G49 Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the G49 Observatory clear sky chart from 2005-11-06 to 2025-02-21.

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	12% 9% 3 8% 5% 5% 4 4 6% 7% 36%	109023
	Night	11% 10% 4 9% 5% 5% 4 4 5% 6% 37%	109743
Transparency	Day	45% 6% 13% 25% 11% 1	112642
	Night	45% 5% 12% 24% 12% 1	114265
Seeing	Day	17% 14% 32% 24% 10% 2	16351
	Night	16% 12% 34% 28% 9% 1	26423

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	9% 13% 5% 19% 7% 6% 5% 3 4 6% 22%	3617
	11th to 20th	Day	5% 11% 6% 13% 7% 7% 9% 8% 9% 5% 20%	3684
	21st to end	Day	5% 16% 7% 13% 5% 4 5% 4 4 5% 31%	4488
February	1st to 10th	Day	9% 12% 5% 10% 8% 5% 6% 5% 6% 7% 29%	1800
	11th to 20th	Day	8% 11% 5% 9% 6% 6% 5% 4 6% 6% 33%	1754
	21st to end	Day	10% 12% 5% 10% 5% 6% 5% 4 5% 6% 31%	1464
March	1st to 10th	Day	12% 12% 4 7% 4 4 4 3 5% 6% 39%	3373
	11th to 20th	Day	10% 10% 3 9% 5% 5% 4 3 5% 7% 40%	3480
	21st to end	Day	23% 12% 4 11% 6% 5% 4 3 4 5% 23%	3843
April	1st to 10th	Day	16% 11% 4 7% 5% 4 4 4 5% 7% 35%	2280
	11th to 20th	Day	19% 12% 3 8% 5% 4 4 4 5% 5% 32%	2272
	21st to end	Day	21% 11% 3 7% 4 5% 4 4 4 5% 31%	2470
May	1st to 10th	Day	17% 6% 2 6% 4 4 4 4 5% 7% 40%	4242
	11th to 20th	Day	13% 8% 2 5% 4 4 4 4 5% 7% 45%	4399
	21st to end	Day	17% 7% 3 7% 5% 4 5% 4 6% 8% 35%	4824
June	1st to 10th	Day	11% 5% 2 5% 4 4 4 5% 7% 9% 46%	2660
	11th to 20th	Day	13% 7% 3 7% 6% 5% 4 4 7% 9% 36%	2660
	21st to end	Day	10% 5% 2 6% 5% 5% 5% 5% 7% 10% 39%	2772
July	1st to 10th	Day	10% 6% 2 7% 5% 6% 5% 5% 8% 10% 37%	4440
	11th to 20th	Day	6% 3 1 4 3 3 3 3 6% 8% 59%	4440
	21st to end	Day	6% 4 2 6% 5% 4 5% 4 8% 10% 47%	4736
August	1st to 10th	Day	12% 6% 2 6% 4 5% 5% 4 6% 8% 42%	4104
	11th to 20th	Day	12% 6% 2 5% 4 4 4 5% 6% 9% 42%	4041
	21st to end	Day	9% 7% 2 7% 4 4 4 3 6% 7% 46%	4344
September	1st to 10th	Day	11% 6% 2 6% 4 3 4 4 5% 8% 48%	2280
	11th to 20th	Day	12% 6% 2 4 3 5% 5% 4 6% 8% 45%	2243
	21st to end	Day	14% 7% 2 6% 4 4 3 4 5% 7% 44%	2005
October	1st to 10th	Day	16% 8% 2 6% 4 4 3 3 5% 6% 42%	1900
	11th to 20th	Day	15% 10% 3 7% 4 4 4 3 5% 6% 39%	1900
	21st to end	Day	17% 11% 4 7% 4 4 3 3 4 6% 37%	2074
November	1st to 10th	Day	13% 12% 4 7% 5% 4 4 4 5% 6% 36%	1634
	11th to 20th	Day	11% 13% 7% 12% 6% 5% 4 3 5% 5% 29%	1600
	21st to end	Day	13% 12% 4 8% 5% 4 4 4 5% 7% 34%	1600
December	1st to 10th	Day	7% 11% 4 13% 12% 7% 6% 4 5% 6% 23%	2610
	11th to 20th	Day	9% 17% 7% 11% 7% 4 5% 4 4 5% 27%	3008
	21st to end	Day	20% 18% 9% 20% 4 4 3 2 3 3 14%	3982
January	1st to 10th	Night	7% 12% 5% 15% 8% 6% 4 3 5% 6% 28%	6348
	11th to 20th	Night	6% 11% 5% 13% 7% 7% 10% 8% 7% 6% 20%	6296
	21st to end	Night	8% 18% 6% 10% 5% 5% 4 3 5% 4 32%	6490
February	1st to 10th	Night	7% 12% 5% 11% 6% 6% 5% 3 5% 5% 34%	2600
	11th to 20th	Night	6% 10% 3 9% 6% 6% 6% 4 5% 6% 39%	2533
