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 2024-02-25.

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	14% 9% 4 7% 6% 4 5% 5% 6% 7% 33%	78240
	Night	15% 10% 4 7% 6% 4 5% 5% 5% 7% 32%	81077
Transparency	Day	49% 8% 14% 19% 9% 1	77948
	Night	52% 8% 13% 17% 9% 1	80891
Seeing	Day	16% 7% 23% 31% 19% 5%	14282
	Night	19% 8% 27% 29% 14% 2	23931

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% 15% 9% 14% 6% 3 5% 4 5% 5% 18%	2524
	11th to 20th	Day	14% 19% 8% 13% 11% 6% 5% 4 4 5% 10%	2530
	21st to end	Day	24% 15% 7% 10% 7% 4 5% 4 3 5% 16%	3073
February	1st to 10th	Day	12% 15% 5% 11% 10% 4 6% 4 6% 7% 20%	1710
	11th to 20th	Day	12% 12% 5% 9% 9% 5% 6% 6% 5% 7% 24%	1724
	21st to end	Day	15% 11% 4 9% 9% 4 6% 5% 5% 7% 25%	1520
March	1st to 10th	Day	13% 10% 5% 10% 8% 5% 6% 5% 6% 6% 27%	1866
	11th to 20th	Day	12% 10% 5% 9% 7% 4 6% 5% 5% 5% 32%	1980
	21st to end	Day	16% 11% 5% 9% 8% 3 5% 5% 5% 5% 29%	2178
April	1st to 10th	Day	14% 13% 5% 8% 6% 3 5% 5% 5% 7% 31%	2071
	11th to 20th	Day	15% 9% 4 6% 4 3 5% 5% 5% 7% 38%	2312
	21st to end	Day	16% 8% 3 7% 6% 3 4 4 5% 8% 35%	2340
May	1st to 10th	Day	15% 8% 3 6% 7% 3 5% 5% 5% 7% 37%	2340
	11th to 20th	Day	16% 7% 3 6% 6% 4 4 4 5% 6% 39%	2301
	21st to end	Day	11% 6% 2 5% 6% 4 4 5% 6% 9% 42%	2646
June	1st to 10th	Day	10% 6% 3 5% 4 3 5% 6% 7% 8% 43%	2698
	11th to 20th	Day	10% 5% 2 4 5% 3 5% 5% 6% 10% 45%	2700
	21st to end	Day	10% 5% 3 6% 5% 3 5% 5% 7% 9% 43%	2700
July	1st to 10th	Day	7% 4 2 4 5% 3 4 5% 6% 9% 51%	2626
	11th to 20th	Day	9% 5% 2 5% 4 3 6% 7% 7% 9% 44%	2520
	21st to end	Day	8% 5% 2 5% 5% 3 6% 6% 7% 10% 44%	2592
August	1st to 10th	Day	9% 5% 2 6% 5% 3 6% 6% 6% 9% 42%	2327
	11th to 20th	Day	8% 4 2 6% 5% 3 5% 6% 7% 9% 44%	2303
	21st to end	Day	11% 6% 2 5% 5% 4 5% 4 6% 8% 45%	2574
September	1st to 10th	Day	10% 6% 3 7% 5% 4 5% 5% 7% 8% 40%	2062
	11th to 20th	Day	13% 5% 2 4 5% 3 4 4 5% 8% 46%	1980
	21st to end	Day	15% 6% 2 6% 4 3 5% 6% 6% 8% 37%	1980
October	1st to 10th	Day	15% 6% 3 5% 6% 4 5% 6% 4 6% 38%	1890
	11th to 20th	Day	20% 10% 3 7% 6% 4 4 5% 6% 6% 30%	1800
	21st to end	Day	23% 11% 3 7% 6% 4 5% 5% 6% 6% 25%	1854
November	1st to 10th	Day	14% 9% 5% 7% 7% 3 6% 5% 6% 6% 31%	1672
	11th to 20th	Day	13% 12% 5% 8% 8% 4 6% 5% 6% 7% 26%	1634
	21st to end	Day	17% 13% 6% 7% 6% 4 6% 6% 5% 7% 23%	1520
December	1st to 10th	Day	14% 15% 8% 9% 8% 4 6% 6% 5% 7% 18%	1520
