TGCO
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the TGCO clear sky chart from 2005-11-06 to 2024-04-10.

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	17% 10% 4 7% 6% 3 5% 5% 5% 7% 32%	83092
	Night	17% 10% 4 7% 6% 3 4 4 5% 6% 33%	85667
Transparency	Day	51% 7% 11% 19% 10% 1	82798
	Night	50% 7% 12% 19% 10% 1	85495
Seeing	Day	25% 17% 28% 18% 9% 3	13995
	Night	23% 16% 28% 24% 9% 1	23390

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	14% 15% 10% 10% 6% 3 4 3 3 5% 28%	2517
	11th to 20th	Day	14% 15% 8% 13% 6% 3 5% 4 4 4 22%	2524
	21st to end	Day	21% 17% 7% 9% 7% 3 4 4 4 5% 20%	3124
February	1st to 10th	Day	16% 12% 5% 10% 7% 4 5% 6% 5% 5% 24%	1710
	11th to 20th	Day	14% 12% 6% 7% 7% 4 5% 4 5% 8% 28%	1748
	21st to end	Day	20% 11% 3 9% 8% 2 4 4 5% 6% 28%	1570
March	1st to 10th	Day	24% 14% 5% 8% 5% 3 3 3 3 4 28%	3148
	11th to 20th	Day	11% 14% 6% 7% 7% 3 4 5% 5% 6% 33%	3480
	21st to end	Day	20% 10% 3 7% 6% 3 4 4 4 6% 34%	4023
April	1st to 10th	Day	19% 11% 4 7% 5% 3 4 3 5% 6% 33%	2270
	11th to 20th	Day	17% 9% 4 6% 5% 4 5% 4 5% 6% 36%	2134
	21st to end	Day	18% 9% 4 7% 5% 3 5% 4 5% 6% 35%	2160
May	1st to 10th	Day	21% 9% 3 6% 5% 4 5% 4 5% 6% 32%	2415
	11th to 20th	Day	20% 7% 3 6% 6% 3 5% 4 5% 7% 33%	2478
	21st to end	Day	15% 6% 3 5% 5% 4 5% 5% 6% 8% 38%	2725
June	1st to 10th	Day	17% 6% 3 5% 7% 4 5% 6% 7% 9% 33%	2520
	11th to 20th	Day	16% 7% 3 7% 6% 3 5% 6% 6% 9% 32%	2520
	21st to end	Day	14% 6% 3 6% 6% 4 5% 6% 6% 10% 35%	2520
July	1st to 10th	Day	11% 6% 3 7% 6% 5% 6% 6% 7% 9% 35%	2520
	11th to 20th	Day	11% 5% 3 5% 5% 4 6% 6% 7% 12% 38%	2520
	21st to end	Day	11% 6% 3 6% 6% 5% 5% 6% 7% 9% 35%	2740
August	1st to 10th	Day	12% 6% 2 7% 6% 3 6% 6% 7% 9% 34%	2327
	11th to 20th	Day	15% 6% 4 6% 5% 4 5% 5% 5% 8% 36%	2190
	21st to end	Day	15% 6% 3 6% 6% 3 4 6% 6% 9% 35%	2376
September	1st to 10th	Day	16% 7% 3 5% 6% 4 6% 4 5% 7% 38%	2160
	11th to 20th	Day	14% 6% 2 5% 5% 4 4 4 5% 8% 44%	2152
	21st to end	Day	18% 7% 2 6% 5% 3 4 5% 7% 8% 36%	1944
October	1st to 10th	Day	18% 7% 2 7% 4 3 5% 4 6% 7% 36%	1800
	11th to 20th	Day	17% 8% 2 6% 6% 3 5% 5% 6% 7% 35%	1800
	21st to end	Day	23% 11% 3 6% 5% 3 4 4 5% 6% 28%	1906
November	1st to 10th	Day	14% 9% 3 6% 6% 2 4 4 5% 4 42%	1671
	11th to 20th	Day	17% 10% 4 8% 6% 3 4 4 4 6% 34%	1682
	21st to end	Day	19% 11% 5% 6% 6% 3 5% 4 5% 6% 30%	1520
December	1st to 10th	Day	19% 14% 5% 8% 6% 3 4 5% 5% 6% 24%	1520
	11th to 20th	Day	22% 13% 6% 8% 5% 2 3 3 4 5% 28%	1906
	21st to end	Day	22% 16% 7% 10% 7% 4 5% 4 4 5% 18%	2772
January	1st to 10th	Night	16% 12% 7% 9% 7% 3 4 4 4 6% 27%	4429
	11th to 20th	Night	14% 16% 7% 12% 8% 3 4 4 4 5% 23%	4433
	21st to end	Night	23% 12% 5% 10% 10% 4 5% 4 3 5% 19%	4532
February	1st to 10th	Night	16% 10% 4 8% 7% 4 4 4 6% 6% 29%	2470
	11th to 20th	Night	15% 11% 5% 9% 7% 3 5% 6% 5% 7% 27%	2318
