FAAC Observing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the FAAC Observing Site clear sky chart from 2005-11-06 to 2024-01-15.

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% 10% 4 7% 6% 4 5% 5% 5% 7% 33%	74696
	Night	15% 10% 4 7% 6% 3 4 4 5% 7% 34%	75060
Transparency	Day	49% 6% 12% 21% 12% 1	74404
	Night	50% 5% 11% 20% 12% 1	74873
Seeing	Day	19% 10% 28% 23% 14% 6%	14443
	Night	20% 9% 28% 29% 12% 1	24503

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% 16% 6% 10% 9% 4 5% 5% 5% 5% 19%	1517
	11th to 20th	Day	17% 16% 7% 11% 9% 4 5% 5% 4 5% 16%	1472
	21st to end	Day	17% 18% 8% 10% 8% 4 4 3 4 5% 18%	1697
February	1st to 10th	Day	15% 14% 7% 11% 10% 3 6% 4 5% 5% 20%	1620
	11th to 20th	Day	16% 11% 6% 13% 10% 3 5% 4 5% 5% 24%	1734
	21st to end	Day	16% 16% 6% 10% 6% 3 4 4 4 7% 24%	1480
March	1st to 10th	Day	15% 11% 5% 7% 8% 4 6% 5% 6% 7% 28%	1810
	11th to 20th	Day	12% 13% 5% 8% 6% 3 4 4 5% 7% 34%	1980
	21st to end	Day	19% 13% 4 7% 7% 3 5% 3 4 6% 29%	2178
April	1st to 10th	Day	18% 11% 5% 6% 7% 4 4 5% 5% 6% 30%	2132
	11th to 20th	Day	17% 9% 3 6% 6% 3 4 5% 5% 7% 34%	2248
	21st to end	Day	18% 9% 3 7% 6% 2 4 4 5% 7% 35%	2340
May	1st to 10th	Day	17% 8% 4 6% 6% 4 5% 5% 5% 7% 33%	2340
	11th to 20th	Day	19% 8% 3 6% 5% 4 5% 4 5% 7% 35%	2301
	21st to end	Day	12% 7% 3 5% 5% 4 6% 4 7% 9% 39%	2572
June	1st to 10th	Day	11% 6% 3 5% 5% 3 5% 6% 5% 9% 43%	2520
	11th to 20th	Day	11% 6% 1 6% 5% 5% 5% 6% 6% 9% 40%	2520
	21st to end	Day	9% 5% 3 6% 6% 3 6% 6% 7% 11% 38%	2520
July	1st to 10th	Day	7% 5% 2 5% 5% 3 5% 6% 7% 10% 46%	2520
	11th to 20th	Day	9% 5% 3 5% 6% 3 6% 5% 7% 9% 43%	2520
	21st to end	Day	7% 5% 3 5% 6% 3 6% 6% 7% 9% 43%	2638
August	1st to 10th	Day	8% 5% 2 6% 6% 4 6% 6% 7% 9% 42%	2327
	11th to 20th	Day	10% 6% 3 6% 7% 4 6% 6% 6% 8% 39%	2303
	21st to end	Day	10% 6% 3 4 6% 3 5% 5% 6% 9% 43%	2504
September	1st to 10th	Day	11% 6% 2 6% 7% 4 5% 6% 5% 7% 40%	2062
	11th to 20th	Day	10% 5% 3 5% 5% 3 4 6% 6% 9% 45%	1980
	21st to end	Day	13% 6% 3 6% 6% 3 5% 6% 6% 8% 38%	1980
October	1st to 10th	Day	13% 6% 4 6% 6% 3 5% 4 6% 7% 40%	1959
	11th to 20th	Day	17% 10% 3 8% 6% 4 5% 5% 4 6% 32%	1800
	21st to end	Day	21% 11% 3 7% 6% 3 4 4 5% 7% 29%	1796
November	1st to 10th	Day	12% 9% 4 6% 6% 3 5% 5% 5% 8% 38%	1672
	11th to 20th	Day	15% 13% 5% 7% 6% 4 5% 4 5% 5% 31%	1710
	21st to end	Day	20% 11% 5% 6% 7% 3 5% 4 4 6% 29%	1710
December	1st to 10th	Day	14% 16% 8% 11% 8% 4 5% 4 4 6% 21%	1571
	11th to 20th	Day	15% 16% 7% 11% 6% 4 4 6% 6% 6% 20%	1880
	21st to end	Day	23% 21% 8% 11% 7% 4 5% 3 3 4 12%	2783
January	1st to 10th	Night	17% 13% 6% 11% 7% 4 4 5% 5% 5% 23%	2648
	11th to 20th	Night	18% 16% 6% 11% 6% 4 5% 4 4 6% 19%	2577
	21st to end	Night	13% 13% 10% 12% 8% 4 4 5% 4 6% 20%	2656
February	1st to 10th	Night	18% 16% 5% 10% 8% 4 5% 4 4 5% 22%	2340
	11th to 20th	Night	15% 13% 6% 9% 8% 4 5% 4 5% 5% 27%	2110