	11th to 20th	Day	17% 14% 6% 9% 7% 4 5% 5% 6% 6% 21%	1742
	21st to end	Day	24% 25% 7% 8% 6% 3 5% 3 5% 5% 10%	2431
January	1st to 10th	Night	18% 13% 7% 10% 6% 3 5% 4 5% 6% 24%	4428
	11th to 20th	Night	12% 16% 8% 13% 10% 8% 5% 5% 4 5% 14%	4440
	21st to end	Night	19% 15% 7% 10% 7% 4 5% 4 5% 5% 19%	4582
February	1st to 10th	Night	14% 15% 6% 10% 6% 4 6% 5% 4 6% 24%	2470
	11th to 20th	Night	13% 12% 5% 9% 6% 4 5% 5% 6% 7% 29%	2338
	21st to end	Night	17% 11% 5% 9% 6% 3 6% 4 5% 7% 27%	1831
March	1st to 10th	Night	13% 11% 5% 8% 7% 4 4 4 3 6% 34%	2093
	11th to 20th	Night	12% 9% 4 7% 6% 3 6% 5% 6% 6% 36%	1980
	21st to end	Night	19% 10% 4 8% 5% 3 5% 4 5% 5% 32%	2178
April	1st to 10th	Night	18% 9% 4 6% 5% 3 4 4 6% 6% 34%	1901
	11th to 20th	Night	18% 6% 3 4 4 4 5% 4 5% 8% 39%	1597
	21st to end	Night	19% 8% 3 7% 5% 2 5% 4 5% 7% 36%	1620
May	1st to 10th	Night	14% 8% 3 6% 6% 5% 4 6% 5% 7% 35%	1620
	11th to 20th	Night	16% 8% 3 5% 5% 2 5% 3 5% 7% 40%	1592
	21st to end	Night	10% 4 2 4 4 3 6% 4 5% 8% 49%	1624
June	1st to 10th	Night	13% 5% 3 5% 4 4 5% 6% 6% 6% 43%	1260
	11th to 20th	Night	11% 5% 3 5% 4 3 4 7% 6% 9% 44%	1260
	21st to end	Night	8% 5% 2 4 6% 3 5% 5% 7% 8% 47%	1260
July	1st to 10th	Night	6% 4 2 5% 3 3 3 5% 7% 8% 55%	1329
	11th to 20th	Night	9% 4 2 4 4 3 5% 5% 6% 10% 49%	1440
	21st to end	Night	7% 5% 2 4 5% 4 5% 6% 7% 8% 47%	1725
August	1st to 10th	Night	8% 5% 2 5% 5% 3 4 5% 7% 8% 48%	1611
	11th to 20th	Night	7% 4 3 4 4 3 5% 6% 7% 10% 48%	1598
	21st to end	Night	10% 6% 2 4 4 2 5% 5% 5% 8% 49%	1782
September	1st to 10th	Night	11% 6% 3 5% 5% 3 4 5% 5% 8% 44%	1875
	11th to 20th	Night	12% 4 2 3 4 3 4 4 4 7% 52%	1980
	21st to end	Night	15% 7% 3 6% 5% 3 4 4 4 6% 41%	1980
October	1st to 10th	Night	16% 6% 3 6% 6% 3 4 4 6% 7% 39%	2070
	11th to 20th	Night	20% 8% 3 6% 6% 3 5% 4 6% 6% 33%	2160
	21st to end	Night	22% 10% 4 8% 7% 3 4 6% 4 6% 26%	2497
November	1st to 10th	Night	14% 9% 3 5% 5% 3 5% 5% 6% 7% 37%	2406
	11th to 20th	Night	14% 12% 4 7% 6% 3 5% 6% 6% 8% 29%	2544
	21st to end	Night	19% 11% 5% 7% 6% 3 4 5% 5% 7% 26%	2660
December	1st to 10th	Night	17% 15% 6% 8% 6% 4 6% 5% 5% 7% 20%	2660
	11th to 20th	Night	15% 12% 6% 11% 6% 3 6% 6% 6% 8% 20%	3450
	21st to end	Night	27% 20% 7% 9% 6% 3 4 4 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% 13% 13% 8% 1	1520
March	1st to 10th	Day	56% 6% 15% 15% 7% 1	1866
