GifNet.US Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the GifNet.US Observatory clear sky chart from 2005-11-06 to 2025-12-03.

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% 6% 2 6% 4 4 4 4 5% 7% 44%	125623
	Night	13% 6% 2 5% 4 4 4 3 5% 7% 47%	125154
Transparency	Day	36% 7% 11% 21% 19% 6%	129229
	Night	34% 6% 11% 20% 20% 9%	129625
Seeing	Day	12% 6% 19% 24% 25% 14%	16577
	Night	14% 5% 22% 33% 22% 4	26304

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% 10% 3 7% 3 3 3 2 5% 5% 43%	4077
	11th to 20th	Day	16% 6% 2 3 3 3 3 2 3 7% 52%	4080
	21st to end	Day	21% 10% 4 6% 3 2 2 2 3 4 43%	4488
February	1st to 10th	Day	18% 9% 2 7% 4 4 3 3 3 6% 40%	1896
	11th to 20th	Day	21% 9% 3 7% 4 4 4 3 4 4 39%	1948
	21st to end	Day	19% 9% 3 8% 5% 4 3 3 3 5% 38%	1650
March	1st to 10th	Day	19% 9% 4 9% 5% 4 4 3 4 5% 34%	4925
	11th to 20th	Day	13% 6% 2 5% 4 4 4 3 5% 7% 48%	4980
	21st to end	Day	13% 8% 4 8% 5% 4 4 3 5% 5% 41%	5589
April	1st to 10th	Day	12% 6% 2 6% 4 5% 5% 4 6% 6% 43%	2400
	11th to 20th	Day	16% 6% 2 5% 4 4 3 4 6% 7% 44%	2374
	21st to end	Day	10% 6% 3 6% 4 4 5% 4 6% 8% 45%	2400
May	1st to 10th	Day	16% 7% 3 7% 4 4 5% 4 5% 8% 38%	5405
	11th to 20th	Day	11% 6% 2 8% 5% 6% 6% 5% 6% 8% 37%	5404
	21st to end	Day	9% 5% 2 6% 4 5% 6% 5% 7% 10% 42%	6288
June	1st to 10th	Day	8% 5% 2 6% 5% 5% 6% 5% 7% 12% 40%	2604
	11th to 20th	Day	5% 4 2 5% 5% 6% 6% 5% 8% 10% 45%	2632
	21st to end	Day	4 4 2 5% 4 5% 5% 5% 8% 9% 48%	2600
July	1st to 10th	Day	5% 5% 2 8% 6% 6% 6% 6% 9% 11% 37%	5900
	11th to 20th	Day	5% 5% 2 6% 4 5% 6% 5% 7% 10% 44%	5900
	21st to end	Day	10% 6% 2 7% 5% 5% 5% 5% 7% 12% 37%	6422
August	1st to 10th	Day	3 2 1 3 4 3 3 3 5% 7% 65%	3980
	11th to 20th	Day	6% 4 2 5% 4 4 5% 5% 8% 11% 48%	3849
	21st to end	Day	9% 5% 2 6% 5% 5% 5% 4 6% 8% 46%	4312
September	1st to 10th	Day	8% 4 2 6% 5% 6% 5% 4 7% 9% 43%	2400
	11th to 20th	Day	12% 5% 2 7% 4 5% 4 3 5% 7% 47%	2400
	21st to end	Day	11% 4 2 5% 3 4 4 3 5% 7% 53%	2153
October	1st to 10th	Day	6% 4 1 5% 3 3 4 3 4 6% 60%	2000
	11th to 20th	Day	10% 4 2 4 3 4 4 2 5% 5% 58%	2000
	21st to end	Day	16% 4 2 4 3 3 3 3 3 5% 54%	2200
November	1st to 10th	Day	12% 5% 1 4 4 3 3 3 4 6% 55%	2058
	11th to 20th	Day	11% 5% 2 5% 3 3 3 4 4 5% 54%	2025
	21st to end	Day	15% 7% 2 6% 4 4 4 3 4 7% 44%	1890
December	1st to 10th	Day	18% 7% 2 6% 4 4 4 3 4 5% 43%	2916
	11th to 20th	Day	17% 9% 4 8% 4 4 3 3 4 4 41%	3008
	21st to end	Day	15% 6% 2 6% 4 4 3 3 4 6% 48%	4470
January	1st to 10th	Night	18% 6% 2 4 3 3 2 2 4 4 52%	5888
	11th to 20th	Night	15% 7% 2 6% 4 3 3 2 4 6% 48%	5900
	21st to end	Night	24% 8% 2 5% 4 3 3 2 3 4 41%	6490
February	1st to 10th	Night	17% 8% 3 6% 4 3 4 3 5% 6% 43%	2500
	11th to 20th	Night	20% 7% 2 6% 4 4 4 2 4 5% 42%	2338
	21st to end	Night	21% 8% 2 5% 4 4 4 2 4 5% 43%	1980
