Allentown(PA)
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Allentown(PA) clear sky chart from 2005-11-06 to 2024-11-01.

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% 7% 2 6% 4 4 4 4 6% 7% 39%	101348
	Night	17% 7% 2 6% 4 4 4 3 5% 6% 41%	97623
Transparency	Day	44% 5% 12% 24% 14% 2	101106
	Night	44% 4 11% 24% 15% 2	97485
Seeing	Day	21% 14% 27% 22% 12% 4	14916
	Night	19% 9% 30% 30% 11% 1	24165

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 5% 4 3 3 3 5% 6% 44%	2517
	11th to 20th	Day	14% 10% 5% 9% 6% 5% 5% 4 4 6% 31%	2580
	21st to end	Day	21% 10% 3 8% 5% 3 4 3 4 6% 33%	3124
February	1st to 10th	Day	16% 7% 3 6% 6% 4 5% 3 6% 7% 37%	1710
	11th to 20th	Day	14% 8% 2 6% 4 4 4 3 5% 7% 39%	1778
	21st to end	Day	20% 9% 2 6% 4 4 4 4 6% 5% 36%	1570
March	1st to 10th	Day	26% 7% 2 6% 4 4 4 4 4 6% 35%	3142
	11th to 20th	Day	10% 6% 2 6% 5% 5% 6% 4 6% 8% 43%	3480
	21st to end	Day	21% 8% 2 5% 3 3 3 3 4 6% 43%	4028
April	1st to 10th	Day	17% 7% 3 6% 5% 4 4 4 6% 7% 37%	2280
	11th to 20th	Day	17% 8% 2 6% 5% 4 3 4 6% 7% 40%	2254
	21st to end	Day	16% 5% 2 6% 4 4 4 5% 6% 7% 39%	2280
May	1st to 10th	Day	27% 7% 2 7% 4 4 4 4 4 7% 30%	4141
	11th to 20th	Day	25% 8% 3 7% 5% 4 4 4 5% 7% 28%	4398
	21st to end	Day	13% 5% 2 6% 3 4 4 4 6% 10% 43%	4837
June	1st to 10th	Day	13% 6% 2 6% 5% 6% 4 5% 7% 9% 37%	2660
	11th to 20th	Day	15% 5% 2 5% 5% 5% 5% 5% 7% 9% 37%	2660
	21st to end	Day	12% 5% 1 5% 5% 5% 4 4 6% 9% 42%	2660
July	1st to 10th	Day	7% 4 2 7% 6% 6% 6% 5% 8% 10% 37%	4440
	11th to 20th	Day	9% 6% 2 5% 4 5% 5% 4 8% 10% 41%	4440
	21st to end	Day	12% 8% 3 8% 6% 5% 5% 4 7% 8% 34%	4752
August	1st to 10th	Day	20% 6% 3 6% 5% 4 5% 4 7% 8% 32%	4104
	11th to 20th	Day	14% 6% 2 5% 4 4 5% 4 6% 8% 42%	3773
	21st to end	Day	14% 5% 2 4 3 4 4 4 6% 8% 46%	4180
September	1st to 10th	Day	15% 6% 2 5% 4 4 5% 3 6% 7% 43%	2280
	11th to 20th	Day	13% 5% 1 5% 3 3 4 3 6% 7% 50%	2261
	21st to end	Day	20% 6% 2 6% 4 4 5% 4 4 6% 40%	2070
October	1st to 10th	Day	18% 6% 2 5% 3 4 4 4 5% 7% 41%	1900
	11th to 20th	Day	16% 5% 2 5% 3 4 4 3 5% 6% 46%	1900
	21st to end	Day	19% 6% 2 6% 3 4 5% 3 5% 6% 41%	2024
November	1st to 10th	Day	14% 7% 2 4 2 3 3 2 4 6% 51%	1671
	11th to 20th	Day	17% 6% 1 4 3 4 4 4 6% 5% 45%	1710
	21st to end	Day	17% 7% 2 6% 3 3 3 4 6% 8% 42%	1546
December	1st to 10th	Day	19% 8% 3 7% 4 4 4 4 5% 7% 35%	1520
	11th to 20th	Day	21% 6% 2 4 4 4 4 4 6% 6% 39%	1906
	21st to end	Day	19% 9% 3 8% 6% 5% 6% 4 5% 6% 29%	2772
January	1st to 10th	Night	16% 7% 2 6% 4 3 4 4 5% 7% 42%	4429
	11th to 20th	Night	16% 9% 3 7% 5% 3 4 4 5% 7% 37%	4376
	21st to end	Night	24% 10% 2 6% 3 3 3 3 5% 5% 35%	4532
February	1st to 10th	Night	17% 8% 3 6% 4 3 4 4 5% 7% 40%	2470
	11th to 20th	Night	17% 8% 3 7% 4 4 4 4 4 5% 41%	2288
	21st to end	Night	19% 8% 2 5% 4 3 4 3 5% 6% 40%	1884