	21st to end	Night	18% 10% 5% 9% 7% 3 4 4 5% 5% 31%	1884
March	1st to 10th	Night	22% 14% 5% 7% 5% 3 3 3 4 4 30%	3678
	11th to 20th	Night	12% 13% 7% 9% 7% 3 4 4 5% 5% 31%	3479
	21st to end	Night	15% 12% 3 7% 7% 3 4 4 4 5% 36%	3608
April	1st to 10th	Night	18% 12% 5% 8% 6% 3 4 4 5% 5% 30%	1900
	11th to 20th	Night	17% 8% 3 7% 5% 3 4 4 5% 7% 37%	1775
	21st to end	Night	20% 7% 3 6% 5% 3 4 5% 5% 6% 37%	1800
May	1st to 10th	Night	21% 10% 3 6% 4 3 4 4 5% 6% 33%	1557
	11th to 20th	Night	15% 6% 3 5% 6% 3 5% 5% 5% 7% 38%	1415
	21st to end	Night	13% 8% 3 5% 6% 3 5% 5% 7% 7% 40%	1550
June	1st to 10th	Night	16% 6% 2 5% 4 4 4 5% 6% 8% 39%	1440
	11th to 20th	Night	15% 6% 2 6% 5% 3 4 4 6% 8% 40%	1440
	21st to end	Night	13% 4 2 6% 5% 3 5% 5% 7% 8% 45%	1440
July	1st to 10th	Night	12% 5% 3 5% 6% 3 6% 4 6% 9% 42%	1440
	11th to 20th	Night	12% 5% 2 6% 4 3 4 5% 7% 10% 42%	1440
	21st to end	Night	11% 5% 3 6% 4 3 5% 5% 6% 8% 43%	1574
August	1st to 10th	Night	10% 7% 2 5% 5% 3 4 7% 8% 8% 41%	1611
	11th to 20th	Night	14% 6% 2 5% 8% 4 5% 5% 6% 8% 37%	1691
	21st to end	Night	14% 5% 2 5% 5% 3 4 4 5% 8% 44%	1980
September	1st to 10th	Night	15% 7% 2 5% 4 3 5% 5% 6% 7% 41%	1800
	11th to 20th	Night	13% 6% 3 4 4 3 3 4 4 7% 50%	1807
	21st to end	Night	16% 6% 3 5% 5% 3 4 4 5% 6% 42%	2014
October	1st to 10th	Night	20% 7% 3 5% 5% 3 3 4 5% 8% 38%	2160
	11th to 20th	Night	19% 8% 3 5% 5% 3 4 4 5% 5% 40%	2160
	21st to end	Night	23% 10% 2 5% 5% 3 4 5% 5% 6% 31%	2448
November	1st to 10th	Night	13% 10% 3 6% 5% 3 4 4 5% 6% 42%	2407
	11th to 20th	Night	20% 10% 3 6% 4 3 4 4 5% 6% 35%	2495
	21st to end	Night	15% 11% 4 6% 5% 4 4 5% 6% 7% 34%	2660
December	1st to 10th	Night	20% 11% 5% 8% 6% 3 5% 5% 5% 6% 24%	2660
	11th to 20th	Night	19% 12% 6% 7% 6% 3 5% 4 4 6% 27%	3288
	21st to end	Night	23% 14% 6% 8% 6% 3 4 4 4 6% 22%	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	59% 5% 10% 20% 5% 1	2518
	11th to 20th	Day	66% 6% 8% 13% 5% 1	2524
	21st to end	Day	66% 6% 9% 14% 5% 1	3124
February	1st to 10th	Day	60% 8% 11% 13% 8% 1	1710
	11th to 20th	Day	55% 6% 10% 20% 9%	1757
	21st to end	Day	57% 5% 9% 19% 8% 2	1570
March	1st to 10th	Day	61% 5% 9% 17% 7% 1	3151
	11th to 20th	Day	48% 10% 12% 20% 9% 1	3480
	21st to end	Day	50% 6% 9% 15% 18% 2	4023
April	1st to 10th	Day	52% 6% 8% 21% 10% 3	2270
	11th to 20th	Day	48% 6% 11% 20% 13% 2	2134
	21st to end	Day	49% 6% 9% 20% 12% 4	2160
May	1st to 10th	Day	52% 7% 10% 18% 11% 2	2415
	11th to 20th	Day	51% 7% 8% 20% 12% 2	2482
	21st to end	Day	44% 8% 14% 20% 12% 1	2725
June	1st to 10th	Day	47% 8% 13% 19% 12% 1	2520
	11th to 20th	Day	48% 8% 12% 20% 10% 1	2520
	21st to end	Day	43% 8% 13% 24% 11%	2520
July	1st to 10th	Day	43% 10% 13% 21% 12% 1	2450
	11th to 20th	Day	37% 10% 16% 24% 13%	2445
	21st to end	Day	42% 10% 13% 19% 14% 1	2587
August	1st to 10th	Day	42% 11% 14% 21% 11% 1	2314
