October	1st to 10th	Night	25% 11% 19% 28% 15% 2	760
	11th to 20th	Night	24% 13% 23% 27% 13% 1	760
	21st to end	Night	30% 13% 26% 23% 7%	836
November	1st to 10th	Night	22% 17% 24% 27% 9%	780
	11th to 20th	Night	25% 18% 25% 23% 8% 1	800
	21st to end	Night	27% 18% 27% 21% 6% 1	800
December	1st to 10th	Night	27% 21% 29% 20% 4	760
	11th to 20th	Night	29% 18% 30% 20% 3	760
	21st to end	Night	30% 20% 28% 18% 3	836

Page generated at 2024-11-27 17:30:49. Version ac07

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