Northeast Philadelphia Airport
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Northeast Philadelphia Airport clear sky chart from 2005-11-06 to 2024-11-06.

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	16% 6% 2 6% 4 4 4 4 6% 7% 40%	101297
	Night	17% 7% 2 6% 4 4 4 3 5% 6% 42%	97758
Transparency	Day	23% 47% 6% 13% 9% 1	104843
	Night	22% 47% 6% 13% 9% 2	102300
Seeing	Day	20% 15% 29% 22% 10% 3	15018
	Night	19% 12% 31% 28% 9% 1	24257

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	15% 7% 2 5% 3 4 3 3 5% 6% 47%	2517
	11th to 20th	Day	14% 9% 3 7% 5% 4 4 3 5% 6% 38%	2557
	21st to end	Day	23% 8% 2 6% 5% 3 4 3 4 6% 36%	3124
February	1st to 10th	Day	16% 7% 3 5% 5% 4 4 3 5% 7% 39%	1710
	11th to 20th	Day	16% 7% 2 6% 4 3 4 4 5% 6% 41%	1818
	21st to end	Day	18% 8% 2 6% 5% 4 4 3 5% 6% 38%	1570
March	1st to 10th	Day	26% 6% 2 6% 3 4 3 3 4 6% 37%	3116
	11th to 20th	Day	10% 5% 2 5% 5% 5% 5% 4 6% 7% 47%	3448
	21st to end	Day	21% 6% 2 5% 3 3 3 3 4 5% 44%	4061
April	1st to 10th	Day	16% 7% 3 6% 4 4 5% 4 5% 7% 40%	2280
	11th to 20th	Day	15% 6% 2 5% 4 4 5% 4 5% 7% 42%	2254
	21st to end	Day	16% 6% 2 5% 5% 4 4 5% 5% 8% 40%	2280
May	1st to 10th	Day	28% 8% 3 6% 4 4 4 3 5% 7% 29%	4043
	11th to 20th	Day	24% 8% 3 7% 5% 5% 5% 4 5% 6% 29%	4398
	21st to end	Day	13% 6% 2 5% 4 4 4 4 6% 9% 44%	4837
June	1st to 10th	Day	13% 5% 2 6% 5% 5% 5% 4 7% 9% 40%	2660
	11th to 20th	Day	12% 6% 2 6% 5% 5% 5% 4 7% 9% 39%	2660
	21st to end	Day	11% 5% 2 6% 4 4 5% 5% 7% 9% 42%	2660
July	1st to 10th	Day	7% 5% 2 7% 7% 6% 7% 5% 9% 10% 36%	4440
	11th to 20th	Day	11% 6% 2 5% 5% 5% 6% 5% 7% 10% 38%	4440
	21st to end	Day	13% 7% 3 8% 6% 5% 6% 4 7% 8% 32%	4766
August	1st to 10th	Day	19% 6% 2 7% 4 5% 5% 4 7% 8% 33%	4083
	11th to 20th	Day	13% 6% 2 6% 4 4 5% 4 6% 10% 41%	3730
	21st to end	Day	11% 5% 2 5% 4 3 5% 3 6% 9% 46%	4180
September	1st to 10th	Day	14% 5% 2 5% 5% 4 4 4 5% 7% 45%	2280
	11th to 20th	Day	14% 4 2 3 3 3 3 3 5% 7% 52%	2237
	21st to end	Day	20% 7% 3 6% 4 4 5% 3 5% 6% 38%	2090
October	1st to 10th	Day	18% 6% 2 5% 3 3 4 4 6% 5% 44%	1920
	11th to 20th	Day	15% 5% 1 4 4 3 4 4 4 8% 48%	1900
	21st to end	Day	18% 7% 2 4 3 3 3 3 5% 6% 46%	2009
November	1st to 10th	Day	13% 6% 2 5% 3 3 3 2 4 6% 53%	1717
	11th to 20th	Day	16% 6% 1 5% 4 3 3 3 5% 6% 48%	1710
	21st to end	Day	15% 5% 2 5% 4 4 3 4 5% 7% 47%	1604
December	1st to 10th	Day	18% 8% 2 5% 4 3 3 4 6% 7% 39%	1520
	11th to 20th	Day	20% 7% 2 5% 3 3 3 3 5% 7% 43%	1906
	21st to end	Day	17% 6% 2 6% 4 5% 6% 5% 7% 7% 36%	2772
January	1st to 10th	Night	17% 6% 2 5% 4 4 4 3 4 6% 46%	4429
	11th to 20th	Night	18% 8% 2 6% 4 3 3 3 4 4 44%	4399
	21st to end	Night	24% 9% 3 5% 4 3 3 3 4 6% 37%	4532
February	1st to 10th	Night	16% 9% 2 6% 4 4 3 3 6% 6% 41%	2470
	11th to 20th	Night	18% 8% 3 6% 4 4 4 3 5% 5% 41%	2247
