Draper Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Draper Park clear sky chart from 2005-11-06 to 2024-11-04.

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	17% 7% 2 6% 4 4 4 4 6% 7% 39%	101292
	Night	18% 7% 2 6% 4 4 4 3 5% 6% 41%	97738
Transparency	Day	42% 6% 12% 22% 15% 2	104837
	Night	42% 6% 12% 23% 16% 2	102282
Seeing	Day	20% 12% 30% 24% 11% 3	14997
	Night	20% 11% 31% 28% 10% 1	24105

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	16% 7% 2 6% 3 3 3 3 5% 5% 47%	2517
	11th to 20th	Day	16% 9% 3 7% 5% 5% 5% 3 4 6% 36%	2520
	21st to end	Day	22% 10% 4 7% 5% 3 4 3 5% 5% 32%	2977
February	1st to 10th	Day	18% 8% 2 6% 4 5% 4 3 6% 6% 38%	1726
	11th to 20th	Day	15% 7% 2 6% 5% 4 4 3 4 5% 44%	1848
	21st to end	Day	19% 9% 3 5% 4 4 4 3 6% 5% 39%	1570
March	1st to 10th	Day	26% 9% 3 5% 3 3 3 3 4 5% 35%	3116
	11th to 20th	Day	10% 5% 2 7% 5% 6% 5% 4 6% 8% 43%	3312
	21st to end	Day	21% 7% 2 6% 3 3 3 3 4 5% 43%	4154
April	1st to 10th	Day	19% 9% 2 6% 4 3 4 3 5% 6% 40%	2280
	11th to 20th	Day	18% 6% 2 5% 4 3 3 3 5% 7% 41%	2254
	21st to end	Day	19% 6% 2 5% 4 4 4 3 6% 7% 40%	2318
May	1st to 10th	Day	28% 9% 2 5% 3 3 3 3 5% 8% 30%	4106
	11th to 20th	Day	23% 8% 3 7% 5% 4 4 4 5% 7% 31%	4357
	21st to end	Day	14% 5% 1 5% 4 4 4 4 6% 8% 44%	4837
June	1st to 10th	Day	17% 6% 2 5% 5% 4 4 4 7% 9% 37%	2660
	11th to 20th	Day	15% 7% 2 6% 4 5% 5% 4 6% 8% 37%	2660
	21st to end	Day	12% 7% 2 7% 5% 4 5% 5% 7% 8% 39%	2660
July	1st to 10th	Day	10% 6% 2 8% 5% 5% 6% 5% 8% 10% 35%	4440
	11th to 20th	Day	12% 6% 2 6% 5% 4 5% 5% 7% 10% 37%	4440
	21st to end	Day	15% 8% 3 8% 5% 5% 6% 5% 6% 8% 31%	4814
August	1st to 10th	Day	21% 7% 2 6% 5% 5% 6% 4 6% 8% 31%	4190
	11th to 20th	Day	14% 6% 2 6% 4 4 5% 4 7% 8% 41%	3730
	21st to end	Day	9% 5% 2 6% 4 5% 4 3 7% 10% 44%	4180
September	1st to 10th	Day	13% 6% 2 7% 4 4 5% 3 6% 6% 44%	2280
	11th to 20th	Day	14% 4 2 5% 3 3 4 3 5% 7% 49%	2190
	21st to end	Day	17% 6% 2 8% 5% 4 4 4 5% 6% 40%	2090
October	1st to 10th	Day	21% 6% 2 5% 3 3 4 3 5% 6% 42%	1995
	11th to 20th	Day	15% 6% 2 5% 4 3 3 3 5% 5% 49%	1900
	21st to end	Day	22% 5% 1 4 3 4 4 4 4 6% 42%	1926
November	1st to 10th	Day	15% 6% 2 5% 3 2 3 3 4 5% 51%	1698
	11th to 20th	Day	20% 6% 2 3 3 2 3 3 5% 6% 46%	1710
	21st to end	Day	15% 6% 2 5% 4 4 3 4 5% 7% 44%	1639
December	1st to 10th	Day	20% 7% 2 6% 5% 3 4 3 6% 7% 37%	1520
	11th to 20th	Day	23% 6% 2 4 3 2 3 3 4 6% 44%	1906
	21st to end	Day	19% 9% 3 8% 5% 5% 4 4 5% 6% 32%	2772
January	1st to 10th	Night	17% 7% 2 5% 3 3 3 3 5% 6% 47%	4429
	11th to 20th	Night	17% 8% 3 7% 4 4 4 3 5% 5% 42%	4440
	21st to end	Night	25% 11% 2 5% 3 3 4 3 4 5% 34%	4678
February	1st to 10th	Night	17% 9% 3 6% 4 3 4 3 4 6% 42%	2452
	11th to 20th	Night	17% 8% 2 6% 4 3 4 4 6% 5% 41%	2218
	21st to end	Night	19% 8% 3 6% 4 4 3 4 5% 5% 41%	1884