	21st to end	Night	11% 10% 4 9% 6% 5% 5% 3 4 7% 37%	1990
March	1st to 10th	Night	8% 8% 3 6% 5% 4 4 3 5% 7% 47%	3510
	11th to 20th	Night	9% 8% 3 9% 4 6% 5% 4 6% 7% 40%	3480
	21st to end	Night	25% 12% 3 11% 4 3 3 3 3 5% 28%	3787
April	1st to 10th	Night	14% 12% 3 7% 3 3 5% 4 5% 6% 37%	1900
	11th to 20th	Night	20% 10% 3 7% 4 3 4 3 5% 6% 34%	1853
	21st to end	Night	18% 10% 4 7% 3 4 4 3 5% 6% 36%	1710
May	1st to 10th	Night	14% 7% 2 7% 5% 4 4 3 5% 6% 41%	2663
	11th to 20th	Night	14% 4 1 4 3 3 4 4 5% 8% 49%	2506
	21st to end	Night	14% 8% 3 6% 4 4 5% 3 5% 7% 41%	2743
June	1st to 10th	Night	10% 5% 2 5% 3 3 5% 4 6% 8% 50%	1520
	11th to 20th	Night	8% 5% 2 5% 5% 5% 5% 4 7% 8% 46%	1520
	21st to end	Night	8% 4 2 4 3 4 4 3 7% 9% 52%	1377
July	1st to 10th	Night	11% 5% 1 5% 4 4 5% 5% 7% 9% 45%	2520
	11th to 20th	Night	3 2 1 4 3 3 4 3 6% 9% 59%	2530
	21st to end	Night	6% 4 2 5% 3 4 4 3 6% 8% 56%	2811
August	1st to 10th	Night	12% 5% 2 5% 4 4 4 4 5% 6% 48%	2836
	11th to 20th	Night	14% 4 1 4 3 3 4 3 6% 8% 51%	2798
	21st to end	Night	9% 6% 2 7% 4 4 4 4 6% 7% 47%	3316
September	1st to 10th	Night	8% 5% 2 5% 3 4 4 3 5% 8% 53%	1900
	11th to 20th	Night	9% 4 2 5% 4 4 4 3 5% 7% 53%	1933
	21st to end	Night	12% 6% 1 5% 3 3 4 3 5% 5% 52%	2156
October	1st to 10th	Night	14% 6% 2 5% 4 4 3 3 5% 5% 49%	2280
	11th to 20th	Night	15% 10% 2 5% 4 4 5% 3 5% 6% 42%	2280
	21st to end	Night	17% 11% 4 7% 4 3 4 3 5% 6% 38%	2522
November	1st to 10th	Night	14% 9% 3 6% 4 4 4 4 5% 6% 41%	2660
	11th to 20th	Night	13% 12% 5% 12% 6% 4 4 3 4 5% 34%	2800
	21st to end	Night	13% 11% 3 9% 6% 5% 5% 3 4 6% 36%	2800
December	1st to 10th	Night	6% 8% 4 14% 7% 7% 6% 4 6% 7% 30%	4580
	11th to 20th	Night	9% 17% 7% 14% 7% 4 4 5% 4 5% 24%	5199
	21st to end	Night	21% 16% 8% 15% 5% 4 3 3 3 4 17%	6996

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	62% 5% 10% 18% 5%	3618
	11th to 20th	Day	60% 5% 9% 17% 9%	3684
	21st to end	Day	55% 5% 15% 17% 7%	4488
February	1st to 10th	Day	53% 5% 14% 19% 8% 1	1800
	11th to 20th	Day	49% 6% 11% 25% 8% 1	1763
	21st to end	Day	52% 6% 11% 20% 11%	1464
March	1st to 10th	Day	46% 5% 13% 26% 10%	3373
	11th to 20th	Day	43% 5% 10% 31% 9% 1	3480
	21st to end	Day	64% 5% 9% 17% 5%	3843
April	1st to 10th	Day	48% 5% 13% 21% 12% 1	2280
	11th to 20th	Day	54% 4 9% 19% 12% 2	2272
	21st to end	Day	55% 4 12% 20% 8% 1	2470
May	1st to 10th	Day	41% 7% 11% 25% 14% 2	4280
	11th to 20th	Day	38% 6% 11% 29% 14% 2	4403
	21st to end	Day	46% 7% 11% 26% 10% 1	4837
June	1st to 10th	Day	33% 7% 14% 31% 13% 2	2660
	11th to 20th	Day	42% 7% 13% 22% 14% 2	2660
	21st to end	Day	36% 8% 16% 28% 10% 2	2772
July	1st to 10th	Day	38% 10% 19% 22% 11% 1	4371
	11th to 20th	Day	22% 6% 16% 37% 18% 2	4365
	21st to end	Day	29% 9% 15% 29% 17% 1	4587
August	1st to 10th	Day	38% 7% 13% 28% 12% 2	4090
	11th to 20th	Day	36% 7% 14% 33% 10%	4080