	21st to end	Night	18% 9% 2 5% 5% 3 3 3 5% 6% 42%	1884
March	1st to 10th	Night	24% 9% 2 6% 3 4 3 3 4 5% 37%	3724
	11th to 20th	Night	11% 5% 2 6% 4 4 4 3 4 6% 50%	3493
	21st to end	Night	18% 9% 3 6% 3 3 3 2 4 4 45%	3570
April	1st to 10th	Night	17% 6% 3 6% 4 4 4 4 5% 6% 41%	1900
	11th to 20th	Night	16% 6% 2 7% 5% 4 4 3 5% 6% 42%	1875
	21st to end	Night	19% 5% 2 5% 3 4 3 3 5% 8% 43%	1900
May	1st to 10th	Night	23% 9% 3 7% 4 4 4 4 6% 8% 30%	2914
	11th to 20th	Night	25% 9% 3 7% 4 4 3 3 5% 7% 31%	2495
	21st to end	Night	14% 6% 2 5% 3 4 4 4 6% 10% 42%	2738
June	1st to 10th	Night	16% 5% 2 5% 5% 4 3 3 6% 8% 43%	1520
	11th to 20th	Night	11% 6% 2 6% 6% 4 5% 4 6% 7% 42%	1520
	21st to end	Night	9% 5% 2 6% 4 5% 4 5% 7% 10% 42%	1520
July	1st to 10th	Night	8% 5% 3 7% 5% 5% 5% 5% 8% 9% 38%	2520
	11th to 20th	Night	12% 6% 2 6% 5% 4 5% 5% 7% 10% 38%	2520
	21st to end	Night	15% 6% 2 7% 4 4 5% 5% 7% 8% 35%	2783
August	1st to 10th	Night	22% 6% 2 6% 4 5% 4 4 7% 8% 33%	2825
	11th to 20th	Night	14% 6% 2 6% 4 4 5% 4 6% 7% 42%	3088
	21st to end	Night	11% 4 2 5% 4 4 5% 4 5% 7% 49%	3476
September	1st to 10th	Night	14% 6% 2 6% 4 3 4 3 5% 7% 46%	1900
	11th to 20th	Night	13% 5% 2 3 3 3 4 3 4 6% 53%	1942
	21st to end	Night	19% 6% 2 6% 4 3 3 4 5% 7% 41%	2090
October	1st to 10th	Night	19% 6% 2 6% 4 3 4 3 5% 5% 44%	2256
	11th to 20th	Night	15% 5% 1 5% 3 3 3 3 5% 6% 52%	2280
	21st to end	Night	18% 6% 2 5% 3 4 3 3 5% 5% 47%	2589
November	1st to 10th	Night	12% 5% 2 5% 4 4 3 3 4 6% 54%	2483
	11th to 20th	Night	17% 5% 2 5% 4 3 3 3 4 5% 48%	2470
	21st to end	Night	13% 5% 2 5% 4 4 5% 3 6% 7% 45%	2574
December	1st to 10th	Night	20% 8% 2 5% 4 4 3 3 5% 6% 40%	2660
	11th to 20th	Night	18% 6% 2 6% 4 3 4 3 6% 7% 41%	3288
	21st to end	Night	18% 7% 3 6% 4 4 4 3 5% 6% 39%	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	25% 38% 8% 17% 9% 3	2518
	11th to 20th	Day	29% 38% 7% 16% 9% 1	2557
	21st to end	Day	33% 41% 8% 11% 5% 1	3124
February	1st to 10th	Day	17% 66% 6% 7% 3 1	1710
	11th to 20th	Day	16% 64% 2 8% 8% 2	1827
	21st to end	Day	16% 66% 4 8% 4 1	1570
March	1st to 10th	Day	34% 42% 4 15% 4 1	3119
	11th to 20th	Day	16% 43% 7% 22% 11% 1	3448
	21st to end	Day	26% 40% 5% 10% 15% 3	4061
April	1st to 10th	Day	18% 65% 3 7% 5% 1	2280
	11th to 20th	Day	14% 66% 5% 9% 6% 1	2254
	21st to end	Day	15% 66% 4 8% 7% 1	2280
May	1st to 10th	Day	37% 42% 7% 10% 3	4056
	11th to 20th	Day	36% 42% 8% 11% 2	4402
	21st to end	Day	20% 42% 8% 17% 11% 1	4837
June	1st to 10th	Day	15% 65% 3 10% 6% 1	2660
	11th to 20th	Day	13% 66% 4 10% 7%	2660
	21st to end	Day	13% 64% 4 10% 8% 1	2660
July	1st to 10th	Day	27% 42% 10% 10% 9% 2	4370
	11th to 20th	Day	27% 39% 11% 14% 9%	4365
	21st to end	Day	33% 38% 6% 12% 10% 1	4614
August	1st to 10th	Day	34% 40% 8% 13% 5%	4070
	11th to 20th	Day	23% 39% 8% 22% 8%	3766
