Harford Community College Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Harford Community College Observatory clear sky chart from 2005-11-06 to 2024-11-10.

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	15% 6% 2 6% 4 4 4 4 6% 8% 41%	101333
	Night	16% 7% 2 6% 4 4 4 3 5% 7% 42%	97778
Transparency	Day	39% 7% 12% 23% 16% 3	104965
	Night	40% 6% 11% 24% 16% 3	102285
Seeing	Day	19% 15% 28% 23% 12% 4	15003
	Night	19% 13% 29% 27% 11% 1	24380

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	16% 6% 2 5% 4 4 3 3 5% 6% 47%	2517
	11th to 20th	Day	13% 10% 3 9% 6% 6% 4 3 4 5% 37%	2748
	21st to end	Day	20% 8% 3 6% 5% 4 5% 3 4 6% 37%	3124
February	1st to 10th	Day	15% 8% 3 6% 5% 4 4 3 5% 7% 40%	1710
	11th to 20th	Day	16% 8% 2 5% 4 4 4 4 5% 8% 40%	1757
	21st to end	Day	18% 11% 3 5% 4 3 3 3 5% 5% 39%	1570
March	1st to 10th	Day	23% 6% 2 5% 4 3 4 3 5% 6% 40%	3264
	11th to 20th	Day	10% 5% 2 6% 4 5% 5% 4 5% 7% 48%	3480
	21st to end	Day	21% 8% 2 5% 4 4 3 2 4 5% 43%	3960
April	1st to 10th	Day	15% 6% 2 6% 5% 5% 5% 4 5% 7% 41%	2280
	11th to 20th	Day	13% 7% 2 5% 5% 4 5% 3 5% 7% 44%	2254
	21st to end	Day	18% 6% 1 6% 4 4 4 4 5% 8% 41%	2280
May	1st to 10th	Day	28% 7% 2 6% 4 4 4 3 5% 6% 30%	3992
	11th to 20th	Day	23% 8% 3 7% 5% 5% 5% 4 6% 7% 28%	4398
	21st to end	Day	12% 5% 2 5% 4 4 4 4 7% 9% 45%	4823
June	1st to 10th	Day	12% 5% 2 6% 5% 5% 4 5% 6% 11% 39%	2660
	11th to 20th	Day	12% 5% 2 6% 4 5% 5% 4 8% 9% 39%	2660
	21st to end	Day	10% 4 2 4 4 4 5% 5% 7% 11% 43%	2660
July	1st to 10th	Day	6% 5% 2 6% 5% 5% 6% 5% 9% 12% 41%	4440
	11th to 20th	Day	9% 5% 2 5% 4 4 6% 5% 9% 11% 39%	4440
	21st to end	Day	10% 7% 2 8% 6% 6% 6% 5% 8% 10% 33%	4536
August	1st to 10th	Day	17% 6% 2 6% 4 5% 6% 4 7% 9% 33%	4104
	11th to 20th	Day	11% 5% 2 5% 4 5% 5% 4 8% 9% 41%	3804
	21st to end	Day	10% 4 2 5% 4 4 5% 4 7% 8% 48%	4180
September	1st to 10th	Day	14% 5% 2 5% 5% 4 4 4 5% 7% 45%	2280
	11th to 20th	Day	12% 4 1 6% 4 4 4 3 5% 7% 50%	2280
	21st to end	Day	20% 7% 3 6% 4 4 4 3 5% 7% 37%	2029
October	1st to 10th	Day	17% 6% 2 6% 4 2 4 4 4 6% 45%	1900
	11th to 20th	Day	16% 4 2 4 3 3 4 3 5% 7% 49%	1900
	21st to end	Day	15% 6% 2 6% 3 3 4 3 4 5% 48%	2090
November	1st to 10th	Day	13% 5% 1 4 4 3 4 4 5% 6% 52%	1762
	11th to 20th	Day	15% 6% 2 4 3 4 3 4 5% 6% 48%	1710
	21st to end	Day	15% 6% 2 6% 4 3 4 3 4 6% 45%	1539
December	1st to 10th	Day	18% 8% 2 5% 4 3 5% 4 5% 7% 40%	1520
	11th to 20th	Day	19% 7% 2 5% 4 4 3 3 5% 8% 41%	1910
	21st to end	Day	16% 7% 3 7% 5% 5% 4 4 5% 7% 37%	2772
January	1st to 10th	Night	16% 7% 2 6% 4 4 4 3 5% 6% 43%	4429
	11th to 20th	Night	19% 7% 3 6% 3 3 4 2 4 5% 44%	4208
	21st to end	Night	22% 8% 2 6% 3 4 3 3 5% 5% 39%	4532
February	1st to 10th	Night	16% 8% 3 6% 5% 3 4 4 4 6% 40%	2470
	11th to 20th	Night	16% 9% 2 6% 4 4 4 3 4 5% 43%	2309
	21st to end	Night	17% 8% 3 6% 5% 4 3 4 4 5% 42%	1884
