Delaware Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Delaware Park clear sky chart from 2005-11-06 to 2024-10-25.

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	13% 9% 3 8% 5% 5% 5% 4 6% 7% 34%	101109
	Night	14% 10% 4 8% 5% 5% 4 4 5% 7% 34%	97669
Transparency	Day	46% 9% 14% 19% 10% 1	100907
	Night	50% 8% 13% 19% 9% 1	97543
Seeing	Day	15% 7% 23% 31% 19% 5%	15297
	Night	19% 8% 27% 29% 15% 2	24712

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	17% 16% 9% 15% 5% 4 4 3 5% 5% 17%	2524
	11th to 20th	Day	14% 20% 7% 14% 10% 8% 4 4 4 5% 10%	2530
	21st to end	Day	24% 15% 7% 10% 6% 5% 5% 4 3 5% 16%	3073
February	1st to 10th	Day	12% 15% 5% 13% 8% 5% 5% 4 6% 6% 20%	1710
	11th to 20th	Day	12% 14% 4 11% 7% 6% 6% 5% 5% 6% 24%	1724
	21st to end	Day	14% 12% 3 11% 7% 5% 6% 4 6% 6% 26%	1570
March	1st to 10th	Day	15% 13% 4 11% 6% 5% 5% 3 5% 5% 29%	3242
	11th to 20th	Day	13% 11% 6% 10% 6% 5% 5% 4 6% 7% 29%	3480
	21st to end	Day	16% 11% 4 11% 6% 5% 5% 4 4 5% 28%	3815
April	1st to 10th	Day	14% 14% 4 8% 5% 4 5% 4 5% 6% 31%	2187
	11th to 20th	Day	16% 10% 3 6% 3 4 4 4 5% 7% 38%	2442
	21st to end	Day	15% 9% 3 8% 5% 4 4 4 5% 7% 36%	2470
May	1st to 10th	Day	14% 8% 3 7% 5% 5% 5% 3 5% 6% 38%	4082
	11th to 20th	Day	17% 9% 3 7% 5% 6% 4 4 5% 7% 33%	4081
	21st to end	Day	10% 6% 2 6% 5% 5% 4 4 6% 7% 46%	4688
June	1st to 10th	Day	10% 7% 3 6% 4 4 5% 5% 7% 8% 42%	2848
	11th to 20th	Day	9% 5% 2 5% 5% 5% 5% 4 7% 10% 44%	2850
	21st to end	Day	10% 6% 2 7% 4 5% 5% 4 7% 8% 41%	2850
July	1st to 10th	Day	10% 5% 2 7% 6% 5% 6% 5% 7% 8% 39%	4616
	11th to 20th	Day	8% 4 1 5% 4 4 5% 5% 7% 9% 48%	4440
	21st to end	Day	7% 5% 2 6% 4 5% 5% 5% 7% 10% 45%	4539
August	1st to 10th	Day	11% 5% 2 6% 5% 5% 5% 5% 6% 8% 40%	4104
	11th to 20th	Day	10% 5% 2 6% 4 5% 5% 5% 8% 9% 40%	4044
	21st to end	Day	9% 6% 2 6% 5% 5% 5% 4 7% 9% 43%	4532
September	1st to 10th	Day	10% 7% 2 8% 4 5% 4 4 7% 8% 41%	2175
	11th to 20th	Day	12% 5% 2 5% 4 4 4 3 5% 8% 47%	2090
	21st to end	Day	16% 7% 2 6% 4 4 6% 4 6% 8% 36%	2090
October	1st to 10th	Day	14% 7% 3 7% 5% 5% 5% 4 5% 7% 40%	1994
	11th to 20th	Day	19% 10% 3 8% 5% 5% 4 4 5% 6% 31%	1900
	21st to end	Day	23% 11% 3 8% 5% 5% 4 4 6% 7% 25%	1900
November	1st to 10th	Day	14% 11% 4 8% 6% 5% 5% 5% 6% 6% 31%	1672
	11th to 20th	Day	13% 13% 5% 9% 6% 5% 6% 4 6% 7% 26%	1634
	21st to end	Day	17% 14% 5% 8% 6% 6% 5% 5% 6% 7% 23%	1520
December	1st to 10th	Day	14% 16% 7% 10% 7% 6% 5% 5% 5% 7% 18%	1520
	11th to 20th	Day	16% 15% 5% 10% 7% 5% 5% 4 6% 6% 21%	1742
	21st to end	Day	23% 26% 7% 9% 5% 4 5% 3 4 5% 10%	2431
January	1st to 10th	Night	18% 14% 6% 11% 5% 5% 4 3 5% 5% 24%	4428
	11th to 20th	Night	12% 17% 7% 16% 8% 9% 5% 4 4 5% 14%	4440
	21st to end	Night	19% 16% 7% 11% 6% 5% 4 3 5% 5% 19%	4582
February	1st to 10th	Night	14% 16% 5% 11% 6% 5% 5% 4 5% 6% 24%	2470
	11th to 20th	Night	13% 13% 5% 10% 5% 5% 5% 4 6% 7% 28%	2338