	21st to end	Night	19% 11% 5% 10% 6% 3 4 4 5% 6% 29%	1776
March	1st to 10th	Night	16% 10% 4 8% 7% 3 4 4 4 6% 34%	2147
	11th to 20th	Night	12% 10% 4 6% 5% 4 5% 5% 5% 8% 37%	1980
	21st to end	Night	19% 8% 4 7% 5% 3 4 4 5% 6% 33%	2178
April	1st to 10th	Night	15% 9% 4 7% 6% 3 5% 4 6% 7% 36%	1841
	11th to 20th	Night	19% 9% 3 4 5% 3 5% 5% 5% 7% 36%	1660
	21st to end	Night	17% 9% 2 5% 6% 3 4 4 4 6% 38%	1620
May	1st to 10th	Night	18% 8% 3 7% 7% 3 5% 5% 5% 8% 32%	1620
	11th to 20th	Night	20% 5% 2 5% 5% 3 5% 5% 5% 7% 39%	1592
	21st to end	Night	10% 6% 2 5% 5% 3 5% 5% 6% 10% 43%	1699
June	1st to 10th	Night	10% 5% 3 4 4 3 5% 5% 5% 8% 47%	1440
	11th to 20th	Night	10% 5% 2 6% 6% 3 4 4 6% 10% 44%	1440
	21st to end	Night	9% 5% 3 5% 4 2 4 4 7% 10% 48%	1440
July	1st to 10th	Night	6% 3 2 5% 5% 3 5% 4 5% 8% 52%	1440
	11th to 20th	Night	8% 4 2 5% 4 2 4 4 5% 9% 52%	1440
	21st to end	Night	5% 4 2 5% 5% 2 5% 5% 7% 9% 52%	1678
August	1st to 10th	Night	7% 4 2 5% 5% 3 5% 4 5% 10% 49%	1611
	11th to 20th	Night	8% 4 2 4 5% 3 5% 5% 6% 9% 49%	1598
	21st to end	Night	8% 4 3 4 5% 4 3 5% 5% 7% 52%	1849
September	1st to 10th	Night	10% 6% 2 5% 5% 4 4 5% 6% 7% 47%	1880
	11th to 20th	Night	10% 5% 2 4 3 3 4 3 4 7% 54%	1980
	21st to end	Night	13% 6% 2 5% 5% 3 5% 4 5% 7% 44%	1980
October	1st to 10th	Night	13% 8% 3 6% 5% 3 4 4 4 6% 44%	1999
	11th to 20th	Night	19% 10% 4 7% 5% 3 4 4 4 6% 34%	2160
	21st to end	Night	22% 10% 3 5% 5% 3 4 5% 5% 6% 33%	2556
November	1st to 10th	Night	13% 10% 2 7% 5% 2 4 4 4 7% 42%	2406
	11th to 20th	Night	15% 11% 5% 6% 7% 3 5% 5% 6% 6% 32%	2470
	21st to end	Night	19% 13% 5% 7% 6% 3 4 4 5% 6% 29%	2470
December	1st to 10th	Night	16% 16% 8% 10% 8% 4 5% 4 4 7% 20%	2596
	11th to 20th	Night	14% 14% 6% 11% 8% 4 5% 5% 5% 6% 22%	3299
	21st to end	Night	26% 22% 7% 9% 6% 3 4 4 4 4 11%	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	65% 6% 10% 14% 6%	1518
	11th to 20th	Day	69% 6% 11% 9% 4	1472
	21st to end	Day	70% 4 8% 12% 6% 1	1697
February	1st to 10th	Day	65% 6% 10% 12% 6% 1	1620
	11th to 20th	Day	63% 4 9% 15% 8% 1	1744
	21st to end	Day	61% 3 11% 15% 7% 1	1480
March	1st to 10th	Day	54% 7% 11% 17% 9% 1	1810
	11th to 20th	Day	51% 5% 10% 19% 13% 3	1980
	21st to end	Day	56% 4 10% 20% 8% 1	2178
April	1st to 10th	Day	54% 5% 9% 20% 11%	2132
	11th to 20th	Day	49% 5% 10% 20% 13% 2	2248
	21st to end	Day	49% 5% 14% 17% 14% 2	2340
May	1st to 10th	Day	50% 6% 12% 21% 10% 2	2340
	11th to 20th	Day	50% 5% 10% 20% 14% 2	2305
	21st to end	Day	40% 6% 15% 24% 13% 2	2572
June	1st to 10th	Day	37% 6% 12% 28% 14% 3	2520
	11th to 20th	Day	39% 6% 13% 24% 17% 2	2520
	21st to end	Day	38% 7% 15% 22% 16% 2	2520
July	1st to 10th	Day	33% 7% 12% 26% 19% 4	2451
	11th to 20th	Day	36% 7% 12% 25% 18% 2	2445
	21st to end	Day	34% 8% 13% 25% 18% 2	2491
August	1st to 10th	Day	36% 8% 13% 29% 13% 1	2314