	11th to 20th	Day	52% 7% 11% 17% 10% 2	1980
	21st to end	Day	55% 6% 12% 18% 7% 1	2178
April	1st to 10th	Day	51% 8% 13% 19% 9% 1	2071
	11th to 20th	Day	45% 6% 15% 17% 14% 2	2312
	21st to end	Day	46% 7% 15% 17% 12% 2	2340
May	1st to 10th	Day	45% 7% 11% 22% 13% 2	2340
	11th to 20th	Day	45% 7% 11% 20% 15% 3	2305
	21st to end	Day	38% 8% 15% 21% 16% 2	2646
June	1st to 10th	Day	37% 8% 14% 25% 14% 2	2698
	11th to 20th	Day	33% 8% 14% 25% 17% 2	2700
	21st to end	Day	36% 9% 14% 26% 15% 1	2700
July	1st to 10th	Day	28% 8% 15% 28% 18% 3	2556
	11th to 20th	Day	31% 10% 16% 28% 14% 2	2445
	21st to end	Day	32% 9% 18% 24% 15% 2	2448
August	1st to 10th	Day	36% 10% 17% 25% 10% 2	2314
	11th to 20th	Day	33% 10% 18% 26% 12% 2	2303
	21st to end	Day	35% 7% 15% 28% 13% 1	2574
September	1st to 10th	Day	39% 10% 16% 22% 11% 2	2062
	11th to 20th	Day	36% 7% 16% 31% 11% 1	1980
	21st to end	Day	42% 9% 16% 23% 9%	1980
October	1st to 10th	Day	45% 8% 12% 23% 10% 1	1890
	11th to 20th	Day	54% 8% 15% 17% 6% 1	1800
	21st to end	Day	59% 7% 13% 16% 4	1854
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	58% 7% 12% 16% 8%	1831
March	1st to 10th	Night	52% 7% 12% 22% 7% 1	2093
	11th to 20th	Night	48% 6% 11% 20% 12% 2	1980
	21st to end	Night	54% 6% 10% 19% 11% 1	2178
April	1st to 10th	Night	50% 6% 10% 20% 12% 2	1901
	11th to 20th	Night	43% 6% 12% 18% 18% 2	1597
	21st to end	Night	48% 6% 10% 18% 14% 4	1620
May	1st to 10th	Night	47% 7% 9% 21% 13% 3	1620
	11th to 20th	Night	44% 5% 10% 19% 18% 4	1593
	21st to end	Night	33% 8% 13% 25% 16% 5%	1625
June	1st to 10th	Night	39% 8% 12% 24% 17% 2	1260
	11th to 20th	Night	34% 8% 13% 23% 19% 3	1260
	21st to end	Night	33% 8% 15% 23% 18% 2	1260
July	1st to 10th	Night	26% 8% 12% 28% 22% 4	1291
	11th to 20th	Night	30% 8% 14% 29% 18% 2	1392
	21st to end	Night	30% 11% 17% 23% 17% 2	1629
August	1st to 10th	Night	31% 8% 16% 30% 14% 1	1600
	11th to 20th	Night	30% 9% 16% 28% 14% 3	1598
	21st to end	Night	32% 9% 14% 30% 15% 1	1782
September	1st to 10th	Night	36% 9% 15% 24% 14% 1	1875
	11th to 20th	Night	33% 6% 13% 33% 15%	1980
	21st to end	Night	43% 8% 12% 28% 9% 1	1980
October	1st to 10th	Night	44% 9% 10% 24% 13% 1	2070
	11th to 20th	Night	52% 7% 14% 19% 7%	2160
	21st to end	Night	59% 8% 12% 14% 6%	2497
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	16% 20% 40% 19% 5%	210
March	1st to 10th	Day	19% 13% 36% 25% 7% 1	306