	21st to end	Night	16% 12% 4 9% 6% 5% 6% 3 6% 7% 26%	1884
March	1st to 10th	Night	13% 13% 4 8% 4 4 3 3 4 7% 38%	3610
	11th to 20th	Night	9% 9% 4 7% 5% 5% 5% 4 6% 7% 40%	3480
	21st to end	Night	16% 10% 4 9% 5% 4 4 3 5% 5% 36%	3817
April	1st to 10th	Night	19% 11% 4 7% 4 3 4 3 6% 6% 34%	2006
	11th to 20th	Night	19% 6% 2 5% 5% 5% 4 3 5% 7% 38%	1687
	21st to end	Night	19% 9% 3 7% 4 3 4 3 5% 7% 36%	1710
May	1st to 10th	Night	15% 9% 3 8% 4 5% 4 4 6% 6% 37%	2813
	11th to 20th	Night	14% 10% 3 8% 5% 5% 4 3 5% 7% 38%	2812
	21st to end	Night	10% 5% 2 4 4 5% 5% 3 5% 8% 50%	2849
June	1st to 10th	Night	13% 6% 2 5% 4 5% 5% 5% 7% 6% 42%	1330
	11th to 20th	Night	11% 5% 3 5% 4 4 5% 5% 6% 9% 44%	1330
	21st to end	Night	8% 6% 2 5% 5% 5% 5% 3 7% 8% 46%	1330
July	1st to 10th	Night	7% 6% 2 7% 4 4 4 4 7% 9% 46%	2335
	11th to 20th	Night	9% 4 1 4 3 3 4 3 6% 8% 53%	2530
	21st to end	Night	6% 4 2 5% 4 5% 6% 5% 7% 9% 47%	3015
August	1st to 10th	Night	10% 6% 2 7% 4 4 4 3 6% 8% 46%	2825
	11th to 20th	Night	11% 6% 3 6% 4 4 4 4 6% 8% 45%	2785
	21st to end	Night	8% 5% 2 6% 4 5% 5% 4 6% 8% 47%	3124
September	1st to 10th	Night	10% 6% 2 6% 4 4 4 4 5% 8% 45%	1981
	11th to 20th	Night	11% 4 1 4 3 4 3 3 5% 6% 53%	2090
	21st to end	Night	16% 7% 3 6% 4 4 4 3 4 6% 40%	2090
October	1st to 10th	Night	15% 6% 3 7% 5% 3 3 3 6% 7% 41%	2185
	11th to 20th	Night	20% 9% 3 7% 5% 4 4 3 5% 6% 34%	2280
	21st to end	Night	22% 10% 3 9% 6% 5% 5% 4 4 7% 27%	2557
November	1st to 10th	Night	14% 10% 2 6% 5% 4 5% 4 6% 7% 37%	2406
	11th to 20th	Night	14% 14% 3 8% 5% 4 5% 4 6% 7% 29%	2544
	21st to end	Night	19% 12% 4 8% 5% 4 4 4 6% 7% 26%	2660
December	1st to 10th	Night	17% 16% 5% 9% 5% 6% 5% 5% 6% 7% 19%	2660
	11th to 20th	Night	15% 13% 6% 11% 6% 5% 5% 5% 7% 7% 20%	3450
	21st to end	Night	27% 21% 7% 10% 5% 4 4 3 4 4 13%	5236

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	68% 11% 11% 9% 1	2525
	11th to 20th	Day	78% 8% 9% 5% 1	2530
	21st to end	Day	71% 8% 14% 6% 2	3073
February	1st to 10th	Day	63% 8% 12% 14% 4	1710
	11th to 20th	Day	59% 6% 13% 15% 6% 1	1733
	21st to end	Day	58% 7% 14% 12% 8% 1	1570
March	1st to 10th	Day	55% 7% 14% 19% 5% 1	3242
	11th to 20th	Day	50% 8% 14% 19% 7% 1	3480
	21st to end	Day	52% 10% 13% 15% 9% 1	3815
April	1st to 10th	Day	51% 8% 12% 19% 9% 1	2187
	11th to 20th	Day	45% 7% 15% 18% 14% 2	2442
	21st to end	Day	46% 7% 14% 18% 12% 2	2470
May	1st to 10th	Day	42% 10% 12% 18% 16% 3	4120
	11th to 20th	Day	44% 13% 13% 19% 9% 2	4085
	21st to end	Day	34% 9% 11% 18% 21% 6%	4702
June	1st to 10th	Day	37% 8% 14% 25% 14% 2	2848
	11th to 20th	Day	33% 8% 14% 26% 17% 2	2850
	21st to end	Day	37% 9% 14% 25% 15% 1	2850
July	1st to 10th	Day	37% 10% 15% 21% 15% 2	4546
	11th to 20th	Day	28% 9% 14% 36% 12% 1	4365
	21st to end	Day	30% 9% 18% 21% 20% 1	4395
August	1st to 10th	Day	38% 10% 15% 23% 13% 1	4091