March	1st to 10th	Night	21% 8% 2 5% 4 4 3 3 4 6% 40%	3587
	11th to 20th	Night	11% 5% 1 5% 4 4 4 3 5% 6% 50%	3480
	21st to end	Night	16% 9% 2 5% 4 3 3 3 3 4 47%	3671
April	1st to 10th	Night	17% 7% 2 5% 4 5% 4 3 5% 7% 40%	1900
	11th to 20th	Night	14% 7% 2 6% 3 3 4 3 5% 7% 45%	1875
	21st to end	Night	19% 6% 2 4 3 3 3 3 5% 6% 45%	1900
May	1st to 10th	Night	25% 8% 2 6% 4 3 4 3 5% 7% 32%	2930
	11th to 20th	Night	26% 10% 4 6% 5% 4 4 3 5% 6% 28%	2495
	21st to end	Night	13% 6% 2 5% 3 3 4 4 6% 11% 42%	2732
June	1st to 10th	Night	13% 5% 3 6% 5% 3 4 3 5% 8% 45%	1520
	11th to 20th	Night	10% 6% 3 6% 5% 5% 5% 4 7% 9% 40%	1520
	21st to end	Night	11% 4 2 6% 4 4 5% 5% 8% 11% 42%	1520
July	1st to 10th	Night	7% 5% 2 7% 6% 6% 6% 5% 7% 10% 39%	2520
	11th to 20th	Night	9% 6% 2 7% 5% 5% 5% 4 7% 10% 38%	2520
	21st to end	Night	13% 8% 3 7% 5% 4 5% 4 6% 9% 37%	3013
August	1st to 10th	Night	19% 5% 2 6% 5% 4 4 4 7% 10% 33%	2825
	11th to 20th	Night	12% 6% 3 8% 5% 4 5% 4 6% 7% 39%	2993
	21st to end	Night	12% 5% 2 6% 3 4 4 4 5% 8% 48%	3476
September	1st to 10th	Night	13% 6% 2 6% 4 4 4 3 5% 7% 45%	1900
	11th to 20th	Night	11% 6% 2 6% 3 3 3 3 3 7% 53%	1900
	21st to end	Night	19% 8% 1 6% 4 4 4 3 4 6% 40%	2146
October	1st to 10th	Night	19% 7% 2 6% 4 3 4 3 4 6% 42%	2280
	11th to 20th	Night	16% 5% 1 5% 3 3 3 3 4 6% 51%	2280
	21st to end	Night	17% 4 1 4 3 3 4 3 4 6% 49%	2508
November	1st to 10th	Night	11% 6% 2 5% 4 3 3 3 5% 6% 53%	2517
	11th to 20th	Night	16% 6% 2 5% 4 3 3 2 5% 5% 48%	2470
	21st to end	Night	13% 5% 2 5% 5% 4 4 3 5% 7% 47%	2639
December	1st to 10th	Night	18% 8% 2 6% 4 4 4 3 5% 6% 40%	2660
	11th to 20th	Night	17% 6% 2 6% 4 4 4 3 5% 7% 42%	3285
	21st to end	Night	16% 7% 3 7% 5% 5% 5% 4 7% 8% 34%	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% 6% 12% 28% 13% 4	2518
	11th to 20th	Day	49% 5% 9% 21% 13% 3	2748
	21st to end	Day	47% 8% 12% 22% 10% 2	3124
February	1st to 10th	Day	43% 5% 14% 24% 12% 2	1710
	11th to 20th	Day	43% 4 10% 25% 15% 3	1766
	21st to end	Day	47% 5% 10% 21% 14% 4	1570
March	1st to 10th	Day	44% 5% 9% 27% 12% 3	3264
	11th to 20th	Day	32% 8% 9% 28% 19% 4	3480
	21st to end	Day	45% 4 9% 20% 18% 4	3960
April	1st to 10th	Day	41% 7% 11% 20% 17% 5%	2280
	11th to 20th	Day	38% 6% 12% 21% 17% 5%	2254
	21st to end	Day	41% 5% 11% 19% 20% 4	2280
May	1st to 10th	Day	52% 7% 10% 18% 11% 2	4027
	11th to 20th	Day	50% 11% 14% 17% 7% 2	4402
	21st to end	Day	33% 9% 13% 26% 17% 2	4837
June	1st to 10th	Day	37% 9% 12% 24% 15% 2	2660
	11th to 20th	Day	38% 9% 12% 24% 13% 3	2660
	21st to end	Day	32% 10% 15% 25% 18% 1	2660
July	1st to 10th	Day	33% 12% 18% 19% 14% 5%	4370
	11th to 20th	Day	35% 10% 17% 26% 10% 2	4365
	21st to end	Day	44% 8% 12% 19% 16% 1	4391
August	1st to 10th	Day	44% 9% 14% 24% 8%	4091
	11th to 20th	Day	37% 8% 11% 28% 14% 1	3842
	21st to end	Day	32% 7% 13% 28% 17% 2	4180