	21st to end	Day	17% 38% 7% 22% 15% 1	4180
September	1st to 10th	Day	16% 60% 5% 10% 8% 1	2280
	11th to 20th	Day	15% 60% 3 10% 9% 2	2237
	21st to end	Day	23% 60% 3 8% 6%	2090
October	1st to 10th	Day	22% 37% 5% 9% 22% 5%	3193
	11th to 20th	Day	10% 37% 6% 16% 25% 6%	3140
	21st to end	Day	10% 36% 9% 19% 22% 5%	3286
November	1st to 10th	Day	16% 58% 6% 10% 9% 2	1717
	11th to 20th	Day	14% 59% 3 10% 12% 1	1710
	21st to end	Day	14% 60% 6% 14% 5% 2	1604
December	1st to 10th	Day	21% 60% 6% 7% 6%	1520
	11th to 20th	Day	22% 48% 6% 16% 6% 1	1906
	21st to end	Day	28% 42% 8% 15% 8%	2772
January	1st to 10th	Night	25% 38% 6% 20% 8% 3	4429
	11th to 20th	Night	28% 37% 6% 17% 10% 2	4399
	21st to end	Night	35% 40% 4 13% 7% 1	4532
February	1st to 10th	Night	15% 65% 6% 10% 2 1	2470
	11th to 20th	Night	16% 64% 2 7% 9% 2	2249
	21st to end	Night	16% 64% 4 8% 5% 3	1884
March	1st to 10th	Night	35% 42% 4 13% 6% 1	3734
	11th to 20th	Night	16% 42% 9% 20% 11% 1	3494
	21st to end	Night	27% 41% 3 9% 17% 3	3570
April	1st to 10th	Night	16% 65% 3 8% 6% 1	1900
	11th to 20th	Night	14% 66% 4 9% 6% 1	1875
	21st to end	Night	15% 65% 3 8% 8% 1	1900
May	1st to 10th	Night	33% 44% 7% 12% 4	2920
	11th to 20th	Night	36% 42% 9% 9% 3	2496
	21st to end	Night	21% 43% 11% 14% 10% 1	2739
June	1st to 10th	Night	14% 65% 3 8% 9% 1	1520
	11th to 20th	Night	14% 66% 3 11% 7%	1520
	21st to end	Night	13% 64% 5% 10% 7% 1	1520
July	1st to 10th	Night	26% 40% 15% 11% 7% 1	2480
	11th to 20th	Night	26% 39% 12% 16% 6%	2472
	21st to end	Night	34% 37% 8% 10% 10% 1	2694
August	1st to 10th	Night	36% 39% 12% 8% 4	2814
	11th to 20th	Night	25% 39% 7% 21% 8%	3118
	21st to end	Night	18% 37% 6% 23% 16%	3476
September	1st to 10th	Night	14% 61% 6% 10% 7% 1	1900
	11th to 20th	Night	14% 60% 4 8% 12% 2	1942
	21st to end	Night	22% 60% 3 8% 7%	2090
October	1st to 10th	Night	24% 38% 6% 14% 15% 2	3763
	11th to 20th	Night	10% 37% 6% 20% 23% 4	3779
	21st to end	Night	12% 36% 7% 23% 18% 3	4262
November	1st to 10th	Night	16% 57% 6% 11% 7% 3	2483
	11th to 20th	Night	14% 59% 3 10% 11% 3	2470
	21st to end	Night	13% 60% 6% 13% 6% 1	2574
December	1st to 10th	Night	21% 60% 4 10% 5%	2660
	11th to 20th	Night	21% 49% 6% 9% 11% 3	3288
	21st to end	Night	29% 40% 8% 16% 7%	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	23% 27% 33% 12% 3 1	180
	11th to 20th	Day	35% 28% 24% 11% 2	192
	21st to end	Day	28% 25% 28% 13% 5%	297
February	1st to 10th	Day	29% 23% 35% 10% 3	270
	11th to 20th	Day	29% 24% 35% 11% 2	426
	21st to end	Day	30% 21% 32% 14% 2	382
March	1st to 10th	Day	26% 22% 30% 18% 3	460
	11th to 20th	Day	24% 25% 32% 13% 4 2	460
	21st to end	Day	27% 20% 31% 16% 5% 1	506
April	1st to 10th	Day	25% 24% 30% 14% 6% 1	460
	11th to 20th	Day	22% 21% 32% 17% 6% 2	452
	21st to end	Day	28% 17% 32% 19% 4 1	460
May	1st to 10th	Day	29% 19% 30% 13% 8% 1	463