	11th to 20th	Day	36% 9% 19% 26% 10% 1	4083
	21st to end	Day	33% 8% 15% 30% 13%	4531
September	1st to 10th	Day	37% 10% 16% 24% 11% 1	2175
	11th to 20th	Day	35% 7% 15% 30% 13% 1	2090
	21st to end	Day	43% 8% 16% 23% 9%	2090
October	1st to 10th	Day	44% 8% 12% 25% 10% 2	1994
	11th to 20th	Day	53% 8% 15% 18% 7% 1	1900
	21st to end	Day	59% 7% 13% 17% 4	1900
November	1st to 10th	Day	52% 9% 11% 19% 8% 1	1672
	11th to 20th	Day	56% 8% 16% 12% 8%	1634
	21st to end	Day	62% 7% 16% 12% 3	1520
December	1st to 10th	Day	68% 9% 14% 7% 2	1520
	11th to 20th	Day	63% 9% 14% 11% 2	1738
	21st to end	Day	78% 7% 8% 5% 1	2431
January	1st to 10th	Night	62% 9% 15% 12% 2	4428
	11th to 20th	Night	73% 8% 10% 7% 1	4440
	21st to end	Night	68% 8% 13% 10% 2	4582
February	1st to 10th	Night	62% 7% 11% 14% 5% 1	2470
	11th to 20th	Night	55% 7% 15% 17% 6%	2340
	21st to end	Night	57% 7% 13% 15% 7%	1884
March	1st to 10th	Night	47% 6% 14% 27% 5% 1	3610
	11th to 20th	Night	41% 8% 16% 22% 12% 1	3480
	21st to end	Night	48% 7% 13% 22% 9% 1	3817
April	1st to 10th	Night	51% 6% 10% 20% 12% 2	2006
	11th to 20th	Night	44% 7% 12% 18% 18% 2	1687
	21st to end	Night	48% 6% 10% 18% 14% 4	1710
May	1st to 10th	Night	44% 8% 10% 20% 14% 4	2840
	11th to 20th	Night	43% 9% 12% 21% 13% 3	2813
	21st to end	Night	31% 9% 12% 23% 19% 7%	2856
June	1st to 10th	Night	39% 8% 12% 23% 16% 2	1330
	11th to 20th	Night	35% 8% 12% 23% 19% 3	1330
	21st to end	Night	34% 8% 14% 24% 17% 2	1330
July	1st to 10th	Night	34% 8% 14% 24% 15% 6%	2297
	11th to 20th	Night	27% 7% 14% 33% 17% 1	2482
	21st to end	Night	29% 10% 18% 19% 21% 2	2919
August	1st to 10th	Night	35% 8% 13% 28% 15% 1	2814
	11th to 20th	Night	35% 8% 16% 25% 13% 2	2812
	21st to end	Night	32% 10% 13% 31% 13% 1	3124
September	1st to 10th	Night	35% 9% 15% 25% 15% 1	1981
	11th to 20th	Night	31% 6% 13% 32% 17% 1	2090
	21st to end	Night	43% 8% 11% 27% 10% 1	2090
October	1st to 10th	Night	42% 8% 11% 24% 14% 1	2185
	11th to 20th	Night	51% 7% 14% 19% 8%	2280
	21st to end	Night	58% 8% 12% 15% 7%	2557
November	1st to 10th	Night	47% 8% 15% 21% 9%	2406
	11th to 20th	Night	54% 9% 17% 14% 5% 1	2544
	21st to end	Night	60% 8% 18% 12% 2	2660
December	1st to 10th	Night	66% 9% 15% 8% 3	2660
	11th to 20th	Night	61% 11% 14% 11% 3	3453
	21st to end	Night	76% 8% 10% 6% 1	5236

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	19% 11% 38% 20% 10% 1	269
	11th to 20th	Day	23% 8% 41% 20% 9%	270
	21st to end	Day	21% 7% 35% 28% 7% 1	297
February	1st to 10th	Day	19% 13% 38% 24% 6% 1	270
	11th to 20th	Day	16% 16% 34% 31% 2	270
	21st to end	Day	15% 20% 42% 19% 5%	225
March	1st to 10th	Day	18% 14% 34% 26% 7% 1	340
	11th to 20th	Day	16% 9% 32% 30% 11% 2	460
	21st to end	Day	21% 8% 29% 32% 9% 1	506
April	1st to 10th	Day	17% 8% 32% 31% 10% 2	460
	11th to 20th	Day	23% 9% 25% 28% 10% 5%	452
	21st to end	Day	19% 5% 27% 33% 15% 1	460