	21st to end	Day	35% 7% 16% 28% 14% 1	4343
September	1st to 10th	Day	34% 6% 14% 32% 13%	2280
	11th to 20th	Day	35% 7% 17% 33% 8%	2243
	21st to end	Day	39% 5% 12% 33% 11% 1	2005
October	1st to 10th	Day	31% 3 9% 35% 22%	3160
	11th to 20th	Day	39% 5% 11% 28% 16% 1	3140
	21st to end	Day	44% 4 14% 29% 9%	3400
November	1st to 10th	Day	48% 5% 13% 19% 13% 2	1634
	11th to 20th	Day	57% 5% 12% 17% 9% 1	1600
	21st to end	Day	50% 5% 16% 21% 7% 1	1600
December	1st to 10th	Day	58% 8% 16% 12% 5% 1	2610
	11th to 20th	Day	58% 5% 15% 17% 5%	3005
	21st to end	Day	77% 4 8% 8% 4	3982
January	1st to 10th	Night	56% 5% 11% 21% 7%	6348
	11th to 20th	Night	60% 5% 11% 14% 10%	6296
	21st to end	Night	54% 5% 11% 23% 7%	6490
February	1st to 10th	Night	51% 5% 12% 21% 10% 1	2600
	11th to 20th	Night	44% 6% 14% 25% 9% 1	2534
	21st to end	Night	47% 5% 12% 22% 12% 1	1990
March	1st to 10th	Night	37% 5% 13% 27% 17% 1	3510
	11th to 20th	Night	39% 6% 10% 27% 16% 1	3480
	21st to end	Night	61% 4 7% 21% 6% 1	3787
April	1st to 10th	Night	48% 4 10% 24% 14% 1	1900
	11th to 20th	Night	50% 4 7% 20% 15% 3	1853
	21st to end	Night	49% 5% 8% 21% 14% 2	1710
May	1st to 10th	Night	41% 6% 10% 20% 21% 1	2690
	11th to 20th	Night	33% 5% 11% 27% 20% 4	2507
	21st to end	Night	41% 7% 11% 25% 15% 1	2751
June	1st to 10th	Night	31% 6% 14% 28% 18% 2	1520
	11th to 20th	Night	33% 9% 15% 23% 18% 2	1520
	21st to end	Night	27% 6% 16% 31% 17% 3	1377
July	1st to 10th	Night	32% 8% 19% 25% 14% 1	2480
	11th to 20th	Night	20% 6% 14% 39% 18% 2	2482
	21st to end	Night	25% 7% 14% 32% 18% 3	2722
August	1st to 10th	Night	35% 7% 11% 29% 14% 4	2826
	11th to 20th	Night	31% 6% 15% 32% 16% 1	2825
	21st to end	Night	34% 8% 16% 27% 13% 2	3316
September	1st to 10th	Night	30% 5% 13% 34% 18% 1	1900
	11th to 20th	Night	29% 6% 16% 31% 17%	1933
	21st to end	Night	34% 5% 13% 32% 17% 1	2156
October	1st to 10th	Night	24% 3 6% 35% 27% 4	3800
	11th to 20th	Night	33% 5% 13% 24% 22% 4	3779
	21st to end	Night	43% 4 12% 28% 12%	4146
November	1st to 10th	Night	43% 5% 12% 24% 13% 2	2660
	11th to 20th	Night	52% 5% 12% 19% 11% 1	2800
	21st to end	Night	50% 5% 16% 22% 7% 1	2800
December	1st to 10th	Night	52% 7% 17% 19% 5%	4580
	11th to 20th	Night	62% 5% 11% 17% 4 1	5201
	21st to end	Night	72% 4 8% 12% 3	6996

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	15% 12% 32% 29% 10% 2	300
	11th to 20th	Day	19% 14% 36% 26% 4 1	300
	21st to end	Day	17% 15% 38% 20% 9% 2	330
February	1st to 10th	Day	16% 18% 41% 19% 4	300
	11th to 20th	Day	14% 23% 34% 24% 5% 1	300
	21st to end	Day	19% 16% 39% 23% 4	225
March	1st to 10th	Day	19% 19% 38% 17% 7%	270
	11th to 20th	Day	19% 14% 38% 21% 7% 1	270
	21st to end	Day	27% 18% 26% 19% 8% 2	314
April	1st to 10th	Day	23% 18% 33% 20% 4	460
	11th to 20th	Day	30% 16% 24% 22% 7% 1	470