March	1st to 10th	Night	23% 10% 3 5% 3 3 3 3 5% 5% 36%	3696
	11th to 20th	Night	11% 7% 2 5% 4 4 4 3 4 6% 48%	3479
	21st to end	Night	17% 9% 3 6% 4 3 3 3 3 4 45%	3604
April	1st to 10th	Night	17% 7% 2 6% 5% 5% 5% 4 5% 7% 38%	1900
	11th to 20th	Night	16% 7% 3 5% 4 4 5% 4 5% 8% 41%	1875
	21st to end	Night	20% 5% 2 4 3 3 4 4 5% 6% 45%	1900
May	1st to 10th	Night	26% 8% 2 6% 4 4 4 3 6% 7% 30%	2830
	11th to 20th	Night	25% 9% 3 8% 5% 4 4 3 5% 6% 29%	2495
	21st to end	Night	13% 6% 2 6% 4 4 4 4 6% 10% 41%	2738
June	1st to 10th	Night	16% 7% 1 5% 4 4 4 3 5% 6% 44%	1520
	11th to 20th	Night	13% 5% 1 5% 4 5% 4 5% 7% 8% 42%	1520
	21st to end	Night	11% 4 2 5% 5% 4 4 4 6% 10% 44%	1520
July	1st to 10th	Night	9% 5% 2 7% 5% 6% 7% 4 7% 8% 38%	2520
	11th to 20th	Night	10% 6% 2 6% 6% 5% 6% 5% 8% 9% 38%	2520
	21st to end	Night	15% 7% 2 6% 4 4 5% 5% 7% 8% 38%	2797
August	1st to 10th	Night	20% 6% 3 7% 4 5% 5% 4 6% 7% 32%	2825
	11th to 20th	Night	16% 7% 3 6% 5% 4 4 3 5% 6% 42%	3024
	21st to end	Night	13% 4 2 5% 3 3 4 4 6% 8% 48%	3476
September	1st to 10th	Night	15% 6% 2 5% 4 4 3 3 4 6% 48%	1900
	11th to 20th	Night	13% 5% 2 4 3 3 4 3 5% 6% 52%	1918
	21st to end	Night	18% 6% 2 6% 4 3 4 3 5% 6% 43%	2107
October	1st to 10th	Night	20% 6% 2 5% 3 3 3 3 5% 6% 43%	2280
	11th to 20th	Night	16% 5% 2 4 3 3 3 3 5% 6% 49%	2280
	21st to end	Night	20% 6% 1 4 3 3 3 3 4 6% 47%	2573
November	1st to 10th	Night	13% 5% 2 5% 3 4 4 3 5% 5% 51%	2414
	11th to 20th	Night	16% 7% 3 5% 4 3 4 3 5% 5% 46%	2470
	21st to end	Night	15% 6% 2 5% 5% 3 4 3 5% 7% 43%	2631
December	1st to 10th	Night	20% 7% 3 6% 5% 5% 5% 4 5% 6% 36%	2660
	11th to 20th	Night	18% 7% 2 6% 4 4 4 4 6% 7% 38%	3288
	21st to end	Night	20% 9% 3 7% 4 4 4 3 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	41% 3 13% 29% 11% 2	2518
	11th to 20th	Day	53% 4 11% 19% 12% 2	2580
	21st to end	Day	53% 3 11% 22% 9% 1	3124
February	1st to 10th	Day	46% 4 14% 23% 13% 1	1710
	11th to 20th	Day	45% 4 10% 25% 15% 2	1787
	21st to end	Day	49% 4 9% 24% 11% 3	1570
March	1st to 10th	Day	51% 4 8% 28% 8% 2	3145
	11th to 20th	Day	38% 4 10% 31% 14% 2	3480
	21st to end	Day	45% 2 10% 19% 21% 4	4028
April	1st to 10th	Day	46% 4 8% 22% 15% 5%	2280
	11th to 20th	Day	42% 4 10% 24% 15% 4	2254
	21st to end	Day	43% 5% 10% 22% 16% 4	2280
May	1st to 10th	Day	55% 3 11% 18% 11% 2	4154
	11th to 20th	Day	57% 3 11% 18% 9% 1	4402
	21st to end	Day	36% 5% 11% 29% 17% 2	4837
June	1st to 10th	Day	42% 6% 13% 25% 14% 1	2660
	11th to 20th	Day	41% 6% 15% 24% 11% 2	2660
	21st to end	Day	38% 6% 14% 27% 14% 1	2660
July	1st to 10th	Day	40% 9% 14% 23% 14% 1	4370
	11th to 20th	Day	36% 7% 17% 26% 13% 1	4365
	21st to end	Day	47% 6% 10% 19% 16% 2	4601
August	1st to 10th	Day	49% 7% 12% 22% 10%	4091
	11th to 20th	Day	39% 5% 13% 31% 13% 1	3810
	21st to end	Day	35% 5% 11% 31% 16% 2	4180