March	1st to 10th	Night	25% 9% 3 5% 3 3 3 3 4 6% 35%	3724
	11th to 20th	Night	12% 6% 2 6% 4 4 4 3 6% 6% 46%	3644
	21st to end	Night	20% 9% 3 5% 4 3 3 3 4 5% 41%	3477
April	1st to 10th	Night	18% 8% 2 6% 5% 4 4 4 5% 7% 37%	1900
	11th to 20th	Night	20% 7% 2 5% 3 3 4 4 6% 7% 40%	1875
	21st to end	Night	19% 7% 2 6% 3 4 3 3 4 6% 43%	1862
May	1st to 10th	Night	26% 9% 3 7% 4 4 4 3 4 7% 29%	2834
	11th to 20th	Night	24% 9% 3 7% 5% 4 4 3 4 6% 32%	2564
	21st to end	Night	17% 7% 2 5% 3 4 3 3 5% 8% 42%	2738
June	1st to 10th	Night	17% 6% 2 5% 4 4 5% 4 5% 7% 41%	1520
	11th to 20th	Night	13% 7% 2 6% 3 4 4 3 7% 8% 42%	1520
	21st to end	Night	11% 5% 2 5% 5% 3 6% 5% 7% 9% 43%	1520
July	1st to 10th	Night	10% 6% 3 7% 6% 6% 5% 5% 7% 9% 36%	2520
	11th to 20th	Night	15% 6% 2 6% 5% 5% 4 4 7% 9% 37%	2520
	21st to end	Night	19% 7% 3 5% 4 4 5% 4 6% 8% 36%	2739
August	1st to 10th	Night	24% 6% 2 7% 5% 4 4 5% 5% 7% 31%	2703
	11th to 20th	Night	14% 7% 2 7% 5% 4 4 4 6% 7% 39%	3097
	21st to end	Night	10% 5% 2 5% 4 3 4 3 5% 8% 52%	3476
September	1st to 10th	Night	15% 5% 2 5% 4 5% 4 3 6% 6% 45%	1900
	11th to 20th	Night	15% 5% 2 4 3 2 3 3 4 6% 53%	1989
	21st to end	Night	18% 6% 2 6% 3 3 3 3 5% 6% 45%	2090
October	1st to 10th	Night	19% 8% 3 7% 4 3 3 2 4 6% 41%	2180
	11th to 20th	Night	16% 5% 2 5% 3 4 3 3 5% 6% 50%	2280
	21st to end	Night	22% 7% 2 5% 2 3 3 3 4 6% 43%	2670
November	1st to 10th	Night	13% 5% 2 5% 4 3 4 3 5% 6% 50%	2453
	11th to 20th	Night	20% 6% 2 4 3 2 3 3 4 5% 47%	2470
	21st to end	Night	15% 6% 2 4 4 4 4 4 4 7% 47%	2540
December	1st to 10th	Night	20% 7% 2 5% 4 4 3 3 5% 7% 40%	2660
	11th to 20th	Night	20% 7% 2 4 4 4 3 3 5% 5% 41%	3288
	21st to end	Night	21% 9% 3 6% 4 4 4 4 5% 5% 36%	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	37% 4 11% 32% 13% 3	2518
	11th to 20th	Day	47% 6% 12% 23% 11% 2	2520
	21st to end	Day	53% 6% 9% 21% 9% 2	2977
February	1st to 10th	Day	45% 5% 13% 22% 13% 2	1726
	11th to 20th	Day	42% 5% 10% 25% 17% 2	1857
	21st to end	Day	45% 5% 12% 21% 14% 3	1570
March	1st to 10th	Day	49% 5% 13% 22% 10% 2	3119
	11th to 20th	Day	32% 10% 14% 30% 12% 2	3312
	21st to end	Day	43% 5% 8% 16% 23% 5%	4154
April	1st to 10th	Day	44% 6% 11% 19% 16% 5%	2280
	11th to 20th	Day	42% 5% 13% 20% 18% 3	2254
	21st to end	Day	42% 7% 11% 21% 16% 4	2318
May	1st to 10th	Day	51% 8% 14% 14% 12% 1	4120
	11th to 20th	Day	50% 9% 14% 19% 8% 2	4361
	21st to end	Day	34% 8% 13% 26% 18% 2	4837
June	1st to 10th	Day	40% 9% 14% 21% 15% 1	2660
	11th to 20th	Day	43% 8% 13% 23% 12% 2	2660
	21st to end	Day	40% 8% 15% 21% 16% 1	2660
July	1st to 10th	Day	42% 8% 12% 21% 15% 1	4370
	11th to 20th	Day	40% 6% 18% 22% 13% 2	4365
	21st to end	Day	49% 7% 12% 16% 14% 2	4661
August	1st to 10th	Day	49% 7% 15% 21% 9%	4176
	11th to 20th	Day	40% 4 14% 30% 11% 1	3766
	21st to end	Day	36% 5% 10% 28% 20% 2	4180