September	1st to 10th	Day	38% 7% 11% 20% 20% 4	2280
	11th to 20th	Day	33% 6% 9% 27% 22% 4	2280
	21st to end	Day	47% 6% 8% 19% 19% 2	2029
October	1st to 10th	Day	36% 5% 7% 19% 28% 5%	3160
	11th to 20th	Day	26% 4 10% 25% 26% 10%	3140
	21st to end	Day	25% 3 10% 30% 27% 5%	3428
November	1st to 10th	Day	32% 5% 13% 25% 21% 4	1762
	11th to 20th	Day	37% 5% 10% 23% 22% 3	1710
	21st to end	Day	39% 5% 11% 30% 13% 3	1539
December	1st to 10th	Day	44% 5% 14% 23% 12% 2	1520
	11th to 20th	Day	42% 5% 11% 30% 10% 2	1906
	21st to end	Day	45% 8% 14% 20% 12%	2772
January	1st to 10th	Night	41% 5% 10% 26% 14% 3	4429
	11th to 20th	Night	42% 5% 10% 26% 14% 2	4208
	21st to end	Night	47% 5% 8% 28% 12% 1	4532
February	1st to 10th	Night	44% 5% 13% 24% 13% 1	2470
	11th to 20th	Night	44% 4 9% 21% 19% 4	2311
	21st to end	Night	45% 4 10% 20% 16% 5%	1884
March	1st to 10th	Night	46% 6% 9% 26% 12% 2	3587
	11th to 20th	Night	33% 6% 11% 31% 16% 3	3480
	21st to end	Night	41% 5% 8% 20% 22% 5%	3671
April	1st to 10th	Night	42% 6% 10% 19% 19% 4	1900
	11th to 20th	Night	38% 6% 12% 20% 19% 5%	1875
	21st to end	Night	40% 6% 10% 21% 18% 5%	1900
May	1st to 10th	Night	51% 6% 9% 19% 13% 2	2960
	11th to 20th	Night	55% 9% 12% 13% 10% 1	2496
	21st to end	Night	34% 10% 15% 23% 14% 4	2739
June	1st to 10th	Night	37% 7% 12% 24% 18% 2	1520
	11th to 20th	Night	38% 8% 13% 24% 15% 1	1520
	21st to end	Night	34% 9% 13% 27% 15% 3	1520
July	1st to 10th	Night	39% 9% 20% 16% 12% 4	2480
	11th to 20th	Night	39% 9% 18% 23% 10% 1	2472
	21st to end	Night	44% 7% 13% 19% 15% 1	2917
August	1st to 10th	Night	45% 8% 18% 20% 9% 1	2814
	11th to 20th	Night	41% 7% 10% 27% 13% 1	3021
	21st to end	Night	34% 6% 10% 31% 17% 2	3476
September	1st to 10th	Night	38% 7% 10% 20% 20% 5%	1900
	11th to 20th	Night	32% 5% 10% 25% 25% 4	1900
	21st to end	Night	45% 5% 9% 19% 19% 3	2146
October	1st to 10th	Night	45% 4 9% 19% 21% 2	3800
	11th to 20th	Night	25% 3 11% 26% 29% 6%	3779
	21st to end	Night	24% 4 11% 32% 24% 6%	4120
November	1st to 10th	Night	32% 5% 10% 26% 21% 5%	2517
	11th to 20th	Night	38% 4 9% 23% 20% 5%	2470
	21st to end	Night	36% 5% 11% 27% 18% 2	2639
December	1st to 10th	Night	45% 5% 11% 24% 14% 1	2660
	11th to 20th	Night	41% 5% 12% 21% 17% 3	3288
	21st to end	Night	43% 9% 15% 22% 10% 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	24% 31% 28% 14% 2 1	180
	11th to 20th	Day	28% 31% 27% 13% 1	245
	21st to end	Day	23% 31% 30% 12% 4 1	297
February	1st to 10th	Day	23% 29% 35% 10% 3	270
	11th to 20th	Day	30% 24% 37% 6% 1	364
	21st to end	Day	29% 26% 29% 13% 3	382
March	1st to 10th	Day	23% 24% 31% 18% 3	460
	11th to 20th	Day	26% 25% 30% 14% 4 1	460
	21st to end	Day	25% 22% 31% 16% 4 1	506
April	1st to 10th	Day	21% 23% 36% 14% 5% 1	460
	11th to 20th	Day	19% 23% 28% 19% 8% 3	452
	21st to end	Day	25% 18% 33% 17% 6% 1	460