March	1st to 10th	Night	16% 7% 2 7% 4 4 5% 3 5% 5% 41%	4971
	11th to 20th	Night	12% 6% 2 5% 3 3 4 3 5% 8% 49%	4980
	21st to end	Night	15% 7% 2 7% 4 4 4 3 5% 6% 44%	5340
April	1st to 10th	Night	11% 5% 2 5% 5% 4 4 3 6% 7% 48%	2000
	11th to 20th	Night	13% 6% 2 6% 3 3 4 3 6% 7% 49%	1975
	21st to end	Night	9% 6% 2 5% 5% 4 3 3 5% 6% 51%	2000
May	1st to 10th	Night	14% 6% 2 7% 4 4 5% 4 6% 9% 38%	4490
	11th to 20th	Night	15% 7% 2 7% 5% 5% 5% 4 7% 7% 36%	4489
	21st to end	Night	10% 5% 2 6% 4 4 6% 5% 7% 9% 42%	4578
June	1st to 10th	Night	5% 5% 1 6% 4 4 4 5% 7% 11% 48%	1749
	11th to 20th	Night	5% 3 1 4 3 3 5% 5% 7% 11% 53%	1707
	21st to end	Night	4 4 1 4 5% 4 4 5% 7% 10% 51%	1800
July	1st to 10th	Night	4 4 2 7% 5% 5% 7% 6% 9% 11% 40%	4078
	11th to 20th	Night	5% 4 2 5% 4 4 6% 5% 9% 12% 45%	4077
	21st to end	Night	8% 6% 2 6% 4 4 4 4 7% 12% 43%	4449
August	1st to 10th	Night	2 2 1 2 2 3 4 2 5% 9% 68%	3170
	11th to 20th	Night	4 3 2 4 4 4 5% 5% 7% 14% 48%	3200
	21st to end	Night	6% 4 2 6% 4 4 5% 4 6% 8% 50%	3586
September	1st to 10th	Night	7% 4 2 5% 4 5% 5% 5% 6% 9% 48%	2000
	11th to 20th	Night	9% 4 3 5% 5% 3 4 3 7% 7% 50%	2000
	21st to end	Night	9% 3 2 4 2 3 4 3 5% 8% 58%	2220
October	1st to 10th	Night	7% 3 1 4 2 3 2 2 4 6% 65%	2400
	11th to 20th	Night	10% 4 2 4 3 3 3 3 3 5% 59%	2400
	21st to end	Night	12% 5% 2 4 2 3 3 3 3 5% 58%	2640
November	1st to 10th	Night	11% 5% 2 5% 3 2 3 2 4 5% 58%	2460
	11th to 20th	Night	11% 5% 2 5% 3 3 3 3 4 6% 56%	2590
	21st to end	Night	14% 5% 2 6% 4 4 4 3 5% 5% 49%	2730
December	1st to 10th	Night	21% 6% 2 4 3 3 3 3 4 5% 45%	4305
	11th to 20th	Night	16% 6% 2 6% 4 4 4 3 4 4 46%	5184
	21st to end	Night	16% 8% 2 6% 4 3 3 3 4 5% 47%	6490

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% 4 6% 25% 20% 3	4078
	11th to 20th	Day	33% 4 9% 21% 27% 7%	4080
	21st to end	Day	47% 3 5% 13% 22% 10%	4488
February	1st to 10th	Day	46% 4 6% 16% 17% 9%	1896
	11th to 20th	Day	49% 4 5% 17% 17% 7%	1958
	21st to end	Day	49% 5% 7% 13% 18% 8%	1650
March	1st to 10th	Day	51% 5% 7% 14% 15% 8%	4925
	11th to 20th	Day	35% 6% 6% 16% 23% 14%	4980
	21st to end	Day	45% 5% 8% 20% 17% 5%	5591
April	1st to 10th	Day	38% 8% 9% 21% 17% 7%	2400
	11th to 20th	Day	39% 6% 10% 17% 21% 7%	2374
	21st to end	Day	35% 8% 11% 21% 22% 3	2400
May	1st to 10th	Day	43% 8% 12% 23% 12% 2	5440
	11th to 20th	Day	40% 10% 15% 18% 17% 1	5408
	21st to end	Day	34% 9% 15% 25% 14% 2	6301
June	1st to 10th	Day	34% 8% 16% 25% 15% 1	2604
	11th to 20th	Day	31% 9% 18% 24% 17% 3	2632
	21st to end	Day	29% 9% 19% 25% 16% 3	2600
July	1st to 10th	Day	36% 12% 21% 20% 10% 1	5836
	11th to 20th	Day	31% 10% 23% 30% 6% 1	5831
	21st to end	Day	38% 9% 19% 27% 7%	6240
August	1st to 10th	Day	18% 6% 13% 31% 29% 3	3966
	11th to 20th	Day	26% 10% 20% 30% 13% 1	3885
	21st to end	Day	35% 8% 13% 21% 21% 3	4311