September	1st to 10th	Day	40% 5% 10% 22% 20% 2	2280
	11th to 20th	Day	33% 3 10% 25% 25% 3	2261
	21st to end	Day	47% 4 8% 19% 20% 2	2070
October	1st to 10th	Day	41% 5% 11% 24% 17% 2	1900
	11th to 20th	Day	39% 4 10% 26% 19% 1	1900
	21st to end	Day	44% 4 10% 24% 17% 2	2024
November	1st to 10th	Day	36% 3 13% 25% 20% 3	1671
	11th to 20th	Day	40% 4 8% 27% 19% 2	1710
	21st to end	Day	40% 4 14% 30% 11% 2	1546
December	1st to 10th	Day	49% 4 14% 20% 11% 1	1520
	11th to 20th	Day	45% 3 17% 24% 10% 1	1906
	21st to end	Day	55% 3 12% 23% 8%	2772
January	1st to 10th	Night	42% 2 11% 30% 11% 3	4429
	11th to 20th	Night	47% 3 12% 26% 10% 2	4376
	21st to end	Night	51% 2 9% 25% 11% 2	4532
February	1st to 10th	Night	45% 4 13% 26% 11% 2	2470
	11th to 20th	Night	47% 3 9% 21% 16% 4	2290
	21st to end	Night	45% 2 8% 24% 17% 4	1884
March	1st to 10th	Night	51% 3 9% 24% 12% 2	3706
	11th to 20th	Night	37% 3 13% 30% 16% 2	3480
	21st to end	Night	45% 3 7% 18% 23% 5%	3604
April	1st to 10th	Night	45% 4 10% 23% 15% 3	1900
	11th to 20th	Night	43% 4 10% 21% 20% 2	1875
	21st to end	Night	39% 5% 9% 23% 19% 5%	1900
May	1st to 10th	Night	54% 4 10% 21% 10% 1	2836
	11th to 20th	Night	57% 4 13% 15% 10% 1	2496
	21st to end	Night	40% 5% 15% 24% 14% 3	2739
June	1st to 10th	Night	40% 5% 11% 23% 19% 2	1520
	11th to 20th	Night	36% 7% 15% 27% 14% 1	1520
	21st to end	Night	34% 7% 14% 30% 14% 1	1520
July	1st to 10th	Night	42% 9% 15% 17% 15% 2	2480
	11th to 20th	Night	39% 7% 14% 26% 13% 1	2472
	21st to end	Night	42% 7% 14% 18% 18% 1	2708
August	1st to 10th	Night	49% 6% 17% 17% 10% 1	2814
	11th to 20th	Night	43% 5% 12% 24% 15% 1	3053
	21st to end	Night	34% 5% 10% 32% 18% 1	3476
September	1st to 10th	Night	39% 5% 10% 24% 21% 3	1900
	11th to 20th	Night	33% 4 10% 24% 26% 4	1918
	21st to end	Night	43% 3 8% 23% 21% 1	2107
October	1st to 10th	Night	43% 4 10% 25% 15% 2	2280
	11th to 20th	Night	37% 2 12% 30% 17% 3	2280
	21st to end	Night	40% 3 10% 27% 18% 2	2573
November	1st to 10th	Night	35% 4 12% 25% 21% 4	2414
	11th to 20th	Night	41% 3 9% 26% 18% 4	2470
	21st to end	Night	40% 4 12% 28% 14% 2	2631
December	1st to 10th	Night	48% 4 12% 23% 12% 1	2660
	11th to 20th	Night	46% 4 13% 20% 15% 2	3288
	21st to end	Night	51% 3 12% 25% 9%	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	26% 24% 27% 19% 2 2	180
	11th to 20th	Day	26% 30% 31% 10% 3 1	196
	21st to end	Day	22% 25% 33% 14% 5% 1	297
February	1st to 10th	Day	23% 25% 37% 11% 4 1	270
	11th to 20th	Day	26% 21% 39% 13% 2	386
	21st to end	Day	32% 18% 28% 20% 3	382
March	1st to 10th	Day	25% 21% 29% 20% 5%	460
	11th to 20th	Day	24% 21% 33% 17% 4 1	460
	21st to end	Day	28% 22% 29% 14% 6% 1	506
April	1st to 10th	Day	23% 24% 31% 15% 6% 1	460
	11th to 20th	Day	23% 23% 27% 16% 8% 3	452
	21st to end	Day	27% 17% 30% 18% 5% 3	460
May	1st to 10th	Day	30% 17% 25% 17% 7% 3	463