	11th to 20th	Day	42% 6% 13% 24% 14% 2	2303
	21st to end	Day	36% 7% 11% 27% 18% 2	2504
September	1st to 10th	Day	41% 7% 14% 22% 14% 2	2062
	11th to 20th	Day	34% 7% 11% 33% 15% 1	1980
	21st to end	Day	41% 6% 14% 25% 15%	1980
October	1st to 10th	Day	42% 7% 10% 26% 14% 2	1959
	11th to 20th	Day	52% 5% 12% 20% 11%	1800
	21st to end	Day	55% 5% 12% 18% 9% 1	1796
November	1st to 10th	Day	45% 6% 11% 23% 14% 1	1672
	11th to 20th	Day	54% 4 12% 20% 8% 2	1710
	21st to end	Day	57% 5% 14% 17% 7% 1	1710
December	1st to 10th	Day	66% 4 10% 15% 4	1571
	11th to 20th	Day	62% 6% 13% 14% 4	1877
	21st to end	Day	78% 4 8% 6% 3	2783
January	1st to 10th	Night	62% 5% 9% 17% 6%	2648
	11th to 20th	Night	66% 5% 13% 10% 6%	2577
	21st to end	Night	64% 5% 11% 13% 5% 1	2656
February	1st to 10th	Night	66% 5% 10% 13% 6% 1	2340
	11th to 20th	Night	59% 5% 9% 17% 9% 1	2111
	21st to end	Night	56% 4 12% 17% 9% 2	1776
March	1st to 10th	Night	51% 5% 11% 22% 11% 1	2147
	11th to 20th	Night	45% 6% 11% 21% 15% 2	1980
	21st to end	Night	53% 4 9% 21% 11% 2	2178
April	1st to 10th	Night	47% 5% 10% 22% 14% 1	1841
	11th to 20th	Night	46% 5% 11% 18% 18% 2	1660
	21st to end	Night	47% 5% 11% 19% 15% 3	1620
May	1st to 10th	Night	50% 5% 11% 21% 10% 2	1620
	11th to 20th	Night	45% 4 10% 19% 19% 3	1593
	21st to end	Night	37% 6% 15% 25% 14% 3	1700
June	1st to 10th	Night	33% 7% 10% 28% 18% 3	1440
	11th to 20th	Night	36% 6% 15% 25% 17% 2	1440
	21st to end	Night	32% 6% 14% 28% 19% 1	1440
July	1st to 10th	Night	31% 6% 11% 29% 20% 4	1400
	11th to 20th	Night	29% 5% 12% 30% 20% 3	1392
	21st to end	Night	25% 7% 18% 25% 20% 4	1585
August	1st to 10th	Night	31% 6% 15% 31% 15% 2	1600
	11th to 20th	Night	31% 7% 14% 31% 14% 3	1598
	21st to end	Night	31% 6% 12% 28% 21% 2	1849
September	1st to 10th	Night	35% 7% 12% 27% 18% 2	1880
	11th to 20th	Night	31% 5% 10% 31% 21% 1	1980
	21st to end	Night	39% 6% 12% 28% 15% 1	1980
October	1st to 10th	Night	40% 6% 10% 25% 18% 1	1999
	11th to 20th	Night	51% 6% 10% 20% 13% 1	2160
	21st to end	Night	52% 6% 10% 22% 9% 1	2556
November	1st to 10th	Night	43% 5% 11% 24% 16% 1	2406
	11th to 20th	Night	51% 5% 15% 20% 9% 1	2470
	21st to end	Night	56% 4 13% 19% 7%	2470
December	1st to 10th	Night	65% 5% 10% 14% 6%	2596
	11th to 20th	Night	61% 6% 12% 15% 6% 1	3301
	21st to end	Night	76% 5% 10% 7% 2	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% 14% 37% 17% 6% 1	270
	11th to 20th	Day	24% 13% 43% 15% 4 1	252
	21st to end	Day	28% 15% 36% 14% 6%	264
February	1st to 10th	Day	28% 22% 35% 13% 3	240
	11th to 20th	Day	30% 21% 36% 11% 1 1	240
	21st to end	Day	32% 26% 31% 10% 1	198
March	1st to 10th	Day	27% 23% 32% 16% 2	250
	11th to 20th	Day	25% 11% 33% 23% 8% 1	420
	21st to end	Day	31% 11% 31% 21% 5% 1	462
April	1st to 10th	Day	24% 12% 34% 22% 8% 1	420
	11th to 20th	Day	28% 14% 31% 13% 8% 5%	412