	11th to 20th	Day	16% 9% 32% 30% 11% 2	420
	21st to end	Day	21% 8% 28% 32% 10% 1	462
April	1st to 10th	Day	17% 8% 32% 30% 11% 2	420
	11th to 20th	Day	23% 8% 24% 28% 11% 6%	412
	21st to end	Day	19% 5% 26% 34% 14% 1	420
May	1st to 10th	Day	16% 5% 23% 37% 15% 3	423
	11th to 20th	Day	17% 3 21% 33% 21% 6%	447
	21st to end	Day	12% 4 15% 32% 28% 9%	485
June	1st to 10th	Day	11% 3 18% 38% 25% 5%	628
	11th to 20th	Day	12% 2 19% 35% 25% 6%	630
	21st to end	Day	13% 3 13% 42% 25% 5%	630
July	1st to 10th	Day	7% 4 10% 34% 34% 10%	621
	11th to 20th	Day	11% 3 14% 37% 29% 6%	618
	21st to end	Day	9% 1 12% 43% 27% 8%	533
August	1st to 10th	Day	10% 3 11% 33% 30% 12%	446
	11th to 20th	Day	9% 1 9% 36% 34% 10%	439
	21st to end	Day	12% 5% 14% 29% 33% 7%	495
September	1st to 10th	Day	12% 4 20% 29% 25% 10%	450
	11th to 20th	Day	12% 4 16% 27% 27% 14%	450
	21st to end	Day	17% 7% 21% 25% 20% 10%	450
October	1st to 10th	Day	19% 8% 24% 24% 18% 8%	450
	11th to 20th	Day	21% 13% 30% 25% 9% 1	450
	21st to end	Day	28% 13% 29% 25% 4 1	369
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	24% 9% 36% 26% 5%	611
March	1st to 10th	Night	18% 8% 33% 31% 10%	720
	11th to 20th	Night	17% 8% 34% 32% 8% 1	720
	21st to end	Night	22% 8% 25% 31% 12% 1	792
April	1st to 10th	Night	22% 8% 29% 31% 10% 1	658
	11th to 20th	Night	20% 5% 29% 31% 12% 4	533
	21st to end	Night	21% 6% 21% 35% 15% 1	540
May	1st to 10th	Night	16% 4 21% 38% 18% 2	540
	11th to 20th	Night	19% 2 19% 36% 21% 3	531
	21st to end	Night	12% 2 14% 36% 30% 6%	465
June	1st to 10th	Night	19% 1 14% 38% 26% 3	360
	11th to 20th	Night	14% 3 15% 39% 27% 3	360
	21st to end	Night	11% 2 14% 41% 30% 3	360
July	1st to 10th	Night	8% 1 9% 42% 34% 5%	416
	11th to 20th	Night	11% 2 11% 35% 36% 6%	522
	21st to end	Night	9% 2 11% 47% 28% 3	591
August	1st to 10th	Night	11% 2 10% 39% 32% 6%	537
	11th to 20th	Night	11% 2 13% 32% 34% 8%	534
	21st to end	Night	13% 2 17% 31% 30% 6%	594
September	1st to 10th	Night	14% 3 19% 31% 23% 10%	669
	11th to 20th	Night	15% 3 15% 31% 27% 8%	720
	21st to end	Night	17% 7% 20% 29% 20% 8%	720
October	1st to 10th	Night	20% 6% 27% 25% 19% 4	720
	11th to 20th	Night	24% 12% 30% 24% 10% 1	720
	21st to end	Night	28% 11% 29% 26% 6%	792
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 2024-02-22 06:05:43. Version ac07

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