	21st to end	Day	26% 18% 30% 18% 7% 2	650
May	1st to 10th	Day	21% 19% 33% 20% 6% 1	653
	11th to 20th	Day	20% 14% 30% 21% 11% 3	675
	21st to end	Day	18% 12% 30% 25% 11% 3	734
June	1st to 10th	Day	11% 10% 32% 30% 14% 2	680
	11th to 20th	Day	16% 13% 40% 22% 7% 1	680
	21st to end	Day	13% 13% 34% 25% 13% 2	680
July	1st to 10th	Day	10% 6% 28% 33% 18% 6%	671
	11th to 20th	Day	10% 10% 30% 30% 16% 4	668
	21st to end	Day	6% 9% 31% 33% 17% 4	739
August	1st to 10th	Day	11% 8% 30% 31% 18% 3	676
	11th to 20th	Day	15% 8% 23% 31% 18% 5%	665
	21st to end	Day	11% 10% 31% 30% 15% 3	638
September	1st to 10th	Day	14% 13% 30% 27% 14% 2	490
	11th to 20th	Day	13% 9% 32% 28% 15% 2	453
	21st to end	Day	18% 18% 29% 21% 13% 2	300
October	1st to 10th	Day	20% 15% 29% 22% 11% 3	300
	11th to 20th	Day	17% 27% 37% 15% 4	300
	21st to end	Day	27% 19% 38% 12% 4	330
November	1st to 10th	Day	23% 18% 35% 17% 6% 1	300
	11th to 20th	Day	21% 22% 40% 15% 2	300
	21st to end	Day	25% 19% 43% 10% 4	300
December	1st to 10th	Day	15% 19% 36% 22% 7% 1	300
	11th to 20th	Day	22% 21% 34% 20% 3	300
	21st to end	Day	30% 15% 35% 18% 2 1	330
January	1st to 10th	Night	11% 15% 38% 27% 7% 1	1000
	11th to 20th	Night	16% 15% 37% 26% 5% 1	1000
	21st to end	Night	18% 15% 37% 25% 5%	1100
February	1st to 10th	Night	14% 15% 39% 25% 6% 1	1000
	11th to 20th	Night	11% 16% 42% 24% 6% 1	979
	21st to end	Night	17% 15% 34% 25% 8% 1	734
March	1st to 10th	Night	16% 13% 36% 26% 8% 1	627
	11th to 20th	Night	18% 13% 36% 25% 7%	570
	21st to end	Night	21% 14% 30% 23% 10% 2	627
April	1st to 10th	Night	22% 15% 33% 25% 6%	570
	11th to 20th	Night	24% 13% 29% 26% 6% 1	563
	21st to end	Night	23% 13% 32% 23% 8% 1	570
May	1st to 10th	Night	20% 12% 34% 29% 5% 1	570
	11th to 20th	Night	16% 9% 38% 26% 11% 1	561
	21st to end	Night	15% 11% 28% 33% 12%	617
June	1st to 10th	Night	12% 6% 34% 38% 10%	570
	11th to 20th	Night	10% 7% 39% 37% 7%	570
	21st to end	Night	11% 6% 28% 39% 15% 1	570
July	1st to 10th	Night	6% 3 28% 36% 25% 1	555
	11th to 20th	Night	6% 7% 30% 40% 15% 1	552
	21st to end	Night	5% 4 32% 39% 18% 2	624
August	1st to 10th	Night	7% 6% 23% 43% 19% 1	567
	11th to 20th	Night	12% 4 23% 37% 21% 2	564
	21st to end	Night	8% 6% 32% 32% 21% 1	627
September	1st to 10th	Night	10% 8% 29% 37% 14% 3	570
	11th to 20th	Night	11% 8% 37% 27% 15% 2	570
	21st to end	Night	13% 13% 32% 26% 14% 1	636
October	1st to 10th	Night	18% 12% 31% 26% 12%	760
	11th to 20th	Night	22% 14% 34% 22% 7% 1	760
	21st to end	Night	24% 14% 30% 25% 7%	836
November	1st to 10th	Night	19% 15% 33% 26% 7%	904
	11th to 20th	Night	19% 18% 33% 23% 6%	1000
	21st to end	Night	19% 19% 34% 23% 6%	1000
December	1st to 10th	Night	17% 13% 37% 26% 6% 1	1000
	11th to 20th	Night	20% 15% 34% 25% 5% 1	1000
	21st to end	Night	25% 15% 33% 23% 4 1	1100

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