September	1st to 10th	Day	39% 7% 12% 22% 18% 2	2280
	11th to 20th	Day	33% 6% 11% 24% 24% 2	2190
	21st to end	Day	44% 6% 10% 19% 18% 3	2090
October	1st to 10th	Day	39% 4 9% 19% 23% 6%	3320
	11th to 20th	Day	27% 4 10% 23% 32% 4	3140
	21st to end	Day	29% 4 14% 25% 25% 4	3151
November	1st to 10th	Day	35% 5% 11% 24% 22% 3	1698
	11th to 20th	Day	39% 4 10% 23% 20% 3	1710
	21st to end	Day	39% 5% 14% 28% 12% 2	1639
December	1st to 10th	Day	45% 6% 15% 20% 13% 1	1520
	11th to 20th	Day	41% 4 15% 24% 14% 2	1906
	21st to end	Day	50% 9% 10% 23% 8%	2772
January	1st to 10th	Night	39% 4 12% 30% 12% 4	4429
	11th to 20th	Night	43% 5% 13% 25% 12% 2	4440
	21st to end	Night	51% 6% 9% 21% 11% 2	4678
February	1st to 10th	Night	44% 5% 12% 24% 13% 2	2452
	11th to 20th	Night	44% 6% 9% 19% 17% 5%	2220
	21st to end	Night	43% 5% 8% 23% 16% 4	1884
March	1st to 10th	Night	50% 5% 10% 21% 11% 3	3734
	11th to 20th	Night	34% 8% 15% 25% 15% 2	3645
	21st to end	Night	44% 5% 7% 15% 23% 5%	3477
April	1st to 10th	Night	45% 6% 11% 20% 15% 3	1900
	11th to 20th	Night	43% 7% 9% 20% 20% 2	1875
	21st to end	Night	43% 6% 8% 21% 18% 4	1862
May	1st to 10th	Night	54% 8% 11% 16% 10% 1	2840
	11th to 20th	Night	52% 8% 14% 14% 10% 1	2565
	21st to end	Night	39% 7% 15% 23% 13% 3	2739
June	1st to 10th	Night	41% 7% 10% 22% 19% 2	1520
	11th to 20th	Night	38% 7% 16% 27% 11% 1	1520
	21st to end	Night	36% 9% 15% 24% 15% 1	1520
July	1st to 10th	Night	44% 8% 14% 18% 14% 2	2480
	11th to 20th	Night	44% 7% 14% 23% 12% 1	2472
	21st to end	Night	46% 5% 15% 15% 18% 2	2651
August	1st to 10th	Night	52% 7% 15% 16% 10% 1	2693
	11th to 20th	Night	43% 6% 12% 28% 10% 1	3127
	21st to end	Night	32% 5% 11% 33% 18% 1	3476
September	1st to 10th	Night	40% 7% 11% 24% 18% 1	1900
	11th to 20th	Night	33% 5% 11% 23% 24% 3	1989
	21st to end	Night	41% 5% 9% 22% 21% 2	2090
October	1st to 10th	Night	40% 4 11% 23% 20% 2	3635
	11th to 20th	Night	25% 4 10% 28% 30% 4	3779
	21st to end	Night	33% 3 12% 29% 22% 2	4395
November	1st to 10th	Night	35% 6% 11% 23% 21% 4	2453
	11th to 20th	Night	40% 4 9% 24% 19% 5%	2470
	21st to end	Night	37% 5% 13% 29% 14% 2	2540
December	1st to 10th	Night	45% 6% 12% 22% 14% 1	2660
	11th to 20th	Night	43% 5% 13% 19% 17% 3	3288
	21st to end	Night	46% 8% 13% 22% 11% 1	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	21% 25% 32% 17% 4 1	180
	11th to 20th	Day	24% 24% 37% 12% 2 1	180
	21st to end	Day	19% 19% 41% 14% 5% 2	258
February	1st to 10th	Day	27% 16% 37% 18% 2	286
	11th to 20th	Day	23% 19% 38% 18% 2	456
	21st to end	Day	25% 18% 34% 19% 4	382
March	1st to 10th	Day	20% 21% 33% 21% 4	460
	11th to 20th	Day	18% 20% 37% 19% 5% 1	460
	21st to end	Day	25% 20% 31% 18% 5% 1	506
April	1st to 10th	Day	24% 19% 32% 17% 7% 1	460
	11th to 20th	Day	21% 16% 34% 18% 9% 2	452
	21st to end	Day	25% 15% 34% 18% 7% 1	460