September	1st to 10th	Day	34% 9% 14% 20% 17% 6%	2400
	11th to 20th	Day	37% 7% 10% 19% 21% 7%	2400
	21st to end	Day	30% 6% 10% 21% 22% 11%	2153
October	1st to 10th	Day	16% 3 5% 14% 25% 36%	3260
	11th to 20th	Day	17% 3 4 14% 35% 27%	3240
	21st to end	Day	25% 3 5% 17% 36% 14%	3538
November	1st to 10th	Day	32% 4 8% 17% 29% 9%	2058
	11th to 20th	Day	32% 5% 7% 18% 26% 12%	2025
	21st to end	Day	40% 4 6% 18% 23% 8%	1890
December	1st to 10th	Day	43% 5% 5% 19% 23% 4	2916
	11th to 20th	Day	46% 5% 4 17% 19% 8%	3005
	21st to end	Day	37% 5% 8% 22% 26% 2	4470
January	1st to 10th	Night	36% 4 6% 25% 24% 4	5888
	11th to 20th	Night	37% 4 5% 19% 26% 9%	5900
	21st to end	Night	47% 4 6% 15% 19% 8%	6490
February	1st to 10th	Night	42% 5% 7% 17% 21% 8%	2500
	11th to 20th	Night	46% 4 6% 17% 19% 8%	2339
	21st to end	Night	45% 5% 7% 14% 17% 13%	1980
March	1st to 10th	Night	44% 5% 8% 12% 19% 12%	4971
	11th to 20th	Night	33% 6% 9% 15% 18% 19%	4980
	21st to end	Night	40% 6% 9% 18% 20% 6%	5340
April	1st to 10th	Night	34% 7% 11% 19% 19% 10%	2000
	11th to 20th	Night	34% 6% 10% 17% 23% 10%	1975
	21st to end	Night	33% 7% 8% 23% 25% 5%	2000
May	1st to 10th	Night	40% 9% 13% 20% 16% 3	4520
	11th to 20th	Night	43% 7% 14% 22% 12% 1	4490
	21st to end	Night	35% 9% 15% 22% 15% 3	4587
June	1st to 10th	Night	28% 10% 19% 24% 18% 2	1749
	11th to 20th	Night	24% 7% 19% 28% 17% 4	1707
	21st to end	Night	26% 9% 18% 27% 17% 4	1800
July	1st to 10th	Night	32% 12% 22% 21% 11% 1	4035
	11th to 20th	Night	27% 10% 30% 24% 9% 1	4026
	21st to end	Night	34% 9% 19% 28% 10% 1	4320
August	1st to 10th	Night	13% 7% 16% 31% 30% 2	3160
	11th to 20th	Night	23% 9% 20% 33% 13% 2	3230
	21st to end	Night	31% 8% 12% 19% 24% 5%	3586
September	1st to 10th	Night	30% 9% 14% 22% 16% 9%	2000
	11th to 20th	Night	32% 7% 13% 17% 22% 9%	2000
	21st to end	Night	25% 6% 10% 25% 23% 13%	2220
October	1st to 10th	Night	14% 3 7% 16% 23% 37%	3920
	11th to 20th	Night	18% 3 4 14% 29% 32%	3899
	21st to end	Night	20% 3 7% 14% 36% 19%	4252
November	1st to 10th	Night	31% 3 8% 18% 27% 13%	2460
	11th to 20th	Night	30% 4 8% 17% 27% 14%	2590
	21st to end	Night	36% 5% 7% 18% 22% 11%	2730
December	1st to 10th	Night	41% 4 7% 19% 24% 5%	4305
	11th to 20th	Night	41% 5% 8% 16% 22% 7%	5186
	21st to end	Night	39% 5% 8% 21% 24% 3	6490

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	20% 13% 40% 20% 6% 1	300
	11th to 20th	Day	24% 13% 34% 21% 7% 1	300
	21st to end	Day	20% 14% 35% 25% 5%	330
February	1st to 10th	Day	23% 9% 34% 24% 9% 2	300
	11th to 20th	Day	29% 18% 29% 18% 5%	300
	21st to end	Day	28% 16% 33% 17% 7%	249
March	1st to 10th	Day	20% 15% 33% 21% 9% 1	300
	11th to 20th	Day	18% 14% 37% 26% 3 1	300
	21st to end	Day	14% 14% 35% 23% 12% 1	380
April	1st to 10th	Day	15% 11% 37% 25% 11% 1	500
	11th to 20th	Day	20% 10% 28% 25% 15% 2	492
