Lord Fairfax Community College
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lord Fairfax Community College 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	13% 6% 2 6% 5% 5% 5% 4 6% 7% 41%	101208
	Night	13% 7% 2 6% 4 4 4 4 6% 7% 42%	97871
Transparency	Day	40% 5% 12% 25% 16% 3	104853
	Night	40% 5% 12% 25% 17% 3	102366
Seeing	Day	18% 12% 25% 24% 15% 6%	14956
	Night	17% 10% 25% 33% 14% 1	24562

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	15% 6% 2 7% 5% 5% 4 4 5% 6% 42%	2737
	11th to 20th	Day	11% 10% 4 9% 5% 5% 4 4 5% 5% 38%	2840
	21st to end	Day	14% 10% 3 8% 5% 5% 4 3 5% 6% 36%	3124
February	1st to 10th	Day	11% 10% 3 7% 6% 5% 4 4 6% 6% 38%	1710
	11th to 20th	Day	16% 7% 3 7% 4 4 4 4 5% 6% 39%	1663
	21st to end	Day	15% 9% 2 6% 6% 4 4 4 5% 5% 40%	1598
March	1st to 10th	Day	19% 10% 3 7% 5% 4 4 3 4 5% 36%	3435
	11th to 20th	Day	9% 6% 2 5% 4 3 4 4 6% 7% 50%	3480
	21st to end	Day	18% 8% 3 7% 4 4 3 4 6% 6% 38%	3815
April	1st to 10th	Day	10% 7% 3 6% 5% 4 6% 4 6% 8% 41%	2264
	11th to 20th	Day	12% 6% 2 6% 5% 4 4 4 5% 6% 46%	2254
	21st to end	Day	18% 5% 2 6% 5% 4 4 4 5% 6% 40%	2323
May	1st to 10th	Day	20% 7% 3 7% 5% 5% 5% 4 6% 7% 30%	4082
	11th to 20th	Day	22% 7% 3 7% 4 4 5% 3 6% 8% 32%	4130
	21st to end	Day	10% 5% 2 6% 4 4 5% 5% 7% 9% 43%	4823
June	1st to 10th	Day	12% 5% 2 5% 5% 5% 4 4 7% 8% 43%	2660
	11th to 20th	Day	10% 5% 2 5% 4 5% 6% 6% 6% 11% 39%	2660
	21st to end	Day	10% 4 1 4 5% 5% 5% 5% 7% 10% 44%	2660
July	1st to 10th	Day	5% 4 2 6% 5% 6% 6% 4 8% 10% 44%	4426
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 4 8% 10% 41%	4120
	21st to end	Day	10% 7% 3 7% 6% 6% 5% 4 7% 9% 37%	4466
August	1st to 10th	Day	14% 6% 2 7% 5% 6% 6% 6% 7% 9% 34%	4104
	11th to 20th	Day	8% 4 2 7% 5% 6% 6% 5% 7% 9% 42%	3980
	21st to end	Day	8% 6% 2 5% 4 4 5% 4 7% 8% 48%	4180
September	1st to 10th	Day	15% 5% 2 6% 5% 4 4 2 5% 6% 46%	2280
	11th to 20th	Day	12% 5% 2 6% 4 3 4 3 6% 8% 46%	2228
	21st to end	Day	20% 7% 2 6% 5% 4 5% 3 5% 5% 39%	2009
October	1st to 10th	Day	16% 6% 2 5% 4 3 3 3 5% 7% 47%	1900
	11th to 20th	Day	14% 4 2 6% 3 4 4 3 5% 6% 48%	1900
	21st to end	Day	14% 5% 2 5% 4 3 3 4 4 6% 51%	2090
November	1st to 10th	Day	10% 5% 2 5% 4 3 4 4 5% 7% 52%	1930
	11th to 20th	Day	14% 6% 2 5% 4 3 4 4 5% 6% 46%	1615
	21st to end	Day	14% 6% 2 5% 4 4 4 3 4 6% 48%	1520
December	1st to 10th	Day	15% 8% 3 7% 4 4 5% 4 6% 7% 38%	1520
	11th to 20th	Day	15% 6% 2 6% 5% 4 4 4 5% 7% 42%	1910
	21st to end	Day	17% 6% 2 6% 5% 5% 6% 4 6% 8% 34%	2772
January	1st to 10th	Night	9% 9% 3 7% 4 4 4 4 5% 7% 43%	4205
	11th to 20th	Night	16% 8% 2 6% 4 4 3 3 5% 5% 44%	4120
	21st to end	Night	17% 10% 3 7% 4 3 4 3 5% 5% 39%	4532
February	1st to 10th	Night	13% 7% 4 6% 5% 4 4 4 6% 6% 41%	2470
	11th to 20th	Night	15% 9% 3 6% 4 4 5% 4 5% 5% 40%	2403
	21st to end	Night	15% 9% 3 7% 5% 5% 4 3 5% 6% 39%	1853