May	1st to 10th	Day	30% 13% 29% 18% 7% 2	463
	11th to 20th	Day	21% 10% 33% 23% 11% 2	487
	21st to end	Day	18% 9% 24% 29% 16% 4	529
June	1st to 10th	Day	17% 9% 27% 29% 15% 4	490
	11th to 20th	Day	16% 10% 28% 32% 12% 2	490
	21st to end	Day	16% 8% 29% 26% 18% 3	490
July	1st to 10th	Day	14% 3 24% 35% 19% 6%	485
	11th to 20th	Day	11% 4 23% 35% 23% 4	484
	21st to end	Day	15% 6% 23% 34% 19% 2	532
August	1st to 10th	Day	13% 5% 20% 36% 18% 8%	486
	11th to 20th	Day	15% 4 21% 34% 21% 4	479
	21st to end	Day	12% 5% 25% 32% 17% 8%	539
September	1st to 10th	Day	18% 6% 27% 23% 19% 7%	490
	11th to 20th	Day	15% 5% 27% 26% 16% 11%	490
	21st to end	Day	21% 9% 28% 26% 12% 4	490
October	1st to 10th	Day	26% 8% 24% 21% 16% 4	490
	11th to 20th	Day	18% 13% 29% 24% 13% 2	490
	21st to end	Day	23% 13% 30% 23% 10% 2	452
November	1st to 10th	Day	17% 13% 30% 26% 11% 3	374
	11th to 20th	Day	21% 16% 34% 22% 6% 1	370
	21st to end	Day	16% 19% 32% 25% 6% 1	299
December	1st to 10th	Day	22% 22% 33% 17% 4 2	180
	11th to 20th	Day	28% 21% 36% 12% 3	180
	21st to end	Day	28% 14% 36% 14% 8% 1	198
January	1st to 10th	Night	20% 14% 43% 20% 4	760
	11th to 20th	Night	23% 16% 34% 23% 4	760
	21st to end	Night	20% 15% 40% 22% 2	836
February	1st to 10th	Night	23% 12% 37% 26% 2	760
	11th to 20th	Night	22% 17% 40% 20% 1	743
	21st to end	Night	25% 15% 35% 21% 4	628
March	1st to 10th	Night	23% 15% 36% 22% 5%	760
	11th to 20th	Night	22% 14% 38% 21% 4 1	760
	21st to end	Night	22% 15% 36% 22% 5%	836
April	1st to 10th	Night	21% 15% 35% 23% 5%	760
	11th to 20th	Night	21% 13% 33% 26% 6%	751
	21st to end	Night	22% 11% 33% 27% 6% 1	722
May	1st to 10th	Night	24% 11% 33% 25% 7% 1	570
	11th to 20th	Night	21% 11% 33% 28% 8%	417
	21st to end	Night	20% 6% 18% 41% 14% 1	411
June	1st to 10th	Night	19% 5% 26% 35% 13% 1	380
	11th to 20th	Night	14% 4 26% 39% 17%	380
	21st to end	Night	10% 3 24% 49% 13% 1	380
July	1st to 10th	Night	11% 3 23% 43% 20%	370
	11th to 20th	Night	12% 4 19% 43% 21% 2	368
	21st to end	Night	15% 4 18% 45% 17% 1	416
August	1st to 10th	Night	14% 2 19% 44% 20% 1	484
	11th to 20th	Night	15% 4 17% 36% 25% 2	750
	21st to end	Night	15% 4 17% 37% 24% 2	836
September	1st to 10th	Night	16% 4 24% 34% 19% 2	760
	11th to 20th	Night	17% 4 22% 33% 19% 4	760
	21st to end	Night	21% 5% 23% 33% 16% 2	760
October	1st to 10th	Night	23% 9% 27% 24% 14% 2	760
	11th to 20th	Night	17% 11% 29% 31% 11% 1	760
	21st to end	Night	25% 11% 32% 24% 8%	836
November	1st to 10th	Night	15% 10% 35% 26% 12% 1	755
	11th to 20th	Night	23% 13% 32% 24% 8% 1	760
	21st to end	Night	19% 13% 35% 25% 7% 1	760
December	1st to 10th	Night	24% 14% 36% 20% 5% 1	760
	11th to 20th	Night	23% 14% 35% 24% 4	760
	21st to end	Night	25% 13% 36% 24% 3	836

Page generated at 2024-11-01 22:47:41. Version ac07

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