May	1st to 10th	Day	30% 15% 29% 16% 8% 2	463
	11th to 20th	Day	22% 14% 30% 22% 10% 2	487
	21st to end	Day	19% 8% 24% 27% 19% 4	529
June	1st to 10th	Day	14% 11% 30% 27% 14% 4	490
	11th to 20th	Day	16% 8% 26% 30% 16% 4	490
	21st to end	Day	14% 8% 31% 30% 13% 5%	490
July	1st to 10th	Day	12% 2 20% 35% 24% 8%	485
	11th to 20th	Day	5% 4 21% 39% 24% 7%	484
	21st to end	Day	12% 8% 23% 31% 22% 4	532
August	1st to 10th	Day	13% 4 22% 33% 21% 7%	486
	11th to 20th	Day	11% 5% 18% 35% 23% 8%	479
	21st to end	Day	11% 5% 24% 31% 20% 9%	539
September	1st to 10th	Day	17% 8% 19% 26% 21% 9%	490
	11th to 20th	Day	14% 5% 23% 32% 18% 8%	490
	21st to end	Day	28% 12% 20% 24% 14% 2	490
October	1st to 10th	Day	23% 10% 23% 23% 15% 6%	490
	11th to 20th	Day	18% 16% 26% 25% 12% 3	490
	21st to end	Day	17% 16% 34% 21% 9% 3	539
November	1st to 10th	Day	17% 13% 36% 20% 11% 3	397
	11th to 20th	Day	19% 22% 30% 22% 7% 1	370
	21st to end	Day	22% 19% 32% 20% 7% 1	199
December	1st to 10th	Day	23% 24% 34% 13% 4 1	180
	11th to 20th	Day	29% 24% 29% 14% 4	180
	21st to end	Day	24% 19% 33% 16% 8%	198
January	1st to 10th	Night	20% 20% 40% 17% 3	760
	11th to 20th	Night	26% 17% 31% 22% 4	760
	21st to end	Night	20% 21% 37% 21% 1	836
February	1st to 10th	Night	21% 19% 35% 23% 2	760
	11th to 20th	Night	24% 23% 37% 14% 1	743
	21st to end	Night	23% 21% 36% 17% 3	628
March	1st to 10th	Night	20% 20% 36% 19% 4	760
	11th to 20th	Night	22% 20% 33% 19% 6%	760
	21st to end	Night	20% 16% 38% 20% 5%	836
April	1st to 10th	Night	22% 20% 34% 19% 5%	760
	11th to 20th	Night	17% 14% 35% 27% 7%	751
	21st to end	Night	22% 14% 29% 27% 7%	760
May	1st to 10th	Night	24% 10% 28% 29% 8% 1	651
	11th to 20th	Night	22% 9% 31% 29% 9%	374
	21st to end	Night	18% 5% 21% 37% 18% 1	411
June	1st to 10th	Night	14% 4 27% 38% 16% 1	380
	11th to 20th	Night	12% 6% 24% 39% 18% 1	380
	21st to end	Night	11% 2 25% 44% 17% 1	380
July	1st to 10th	Night	11% 4 20% 40% 22% 4	370
	11th to 20th	Night	8% 2 16% 41% 29% 4	368
	21st to end	Night	9% 3 17% 45% 23% 3	576
August	1st to 10th	Night	13% 2 16% 39% 27% 3	567
	11th to 20th	Night	14% 3 16% 34% 29% 3	682
	21st to end	Night	14% 4 16% 38% 25% 3	836
September	1st to 10th	Night	17% 5% 21% 31% 24% 3	760
	11th to 20th	Night	14% 4 18% 35% 25% 4	760
	21st to end	Night	22% 5% 22% 30% 19% 2	760
October	1st to 10th	Night	22% 7% 23% 25% 17% 5%	760
	11th to 20th	Night	18% 11% 28% 31% 12% 1	760
	21st to end	Night	19% 13% 30% 25% 13%	836
November	1st to 10th	Night	15% 12% 34% 28% 11% 1	779
	11th to 20th	Night	20% 17% 29% 25% 8% 1	760
	21st to end	Night	16% 19% 32% 24% 8% 1	760
December	1st to 10th	Night	24% 16% 33% 19% 7% 1	760
	11th to 20th	Night	19% 17% 37% 22% 5%	760
	21st to end	Night	20% 18% 33% 26% 3	836

Page generated at 2024-11-07 06:55:45. Version ac07

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