March	1st to 10th	Night	19% 8% 3 7% 4 4 5% 4 5% 5% 37%	3418
	11th to 20th	Night	11% 7% 2 6% 4 4 5% 3 5% 7% 48%	3480
	21st to end	Night	12% 6% 2 6% 4 4 4 3 4 5% 48%	3817
April	1st to 10th	Night	13% 9% 2 7% 5% 4 4 4 6% 7% 39%	1914
	11th to 20th	Night	11% 6% 1 6% 5% 3 3 4 6% 8% 44%	1875
	21st to end	Night	15% 5% 2 4 5% 4 5% 4 5% 7% 43%	1873
May	1st to 10th	Night	21% 8% 2 7% 5% 4 5% 4 5% 7% 31%	2813
	11th to 20th	Night	22% 9% 2 6% 5% 4 4 3 6% 6% 34%	2760
	21st to end	Night	10% 5% 2 5% 4 5% 4 5% 8% 10% 43%	2732
June	1st to 10th	Night	10% 4 2 5% 4 5% 5% 5% 7% 9% 45%	1520
	11th to 20th	Night	10% 5% 3 5% 5% 4 5% 4 6% 9% 43%	1520
	21st to end	Night	8% 4 2 6% 4 5% 5% 4 9% 11% 43%	1520
July	1st to 10th	Night	6% 4 2 6% 5% 5% 7% 5% 8% 11% 41%	2520
	11th to 20th	Night	6% 6% 2 7% 6% 6% 6% 5% 8% 11% 38%	2835
	21st to end	Night	9% 6% 3 8% 6% 5% 5% 5% 7% 9% 37%	3087
August	1st to 10th	Night	13% 5% 2 7% 6% 5% 5% 5% 7% 10% 34%	2825
	11th to 20th	Night	8% 6% 2 7% 5% 6% 5% 5% 7% 9% 41%	2817
	21st to end	Night	9% 5% 2 6% 4 4 4 4 6% 9% 47%	3476
September	1st to 10th	Night	13% 5% 2 6% 5% 4 5% 3 6% 6% 45%	1900
	11th to 20th	Night	11% 5% 2 6% 4 4 3 3 4 6% 51%	1947
	21st to end	Night	19% 7% 2 5% 3 4 3 3 4 6% 44%	2170
October	1st to 10th	Night	19% 5% 2 4 3 3 4 3 4 5% 47%	2280
	11th to 20th	Night	13% 4 2 5% 3 3 4 3 5% 6% 52%	2280
	21st to end	Night	13% 5% 2 5% 3 3 3 4 5% 6% 51%	2508
November	1st to 10th	Night	9% 7% 2 5% 4 3 4 3 5% 6% 53%	2350
	11th to 20th	Night	12% 7% 3 5% 4 3 4 3 5% 7% 47%	2562
	21st to end	Night	13% 5% 2 5% 5% 4 4 4 6% 7% 46%	2660
December	1st to 10th	Night	15% 8% 2 7% 4 4 4 3 5% 6% 41%	2660
	11th to 20th	Night	15% 7% 3 6% 4 4 4 4 5% 7% 42%	3285
	21st to end	Night	15% 7% 2 7% 5% 5% 6% 5% 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	43% 3 7% 29% 15% 3	2738
	11th to 20th	Day	49% 2 9% 19% 15% 5%	2840
	21st to end	Day	50% 2 11% 22% 13% 2	3124
February	1st to 10th	Day	46% 4 13% 22% 13% 3	1710
	11th to 20th	Day	45% 4 9% 22% 17% 2	1672
	21st to end	Day	46% 3 11% 20% 17% 4	1598
March	1st to 10th	Day	51% 3 8% 21% 13% 3	3435
	11th to 20th	Day	34% 3 6% 30% 23% 3	3480
	21st to end	Day	46% 3 12% 20% 14% 3	3815
April	1st to 10th	Day	41% 5% 12% 20% 18% 5%	2264
	11th to 20th	Day	39% 3 10% 22% 20% 6%	2254
	21st to end	Day	45% 5% 9% 23% 15% 4	2323
May	1st to 10th	Day	52% 4 11% 21% 10% 1	4120
	11th to 20th	Day	50% 5% 11% 24% 8% 1	4134
	21st to end	Day	36% 5% 15% 24% 17% 3	4837
June	1st to 10th	Day	38% 5% 14% 25% 16% 1	2660
	11th to 20th	Day	38% 7% 16% 23% 14% 2	2660
	21st to end	Day	34% 6% 16% 27% 16% 2	2660
July	1st to 10th	Day	33% 8% 17% 25% 11% 5%	4356
	11th to 20th	Day	35% 7% 15% 31% 10% 1	4051
	21st to end	Day	43% 6% 9% 24% 17% 1	4324
August	1st to 10th	Day	45% 7% 15% 24% 8%	4091
	11th to 20th	Day	35% 8% 13% 28% 15% 1	4019