May	1st to 10th	Day	15% 6% 24% 37% 15% 3	463
	11th to 20th	Day	16% 3 21% 33% 22% 5%	487
	21st to end	Day	12% 4 15% 34% 27% 9%	529
June	1st to 10th	Day	11% 3 19% 37% 25% 5%	678
	11th to 20th	Day	11% 2 18% 37% 26% 6%	680
	21st to end	Day	13% 4 13% 43% 24% 4	680
July	1st to 10th	Day	8% 4 10% 35% 33% 10%	671
	11th to 20th	Day	11% 3 13% 38% 29% 7%	668
	21st to end	Day	8% 1 11% 40% 31% 8%	579
August	1st to 10th	Day	10% 3 12% 34% 31% 11%	486
	11th to 20th	Day	9% 2 9% 36% 33% 11%	479
	21st to end	Day	11% 5% 13% 29% 34% 7%	539
September	1st to 10th	Day	12% 4 20% 29% 25% 10%	490
	11th to 20th	Day	11% 4 15% 25% 27% 18%	490
	21st to end	Day	18% 7% 20% 26% 20% 10%	490
October	1st to 10th	Day	18% 7% 25% 24% 18% 8%	490
	11th to 20th	Day	21% 12% 29% 25% 11% 2	490
	21st to end	Day	27% 13% 29% 25% 6% 2	387
November	1st to 10th	Day	20% 12% 26% 28% 13% 2	270
	11th to 20th	Day	21% 18% 31% 23% 5% 3	234
	21st to end	Day	25% 10% 39% 22% 3	180
December	1st to 10th	Day	21% 17% 39% 17% 7%	180
	11th to 20th	Day	24% 22% 33% 19% 2	180
	21st to end	Day	26% 14% 35% 22% 2	198
January	1st to 10th	Night	23% 13% 37% 21% 7% 1	950
	11th to 20th	Night	22% 14% 34% 24% 6% 1	950
	21st to end	Night	19% 8% 35% 30% 8%	860
February	1st to 10th	Night	22% 10% 36% 27% 5%	760
	11th to 20th	Night	21% 13% 32% 28% 7%	743
	21st to end	Night	23% 9% 37% 26% 4	628
March	1st to 10th	Night	18% 8% 33% 31% 10%	760
	11th to 20th	Night	16% 9% 35% 32% 8% 1	760
	21st to end	Night	22% 9% 25% 31% 12% 1	836
April	1st to 10th	Night	22% 9% 29% 31% 10% 1	694
	11th to 20th	Night	20% 5% 29% 31% 11% 4	563
	21st to end	Night	21% 7% 22% 34% 15% 1	570
May	1st to 10th	Night	15% 5% 21% 39% 18% 2	570
	11th to 20th	Night	19% 3 19% 35% 22% 3	561
	21st to end	Night	12% 2 15% 36% 29% 6%	491
June	1st to 10th	Night	18% 2 14% 37% 26% 2	380
	11th to 20th	Night	13% 2 15% 40% 27% 3	380
	21st to end	Night	11% 2 14% 41% 29% 2	380
July	1st to 10th	Night	8% 2 9% 43% 33% 5%	440
	11th to 20th	Night	10% 2 11% 35% 36% 6%	552
	21st to end	Night	9% 2 10% 45% 29% 4	624
August	1st to 10th	Night	11% 2 11% 39% 31% 6%	567
	11th to 20th	Night	11% 2 13% 32% 34% 8%	564
	21st to end	Night	13% 2 17% 32% 30% 6%	627
September	1st to 10th	Night	14% 3 20% 30% 23% 10%	707
	11th to 20th	Night	15% 3 15% 29% 28% 10%	760
	21st to end	Night	18% 6% 19% 29% 20% 8%	760
October	1st to 10th	Night	19% 6% 28% 25% 19% 4	760
	11th to 20th	Night	24% 12% 29% 24% 11% 1	760
	21st to end	Night	28% 11% 29% 26% 6%	812
November	1st to 10th	Night	21% 11% 30% 25% 11% 1	740
	11th to 20th	Night	20% 17% 35% 20% 9%	760
	21st to end	Night	26% 14% 34% 21% 5%	760
December	1st to 10th	Night	27% 16% 36% 16% 5%	760
	11th to 20th	Night	22% 16% 38% 20% 4	878
	21st to end	Night	29% 13% 35% 21% 2	1045

Page generated at 2024-10-22 20:20:59. Version ac07

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