	11th to 20th	Day	22% 15% 31% 23% 8% 2	487
	21st to end	Day	18% 10% 25% 28% 17% 3	529
June	1st to 10th	Day	15% 13% 28% 27% 14% 3	490
	11th to 20th	Day	15% 11% 31% 28% 11% 3	490
	21st to end	Day	13% 10% 31% 31% 12% 3	490
July	1st to 10th	Day	10% 6% 23% 34% 21% 6%	485
	11th to 20th	Day	8% 3 25% 36% 23% 5%	484
	21st to end	Day	12% 7% 29% 32% 16% 4	532
August	1st to 10th	Day	12% 5% 27% 33% 17% 7%	486
	11th to 20th	Day	13% 4 22% 36% 19% 6%	479
	21st to end	Day	14% 8% 25% 28% 17% 9%	539
September	1st to 10th	Day	16% 10% 25% 26% 17% 7%	490
	11th to 20th	Day	15% 6% 26% 29% 17% 9%	490
	21st to end	Day	25% 13% 23% 23% 9% 6%	490
October	1st to 10th	Day	24% 8% 27% 22% 13% 7%	490
	11th to 20th	Day	17% 15% 30% 23% 11% 3	490
	21st to end	Day	18% 16% 33% 19% 11% 2	496
November	1st to 10th	Day	20% 12% 32% 23% 12% 2	381
	11th to 20th	Day	23% 19% 32% 20% 6%	370
	21st to end	Day	20% 18% 36% 19% 6% 1	264
December	1st to 10th	Day	25% 27% 33% 8% 7%	180
	11th to 20th	Day	33% 18% 34% 11% 4	180
	21st to end	Day	28% 20% 32% 13% 7% 1	198
January	1st to 10th	Night	20% 18% 37% 21% 4	760
	11th to 20th	Night	24% 17% 32% 24% 3	760
	21st to end	Night	17% 19% 39% 23% 2	836
February	1st to 10th	Night	20% 17% 37% 24% 1	760
	11th to 20th	Night	24% 22% 36% 17% 1	743
	21st to end	Night	23% 19% 37% 18% 2	628
March	1st to 10th	Night	22% 18% 35% 21% 4	760
	11th to 20th	Night	22% 20% 36% 17% 5%	760
	21st to end	Night	22% 15% 39% 19% 5%	836
April	1st to 10th	Night	21% 19% 38% 17% 5%	760
	11th to 20th	Night	19% 14% 38% 24% 5%	751
	21st to end	Night	21% 12% 35% 26% 5%	760
May	1st to 10th	Night	21% 13% 35% 24% 7%	624
	11th to 20th	Night	18% 12% 37% 26% 6% 1	374
	21st to end	Night	16% 5% 26% 39% 11% 1	411
June	1st to 10th	Night	17% 6% 30% 38% 9% 1	380
	11th to 20th	Night	12% 7% 29% 42% 10%	380
	21st to end	Night	9% 4 28% 48% 11%	380
July	1st to 10th	Night	10% 4 26% 41% 16% 2	370
	11th to 20th	Night	7% 3 24% 45% 19% 2	368
	21st to end	Night	9% 4 26% 41% 19%	436
August	1st to 10th	Night	12% 2 20% 43% 21% 2	567
	11th to 20th	Night	13% 5% 19% 38% 22% 2	741
	21st to end	Night	14% 4 19% 39% 22% 2	836
September	1st to 10th	Night	15% 4 27% 35% 16% 2	760
	11th to 20th	Night	14% 4 22% 35% 21% 4	760
	21st to end	Night	23% 6% 22% 31% 18% 1	760
October	1st to 10th	Night	22% 7% 24% 27% 16% 3	760
	11th to 20th	Night	17% 9% 28% 33% 12% 1	760
	21st to end	Night	21% 11% 32% 26% 9% 1	836
November	1st to 10th	Night	15% 10% 35% 29% 10% 1	764
	11th to 20th	Night	20% 16% 29% 26% 8% 1	760
	21st to end	Night	17% 15% 35% 26% 7% 1	760
December	1st to 10th	Night	25% 16% 33% 20% 6% 1	760
	11th to 20th	Night	19% 15% 36% 24% 5%	760
	21st to end	Night	21% 16% 34% 27% 2	836

Page generated at 2024-11-03 13:19:04. Version ac07

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