	21st to end	Day	32% 6% 16% 28% 16% 1	4180
September	1st to 10th	Day	40% 4 12% 19% 21% 4	2280
	11th to 20th	Day	37% 4 8% 28% 20% 3	2228
	21st to end	Day	47% 4 7% 22% 17% 2	2009
October	1st to 10th	Day	33% 4 9% 20% 27% 6%	3160
	11th to 20th	Day	27% 3 8% 30% 24% 8%	3140
	21st to end	Day	24% 3 10% 29% 30% 5%	3428
November	1st to 10th	Day	33% 3 11% 25% 24% 4	1930
	11th to 20th	Day	40% 2 10% 21% 22% 5%	1615
	21st to end	Day	39% 3 11% 28% 18% 2	1520
December	1st to 10th	Day	46% 4 13% 24% 11% 2	1520
	11th to 20th	Day	42% 3 10% 29% 12% 4	1906
	21st to end	Day	47% 4 14% 24% 11% 1	2772
January	1st to 10th	Night	40% 4 9% 27% 17% 3	4205
	11th to 20th	Night	43% 3 10% 25% 16% 4	4120
	21st to end	Night	48% 3 9% 26% 13% 1	4532
February	1st to 10th	Night	43% 4 11% 25% 14% 1	2470
	11th to 20th	Night	45% 3 9% 23% 16% 4	2405
	21st to end	Night	48% 3 10% 21% 13% 5%	1853
March	1st to 10th	Night	47% 4 9% 28% 11% 2	3418
	11th to 20th	Night	36% 3 9% 28% 21% 3	3480
	21st to end	Night	39% 3 10% 25% 19% 4	3817
April	1st to 10th	Night	43% 5% 10% 21% 18% 4	1914
	11th to 20th	Night	38% 4 12% 22% 19% 5%	1875
	21st to end	Night	40% 5% 10% 27% 14% 4	1873
May	1st to 10th	Night	53% 4 11% 18% 11% 2	2840
	11th to 20th	Night	51% 5% 11% 23% 9% 1	2761
	21st to end	Night	35% 5% 18% 27% 10% 4	2739
June	1st to 10th	Night	34% 7% 12% 29% 15% 2	1520
	11th to 20th	Night	36% 7% 16% 26% 14% 1	1520
	21st to end	Night	33% 6% 17% 25% 17% 2	1520
July	1st to 10th	Night	35% 9% 20% 19% 12% 5%	2480
	11th to 20th	Night	36% 10% 17% 24% 11% 1	2782
	21st to end	Night	40% 7% 16% 21% 15% 1	2988
August	1st to 10th	Night	44% 8% 16% 25% 7% 1	2814
	11th to 20th	Night	38% 8% 13% 25% 16%	2844
	21st to end	Night	33% 6% 15% 30% 15% 2	3476
September	1st to 10th	Night	38% 5% 12% 21% 19% 5%	1900
	11th to 20th	Night	34% 4 8% 31% 21% 2	1947
	21st to end	Night	43% 4 10% 24% 18% 2	2170
October	1st to 10th	Night	39% 4 10% 23% 21% 3	3800
	11th to 20th	Night	24% 4 10% 23% 32% 6%	3779
	21st to end	Night	23% 3 10% 32% 27% 5%	4120
November	1st to 10th	Night	32% 3 11% 26% 23% 5%	2350
	11th to 20th	Night	38% 3 7% 25% 22% 6%	2562
	21st to end	Night	38% 3 11% 25% 19% 3	2660
December	1st to 10th	Night	45% 4 10% 26% 12% 2	2660
	11th to 20th	Night	43% 3 10% 24% 17% 3	3288
	21st to end	Night	46% 4 16% 21% 13% 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	28% 25% 26% 17% 4	241
	11th to 20th	Day	29% 23% 28% 16% 4	270
	21st to end	Day	24% 26% 30% 14% 5% 1	297
February	1st to 10th	Day	26% 21% 34% 12% 6%	270
	11th to 20th	Day	36% 26% 30% 8%	270
	21st to end	Day	29% 19% 30% 20% 2	372
March	1st to 10th	Day	25% 24% 24% 23% 3 1	460
	11th to 20th	Day	24% 22% 30% 16% 6% 2	460
	21st to end	Day	22% 18% 32% 21% 5% 2	506
April	1st to 10th	Day	22% 19% 29% 20% 8% 1	460
	11th to 20th	Day	17% 18% 27% 24% 10% 5%	452
	21st to end	Day	26% 13% 29% 19% 11% 2	460