	21st to end	Day	24% 12% 30% 21% 9% 3	420
May	1st to 10th	Day	26% 10% 31% 20% 10% 3	423
	11th to 20th	Day	21% 10% 28% 21% 13% 7%	447
	21st to end	Day	17% 7% 22% 26% 20% 9%	526
June	1st to 10th	Day	12% 6% 30% 30% 17% 5%	630
	11th to 20th	Day	14% 6% 28% 29% 19% 4	630
	21st to end	Day	12% 7% 29% 29% 17% 6%	630
July	1st to 10th	Day	10% 3 20% 29% 27% 12%	621
	11th to 20th	Day	13% 4 26% 28% 19% 9%	618
	21st to end	Day	9% 3 25% 29% 23% 10%	579
August	1st to 10th	Day	10% 2 18% 27% 25% 17%	446
	11th to 20th	Day	14% 3 18% 25% 28% 12%	439
	21st to end	Day	14% 3 20% 27% 25% 11%	495
September	1st to 10th	Day	15% 5% 20% 25% 23% 12%	450
	11th to 20th	Day	11% 4 18% 25% 27% 14%	450
	21st to end	Day	17% 10% 22% 23% 20% 9%	450
October	1st to 10th	Day	18% 6% 30% 24% 16% 7%	450
	11th to 20th	Day	22% 16% 28% 25% 9%	450
	21st to end	Day	31% 16% 32% 15% 5%	311
November	1st to 10th	Day	16% 19% 33% 23% 9% 1	270
	11th to 20th	Day	23% 19% 34% 18% 6% 1	270
	21st to end	Day	26% 17% 40% 11% 5%	270
December	1st to 10th	Day	31% 18% 31% 13% 7%	203
	11th to 20th	Day	27% 20% 38% 10% 4	240
	21st to end	Day	26% 21% 35% 15% 2	297
January	1st to 10th	Night	24% 13% 36% 21% 5% 1	950
	11th to 20th	Night	26% 13% 35% 22% 5% 1	921
	21st to end	Night	20% 11% 35% 28% 6%	874
February	1st to 10th	Night	28% 13% 35% 23% 2	720
	11th to 20th	Night	24% 13% 35% 25% 3	703
	21st to end	Night	26% 15% 35% 21% 3	592
March	1st to 10th	Night	22% 13% 34% 25% 6%	720
	11th to 20th	Night	20% 14% 35% 25% 6% 1	720
	21st to end	Night	25% 10% 30% 26% 8% 1	792
April	1st to 10th	Night	19% 14% 35% 26% 5% 1	581
	11th to 20th	Night	23% 10% 33% 24% 9% 1	533
	21st to end	Night	22% 6% 32% 29% 9%	540
May	1st to 10th	Night	23% 6% 29% 32% 9% 1	540
	11th to 20th	Night	23% 3 28% 31% 14% 1	531
	21st to end	Night	13% 2 24% 39% 20% 2	584
June	1st to 10th	Night	12% 3 23% 45% 17% 1	540
	11th to 20th	Night	13% 3 20% 44% 20% 1	540
	21st to end	Night	11% 3 19% 45% 20% 2	540
July	1st to 10th	Night	10% 1 14% 41% 30% 5%	525
	11th to 20th	Night	11% 1 18% 40% 27% 3	522
	21st to end	Night	6% 2 19% 46% 26% 2	591
August	1st to 10th	Night	9% 1 14% 45% 28% 3	537
	11th to 20th	Night	10% 2 14% 40% 29% 4	534
	21st to end	Night	10% 2 16% 39% 29% 4	594
September	1st to 10th	Night	13% 4 17% 35% 26% 4	620
	11th to 20th	Night	13% 4 15% 34% 29% 4	720
	21st to end	Night	17% 6% 19% 32% 21% 6%	720
October	1st to 10th	Night	17% 5% 27% 31% 17% 3	720
	11th to 20th	Night	24% 10% 30% 27% 8% 1	720
	21st to end	Night	28% 11% 32% 23% 6%	792
November	1st to 10th	Night	19% 10% 31% 27% 11% 1	740
	11th to 20th	Night	22% 15% 35% 20% 8% 1	760
	21st to end	Night	26% 12% 34% 23% 5%	760
December	1st to 10th	Night	24% 14% 34% 22% 5%	760
	11th to 20th	Night	24% 12% 37% 23% 3 1	922
	21st to end	Night	33% 11% 33% 21% 2	1045

Page generated at 2024-01-11 22:33:47. Version ac07

Copyright 2024 Attilla Danko