	11th to 20th	Day	23% 14% 28% 22% 11% 2	487
	21st to end	Day	20% 8% 24% 22% 21% 5%	529
June	1st to 10th	Day	16% 15% 26% 22% 16% 4	490
	11th to 20th	Day	16% 11% 26% 26% 17% 5%	490
	21st to end	Day	15% 10% 29% 27% 15% 4	490
July	1st to 10th	Day	10% 5% 22% 30% 25% 8%	485
	11th to 20th	Day	11% 4 21% 32% 25% 7%	484
	21st to end	Day	15% 5% 25% 32% 16% 7%	532
August	1st to 10th	Day	14% 7% 20% 29% 22% 9%	486
	11th to 20th	Day	16% 5% 18% 30% 22% 9%	479
	21st to end	Day	14% 7% 22% 27% 19% 11%	539
September	1st to 10th	Day	18% 8% 22% 23% 20% 9%	490
	11th to 20th	Day	15% 5% 22% 27% 18% 14%	490
	21st to end	Day	24% 11% 23% 22% 14% 6%	490
October	1st to 10th	Day	24% 8% 25% 22% 15% 7%	490
	11th to 20th	Day	17% 12% 32% 23% 13% 3	490
	21st to end	Day	22% 13% 33% 20% 11% 2	504
November	1st to 10th	Day	18% 12% 29% 26% 13% 3	365
	11th to 20th	Day	21% 19% 29% 22% 6% 1	370
	21st to end	Day	21% 23% 34% 16% 5% 1	206
December	1st to 10th	Day	25% 26% 31% 11% 7% 1	180
	11th to 20th	Day	32% 24% 26% 13% 6%	180
	21st to end	Day	26% 20% 30% 17% 6% 2	198
January	1st to 10th	Night	19% 16% 39% 21% 4	760
	11th to 20th	Night	24% 13% 34% 25% 3	760
	21st to end	Night	19% 14% 39% 25% 3	836
February	1st to 10th	Night	20% 14% 37% 26% 3	760
	11th to 20th	Night	21% 19% 41% 17% 2	743
	21st to end	Night	21% 18% 39% 20% 3	628
March	1st to 10th	Night	22% 14% 36% 25% 4	760
	11th to 20th	Night	22% 16% 36% 20% 6%	760
	21st to end	Night	22% 12% 37% 23% 5% 1	836
April	1st to 10th	Night	21% 17% 37% 21% 5%	760
	11th to 20th	Night	20% 11% 37% 25% 7%	751
	21st to end	Night	23% 9% 33% 28% 7%	760
May	1st to 10th	Night	25% 9% 31% 26% 8% 1	579
	11th to 20th	Night	20% 6% 33% 30% 10%	374
	21st to end	Night	17% 3 23% 41% 15% 1	411
June	1st to 10th	Night	17% 5% 27% 32% 19%	380
	11th to 20th	Night	12% 7% 24% 43% 14%	380
	21st to end	Night	13% 3 23% 48% 13%	380
July	1st to 10th	Night	13% 3 17% 44% 22% 1	370
	11th to 20th	Night	9% 3 20% 41% 26% 2	368
	21st to end	Night	13% 4 19% 38% 24% 2	450
August	1st to 10th	Night	13% 2 13% 46% 24% 2	567
	11th to 20th	Night	15% 4 15% 37% 28% 2	701
	21st to end	Night	15% 3 14% 41% 25% 2	836
September	1st to 10th	Night	18% 3 21% 36% 20% 2	760
	11th to 20th	Night	14% 3 17% 36% 26% 4	760
	21st to end	Night	21% 4 21% 33% 18% 2	760
October	1st to 10th	Night	22% 5% 24% 29% 17% 3	760
	11th to 20th	Night	17% 8% 29% 34% 11% 1	760
	21st to end	Night	23% 7% 31% 28% 10%	836
November	1st to 10th	Night	16% 6% 35% 31% 12% 1	743
	11th to 20th	Night	19% 13% 30% 29% 8% 1	760
	21st to end	Night	18% 12% 35% 27% 7%	760
December	1st to 10th	Night	24% 11% 36% 23% 6% 1	760
	11th to 20th	Night	21% 11% 36% 26% 5%	760
	21st to end	Night	21% 12% 37% 27% 3	836

Page generated at 2024-10-29 11:20:51. Version ac07

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