May	1st to 10th	Day	24% 13% 28% 19% 12% 5%	463
	11th to 20th	Day	23% 11% 26% 23% 13% 4	487
	21st to end	Day	18% 6% 23% 29% 18% 6%	529
June	1st to 10th	Day	17% 8% 23% 27% 19% 6%	490
	11th to 20th	Day	14% 7% 26% 27% 19% 8%	490
	21st to end	Day	12% 5% 26% 29% 21% 7%	490
July	1st to 10th	Day	10% 2 18% 31% 26% 13%	485
	11th to 20th	Day	7% 2 18% 34% 29% 11%	484
	21st to end	Day	14% 3 20% 32% 25% 7%	532
August	1st to 10th	Day	10% 4 19% 26% 29% 12%	486
	11th to 20th	Day	11% 3 17% 31% 25% 13%	479
	21st to end	Day	9% 1 18% 30% 25% 16%	539
September	1st to 10th	Day	17% 6% 16% 23% 24% 13%	490
	11th to 20th	Day	14% 3 15% 30% 24% 13%	490
	21st to end	Day	25% 11% 18% 24% 17% 5%	490
October	1st to 10th	Day	19% 7% 18% 27% 20% 9%	490
	11th to 20th	Day	13% 14% 26% 26% 16% 4	490
	21st to end	Day	17% 11% 32% 24% 12% 3	539
November	1st to 10th	Day	16% 11% 28% 27% 14% 3	482
	11th to 20th	Day	19% 17% 26% 25% 11% 1	275
	21st to end	Day	18% 19% 34% 22% 6% 1	180
December	1st to 10th	Day	21% 19% 32% 18% 9% 1	180
	11th to 20th	Day	26% 13% 30% 23% 8%	180
	21st to end	Day	21% 14% 30% 25% 10% 1	198
January	1st to 10th	Night	17% 18% 34% 27% 4	760
	11th to 20th	Night	21% 14% 30% 29% 5%	760
	21st to end	Night	19% 16% 37% 27% 2	836
February	1st to 10th	Night	17% 16% 33% 32% 2	760
	11th to 20th	Night	24% 21% 32% 22% 1	743
	21st to end	Night	23% 16% 33% 24% 3	628
March	1st to 10th	Night	19% 18% 35% 25% 4	760
	11th to 20th	Night	23% 19% 29% 24% 5% 1	760
	21st to end	Night	18% 16% 35% 24% 6% 1	836
April	1st to 10th	Night	19% 19% 33% 24% 5%	760
	11th to 20th	Night	16% 12% 34% 27% 10% 1	751
	21st to end	Night	18% 12% 29% 32% 8%	733
May	1st to 10th	Night	22% 5% 24% 32% 16% 1	570
	11th to 20th	Night	19% 4 23% 37% 16% 1	535
	21st to end	Night	14% 3 18% 42% 21% 2	411
June	1st to 10th	Night	10% 3 23% 40% 23% 1	380
	11th to 20th	Night	9% 4 16% 43% 24% 3	380
	21st to end	Night	9% 4 16% 48% 21% 1	380
July	1st to 10th	Night	10% 2 11% 40% 31% 5%	370
	11th to 20th	Night	7% 1 8% 40% 39% 4	548
	21st to end	Night	8% 1 8% 46% 32% 4	624
August	1st to 10th	Night	9% 2 7% 45% 33% 3	567
	11th to 20th	Night	11% 2 9% 43% 32% 4	583
	21st to end	Night	12% 2 11% 41% 30% 4	836
September	1st to 10th	Night	16% 3 10% 36% 31% 5%	760
	11th to 20th	Night	13% 2 14% 35% 31% 4	760
	21st to end	Night	22% 5% 17% 33% 22% 2	760
October	1st to 10th	Night	22% 5% 15% 32% 23% 3	760
	11th to 20th	Night	16% 9% 24% 35% 16% 1	760
	21st to end	Night	17% 11% 24% 36% 11% 1	836
November	1st to 10th	Night	14% 8% 26% 38% 12% 1	779
	11th to 20th	Night	17% 14% 28% 30% 9% 1	760
	21st to end	Night	17% 14% 29% 32% 8% 1	760
December	1st to 10th	Night	20% 14% 30% 30% 7%	760
	11th to 20th	Night	18% 9% 34% 35% 4	760
	21st to end	Night	16% 13% 28% 39% 4	836

Page generated at 2024-11-07 06:55:48. Version ac07

Copyright © 2024 Attilla Danko.