	11th to 20th	Day	46% 9% 14% 22% 9%	2190
	21st to end	Day	43% 8% 13% 21% 13% 2	2376
September	1st to 10th	Day	45% 8% 12% 21% 13% 1	2160
	11th to 20th	Day	39% 7% 12% 21% 20% 1	2152
	21st to end	Day	44% 6% 12% 22% 14% 2	1944
October	1st to 10th	Day	46% 8% 12% 20% 12% 2	1800
	11th to 20th	Day	47% 7% 11% 23% 11% 1	1800
	21st to end	Day	56% 6% 12% 16% 8% 1	1906
November	1st to 10th	Day	43% 7% 12% 21% 14% 2	1671
	11th to 20th	Day	51% 6% 12% 18% 11% 2	1682
	21st to end	Day	54% 7% 13% 19% 6% 1	1520
December	1st to 10th	Day	60% 7% 14% 12% 6% 1	1520
	11th to 20th	Day	59% 6% 15% 16% 5%	1906
	21st to end	Day	69% 6% 9% 12% 4	2772
January	1st to 10th	Night	56% 7% 13% 17% 6% 1	4429
	11th to 20th	Night	61% 8% 11% 15% 5% 1	4433
	21st to end	Night	68% 6% 7% 14% 5% 1	4532
February	1st to 10th	Night	55% 6% 13% 17% 9% 1	2470
	11th to 20th	Night	55% 7% 12% 17% 9% 1	2320
	21st to end	Night	55% 5% 9% 20% 10% 2	1884
March	1st to 10th	Night	58% 5% 10% 17% 10% 1	3688
	11th to 20th	Night	50% 10% 14% 20% 7% 1	3480
	21st to end	Night	46% 8% 9% 19% 15% 3	3608
April	1st to 10th	Night	55% 6% 9% 17% 11% 2	1900
	11th to 20th	Night	46% 7% 11% 20% 16% 1	1775
	21st to end	Night	47% 6% 11% 20% 13% 3	1800
May	1st to 10th	Night	52% 7% 8% 20% 11% 2	1557
	11th to 20th	Night	45% 7% 10% 22% 14% 2	1416
	21st to end	Night	41% 9% 15% 22% 11% 2	1551
June	1st to 10th	Night	42% 7% 11% 24% 14% 1	1440
	11th to 20th	Night	41% 7% 17% 24% 10% 1	1440
	21st to end	Night	34% 10% 16% 26% 13% 1	1440
July	1st to 10th	Night	38% 8% 16% 23% 14% 2	1400
	11th to 20th	Night	35% 10% 16% 26% 11% 1	1392
	21st to end	Night	37% 9% 16% 22% 14% 2	1486
August	1st to 10th	Night	37% 10% 15% 26% 12% 1	1600
	11th to 20th	Night	43% 9% 15% 22% 11%	1691
	21st to end	Night	39% 7% 13% 23% 17% 1	1980
September	1st to 10th	Night	41% 6% 14% 24% 13% 2	1800
	11th to 20th	Night	35% 6% 11% 25% 22% 1	1807
	21st to end	Night	42% 6% 9% 23% 18% 1	2014
October	1st to 10th	Night	44% 8% 12% 21% 14% 1	2160
	11th to 20th	Night	45% 6% 14% 22% 11% 2	2160
	21st to end	Night	52% 7% 12% 18% 9% 1	2448
November	1st to 10th	Night	43% 5% 13% 21% 17% 2	2407
	11th to 20th	Night	48% 6% 13% 19% 12% 2	2495
	21st to end	Night	48% 7% 16% 21% 8%	2660
December	1st to 10th	Night	58% 8% 13% 16% 5%	2660
	11th to 20th	Night	57% 7% 12% 16% 7% 1	3288
	21st to end	Night	63% 7% 11% 15% 4	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	30% 28% 29% 10% 2 1	180
	11th to 20th	Day	39% 28% 23% 8% 2	182
	21st to end	Day	28% 28% 31% 10% 3	297
February	1st to 10th	Day	33% 31% 28% 8%	270
	11th to 20th	Day	35% 29% 29% 6% 1	355
	21st to end	Day	36% 25% 27% 10% 3	382
March	1st to 10th	Day	35% 18% 31% 13% 3	460
	11th to 20th	Day	30% 28% 26% 12% 4	460
	21st to end	Day	33% 26% 25% 10% 4 2	506
April	1st to 10th	Day	34% 23% 26% 13% 4 1	457
	11th to 20th	Day	30% 24% 25% 11% 7% 3	412
	21st to end	Day	28% 22% 29% 15% 4 2	420