	21st to end	Day	12% 10% 25% 28% 20% 4	500
May	1st to 10th	Day	15% 6% 24% 35% 18% 2	503
	11th to 20th	Day	13% 4 20% 29% 23% 10%	527
	21st to end	Day	8% 3 17% 32% 26% 14%	721
June	1st to 10th	Day	9% 2 11% 29% 32% 16%	730
	11th to 20th	Day	5% 2 11% 30% 37% 15%	730
	21st to end	Day	6% 2 8% 24% 36% 24%	730
July	1st to 10th	Day	5% 2 6% 20% 42% 25%	721
	11th to 20th	Day	5% 2 5% 17% 40% 31%	718
	21st to end	Day	7% 1 4 19% 42% 27%	794
August	1st to 10th	Day	5% 5% 17% 41% 32%	576
	11th to 20th	Day	9% 3 14% 39% 34%	519
	21st to end	Day	14% 2 4 13% 31% 36%	583
September	1st to 10th	Day	8% 1 8% 22% 35% 26%	530
	11th to 20th	Day	12% 2 5% 17% 34% 30%	530
	21st to end	Day	13% 4 10% 22% 33% 18%	465
October	1st to 10th	Day	7% 2 15% 33% 28% 15%	330
	11th to 20th	Day	6% 4 23% 31% 26% 10%	330
	21st to end	Day	17% 7% 22% 27% 19% 8%	363
November	1st to 10th	Day	16% 8% 22% 25% 21% 8%	330
	11th to 20th	Day	9% 7% 32% 33% 15% 4	330
	21st to end	Day	16% 8% 32% 27% 12% 4	330
December	1st to 10th	Day	19% 9% 35% 25% 10% 3	306
	11th to 20th	Day	19% 10% 33% 21% 15% 2	300
	21st to end	Day	19% 13% 35% 22% 7% 3	330
January	1st to 10th	Night	20% 9% 33% 31% 6%	1000
	11th to 20th	Night	22% 9% 34% 28% 8%	1000
	21st to end	Night	23% 8% 34% 31% 4	1100
February	1st to 10th	Night	20% 9% 34% 31% 5%	900
	11th to 20th	Night	23% 11% 33% 28% 4	783
	21st to end	Night	24% 12% 34% 27% 3	660
March	1st to 10th	Night	18% 8% 33% 32% 7%	628
	11th to 20th	Night	14% 9% 37% 34% 5%	600
	21st to end	Night	16% 7% 34% 32% 11%	660
April	1st to 10th	Night	12% 9% 35% 36% 9%	600
	11th to 20th	Night	14% 8% 31% 35% 10% 1	593
	21st to end	Night	12% 6% 30% 36% 15% 1	600
May	1st to 10th	Night	12% 5% 22% 46% 14% 2	600
	11th to 20th	Night	11% 3 22% 39% 23% 1	591
	21st to end	Night	6% 4 14% 38% 33% 5%	650
June	1st to 10th	Night	6% 3 9% 40% 39% 5%	600
	11th to 20th	Night	4 1 9% 31% 50% 5%	600
	21st to end	Night	5% 1 8% 29% 45% 13%	600
July	1st to 10th	Night	4 2 5% 27% 52% 10%	585
	11th to 20th	Night	6% 1 4 26% 47% 15%	582
	21st to end	Night	5% 1 5% 27% 51% 13%	657
August	1st to 10th	Night	3 1 6% 23% 52% 16%	597
	11th to 20th	Night	8% 1 4 25% 50% 12%	594
	21st to end	Night	11% 1 3 24% 45% 15%	660
September	1st to 10th	Night	8% 2 6% 33% 44% 8%	600
	11th to 20th	Night	10% 2 8% 29% 43% 8%	600
	21st to end	Night	10% 2 9% 36% 39% 5%	760
October	1st to 10th	Night	7% 1 12% 36% 39% 4	800
	11th to 20th	Night	11% 3 20% 39% 24% 3	800
	21st to end	Night	15% 5% 19% 38% 21% 2	880
November	1st to 10th	Night	12% 5% 22% 36% 22% 3	820
	11th to 20th	Night	12% 5% 28% 39% 15%	840
	21st to end	Night	16% 6% 29% 32% 15% 2	840
December	1st to 10th	Night	20% 8% 29% 34% 9%	824
	11th to 20th	Night	21% 8% 28% 35% 9%	1000
	21st to end	Night	22% 9% 29% 32% 8% 1	1100

Page generated at 2025-11-30 00:00:53. Version ac07

Copyright © 2025 Attilla Danko.