May	1st to 10th	Day	33% 16% 29% 11% 8% 2	423
	11th to 20th	Day	25% 17% 28% 20% 7% 2	447
	21st to end	Day	21% 11% 26% 23% 14% 4	485
June	1st to 10th	Day	19% 16% 31% 22% 9% 2	450
	11th to 20th	Day	21% 15% 26% 23% 14% 1	450
	21st to end	Day	16% 15% 33% 24% 10% 2	450
July	1st to 10th	Day	15% 8% 27% 28% 17% 5%	445
	11th to 20th	Day	12% 7% 28% 30% 19% 4	444
	21st to end	Day	15% 9% 35% 26% 11% 4	488
August	1st to 10th	Day	12% 8% 29% 25% 19% 7%	446
	11th to 20th	Day	18% 7% 25% 27% 18% 5%	439
	21st to end	Day	14% 10% 29% 25% 14% 8%	495
September	1st to 10th	Day	20% 12% 23% 20% 18% 7%	450
	11th to 20th	Day	15% 8% 27% 25% 16% 10%	450
	21st to end	Day	24% 11% 27% 21% 13% 4	450
October	1st to 10th	Day	26% 12% 23% 21% 14% 5%	450
	11th to 20th	Day	23% 18% 28% 22% 8% 1	450
	21st to end	Day	32% 16% 26% 19% 5%	457
November	1st to 10th	Day	27% 17% 22% 22% 9% 3	365
	11th to 20th	Day	30% 22% 28% 15% 5% 1	342
	21st to end	Day	35% 21% 34% 7% 3	180
December	1st to 10th	Day	34% 29% 24% 9% 3 1	180
	11th to 20th	Day	35% 25% 27% 10% 3	180
	21st to end	Day	34% 23% 31% 11% 1	198
January	1st to 10th	Night	25% 26% 32% 15% 3	760
	11th to 20th	Night	27% 21% 30% 18% 3	760
	21st to end	Night	21% 26% 35% 16% 2	836
February	1st to 10th	Night	27% 20% 33% 19% 1	760
	11th to 20th	Night	28% 27% 33% 12% 1	743
	21st to end	Night	31% 21% 32% 13% 3	628
March	1st to 10th	Night	29% 22% 30% 17% 2	760
	11th to 20th	Night	26% 24% 30% 16% 4	760
	21st to end	Night	24% 23% 31% 16% 5%	836
April	1st to 10th	Night	26% 21% 31% 19% 3	760
	11th to 20th	Night	23% 19% 33% 18% 6% 1	711
	21st to end	Night	24% 17% 29% 23% 5%	720
May	1st to 10th	Night	27% 14% 28% 22% 9%	477
	11th to 20th	Night	17% 13% 33% 29% 7% 1	354
	21st to end	Night	15% 7% 28% 34% 15% 1	389
June	1st to 10th	Night	17% 8% 21% 41% 13%	360
	11th to 20th	Night	16% 9% 24% 38% 13%	360
	21st to end	Night	12% 6% 25% 45% 12%	360
July	1st to 10th	Night	13% 4 22% 39% 21% 1	350
	11th to 20th	Night	13% 3 19% 45% 19% 1	348
	21st to end	Night	14% 6% 21% 40% 19% 1	394
August	1st to 10th	Night	14% 1 21% 42% 19% 2	537
	11th to 20th	Night	14% 4 15% 38% 26% 3	627
	21st to end	Night	15% 6% 19% 34% 24% 1	792
September	1st to 10th	Night	19% 6% 23% 33% 18% 2	720
	11th to 20th	Night	15% 6% 23% 30% 21% 5%	720
	21st to end	Night	19% 9% 23% 31% 16% 2	720
October	1st to 10th	Night	24% 11% 23% 24% 17% 1	720
	11th to 20th	Night	23% 13% 28% 29% 7%	720
	21st to end	Night	30% 14% 29% 21% 5%	792
November	1st to 10th	Night	19% 15% 33% 24% 8%	740
	11th to 20th	Night	26% 18% 30% 19% 6% 1	760
	21st to end	Night	23% 18% 33% 21% 4 1	760
December	1st to 10th	Night	29% 20% 31% 16% 4	760
	11th to 20th	Night	25% 23% 29% 20% 3	760
	21st to end	Night	29% 20% 33% 16% 2	836

Page generated at 2024-04-07 09:28:12. Version ac07

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